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Document and Entity Information - USD ($)	12 Months Ended
Document and Entity Information - USD ($)	Dec. 31, 2019	Feb. 28, 2020	Jun. 28, 2019
Cover [Abstract]
Entity Registrant Name	FATE THERAPEUTICS INC
Entity Central Index Key	0001434316
Document Type	10-K
Document Period End Date	Dec. 31, 2019
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Interactive Data Current	Yes
Entity Shell Company	false
Entity Small Business	false
Entity Emerging Growth Company	false
Trading Symbol	FATE
Title of 12(b) Security	Common Stock, $0.001 par value
Security Exchange Name	NASDAQ
Document Annual Report	true
Document Transition Report	false
Entity Public Float			$ 1,055,849,000
Entity Common Stock, Shares Outstanding		75,931,385
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Entity Tax Identification Number	65-1311552
Entity File Number	001-36076
Entity Incorporation, State or Country Code	DE
Entity Address, Address Line One	3535 General Atomics Court
Entity Address, Address Line Two	Suite 200
Entity Address, City or Town	San Diego
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	92121
City Area Code	858
Local Phone Number	875-1800
Documents Incorporated by Reference	Portions of the registrant’s definitive proxy statement to be filed with the Securities and Exchange Commission, or SEC, on or before the date 120 days after the conclusion of the registrant’s fiscal year ended December 31, 2019 pursuant to Regulation 14A in connection with the registrant’s 2020 Annual Meeting of Stockholders are incorporated by reference into Part III of this annual report on Form 10-K.

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 99,814	$ 190,514
Accounts receivable		500
Short-term investments and related maturity receivables	121,613	10,493
Prepaid expenses and other current assets	5,662	3,689
Total current assets	227,089	205,196
Long-term investments	39,440
Property and equipment, net	11,419	5,125
Operating lease right-of-use assets	22,752
Restricted cash	227	227
Collaboration contract asset	1,338	1,958
Other assets	9	526
Total assets	302,274	213,032
Current liabilities:
Accounts payable	5,822	4,205
Accrued expenses	14,697	10,926
CIRM award liability, current portion	2,808	2,106
Deferred revenue, current portion	2,787	7,588
Operating lease liabilities, current portion	1,692
Long-term debt, current portion		2,438
Total current liabilities	27,806	27,263
Deferred rent		3,401
Accrued expenses		549
Deferred revenue, net of current portion	3,775	7,500
CIRM award liability, net of current portion	702	1,404
Operating lease liabilities, net of current portion	25,235
Long-term debt, net of current portion		12,446
Commitments and contingencies
Stockholders’ equity:
Preferred stock, $0.001 par value; authorized shares—5,000,000 at December 31, 2019 and December 31, 2018; designated Class A Convertible Preferred shares—2,819,549 at December 31, 2019 and December 31, 2018; Class A Convertible Preferred shares issued and outstanding—2,794,549 at December 31, 2019 and 2,819,549 at December 31, 2018	3	3
Common stock, $0.001 par value; authorized shares—150,000,000 at December 31, 2019 and December 31, 2018; issued and outstanding—75,730,260 at December 31, 2019 and 64,693,681 at December 31, 2018	76	65
Additional paid-in capital	628,200	445,799
Accumulated other comprehensive gain (loss)	22	(2)
Accumulated deficit	(383,545)	(285,396)
Total stockholders’ equity	244,756	160,469
Total liabilities and stockholders’ equity	$ 302,274	$ 213,032

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2019	Dec. 31, 2018
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized	5,000,000	5,000,000
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, authorized shares	150,000,000	150,000,000
Common stock issued	75,730,260	64,693,681
Common stock, outstanding shares	75,730,260	64,693,681
Class A Convertible Preferred Shares
Preferred stock designated	2,819,549	2,819,549
Preferred stock, issued shares	2,794,549	2,819,549
Preferred stock, outstanding shares	2,794,549	2,819,549

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Statement [Abstract]
Collaboration revenue	$ 10,680	$ 4,740	$ 4,106
Type of Revenue [Extensible List]	us-gaap:LicenseMember	us-gaap:LicenseMember	us-gaap:LicenseMember
Operating expenses:
Research and development	$ 87,770	$ 56,024	$ 34,358
General and administrative	23,637	15,808	11,873
Total operating expenses	111,407	71,832	46,231
Loss from operations	(100,727)	(67,092)	(42,125)
Other income (expense):
Interest income	4,330	2,190	559
Interest expense	(1,752)	(1,696)	(1,268)
Loss on extinguishment of debt			(118)
Total other income (expense), net	2,578	494	(827)
Net loss	(98,149)	(66,598)	(42,952)
Other comprehensive loss:
Unrealized gain (loss) on available-for-sale securities, net	24	1	(2)
Comprehensive loss	$ (98,125)	$ (66,597)	$ (42,954)
Net loss per common share, basic and diluted	$ (1.44)	$ (1.19)	$ (1.02)
Weighted-average common shares used to compute basic and diluted net loss per share	68,190,741	56,195,650	41,982,167

Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid In Capital	Accumulated Other Comprehensive Gain (Loss)	Accumulated Deficit	Convertible Preferred Stock
Balance at Dec. 31, 2016	$ 73,154	$ 41	$ 248,957	$ (1)	$ (175,846)	$ 3
Balance (in shares) at Dec. 31, 2016		41,386,506				2,819,549
Exercise of stock options, net of issuance costs	226		226
Exercise of stock options, net of issuance costs (in shares)		83,220
Issuance of common stock upon vesting of restricted stock units		$ 1	(1)
Issuance of common stock upon vesting of restricted stock units (in shares)		225,125
Stock–based compensation	3,606		3,606
Public offering of common stock, net of offering costs	42,979	$ 11	42,968
Public offerings of common stock, net of offering costs (in shares)		10,953,750
Private placement issuances of common stock, net of offering costs	(13)		(13)
Private placement issuance of Series A convertible preferred stock, net of offering costs	(26)		(26)
Issuance of warrants for common stock	217		217
Unrealized (loss) gain on investments	(2)			(2)
Net loss	(42,952)				(42,952)
Balance at Dec. 31, 2017	77,189	$ 53	295,934	(3)	(218,798)	$ 3
Balance (in shares) at Dec. 31, 2017		52,648,601				2,819,549
Exercise of stock options, net of issuance costs	2,693	$ 1	2,692
Exercise of stock options, net of issuance costs (in shares)		694,830
Stock–based compensation	6,293		6,293
Public offering of common stock, net of offering costs	134,791	$ 11	134,780
Public offerings of common stock, net of offering costs (in shares)		10,648,149
Issuance of common stock upon cashless warrant exercise		102,101
Issuance of common stock for license agreements	6,100		6,100
Issuance of common stock for license agreements (in shares)		600,000
Unrealized (loss) gain on investments	1			1
Net loss	(66,598)				(66,598)
Balance at Dec. 31, 2018	160,469	$ 65	445,799	(2)	(285,396)	$ 3
Balance (in shares) at Dec. 31, 2018		64,693,681				2,819,549
Exercise of stock options, net of issuance costs	2,596	$ 1	2,595
Exercise of stock options, net of issuance costs (in shares)		787,434
Issuance of common stock upon vesting of restricted stock units (in shares)		172,625
Stock–based compensation	17,410		17,410
Public offering of common stock, net of offering costs	162,406	$ 10	162,396
Public offerings of common stock, net of offering costs (in shares)		9,890,000
Issuance of common stock upon cashless warrant exercise		61,520
Conversion Of Preferred Shares To Common Stocks, Shares		125,000				(25,000)
Unrealized (loss) gain on investments	24			24
Net loss	(98,149)				(98,149)
Balance at Dec. 31, 2019	$ 244,756	$ 76	$ 628,200	$ 22	$ (383,545)	$ 3
Balance (in shares) at Dec. 31, 2019		75,730,260				2,794,549

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating activities:
Net loss	$ (98,149)	$ (66,598)	$ (42,952)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation and amortization	2,193	1,204	971
Stock–based compensation	17,410	6,293	3,606
Amortization of debt discounts and debt issuance costs	115	76	81
Accretion and amortization of premiums and discounts on investments, net	(478)	(335)	(25)
Amortization of collaboration contract asset	620	42
Noncash interest expense		373	321
Deferred rent		192	1,085
Deferred revenue	(8,526)	12,259	(2,105)
Issuance on common stock for license agreement		6,100
Non-cash loss on extinguishment of debt			30
Cash payments included in loss on extinguishment of debt			88
Changes in assets and liabilities:
Accounts receivable	500	(500)
Prepaid expenses and other assets	(1,911)	(2,010)	(428)
Accounts payable and accrued expenses	4,277	4,254	2,511
Right-of-use assets and lease liabilities, net	774
Net cash used in operating activities	(83,175)	(38,650)	(36,817)
Investing activities
Purchases of property and equipment	(7,395)	(2,303)	(1,725)
Purchases of investments	(248,858)	(55,660)	(39,971)
Maturities of investments	98,800	57,500	31,500
Net cash used in investing activities	(157,453)	(463)	(10,196)
Financing activities
Issuance of common stock from equity incentive plans, net of repurchases and issuance costs	2,522	2,693	205
Proceeds from public offering of common stock, net of issuance costs	162,406	134,577	43,206
Proceeds from CIRM award		3,510
Proceeds from long–term debt			15,000
Payments of debt issuance costs			(10)
Payments included in loss on extinguishment of debt			(88)
Principal repayments of long–term debt	(15,000)		(10,764)
Net cash provided by financing activities	149,928	140,780	47,356
Net change in cash, cash equivalents and restricted cash	(90,700)	101,667	343
Cash, cash equivalents and restricted cash at beginning of the period	190,741	89,074	88,731
Cash, cash equivalents and restricted cash at end of the period	100,041	190,741	89,074
Supplemental disclosure of cash flow information
Interest paid	2,291	1,242	2,314
Supplemental schedule of noncash investing and financing activities
Issuance of warrants for common stock in connection with long–term debt			217
Purchases of property and equipment in accounts payable	$ 602	$ 37	48
Common Stock
Financing activities
Proceeds from private placement issuances of stock, net of issuance costs			(65)
Preferred Stock
Financing activities
Proceeds from private placement issuances of stock, net of issuance costs			$ (128)

Organization and Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2019

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Organization and Summary of Significant Accounting Policies

1. Organization and Summary of Significant Accounting Policies

Organization

Fate Therapeutics, Inc. (the Company) was incorporated in the state of Delaware on April 27, 2007 and has its principal operations in San Diego, California. The Company is a clinical-stage biopharmaceutical company dedicated to the development of programmed cellular immunotherapies for cancer and immune disorders. The Company’s therapeutic pipeline is comprised of immuno-oncology programs, including off-the-shelf engineered NK- and T-cell product candidates derived from clonal master induced pluripotent stem cell (iPSC) lines, and immuno-regulatory programs, including product candidates to prevent life-threatening complications in patients undergoing hematopoietic cell transplantation. The Company’s product candidates are based on its proprietary cell programming approach, which it applies to modulate the therapeutic function and direct the fate of immune cells.

As of December 31, 2019, the Company has devoted substantially all of its efforts to product development, raising capital and building infrastructure and has not generated any revenues from any sales of its therapeutic products. To date, the Company’s revenues have been derived from collaboration agreements and government grants.

Public Equity Offerings

In September 2019, the Company completed a public offering of common stock in which investors, certain of which are affiliated with the directors of the Company, purchased 9,890,000 shares of its common stock at a price of $17.50 per share under a shelf registration statement. Gross proceeds from the offering were $173.1 million, and, after giving effect to $10.7 million of costs related to the offering, net proceeds were $162.4 million.

In September 2018, the Company completed a public offering of common stock in which investors, including investors affiliated with the directors of the Company, purchased 10,648,149 shares of its common stock at a price of $13.50 per share under a shelf registration statement. Gross proceeds from the offering were $143.8 million, and, after giving effect to $8.9 million of costs related to the offering, net proceeds were $134.9 million.

In December 2017, the Company completed a public offering of common stock in which investors purchased 10,953,750 shares of its common stock at a price of $4.20 per share under a shelf registration statement. Gross proceeds from the offering were $46.0 million, and after giving effect to $3.0 million of costs related to the offering (of which $0.3 million was paid during the year ended December 31, 2018), net proceeds were $43.0 million.

Use of Estimates

The Company’s consolidated financial statements are prepared in accordance with United States generally accepted accounting principles (GAAP). The preparation of the Company’s consolidated financial statements requires it to make estimates and assumptions that impact the reported amounts of assets, liabilities, revenues and expenses and the disclosure of contingent assets and liabilities in the Company’s consolidated financial statements and accompanying notes. The most significant estimates in the Company’s consolidated financial statements relate to accrued expenses. Although these estimates are based on the Company’s knowledge of current events and actions it may undertake in the future, actual results may ultimately materially differ from these estimates and assumptions.

Principles of Consolidation

The consolidated financial statements include the accounts of the Company and its subsidiaries, Fate Therapeutics Ltd., incorporated in the United Kingdom, Fate Therapeutics, B.V., incorporated in the Netherlands and Tfinity Therapeutics, Inc., incorporated in the United States. To date, the aggregate operations of these subsidiaries have not been significant and all intercompany transactions and balances have been eliminated in consolidation.

Segment Reporting

Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision-maker in making decisions regarding resource allocation and assessing performance. The Company views its operations and manages its business in one operating and reportable segment.

Fair Value of Financial Instruments

The carrying amounts of accounts payable and accrued liabilities are considered to be representative of their respective fair values because of the relatively short-term nature of those instruments. Based on the borrowing rates available to the Company for loans with similar terms, which is considered a Level 2 input as described below, the Company believes that the fair value of long-term debt approximates its carrying value.

The accounting guidance defines fair value, establishes a consistent framework for measuring fair value and expands disclosure for each major asset and liability category measured at fair value on either a recurring or nonrecurring basis. Fair value is defined as an exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or liability. As a basis for considering such assumptions, the accounting guidance establishes a three- tier fair value hierarchy, which prioritizes the inputs used in measuring fair value as follows:

Level 1: Observable inputs such as quoted prices in active markets;

Level 2: Inputs, other than the quoted prices in active markets, that are observable either directly or indirectly; and

Level 3: Unobservable inputs in which there is little or no market data, which require the reporting entity to develop its own assumptions.

Financial assets measured at fair value on a recurring basis consist of the Company’s cash equivalents and investments. Cash equivalents consisted of money market funds and investments consisted of U.S. treasuries and corporate debt securities. The following table presents the Company’s assets which were measured at fair value on a recurring basis as of December 31, 2019 and 2018 (in thousands):

			Fair Value Measurements at Reporting Date Using
	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
As of December 31, 2019:
Cash equivalents
Money market funds	$	84,814	$	84,814	$	—	$	—
Investments
U.S. Treasury debt securities		60,303		60,303		—		—
Corporate debt securities		100,750		—		100,750		—
Total assets measured at fair value on a recurring basis	$	245,867	$	145,117	$	100,750	$	—

As of December 31, 2018:
Cash equivalents
Money market funds	$	190,514	$	190,514	$	—	$	—
Investments
U.S. Treasury debt securities		10,493		10,493		—		—
Total assets measured at fair value on a recurring basis	$	201,007	$	201,007	$	—	$	—

The Company obtains pricing information from its investment manager and generally determines the fair value of investment securities using standard observable inputs, including reported trades, broker/dealer quotes, and bid and/or offers.

None of the Company’s non-financial assets or liabilities are recorded at fair value on a non-recurring basis. No transfers between levels have occurred during the periods presented.

As of December 31, 2019 and 2018, the Company had no material liabilities measured at fair value on a recurring basis.

Cash, Cash Equivalents and Restricted Cash

Cash and cash equivalents include cash in readily available checking and savings accounts, money market accounts and money market funds. The Company considers all highly liquid investments with an original maturity of three months or less from the date of purchase to be cash equivalents.

The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the consolidated balance sheets that sum to the total of the same such amounts shown in the consolidated statements of cash flows as of December 31, 2019, 2018 and 2017 (in thousands):

	Years Ended December 31,
	2019		2018		2017
Cash and cash equivalents	$	99,814	$	190,514	$	88,952
Restricted cash		227		227		122
Total cash, cash equivalents, and restricted cash shown in the consolidated statement of cash flows	$	100,041	$	190,741	$	89,074

Amounts included in restricted cash represent security deposits required to secure the Company’s credit card limit and its facilities lease.

Investments

Investments are accounted for as available-for-sale securities and are carried at fair value, with the unrealized gains and losses reported in other comprehensive income (loss). The amortized cost of investments classified as available-for-sale debt securities is adjusted for amortization of premiums and accretion of discounts to maturity. Such amortization and accretion are included in interest income. Realized gains and losses and declines in value judged to be other-than-temporary, if any, on investments classified as available-for-sale securities are included in other income or expense. The cost of securities sold is based on the specific identification method. Interest and dividends on securities classified as available-for-sale are included in interest income.

