Regulus Therapeutics (RGLS) 10-K 9 Mar 21 2020 FY Annual report Financial data

Cover

Cover - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Mar. 05, 2021	Jun. 30, 2020
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2020
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Entity File Number	001-35670
Entity Registrant Name	REGULUS THERAPEUTICS INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	26-4738379
Entity Address, Address Line One	10628 Science Center Drive, Suite 225
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	202-6300
Title of 12(b) Security	Common Stock, par value $0.001 per share
Trading Symbol	RGLS
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 22.5
Entity Common Stock, Shares Outstanding		72,504,772
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Entity Central Index Key	0001505512
Amendment Flag	false

Balance Sheets

Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 31,087	$ 34,121
Contract and other receivables	503	1,141
Prepaid materials, net	3,314	3,924
Prepaid expenses and other current assets	1,826	1,221
Total current assets	36,730	40,407
Property and equipment, net	472	921
Intangibles, net	125	266
Other assets	277	487
Total assets	37,604	42,081
Current liabilities:
Accounts payable	535	1,321
Accrued liabilities	581	770
Accrued research and development expenses	1,097	147
Accrued compensation	1,743	1,676
Current portion of term loan, less debt issuance costs	4,652	14,631
Current portion of contract liabilities	0	6
Other current liabilities	2,970	3,047
Total current liabilities	11,578	21,598
Other long-term liabilities	0	468
Total liabilities	11,578	22,066
Stockholders’ equity (deficit):
Common stock, $0.001 par value; 200,000,000 shares authorized, 67,432,712 and 21,018,663 shares issued and outstanding at December 31, 2020 and 2019, respectively	67	21
Additional paid-in capital	453,002	431,305
Accumulated deficit	(427,045)	(411,315)
Total stockholders’ equity	26,026	20,015
Total liabilities and stockholders’ equity	37,604	42,081
Class A-1 Convertible Preferred Stock
Stockholders’ equity (deficit):
Convertible preferred stock	0	1
Class A-2 Convertible Preferred Stock
Stockholders’ equity (deficit):
Convertible preferred stock	1	3
Class A-3 Convertible Preferred Stock
Stockholders’ equity (deficit):
Convertible preferred stock	$ 1	$ 0

Balance Sheets (Parenthetical)

Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2020	Dec. 31, 2019
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	200,000,000	200,000,000
Common stock, shares issued (shares)	67,432,712	21,018,663
Common stock, shares outstanding (in shares)	67,432,712	21,018,663
Class A-1 Convertible Preferred Stock
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	256,700	415,898
Preferred stock, shares issued (in shares)	256,700	415,898
Preferred stock, shares outstanding (in shares)	256,700	415,898
Class A-2 Convertible Preferred Stock
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	1,416,453	3,288,390
Preferred stock, shares issued (in shares)	1,416,453	3,288,390
Preferred stock, shares outstanding (in shares)	1,416,453	3,288,390
Class A-3 Convertible Preferred Stock
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	258,707	0
Preferred stock, shares issued (in shares)	258,707	0
Preferred stock, shares outstanding (in shares)	258,707	0

Statements of Operations and Co

Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Revenues:
Total revenues	$ 10,006	$ 6,832
Operating expenses:
Research and development	15,347	12,349
General and administrative	8,814	11,317
Total operating expenses	24,161	23,666
Loss from operations	(14,155)	(16,834)
Other income (expense):
Interest and other income	233	374
Interest and other expense	(1,808)	(2,131)
Loss before income taxes	(15,730)	(18,591)
Income tax expense	0	(1)
Net loss and comprehensive net loss	$ (15,730)	$ (18,592)
Net loss per share - basic and diluted (in dollars per share)	$ (0.45)	$ (1.08)
Weighted average shares used to compute basic and diluted net loss per share (in shares)	34,977,378	17,260,176
Revenue under collaborations
Revenues:
Total revenues	$ 10,006	$ 6,832

Statements of Stockholders' Equ

Statements of Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Common stock	Additional paid-in capital	Accumulated deficit	Convertible Preferred Stock
Beginning balance (in shares) at Dec. 31, 2018		8,818,019			0
Beginning balance at Dec. 31, 2018	$ (5,854)	$ 9	$ 386,860	$ (392,723)	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of options (in shares)		2,750
Issuance of common stock upon exercise of options	3		3
Issuance of common stock upon vesting of restricted stock units (in shares)		559,445
Issuance of common stock, preferred stock and warrants from private placement, net of offering costs (in shares)		9,730,534			3,704,288
Issuance of common stock, preferred stock and warrants from private placement, net of offering costs	40,084	$ 10	40,070		$ 4
Stock-based compensation expense	2,288		2,288
Issuance of common stock under Employee Stock Purchase Plan (in shares)		4,035
Issuance of common stock under Employee Stock Purchase Plan	3		3
Issuance of common stock through ATM (in shares)		1,903,880
Issuance of common stock through ATM	2,083	$ 2	2,081
Net loss	(18,592)			(18,592)
Ending balance (in shares) at Dec. 31, 2019		21,018,663			3,704,288
Ending balance at Dec. 31, 2019	20,015	$ 21	431,305	(411,315)	$ 4
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of options (in shares)		6,842
Issuance of common stock upon exercise of options	5		5
Issuance of common stock upon exercise of warrants (in shares)		1,038,970
Issuance of common stock upon exercise of warrants	692	$ 1	691
Issuance of common stock upon vesting of restricted stock units (in shares)		75,384
Issuance of common stock, preferred stock and warrants from private placement, net of offering costs (in shares)		24,341,607			272,970
Issuance of common stock, preferred stock and warrants from private placement, net of offering costs	18,166	$ 25	18,141
Stock-based compensation expense	2,614		2,614
Issuance of common stock under Employee Stock Purchase Plan (in shares)		4,998
Issuance of common stock under Employee Stock Purchase Plan	2		2
Issuance of common stock through ATM (in shares)		492,268
Issuance of common stock through ATM	262		262
Conversions of convertible preferred stock (in shares)		20,453,980			(2,045,398)
Conversions of convertible preferred stock		$ 20	(18)		$ (2)
Net loss	(15,730)			(15,730)
Ending balance (in shares) at Dec. 31, 2020		67,432,712			1,931,860
Ending balance at Dec. 31, 2020	$ 26,026	$ 67	$ 453,002	$ (427,045)	$ 2

Statements of Cash Flows

Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Operating activities
Net loss	$ (15,730)	$ (18,592)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation and amortization expense	467	931
Stock-based compensation	2,614	2,288
Gain on reduction of lease liability	0	1,839
Other	154	293
Change in operating assets and liabilities:
Contracts and other receivables	638	(1,115)
Prepaid materials	610	270
Prepaid expenses and other assets	(395)	(242)
Accounts payable	(786)	(393)
Accrued liabilities	(188)	(281)
Accrued research and development expenses	949	(427)
Accrued compensation	66	75
Contract liabilities	(6)	(2,572)
Other liabilities	(929)	(1,895)
Net cash used in operating activities	(12,536)	(19,821)
Investing activities
Purchases of property and equipment	0	(221)
Sales of property and equipment	0	318
Acquisition of intangibles	(11)	(23)
Net cash (used in) provided by investing activities	(11)	74
Financing activities
Proceeds from issuance of securities through private placement, net of issuance costs	18,166	40,084
Proceeds from issuance of common stock, net	957	2,086
Proceeds from borrowing under Paycheck Protection Program	662	0
Proceeds from exercise of common stock options	5	3
Payments on financing leases	(277)	(263)
Principal payments on term loan	(10,000)	(1,977)
Net cash provided by financing activities	9,513	39,933
Net (decrease) increase in cash and cash equivalents	(3,034)	20,186
Cash and cash equivalents at beginning of period	34,121	13,935
Cash and cash equivalents at end of period	31,087	34,121
Supplemental disclosure of cash flow information
Interest paid	(1,356)	(1,655)
Income taxes paid	(1)	(1)
Supplemental disclosure of non-cash investing and financing activities
Unsettled sales of common stock through ATM	392	0
Non-cash acquisition of property and equipment	$ 0	$ 3

The Business, Basis of Presenta

The Business, Basis of Presentation and Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
The Business, Basis of Presentation and Summary of Significant Accounting Policies	The Business, Basis of Presentation and Summary of Significant Accounting Policies We are a biopharmaceutical company focused on discovering and developing first-in-class drugs that target microRNAs to treat a broad range of diseases. We were formed in 2007 when Alnylam and Ionis contributed significant intellectual property, know-how and financial and human capital to pursue the development of drugs targeting micro RNAs pursuant to a license and collaboration agreement. Regulus Therapeutics Inc. was converted to a Delaware corporation on January 2, 2009. As used in this report, unless the context suggests otherwise, “the Company,” “our,” “us” and “we” means Regulus Therapeutics Inc. Liquidity The accompanying financial statements have been prepared on a basis which assumes we are a going concern, and does not include any adjustments to reflect the possible future effects on the recoverability and classification of assets or the amounts and classifications of liabilities that may result from any uncertainty related to our ability to continue as a going concern. Through the date of the issuance of these financial statements, we have principally been financed through proceeds received from the sale of our common stock and other equity securities, debt financings, up-front payments and milestones received from collaboration agreements, totaling $483.4 million. As of December 31, 2020, we had approximately $31.1 million of cash and cash equivalents. Based on our operating plans, we believe our cash and cash equivalents may not be sufficient to fund our operations for the period one year following the issuance of these financial statements. As a result, there is substantial doubt about our ability to continue as a going concern. All amo unts due under the Term Loan (see note 9) have been classified as a current liability as of December 31, 2020 and 2019, due to the considerations discussed above and the assessment that the material adverse change clause under the Term Loan is not within our control. During the period after December 31, 2020, we received a waiver from the Lender (as defined below) with respect to noncompliance with a covenant under the Loan Agreement (as defined below) and are in compliance with all Loan Agreement covenants as of the date of the filing of this Form 10-K. We intend to seek additional capital through equity and/or debt financings, collaborative or other funding arrangements with partners or through other sources of financing. Should we seek additional financing from outside sources, we may not be able to raise such financing on terms acceptable to us or at all. If we are unable to raise additional capital when required or on acceptable terms, we may be required to scale back or discontinue the advancement of product candidates, reduce headcount, file for bankruptcy, reorganize, merge with another entity, or cease operations. If we become unable to continue as a going concern, we may have to liquidate our assets, and might realize significantly less than the values at which they are carried on our financial statements, and stockholders may lose all or part of their investment in our common stock. Use of Estimates Our financial statements are prepared in accordance with GAAP, which requires us to make estimates and assumptions that affect the reported amounts of assets, liabilities, revenues and expenses and the disclosure of contingent assets and liabilities in our financial statements and accompanying notes. An estimated loss contingency is accrued in our financial statements if it is probable that a liability has been incurred and the amount of the loss can be reasonably estimated. Although these estimates are based on our knowledge of current events and actions we may undertake in the future, actual results may ultimately differ from these estimates and assumptions. Though the impact of the COVID-19 pandemic to our business and operating results presents additional uncertainty, we continue to use the best information available to inform our critical accounting estimates. Revenue Recognition Our revenues generally consist of upfront payments for licenses or options to obtain licenses in the future, milestone payments and payments for other research services under license and collaboration agreements. We recognize revenue when we transfer promised goods or services to customers in an amount that reflects the consideration to which we expect to be entitled in exchange for those goods or services. To determine revenue recognition for contracts with customers we perform the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligation(s) in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligation(s) in the contract; and (v) recognize revenue when (or as) we satisfy the performance obligation(s). At contract inception, we assess the goods or services promised within each contract, assess whether each promised good or service is distinct and identify those that are performance obligations. We recognize as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied. Collaborative Arrangements We enter into collaborative arrangements with partners that typically include payment to us of one of more of the following: (i) license fees; (ii) payments related to the achievement of developmental, regulatory, or commercial milestones; and (iii) royalties on net sales of licensed products. Where a portion of non-refundable up-front fees or other payments received are allocated to continuing performance obligations under the terms of a collaborative arrangement, they are recorded as contract liabilities and recognized as revenue when (or as) the underlying performance obligation is satisfied. As part of the accounting for these arrangements, we must develop estimates and assumptions that require judgment to determine the underlying stand-alone selling price for each performance obligation which determines how the transaction price is allocated among the performance obligation(s). The stand-alone selling price may include items such as forecasted revenues, development timelines, discount rates, and probabilities of technical and regulatory success. We evaluate each performance obligation to determine if it can be satisfied at a point in time, or over time. In addition, variable consideration must be evaluated to determine if it is constrained and, therefore, excluded from the transaction price. License Fees If a license to our intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, we recognize revenues from non-refundable, up-front fees allocated to the license when the license is transferred to the licensee and the licensee is able to use and benefit from the license. For licenses that are bundled with other performance obligations, we use judgment to assess the nature of the combined performance obligation to determine whether it is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue. We evaluate the measure of progress each reporting period and, if necessary, adjust the measure of performance and related revenue recognition. Milestone Payments At the inception of each arrangement that includes milestone payments (variable consideration), we evaluate whether the milestones are considered probable of being reached and estimate the amount to be included in the transaction price. If it is probable that a milestone event would occur at the inception of an arrangement, the associated milestone value is included in the transaction price. Milestone payments that are contingent upon the achievement of events that are uncertain or not controllable, such as regulatory approvals, are generally not considered probable of being achieved until those approvals are received, and therefore not included in the transaction price. The transaction price is then allocated to each performance obligation on a relative stand-alone selling price basis, for which we recognize revenue as or when the performance obligations under the contract are satisfied. At the end of each reporting period, we evaluate the probability of achievement of such milestones and any related constraint(s), and if necessary, may adjust our estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which could affect license, collaboration or other revenues and earnings in the period of adjustment. Royalties For arrangements that include sales-based royalties, including milestone payments based on the level of sales, and for which the license is deemed to be the predominant item to which the royalties relate, we recognize revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). To date, we have not recognized any royalty revenue resulting from any of our collaborative arrangements. Stock-Based Compensation We account for stock-based compensation expense related to stock options granted to employees and members of our board of directors by estimating the fair value of each stock option on the date of grant using the Black-Scholes option pricing model. We recognize stock-based compensation expense using the accelerated multiple-option approach. Under the accelerated multiple-option approach (also known as the graded-vesting method), we recognize compensation expense over the requisite service period for each separately vesting tranche of the award as though the award was in substance multiple awards, resulting in accelerated expense recognition over the vesting period. For performance-based awards granted to employees (i) the fair value of the award is determined on the grant date, (ii) we assess the probability of the individual milestones under the award being achieved and (iii) the fair value of the shares subject to the milestone is expensed over the implicit service period commencing once management believes the performance criteria is probable of being met. We account for restricted stock units by determining the fair value of each restricted stock unit based on the closing market price of our common stock on the date of grant. We recognize stock-based compensation expense using the accelerated multiple-option approach over the requisite service periods of the awards. Clinical Trial and Preclinical Study Accruals We make estimates of our accrued expenses for clinical trial and preclinical study activities as of each balance sheet date in our financial statements based on the facts and circumstances known to us at that time. These accruals are based upon estimates of costs incurred and fees that may be associated with services provided by clinical trial investigational sites and CROs and for other clinical trial-related activities. Payments under certain contracts with such parties depend on factors such as successful enrollment of patients, site initiation and the completion of clinical trial milestones. In accruing for these services, we estimate the time period over which services will be performed and the level of effort to be expended in each period. If possible, we obtain information regarding unbilled services directly from these service providers. However, we may be required to estimate these services based on other information available to us. If we underestimate or overestimate the activities or fees associated with a study or service at a given point in time, adjustments to research and development expenses may be necessary in future periods. Historically, our estimated accrued liabilities have approximated actual expense incurred. Subsequent changes in estimates may result in a material change in our accruals. Prepaid Materials We capitalize the purchase of certain raw materials and related supplies for use in the manufacturing of drug product in our preclinical and clinical development programs, as we have determined that these materials have alternative future use. We can use these raw materials and related supplies in multiple clinical drug products, and therefore have future use independent of the development status of any particular drug program until it is utilized in the manufacturing process. We expense the cost of materials when used. We periodically review these capitalized materials for continued alternative future use and write down the asset to its net realizable value in the period in which an impairment is identified. Research and Development Research and development costs are expensed as incurred and consist of costs associated with research activities supporting our drug discovery efforts, compensation and related benefits, non-cash stock-based compensation, license fees, laboratory supplies and associated overhead and facility costs. Income Taxes Income taxes are accounted for under the asset and liability method. This approach requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of the differences between the tax basis of assets or liabilities and their carrying amounts in the financial statements using the enacted tax rates and laws that are anticipated to be in effect when the differences are expected to reverse. We provide a valuation allowance against net deferred tax assets if it is more likely than not that these items will either expire before we are able to realize their benefit or if future deductibility is uncertain. In accordance with the accounting standards for uncertain tax positions, we evaluate the recognition threshold and measurement attribute criteria for the financial statement recognition and measurement of tax positions taken or expected to be taken in a tax return. For those benefits to be recognized, a tax position must be more likely than not to be sustained upon examination by taxing authorities. Cash and Cash Equivalents We classify time deposits and other investments that are highly liquid and have maturities of 90 days or less at the date of purchase as cash equivalents. The carrying amounts approximate fair value due to the short maturities of these instruments. Concentrations of Credit Risk Financial instruments that potentially subject us to significant concentrations of credit risk consist primarily of cash equivalents. We maintain deposits in federally insured financial institutions in excess of federally insured limits. We have not experienced any material losses in such accounts and believe we are not exposed to significant risk. We maintain our cash equivalents with two highly accredited financial institutions. We have historically invested our excess cash primarily in certificates of deposit and debt instruments of financial institutions and corporations, United States Treasury securities and United States government-sponsored enterprise securities. Additionally, we adhere to established guidelines regarding approved investments and maturities of investments, which are designed to preserve their principal value and maintain liquidity. Property and Equipment We carry our property and equipment at cost, which consists of lab equipment, computer equipment and software, furniture and fixtures and leasehold improvements. Property and equipment is depreciated using the straight-line method over the estimated useful lives (generally three Intangibles We capitalize costs which consist principally of outside legal costs and filing fees related to obtaining patents. We review our capitalized patent costs periodically to determine that they include costs for patent applications that have future value and an alternative future use. We evaluate costs related to patents that w e are not actively pursuing and write off these costs. We amortize patent costs over their patent lives, beginning with the date the patents are issued. We obtain licenses from third parties and capitalize the costs related to exclusive licenses that have alternative future use within multiple potential programs. We amortize capitalized licenses over their estimated useful life or term of the agreement. We did not have any licenses capitalized on our balance sheet at December 31, 2020 and 2019. Impairment of Long-Lived Assets We regularly review the carrying amount of our property, equipment and intangible assets to determine whether indicators of impairment may exist which warrant adjustments to carrying values or estimated useful lives. If indications of impairment exist, projected future undiscounted cash flows associated with the asset are compared to the carrying amount to determine whether the asset’s value is recoverable. If the carrying value of the asset exceeds such projected undiscounted cash flows, the asset will be written down to its estimated fair value. No impairment charges were recorded during the years ended December 31, 2020 or 2019. 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. To date, we have viewed our operations and managed our business as one segment operating primarily within the United States. Comprehensive Loss Comprehensive loss is defined as the change in equity during a period from transactions and other events and/or circumstances from non-owner sources. There were no transactions resulting in other comprehensive income or loss during the periods presented; as such, net loss equals other comprehensive loss for all periods presented. Leases At the inception of a contractual arrangement, we determine whether the contract contains a lease by assessing whether there is an identified asset and whether the contract conveys the right to control the use of the identified asset in exchange for consideration over a period of time. For operating leases with an initial term greater than 12 months, we recognize operating lease ROU assets and operating lease liabilities based on the present value of lease payments over the lease term at the commencement date. Operating lease ROU assets are comprised of the lease liability plus any lease payments made and excludes lease incentives. Lease terms include options to renew or terminate the lease when we are reasonably certain that the renewal option will be exercised or when it is reasonably certain that the termination option will not be exercised. For our operating leases, we generally cannot determine the interest rate implicit in the lease, in which case we use our incremental borrowing rate as the discount rate for the lease. We estimate our incremental borrowing rate for our operating leases based on what we would normally pay to borrow on a collateralized basis over a similar term for an amount equal to the lease payments. Operating lease expense is recognized on a straight-line basis over the lease term. Leases with an initial lease term of 12 months or less are not recorded on the balance sheet. Instead, we recognize lease expense for these leases on a straight-line basis over the lease term. Our lease agreements do not contain any material variable lease payments, residual value guarantees or restrictive covenants. Certain leases require us to pay taxes, insurance, utilities, and maintenance costs for the building, which do not represent lease components. We elected to not separate lease and non-lease components. Operating lease ROU assets are recorded within our balance sheets as other assets and operating lease liabilities are recorded within our balance sheets as other current liabilities and other long-term liabilities. Finance lease ROU assets are recorded in property and equipment, net and current and non-current finance lease liabilities are recorded in other current liabilities and other long-term liabilities, respectively, in our balance sheets. Recent Accounting Pronouncements In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments . Subsequently, in November 2018, the FASB issued ASU 2018-19, Codification Improvements to Topic 326, Financial Instruments-Credit Losses . ASU 2016-13 requires entities to measure all expected credit losses for most financial assets held at the reporting date based on an expected loss model which includes historical experience, current conditions, and reasonable and supportable forecasts. ASU 2016-13 also requires enhanced disclosures to help financial statement users better understand significant estimates and judgments used in estimating credit losses. This ASU is effective for smaller reporting companies for fiscal years beginning after December 15, 2022, with early adoption permitted. We are assessing the impact this standard will have on our financial statements and disclosures In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement: Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement , which updates and modifies the disclosure requirements on fair value measurements in Topic 820, primarily in relation to Level 3 fair value measurements. This update is effective for annual periods beginning after December 15, 2019, and interim periods within those periods. The adoption of this guidance on January 1, 2020 did not have a material impact on our financial statements. In November 2018, the FASB issued ASU No. 2018-18, Collaborative Arrangements , which clarifies the interaction between Topic 808 , Collaborative Arrangements and Topic 606, including clarification around certain transactions between collaborative arrangement participants and adding unit-of-account guidance to Topic 808. This update is effective for annual periods beginning after December 15, 2019, and interim periods within those periods. The adoption of this guidance on January 1, 2020 did not have a material impact on our financial statements. In December 2019, the FASB issued ASU No. 2019-12, Income Taxes - Simplifying the Accounting for Income Taxes (“ASU 2019-12”). The guidance removes exceptions to the general principles in Income Taxes (Topic 740) for allocating tax expense between financial statement components, accounting basis differences stemming from an ownership change in foreign investments and interim period income tax accounting for year-to-date losses that exceed projected losses. The guidance becomes effective for annual reporting periods beginning after December 15, 2020 and interim periods within those fiscal years with early adoption permitted. The adoption of this guidance on January 1, 2020 had no impact on our financial statements. In March 2020, the FASB issued ASU No. 2020-04, Reference Rate Reform (Topic 848), which provides guidance around reference rate reform initiatives to identify alternative reference rates that are more observable or transaction-based and less susceptible to manipulation in response to concerns about structural risks of interbank offered rates and the risk of cessation of the London Interbank Offered Rate ("LIBOR"). The amendments in the ASU provide option expedients and exceptions for applying GAAP to contracts, hedging relationships and other transactions affected by reference rate reform and apply only if such contracts, hedging relationships and other transactions that reference LIBOR or another reference rate are expected to be discontinued because of reference rate reform. The guidance does not apply to contract modifications made, and hedging

Net Loss Per Share

Net Loss Per Share	12 Months Ended
	Dec. 31, 2020
Earnings Per Share [Abstract]
Net Loss Per Share	Net Loss Per ShareBasic net loss per share is calculated by dividing net loss by the weighted average number of common shares outstanding for the period, without consideration for common stock equivalents. Diluted net loss per share is calculated by dividing net loss by the weighted-average number of common share equivalents outstanding for the period determined using the treasury-stock method or if-converted method. Dilutive common stock equivalents are comprised of stock options, restricted stock units and convertible preferred stock outstanding. For all periods presented, there is no difference in the number of shares used to calculate basic and diluted net loss per share.Potentially dilutive securities not included in the calculation of diluted net loss per common share, because to do so would be anti-dilutive were (in common stock equivalent shares) 23,741,466 for the year ended December 31, 2020, consisting of convertible preferred stock, stock options and restricted stock units, and 6,569,337 for the year ended December 31, 2019, consisting of convertible preferred stock, stock options and restricted stock units.

Investments

Investments	12 Months Ended
	Dec. 31, 2020
Investments, Debt and Equity Securities [Abstract]
Investments	InvestmentsHistorically, we have invested our excess cash primarily in debt instruments of financial institutions, corporations, U.S. government-sponsored agencies and the U.S. treasury. We generally hold our investments until to maturity and do not sell our investments before we have recovered our amortized cost basis. As of December 31, 2020 and 2019, our cash balance was comprised entirely of cash and cash equivalents (money market funds) and there was no unrealized gain or loss in either period.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements We have certain financial assets recorded at fair value which have been classified as Level 1, 2, or 3 within the fair value hierarchy as described in the accounting standards for fair value measurements. Accounting standards define fair value as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants as of the measurement date. Market participants are buyers and sellers in the principal market that are (i) independent, (ii) knowledgeable, (iii) able to transact, and (iv) willing to transact. The accounting standards provide an established hierarchy for inputs used in measuring fair value that maximizes the use of observable inputs and minimizes the use of unobservable inputs by requiring that the most observable inputs be used when available. Observable inputs are inputs that market participants would use in valuing the asset or liability and are developed based on market data obtained from independent sources. Unobservable inputs are inputs that reflect our assumptions about the factors that market participants would use in valuing the asset or liability. The accounting standards prioritize the inputs used in measuring the fair value into the following hierarchy: • Level 1 includes financial instruments for which quoted market prices for identical instruments are available in active markets. • Level 2 includes financial instruments for which there are inputs other than quoted prices included within Level 1 that are observable for the instrument such as quoted prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets with insufficient volume or infrequent transactions (less active markets) or model-driven valuations in which significant inputs are observable or can be derived principally from, or corroborated by, observable market data. • Level 3 includes financial instruments for which fair value is derived from valuation techniques in which one or more significant inputs are unobservable, including management’s own assumptions. Financial Assets Measured at Fair Value The following table presents our fair value hierarchy for assets measured at fair value on a recurring basis as of December 31, 2020 and 2019 (in thousands): Fair value as of December 31, 2020 Total Level 1 Level 2 Level 3 Assets: Cash equivalents (money market funds) $ 26,901 $ 26,901 $ — $ — $ 26,901 $ 26,901 $ — $ — Fair value as of December 31, 2019 Total Level 1 Level 2 Level 3 Assets: Cash equivalents (money market funds) $ 8,909 $ 8,909 $ — $ — $ 8,909 $ 8,909 $ — $ —