Concentration of Credit Risk

Financial instruments, which potentially subject the Company to a significant concentration of credit risk, consist primarily of cash and cash equivalents and investments. The Company maintains deposits in federally insured financial institutions in excess of federally insured limits. The Company has not experienced any losses in such accounts and management believes that the Company is not exposed to significant credit risk due to the financial position of the depository institutions in which those deposits and investments are held.

Property and Equipment

Property and equipment are recorded at cost and depreciated using the straight-line method over the estimated useful lives of the assets (generally two to five years) and generally consist of furniture and fixtures, computers, scientific and office equipment, and in-process costs related to facilities construction. Repairs and maintenance costs are charged to expense as incurred.

Impairment of Long-Lived Assets

Long-lived assets are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. An impairment loss is recorded if and when events and circumstances indicate that assets might be impaired and the undiscounted cash flows estimated to be generated by those assets are less than the carrying amount of those assets. If the carrying amount is not recoverable, the Company measures the amount of any impairment by comparing the carrying value of the asset to the present value of the expected future cash flows associated with the use of the asset. While the Company’s current and historical operating losses and negative cash flows are indicators of impairment, management believes that future cash flows to be received support the carrying value of its long-lived assets and, accordingly, has not recognized any impairment losses since inception.

Leases

Effective January 1, 2019, the Company determines if a contract contains a lease at the inception of the contract. The Company currently has leases related to its facilities leased for office and laboratory space, which are classified as operating leases. These leases result in operating right-of-use (ROU) assets, current operating lease liabilities, and non-current operating lease liabilities in the condensed consolidated balance sheets. The Company does not have any financing leases. Leases with a term of 12 months or less are considered short-term and a ROU asset and lease obligation are not recognized. Payments associated with short-term leases are expensed on a straight-line basis over the lease term.

Lease liabilities represent an obligation to make lease payments arising from the lease and ROU assets represent the right to use the underlying asset identified in the lease for the lease term. Lease liabilities are measured at the present value of the lease payments not yet paid discounted using the discount rate for the lease established at the lease commencement date. To determine the present value, the implicit rate is used when readily determinable. For those leases where the implicit rate is not provided, the Company determines an incremental borrowing rate based on the information available at the lease commencement date in determining the present value of lease payments. ROU assets are measured as the present value of the lease payments and also include any prepaid lease payments made and any other indirect costs, and exclude any lease incentives received. Lease terms may include the impact of options to extend or terminate the lease when it is reasonably certain that the Company will exercise that option. Lease expense for operating leases is recognized on a straight-line basis over the lease term. The Company aggregates all lease and non-lease components for each class of underlying assets into a single lease component.

Revenue Recognition

The Company recognizes revenue in a manner that depicts the transfer of control of a product or a service to a customer and reflects the amount of the consideration the Company is entitled to receive in exchange for such product or service. In doing so, the Company follows a five-step approach: (i) identify the contract with a customer, (ii) identify the performance obligations in the contract, (iii) determine the transaction price, (iv) allocate the transaction price to the performance obligations, and (v) recognize revenue when (or as) the customer obtains control of the product or service. The Company considers the terms of a contract and all relevant facts and circumstances when applying the revenue recognition standard. The Company applies the revenue recognition standard, including the use of any practical expedients, consistently to contracts with similar characteristics and in similar circumstances.

A customer is a party that has entered into a contract with the Company, where the purpose of the contract is to obtain a product or a service that is an output of the Company’s ordinary activities in exchange for consideration. To be considered a contract, (i) the contract must be approved (in writing, orally, or in accordance with other customary business practices), (ii) each party’s rights regarding the product or the service to be transferred can be identified, (iii) the payment terms for the product or the service to be transferred can be identified, (iv) the contract must have commercial substance (that is, the risk, timing or amount of future cash flows is expected to change as a result of the contract), and (v) it is probable that the Company will collect substantially all of the consideration to which it is entitled to receive in exchange for the transfer of the product or the service.

A performance obligation is defined as a promise to transfer a product or a service to a customer. The Company identifies each promise to transfer a product or a service (or a bundle of products or services, or a series of products and services that are substantially the same and have the same pattern of transfer) that is distinct. A product or a service is distinct if both (i) the customer can benefit from the product or the service either on its own or together with other resources that are readily available to the customer and (ii) the Company’s promise to transfer the product or the service to the customer is separately identifiable from other promises in the contract. Each distinct promise to transfer a product or a service is a unit of accounting for revenue recognition. If a promise to transfer a product or a service is not separately identifiable from other promises in the contract, such promises should be combined into a single performance obligation.

The transaction price is the amount of consideration the Company is entitled to receive in exchange for the transfer of control of a product or a service to a customer. To determine the transaction price, the Company considers the existence of any significant financing component, the effects of any variable elements, noncash considerations and consideration payable to the customer. If a significant financing component exists, the transaction price is adjusted for the time value of money. If an element of variability exists, the Company must estimate the consideration it expects to receive and uses that amount as the basis for recognizing revenue as the product or the service is transferred to the customer. There are two methods for determining the amount of variable consideration: (i) the expected value method, which is the sum of probability-weighted amounts in a range of possible consideration amounts, and (ii) the mostly likely amount method, which identifies the single most likely amount in a range of possible consideration amounts.

If a contract has multiple performance obligations, the Company allocates the transaction price to each distinct performance obligation in an amount that reflects the consideration the Company is entitled to receive in exchange for satisfying each distinct performance obligation. For each distinct performance obligation, revenue is recognized when (or as) the Company transfers control of the product or the service applicable to such performance obligation.

In those instances where the Company first receives consideration in advance of satisfying its performance obligation, the Company classifies such consideration as deferred revenue until (or as) the Company satisfies such performance obligation. In those instances where the Company first satisfies its performance obligation prior to its receipt of consideration, the consideration is recorded as accounts receivable.

The Company expenses incremental costs of obtaining and fulfilling a contract as and when incurred if the expected amortization period of the asset that would be recognized is one year or less, or if the amount of the asset is immaterial. Otherwise, such costs are capitalized as contract assets if they are incremental to the contract and amortized to expense proportionate to revenue recognition of the underlying contract.

Research and Development Costs

All research and development costs are expensed as incurred.

Patent Costs

Costs related to filing and pursuing patent applications are recorded as general and administrative expense and expensed as incurred since recoverability of such expenditures is uncertain.

Stock-Based Compensation

Stock-based compensation expense represents the cost of the grant date fair value of employee stock option and restricted stock unit grants recognized over the requisite service period of the awards (usually the vesting period) on a straight-line basis. For stock option grants for which vesting is subject to performance-based milestones, the expense is recorded over the remaining service period after the point when the achievement of the milestone is probable or the performance condition has been achieved. For stock option grants for which vesting is subject to both performance-based milestones and market conditions, expense is recorded over the derived service period after the point when the achievement of the performance-based milestone is probable or the performance condition has been achieved. The Company estimates the fair value of stock option grants using the Black-Scholes option pricing model, with the exception of option grants for which vesting is subject to both performance-based milestones and market conditions, which are valued using a lattice-based model. The fair value of restricted stock units is based on the closing price of the Company’s common stock as reported on The Nasdaq Global Market on the date of grant. The Company recognizes forfeitures for all awards as such forfeitures occur.

Convertible Preferred Stock

The Company applies the relevant accounting standards to distinguish liabilities from equity when assessing the classification and measurement of preferred stock. Preferred shares subject to mandatory redemptions are considered liabilities and measured at fair value. Conditionally redeemable preferred shares are considered temporary equity. All other preferred shares are considered as stockholders’ equity.

The Company applies the relevant accounting standards for derivatives and hedging (in addition to distinguishing liabilities from equity) when accounting for hybrid contracts that contain conversion options. Conversion options must be bifurcated from the host instruments and accounted for as free-standing financial instruments according to certain criteria. These criteria include circumstances when (i) the economic characteristics and risks of the embedded derivative instruments are not clearly and closely related to the economic characteristics and risks of the host contract, (ii) the hybrid instrument that embodies both the embedded derivative instrument and the host contract is not re-measured at fair value under otherwise applicable accounting principles with changes in fair value reported in earnings as they occurred, and (iii) a separate instrument with the same terms as the embedded derivative instrument would be considered a derivative instrument. The derivative is subsequently measured at fair value at each reporting date, with the changes in fair value reported in earnings.

Income Taxes

The Company accounts for income taxes under the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the financial statements. Under this method, deferred tax assets and liabilities are determined on the basis of the differences between the financial statements and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. The effect of a change in tax rates on deferred tax assets and liabilities is recognized in income in the period that includes the enactment date.

The Company recognizes net deferred tax assets to the extent that the Company believes these assets are more likely than not to be realized. In making such a determination, management considers all available positive and negative evidence, including future reversals of existing taxable temporary differences, projected future taxable income, tax-planning strategies, and results of recent operations. If management determines that the Company would be able to realize its deferred tax assets in the future in excess of their net recorded amount, management would make an adjustment to the deferred tax asset valuation allowance, which would reduce the provision for income taxes.

The Company records uncertain tax positions on the basis of a two-step process whereby (1) management determines whether it is more likely than not that the tax positions will be sustained on the basis of the technical merits of the position and (2) for those tax positions that meet the more- likely-than-not recognition threshold, management recognizes the largest amount of tax benefit that is more than 50 percent likely to be realized upon ultimate settlement with the related tax authority. The Company recognizes interest and penalties related to unrecognized tax benefits within income tax expense. Any accrued interest and penalties are included within the related tax liability.

Comprehensive Loss

Comprehensive loss is defined as a change in equity during a period from transactions and other events and circumstances from non-owner sources. Other comprehensive loss included unrealized gains and losses on investments classified as available-for-sale securities, which was the only difference between net loss and comprehensive loss for the applicable periods.

Net Loss Per Common Share

Basic net loss per common share is calculated by dividing the net loss by the weighted-average number of common shares outstanding for the period, without consideration for common stock equivalents. Dilutive common stock equivalents comprised convertible preferred stock, warrants for the purchase of common stock, and common stock options and restricted stock units outstanding under the Company’s stock option plans. For all periods presented, there is no difference in the number of common shares used to calculate basic and diluted common shares outstanding due to the Company’s net loss position.

Potentially dilutive securities not included in the calculation of diluted net loss per common share because to do so would be anti-dilutive are as follows (in common stock equivalent shares):

	As of December 31,
	2019		2018		2017
Warrants for common stock		—		85,094		225,756
Common stock options		9,327,742		6,980,581		5,458,043
Restricted stock units		520,000		188,625		212,625
Series A convertible preferred stock (if converted)		13,972,745		14,097,745		14,097,745
Total		23,820,487		21,352,045		19,994,169

Going Concern Assessment

Substantial doubt about an entity’s ability to continue as a going concern exists when relevant conditions and events, considered in the aggregate, indicate that it is probable that the entity will be unable to meet its obligations as they become due within one year from the financial statement issuance date. The Company determined that there are no conditions or events that raise substantial doubt about its ability to continue as a going concern as of the date of the issuance of these financial statements.

Recently Adopted Accounting Pronouncements

In June 2018, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) 2018-07. ASU 2018-07 expands the scope of Accounting Standards Codification (ASC) 718, Compensation-Stock Compensation, to include share-based payment transactions for acquiring goods and services from nonemployees. Consistent with the accounting requirement for employee share-based payment awards, nonemployee share-based payment awards within the scope of ASC 718 will be measured at the grant-date fair value of the equity instruments that an entity is obligated to issue when the good has been delivered or the service has been rendered. ASU 2018-07 is effective for fiscal years beginning after December 15, 2018. The Company adopted the update in the first quarter of fiscal year 2019 using the modified retrospective method. The adoption did not have a material effect on the Company’s consolidated financial statements.

In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) (ASC 842), which requires a lessee to recognize a lease liability and a right-of-use asset for all leases with lease terms of more than 12 months. This guidance is effective for annual reporting periods beginning after December 15, 2018, including interim periods within those years, and early adoption is permitted. Companies may adopt this guidance using a modified retrospective approach for leases that exist or are entered into after the beginning of the earliest comparative period in the financial statements. In July 2018, the FASB issued ASU 2018-11, which provides the option of an additional transition method that allows entities to initially apply the new lease guidance at the adoption date and recognize a cumulative-effect adjustment to the opening balance of retained earnings in the period of adoption.

The Company adopted the standard effective January 1, 2019 using the optional transition method as detailed in ASU 2018-11, which resulted in an increase in operating right-of-use assets of $16.6 million and an increase in total liabilities of $18.2 million on the consolidated balance sheet as of the effective date. There was no material impact on the Company’s consolidated statement of operations and comprehensive loss for the year ended December 31, 2019 as a result of the adoption of ASU 2016-02. There was no impact to the consolidated financial statements for the prior periods presented due to the transition method elected. The Company elected the package of practical expedients permitted under the transition guidance, which among other things, allowed the Company to carry forward the historical lease classification. Additionally, the Company elected the hindsight provision for determining the lease term and elected to aggregate all lease and non-lease components for each class of underlying assets into a single lease component.

Recently Issued Accounting Pronouncements

In November 2018, the FASB issued ASU 2018-18, which clarifies the interaction between ASC Topic 808, Collaborative Arrangements, and ASC Topic 606, Revenue from Contracts with Customers. The guidance, among other items, clarifies that certain transactions between collaborative participants should be accounted for as revenue under Topic 606 when the collaborative arrangement participant is a customer in the context of a unit of account. ASU 2018-18 is effective for fiscal years beginning after December 15, 2019. The Company is currently evaluating the expected impact of the guidance, but does not believe the adoption of this guidance will have a material impact on the Company’s consolidated financial statements.

In August 2018, the FASB issued ASU No. 2018-13 (ASU 2018-13). ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement, amends the disclosure requirements in ASC 820 by adding, changing, or removing certain disclosures. ASU 2018-13 is effective for fiscal years beginning after December 15, 2019. The Company is currently evaluating the expected impact of the guidance, but does not believe the adoption of this guidance will have a material impact on the Company’s consolidated financial statements.

In June 2016, the FASB issued ASU 2016-13, Financial Instruments - Credit Losses: Measurement of Credit Losses on Financial Instruments, which amends the impairment model by requiring entities to use a forward-looking approach based on expected losses to estimate credit losses on certain types of financial instruments, including trade receivables and available-for-sale debt securities. The standard is effective for fiscal years beginning after December 15, 2019, with early adoption permitted. The Company is currently evaluating the expected impact of the guidance, but does not believe the adoption of this guidance will have a material impact on the Company’s consolidated financial statements.

Collaboration and License Agreements

12 Months Ended

Dec. 31, 2019

Collaboration And License Agreements Disclosure [Abstract]

Collaboration and License Agreements

2. Collaboration and License Agreements

Ono Collaboration and Option Agreement

On September 14, 2018, the Company entered into a Collaboration and Option Agreement (the Ono Agreement) with Ono Pharmaceutical Co. Ltd. (Ono) for the joint development and commercialization of two off-the-shelf iPSC-derived chimeric antigen receptor (CAR) T-cell product candidates. The first off-the-shelf, iPSC-derived CAR T-cell candidate (Candidate 1) targets an antigen expressed on certain lymphoblastic leukemias, and the second off-the-shelf, iPSC-derived CAR T-cell candidate (Candidate 2) targets a novel antigen identified by Ono expressed on certain solid tumors (each a Candidate and collectively the Candidates).

Pursuant to the Ono Agreement, the Company and Ono are jointly conducting research and development activities under a joint development plan, with the goal of advancing each Candidate to a pre-defined preclinical milestone. The Company has granted to Ono, during a specified period of time, an option to obtain an exclusive license under certain intellectual property rights to develop and commercialize (a) Candidate 1 in Asia, with the Company retaining rights for development and commercialization in all other territories of the world and (b) Candidate 2 in all territories of the world, with the Company retaining the right to co-develop and co-commercialize Candidate 2 in the United States and Europe under a joint arrangement whereby it is eligible to share at least 50% of the profits and losses (each, an Option).

For each Candidate, the Option will expire upon the earliest of: (a) the achievement of the pre-defined preclinical milestone, (b) termination by Ono of research and development activities for the Candidate and (c) the date that is the later of (i) four years after the Effective Date and (ii) completion of all applicable activities contemplated under the joint development plan (the Option Period). The Company has maintained worldwide rights of manufacture for both Candidates.

Under the terms of the Ono Agreement, Ono paid the Company an upfront, non-refundable and non-creditable payment of $10.0 million in connection with entering into the Ono Agreement. Additionally, as consideration for the Company’s conduct of research and preclinical development under a joint development plan, Ono pays the Company annual research and development fees set forth in the annual budget included in the joint development plan, which fees are estimated to be $20.0 million in aggregate over the course of the joint development plan. The Company received $5.0 million in October 2018 as a prepayment for the first year of research and development.

Further, under the terms of the Ono Agreement, Ono has agreed to pay the Company up to an additional $40.0 million, subject to the achievement of a preclinical milestone (Option Milestone) and the exercise by Ono of the Options (Option Exercise Fees) during the Option Period. Such fees are in addition to the upfront payment and research and development fees.

Subject to Ono’s exercise of the Options and to the achievement of certain clinical, regulatory and commercial milestones (Milestones) with respect to each Candidate in specified territories, the Company is entitled to receive an aggregate of up to $285.0 million in milestone payments for Candidate 1 and an aggregate of up to $895.0 million in milestone payments for Candidate 2, with the applicable milestone payments for Candidate 2 for the United States and Europe subject to reduction by 50% if the Company elects to co-develop and co-commercialize Candidate 2 as described above. The Company is also eligible to receive tiered royalties (Royalties) ranging from the mid-single digits to the low-double digits based on annual net sales by Ono of each Candidate in specified territories, with such royalties subject to certain reductions.

The Ono Agreement will terminate with respect to a Candidate if Ono does not exercise its Option for a Candidate within the Option Period, or in its entirety if Ono does not exercise any of its Options for the Candidates within their respective Option Periods. In addition, either party may terminate the Ono Agreement in the event of breach, insolvency or patent challenges by the other party; provided, that Ono may terminate the Ono Agreement in its sole discretion (x) on a Candidate-by-Candidate basis at any time after the second anniversary of the effective date of the Ono Agreement or (y) on a Candidate-by-Candidate or country-by-country basis at any time after the expiration of the Option Period, subject to certain limitations. The Ono Agreement will expire on a Candidate-by-Candidate and country-by-country basis upon the expiration of the applicable royalty term, or in its entirety upon the expiration of all applicable payment obligations under the Ono Agreement.

The Company applied ASC 808, Collaborative Arrangements and determined that the Ono Agreement is applicable to such guidance. The Company concluded that Ono represented a customer and applied relevant guidance from ASC 606, Revenue from Contracts with Customers (ASC 606) to evaluate the appropriate accounting for the Ono Agreement. In accordance with this guidance, the Company identified its performance obligations, including its grant of a license to Ono to certain of its intellectual property subject to certain conditions, its conduct of research services, and its participation in a joint steering committee. The Company determined that its grant of a license to Ono to certain of its intellectual property subject to certain conditions was not distinct from other performance obligations because such grant is dependent on the conduct and results of the research services. As a result, the license is classified as symbolic intellectual property under ASC 606. Additionally, the Company determined that its conduct of research services was not distinct from other performance obligations since such conduct is dependent on the guidance of the joint steering committee. Accordingly, the Company determined that all performance obligations should be accounted for as one combined performance obligation, and that the combined performance obligation is transferred over the expected term of the conduct of the research services, which is estimated to be four years.

The Company also assessed, in connection with the upfront, non-refundable and non-creditable payment of $10.0 million received in September 2018 and the $5.0 million prepayment of the first-year research and development fees in October 2018, whether a significant financing component exists under the Ono Agreement. Such assessment evaluated whether: (i) a substantial amount of the consideration is variable, (ii) the amount, or timing of payment, of the consideration would have varied based on the occurrence or non-occurrence of future events that are not substantially within the control of the Company or Ono, and (iii) the timing of the transfer of the performance obligations is at the discretion of Ono. Based on its assessment, the Company concluded that there was not a significant financing component.

The Company also assessed the effects of any variable elements under the Ono Agreement. Such assessment evaluated, among other things, the likelihood of receiving (i) preclinical milestone and option fees, (ii) various clinical, regulatory and commercial milestone payments, and (iii) royalties on net sales of either product Candidate. Based on its assessment, the Company concluded that, based on the likelihood of these variable components occurring, there was not a significant variable element included in the transaction price.

In accordance with ASC 606, the Company determined that the initial transaction price under the Ono Agreement equals $30.0 million, consisting of the upfront, non-refundable and non-creditable payment of $10.0 million and the aggregate estimated research and development fees of $20.0 million. The upfront payment of $10.0 million was recorded as deferred revenue and will be recognized as revenue over time in conjunction with the Company’s conduct of research services over the estimated four-year period based on actual costs incurred compared to estimated total costs expected to be incurred under the Ono Agreement, as the research and development activities are the primary component of the combined performance obligation. The Company recorded the $5.0 million prepayment of the first-year research and development fees as deferred revenue, and such fees were recognized as revenue as the research services were delivered. To date, the Company has received $6.5 million of research and development fees.

The Company has not assigned a transaction price to any Option Milestone, Milestones or Option Exercise Fees given the substantial uncertainty related to their achievement and has not assigned a transaction price to any Royalties.

As a direct result of the Company’s entry into the Ono Agreement, the Company incurred an aggregate of $2.0 million in sublicense consideration to existing licensors of the Company. The $2.0 million in sublicense consideration represents an asset under ASC 340, Other Assets and Deferred Costs and is amortized to research and development expense in conjunction with the Company’s revenue recognition under the Ono Agreement. During the year ended December 31, 2019, the Company recognized $0.6 million of such expense. As of December 31, 2019, the contract asset had a balance of $1.3 million.

The Company recognized revenue of $9.3 million under the Ono Agreement during the year ended December 31, 2019. Such revenue comprised $6.2 million associated with research services and $3.1 million associated with the upfront payment. During the year ended December 31, 2018, the Company recognized revenue of $0.6 million under the Ono Agreement. Such revenue comprised $0.4 million associated with research services and $0.2 million associated with the upfront payment. As of December 31, 2019, aggregate deferred revenue related to the Ono Agreement was $6.6 million, of which $2.8 million is classified as current.

Juno Collaboration and License Agreement

On May 4, 2015, the Company entered into a strategic research collaboration and license agreement (the Juno Agreement) with Juno Therapeutics, Inc. (Juno) to screen for and identify small molecules that enhance the therapeutic properties of Juno’s genetically-engineered T-cell immunotherapies. The four-year initial research term under the Juno Agreement concluded as scheduled on May 4, 2019, and the overall agreement was terminated upon the receipt of the last quarterly research payment of $0.2 million, which occurred in May 2019. No additional funding is expected from Juno.

The Company applied ASC 606 to evaluate the appropriate accounting for the Juno Agreement. In accordance with this guidance, the Company identified its performance obligations, including its grant of an exclusive worldwide license to certain of its intellectual property subject to certain conditions, its conduct of research services and its participation in a joint research committee.

Total revenue recognized under the Juno Agreement during the year ended December 31, 2019 was $1.4 million, which comprised $0.7 million associated with the upfront fee and equity premium, and $0.7 million associated with research services. Total revenue recognized under the Juno Agreement for the year ended December 31, 2018 was $4.1 million, which comprised $2.1 million associated with the upfront fee and the equity premium and $2.0 million associated with research services. Total revenue recognized under the Juno Agreement for the year ended December 31, 2017 was $4.1 million, which comprised $2.1 million associated with the upfront fee and the equity premium and $2.0 million associated with research services. No additional revenue is expected to be recognized under the Juno Agreement in future periods.

Memorial Sloan Kettering Cancer Center License Agreement

On May 15, 2018, the Company entered into an Amended and Restated Exclusive License Agreement (the Amended MSK License) with Memorial Sloan Kettering Cancer Center (MSK). The Amended MSK License amends and restates the Exclusive License Agreement entered into between the Company and MSK on August 19, 2016 (the Original MSK License), pursuant to which the Company entered into an exclusive license agreement with MSK for rights relating to compositions and methods covering iPSC-derived cellular immunotherapy, including T-cells and NK-cells derived from iPSCs engineered with CARs.

Pursuant to the Amended MSK License, MSK granted to the Company additional licenses to certain patents and patent applications relating to new CAR constructs and off-the-shelf CAR T cells, including the use of clustered regularly interspaced short palindromic repeat (CRISPR) and other innovative technologies for their production, in each case to research, develop, and commercialize licensed products in the field of all human therapeutic uses worldwide. The Company has the right to grant sublicenses to certain licensed rights in accordance with the terms of the Amended MSK License, in which case it is obligated to pay MSK a percentage of certain sublicense income received by the Company.

The Company issued 500,000 shares of the Company’s common stock to MSK (the MSK Shares) and, in return, MSK returned its entire interest in Tfinity Therapeutics, Inc. (Tfinity) to the Company. As a result, as of the effective date of the Amended MSK License, Tfinity is a wholly-owned subsidiary of the Company. The MSK Shares were issued pursuant to an exemption from registration under the Securities Act of 1933, as amended (the Securities Act), in reliance on Section 4(a)(2) of the Securities Act regarding transactions by an issuer not involving a public offering.

Additionally, the Company paid an upfront fee of $0.5 million. The Company is also obligated to pay to MSK an annual license maintenance fee during the term of the agreement, and milestone payments upon the achievement of specified clinical, regulatory and commercial milestones for licensed products as well as royalty payments on net sales of licensed products.

Furthermore, in the event a licensed product achieves a specified clinical milestone, MSK is then eligible to receive additional milestone payments, where the amount of such payments owed to MSK are contingent upon certain increases in the price of the Company’s common stock following the date of achievement of such clinical milestone.

Given the high degree of uncertainty surrounding the achievement of clinical milestones and the requisite increase in the price of the Company’s common stock, the Company has not recorded a liability for such payments.

During the year ended December 31, 2018, the Company recognized an aggregate of $5.3 million of research and development expenses, consisting of the $0.5 million upfront cash payment to MSK and the issuance of the MSK Shares, valued at $4.8 million, associated with the Amended MSK License.

Gladstone License Agreement

On September 11, 2018, the Company entered into an exclusive license agreement (the Gladstone License Agreement) with the J. David Gladstone Institutes (Gladstone).

Pursuant to the Gladstone License Agreement, Gladstone granted to the Company exclusive licenses to certain patents and patent applications (the Patent Rights) for the research, development, manufacturing, and commercialization of human therapeutics derived from iPSCs. The Patent Rights cover the use of the CRISPR and engineered nuclease-deactivated CRISPR-associated protein-9 (dCas9) system, known as the CRISPR activation (CRISPRa) system, for cellular reprogramming and iPSC generation.

In consideration for the rights granted under the Gladstone License Agreement, the Company issued to Gladstone 100,000 shares of the Company’s common stock (the Gladstone Shares). The Gladstone Shares were issued pursuant to an exemption from registration under the Securities Act, in reliance on Section 4(a)(2) of the Securities Act regarding transactions by an issuer not involving a public offering.

Additionally, the Company paid Gladstone an upfront fee of $0.1 million and is obligated to pay Gladstone milestone payments in an aggregate amount of up to approximately $1.9 million upon the achievement of specified clinical, regulatory and commercial milestones as well as tiered royalties in the low single digits on net sales of human therapeutic products covered by the Patent Rights. The Company is also obligated to pay Gladstone a tiered percentage in the low- to mid-single digits of certain income received by the Company in connection with the sublicense of the Patent Rights.

During the year ended December 31, 2018, the Company recognized an aggregate of $1.4 million of research and development expenses, consisting of the $0.1 million upfront cash payment to Gladstone and the issuance of the Gladstone Shares, valued at $1.3 million, associated with the Gladstone License Agreement.

California Institute for Regenerative Medicine Award

12 Months Ended

Dec. 31, 2019

Award From California Institute For Regenerative Medicine [Abstract]

California Institute for Regenerative Medicine Award

3.	California Institute for Regenerative Medicine Award

On April 5, 2018, the Company executed an award agreement with the California Institute for Regenerative Medicine (CIRM) pursuant to which CIRM awarded the Company $4.0 million to advance the Company’s FT516 product candidate into a first-in-human clinical trial for the treatment of subjects with advanced solid tumors, including in combination with monoclonal antibody therapy (the Award). Pursuant to the terms of the Award, the Company is eligible to receive five disbursements in varying amounts totaling $4.0 million, with one disbursement receivable upon the execution of the Award, and four disbursements receivable upon the completion of certain milestones throughout the project period. The Award is subject to certain co-funding requirements by the Company, and the Company is required to provide CIRM progress and financial update reports under the Award. In December 2018, the Company discussed with CIRM its intent to pursue the clinical development of FT516 in relapsed / refractory hematologic malignancies in addition to advanced solid tumors, and the Company’s preference to first submit an IND application for FT516 in relapsed / refractory hematologic malignancies rather than in advanced solid tumors. In January 2019, the Company submitted its IND application for FT516 in relapsed / refractory hematologic malignancies, which IND submission was allowed by the FDA in February 2019. The Company and CIRM agreed to suspend the Award until such time as the Company elected to proceed with its submission of an IND application for FT516 in advanced solid tumors. In November 2019, the Company filed an IND application for FT516 in advanced solid tumors and the Award was taken off of suspension by CIRM in January 2020. In February 2020, the Company received a $0.4 million disbursement based on a milestone achievement.

Pursuant to the terms of the Award, the Company, in its sole discretion, has the option to treat the Award either as a loan or as a grant. In the event the Company elects to treat the Award as a loan, the Company will be obligated to repay i) 60%, ii) 80%, iii) 100% or iv) 100% plus interest at 7% plus LIBOR, of the total Award to CIRM, where such repayment rate is dependent upon the phase of clinical development of FT516 at the time of the Company’s election. If the Company does not elect to treat the Award as a loan within 10 years of the date of the Award, the Award will be considered a grant and the Company will be obligated to pay to CIRM a royalty on commercial sales of FT516 until such royalty payments equal nine times the total amount awarded to the Company under the Award.

Since the Company may, at its election, repay some or all of the Award, the Company accounts for the Award as a liability until the time of election. As of December 31, 2019, the Company has received aggregate disbursements under the Award in the amount of $3.5 million. The aggregate amount received is recorded as a CIRM Liability on the accompanying consolidated balance sheets and classified as current or non-current based on the potential amount payable within twelve months of the current balance sheet date.

Investments

12 Months Ended

Dec. 31, 2019

Investments [Abstract]

Investments

4. Investments

The Company invests portions of excess cash in United States treasuries and corporate debt securities with maturities ranging from three to eighteen months from the purchase date. These securities are classified as short-term and long-term investments in the accompanying consolidated balance sheets based on each security’s contractual maturity date and are accounted for as available-for-sale securities.

The following table summarizes the Company’s investments accounted for as available-for-sale securities as of December 31, 2019 and 2018 (in thousands):

	Maturity (in years)	Amortized Cost		Unrealized Losses			Unrealized Gains		Estimated Fair Value
December 31, 2019
Classified as current assets:
U.S. Treasury debt securities	1 or less	$	50,445	$	(4	)	$	16	$	50,457
Corporate debt securities	1 or less		71,171		(24	)		9		71,156
Total short-term investments		$	121,616	$	(28	)	$	25	$	121,613
Classified as non-current assets:
U.S. Treasury debt securities	Greater than 1	$	9,841	$	—		$	5	$	9,846
Corporate debt securities	Greater than 1		29,572		(1	)		23		29,594
Total long-term investments		$	39,413	$	(1	)	$	28	$	39,440

December 31, 2018
Classified as current assets:
U.S. Treasury debt securities	1 or less	$	10,495	$	(2	)	$	—	$	10,493
Total short-term investments		$	10,495	$	(2	)	$	—	$	10,493

The Company reviews its investment holdings at the end of each reporting period and determines if any unrealized losses are other-than-temporary using a variety of factors including the Company’s intent to sell the underlying securities prior to maturity and whether it is more likely than not that the Company would be required to sell the securities before the recovery of their amortized basis. During the years ended December 31, 2019, 2018 and 2017 the Company did not recognize any impairment or realized gains or losses on sales of investments and the Company does not consider any of its investments as other-than-temporarily impaired.

Property and Equipment

12 Months Ended

Dec. 31, 2019

Property Plant And Equipment [Abstract]

Property and Equipment

5. Property and Equipment

Property and equipment consist of the following (in thousands):

	December 31,
	2019			2018
Furniture and fixtures	$	899		$	516
Computer and office equipment		917			688
Software		103			103
Leasehold improvements—building		2,465			288
Scientific equipment		15,355			7,868
Construction-in-process		198			1,987
Total property and equipment, gross		19,937			11,450
Less accumulated depreciation and amortization		(8,518	)		(6,325	)
Total property and equipment, net	$	11,419		$	5,125

Depreciation expense related to property and equipment was $2.2 million, $1.2 million, and $1.0 million, for the years ended December 31, 2019, 2018, and 2017, respectively. No material gains or losses on the disposal of property and equipment have been recorded for the years ended December 31, 2019, 2018, and 2017. As of December 31, 2019, $0.6 million of fixed assets had not been paid.

Accrued Expenses and Long-Term Debt

12 Months Ended

Dec. 31, 2019

Accrued Expenses And Long Term Debt Disclosure [Abstract]

Accrued Expenses and Long-Term Debt

6. Accrued Expenses and Long-Term Debt

Accrued Expenses

Current accrued expenses consist of the following (in thousands):

	December 31,
	2019		2018
Accrued payroll and other employee benefits	$	5,329	$	2,938
Accrued clinical trial related costs		5,976		4,729
Accrued other		3,392		3,259
Total current accrued expenses	$	14,697	$	10,926

Long-term accrued expenses represented the accrual for the final payment fee associated with our long-term debt.