Collaborations

Collaborations	12 Months Ended
	Dec. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Collaborations	Collaborations Revenue recognized from our strategic collaborations was $10.0 million for the year ended December 31, 2020 and $6.8 million for the year ended December 31, 2019. Sanofi In July 2012, we amended and restated our collaboration and license agreement with Sanofi to expand the potential therapeutic applications of the micro RNA alliance targets to be developed under such agreement. We determined that the elements within the strategic collaboration agreement with Sanofi should be treated as a single unit of accounting because the delivered elements did not have stand-alone value to Sanofi. The following elements were delivered as part of the strategic collaboration with Sanofi: (1) a license for up to four micro RNA targets; and (2) a research license under our technology collaboration. In June 2013, the original research term expired, upon which we and Sanofi entered into an option agreement pursuant to which Sanofi was granted an exclusive right to negotiate the co-development and commercialization of certain of our unencumbered micro RNA programs and we were granted the exclusive right to negotiate with Sanofi for co-development and commercialization of certain miR-21 anti-miRs in oncology and Alport syndrome. In July 2013, we received an upfront payment of $2.5 million, of which $1.25 million is creditable against future amounts payable by Sanofi to us under any future co-development and commercialization agreement we enter pursuant to the option agreement. Revenue associated with the creditable portion of this option payment was deferred as of December 31, 2017, and recorded as an adjustment to accumulated deficit upon our adoption of Topic 606 on January 1, 2018. The non-creditable portion of this payment, $1.25 million, was recognized as revenue over the option period from the effective date of the option agreement in June 2013 through the expiration of the option period in January 2014. In February 2014, we and Sanofi entered into a second amended and restated collaboration and license agreement (the “2014 Sanofi Amendment”) to renew our strategic collaboration to discover, develop and commercialize micro RNA therapeutics to focus on specific orphan disease and oncology targets. Under the terms of the 2014 Sanofi Amendment, Sanofi had opt-in rights to our clinical fibrosis program targeting miR-21 for the treatment of Alport syndrome, our preclinical program targeting miR-21 for oncology indications, and our preclinical program targeting miR-221/222 for HCC. We were responsible for developing each of these programs to proof-of-concept, at which time Sanofi had an exclusive option on each program. If Sanofi chooses to exercise its option on any of these programs, Sanofi would reimburse us for a significant portion of our preclinical and clinical development costs and would also pay us an option exercise fee for any such program, provided that $1.25 million of the $2.5 million upfront option fee paid to us by Sanofi in connection with the June 2013 option agreement will be creditable against such option exercise fee. We are eligible to receive royalties on micro RNA therapeutic products commercialized by Sanofi and will have the right to co-promote these products relating to our preclinical program targeting miR-221/222. As indicated below, we entered into an additional amendment with Sanofi in November 2018, under which Sanofi's opt-in rights to our miR-21 programs under the 2014 Sanofi Amendment were relinquished. Sanofi's opt-in rights with regard to our miR-221/222 preclinical program under the 2014 Sanofi Amendment remained unchanged. In connection with the 2014 Sanofi Amendment, we entered into a Common Stock Purchase Agreement (the “ Sanofi Purchase Agreement”), pursuant to which we sold 108,648 shares of our common stock to Aventisub LLC (“Aventis”), an entity affiliated with Sanofi, in a private placement at a price per share of $92.04 for an aggregate purchase price of $10.0 million. Under the terms of the Sanofi Purchase Agreement, Aventis was not permitted to sell, transfer, make any short sale of, or grant any option for the sale of any common stock for the 12-month period following its effective date. The Sanofi Purchase Agreement and the 2014 Sanofi Amendment were negotiated concurrently and were therefore evaluated as a single agreement. Based upon restricted stock studies of similar duration and a Black-Scholes valuation to measure the discount for lack of marketability, approximately $0.4 million of the proceeds from the Sanofi Purchase Agreement was attributed to the 2014 Sanofi Amendment, and represents consideration for the value of the program targeting miR-221/222 for HCC. We recognized the $0.4 million allocated consideration into revenue ratably over the estimated period of performance of the miR-221/222 program. We are eligible to receive milestone payments related to the development and commercialization of miR-221/222 for HCC of up to $38.8 million for proof-of-concept option exercise fees (net of $1.25 million creditable, as noted above), $25.0 million for clinical milestones and up to $130.0 million for regulatory and commercial milestones. In addition, we are entitled to receive royalties based on a percentage of net sales of any products from the miR-221/222 program which, in the case of sales in the United States, will be in the middle of the 10% to 20% range, and, in the case of sales outside of the United States, will range from the low end to the middle of the 10% to 20% range, depending upon the volume of sales. If we exercise our option to co-promote a miR-221/222 product, we will continue to be eligible to receive royalties on net sales of each product in the United States at the same rate, unless we elect to share a portion of Sanofi’s profits from sales of such product in the United States in lieu of royalties. In November 2018, we entered into an amendment to the 2014 Sanofi Amendment with Sanofi to modify the parties’ rights and obligations with respect to our miR-21 programs, including our RG-012 program (the “2018 Sanofi Amendment”). Under the terms of the 2018 Sanofi Amendment, we have granted Sanofi a worldwide, royalty-free, fee-bearing, exclusive license, with the right to grant sublicenses, under our know-how and patents to develop and commercialize miR-21 compounds and products for all indications, including Alport Syndrome. Sanofi will control and will assume all responsibilities and obligations for developing and commercializing each of our miR-21 programs, including our obligations regarding the administration and expense of clinical trials and all other costs, including in-license royalties and other in-license payments, related to our miR-21 programs. Under the terms of the 2018 Sanofi Amendment, we have assigned to Sanofi certain agreements, product-specific patents and all materials directed to miR-21 or to any miR-21 compound or product and are required to provide reasonable technical assistance to Sanofi for a period of 24 months after the date of the 2018 Sanofi Amendment. Under the terms of the 2018 Sanofi Amendment, we were eligible to receive approximately $6.8 million in upfront payments for the license and for miR-21 program-related materials (collectively, the “Upfront Amendment Payments”). We were also eligible to receive up to $40.0 million in development milestone payments, including a $10.0 million payment for an interim enrollment milestone (the "Enrollment Milestone"). In addition, Sanofi has agreed to reimburse us for certain out-of-pocket transition activities and assume our upstream license royalty obligations. We and Sanofi also agreed to a general release of claims against each other for any claims that arose at any time prior to the date of the 2018 Sanofi Amendment, or that thereafter could arise based on anything that occurred prior to the date of the 2018 Sanofi Amendment. In 2019, we completed the performance obligations under the 2018 Sanofi Amendment and recognized revenue for the $6.8 million in Upfront Amendment Payments. As of December 31, 2019, the $40.0 million in development milestone payments (variable consideration) was fully constrained and therefore, did not meet the criteria for revenue recognition. In August 2020, we entered into an amendment to the 2018 Sanofi Amendment (the "2020 Sanofi Amendment"). Under the terms of the 2020 Sanofi Amendment, we agreed to transfer to Sanofi additional RG-012 development program materials (the “Materials”) in exchange for a payment from Sanofi of $1.0 million (the “Transfer Payment”). In addition, in lieu of the $10.0 million Enrollment Milestone under the 2018 Sanofi Amendment, Sanofi agreed to pay us a $4.0 million milestone upon the completion of the transfer and verification of the Materials, and $5.0 million upon achievement of the Enrollment Milestone. Additionally, we are eligible to receive $25.0 million upon achievement of an additional development milestone related to Sanofi's development of the miR-21 compounds. In September 2020, we received $1.0 million in exchange for the transfer of the Materials to Sanofi, and received an additional $4.0 million in October 2020 as a result of Sanofi's completion and verification of the Materials in September 2020. As the performance obligations associated with both of these payments had been satisfied under Topic 606 as of September 30, 2020, both amounts were recognized as revenue in the third quarter of 2020. In November 2020, we received $5.0 million upon achievement of the Enrollment Milestone. As the performance obligations associated with this payment had been satisfied under Topic 606 as of December 31, 2020, this amount was recognized as revenue in the fourth quarter of 2020. As of December 31, 2020, the $25.0 million development milestone payment (variable consideration) is fully constrained and therefore, does not meet the criteria for revenue recognition.

Property and Equipment, net

Property and Equipment, net	12 Months Ended
	Dec. 31, 2020
Property, Plant and Equipment [Abstract]
Property and Equipment, net	Property and Equipment, net The following table summarizes our major classes of property and equipment (in thousands): December 31, 2020 2019 Laboratory equipment $ 4,967 $ 4,967 Computer equipment and software 281 281 Furniture and fixtures — — Leasehold improvements 83 83 5,331 5,331 Less accumulated depreciation and amortization (4,859) (4,410) Property and equipment, net $ 472 $ 921 Depreciation and amortization of property and equipment of $0.5 million and $0.9 million was recorded for the years ended December 31, 2020 and 2019, respectively.

Intangible Assets, net

Intangible Assets, net	12 Months Ended
	Dec. 31, 2020
Goodwill and Intangible Assets Disclosure [Abstract]
Intangible Assets, net	Intangible Assets, net The following table summarizes our major classes of intangible assets (in thousands): December 31, 2020 2019 Patents $ 219 $ 465 Accumulated amortization - Patents (94) (199) Intangibles, net $ 125 $ 266 Intangible asset amortization of less than $0.1 million was recorded for the years ended December 31, 2020 and 2019. Amortization of intangible assets over the next five years is expected to be less than $0.1 million per year. The weighted-average period over which the amortization remaining at December 31, 2020 is expected to be recognized is approximately 13.9 years.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2020
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies License Agreements We have license agreements with third parties that require us to make annual license maintenance payments and future payments upon the success of licensed products that include milestones and/or royalties. Minimum future payments over the next five years are not material.

Debt

Debt	12 Months Ended
	Dec. 31, 2020
Debt Disclosure [Abstract]
Debt	Debt On June 17, 2016, we entered into a loan and security agreement ("Loan Agreement") with Oxford Finance, LLC, ("Oxford" or sometimes referred to as the “ Lender ” ), pursuant to which we received $20.0 million in proceeds, net of debt issuance costs on June 22, 2016 (the "Term Loan"). The outstanding Term Loan will mature on May 1, 2022 (the “Maturity Date”) and bears interest at a floating per annum rate equal to (i) 8.51% plus (ii) the greater of (a) the 30 day U.S. Dollar LIBOR rate reported in The Wall Street Journal on the last business day of the month that immediately precedes the month in which the interest will accrue and (b) 0.44%. Under the original Loan Agreement, we were required to make interest-only payments through June 1, 2018, followed by 24 equal monthly payments of principal and unpaid accrued interest. In August 2018, we and Oxford entered into an amendment to our Loan Agreement, providing for a modification of the loan amortization period. Under the terms of the amendment, principal amortization and repayment was deferred between August 2018 through October 2018, and during this period, we were required to make payments of interest-only. Amortization payments recommenced in November 2018. Pursuant to the amendment, we granted the Lender a security interest in our intellectual property as additional collateral for the repayment of the Term Loan. In November 2018, and in connection with the 2018 Sanofi Amendment, we entered into a fourth amendment to the Loan Agreement with the Lender (the "Fourth Amendment"). Under the terms of the Fourth Amendment, the Lender consented to the 2018 Sanofi Amendment and our license, assignment and transfer to Sanofi of certain of our intellectual property, as required to be delivered to Sanofi under the 2018 Sanofi Amendment (the “Assigned Assets”), which previously served as collateral under the Loan Agreement, and released its liens in the Assigned Assets, provided that the Lender will continue to have liens on all proceeds received by us pursuant to our collaboration and license agreement with Sanofi dated February 4, 2014 (the “Sanofi License Agreement”). Under the terms of the Fourth Amendment, we have the option to prepay part of the Term Loan at any time and in any amount after 10 days’ prior written notice. We are also required to prepay a portion of the Term Loan with 25% of certain payments we receive under the 2018 Sanofi Amendment, which payments consist of the Upfront Amendment Payments and the first development milestone payment in the amount of $10.0 million. In accordance with this term, we prepaid $0.6 million pursuant to our receipt of $2.5 million in Upfront Amendment Payments in November 2018. Additionally, we prepaid $0.4 million pursuant to our receipt of $1.8 million in Upfront Amendment Payments in March 2019. We are required to pay the applicable 5.5% final payment fee related to each such 2018 Sanofi Amendment prepayment. On January 31, 2019, we entered into a fifth amendment to the Loan Agreement with the Lender (the "Fifth Amendment"). Under the terms of the Fifth Amendment, our required monthly payment to the Lender for the month of February 2019 was comprised of interest only. On March 7, 2019, we entered into a sixth amendment to the Loan Agreement with the Lender (the "Sixth Amendment"). Under the terms of the Sixth Amendment, our required monthly payment to the Lender for the month of March 2019 was comprised of interest only. On April 9, 2019 we entered into a seventh amendment to the Loan Agreement with the Lender (the "Seventh Amendment"). Under the terms of the Seventh Amendment, our required monthly payments to the Lender were to be comprised of interest only through and including the payment date immediately preceding the following date (the “Second Amortization Date”): (i) April 1, 2019, if we did not receive unrestricted gross cash proceeds of not less than $10 million on or before April 30, 2019 from (a) the issuance and sale of our unsecured subordinated convertible debt and/or equity securities and/or (b) “up front” or milestone payments in connection with a joint venture, collaboration or other partnering transaction other than pursuant to the Sanofi License Agreement (the receipt of such net proceeds, the “ Seventh Amendment Capital Event”), and (ii) May 1, 2019, if the Seventh Amendment Capital Event occurs. The Seventh Amendment Capital event did not occur on or before April 30, 2019. Commencing on the Second Amortization Date, and continuing on each successive payment date thereafter, we were to be required to make consecutive equal monthly payments of principal, together with applicable interest, in arrears, to the Lender; provided, however, that we were required to make the monthly principal payment due April 1, 2019 on May 1, 2019 (in addition to all other payments due on May 1, 2019) if the Seventh Amendment Capital Event did not occur. The Seventh Amendment also provided that we can irrevocably elect to increase the prepayment percentage for the funds that we are required to prepay under the Term Loan in the event we receive $10.0 million from the first development milestone under the Enrollment Milestone from 25% to 75% (the “Applicable Sanofi Percentage”). Under the Seventh Amendment, we are required to maintain cash in a collateral account controlled by the Lender of (i) $10.0 million if the Applicable Sanofi Percentage is 25% and if we had not prepaid an aggregate of $5 million under the Term Loan (which amount shall not include any Sanofi License Agreement prepayments) on or before April 30, 2019 (such prepayment, the “Principal Paydown Event”), (ii) $5.0 million if the Applicable Sanofi Percentage is 75% and the Principal Paydown Event had not occurred and (iii) zero if the Principal Paydown Event had occurred. On May 3, 2019, concurrently with our Securities Purchase Agreement dated May 2019 (the "May 2019 SPA") (as described in further detail in Note 10), we entered into an eighth amendment to the Loan Agreement with the Lender (the "Eighth Amendment"). Pursuant to the terms of the Eighth Amendment and as a result of the completion of the initial closing under the May 2019 SPA, our required monthly payments to the Lender were comprised of interest only from May 2019 through and including the payment to be made in April 2020, in exchange for an interest-only period extension fee of $0.1 million. Additionally, under the Eighth Amendment, the Term Loan maturity date was extended from June 2020 to May 2022, in exchange for a maturity date extension fee of $0.7 million. Pursuant to the Eighth Amendment, as a result of our receipt of over $20.0 million in capital in December 2019 under the second and final closing under the May 2019 SPA, our required monthly payments to the Lender are comprised of interest only through and including the payment to be made in April 2021. Commencing in May 2021, and continuing on each successive payment date thereafter, we are required to make consecutive equal monthly payments of principal, together with applicable interest, in arrears, to the Lender. The Eighth Amendment also provides for an increase in the prepayment percentage for the funds that we are required to prepay under the Term Loan, in the event that we receive the $10.0 million Enrollment Milestone, from 75% to 100% of the Milestone Payment. Upon payment of the Milestone Payment to the Lender, we will no longer be required to maintain cash in a collateral account controlled by Lender and the positive lien on our intellectual property will be released. On May 1, 2020 we entered into a ninth amendment to the Term Loan with the Lender (the “Ninth Amendment”). Pursuant to the terms of the Ninth Amendment, (i) the approximately $0.7 million of loan proceeds (the "PPP Loan") we received under the Paycheck Protection Program ("PPP") was included as permitted indebtedness under the terms of the Term Loan, (ii) we agreed to apply for forgiveness of the maximum amount of PPP Loan permissible in accordance with the Coronavirus Aid, Relief, and Economic Security Act (the “CARES Act”) and use best efforts to cause not less than $0.5 million of the PPP Loan to be forgiven by the PPP Loan lender on or before September 30, 2020 and (iii) we agreed not to amend any material provision in any document relating to the PPP Loan nor make any prepayment of the PPP Loan unless such prepayment is necessary or advisable due to change in the applicable law or guidance issued by the U.S. Small Business Administration (“SBA”). On August 25, 2020 we entered into a tenth amendment to the Term Loan with the Lender (the "Tenth Amendment"). Pursuant to the terms of the Tenth Amendment, we are eligible for up to an additional seven months of interest only payments in the event we paid down $10 million in loan principal before April 30, 2021 (the "Principal Paydown Event"). In the event the Principal Paydown Event did not occur by April 30, 2021, we would make principal and accrued interest payments, in arrears, commencing May 1, 2021, in accordance with the terms of the Eighth Amendment. If the Principal Paydown Event occured after April 30, 2021 but on or before July 31, 2021, we would recommence an extended interest only payment period through December 31, 2021. In the event we received the additional interest only period, principal and accrued interest payments would recommence on January 1, 2022. We received $1.0 million, $4.0 million and $5.0 million in proceeds from Sanofi (see Note 7) on September 30, 2020, October 8, 2020 and November 30, 2020, respectively. Under the terms of the Tenth Amendment, we prepaid $1.0 million, $4.0 million and $5.0 million of outstanding principal to the Lender on September 30, 2020, October 8, 2020 and November 30, 2020, respectively, for a total of $10.0 million. We also paid the applicable 5.5% final payment fees related to the three prepayments to the Lender. As the Principal Paydown Even t occurred by April 30, 2021, we received an additional seven months of interest only payment extension and are not obligated to make principal payments on the Term Loan until January 1, 2022. We used the proceeds from the Term Loan solely for working capital and to fund our general business requirements. Our obligations under the Loan Agreement are secured by a first priority security interest in substantially all of our current and future assets, other than our intellectual property, for which Oxford currently has a positive lien, and certain assets under finance lease obligations. We have also agreed not to encumber our intellectual property assets, except as permitted by the Loan Agreement. The Loan Agreement includes customary events of default, including instances of a material adverse change in our operations, that may require prepayment of the outstanding Term Loan. During the period after December 31, 2020, we received a waiver from the Lender with respect to noncompliance with a covenant under the Loan Agreement and are in compliance with all Loan Agreement covenants as of the date of the filing of this Form 10-K. As of December 31, 2020, $4.7 million was outstanding under the Term Loan. An additional $1.3 million is also payable at the conclusion of the Term Loan ( presented in other current liabilities on our balance sheet at December 31, 2020) . We had less than $0.1 million of debt issuance costs outstanding as of December 31, 2020, which are being accreted to interest expense over the life of the T erm Loan using an effective interest rate of 8.98%. The exit fees are being accrued over the life of the Term Loan through interest expense. As of December 31, 2020, future principal payments for the Term Loan due under the Loan Agreement are as follows (in thousands): 2021 — 2022 4,681 $ 4,681 Paycheck Protection Program Loan On April 23, 2020, we received the proceeds from the PPP Loan in the amount of approximately $0.7 million from Silicon Valley Bank, as lender, pursuant to the PPP of the CARES Act. The PPP Loan matures on April 23, 2022 and bears interest at a rate of 1.0% per annum. The PPP Loan is evidenced by a promissory note dated April 23, 2020, which contains customary events of default relating to, among other things, payment defaults and breaches of representations and warranties. The PPP Loan may be prepaid by us at any time prior to maturity with no prepayment penalties. All or a portion of the PPP Loan may be forgiven by the SBA upon our application and upon documentation of expenditures in accordance with the SBA requirements. Under the CARES Act and PPP Flexibility Act, loan forgiveness is available for the sum of documented payroll costs, covered mortgage interest, covered rent payments and covered utilities