Long-Term Debt

Long-term debt and unamortized discount balances are as follows (in thousands):

	December 31,
	2019		2018
Long-term debt	$	—	$	15,000
Less debt issuance costs and discount, net of current portion		—		(54	)
Long-term debt, net of long-term portion of debt issuance costs and discount		—		14,946
Less current portion of long-term debt		—		(2,500	)
Long-term debt, net	$	—	$	12,446
Current portion of long-term debt	$	—	$	2,500
Less current portion of debt issuance costs and discount		—		(62	)
Current portion of long-term debt, net	$	—	$	2,438

Silicon Valley Bank Debt Facilities

On July 30, 2014, the Company entered into the Amended and Restated Loan and Security Agreement (the Restated LSA) with Silicon Valley Bank (the Bank), collateralized by substantially all of the Company’s assets, excluding certain intellectual property. The Restated LSA amends and restates the Loan and Security Agreement, dated as of January 5, 2009, as amended, by and between the Company and the Bank (Loan Agreement). Pursuant to the Restated LSA, the Bank agreed to make loans to the Company in an aggregate principal amount of up to $20.0 million, comprised of (i) a $10.0 million term loan, funded at the closing date (the Term A Loan) and (ii) subject to the achievement of a specified clinical milestone, additional term loans totaling up to $10.0 million in the aggregate, which were available until December 31, 2014 (each, a Term B Loan). On December 24, 2014, the Company elected to draw on the full $10.0 million under a Term B Loan.

On July 14, 2017 (the First Amendment Effective Date), the Company and the Bank entered into the First Amendment (the SVB Loan Amendment) to the Restated LSA between the Company and the Bank dated July 30, 2014. Pursuant to the SVB Loan Amendment, the Bank extended an additional term loan to the Company on July 14, 2017 in the principal amount of $15.0 million (the 2017 Term Loan), a portion of which was applied to repay in full the Company’s existing outstanding debt with the Bank under the Restated LSA, which included outstanding principal, accrued interest, and final payment fees. Following such repayment in full of the Company’s existing outstanding debt with the Bank under the Restated LSA, cash proceeds to the Company from the remaining portion of the 2017 Term Loan were $7.5 million. The Company determined the repayment of the Restated LSA and issuance of the 2017 Term Loan was a debt extinguishment and accounted for the 2017 Term Loan at fair value as of the First Amendment Effective Date accordingly.

On November 13, 2019, the Company repaid in full all outstanding obligations under the 2017 Term Loan. The Company used cash on hand in the amount of $14.2 million for the repayment of such obligations associated with the 2017 Term Loan, including the repayment of $13.0 million in principal and $1.2 million associated with the final fee and outstanding interest. The Company expensed the remaining debt issuance cost capitalized of $0.1 million to interest expense upon the repayment of the 2017 Term Loan.

The 2017 Term Loan was scheduled to mature on January 1, 2022 (the Term Loan Maturity Date) and beared interest at a floating per annum rate equal to the greater of (i) 3.50% above the Prime Rate (as defined in the SVB Loan Amendment) or (ii) 7.25%; provided, however, that in no event would such interest rate exceed 8.25%. Interest was payable on a monthly basis on the first day of each month.

From August 1, 2017 through January 1, 2019 (the Interest-only Period), the Company was required to make monthly payments of interest only. In January 2019, after achievement of a product development milestone, the Company elected to extend the Interest-only Period from January 1, 2019 through and including to July 31, 2019. The Company was required to repay the principal, plus monthly payments of accrued interest, in 30 equal monthly installments based on a 30-month amortization schedule.

The Company’s final payment in November 2019 included all outstanding principal and accrued and unpaid interest under the 2017 Term Loan, plus a 7.5%, or $1.1 million, final payment fee. This final payment fee was accrued as interest expense over the term of the 2017 Term Loan and recorded in accrued expenses. As a result of the Company’s early repayment of the 2017 Term Loan during November 2019, the unaccrued balance of the final payment fee of $0.3 million was recorded in interest expense during the year ended December 31, 2019.

For the years ended December 31, 2019, 2018, and 2017, the Company recorded $1.8 million, $1.7 million, and $0.8 million respectively, in aggregate interest expense related to the 2017 Term Loan.

Warrants

In connection with the funding of the Term B Loan under the Restated LSA, the Company issued the Bank and one of its affiliates fully-exercisable warrants to purchase an aggregate of 98,039 shares of the Company’s common stock (the 2014 Warrants) at an exercise price of $4.08 per share. In March 2018, a portion of the 2014 Warrants were exercised in exchange for 34,149 shares of the Company’s common stock in a cashless transaction. During July 2019, the remaining balance of the 2014 Warrants outstanding was exercised for 39,263 shares of the Company’s common stock in a cashless transaction. As a result, none of the 2014 Warrants remain outstanding as of December 31, 2019.

In connection with the SVB Loan Amendment, the Company issued to the Bank on the First Amendment Effective Date a fully exercisable warrant (the 2017 Warrant), expiring in July 2024, to purchase up to an aggregate of 91,463 shares of the Company’s common stock, subject to adjustment, at an exercise price equal to $3.28 per share. The aggregate fair value of the 2017 Warrant was determined to be $0.2 million using the Black-Scholes option pricing model and was recorded as a debt discount on the 2017 Term Loan. This debt discount is amortized to interest expense over the term of the 2017 Term Loan using the effective interest method. The Company determined the effective interest rate of the 2017 Term Loan to be 10.2% as of the First Amendment Effective Date. During September 2018, the 2017 Warrant was fully exercised in exchange for 67,952 shares of the Company’s common stock in a cashless transaction.

In connection with a prior debt agreement between the Company and the Bank in 2009, the Company issued the Bank fully exercisable warrants to purchase an aggregate of 36,074 shares of the Company’s common stock at a weighted-average exercise price of $7.21 per share. During January 2019, a portion of the warrants were exercised in exchange for 1,245 shares of the Company’s common stock in a cashless transaction. During July 2019, the remaining balance of the warrants outstanding was exercised for 21,012 shares of the Company’s common stock in a cashless transaction. No warrants related to the prior debt agreement remain outstanding as of December 31, 2019.

Leases

12 Months Ended

Dec. 31, 2019

Leases [Abstract]

Leases

7. Leases

The Company leases its headquarters office and laboratory space under a non-cancelable operating lease. In May 2018, the Company amended this lease, extending the term of the lease through the end of 2028 and agreeing to lease additional space in the same building as its existing space beginning in January 2019. The additional space leased as a result of the amendment was considered a separate lease under ASC 842 and was recorded on the consolidated balance sheets as of the lease inception date during January 2019, resulting in an increase in operating right-of-use assets of $7.7 million and an increase in the aggregate lease liability of $9.6 million. The Company can extend the term of each lease for five years after the end of 2028 at the then prevalent market rate, subject to the Company's delivery to the landlord of twelve months' prior written notice. Additionally, the Company maintains the right to terminate each lease after October 2025, subject to the Company's delivery to the landlord of twelve month's prior written notice and an early termination payment of $2.5 million. As of the date of adoption of ASC 842 and upon the lease inception date, the Company was not reasonably certain that it would exercise the extension option or the termination option, and as such, did not include these options in the determination of the total lease terms. The leases are subject to additional variable charges for common area maintenance and other variable costs. Given the variable nature of such costs, they are recognized as expense as incurred. Further, the leases are subject to certain fixed amenities fees for the duration of the lease. These costs are considered non-lease components, which have been aggregated with the lease components into a single lease component for purposes of determining the total future lease payments. In connection with the leases, the Company has a cash-collateralized irrevocable standby letter of credit in the amount of $0.2 million.

As of December 31, 2019, future minimum payments under the Company’s operating leases were $38.2 million, which will be paid over a remaining weighted-average lease term of 9.0 years. The weighted-average discount rate for the operating lease liabilities was 8.0%, which was the Company's incremental borrowing rate at the date of adopting ASC 842 and upon lease inception.

For the year ended December 31, 2019, total operating lease expense was $6.1 million, which consisted of $3.8 million associated with the straight-line recognition of fixed payments, and $2.3 million associated with variable costs associated with the leases. For both the years ended December 31, 2018 and 2017, aggregate contractual rent expense was $2.3 million.

Total short-term lease expense associated with short-term leases for the year ended December 31, 2019 was $1.1 million.

Future minimum payments under the Company’s operating leases as of December 31, 2019 are as follows (in thousands):

	Operating Lease Payments
Years Ending December 31,
2020	$	3,760
2021		3,873
2022		3,989
2023		4,109
2024		4,232
Thereafter		18,238
Total undiscounted lease payments	$	38,201
Less: imputed interest		(11,274	)
Total lease liability	$	26,927

The Company has an additional operating lease for office and laboratory space in New York that had not yet commenced as of December 31, 2019. The lease commenced in January 2020 and has a lease term of two years. Total future minimum payments under the operating lease are $0.3 million.

In January 2020, the Company entered into a lease agreement for office, laboratory, and GMP manufacturing space (the Premises). The Premises are located in San Diego, California and the Company intends to move its corporate headquarters to the Premises in the middle of 2021. See Note 13 of the notes to the consolidated financial statements for additional information on this lease.

Convertible Preferred Stock and Stockholders' Equity

12 Months Ended

Dec. 31, 2019

Convertible Preferred Stock And Stockholders Deficit Disclosure [Abstract]

Convertible Preferred Stock and Stockholders’ Equity

8. Convertible Preferred Stock and Stockholders’ Equity

Convertible Preferred Stock

In November 2016, the Company completed a private placement of stock in which investors, including investors affiliated with the directors and officers of the Company, purchased convertible preferred stock and common stock of the Company (the November 2016 Placement). The Company issued 2,819,549 shares of non-voting Class A Convertible Preferred Stock (the Class A Preferred) at $13.30 per share, each of which is convertible into five shares of common stock upon certain conditions defined in the Certificate of Designation of Preferences, Rights and Limitations of the Class A Preferred filed with the Delaware Secretary of State on November 22, 2016 (the CoD). The Class A Preferred were purchased exclusively by entities affiliated with Redmile Group, LLC (collectively, Redmile). The terms of the CoD prohibited Redmile from converting the Class A Preferred into shares of the Company’s common stock if, as a result of conversion, Redmile, together with its affiliates, would own more than 9.99% of the Company’s common stock then issued and outstanding (the Redmile Percentage Limitation), which percentage could change at Redmile’s election upon 61 days’ notice to the Company to (i) any other number less than or equal to 19.99% or (ii) subject to approval of the Company’s stockholders to the extent required in accordance with the NASDAQ Global Market rules, any number in excess of 19.99%. On May 2, 2017, the Company’s stockholders approved the issuance of up to an aggregate of 14,097,745 shares of common stock upon the conversion of the outstanding shares of Class A Preferred. As a result, Redmile has the right to increase the Redmile Percentage Limitation to any percentage in excess of 19.99% at its election. The Company also issued 7,236,837 shares of common stock at $2.66 per share as part of the November 2016 Placement.

The Class A Preferred are non-voting shares and have a stated par value of $0.001 per share and are convertible into five shares of the Company’s common stock at a conversion price of $2.66 per share, which was the fair value of the Company’s common stock on the date of issuance. Holders of the Class A Preferred have the same dividend rights as holders of the Company’s common stock. Additionally, the liquidation preferences of the Class A Preferred are pari passu among holders of the Company’s common stock and holders of the Class A Preferred, pro rata based on the number of shares held by each such holder (treated for this purpose as if the Class A Preferred had been converted to common stock).

During the year ended December 31, 2019, 25,000 shares of the Company’s Class A Preferred were converted into 125,000 shares of the Company’s common stock.

Description of Securities

Dividends

As of December 31, 2019, the Board of Directors of the Company has not declared any dividends.

2013 Stock Option and Incentive Plan, and Inducement Equity Plan

2013 Stock Option and Incentive Plan

On August 28, 2013, the Company’s board of directors and stockholders approved and adopted the 2013 Stock Option and Incentive Plan (the 2013 Plan). The 2013 Plan became effective immediately prior to the Company’s IPO. The 2013 Plan was subsequently amended in May 2017. Under the 2013 Plan, the Company may grant stock options, stock appreciation rights, restricted stock, restricted stock units and other awards to individuals who are then employees, officers, directors or consultants of the Company or its subsidiaries. A total of 1,020,000 shares of common stock were initially reserved for issuance under the 2013 Plan, and in May 2017, stockholders approved an additional 2,500,000 shares of common stock for issuance under the 2013 Plan. The shares issuable pursuant to awards granted under the 2013 Plan will be authorized, but unissued shares. The shares of common stock underlying any awards from the 2013 Plan and a previously existing equity plan from 2007 that are forfeited, cancelled, held back upon exercise or settlement of an award to satisfy the exercise price or tax withholding, reacquired by us prior to vesting, satisfied without any issuance of common stock, expire or are otherwise terminated (other than by exercise) will be added back to the shares of common stock available for issuance under the 2013 Plan.

In addition, the number of shares of stock available for issuance under the 2013 Plan will be automatically increased each January 1 by 4% of the outstanding number of shares of the Company’s common stock on the immediately preceding December 31 or such lesser number as determined by the compensation committee of the Company’s board of directors.

Recipients of stock options under the 2013 Plan shall be eligible to purchase shares of the Company’s common stock at an exercise price equal to no less than the estimated fair value of such stock on the date of grant. Under the 2013 Plan, stock options generally vest 25% on the first anniversary of the original vesting date, with the balance vesting monthly over the remaining three years, or vest monthly over four years, unless they contain specific performance and/or market-based vesting provisions. The maximum term of stock options granted under the 2013 Plan is ten years. Under the 2013 Plan, restricted stock units generally vest annually over four years.

Inducement Plan

On May 10, 2016, the Company’s board of directors approved the Fate Therapeutics, Inc. Inducement Equity Plan (the Inducement Plan), the purpose of which is to enable the Company to grant equity awards to induce highly-qualified prospective officers and employees who are not employed by the Company to accept employment with the Company. Under the Inducement Plan, the Company may grant non-qualified stock options and restricted stock units. A total of 500,000 shares of common stock were initially reserved for issuance under the Inducement Plan. In January 2019 and January 2018, an additional 200,000 shares and 400,000 shares, respectively, of common stock were reserved for issuance under the Inducement Plan. The shares of common stock underlying any awards from the Inducement Plan that are forfeited, cancelled, held back upon exercise or settlement of an award to satisfy the exercise price or tax withholding, reacquired by us prior to vesting, satisfied without any issuance of common stock, expire or are otherwise terminated (other than by exercise) under the Inducement Plan will be added back to the shares of common stock available for issuance under the Inducement Plan.

Employee Stock Purchase Plan

On September 13, 2013, the Company’s board of directors approved and adopted the 2013 Employee Stock Purchase Plan (the ESPP). A total of 729,000 shares of common stock were initially reserved for issuance under the ESPP. In addition, the number of shares of stock available for issuance under the ESPP will be automatically increased each January 1, beginning on January 1, 2015, by the lesser of (i) 2% of the outstanding number of shares of the Company’s common stock on the immediately preceding December 31, (ii) 450,000 shares, or (iii) such lesser number as determined by the compensation committee of the Company’s board of directors.

No purchases have been made to date under the ESPP.

Stock Options and Restricted Stock Unit Awards

Stock Options. The following table summarizes stock option activity and related information under all equity plans for the years ended December 31, 2019, 2018 and 2017:

	Options			Weighted Average Exercise Price Per Share		Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value (in 000s)
Outstanding at December 31, 2016		3,910,350		$	3.77		8.28	$	682
Granted		2,522,920			3.09
Exercised		(83,220	)		2.79
Cancelled		(892,007	)		3.50
Outstanding at December 31, 2017		5,458,043		$	3.52		7.99	$	14,754
Granted		3,251,980			8.30
Exercised		(694,830	)		3.88
Cancelled		(1,034,612	)		4.36
Outstanding at December 31, 2018		6,980,581		$	5.58		7.87	$	51,497
Granted		3,488,200			16.52
Exercised		(787,434	)		3.31
Cancelled		(353,605	)		10.70
Outstanding at December 31, 2019		9,327,742		$	9.67		7.73	$	92,567
Options vested and expected to vest at December 31, 2019		9,323,962		$	9.66		7.73	$	92,550
Options exercisable at December 31, 2019		4,594,888		$	6.43		6.80	$	60,403

For the year ended December 31, 2019, the weighted average grant date fair value of stock options granted per share was equal to $11.52. For the years ended December 31, 2018 and 2017, the weighted average grant date fair value of stock options granted to employees and directors was equal to $8.28 and $2.29, respectively.

As of December 31, 2019, 2018 and 2017, the unrecognized compensation cost related to outstanding options (excluding those with unachieved performance-based conditions) was $40.4 million, $15.9 million and $5.8 million, respectively, which was expected to be recognized as expense over approximately 2.9 years, 3.1 years and 2.6 years, respectively.

The total intrinsic value, which is the amount by which the exercise price was exceeded by the price of the Company’s common stock on the date of exercise, of stock options exercised during the years ended December 31, 2019, 2018, and 2017, was $10.7 million, $5.5 million, and $0.1 million, respectively. Total cash received upon the exercise of stock options was $2.5 million for the year ended December 31, 2019.

Restricted Stock Units. The following table summarizes restricted stock unit activity and related information under all equity plans for the years ended December 31, 2019, 2018 and 2017:

	Number of Restricted Stock Units			Weighted Average Grant Date Fair Value Per Share		Weighted Average Remaining Vesting Period		Aggregate Intrinsic Value (in 000s)
Outstanding at December 31, 2016		525,250		$	4.89		2.80	$	1,318
Granted		—			—
Vested		(225,125	)		4.89
Cancelled		(87,500	)		4.89
Outstanding at December 31, 2017		212,625		$	4.89		1.80	$	1,299
Granted		—			—
Vested		—			—
Cancelled		(24,000	)		4.89
Outstanding at December 31, 2018		188,625		$	4.89		0.80	$	1,299
Granted		520,000			16.41
Vested		(172,625	)		4.89
Cancelled		(16,000	)		4.89
Outstanding at December 31, 2019		520,000		$	16.41		2.64	$	10,176
Restricted stock units expected to vest at December 31, 2019		520,000		$	16.41		2.64	$	10,176

As of December 31, 2019, 2018 and 2017, the unrecognized compensation cost related to outstanding restricted stock units was $6.2 million, $0.4 million, and $0.9 million respectively, which was expected to be recognized as expense over approximately 2.7 years, 0.8 years, and 1.8 years respectively.

Stock-Based Compensation Expense

The allocation of stock-based compensation for all stock awards is as follows (in thousands):

	Years Ended December 31,
	2019		2018		2017
Research and development	$	9,804	$	3,654	$	2,095
General and administrative		7,606		2,639		1,511
Total stock-based compensation expense	$	17,410	$	6,293	$	3,606

Stock Option Grants Valuation. As of January 1, 2019, the Company adopted ASU 2018-07, which aligned the guidance on share-based payments to nonemployees with that for share-based payments to employees. In accordance with ASU 2018-07, the measurement of equity-classified nonemployee awards is fixed at the grant date and entities are not required to remeasure nonemployee equity awards at each reporting date until such time that the measurement date is established. The weighted-average assumptions used in the Black-Scholes option pricing model to determine the fair value of the employee and nonemployee stock option grants were as follows:

	Years Ended December 31,
	2019			2018			2017
Risk–free interest rate		2.4	%		2.5	%		2.0	%
Expected volatility		80.1	%		79.3	%		90.1	%
Expected term (in years)		6.1			6.0			6.0
Expected dividend yield		0.0	%		0.0	%		0.0	%

Risk-free interest rate. The Company bases the risk-free interest rate assumption on observed interest rates appropriate for the expected term of the stock option grants.

Expected dividend yield. The Company bases the expected dividend yield assumption on the fact that it has never paid cash dividends and has no present intention to pay cash dividends.

Expected volatility. Due to the Company’s limited operating history and limited company-specific historical or implied volatility, the expected volatility assumption is based on historical volatilities of a peer group of similar companies whose share prices are publicly available. The peer group was developed based on companies in the biotechnology industry.

Expected term. The expected term represents the period of time that options are expected to be outstanding. As the Company does not have sufficient historical exercise behavior, it determines the expected life assumption using the simplified method, which is an average of the contractual term of the option and its vesting period.

Warrants to Purchase Common Stock in Connection with Debt Issuance

As a result of the financing of the Loan Amendment on July 14, 2017, the Company issued SVB fully-exercisable warrants to purchase an aggregate of 91,463 shares of the Company’s common stock at an exercise price of $3.28 per share. The warrants would have expired in July 2024. In September 2018, the 2017 Warrant was fully exercised in exchange for 67,952 shares of the Company’s common stock in a cashless transaction. See Note 6 of the notes to the consolidated financial statements for additional information on the debt issuance.

The fair value of the warrants was determined to be $0.2 million, which was recorded to additional paid-in capital as a debt discount. The weighted- average assumptions used in the Black-Scholes option pricing model to determine the fair value of the warrants issued were as follows:

	As of July 14, 2017
Risk–free interest rate		2.1	%
Expected volatility		88	%
Expected term (in years)		7.0
Expected dividend yield		0.0	%

Common Stock Reserved for Future Issuance

Common stock reserved for future issuance is as follows:

	December 31,
	2019		2018
Common stock warrants		—		85,094
Convertible preferred stock (if converted)		13,972,745		14,097,745
Common stock options		9,327,742		6,980,581
Restricted stock units		520,000		188,625
Awards available under the 2013 Plan		2,880,235		3,605,510
Awards available under the Inducement Plan		279,178		379,178
Employee stock purchase plan		729,000		729,000
Total		27,708,900		26,065,733

Income Taxes

12 Months Ended

Dec. 31, 2019

Income Tax Disclosure [Abstract]

Income Taxes

9. Income Taxes

The following is a reconciliation of the Company’s expected federal income tax provision (benefit) to the actual income tax provision (in thousands):

	Years Ended December 31,
	2019			2018			2017
Tax computed at federal statutory rate	$	(20,611	)	$	(13,985	)	$	(14,603	)
State tax, net of federal tax benefit		(2,088	)		(1,620	)		(1,315	)
Permanent differences		175			22			795
Stock compensation		359			(307	)		539
R&D tax credits		(7,285	)		(3,301	)		(2,934	)
Reserve for uncertain tax positions		2,163			1,160			1,326
Tax Cuts and Jobs Act		—			—			25,280
Other		77			304			46
Valuation allowance		27,210			17,727			(9,134	)
Income tax expense	$	—		$	—		$	—

Significant components of the Company’s deferred tax assets are summarized as follows (in thousands):

	December 31,
	2019			2018
Deferred tax assets:
Section 59e amortization	$	32,781		$	19,069
Net operating losses		37,563			30,981
R&D tax credits		16,391			9,163
Depreciation and amortization		1,650			1,653
Deferred revenue		2,115			3,906
Stock compensation		2,346			1,482
Lease liability		5,655			—
Other		846			1,106
Total deferred tax assets		99,347			67,360
Deferred tax liabilities:
Right-of-use assets		(4,778	)		—
Total deferred tax liabilities		(4,778	)		—
Net of deferred tax assets and liabilities		94,569			67,360
Valuation allowance		(94,569	)		(67,360	)
Net deferred tax assets	$	—		$	—

A valuation allowance of $94.6 million and $67.4 million at December 31, 2019 and 2018, respectively, has been established to offset the deferred tax assets, as realization of such assets is uncertain.

At December 31, 2019, the Company had federal and California net operating loss (NOL) carryforwards of $168.2 million and $168.2 million, respectively, which may be available to offset future taxable income. The federal and California NOL carryforwards begin to expire in 2027 and 2028, respectively, unless previously utilized. At December 31, 2019, the Company had federal and California research and development (R&D) credit carryforwards of $13.4 million and $8.5 million, respectively. The federal R&D tax credit carryforwards will begin to expire in 2035 unless previously utilized. The California R&D credit carryforwards will carry forward indefinitely.

Under Sections 382 and 383 of the Internal Revenue Code of 1986, as amended, (the Code), substantial changes in the Company’s ownership may limit the amount of net operating loss and research and development credit carryforwards that could be used annually in the future to offset taxable income. The tax benefits related to future utilization of federal and state net operating loss carryforwards, credit carryforwards, and other deferred tax assets may be limited or lost if cumulative changes in ownership exceeds 50% within any three-year period. The Company completed a study to assess whether an ownership change, as defined by Section 382 of the Code, had occurred from the Company’s formation through December 31, 2015. Based upon this study, the Company determined that several ownership changes had occurred. Accordingly, the Company reduced its deferred tax assets related to the federal NOL carryforwards and the federal R&D credit carryforwards that are anticipated to expire unused as a result of these ownership changes. These tax attributes were excluded from deferred tax assets with a corresponding reduction of the valuation allowance with no net effect on income tax expense or the effective tax rate. The Company updated the study through December 31, 2019 and concluded there were no ownership changes subsequent to December 31, 2015. Future ownership changes may further limit the Company’s ability to utilize its remaining tax attributes.

The Company files income tax returns in the United States and California, and has historically filed income tax returns in Canada. The Company currently has no years under examination by any jurisdiction; however, the Company is subject to income tax examination by federal, Californian and Canadian tax authorities for years beginning in 2016, 2015, and 2015, respectively. However, to the extent allowed by law, the taxing authorities may have the right to examine prior periods where NOLs and tax credits were generated and carried forward, and make adjustments up to the amount of the carryforwards.

The change in the Company’s unrecognized tax benefits is summarized as follows (in thousands):

	December 31,
	2019		2018			2017
Beginning unrecognized tax benefits	$	13,547	$	11,800		$	7,730
Increase related to current year tax positions		3,196		1,798			4,077
Increase related to prior year tax positions		79		148			6
Decrease related to prior year tax positions		—		(199	)		(13	)
Ending unrecognized tax benefits	$	16,822	$	13,547		$	11,800

The Company does not anticipate that the amount of unrecognized tax benefits as of December 31, 2019 will significantly change within the next twelve months. Due to the valuation allowance recorded against the Company’s deferred tax assets, none of the total unrecognized tax benefits as of December 31, 2019 would reduce the effective tax rate if recognized. The Company has not recognized interest or penalties in its consolidated statements of operations and comprehensive loss since inception.

The Tax Cuts and Jobs Act (the Act) was enacted on December 22, 2017. The Act reduces the US federal corporate tax rate from 34% to 21%. The reduction in the federal corporate tax rate caused the Company to remeasure its deferred tax assets and liabilities at December 31, 2017. The remeasurement resulted in a provisional income tax expense of $25.3 million, offset by an equal reduction in the valuation allowance during the year ended December 31, 2017. During 2018, the Company finalized its analysis of the provisional impact associated with the remeasurement of deferred tax assets. There was no change in the provisional remeasurement amount previously recorded during 2017.

Employee Benefits

12 Months Ended

Dec. 31, 2019

Compensation And Retirement Disclosure [Abstract]

Employee Benefits

10. Employee Benefits

Effective January 1, 2009, the Company adopted a defined contribution 401(k) plan for employees who are at least 21 years of age. Employees are eligible to participate in the plan beginning on the first day of the calendar quarter following date of hire. Under the terms of the plan, employees may make voluntary contributions as a percent of compensation. No matching contributions have been made by the Company since the adoption of the 401(k) plan.

Commitment and Contingencies

12 Months Ended

Dec. 31, 2019

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

11. Commitments and Contingencies

License Agreements

The Company has entered into exclusive license agreements with certain academic institutions and universities pursuant to which the Company acquired certain intellectual property. Pursuant to each agreement, as consideration for an exclusive license to the intellectual property, the Company paid a license fee, reimbursed the institution for historical patent costs and, in certain instances, issued the institution shares of restricted common stock. Additionally, under each agreement, the institution is generally eligible to receive future consideration including, but not limited to, annual maintenance fees, royalties, milestone payments and sublicensing fees. Each of the license agreements is generally cancelable by the Company, given appropriate prior written notice. Minimum annual payments to maintain these cancelable licenses total an aggregate of $0.4 million.

Selected Quarterly Financial Data

12 Months Ended

Dec. 31, 2019

Quarterly Financial Information Disclosure [Abstract]

Selected Quarterly Financial Data (Unaudited)

12. Selected Quarterly Financial Data (Unaudited)

The following tables show a summary of the Company’s quarterly financial information for each quarter of 2019 and 2018 (in thousands, except per share data):

	First Quarter			Second Quarter			Third Quarter			Fourth Quarter
2019
Revenues	$	2,632		$	2,817		$	2,429		$	2,802
Total operating expenses		23,078			26,901			29,548			31,880
Net loss		(19,760	)		(23,478	)		(26,609	)		(28,302	)
Basic and diluted net loss per common share⁽¹⁾	$	(0.30	)	$	(0.36	)	$	(0.40	)	$	(0.37	)
2018
Revenues	$	1,026		$	1,027		$	1,026		$	1,661
Total operating expenses		15,080			20,632			17,718			18,402
Net loss		(14,135	)		(19,654	)		(16,782	)		(16,027	)
Basic and diluted net loss per common share⁽¹⁾	$	(0.27	)	$	(0.37	)	$	(0.31	)	$	(0.25	)

(1)

Basic and diluted loss per share are computed independently for each of the quarters presented. As such, the sum of the quarterly basic and diluted loss per share information may not equal annual basic and diluted loss per share information.

Subsequent Events

12 Months Ended

Dec. 31, 2019

Subsequent Events [Abstract]

Subsequent Events

13. Subsequent Events

In January 2020, the Company entered into a lease agreement for office, laboratory, and GMP manufacturing space (the Premises). The Premises is located in San Diego, California and the Company intends to move its corporate headquarters to the Premises in the middle of 2021.

Lease payments shall commence, subject to certain conditions, in May 2021 (the Rent Commencement Date) and the lease has a lease term of 15 years starting from the Rent Commencement Date. The Company has the option to extend the lease for two successive five-year terms. The Company also has a one-time option to terminate the lease after 10 years from the Rent Commencement Date, subject to payment of a $30.0 million early termination fee.

Total future minimum payments under the lease, assuming a 15-year term from the Rent Commencement Date, are $157.6 million, which are to be paid in monthly installments beginning May 2021. The landlord of the Premises will contribute an aggregate of up to $30.0 million toward tenant improvements of the Premises. In connection with the lease, the Company will maintain a letter of credit for the benefit of the landlord in an initial amount of $15.0 million, which amount is subject to reduction over time.

Organization and Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2019

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Public Equity Offerings

Use of Estimates

Principles of Consolidation

Segment Reporting

Fair Value of Financial Instruments

Level 1: Observable inputs such as quoted prices in active markets;

Level 2: Inputs, other than the quoted prices in active markets, that are observable either directly or indirectly; and

Level 3: Unobservable inputs in which there is little or no market data, which require the reporting entity to develop its own assumptions.

			Fair Value Measurements at Reporting Date Using
	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
As of December 31, 2019:
Cash equivalents
Money market funds	$	84,814	$	84,814	$	—	$	—
Investments
U.S. Treasury debt securities		60,303		60,303		—		—
Corporate debt securities		100,750		—		100,750		—
Total assets measured at fair value on a recurring basis	$	245,867	$	145,117	$	100,750	$	—

As of December 31, 2018:
Cash equivalents
Money market funds	$	190,514	$	190,514	$	—	$	—
Investments
U.S. Treasury debt securities		10,493		10,493		—		—
Total assets measured at fair value on a recurring basis	$	201,007	$	201,007	$	—	$	—

None of the Company’s non-financial assets or liabilities are recorded at fair value on a non-recurring basis. No transfers between levels have occurred during the periods presented.

As of December 31, 2019 and 2018, the Company had no material liabilities measured at fair value on a recurring basis.

Cash, Cash Equivalents and Restricted Cash

	Years Ended December 31,
	2019		2018		2017
Cash and cash equivalents	$	99,814	$	190,514	$	88,952
Restricted cash		227		227		122
Total cash, cash equivalents, and restricted cash shown in the consolidated statement of cash flows	$	100,041	$	190,741	$	89,074

Amounts included in restricted cash represent security deposits required to secure the Company’s credit card limit and its facilities lease.

Investments

Concentration of Credit Risk

Property and Equipment

Impairment of Long-Lived Assets

Leases

Revenue Recognition

Research and Development Costs

All research and development costs are expensed as incurred.

Patent Costs

Costs related to filing and pursuing patent applications are recorded as general and administrative expense and expensed as incurred since recoverability of such expenditures is uncertain.