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2020
Equity [Abstract]
Stockholders’ Equity	Stockholders’ Equity Common Stock As of December 31, 2020, there were 67,432,712 shares of common stock outstanding. Each share of common stock is entitled to one vote. The holders of the common stock are also entitled to receive dividends whenever funds are legally available and when declared by our Board of Directors. 2019 Equity Incentive Plan On June 15, 2019 the Company's board of directors approved, and on August 1, 2019 the Company's stockholders approved, the Company's 2019 Equity Ince ntive Plan (the "2019 Plan"). The 2019 Plan is intended as the successor to and continuation of the Company's 2012 Equity Incentive Plan. As of December 31, 2020, 868,432 shares of common stock were available for new equity award grants under the 2019 Plan and 6,847,361 shares of common stock are reserved for issuance pursuant to equity awards outstanding as of December 31, 2020. The number of shares authorized for issuance under the 2019 Plan may be increased by (a) the shares subject to outstanding stock awards granted under the Company’s 2009 Equity Incentive Plan (the “2009 Plan”) and the Company’s 2012 Equity Incentive Plan (together the with 2009 Plan, the “Prior Plans”) that on or after the effective date of the 2019 Plan (i) expire or terminate for any reason prior to exercise or settlement; (ii) are forfeited because of the failure to meet a contingency or condition required to vest such shares or otherwise return to the Company, or (iii) are reacquired, withheld (or not issued) to satisfy a tax withholding obligation in connection with an award or to satisfy the purchase price or exercise price of a stock award. No further grants will be made under the Prior Plans. In addition, on January 22, 2020, an additional 4,166,860 shares of common stock became available for issuance under the 2019 Plan pursuant to the Milestone Closing of the May 2019 SPA. Further, on January 1 st of each year, for a period of not more than ten years, beginning on January 1, 2021 and continuing through January 1, 2029, the number of shares authorized for issuance under the 2019 Plan will increase by 5.0% of the total number of shares of our capital stock outstanding on December 31 of the preceding calendar year, or a lesser number of shares as may be determined by our Board of Directors. Private Placements of Common Stock, Non-Voting Preferred Stock and Warrants On May 3, 2019, we entered into the May 2019 SPA with certain institutional and other accredited investors, including certain directors, executive officers and employees of the Company (the “Purchasers”), pursuant to which we agreed to sell and issue shares of our common stock, shares of our newly designated non-voting convertible preferred stock, and warrants to purchase common stock, in up to two closings, in a private placement transaction (the “Private Placement”). At an initial closing under the May 2019 SPA that occurred on May 7, 2019 (the “Initial Closing”), we sold and issued to the Purchasers (i) 9,730,534 shares of common stock and accompanying warrants to purchase up to an aggregate of 9,730,534 shares of common stock at a combined purchase price of $1.205 per share, and (ii) 415,898 shares of non-voting Class A-1 convertible preferred stock, in lieu of shares of common stock, at a price of $10.80 per share, and accompanying warrants to purchase an aggregate of 4,158,980 shares of common stock at a price of $0.125 for each share of common stock underlying such warrants. Total gross proceeds from the Initial Closing were approximately $16.7 million, which does not include any proceeds that may be received upon exercise of the warrants. Each share of non-voting Class A-1 convertible preferred stock is convertible into 10 shares of Common Stock, subject to certain beneficial ownership conversion limitations. The warrants are exercisable for a period of five years following the date of issuance and have an exercise price of $1.08 per share, subject to proportional adjustments in the event of stock splits or combinations or similar events. The warrants are exercisable on a net exercise "cashless" basis. An aggregate of 526,083 shares of common stock and warrants to purchase up to 526,083 shares of common stock were purchased for $0.6 million by certain directors and executive officers of the Company under the Initial Closing. Pursuant to the May 2019 SPA, in the event our Board of Directors unanimously resolves to recommence our Phase 1 multiple ascending dose clinical trial of our RGLS4326 product candidate for the treatment of ADPKD") (the “Phase 1 Trial”) based on correspondence from the U.S. Food and Drug Administration’s Division of Cardiovascular and Renal Products, and thereafter but on or before December 31, 2019 we make a public announcement of our plan to recommence the Phase 1 Trial (the “Public Announcement”), we may sell and the Purchasers may purchase, at a second closing under the May 2019 SPA (“Milestone Closing”), shares of our non-voting convertible preferred stock and accompanying warrants to purchase shares of Common Stock (collectively, “Milestone Securities”). On December 15, 2019, the Company’s Board of Directors unanimously resolved to recommence the Phase 1 Trial based on correspondence from the U.S. Food & Drug Administration’s Division of Cardiovascular and Renal Products and on December 16, 2019, we made the related Public Announcement, triggering the Milestone Closing, which occurred on December 24, 2019. At the Milestone Closing, we sold and issued to the Purchasers 3,288,390 shares of non-voting Class A-2 convertible preferred stock and accompanying warrants to purchase an aggregate of 32,883,900 shares of common stock for an aggregate purchase price of approximately $26.0 million. Net proceeds to the Company from the Milestone Closing were approximately $24.6 million. Each share of non-voting Class A-2 convertible preferred stock is convertible into 10 shares of Common Stock, subject to certain beneficial ownership conversion limitations. The warrants will be exercisable for a period of five years following the date of issuance and have an exercise price of $0.666 per share, subject to proportional adjustments in the event of stock splits or combinations or similar events. The warrants are exercisable on a net exercise “cashless” basis. An aggregate of 121,581 shares of Class A-2 convertible preferred stock and warrants to purchase up to 1,215,810 shares of common stock were purchased for approximately $1.0 million by certain directors and executive officers of the Company under the Milestone Closing. We evaluated the non-voting Class A-1 convertible preferred stock and common stock warrants sold in the Initial Closing and the Class A-2 convertible preferred stock and common stock warrants sold in the Milestone Closing under ASC 480, Distinguishing Liabilities from Equity, and ASC 815, Derivatives and Hedging, and determined permanent equity treatment was appropriate for these freestanding financial instruments. The Initial Closing and Milestone Closing did not include any embedded features that required bifurcation. The non-voting Class A-2 convertible preferred stock and warrants issuable under the Milestone Closing were not subject to accounting recognition until the Milestone Closing occurred, as the terms of the Milestone Closing did not provide a right or an obligation on either the Company nor the Purchasers. On December 1, 2020, we entered into a Securities Purchase Agreement (the "December 2020 SPA") with certain institutional and other accredited investors, including certain directors, executive officers and employees of the Company (the “2020 Purchasers”), pursuant to which we agreed to sell and issue shares of our common stock, shares of newly designated non-voting convertible preferred stock and warrants to purchase common stock (the “2020 PIPE”). At the closing under the December 2020 SPA that occurred on December 4, 2020 (the “2020 Closing”), we sold and issued to the 2020 Purchasers (i) 24,341,607 shares of common stock and accompanying warrants to purchase up to an aggregate of 18,256,204 shares of common stock at a combined purchase price of $0.7464 per share, and (ii) 272,970 shares of non-voting Class A-3 convertible preferred stock, in lieu of shares of common stock, at a price of $6.22 per share, and accompanying warrants to purchase an aggregate of 2,047,276 shares of common stock at a price of $0.125 for each share of common stock underlying such warrants. Total gross proceeds from the 2020 Closing were approximately $19.4 million, which does not include any proceeds that may be received upon exercise of the warrants. Each share of non-voting Class A-3 convertible preferred stock is convertible into 10 shares of common stock, subject to certain beneficial ownership conversion limitations. The warrants are exercisable for a period of five years following the date of issuance and have an exercise price of $0.622 per share, subject to proportional adjustments in the event of stock splits or combinations or similar events. The warrants are exercisable on a net exercise "cashless" basis. An aggregate of 833,208 shares of common stock and warrants to purchase up to 624,906 shares of common stock were purchased for $0.6 million by certain directors and executive officers of the Company at the 2020 Closing. We evaluated the non-voting Class A-3 convertible preferred stock and common stock warrants sold in the 2020 PIPE under ASC 480, Distinguishing Liabilities from Equity, and ASC 815, Derivatives and Hedging, and determined permanent equity treatment was appropriate for these freestanding financial instruments and there were no embedded features that required bifurcation. The following table summarizes preferred stock conversions and warrant exercises (and the related impact on common stock) under the 2019 SPA and 2020 SPA for the years ended December 31, 2020 and 2019 (in thousands): Class A-1 Convertible Preferred Stock Class A-2 Convertible Preferred Stock Class A-3 Convertible Preferred Stock Warrants Common Stock Balance at December 31, 2018 — — — — — Initial Closing 416 — — 13,890 9,731 Milestone Closing — 3,288 — 32,884 — Conversions/Exercises — — — — — Balance at December 31, 2019 416 3,288 — 46,774 9,731 2020 Closing — — 273 20,303 24,342 Conversions/Exercises (159) (1,872) (14) (1,039) 21,493 Balance at December 31, 2020 257 1,416 259 66,038 55,566 ATM Offering On December 12, 2018, we entered into a Common Stock Sales Agreement (the “Stock Sales Agreement”) with H.C. Wainwright & Co., LLC (“HCW”), pursuant to which we may sell and issue shares of our common stock from time to time through HCW, as our sales agent (the “ATM Offering”). We have no obligation to sell any shares of common stock in the ATM Offering, and may at any time suspend offers under the Stock Sales Agreement or terminate the Stock Sales Agreement. Subject to the terms and conditions of the Stock Sales Agreement, HCW will use its commercially reasonable efforts to sell shares of our common stock from time to time based upon our instructions (including any price, time or size limits or other parameters or conditions the we may impose, subject to certain restrictions). We pay HCW a commission of 3.0% of the gross sales price of any shares sold under the Stock Sales Agreement. A total of 492,268 shares were sold and settled for proceeds of $0.3 million (net of less than $0.1 million in commissions) under the ATM Offering during the year ended December 31, 2020. We sold a total of 309,485 shares for proceeds of $0.4 million (net of less than $0.1 million in commissions) under the ATM Offering during the year ended December 31, 2020 that had not been settled as of December 31, 2020. Those shares were settled as of January 5, 2021. A total of 1,903,880 shares were sold for proceeds of $2.1 million (net of approximately $0.1 million in commissions) under the ATM Offering during the year ended December 31, 2019. At December 31, 2020, approximately $7.1 million remained eligible to be drawn down under the ATM Offering. A total of 3,096,003 shares were sold under the ATM Offering subsequent to December 31, 2020 for proceeds of $4.4 million (net of approximately $0.1 million in commissions). The ATM Offering is no longer available for use. Shares Reserved for Future Issuance The following shares of common stock were reserved for future issuance as of December 31, 2020 (in thousands): Class A-1 convertible preferred stock outstanding (as-converted) 2,567 Class A-2 convertible preferred stock outstanding (as-converted) 14,165 Class A-3 convertible preferred stock outstanding (as-converted) 2,587 2019 PIPE Initial Closing warrants 13,890 2019 PIPE Milestone Closing warrants 31,845 2020 PIPE warrants 20,303 Common stock options outstanding 6,813 RSUs outstanding 34 Common stock available for future grant under the 2019 Equity Incentive Plan 868 Employee Stock Purchase Plan 188 Total common shares reserved for future issuance 93,260 The following table summarizes our stock option activity under all equity incentive plans for the year ended December 31, 2020 (shares and aggregate intrinsic value in thousands): Number of Weighted Weighted average remaining contractual term Aggregate intrinsic value Options outstanding at December 31, 2019 3,098 $ 1.17 Granted 3,889 $ 1.19 Exercised (7) $ 0.70 Canceled/forfeited/expired (167) $ 4.63 Options outstanding at December 31, 2020 6,813 $ 1.10 8.57 $ 2,662 Exercisable at December 31, 2020 1,953 $ 1.33 7.51 $ 971 The weighted average grant date fair value per share of employee stock options granted during the years ended December 31, 2020 and 2019 was $0.91 and $0.52, respectively. The total intrinsic value of stock options exercised was less than $0.1 million for the years ended December 31, 2020 and 2019. Cash received from the exercise of stock options was less than $0.1 million for the years ended December 31, 2020 and 2019. The total compensation cost related to stock options not yet recognized was $1.8 million as of December 31, 2020. The weighted-average period over which this expense is expected to be recognized is approximately 2.1 years . The following table summarizes our RSU activity under all equity incentive plans for the year ended December 31, 2020 (shares and aggregate intrinsic value in thousands): Number of Weighted Weighted average remaining contractual term Aggregate intrinsic value RSUs outstanding at December 31, 2019 129 $ 1.50 Granted — $ — Vested (76) $ 1.50 Canceled/forfeited/expired (19) $ 1.50 RSUs outstanding at December 31, 2020 34 $ 1.50 0.25 $ 46 The total compensation cost related to non-vested RSUs not yet recognized was $0.1 million as of December 31, 2020. The weighted-average period over which this expense is expected to be recognized is approximately 0.3 years Stock-Based Compensation The following table su mmarizes the weighted average assumptions used to estimate the fair value of stock options and performance stock awards granted to employees under our 2012 Equity Incentive Plan, 2015 Inducement Plan, 2019 Equity Incentive Plan and the shares purchasable under our Employee Stock Purchase Plan during the periods presented: Year ended December 31, 2020 2019 Stock options Risk-free interest rate 1.1 % 1.7 % Volatility 95.4 % 94.6 % Dividend yield — — Expected term (years) 6.1 6.1 Performance stock options Risk-free interest rate 1.4 % 2.6 % Volatility 95.4 % 93.8 % Dividend yield — — Expected term (years) 6.1 6.1 Employee stock purchase plan shares Risk-free interest rate 0.6 % 2.3 % Volatility 98.0 % 110.5 % Dividend yield — — Expected term (years) 0.5 0.5 Risk-free interest rate - The risk-free interest rate assumption was based on observed interest rates appropriate for the expected term of the stock option grants. Expected dividend yield - The expected dividend yield assumption was based on the fact that we have never paid cash dividends and have no present intention to pay cash dividends. Expected volatility - The expected volatility assumption was based on the historical volatility of the trading price of our common stock. Expected term - The expected term represents the period of time that options are expected to be outstanding. Because we do not have sufficient historical exercise behavior data, we determine the expected life using the simplified method, which was an average of the contractual term of the option and its ordinary vesting period. Forfeitures - We account for forfeitures as they occur. The following table summarizes the allocation of our stock-based compensation expense for all stock awards during the periods presented (in thousands): Year ended December 31, 2020 2019 Research and development $ 693 $ 309 General and administrative 1,921 1,979 Total $ 2,614 $ 2,288 Employee Stock Purchase Plan