Stock-Based Compensation

Convertible Preferred Stock

Income Taxes

Comprehensive Loss

Net Loss Per Common Share

Potentially dilutive securities not included in the calculation of diluted net loss per common share because to do so would be anti-dilutive are as follows (in common stock equivalent shares):

	As of December 31,
	2019		2018		2017
Warrants for common stock		—		85,094		225,756
Common stock options		9,327,742		6,980,581		5,458,043
Restricted stock units		520,000		188,625		212,625
Series A convertible preferred stock (if converted)		13,972,745		14,097,745		14,097,745
Total		23,820,487		21,352,045		19,994,169

Going Concern Assessment

Recently Adopted and Issued Accounting Pronouncements

Recently Adopted Accounting Pronouncements

Recently Issued Accounting Pronouncements

Organization and Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2019

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Schedule of Assets Measured at Fair Value on Recurring Basis

The following table presents the Company’s assets which were measured at fair value on a recurring basis as of December 31, 2019 and 2018 (in thousands):

			Fair Value Measurements at Reporting Date Using
	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
As of December 31, 2019:
Cash equivalents
Money market funds	$	84,814	$	84,814	$	—	$	—
Investments
U.S. Treasury debt securities		60,303		60,303		—		—
Corporate debt securities		100,750		—		100,750		—
Total assets measured at fair value on a recurring basis	$	245,867	$	145,117	$	100,750	$	—

As of December 31, 2018:
Cash equivalents
Money market funds	$	190,514	$	190,514	$	—	$	—
Investments
U.S. Treasury debt securities		10,493		10,493		—		—
Total assets measured at fair value on a recurring basis	$	201,007	$	201,007	$	—	$	—

Reconciliation of Cash, Cash Equivalents, and Restricted Cash

	Years Ended December 31,
	2019		2018		2017
Cash and cash equivalents	$	99,814	$	190,514	$	88,952
Restricted cash		227		227		122
Total cash, cash equivalents, and restricted cash shown in the consolidated statement of cash flows	$	100,041	$	190,741	$	89,074

Schedule of Anti-Dilutive Securities not Included in Calculation of Diluted Net Loss Per Common Share

Potentially dilutive securities not included in the calculation of diluted net loss per common share because to do so would be anti-dilutive are as follows (in common stock equivalent shares):

	As of December 31,
	2019		2018		2017
Warrants for common stock		—		85,094		225,756
Common stock options		9,327,742		6,980,581		5,458,043
Restricted stock units		520,000		188,625		212,625
Series A convertible preferred stock (if converted)		13,972,745		14,097,745		14,097,745
Total		23,820,487		21,352,045		19,994,169

Investments (Tables)

12 Months Ended

Dec. 31, 2019

Investments [Abstract]

Summary of Investments

The following table summarizes the Company’s investments accounted for as available-for-sale securities as of December 31, 2019 and 2018 (in thousands):

	Maturity (in years)	Amortized Cost		Unrealized Losses			Unrealized Gains		Estimated Fair Value
December 31, 2019
Classified as current assets:
U.S. Treasury debt securities	1 or less	$	50,445	$	(4	)	$	16	$	50,457
Corporate debt securities	1 or less		71,171		(24	)		9		71,156
Total short-term investments		$	121,616	$	(28	)	$	25	$	121,613
Classified as non-current assets:
U.S. Treasury debt securities	Greater than 1	$	9,841	$	—		$	5	$	9,846
Corporate debt securities	Greater than 1		29,572		(1	)		23		29,594
Total long-term investments		$	39,413	$	(1	)	$	28	$	39,440

December 31, 2018
Classified as current assets:
U.S. Treasury debt securities	1 or less	$	10,495	$	(2	)	$	—	$	10,493
Total short-term investments		$	10,495	$	(2	)	$	—	$	10,493

Property and Equipment (Tables)

12 Months Ended

Dec. 31, 2019

Property Plant And Equipment [Abstract]

Schedule of property and equipment

Property and equipment consist of the following (in thousands):

	December 31,
	2019			2018
Furniture and fixtures	$	899		$	516
Computer and office equipment		917			688
Software		103			103
Leasehold improvements—building		2,465			288
Scientific equipment		15,355			7,868
Construction-in-process		198			1,987
Total property and equipment, gross		19,937			11,450
Less accumulated depreciation and amortization		(8,518	)		(6,325	)
Total property and equipment, net	$	11,419		$	5,125

Accrued Expenses and Long-Term Debt (Tables)

12 Months Ended

Dec. 31, 2019

Accrued Expenses And Long Term Debt Disclosure [Abstract]

Schedule of accrued expenses

Current accrued expenses consist of the following (in thousands):

	December 31,
	2019		2018
Accrued payroll and other employee benefits	$	5,329	$	2,938
Accrued clinical trial related costs		5,976		4,729
Accrued other		3,392		3,259
Total current accrued expenses	$	14,697	$	10,926

Schedule of long-term debt and unamortized discount balances

Long-term debt and unamortized discount balances are as follows (in thousands):

	December 31,
	2019		2018
Long-term debt	$	—	$	15,000
Less debt issuance costs and discount, net of current portion		—		(54	)
Long-term debt, net of long-term portion of debt issuance costs and discount		—		14,946
Less current portion of long-term debt		—		(2,500	)
Long-term debt, net	$	—	$	12,446
Current portion of long-term debt	$	—	$	2,500
Less current portion of debt issuance costs and discount		—		(62	)
Current portion of long-term debt, net	$	—	$	2,438

- Definition

Tabular disclosure of long-debt instruments or arrangements, including identification, terms, features, collateral requirements and other information necessary to a fair presentation. These are debt arrangements that originally required repayment more than twelve months after issuance or greater than the normal operating cycle of the entity, if longer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28541-108399

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21506-112644

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(e),(f))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
-Topic 835
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Reference 6: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
-Topic 505
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-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21521-112644

Reference 7: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
-Topic 505
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-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21538-112644

Reference 8: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
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-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=75038535&loc=d3e64711-112823

Reference 9: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400

Reference 10: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21475-112644

+ Details

Leases (Tables)

12 Months Ended

Dec. 31, 2019

Leases [Abstract]

Schedule of Future Minimum Payments Under Non-cancelable Operating Leases

Future minimum payments under the Company’s operating leases as of December 31, 2019 are as follows (in thousands):

	Operating Lease Payments
Years Ending December 31,
2020	$	3,760
2021		3,873
2022		3,989
2023		4,109
2024		4,232
Thereafter		18,238
Total undiscounted lease payments	$	38,201
Less: imputed interest		(11,274	)
Total lease liability	$	26,927

Convertible Preferred Stock and Stockholders' Equity (Tables)

12 Months Ended

Dec. 31, 2019

Stockholders' Equity

Summary of stock option activity and related information under all equity plans

The following table summarizes stock option activity and related information under all equity plans for the years ended December 31, 2019, 2018 and 2017:

	Options			Weighted Average Exercise Price Per Share		Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value (in 000s)
Outstanding at December 31, 2016		3,910,350		$	3.77		8.28	$	682
Granted		2,522,920			3.09
Exercised		(83,220	)		2.79
Cancelled		(892,007	)		3.50
Outstanding at December 31, 2017		5,458,043		$	3.52		7.99	$	14,754
Granted		3,251,980			8.30
Exercised		(694,830	)		3.88
Cancelled		(1,034,612	)		4.36
Outstanding at December 31, 2018		6,980,581		$	5.58		7.87	$	51,497
Granted		3,488,200			16.52
Exercised		(787,434	)		3.31
Cancelled		(353,605	)		10.70
Outstanding at December 31, 2019		9,327,742		$	9.67		7.73	$	92,567
Options vested and expected to vest at December 31, 2019		9,323,962		$	9.66		7.73	$	92,550
Options exercisable at December 31, 2019		4,594,888		$	6.43		6.80	$	60,403

Summary of restricted stock unit activity and related information under all equity plans

The following table summarizes restricted stock unit activity and related information under all equity plans for the years ended December 31, 2019, 2018 and 2017:

	Number of Restricted Stock Units			Weighted Average Grant Date Fair Value Per Share		Weighted Average Remaining Vesting Period		Aggregate Intrinsic Value (in 000s)
Outstanding at December 31, 2016		525,250		$	4.89		2.80	$	1,318
Granted		—			—
Vested		(225,125	)		4.89
Cancelled		(87,500	)		4.89
Outstanding at December 31, 2017		212,625		$	4.89		1.80	$	1,299
Granted		—			—
Vested		—			—
Cancelled		(24,000	)		4.89
Outstanding at December 31, 2018		188,625		$	4.89		0.80	$	1,299
Granted		520,000			16.41
Vested		(172,625	)		4.89
Cancelled		(16,000	)		4.89
Outstanding at December 31, 2019		520,000		$	16.41		2.64	$	10,176
Restricted stock units expected to vest at December 31, 2019		520,000		$	16.41		2.64	$	10,176

Schedule of weighted-average assumptions used to determine the fair value of employee and nonemployee stock option grants

The weighted-average assumptions used in the Black-Scholes option pricing model to determine the fair value of the employee and nonemployee stock option grants were as follows

	Years Ended December 31,
	2019			2018			2017
Risk–free interest rate		2.4	%		2.5	%		2.0	%
Expected volatility		80.1	%		79.3	%		90.1	%
Expected term (in years)		6.1			6.0			6.0
Expected dividend yield		0.0	%		0.0	%		0.0	%

Schedule of common stock reserved for future issuance

Common stock reserved for future issuance is as follows:

	December 31,
	2019		2018
Common stock warrants		—		85,094
Convertible preferred stock (if converted)		13,972,745		14,097,745
Common stock options		9,327,742		6,980,581
Restricted stock units		520,000		188,625
Awards available under the 2013 Plan		2,880,235		3,605,510
Awards available under the Inducement Plan		279,178		379,178
Employee stock purchase plan		729,000		729,000
Total		27,708,900		26,065,733

Warrant

Stockholders' Equity

Schedule of weighted-average assumptions used to determine the fair value of warrants issued

The weighted- average assumptions used in the Black-Scholes option pricing model to determine the fair value of the warrants issued were as follows:

	As of July 14, 2017
Risk–free interest rate		2.1	%
Expected volatility		88	%
Expected term (in years)		7.0
Expected dividend yield		0.0	%

Stock Option And Incentive Plan 2013

Stockholders' Equity

Schedule of allocation of stock-based compensation for all stock awards

The allocation of stock-based compensation for all stock awards is as follows (in thousands):

	Years Ended December 31,
	2019		2018		2017
Research and development	$	9,804	$	3,654	$	2,095
General and administrative		7,606		2,639		1,511
Total stock-based compensation expense	$	17,410	$	6,293	$	3,606

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2019

Income Tax Disclosure [Abstract]

Schedule of reconciliation of the Company's expected federal income tax provision (benefit) to the actual income tax provision

The following is a reconciliation of the Company’s expected federal income tax provision (benefit) to the actual income tax provision (in thousands):

	Years Ended December 31,
	2019			2018			2017
Tax computed at federal statutory rate	$	(20,611	)	$	(13,985	)	$	(14,603	)
State tax, net of federal tax benefit		(2,088	)		(1,620	)		(1,315	)
Permanent differences		175			22			795
Stock compensation		359			(307	)		539
R&D tax credits		(7,285	)		(3,301	)		(2,934	)
Reserve for uncertain tax positions		2,163			1,160			1,326
Tax Cuts and Jobs Act		—			—			25,280
Other		77			304			46
Valuation allowance		27,210			17,727			(9,134	)
Income tax expense	$	—		$	—		$	—

Summary of significant components of the Company's deferred tax assets

Significant components of the Company’s deferred tax assets are summarized as follows (in thousands):

	December 31,
	2019			2018
Deferred tax assets:
Section 59e amortization	$	32,781		$	19,069
Net operating losses		37,563			30,981
R&D tax credits		16,391			9,163
Depreciation and amortization		1,650			1,653
Deferred revenue		2,115			3,906
Stock compensation		2,346			1,482
Lease liability		5,655			—
Other		846			1,106
Total deferred tax assets		99,347			67,360
Deferred tax liabilities:
Right-of-use assets		(4,778	)		—
Total deferred tax liabilities		(4,778	)		—
Net of deferred tax assets and liabilities		94,569			67,360
Valuation allowance		(94,569	)		(67,360	)
Net deferred tax assets	$	—		$	—

Summary of the change in the Company's unrecognized tax benefits

The change in the Company’s unrecognized tax benefits is summarized as follows (in thousands):

	December 31,
	2019		2018			2017
Beginning unrecognized tax benefits	$	13,547	$	11,800		$	7,730
Increase related to current year tax positions		3,196		1,798			4,077
Increase related to prior year tax positions		79		148			6
Decrease related to prior year tax positions		—		(199	)		(13	)
Ending unrecognized tax benefits	$	16,822	$	13,547		$	11,800

Selected Quarterly Financial Data (Tables)

12 Months Ended

Dec. 31, 2019

Quarterly Financial Information Disclosure [Abstract]

Schedule of selected quarterly financial data

	First Quarter			Second Quarter			Third Quarter			Fourth Quarter
2019
Revenues	$	2,632		$	2,817		$	2,429		$	2,802
Total operating expenses		23,078			26,901			29,548			31,880
Net loss		(19,760	)		(23,478	)		(26,609	)		(28,302	)
Basic and diluted net loss per common share⁽¹⁾	$	(0.30	)	$	(0.36	)	$	(0.40	)	$	(0.37	)
2018
Revenues	$	1,026		$	1,027		$	1,026		$	1,661
Total operating expenses		15,080			20,632			17,718			18,402
Net loss		(14,135	)		(19,654	)		(16,782	)		(16,027	)
Basic and diluted net loss per common share⁽¹⁾	$	(0.27	)	$	(0.37	)	$	(0.31	)	$	(0.25	)

(1)

Organization and Summary of Significant Accounting Policies (Details) $ / shares in Units, $ in Thousands	1 Months Ended			12 Months Ended
	Sep. 30, 2019 USD ($) $ / shares shares	Sep. 30, 2018 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2019 USD ($) segment	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($) $ / shares	Jan. 01, 2019 USD ($)
Organization and summary of significant accounting policies
Gross proceeds from issuance of shares				$ 162,406	$ 134,577	$ 43,206
Number of operating segments \| segment				1
Number of reportable segments \| segment				1
Short-term leases term excluded from calculation of ROU and lease liabilities				12 months
Operating lease right-of-use assets				$ 22,752
Operating lease liabilities				$ 26,927
ASU 2016-02 \| Difference Between Lease Guidance in Effect Before and After Topic 842
Organization and summary of significant accounting policies
Operating lease right-of-use assets							$ 16,600
Operating lease liabilities							$ 18,200
September 2018 Public Equity Offering
Organization and summary of significant accounting policies
Issuance of common stock in conjunction with public offering \| shares		10,648,149
Share issue price (in dollars per share) \| $ / shares		$ 13.50
Gross proceeds from issuance of shares		$ 143,800
Net proceeds from issuance of shares after related cash costs		134,900
Costs related to equity offering		$ 8,900
September 2019 Public Equity Offering
Organization and summary of significant accounting policies
Issuance of common stock in conjunction with public offering \| shares	9,890,000
Share issue price (in dollars per share) \| $ / shares	$ 17.50
Gross proceeds from issuance of shares	$ 173,100
Net proceeds from issuance of shares after related cash costs	162,400
Costs related to equity offering	$ 10,700
December 2017 Public Equity Offering
Organization and summary of significant accounting policies
Issuance of common stock in conjunction with public offering \| shares			10,953,750
Share issue price (in dollars per share) \| $ / shares			$ 4.20			$ 4.20
Gross proceeds from issuance of shares			$ 46,000
Net proceeds from issuance of shares after related cash costs			43,000
Costs related to equity offering			$ 3,000
Costs related to equity offering paid					$ 3,000

Organization and Summary of Significant Accounting Policies (Details 2) - Fair Value Measurements Recurring - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total assets measured at fair value on a recurring basis	$ 245,867	$ 201,007
U.S. Treasury debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investments	60,303	10,493
Corporate debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investments	100,750
Money market funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	84,814	190,514
Quoted prices in Active Market for Identical Assets (Level 1)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total assets measured at fair value on a recurring basis	145,117	201,007
Quoted prices in Active Market for Identical Assets (Level 1) \| U.S. Treasury debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investments	60,303	10,493
Quoted prices in Active Market for Identical Assets (Level 1) \| Money market funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	84,814	$ 190,514
Significant Other Observable Inputs (Level 2)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total assets measured at fair value on a recurring basis	100,750
Significant Other Observable Inputs (Level 2) \| Corporate debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investments	$ 100,750

Organization and Summary of Significant Accounting Policies (Details 3) - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Transfer of assets from level 1 to level 2	$ 0
Transfer of assets from level 2 to level 1	0
Transfer of liabilities from level 1 to level 2	0
Transfer of liabilities from level 2 to level 1	0
Fair Value Measurements Nonrecurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Non-financial assets	0
Non-financial liabilities	0
Fair Value Measurements Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Non-financial assets	245,867,000	$ 201,007,000
Liabilities measured at fair value	$ 0	$ 0

Organization and Summary of Significant Accounting Policies (Details 4) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Cash and cash equivalents	$ 99,814	$ 190,514	$ 88,952
Restricted cash	227	227	122
Total cash, cash equivalents, and restricted cash shown in the consolidated statement of cash flows	$ 100,041	$ 190,741	$ 89,074	$ 88,731

Organization and Summary of Significant Accounting Policies (Details 5)	12 Months Ended
	Dec. 31, 2019
Furniture And Fixtures \| Minimum
Property and equipment
Estimated useful lives	2 years
Furniture And Fixtures \| Maximum
Property and equipment
Estimated useful lives	5 years
Computer Equipment \| Minimum
Property and equipment
Estimated useful lives	2 years
Computer Equipment \| Maximum
Property and equipment
Estimated useful lives	5 years
Scientific Equipment \| Minimum
Property and equipment
Estimated useful lives	2 years
Scientific Equipment \| Maximum
Property and equipment
Estimated useful lives	5 years
Office Equipment \| Minimum
Property and equipment
Estimated useful lives	2 years
Office Equipment \| Maximum
Property and equipment
Estimated useful lives	5 years
Construction-in-Process \| Minimum
Property and equipment
Estimated useful lives	2 years
Construction-in-Process \| Maximum
Property and equipment
Estimated useful lives	5 years