Defined Contribution Plan

Defined Contribution Plan	12 Months Ended
	Dec. 31, 2020
Retirement Benefits [Abstract]
Defined Contribution Plan	Defined Contribution Plan In 2009, we established an employee 401(k) salary deferral plan (“401(k) Plan”) covering all eligible employees. Active employees who are at least 18 years old and are not otherwise disqualified under the terms of the 401(k) Plan are eligible to participate. Employees may contribute up to 50% of their compensation per year (subject to a maximum limit prescribed by federal tax law). Under the 401(k) Plan, we may elect to match a discretionary percentage of employee contributions. We elected to match 50% of employees’ contributions up to 6% of the employees’ eligible salary for the per iods presented. We made matching contributions of $0.1 million for the years ended December 31, 2020 and 2019.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The following table summarizes the components of our income tax (benefit) expense (in thousands): Year ended December 31, 2020 2019 Current: Federal $ (13) $ (13) State 1 1 (12) (12) Deferred: Federal 12 13 State — — 12 13 Income tax expense $ — $ 1 The following is a reconciliation of the expected statutory federal income tax provision to our actual income tax provision (in thousands): Year ended December 31, 2020 2019 Expected income tax benefit at federal statutory tax rate $ (3,309) $ (3,904) State income taxes, net of federal benefit (927) (1,390) Tax credits (1,216) (374) Change in valuation allowance 2,606 603 Return to provision adjustments (14) (358) Stock compensation 1,644 3,934 Reserve for uncertain tax positions 1,179 1,444 Other 37 46 Income tax expense $ — $ 1 The following table summarizes the significant components of our deferred tax assets and liabilities (in thousands): December 31, 2020 2019 Deferred tax assets: Net operating loss carryovers $ 82,747 $ 79,675 Research and development and other tax credits 34,337 33,429 Deferred revenue — 1 Intangibles and property and equipment basis difference 715 782 Stock compensation expense 283 1,389 Lease liability 88 164 Other 281 461 Total deferred tax assets 118,451 115,901 Total deferred tax liabilities (282) (325) Net deferred tax asset 118,169 115,576 Valuation allowance (118,169) (115,564) Net deferred tax asset $ — $ 12 For all periods presented, we have determined that it is more likely than not that our deferred tax asset will not be realized, with the exception of the refundable AMT tax credit. Accordingly, we have recorded a valuation allowance to offset the net deferred tax asset of $118.2 million. As of December 31, 2020, we had NOL carryforwards for U.S. federal and California state tax purposes of $342.4 million and $289.2 million, respectively, portions of which begin to expire in 2030 and 2031, respectively. Our federal NOL carryforwards generated in tax years beginning after December 31, 2017, of $79.0 million will carry forward indefinitely. On March 27, 2020, the CARES Act was signed into law in response to the economic challenges facing US businesses. Under the CARES Act, the Internal Revenue Code was amended to allow for federal NOL carrybacks for five years to offset previous years income, or can be carried forward indefinitely to offset 100% of taxable income for the tax year 2020 and 80% of taxable income for tax years 2021 and thereafter. As of December 31, 2020, we also had federal and California research and development tax credit carryforwards of $32.1 million and $9.4 million, respectively. The federal research and development tax credit carryforwards will begin to expire in 2029. The California research and development tax credit carryforwards are available indefinitely. Pursuant to Sections 382 and 383, use of the Company’s net operating loss and credit carryforwards may be limited if a cumulative change in ownership of more than 50% (by value) occurs within a three-year period. The Company has not performed an analysis through December 31, 2020 to determine whether its net operating loss and research and development credit carryforwards are subject to annual limitation under Sections 382 or 383 of the Code, and these financial statements do not contain any adjustment relating to such potential limitations. However, if the Company experienced an ownership change that resulted in an annual limitation on the Company’s net operating loss carryforwards under Section 382 of the Code there would be no material impact to the Company’s financial statements. The following table summarizes the changes in the amount of our unrecognized tax benefits (in thousands): Year Ended December 31, 2020 2019 Beginning balance of unrecognized tax benefits $ 16,573 $ 14,700 Decrease for prior year tax positions (1) (7) Increase for current year tax positions 1,367 1,880 Total $ 17,939 $ 16,573 Included in unrecognized tax benefits of $17.9 million at December 31, 2020 was $14.5 million of tax benefits that, if recognized, would reduce our annual effective tax rate, subject to valuation allowance. We do not expect that there will be a significant change in the unrecognized tax benefits over the next 12 months. We are subject to taxation in the United States and state jurisdictions where applicable. Our tax years for 2010 and forward are subject to examination by the U.S. tax authorities and our tax years for 2011 and forward are subject to examination by the California tax authorities due to carryforward of unutilized net operating losses and research and development credits. It is our practice to recognize interest and/or penalties related to income tax matters in income tax expense. For the years ended December 31, 2020 and 2019, we have not recognized any interest or penalties related to income taxes.

Leases

Leases	12 Months Ended
	Dec. 31, 2020
Leases [Abstract]
Leases	Leases In July 2015, we entered into an operating lease agreement (the "Prior Lease") for approximately 59,248 square feet of office and laboratory facility space located at 10614 Science Center Drive, San Diego, California 92121. The lease term was 96 months from the lease commencement date, and we moved our headquarters into this facility in May 2016. In conjunction with the lease, we received $1.4 million of lease incentives and $8.2 million of tenant improvement allowance, which was to be used for non-structural leasehold improvements. The lease incentives and tenant improvement allowance were included within deferred rent. The Prior Lease agreement was with ARE SD Region No. 44 LLC (“Landlord”). On February 19, 2019, we entered into an agreement, the (“Space Swap Agreement"), with Nitto Biopharma, Inc. ("Nitto"), pursuant to which we agreed, contingent upon the execution of a new lease agreement (the "February Lease") for Nitto's space with Landlord and the termination of the Prior Lease, to, among other things, (i) swap buildings with Nitto, and (ii) sell, convey and transfer all right, title and interest in certain furniture, fixtures and equipment to Nitto, as set forth in the Space Swap Agreement. Under the Space Swap Agreement, we paid Nitto (a) a relocation assistance payment in the amount of $0.1 million; (b) $0.2 million representing the difference between the security deposits under the Prior Lease and Nitto’s prior lease, and (c) $1.3 million as reimbursement for the six monthly installments of base monthly rent due pursuant to the new lease between Nitto and Landlord, subject to certain adjustments, which reimbursements were to be paid as rent comes due for Nitto under its new lease. On February 25, 2019, we and Landlord entered into a second amendment (the “Prior Lease Amendment”) to the Prior Lease. Under the terms of the Prior Lease Amendment, the expiration date of the Prior Lease was accelerated from April 30, 2024 to March 31, 2019 and the Prior Lease terminated on April 1, 2019. The Prior Lease Amendment eliminated all further cash payments due under the Prior Lease, including aggregate base rent over its remaining term of approximately $14.4 million. On February 25, 2019, we entered into the February Lease with Landlord, for the lease of approximately 24,562 square feet of rentable area of the building located at 10628 Science Center Drive, San Diego, California, 92121 (the "Premises"), which Premises were previously occupied by Nitto. The commencement date of the February Lease was April 1, 2019 (the “Commencement Date”). The Premises served as our new principal executive offices and as a laboratory for research and development, manufacturing and other related uses. The term of the February Lease (“Initial Term”) was 51 months, ending June 30, 2023. The aggregate base rent due over the Initial Term was approximately $4.8 million. We were also responsible for the payment of additional rent to cover our share of the annual operating expenses, the annual tax expenses and the annual utilities costs related to the February Lease. The base rent payments due were: $0.6 million in 2019, $1.2 million in 2020, $1.2 million in 2021, $1.2 million in 2022, and $0.6 million in 2023. The execution of the February Lease and Prior Lease Amendment resulted in a modification which was not accounted for as a separate contract. Rather, we accounted for the two contracts with Landlord in combination as they were entered into at the same time and negotiated as a package to achieve the same commercial objective. The leasehold improvements under the Prior Lease were accounted for as non-cash consideration of $5.6 million paid by us upon termination of the Prior Lease to the Landlord. We accounted for a $1.3 million portion of the reduction in the lease liability for the Prior Lease as a non-cash gain in the statement of operations due to the reduction in lease term and leased space with Landlord and a $0.9 million portion of the reduction of the lease liability as a deferred credit that is amortized as a reduction to rent expense over the term of the Lease. The $1.6 million obligation to reimburse Nitto for six monthly installments of base rent of the Prior Lease and certain other costs were accounted for as cost of terminating the Prior Lease in the statement of operations. The net impact of the modification was a $0.4 million charge in the statement of operations. Our payment obligations to Nitto under the Space Swap Agreement were fully satisfied as of September 2019 and no assets or liabilities remained with respect to the Prior Lease as of December 31, 2019. The commencement date of the February Lease did not occur until April 1, 2019 and therefore, as of March 31, 2019, the lease liability for the February Lease was zero. On April 1, 2019, we recorded a $3.8 million lease liability for the February Lease, which was calculated as the present value of future lease payments to be made under the February Lease. A $2.9 million ROU asset was also recorded on April 1, 2019, which represents the difference between the lease liability and the $0.9 million deferred credit for the reduction of the lease liability under the Prior Lease. On June 19, 2019, we entered into a lease agreement (the “New Lease”) with Landlord for the lease of approximately 8,727 square feet of rentable area of the building located at 10628 Science Center Drive, Suite 225, San Diego, California 92121 (the “New Premises”). The commencement date of the New Lease was July 1, 2019 (the “New Commencement Date”). We are using the New Premises as our new principal executive offices and as a laboratory for research and development and other related uses. The term of the New Lease (the “New Initial Term”) is two years, six months, ending December 31, 2021. The base rent payments due for the New Premises were $0.1 million in 2019 and $0.4 million in 2020 and is $0.4 million in 2021, net of certain rent abatement terms. We will also be responsible for the payment of additional rent to cover our share of the annual operating expenses of the building, the annual tax expenses of the building and the annual utilities cost of the building. On June 19, 2019, we entered into a first amendment to the February Lease with Landlord (the “February Lease Amendment”). Under the terms of the February Lease Amendment, the expiration date of the February Lease was accelerated from June 30, 2023 to June 30, 2019 and the February Lease terminated upon the Commencement Date of the New Lease. The February Lease Amendment eliminated all further rents due under the February Lease, including aggregate base rent over its remaining term of approximately $4.8 million. The execution of the New Lease and February Lease Amendment resulted in a modification which was not accounted for as a separate contract. Rather, we accounted for the two contracts with Landlord in combination as they were entered into at the same time and negotiated as a package to achieve the same commercial objective. We accounted for a $0.5 million portion of the reduction in the lease liability for the February Lease as a non-cash gain in the statement of operations due to the reduction in lease term and leased space with Landlord and a $0.2 million portion of the reduction of the lease liability as a deferred credit that is amortized as a reduction to rent expense over the term of the New Lease. No other assets or liabilities remained with respect to the February Lease as of December 31, 2019. The commencement date of the New Lease did not occur until July 1, 2019 and therefore, as of June 30, 2019, the lease liability for the New Lease was zero. On July 1, 2019, we recorded a $0.8 million lease liability for the New Lease, which was calculated as the present value of future lease payments to be made under the New Lease. A $0.6 million ROU asset was also recorded on July 1, 2019, which represents the difference between the lease liability and the remaining $0.2 million deferred credit for the reduction of the lease liability under the February Lease. The table below summarizes our lease liabilities and corresponding ROU assets as of December 31, 2020 and 2019 (in thousands): Year Ended December 31, 2020 2019 Assets Operating $ 253 $ 464 Financing 288 466 Total ROU assets $ 541 $ 930 Liabilities Current: Operating $ 417 $ 361 Financing 56 277 Long-term: Operating — 417 Financing — 56 Total lease liabilities $ 473 $ 1,111 The table below summarizes our lease costs from our statement of operations and cash payments from our statement of cash flows during the years ended December 31, 2020 and 2019 (in thousands): Year Ended December 31, 2020 2019 Lease cost: Operating lease cost $ 278 $ 715 Finance lease cost: Amortization of right-of-use assets 178 182 Interest expense on lease liabilities 10 5 Total finance lease cost $ 188 $ 187 Cash payment information: Operating cash used for operating leases $ 429 $ 756 Operating cash used for finance leases 10 24 Financing cash used for finance leases 277 263 Total cash paid for amounts included in the measurement of lease liabilities $ 716 $ 1,043 The table below summarizes other non-cash information under our operating and financing lease obligations as of December 31, 2020 and 2019 (in thousands, except years and rates): Year Ended December 31, 2020 2019 Supplemental non-cash information: Operating lease liabilities arising from obtaining right-of-use assets $ — $ 778 Weighted-average remaining lease term (years) - operating leases 1.0 2.0 Weighted-average remaining lease term (years) - finance leases 0.2 1.2 Weighted-average discount rate - operating leases 10.9 % 10.9 % Weighted-average discount rate - finance leases 4.9 % 4.9 % Our future lease payments under operating and finance leases at December 31, 2020 are as follows (in thousands): Operating Leases Finance Leases 2021 $ 442 $ 56 Total lease payments 442 56 Less: amount representing interest (25) — Present value of obligations under leases 417 56 Less: current portion (417) (56) Long-term lease obligations $ — $ —
Leases	Leases In July 2015, we entered into an operating lease agreement (the "Prior Lease") for approximately 59,248 square feet of office and laboratory facility space located at 10614 Science Center Drive, San Diego, California 92121. The lease term was 96 months from the lease commencement date, and we moved our headquarters into this facility in May 2016. In conjunction with the lease, we received $1.4 million of lease incentives and $8.2 million of tenant improvement allowance, which was to be used for non-structural leasehold improvements. The lease incentives and tenant improvement allowance were included within deferred rent. The Prior Lease agreement was with ARE SD Region No. 44 LLC (“Landlord”). On February 19, 2019, we entered into an agreement, the (“Space Swap Agreement"), with Nitto Biopharma, Inc. ("Nitto"), pursuant to which we agreed, contingent upon the execution of a new lease agreement (the "February Lease") for Nitto's space with Landlord and the termination of the Prior Lease, to, among other things, (i) swap buildings with Nitto, and (ii) sell, convey and transfer all right, title and interest in certain furniture, fixtures and equipment to Nitto, as set forth in the Space Swap Agreement. Under the Space Swap Agreement, we paid Nitto (a) a relocation assistance payment in the amount of $0.1 million; (b) $0.2 million representing the difference between the security deposits under the Prior Lease and Nitto’s prior lease, and (c) $1.3 million as reimbursement for the six monthly installments of base monthly rent due pursuant to the new lease between Nitto and Landlord, subject to certain adjustments, which reimbursements were to be paid as rent comes due for Nitto under its new lease. On February 25, 2019, we and Landlord entered into a second amendment (the “Prior Lease Amendment”) to the Prior Lease. Under the terms of the Prior Lease Amendment, the expiration date of the Prior Lease was accelerated from April 30, 2024 to March 31, 2019 and the Prior Lease terminated on April 1, 2019. The Prior Lease Amendment eliminated all further cash payments due under the Prior Lease, including aggregate base rent over its remaining term of approximately $14.4 million. On February 25, 2019, we entered into the February Lease with Landlord, for the lease of approximately 24,562 square feet of rentable area of the building located at 10628 Science Center Drive, San Diego, California, 92121 (the "Premises"), which Premises were previously occupied by Nitto. The commencement date of the February Lease was April 1, 2019 (the “Commencement Date”). The Premises served as our new principal executive offices and as a laboratory for research and development, manufacturing and other related uses. The term of the February Lease (“Initial Term”) was 51 months, ending June 30, 2023. The aggregate base rent due over the Initial Term was approximately $4.8 million. We were also responsible for the payment of additional rent to cover our share of the annual operating expenses, the annual tax expenses and the annual utilities costs related to the February Lease. The base rent payments due were: $0.6 million in 2019, $1.2 million in 2020, $1.2 million in 2021, $1.2 million in 2022, and $0.6 million in 2023. The execution of the February Lease and Prior Lease Amendment resulted in a modification which was not accounted for as a separate contract. Rather, we accounted for the two contracts with Landlord in combination as they were entered into at the same time and negotiated as a package to achieve the same commercial objective. The leasehold improvements under the Prior Lease were accounted for as non-cash consideration of $5.6 million paid by us upon termination of the Prior Lease to the Landlord. We accounted for a $1.3 million portion of the reduction in the lease liability for the Prior Lease as a non-cash gain in the statement of operations due to the reduction in lease term and leased space with Landlord and a $0.9 million portion of the reduction of the lease liability as a deferred credit that is amortized as a reduction to rent expense over the term of the Lease. The $1.6 million obligation to reimburse Nitto for six monthly installments of base rent of the Prior Lease and certain other costs were accounted for as cost of terminating the Prior Lease in the statement of operations. The net impact of the modification was a $0.4 million charge in the statement of operations. Our payment obligations to Nitto under the Space Swap Agreement were fully satisfied as of September 2019 and no assets or liabilities remained with respect to the Prior Lease as of December 31, 2019. The commencement date of the February Lease did not occur until April 1, 2019 and therefore, as of March 31, 2019, the lease liability for the February Lease was zero. On April 1, 2019, we recorded a $3.8 million lease liability for the February Lease, which was calculated as the present value of future lease payments to be made under the February Lease. A $2.9 million ROU asset was also recorded on April 1, 2019, which represents the difference between the lease liability and the $0.9 million deferred credit for the reduction of the lease liability under the Prior Lease. On June 19, 2019, we entered into a lease agreement (the “New Lease”) with Landlord for the lease of approximately 8,727 square feet of rentable area of the building located at 10628 Science Center Drive, Suite 225, San Diego, California 92121 (the “New Premises”). The commencement date of the New Lease was July 1, 2019 (the “New Commencement Date”). We are using the New Premises as our new principal executive offices and as a laboratory for research and development and other related uses. The term of the New Lease (the “New Initial Term”) is two years, six months, ending December 31, 2021. The base rent payments due for the New Premises were $0.1 million in 2019 and $0.4 million in 2020 and is $0.4 million in 2021, net of certain rent abatement terms. We will also be responsible for the payment of additional rent to cover our share of the annual operating expenses of the building, the annual tax expenses of the building and the annual utilities cost of the building. On June 19, 2019, we entered into a first amendment to the February Lease with Landlord (the “February Lease Amendment”). Under the terms of the February Lease Amendment, the expiration date of the February Lease was accelerated from June 30, 2023 to June 30, 2019 and the February Lease terminated upon the Commencement Date of the New Lease. The February Lease Amendment eliminated all further rents due under the February Lease, including aggregate base rent over its remaining term of approximately $4.8 million. The execution of the New Lease and February Lease Amendment resulted in a modification which was not accounted for as a separate contract. Rather, we accounted for the two contracts with Landlord in combination as they were entered into at the same time and negotiated as a package to achieve the same commercial objective. We accounted for a $0.5 million portion of the reduction in the lease liability for the February Lease as a non-cash gain in the statement of operations due to the reduction in lease term and leased space with Landlord and a $0.2 million portion of the reduction of the lease liability as a deferred credit that is amortized as a reduction to rent expense over the term of the New Lease. No other assets or liabilities remained with respect to the February Lease as of December 31, 2019. The commencement date of the New Lease did not occur until July 1, 2019 and therefore, as of June 30, 2019, the lease liability for the New Lease was zero. On July 1, 2019, we recorded a $0.8 million lease liability for the New Lease, which was calculated as the present value of future lease payments to be made under the New Lease. A $0.6 million ROU asset was also recorded on July 1, 2019, which represents the difference between the lease liability and the remaining $0.2 million deferred credit for the reduction of the lease liability under the February Lease. The table below summarizes our lease liabilities and corresponding ROU assets as of December 31, 2020 and 2019 (in thousands): Year Ended December 31, 2020 2019 Assets Operating $ 253 $ 464 Financing 288 466 Total ROU assets $ 541 $ 930 Liabilities Current: Operating $ 417 $ 361 Financing 56 277 Long-term: Operating — 417 Financing — 56 Total lease liabilities $ 473 $ 1,111 The table below summarizes our lease costs from our statement of operations and cash payments from our statement of cash flows during the years ended December 31, 2020 and 2019 (in thousands): Year Ended December 31, 2020 2019 Lease cost: Operating lease cost $ 278 $ 715 Finance lease cost: Amortization of right-of-use assets 178 182 Interest expense on lease liabilities 10 5 Total finance lease cost $ 188 $ 187 Cash payment information: Operating cash used for operating leases $ 429 $ 756 Operating cash used for finance leases 10 24 Financing cash used for finance leases 277 263 Total cash paid for amounts included in the measurement of lease liabilities $ 716 $ 1,043 The table below summarizes other non-cash information under our operating and financing lease obligations as of December 31, 2020 and 2019 (in thousands, except years and rates): Year Ended December 31, 2020 2019 Supplemental non-cash information: Operating lease liabilities arising from obtaining right-of-use assets $ — $ 778 Weighted-average remaining lease term (years) - operating leases 1.0 2.0 Weighted-average remaining lease term (years) - finance leases 0.2 1.2 Weighted-average discount rate - operating leases 10.9 % 10.9 % Weighted-average discount rate - finance leases 4.9 % 4.9 % Our future lease payments under operating and finance leases at December 31, 2020 are as follows (in thousands): Operating Leases Finance Leases 2021 $ 442 $ 56 Total lease payments 442 56 Less: amount representing interest (25) — Present value of obligations under leases 417 56 Less: current portion (417) (56) Long-term lease obligations $ — $ —

Selected Quarterly Financial Da

Selected Quarterly Financial Data (Unaudited)	12 Months Ended
	Dec. 31, 2020
Quarterly Financial Information Disclosure [Abstract]
Selected Quarterly Financial Data (Unaudited)	Selected Quarterly Financial Data (Unaudited) The following financial information reflects all normal recurring adjustments, which are, in the opinion of management, necessary for a fair statement of the results of the interim periods. Summarized quarterly data for 2020 and 2019 are as follows (in thousands, except per share data): For the quarters ending March 31 June 30 September 30 December 31 2020 Total revenues $ 6 $ — $ 5,000 $ 5,000 Total operating expenses (5,541) (6,496) (6,095) (6,028) Net loss (5,937) (6,947) (1,524) (1,322) Net loss per share, basic and diluted (1) $ (0.25) $ (0.23) $ (0.04) $ (0.03) 2019 Total revenues $ 6,778 $ 18 $ 18 $ 18 Total operating expenses (9,516) (4,686) (5,011) (4,453) Net loss (3,260) (5,016) (5,423) (4,893) Net loss per share, basic and diluted (1) $ (0.31) $ (0.30) $ (0.26) $ (0.23) (1) Net loss per share is computed independently for each of the quarters presented. Therefore, the sum of the quarterly per-share calculations will not necessarily equal the annual per share calculation.