Organization and Summary of Significant Accounting Policies (Details 6) - shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net Loss per Common Share [Abstract]
Uncertain tax position description	more than 50 percent
Anti-dilutive securities (in shares)	23,820,487	21,352,045	19,994,169
Warrants For Common Stock
Net Loss per Common Share [Abstract]
Anti-dilutive securities (in shares)		85,094	225,756
Common Stock Options
Net Loss per Common Share [Abstract]
Anti-dilutive securities (in shares)	9,327,742	6,980,581	5,458,043
Restricted Stock Units (RSUs)
Net Loss per Common Share [Abstract]
Anti-dilutive securities (in shares)	520,000	188,625	212,625
Series A Convertible Preferred Stock (if converted)
Net Loss per Common Share [Abstract]
Anti-dilutive securities (in shares)	13,972,745	14,097,745	14,097,745

Collaboration and License Agreements (Details) - USD ($)					1 Months Ended	3 Months Ended								12 Months Ended
	May 04, 2019	Sep. 14, 2018	Sep. 11, 2018	May 15, 2018	Oct. 31, 2018	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	May 31, 2019
Collaboration agreement
Collaboration contract asset						$ 1,338,000				$ 1,958,000				$ 1,338,000	$ 1,958,000
Revenue recognized						$ 2,802,000	$ 2,429,000	$ 2,817,000	$ 2,632,000	$ 1,661,000	$ 1,026,000	$ 1,027,000	$ 1,026,000	$ 10,680,000	$ 4,740,000	$ 4,106,000
Common stock issued						75,730,260				64,693,681				75,730,260	64,693,681
Research and development														$ 87,770,000	$ 56,024,000	34,358,000
Issuance of common stock for license agreements															6,100,000
Ono Pharmaceutical Co. Ltd
Collaboration agreement
Non-refundable upfront payments recorded as deferred revenue		$ 10,000,000
Aggregate research and development fees payments receivable		20,000,000
Payments for research and development fees					$ 5,000,000
Collaborative arrangement potential additional milestones		40,000,000
Transaction price of the agreement		30,000,000
Non-refundable upfront payments recorded as deferred revenue		$ 10,000,000
Recognition period of deferred revenue		4 years
Collaborative arrangement annual payments receivable recorded as deferred revenue		$ 6,500,000			$ 5,000,000
Revenue recognized														9,300,000	600,000
Ono Pharmaceutical Co. Ltd \| Candidate 2
Collaboration agreement
Percentage of reduction on milestone payments		50.00%
Ono Pharmaceutical Co. Ltd \| Maximum \| Candidate 1
Collaboration agreement
Aggregate milestone payments		$ 285,000,000
Ono Pharmaceutical Co. Ltd \| Maximum \| Candidate 2
Collaboration agreement
Aggregate milestone payments		$ 895,000,000
Ono Pharmaceutical Co. Ltd \| Collaborative Arrangement
Collaboration agreement
Amortization of sublicense consideration														600,000
Deferred revenue						$ 6,600,000								6,600,000
Deferred revenue classified as current						2,800,000								2,800,000
Ono Pharmaceutical Co. Ltd \| Collaborative Arrangement \| Research services
Collaboration agreement
Revenue recognized														6,200,000	400,000
Ono Pharmaceutical Co. Ltd \| Collaborative Arrangement \| Upfront Fee
Collaboration agreement
Revenue recognized														3,100,000	200,000
Ono Pharmaceutical Co. Ltd \| Collaborative Arrangement \| Other Assets And Deferred Costs
Collaboration agreement
Collaboration contract asset						2,000,000								2,000,000
Ono Pharmaceutical Co. Ltd \| Collaborative Arrangement \| Minimum
Collaboration agreement
Profits and losses sharing percentage		50.00%
Ono Pharmaceutical Co. Ltd \| Sublicense Consideration
Collaboration agreement
Sublicense consideration paid						2,000,000								2,000,000
Collaboration contract asset						$ 1,300,000								1,300,000
Juno Therapeutics, Inc \| Collaborative Arrangement
Collaboration agreement
Revenue recognized														1,400,000	4,100,000	4,100,000
Research term	4 years
Collaboration agreement expiration date	May 04, 2015
Agreement to terminate upon the receipt of research payment																	$ 200,000
Collaborative additional research payment																	$ 0
Juno Therapeutics, Inc \| Collaborative Arrangement \| Research services
Collaboration agreement
Revenue recognized														700,000	2,000,000	2,000,000
Juno Therapeutics, Inc \| Collaborative Arrangement \| Upfront Fee and Equity Premium
Collaboration agreement
Revenue recognized														$ 700,000	$ 2,100,000	$ 2,100,000
MSK \| Amended MSK License
Collaboration agreement
Common stock issued				500,000
Upfront cash payment				$ 500,000
Research and development				5,300,000
Issuance of common stock for license agreements				$ 4,800,000
Gladstone \| Gladstone License Agreement
Collaboration agreement
Aggregate milestone payments			$ 1,900,000
Common stock issued			100,000
Upfront cash payment			$ 100,000
Research and development			1,400,000
Issuance of common stock for license agreements			$ 1,300,000

California Institute For Regenerative Medicine Award (Details) $ in Millions		1 Months Ended		12 Months Ended
	Apr. 05, 2018 USD ($) Disbursement	Jun. 30, 2019	Jan. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)
Award from California institute for regenerative medicine
Period to treat award as grant, if award not treated as loan				10 years
California Institute for Regenerative Medicine
Award from California institute for regenerative medicine
Receipt of first disbursement under the Award \| $				$ 3.5
California Institute for Regenerative Medicine \| LIBOR
Award from California institute for regenerative medicine
Award considered as a loan, interest rate		7.00%
California Institute for Regenerative Medicine \| Loan Repayment Rate One
Award from California institute for regenerative medicine
Repayment percentage of award amount		60.00%
California Institute for Regenerative Medicine \| Loan Repayment Rate Two
Award from California institute for regenerative medicine
Repayment percentage of award amount		80.00%
California Institute for Regenerative Medicine \| Loan Repayment Rate Three
Award from California institute for regenerative medicine
Repayment percentage of award amount		100.00%
California Institute for Regenerative Medicine \| Loan Repayment Rate Four
Award from California institute for regenerative medicine
Repayment percentage of award amount		100.00%
California Institute for Regenerative Medicine \| FT516
Award from California institute for regenerative medicine
Award agreement executed date	Apr. 05, 2018
Award for first-in-human clinical trial \| $	$ 4.0
Number of disbursements \| Disbursement	5
Number of disbursement receivable upon the execution of the award \| Disbursement	1
Number of disbursements receivable based on completion of certain operating milestones \| Disbursement	4
Additional amount available for funding under award \| $			$ 0.4

Investments (Details) - USD ($)	12 Months Ended
Investments (Details) - USD ($)	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale securities, impairment	$ 0	$ 0	$ 0
Available-for-sale securities, realized gains (losses) on sales	$ 0	$ 0	$ 0
Treasuries and Corporate Debt Securities
Schedule Of Available For Sale Securities [Line Items]
Short term investments, maturity start range	3 months
Short term investments, maturity end range	18 months

Investments (Details 2) - USD ($) $ in Thousands	12 Months Ended
Investments (Details 2) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Short-term Investments [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 121,616	$ 10,495
Unrealized Losses	(28)	(2)
Unrealized Gains	25
Estimated Fair Value	121,613	$ 10,493
Long-term Investments [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	39,413
Unrealized Losses	(1)
Unrealized Gains	28
Estimated Fair Value	$ 39,440
U.S. Treasury debt securities \| Current Assets [Member]
Schedule Of Available For Sale Securities [Line Items]
Maturity (in years)	1 or less	1 or less
Amortized Cost	$ 50,445	$ 10,495
Unrealized Losses	(4)	(2)
Unrealized Gains	16
Estimated Fair Value	$ 50,457	$ 10,493
U.S. Treasury debt securities \| Non-current Assets [Member]
Schedule Of Available For Sale Securities [Line Items]
Maturity (in years)	Greater than 1
Amortized Cost	$ 9,841
Unrealized Gains	5
Estimated Fair Value	$ 9,846
Corporate debt securities \| Current Assets [Member]
Schedule Of Available For Sale Securities [Line Items]
Maturity (in years)	1 or less
Amortized Cost	$ 71,171
Unrealized Losses	(24)
Unrealized Gains	9
Estimated Fair Value	$ 71,156
Corporate debt securities \| Non-current Assets [Member]
Schedule Of Available For Sale Securities [Line Items]
Maturity (in years)	Greater than 1
Amortized Cost	$ 29,572
Unrealized Losses	(1)
Unrealized Gains	23
Estimated Fair Value	$ 29,594

Property and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
Property and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Property and equipment
Property and equipment, gross	$ 19,937	$ 11,450
Less accumulated depreciation and amortization	(8,518)	(6,325)
Total property and equipment, net	11,419	5,125
Depreciation expense	2,193	1,204	$ 971
Fixed assets not yet paid	602	37	$ 48
Furniture And Fixtures
Property and equipment
Property and equipment, gross	899	516
Computer And Office Equipment
Property and equipment
Property and equipment, gross	917	688
Software And Software Development Costs
Property and equipment
Property and equipment, gross	103	103
Leasehold Improvements
Property and equipment
Property and equipment, gross	2,465	288
Scientific Equipment
Property and equipment
Property and equipment, gross	15,355	7,868
Construction-in-Process
Property and equipment
Property and equipment, gross	$ 198	$ 1,987

Accrued Expenses and Long-Term Debt (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Current accrued expenses
Accrued payroll and other employee benefits	$ 5,329	$ 2,938
Accrued clinical trial related costs	5,976	4,729
Accrued other	3,392	3,259
Total current accrued expenses	$ 14,697	$ 10,926

Accrued Expenses and Long-Term Debt (Details 2) $ in Thousands	Dec. 31, 2018 USD ($)
Debt Disclosure [Abstract]
Long-term debt	$ 15,000
Less debt issuance costs and discount, net of current portion	(54)
Long-term debt, net of long-term portion of debt issuance costs and discount	14,946
Less current portion of long-term debt	(2,500)
Long-term debt, net	12,446
Current portion of long-term debt	2,500
Less current portion of debt issuance costs and discount	(62)
Current portion of long-term debt, net	$ 2,438

Accrued Expenses and Long-Term Debt (Amended and Restated Loan and Security Agreement) (Details 3) - USD ($)	Jul. 14, 2017	Dec. 24, 2014	Jul. 30, 2014
Debt
Principal amount	$ 15,000,000
Amended And Restated Loan And Security Agreement \| Maximum \| Silicon Valley Bank Debt Facilities
Debt
Principal amount			$ 20,000,000
Amended And Restated Loan And Security Agreement \| Term A Loan \| Silicon Valley Bank Debt Facilities
Debt
Principal amount			10,000,000
Amended And Restated Loan And Security Agreement \| Term B Loan \| Maximum \| Silicon Valley Bank Debt Facilities
Debt
Principal amount			$ 10,000,000
Amended And Restated Loan And Security Agreement \| Term B Loan Tranche 1 \| Silicon Valley Bank Debt Facilities
Debt
Principal amount		$ 10,000,000

Accrued Expenses and Long-Term Debt (2017 Term Loan) (Details 3) - USD ($)			12 Months Ended
	Nov. 13, 2019	Jul. 14, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Debt
Principal amount		$ 15,000,000
Cash proceeds from remaining portion of debt		$ 7,500,000
Debt instrument, maturity date		Jan. 01, 2022
Debt instrument, variable rate description			The 2017 Term Loan was scheduled to mature on January 1, 2022 (the Term Loan Maturity Date) and beared interest at a floating per annum rate equal to the greater of (i) 3.50% above the Prime Rate (as defined in the SVB Loan Amendment) or (ii) 7.25%; provided, however, that in no event would such interest rate exceed 8.25%.
Debt instrument, interest payment terms			Interest was payable on a monthly basis on the first day of each month.
Debt instrument, frequency of periodic payment			monthly
Debt instrument interest only payment period			August 1, 2017 through January 1, 2019
Debt instrument extended interest only payment period			January 1, 2019 through and including to July 31, 2019
Number of equal monthly installments to repay principal and accrued interest		30 months
Final payment fee		$ 1,100,000
Final payment fee		7.50%
Unaccrued final payment fee (amounts in dollars)			$ 300,000
Aggregate interest expense			$ 1,800,000	$ 1,700,000	$ 800,000
2017 Term Loan
Debt
Repayments of debt amount	$ 14,200,000
principal amount of the final fee payment	13,000,000
Final payment fee	1,200,000
Remaining debt issuance costs capitalized	$ 100,000
2017 Term Loan \| Minimum \| SVB Loan Amendment
Debt
Debt instrument, floating rate		7.25%
2017 Term Loan \| Minimum \| Prime Rate \| SVB Loan Amendment
Debt
Debt instrument, floating rate		3.50%
2017 Term Loan \| Maximum \| SVB Loan Amendment
Debt
Debt instrument, floating rate		8.25%

Accrued Expenses and Long-Term Debt (Warrants) (Details 3) - USD ($) $ / shares in Units, $ in Millions			1 Months Ended				12 Months Ended
	Jul. 14, 2017	Dec. 24, 2014	Jul. 31, 2019	Jan. 31, 2019	Sep. 30, 2018	Mar. 31, 2018	Dec. 31, 2009	Dec. 31, 2019
Term B Loan \| Warrant
Warrants
Fair values of warrants issued	$ 0.2
Amended And Restated Loan And Security Agreement \| Term B Loan \| 2014 Warrants
Warrants
Warrants to purchase shares of common stock issued on conversion		98,039
Exercise price (in dollars per share)		$ 4.08
Common stock shares received upon exercise of warrant			39,263			34,149
Number of remaining warrants outstanding								0
SVB Loan Amendment \| 2017 Term Loan
Warrants
Effective interest rate	10.20%
SVB Loan Amendment \| 2017 Term Loan \| 2017 Warrant
Warrants
Warrants to purchase shares of common stock issued on conversion	91,463
Exercise price (in dollars per share)	$ 3.28
Common stock shares received upon exercise of warrant					67,952
Warrants expiration date	2024-07
Fair values of warrants issued	$ 0.2
Historical Debt Agreement \| Warrant
Warrants
Warrants to purchase shares of common stock issued on conversion							36,074
Exercise price (in dollars per share)							$ 7.21
Common stock shares received upon exercise of warrant			21,012	1,245
Number of remaining warrants outstanding								0

Leases (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
Leases (Details) - USD ($) $ in Thousands	May 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 31, 2020
Lessee Lease Description [Line Items]
Lease expiration period	2028
Lessee, operating lease, existence of option to extend		true
Lessee, operating lease, option to extend		The Company can extend the term of each lease for five years after the end of 2028 at the then prevalent market rate, subject to the Company's delivery to the landlord of twelve months' prior written notice.
Additional operating lease term	5 years
Lessee, operating lease, existence of option to terminate		true
Early termination payment description		the Company maintains the right to terminate each lease after October 2025, subject to the Company's delivery to the landlord of twelve month's prior written notice and an early termination payment of $2.5 million.
Lease early termination period option	2025-10
Payment for early termination of lease	$ 2,500
Cash-collateralized irrevocable standby letter of credit	$ 200
Changes in operating right-of-use assets		$ 7,700
Changes in operating lease liability		9,600
Future minimum payments under the operating leases		$ 38,201
Remaining weighted-average lease term		9 years
Operating lease liabilities, weighted-average discount rate		8.00%
Operating lease expense		$ 6,100
Straight-line recognition of fixed payments		3,800
Variable lease cost		2,300
Total short-term lease expense		$ 1,100
Rent expense			$ 2,300	$ 2,300
Subsequent Event
Lessee Lease Description [Line Items]
Future minimum payments under the operating leases					$ 300
Lease term					2 years

Leases (Details 2) $ in Thousands	Dec. 31, 2019 USD ($)
Operating Lease Liabilities Payments Due [Abstract]
2020	$ 3,760
2021	3,873
2022	3,989
2023	4,109
2024	4,232
Thereafter	18,238
Total undiscounted lease payments	38,201
Less: imputed interest	(11,274)
Total lease liability	$ 26,927

Convertible Preferred Stock and Stockholders' Equity (Details) - USD ($)			1 Months Ended		12 Months Ended			76 Months Ended
	Jul. 14, 2017	Sep. 13, 2013	Sep. 30, 2018	Nov. 30, 2016	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2019	Jan. 31, 2019	Jan. 31, 2018	May 31, 2017	May 02, 2017	May 10, 2016	Aug. 28, 2013
Temporary Equity [Line Items]
Preferred stock, par value (in dollars per share)					$ 0.001	$ 0.001		$ 0.001
Dividends declared					$ 0
Shares reserved for issuance					27,708,900	26,065,733		27,708,900
Stock purchases under the plan (in shares)								0
Issuance of common stock from equity incentive plans, net of repurchases and issuance costs					$ 2,522,000	$ 2,693,000	$ 205,000
SVB Loan Amendment
Temporary Equity [Line Items]
Warrants to purchase shares of common stock issued on conversion	91,463
Warrants expiration date	2024-07
Employee And Non Employee Stock Option
Temporary Equity [Line Items]
Total intrinsic value of stock options exercised					10,700,000	$ 5,500,000	$ 100,000
Issuance of common stock from equity incentive plans, net of repurchases and issuance costs					$ 2,500,000
Employee Stock
Temporary Equity [Line Items]
Shares reserved for issuance		729,000			729,000	729,000		729,000
Additional shares authorized (as a percent)		2.00%
Additional shares authorized		450,000
Restricted Stock Units (RSUs)
Temporary Equity [Line Items]
Shares reserved for issuance					520,000	188,625		520,000
Expected recognition period of unrecognized compensation cost					2 years 8 months 12 days	9 months 18 days	1 year 9 months 18 days
Unrecognized compensation cost related to unvested restricted shares					$ 6,200,000	$ 400,000	$ 900,000	$ 6,200,000
Stock Option And Incentive Plan 2013
Temporary Equity [Line Items]
Shares reserved for issuance											2,500,000			1,020,000
Additional shares authorized (as a percent)														4.00%
Stock Option And Incentive Plan 2013 \| Employee And Non Employee Stock Option
Temporary Equity [Line Items]
Stock options generally vested on anniversary grant date (as a percent)					25.00%
General vesting period after first year					3 years
Monthly vesting period					4 years
Term of stock awards					10 years
Annually vesting period					4 years
Weighted-average grant date fair value per share of employee options granted					$ 11.52
Unrecognized compensation cost related to outstanding options					$ 40,400,000	$ 15,900,000	$ 5,800,000	$ 40,400,000
Expected recognition period of unrecognized compensation cost					2 years 10 months 24 days	3 years 1 month 6 days	2 years 7 months 6 days
Stock Option And Incentive Plan 2013 \| Employee and Directors Stock Option
Temporary Equity [Line Items]
Weighted-average grant date fair value per share of employee options granted						$ 8.28	$ 2.29
Inducement Plan
Temporary Equity [Line Items]
Shares reserved for issuance					279,178	379,178		279,178					500,000
Additional shares reserved for issuance									200,000	400,000
Common Stock
Temporary Equity [Line Items]
Issuance of common stock in conjunction with public offering					9,890,000	10,648,149	10,953,750
Conversion of preferred shares to common stock					125,000
Warrant
Temporary Equity [Line Items]
Shares reserved for issuance						85,094
Warrant \| SVB Loan Amendment
Temporary Equity [Line Items]
Exercise price (in dollars per share)	$ 3.28
Warrant \| Term B Loan
Temporary Equity [Line Items]
Fair values of warrants issued	$ 200,000
2017 Warrant \| SVB Loan Amendment
Temporary Equity [Line Items]
Warrants issued to cashless exercised in exchange			67,952
Non-Voting Class A Preferred Stock \| Redmile Group, LLC and Affiliates
Temporary Equity [Line Items]
Terms of conversion					The Class A Preferred were purchased exclusively by entities affiliated with Redmile Group, LLC (collectively, Redmile). The terms of the CoD prohibited Redmile from converting the Class A Preferred into shares of the Company’s common stock if, as a result of conversion, Redmile, together with its affiliates, would own more than 9.99% of the Company’s common stock then issued and outstanding (the Redmile Percentage Limitation), which percentage could change at Redmile’s election upon 61 days’ notice to the Company to (i) any other number less than or equal to 19.99% or (ii) subject to approval of the Company’s stockholders to the extent required in accordance with the NASDAQ Global Market rules, any number in excess of 19.99%. On May 2, 2017, the Company’s stockholders approved the issuance of up to an aggregate of 14,097,745 shares of common stock upon the conversion of the outstanding shares of Class A Preferred. As a result, Redmile has the right to increase the Redmile Percentage Limitation to any percentage in excess of 19.99% at its election.
Non-Voting Class A Preferred Stock \| Maximum
Temporary Equity [Line Items]
Number of shares to be issued upon conversion												14,097,745
Non-Voting Class A Preferred Stock \| Maximum \| Redmile Group, LLC and Affiliates
Temporary Equity [Line Items]
Percentage of common stock ownership upon preferred stock conversion				9.99%
Preferred shares converted into common stock percentage of ownership change upon notice				19.99%
Class A Convertible Preferred Shares
Temporary Equity [Line Items]
Preferred stock, issued shares					2,794,549	2,819,549		2,794,549
Conversion of preferred shares to common stock					(25,000)
November 2016 Placement \| Common Stock
Temporary Equity [Line Items]
Share issue price (in dollars per share)				$ 2.66
Issuance of common stock in conjunction with public offering				7,236,837
November 2016 Placement \| Non-Voting Class A Preferred Stock
Temporary Equity [Line Items]
Preferred stock, issued shares				2,819,549
Share issue price (in dollars per share)				$ 13.30
Number of shares to be issued upon conversion				5
Preferred stock, par value (in dollars per share)				$ 0.001
Conversion price				$ 2.66

Convertible Preferred Stock and Stockholders' Equity (Details 2) - Stock Option And Incentive Plan 2013 - Employee And Non Employee Stock Option - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Number of Options
Balance at the beginning of the period	6,980,581	5,458,043	3,910,350
Granted	3,488,200	3,251,980	2,522,920
Exercised	(787,434)	(694,830)	(83,220)
Cancelled	(353,605)	(1,034,612)	(892,007)
Balance at the end of the period	9,327,742	6,980,581	5,458,043	3,910,350
Vested and expected to vest at the end of the period	9,323,962
Exercisable at the end of the period	4,594,888
Weighted-Average Price
Balance at the beginning of the period	$ 5.58	$ 3.52	$ 3.77
Granted	16.52	8.30	3.09
Exercised	3.31	3.88	2.79
Cancelled	10.70	4.36	3.50
Balance at the end of the period	9.67	$ 5.58	$ 3.52	$ 3.77
Vested and expected to vest at the end of the period	9.66
Exercisable at the end of the period	$ 6.43
Weighted Average Remaining Contractual Term
Outstanding at the end of the period	7 years 8 months 23 days	7 years 10 months 14 days	7 years 11 months 26 days	8 years 3 months 11 days
Vested and expected to vest at the end of the period	7 years 8 months 23 days
Exercisable at the end of the period	6 years 9 months 18 days
Aggregate Intrinsic Value
Outstanding at the end of the period	$ 92,567	$ 51,497	$ 14,754	$ 682
Vested and expected to vest at the end of the period	92,550
Exercisable at the end of the period	$ 60,403

Convertible Preferred Stock and Stockholders' Equity (Details 3) - Restricted Stock Units (RSUs) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Number of Restricted Stock Units
Balance at the beginning of the period	188,625	212,625	525,250
Granted	520,000
Vested	(172,625)		(225,125)
Cancelled	(16,000)	(24,000)	(87,500)
Balance at the end of the period	520,000	188,625	212,625	525,250
Expected to vest at the end of the period	520,000
Weighted-Average Grant Date Fair Value per Share
Balance at the beginning of the period	$ 4.89	$ 4.89	$ 4.89
Granted	16.41
Vested	4.89		4.89
Cancelled	4.89	4.89	4.89
Balance at the end of the period	16.41	$ 4.89	$ 4.89	$ 4.89
Expected to vest at the end of the period	$ 16.41
Weighted Average Remaining Vesting Period
Outstanding at the end of the period	2 years 7 months 20 days	9 months 18 days	1 year 9 months 18 days	2 years 9 months 18 days
Expected to vest at the end of the period	2 years 7 months 20 days
Aggregate Intrinsic Value
Outstanding at the end of the period (in dollars)	$ 10,176	$ 1,299	$ 1,299	$ 1,318
Restricted stock units expected to vest at December 31, 2019	$ 10,176

Convertible Preferred Stock and Stockholders' Equity (Details 4) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Temporary Equity [Line Items]
Total stock-based compensation expense	$ 17,410	$ 6,293	$ 3,606
Research And Development
Temporary Equity [Line Items]
Total stock-based compensation expense	9,804	3,654	2,095
General And Administrative
Temporary Equity [Line Items]
Total stock-based compensation expense	$ 7,606	$ 2,639	$ 1,511

Convertible Preferred Stock and Stockholders' Equity (Details 5)		12 Months Ended
	Jul. 14, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Warrant
Weighted-average assumptions to determine fair value of stock options
Risk–free interest rate	2.10%
Expected volatility	88.00%
Expected term (in years)	7 years
Expected dividend yield	0.00%
Employee And Non Employee Stock Option
Weighted-average assumptions to determine fair value of stock options
Risk–free interest rate		2.40%	2.50%	2.00%
Expected volatility		80.10%	79.30%	90.10%
Expected term (in years)		6 years 1 month 6 days	6 years	6 years
Expected dividend yield		0.00%	0.00%	0.00%

Convertible Preferred Stock and Stockholders' Equity (Details 6) - shares	Dec. 31, 2019	Dec. 31, 2018	May 10, 2016	Sep. 13, 2013
Weighted-average assumptions to determine fair value of stock options
Shares reserved for issuance	27,708,900	26,065,733
Convertible Preferred Stock (if converted)
Weighted-average assumptions to determine fair value of stock options
Shares reserved for issuance	13,972,745	14,097,745
Inducement Plan
Weighted-average assumptions to determine fair value of stock options
Shares reserved for issuance	279,178	379,178	500,000
Employee Stock Option
Weighted-average assumptions to determine fair value of stock options
Shares reserved for issuance	9,327,742	6,980,581
Stock Compensation Plan
Weighted-average assumptions to determine fair value of stock options
Shares reserved for issuance	2,880,235	3,605,510
Restricted Stock Units (RSUs)
Weighted-average assumptions to determine fair value of stock options
Shares reserved for issuance	520,000	188,625
Employee Stock
Weighted-average assumptions to determine fair value of stock options
Shares reserved for issuance	729,000	729,000		729,000
Warrant
Weighted-average assumptions to determine fair value of stock options
Shares reserved for issuance		85,094

Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
Income Taxes (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reconciliation of the Company's expected federal income tax provision (benefit) to the actual income tax provision
Tax computed at federal statutory rate	$ (20,611)	$ (13,985)	$ (14,603)
State tax, net of federal tax benefit	(2,088)	(1,620)	(1,315)
Permanent differences	175	22	795
Stock compensation	359	(307)	539
R&D tax credits	(7,285)	(3,301)	(2,934)
Reserve for uncertain tax positions	2,163	1,160	1,326
Tax Cuts and Jobs Act			25,280
Other	77	304	46
Valuation allowance	27,210	17,727	$ (9,134)
Deferred tax assets:
Section 59e amortization	32,781	19,069
Net operating losses	37,563	30,981
R&D tax credits	16,391	9,163
Depreciation and amortization	1,650	1,653
Deferred revenue	2,115	3,906
Stock compensation	2,346	1,482
Lease liability	5,655
Other	846	1,106
Total deferred tax assets	99,347	67,360
Deferred tax liabilities:
Right-of-use assets	(4,778)
Total deferred tax liabilities	(4,778)
Net of deferred tax assets and liabilities	94,569	67,360
Valuation allowance	$ (94,569)	$ (67,360)

Income Taxes (Details 2) - USD ($) $ in Thousands	12 Months Ended
Income Taxes (Details 2) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Operating Loss Carryforwards [Line Items]
Valuation allowance	$ 94,569	$ 67,360
U.S. Federal
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	$ 168,200
Net operating loss carryforward expiration year	2027
California
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	$ 168,200
Net operating loss carryforward expiration year	2028

Income Taxes (Details 3) $ in Millions	12 Months Ended
Income Taxes (Details 3) $ in Millions	Dec. 31, 2019 USD ($)
Tax Credit Carryforward [Line Items]
Cumulative changes in ownership percentage	50.00%
Period of change in ownership	3 years
Californian
Tax Credit Carryforward [Line Items]
Income tax examination, year under examination	2015
Canadian
Tax Credit Carryforward [Line Items]
Income tax examination, year under examination	2015
U.S. Federal
Tax Credit Carryforward [Line Items]
Income tax examination, year under examination	2016
U.S. Federal \| Research and development
Tax Credit Carryforward [Line Items]
Tax credit carryforwards	$ 13.4
Tax credit carryforward expiration year	2035
California \| Research and development
Tax Credit Carryforward [Line Items]
Tax credit carryforwards	$ 8.5

Income Taxes (Details 4) - USD ($)	12 Months Ended
Income Taxes (Details 4) - USD ($)	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Change in the Company's unrecognized tax benefits
Beginning unrecognized tax benefits	$ 13,547,000	$ 11,800,000	$ 7,730,000
Increase related to current year tax positions	3,196,000	1,798,000	4,077,000
Increase related to prior year tax positions	79,000	148,000	6,000
Decrease related to prior year tax positions		(199,000)	(13,000)
Ending unrecognized tax benefits	16,822,000	$ 13,547,000	$ 11,800,000
Income Taxes
Unrecognized tax benefit	0
Unrecognized tax benefits that, if recognized, would reduce the effective tax rate	$ 0

Income Taxes (Details 5) - USD ($) $ in Millions	12 Months Ended
Income Taxes (Details 5) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2017
Income Tax Uncertainties [Abstract]
Corporate tax rate	21.00%	34.00%
Remeasurement of deferred tax assets and liabilities		$ 25.3

Employee Benefits (Details) - USD ($)		12 Months Ended
Employee Benefits (Details) - USD ($)	Jan. 02, 2009	Dec. 31, 2019
Compensation And Retirement Disclosure [Abstract]
Minimum age of employees	21 years
Matching contributions under 401(k) plan		$ 0

Commitments and Contingencies (Details) $ in Millions	12 Months Ended
Commitments and Contingencies (Details) $ in Millions	Dec. 31, 2019 USD ($)
Commitments And Contingencies Disclosure [Abstract]
Minimum annual payments to maintain licenses	$ 0.4

Selected Quarterly Financial Data (Details) - USD ($)
$ / shares in Units, $ in Thousands

3 Months Ended

12 Months Ended

Dec. 31, 2019

Sep. 30, 2019

Jun. 30, 2019

Mar. 31, 2019

Dec. 31, 2018

Sep. 30, 2018

Jun. 30, 2018

Mar. 31, 2018

Dec. 31, 2019

Dec. 31, 2018

Dec. 31, 2017

Quarterly Financial Information Disclosure [Abstract]

Collaboration revenue

$ 2,802

$ 2,429

$ 2,817

$ 2,632

$ 1,661

$ 1,026

$ 1,027

$ 1,026

$ 10,680

$ 4,740

$ 4,106

Type of Revenue [Extensible List]

us-gaap:LicenseMember

Total operating expenses

$ 31,880

$ 29,548

$ 26,901

$ 23,078

$ 18,402

$ 17,718

$ 20,632

$ 15,080

$ 111,407

$ 71,832

$ 46,231

Net loss

$ (28,302)

$ (26,609)

$ (23,478)

$ (19,760)

$ (16,027)

$ (16,782)

$ (19,654)

$ (14,135)

$ (98,149)

$ (66,598)

$ (42,952)

Basic and diluted net loss per common share (in dollars per share)

$ (0.37)

^[1]

$ (0.40)

^[1]

$ (0.36)

^[1]

$ (0.30)

^[1]

$ (0.25)

^[1]

$ (0.31)

^[1]

$ (0.37)

^[1]

$ (0.27)

^[1]

$ (1.44)

$ (1.19)

$ (1.02)

[1]	Basic and diluted loss per share are computed independently for each of the quarters presented. As such, the sum of the quarterly basic and diluted loss per share information may not equal annual basic and diluted loss per share information.

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

Subsequent Events (Details) - USD ($)	1 Months Ended	12 Months Ended
Subsequent Events (Details) - USD ($)	May 31, 2021	Dec. 31, 2019
Debt Instrument [Line Items]
Lessee, operating lease, option to extend		The Company can extend the term of each lease for five years after the end of 2028 at the then prevalent market rate, subject to the Company's delivery to the landlord of twelve months' prior written notice.
Future minimum payments under the operating leases		$ 38,201,000
Scenario Forecast
Debt Instrument [Line Items]
Lease term	15 years
Lessee, operating lease, option to extend	two successive five-year
Option to terminate lease	10 years
Early termination fees	$ 30,000,000
Future minimum payments under the operating leases	157,600,000
Scenario Forecast \| Letter of Credit
Debt Instrument [Line Items]
Line of credit maintained for benefit of landlord	15,000,000
Scenario Forecast \| Maximum
Debt Instrument [Line Items]
Aggregate tenant improvements of the premises	$ 30,000,000