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2020
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events Corporate Headquarters Lease Agreement On February 11, 2021, we entered into a lease agreement (the "Campus Point Lease") with ARE-SD Region No. 58 LLC ("Campus Point Landlord"), for the lease of approximately 13,438 square feet of rentable area located at 4224 Campus Point Court, Suite 210, San Diego, California, 92121 (the "Campus Point Premises"). The commencement date of the Campus Point Lease is targeted at nine weeks subsequent to the mutual execution and delivery of the Campus Point Lease by both the Company and the Campus Point Landlord, or April 15, 2021. We expect to use the Campus Point Premises as our new principal executive offices and as a laboratory for research and development, manufacturing and other related uses. The term of the Campus Point Lease (“Campus Point Initial Term”) is 60 months, ending April 30, 2026 (assuming an April 15, 2021 commencement date). The aggregate base rent due over the initial term of the Campus Point Lease is approximately $3.8 million. We will also be responsible for the payment of additional amounts to cover our share of the annual operating expenses of the building, the annual tax expenses of the building and the utilities costs for the building.

The Business, Basis of Presen_2

The Business, Basis of Presentation and Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Use of Estimates	Use of EstimatesOur financial statements are prepared in accordance with GAAP, which requires us to make estimates and assumptions that affect the reported amounts of assets, liabilities, revenues and expenses and the disclosure of contingent assets and liabilities in our financial statements and accompanying notes. An estimated loss contingency is accrued in our financial statements if it is probable that a liability has been incurred and the amount of the loss can be reasonably estimated. Although these estimates are based on our knowledge of current events and actions we may undertake in the future, actual results may ultimately differ from these estimates and assumptions. Though the impact of the COVID-19 pandemic to our business and operating results presents additional uncertainty, we continue to use the best information available to inform our critical accounting estimates.
Revenue Recognition	Revenue Recognition Our revenues generally consist of upfront payments for licenses or options to obtain licenses in the future, milestone payments and payments for other research services under license and collaboration agreements. We recognize revenue when we transfer promised goods or services to customers in an amount that reflects the consideration to which we expect to be entitled in exchange for those goods or services. To determine revenue recognition for contracts with customers we perform the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligation(s) in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligation(s) in the contract; and (v) recognize revenue when (or as) we satisfy the performance obligation(s). At contract inception, we assess the goods or services promised within each contract, assess whether each promised good or service is distinct and identify those that are performance obligations. We recognize as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied. Collaborative Arrangements We enter into collaborative arrangements with partners that typically include payment to us of one of more of the following: (i) license fees; (ii) payments related to the achievement of developmental, regulatory, or commercial milestones; and (iii) royalties on net sales of licensed products. Where a portion of non-refundable up-front fees or other payments received are allocated to continuing performance obligations under the terms of a collaborative arrangement, they are recorded as contract liabilities and recognized as revenue when (or as) the underlying performance obligation is satisfied. As part of the accounting for these arrangements, we must develop estimates and assumptions that require judgment to determine the underlying stand-alone selling price for each performance obligation which determines how the transaction price is allocated among the performance obligation(s). The stand-alone selling price may include items such as forecasted revenues, development timelines, discount rates, and probabilities of technical and regulatory success. We evaluate each performance obligation to determine if it can be satisfied at a point in time, or over time. In addition, variable consideration must be evaluated to determine if it is constrained and, therefore, excluded from the transaction price. License Fees If a license to our intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, we recognize revenues from non-refundable, up-front fees allocated to the license when the license is transferred to the licensee and the licensee is able to use and benefit from the license. For licenses that are bundled with other performance obligations, we use judgment to assess the nature of the combined performance obligation to determine whether it is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue. We evaluate the measure of progress each reporting period and, if necessary, adjust the measure of performance and related revenue recognition. Milestone Payments At the inception of each arrangement that includes milestone payments (variable consideration), we evaluate whether the milestones are considered probable of being reached and estimate the amount to be included in the transaction price. If it is probable that a milestone event would occur at the inception of an arrangement, the associated milestone value is included in the transaction price. Milestone payments that are contingent upon the achievement of events that are uncertain or not controllable, such as regulatory approvals, are generally not considered probable of being achieved until those approvals are received, and therefore not included in the transaction price. The transaction price is then allocated to each performance obligation on a relative stand-alone selling price basis, for which we recognize revenue as or when the performance obligations under the contract are satisfied. At the end of each reporting period, we evaluate the probability of achievement of such milestones and any related constraint(s), and if necessary, may adjust our estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which could affect license, collaboration or other revenues and earnings in the period of adjustment. Royalties For arrangements that include sales-based royalties, including milestone payments based on the level of sales, and for which the license is deemed to be the predominant item to which the royalties relate, we recognize revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). To date, we have not recognized any royalty revenue resulting from any of our collaborative arrangements.
Stock-Based Compensation	Stock-Based Compensation We account for stock-based compensation expense related to stock options granted to employees and members of our board of directors by estimating the fair value of each stock option on the date of grant using the Black-Scholes option pricing model. We recognize stock-based compensation expense using the accelerated multiple-option approach. Under the accelerated multiple-option approach (also known as the graded-vesting method), we recognize compensation expense over the requisite service period for each separately vesting tranche of the award as though the award was in substance multiple awards, resulting in accelerated expense recognition over the vesting period. For performance-based awards granted to employees (i) the fair value of the award is determined on the grant date, (ii) we assess the probability of the individual milestones under the award being achieved and (iii) the fair value of the shares subject to the milestone is expensed over the implicit service period commencing once management believes the performance criteria is probable of being met. We account for restricted stock units by determining the fair value of each restricted stock unit based on the closing market price of our common stock on the date of grant. We recognize stock-based compensation expense using the accelerated multiple-option approach over the requisite service periods of the awards.
Clinical Trial and Preclinical Study Accruals	Clinical Trial and Preclinical Study Accruals We make estimates of our accrued expenses for clinical trial and preclinical study activities as of each balance sheet date in our financial statements based on the facts and circumstances known to us at that time. These accruals are based upon estimates of costs incurred and fees that may be associated with services provided by clinical trial investigational sites and CROs and for other clinical trial-related activities. Payments under certain contracts with such parties depend on factors such as successful enrollment of patients, site initiation and the completion of clinical trial milestones. In accruing for these services, we estimate the time period over which services will be performed and the level of effort to be expended in each period. If possible, we obtain information regarding unbilled services directly from these service providers. However, we may be required to estimate these services based on other information available to us. If we underestimate or overestimate the activities or fees associated with a study or service at a given point in time, adjustments to research and development expenses may be necessary in future periods. Historically, our estimated accrued liabilities have approximated actual expense incurred. Subsequent changes in estimates may result in a material change in our accruals.
Prepaid Materials	Prepaid Materials We capitalize the purchase of certain raw materials and related supplies for use in the manufacturing of drug product in our preclinical and clinical development programs, as we have determined that these materials have alternative future use. We can use these raw materials and related supplies in multiple clinical drug products, and therefore have future use independent of the development status of any particular drug program until it is utilized in the manufacturing process. We expense the cost of materials when used. We periodically review these capitalized materials for continued alternative future use and write down the asset to its net realizable value in the period in which an impairment is identified.
Research and Development	Research and Development Research and development costs are expensed as incurred and consist of costs associated with research activities supporting our drug discovery efforts, compensation and related benefits, non-cash stock-based compensation, license fees, laboratory supplies and associated overhead and facility costs.
Income Taxes	Income Taxes Income taxes are accounted for under the asset and liability method. This approach requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of the differences between the tax basis of assets or liabilities and their carrying amounts in the financial statements using the enacted tax rates and laws that are anticipated to be in effect when the differences are expected to reverse. We provide a valuation allowance against net deferred tax assets if it is more likely than not that these items will either expire before we are able to realize their benefit or if future deductibility is uncertain.
Cash and Cash Equivalents	Cash and Cash Equivalents We classify time deposits and other investments that are highly liquid and have maturities of 90 days or less at the date of purchase as cash equivalents. The carrying amounts approximate fair value due to the short maturities of these instruments.
Concentration of Credit Risk	Concentrations of Credit Risk Financial instruments that potentially subject us to significant concentrations of credit risk consist primarily of cash equivalents. We maintain deposits in federally insured financial institutions in excess of federally insured limits. We have not experienced any material losses in such accounts and believe we are not exposed to significant risk. We maintain our cash equivalents with two highly accredited financial institutions. We have historically invested our excess cash primarily in certificates of deposit and debt instruments of financial institutions and corporations, United States Treasury securities and United States government-sponsored enterprise securities. Additionally, we adhere to established guidelines regarding approved investments and maturities of investments, which are designed to preserve their principal value and maintain liquidity.
Property and Equipment	Property and Equipment three
Intangibles	Intangibles We capitalize costs which consist principally of outside legal costs and filing fees related to obtaining patents. We review our capitalized patent costs periodically to determine that they include costs for patent applications that have future value and an alternative future use. We evaluate costs related to patents that w e are not actively pursuing and write off these costs. We amortize patent costs over their patent lives, beginning with the date the patents are issued.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets We regularly review the carrying amount of our property, equipment and intangible assets to determine whether indicators of impairment may exist which warrant adjustments to carrying values or estimated useful lives. If indications of impairment exist, projected future undiscounted cash flows associated with the asset are compared to the carrying amount to determine whether the asset’s value is recoverable. If the carrying value of the asset exceeds such projected undiscounted cash flows, the asset will be written down to its estimated fair value.
Segment Reporting	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. To date, we have viewed our operations and managed our business as one segment operating primarily within the United States.
Comprehensive Loss	Comprehensive Loss Comprehensive loss is defined as the change in equity during a period from transactions and other events and/or circumstances from non-owner sources. There were no transactions resulting in other comprehensive income or loss during the periods presented; as such, net loss equals other comprehensive loss for all periods presented.
Recent Accounting Pronouncements	At the inception of a contractual arrangement, we determine whether the contract contains a lease by assessing whether there is an identified asset and whether the contract conveys the right to control the use of the identified asset in exchange for consideration over a period of time. For operating leases with an initial term greater than 12 months, we recognize operating lease ROU assets and operating lease liabilities based on the present value of lease payments over the lease term at the commencement date. Operating lease ROU assets are comprised of the lease liability plus any lease payments made and excludes lease incentives. Lease terms include options to renew or terminate the lease when we are reasonably certain that the renewal option will be exercised or when it is reasonably certain that the termination option will not be exercised. For our operating leases, we generally cannot determine the interest rate implicit in the lease, in which case we use our incremental borrowing rate as the discount rate for the lease. We estimate our incremental borrowing rate for our operating leases based on what we would normally pay to borrow on a collateralized basis over a similar term for an amount equal to the lease payments. Operating lease expense is recognized on a straight-line basis over the lease term. Leases with an initial lease term of 12 months or less are not recorded on the balance sheet. Instead, we recognize lease expense for these leases on a straight-line basis over the lease term. Our lease agreements do not contain any material variable lease payments, residual value guarantees or restrictive covenants. Certain leases require us to pay taxes, insurance, utilities, and maintenance costs for the building, which do not represent lease components. We elected to not separate lease and non-lease components. Operating lease ROU assets are recorded within our balance sheets as other assets and operating lease liabilities are recorded within our balance sheets as other current liabilities and other long-term liabilities. Finance lease ROU assets are recorded in property and equipment, net and current and non-current finance lease liabilities are recorded in other current liabilities and other long-term liabilities, respectively, in our balance sheets. Recent Accounting Pronouncements In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments . Subsequently, in November 2018, the FASB issued ASU 2018-19, Codification Improvements to Topic 326, Financial Instruments-Credit Losses . ASU 2016-13 requires entities to measure all expected credit losses for most financial assets held at the reporting date based on an expected loss model which includes historical experience, current conditions, and reasonable and supportable forecasts. ASU 2016-13 also requires enhanced disclosures to help financial statement users better understand significant estimates and judgments used in estimating credit losses. This ASU is effective for smaller reporting companies for fiscal years beginning after December 15, 2022, with early adoption permitted. We are assessing the impact this standard will have on our financial statements and disclosures In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement: Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement , which updates and modifies the disclosure requirements on fair value measurements in Topic 820, primarily in relation to Level 3 fair value measurements. This update is effective for annual periods beginning after December 15, 2019, and interim periods within those periods. The adoption of this guidance on January 1, 2020 did not have a material impact on our financial statements. In November 2018, the FASB issued ASU No. 2018-18, Collaborative Arrangements , which clarifies the interaction between Topic 808 , Collaborative Arrangements and Topic 606, including clarification around certain transactions between collaborative arrangement participants and adding unit-of-account guidance to Topic 808. This update is effective for annual periods beginning after December 15, 2019, and interim periods within those periods. The adoption of this guidance on January 1, 2020 did not have a material impact on our financial statements. In December 2019, the FASB issued ASU No. 2019-12, Income Taxes - Simplifying the Accounting for Income Taxes (“ASU 2019-12”). The guidance removes exceptions to the general principles in Income Taxes (Topic 740) for allocating tax expense between financial statement components, accounting basis differences stemming from an ownership change in foreign investments and interim period income tax accounting for year-to-date losses that exceed projected losses. The guidance becomes effective for annual reporting periods beginning after December 15, 2020 and interim periods within those fiscal years with early adoption permitted. The adoption of this guidance on January 1, 2020 had no impact on our financial statements. In March 2020, the FASB issued ASU No. 2020-04, Reference Rate Reform (Topic 848), which provides guidance around reference rate reform initiatives to identify alternative reference rates that are more observable or transaction-based and less susceptible to manipulation in response to concerns about structural risks of interbank offered rates and the risk of cessation of the London Interbank Offered Rate ("LIBOR"). The amendments in the ASU provide option expedients and exceptions for applying GAAP to contracts, hedging relationships and other transactions affected by reference rate reform and apply only if such contracts, hedging relationships and other transactions that reference LIBOR or another reference rate are expected to be discontinued because of reference rate reform. The guidance does not apply to contract modifications made, and hedging
Fair Value Measurements	Fair Value Measurements We have certain financial assets recorded at fair value which have been classified as Level 1, 2, or 3 within the fair value hierarchy as described in the accounting standards for fair value measurements. Accounting standards define fair value as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants as of the measurement date. Market participants are buyers and sellers in the principal market that are (i) independent, (ii) knowledgeable, (iii) able to transact, and (iv) willing to transact. The accounting standards provide an established hierarchy for inputs used in measuring fair value that maximizes the use of observable inputs and minimizes the use of unobservable inputs by requiring that the most observable inputs be used when available. Observable inputs are inputs that market participants would use in valuing the asset or liability and are developed based on market data obtained from independent sources. Unobservable inputs are inputs that reflect our assumptions about the factors that market participants would use in valuing the asset or liability. The accounting standards prioritize the inputs used in measuring the fair value into the following hierarchy: • Level 1 includes financial instruments for which quoted market prices for identical instruments are available in active markets. • Level 2 includes financial instruments for which there are inputs other than quoted prices included within Level 1 that are observable for the instrument such as quoted prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets with insufficient volume or infrequent transactions (less active markets) or model-driven valuations in which significant inputs are observable or can be derived principally from, or corroborated by, observable market data. • Level 3 includes financial instruments for which fair value is derived from valuation techniques in which one or more significant inputs are unobservable, including management’s own assumptions.

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Fair Value Hierarchy for Assets	The following table presents our fair value hierarchy for assets measured at fair value on a recurring basis as of December 31, 2020 and 2019 (in thousands): Fair value as of December 31, 2020 Total Level 1 Level 2 Level 3 Assets: Cash equivalents (money market funds) $ 26,901 $ 26,901 $ — $ — $ 26,901 $ 26,901 $ — $ — Fair value as of December 31, 2019 Total Level 1 Level 2 Level 3 Assets: Cash equivalents (money market funds) $ 8,909 $ 8,909 $ — $ — $ 8,909 $ 8,909 $ — $ —

Property and Equipment, net (Ta

Property and Equipment, net (Tables)	12 Months Ended
	Dec. 31, 2020
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment	The following table summarizes our major classes of property and equipment (in thousands): December 31, 2020 2019 Laboratory equipment $ 4,967 $ 4,967 Computer equipment and software 281 281 Furniture and fixtures — — Leasehold improvements 83 83 5,331 5,331 Less accumulated depreciation and amortization (4,859) (4,410) Property and equipment, net $ 472 $ 921

Intangible Assets, net (Tables)

Intangible Assets, net (Tables)	12 Months Ended
	Dec. 31, 2020
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Finite-Lived Intangible Assets	The following table summarizes our major classes of intangible assets (in thousands): December 31, 2020 2019 Patents $ 219 $ 465 Accumulated amortization - Patents (94) (199) Intangibles, net $ 125 $ 266

Debt (Tables)

Debt (Tables)	12 Months Ended
	Dec. 31, 2020
Debt Disclosure [Abstract]
Schedule of Future Principal Payments	As of December 31, 2020, future principal payments for the Term Loan due under the Loan Agreement are as follows (in thousands): 2021 — 2022 4,681 $ 4,681

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2020
Equity [Abstract]
Activity of Shares Issued, Converted or Exercised	The following table summarizes preferred stock conversions and warrant exercises (and the related impact on common stock) under the 2019 SPA and 2020 SPA for the years ended December 31, 2020 and 2019 (in thousands): Class A-1 Convertible Preferred Stock Class A-2 Convertible Preferred Stock Class A-3 Convertible Preferred Stock Warrants Common Stock Balance at December 31, 2018 — — — — — Initial Closing 416 — — 13,890 9,731 Milestone Closing — 3,288 — 32,884 — Conversions/Exercises — — — — — Balance at December 31, 2019 416 3,288 — 46,774 9,731 2020 Closing — — 273 20,303 24,342 Conversions/Exercises (159) (1,872) (14) (1,039) 21,493 Balance at December 31, 2020 257 1,416 259 66,038 55,566
Common Stock Reserved for Future Issuance	The following shares of common stock were reserved for future issuance as of December 31, 2020 (in thousands): Class A-1 convertible preferred stock outstanding (as-converted) 2,567 Class A-2 convertible preferred stock outstanding (as-converted) 14,165 Class A-3 convertible preferred stock outstanding (as-converted) 2,587 2019 PIPE Initial Closing warrants 13,890 2019 PIPE Milestone Closing warrants 31,845 2020 PIPE warrants 20,303 Common stock options outstanding 6,813 RSUs outstanding 34 Common stock available for future grant under the 2019 Equity Incentive Plan 868 Employee Stock Purchase Plan 188 Total common shares reserved for future issuance 93,260
Stock Option Activity	The following table summarizes our stock option activity under all equity incentive plans for the year ended December 31, 2020 (shares and aggregate intrinsic value in thousands): Number of Weighted Weighted average remaining contractual term Aggregate intrinsic value Options outstanding at December 31, 2019 3,098 $ 1.17 Granted 3,889 $ 1.19 Exercised (7) $ 0.70 Canceled/forfeited/expired (167) $ 4.63 Options outstanding at December 31, 2020 6,813 $ 1.10 8.57 $ 2,662 Exercisable at December 31, 2020 1,953 $ 1.33 7.51 $ 971
Schedule of Restricted Stock Units Activity	The following table summarizes our RSU activity under all equity incentive plans for the year ended December 31, 2020 (shares and aggregate intrinsic value in thousands): Number of Weighted Weighted average remaining contractual term Aggregate intrinsic value RSUs outstanding at December 31, 2019 129 $ 1.50 Granted — $ — Vested (76) $ 1.50 Canceled/forfeited/expired (19) $ 1.50 RSUs outstanding at December 31, 2020 34 $ 1.50 0.25 $ 46
Assumptions Used to Estimate Fair Value of Stock Options and Performance Stock and Employee Stock Purchase Plan	The following table summarizes the weighted average assumptions used to estimate the fair value of stock options and performance stock awards granted to employees under our 2012 Equity Incentive Plan, 2015 Inducement Plan, 2019 Equity Incentive Plan and the shares purchasable under our Employee Stock Purchase Plan during the periods presented: Year ended December 31, 2020 2019 Stock options Risk-free interest rate 1.1 % 1.7 % Volatility 95.4 % 94.6 % Dividend yield — — Expected term (years) 6.1 6.1 Performance stock options Risk-free interest rate 1.4 % 2.6 % Volatility 95.4 % 93.8 % Dividend yield — — Expected term (years) 6.1 6.1 Employee stock purchase plan shares Risk-free interest rate 0.6 % 2.3 % Volatility 98.0 % 110.5 % Dividend yield — — Expected term (years) 0.5 0.5
Stock-Based Compensation	The following table summarizes the allocation of our stock-based compensation expense for all stock awards during the periods presented (in thousands): Year ended December 31, 2020 2019 Research and development $ 693 $ 309 General and administrative 1,921 1,979 Total $ 2,614 $ 2,288

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Schedule of Components of Income Tax Expense (Benefit)	The following table summarizes the components of our income tax (benefit) expense (in thousands): Year ended December 31, 2020 2019 Current: Federal $ (13) $ (13) State 1 1 (12) (12) Deferred: Federal 12 13 State — — 12 13 Income tax expense $ — $ 1
Schedule of Effective Income Tax Rate Reconciliation	The following is a reconciliation of the expected statutory federal income tax provision to our actual income tax provision (in thousands): Year ended December 31, 2020 2019 Expected income tax benefit at federal statutory tax rate $ (3,309) $ (3,904) State income taxes, net of federal benefit (927) (1,390) Tax credits (1,216) (374) Change in valuation allowance 2,606 603 Return to provision adjustments (14) (358) Stock compensation 1,644 3,934 Reserve for uncertain tax positions 1,179 1,444 Other 37 46 Income tax expense $ — $ 1
Schedule of Deferred Tax Assets and Liabilities	The following table summarizes the significant components of our deferred tax assets and liabilities (in thousands): December 31, 2020 2019 Deferred tax assets: Net operating loss carryovers $ 82,747 $ 79,675 Research and development and other tax credits 34,337 33,429 Deferred revenue — 1 Intangibles and property and equipment basis difference 715 782 Stock compensation expense 283 1,389 Lease liability 88 164 Other 281 461 Total deferred tax assets 118,451 115,901 Total deferred tax liabilities (282) (325) Net deferred tax asset 118,169 115,576 Valuation allowance (118,169) (115,564) Net deferred tax asset $ — $ 12
Summary of Income Tax Contingencies	The following table summarizes the changes in the amount of our unrecognized tax benefits (in thousands): Year Ended December 31, 2020 2019 Beginning balance of unrecognized tax benefits $ 16,573 $ 14,700 Decrease for prior year tax positions (1) (7) Increase for current year tax positions 1,367 1,880 Total $ 17,939 $ 16,573

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2020
Leases [Abstract]
Schedule of Lease Liabilities and ROU Assets	The table below summarizes our lease liabilities and corresponding ROU assets as of December 31, 2020 and 2019 (in thousands): Year Ended December 31, 2020 2019 Assets Operating $ 253 $ 464 Financing 288 466 Total ROU assets $ 541 $ 930 Liabilities Current: Operating $ 417 $ 361 Financing 56 277 Long-term: Operating — 417 Financing — 56 Total lease liabilities $ 473 $ 1,111
Schedule of Lease Cost	The table below summarizes our lease costs from our statement of operations and cash payments from our statement of cash flows during the years ended December 31, 2020 and 2019 (in thousands): Year Ended December 31, 2020 2019 Lease cost: Operating lease cost $ 278 $ 715 Finance lease cost: Amortization of right-of-use assets 178 182 Interest expense on lease liabilities 10 5 Total finance lease cost $ 188 $ 187 Cash payment information: Operating cash used for operating leases $ 429 $ 756 Operating cash used for finance leases 10 24 Financing cash used for finance leases 277 263 Total cash paid for amounts included in the measurement of lease liabilities $ 716 $ 1,043 The table below summarizes other non-cash information under our operating and financing lease obligations as of December 31, 2020 and 2019 (in thousands, except years and rates): Year Ended December 31, 2020 2019 Supplemental non-cash information: Operating lease liabilities arising from obtaining right-of-use assets $ — $ 778 Weighted-average remaining lease term (years) - operating leases 1.0 2.0 Weighted-average remaining lease term (years) - finance leases 0.2 1.2 Weighted-average discount rate - operating leases 10.9 % 10.9 % Weighted-average discount rate - finance leases 4.9 % 4.9 %
Schedule of Operating Lease, Liability, Maturity	Our future lease payments under operating and finance leases at December 31, 2020 are as follows (in thousands): Operating Leases Finance Leases 2021 $ 442 $ 56 Total lease payments 442 56 Less: amount representing interest (25) — Present value of obligations under leases 417 56 Less: current portion (417) (56) Long-term lease obligations $ — $ —
Schedule of Finance Lease, Liability, Maturity	Our future lease payments under operating and finance leases at December 31, 2020 are as follows (in thousands): Operating Leases Finance Leases 2021 $ 442 $ 56 Total lease payments 442 56 Less: amount representing interest (25) — Present value of obligations under leases 417 56 Less: current portion (417) (56) Long-term lease obligations $ — $ —

Selected Quarterly Financial _2

Selected Quarterly Financial Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2020
Quarterly Financial Information Disclosure [Abstract]
Schedule of Quarterly Financial Information	Summarized quarterly data for 2020 and 2019 are as follows (in thousands, except per share data): For the quarters ending March 31 June 30 September 30 December 31 2020 Total revenues $ 6 $ — $ 5,000 $ 5,000 Total operating expenses (5,541) (6,496) (6,095) (6,028) Net loss (5,937) (6,947) (1,524) (1,322) Net loss per share, basic and diluted (1) $ (0.25) $ (0.23) $ (0.04) $ (0.03) 2019 Total revenues $ 6,778 $ 18 $ 18 $ 18 Total operating expenses (9,516) (4,686) (5,011) (4,453) Net loss (3,260) (5,016) (5,423) (4,893) Net loss per share, basic and diluted (1) $ (0.31) $ (0.30) $ (0.26) $ (0.23) (1) Net loss per share is computed independently for each of the quarters presented. Therefore, the sum of the quarterly per-share calculations will not necessarily equal the annual per share calculation.

The Business, Basis of Presen_3

The Business, Basis of Presentation and Summary of Significant Accounting Policies - Liquidity (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Accounting Policies [Abstract]
Financing from sale proceeds, debt, and agreement revenues	$ 483,400
Cash and cash equivalents	$ 31,087	$ 34,121

The Business, Basis of Presen_4

The Business, Basis of Presentation and Summary of Significant Accounting Policies - Property and Equipment (Details)	12 Months Ended
	Dec. 31, 2020
Minimum
Property, Plant and Equipment [Line Items]
Useful life, in years	3 years
Maximum
Property, Plant and Equipment [Line Items]
Useful life, in years	5 years

The Business, Basis of Presen_5

The Business, Basis of Presentation and Summary of Significant Accounting Policies - Impairment of Long-Lived Assets (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Accounting Policies [Abstract]
Asset impairment charges	$ 0	$ 0

The Business, Basis of Presen_6

The Business, Basis of Presentation and Summary of Significant Accounting Policies - Segment Reporting (Details)	12 Months Ended
	Dec. 31, 2020segment
Accounting Policies [Abstract]
Number of operating segments	1

Net Loss Per Share - Potentiall

Net Loss Per Share - Potentially Dilutive Securities Not Included in Calculation of Diluted Net Loss per Share (Details) - shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Earnings Per Share [Abstract]
Potentially dilutive securities not included in calculation of diluted net loss per share (in shares)	23,741,466	6,569,337

Investments - Narrative (Detail

Investments - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Investments, Debt and Equity Securities [Abstract]
Unrealized gain (loss)	$ 0	$ 0

Fair Value Measurements - Fair

Fair Value Measurements - Fair Value Hierarchy for Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, fair value disclosure	$ 26,901	$ 8,909
Cash equivalents (money market funds)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, fair value disclosure	26,901	8,909
Fair Value, Inputs, Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, fair value disclosure	26,901	8,909
Fair Value, Inputs, Level 1 | Cash equivalents (money market funds)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, fair value disclosure	26,901	8,909
Fair Value, Inputs, Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, fair value disclosure	0	0
Fair Value, Inputs, Level 2 | Cash equivalents (money market funds)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, fair value disclosure	0	0
Fair Value, Inputs, Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, fair value disclosure	0	0
Fair Value, Inputs, Level 3 | Cash equivalents (money market funds)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, fair value disclosure	$ 0	$ 0

Collaborations (Details)

Collaborations (Details)

1 Months Ended

3 Months Ended

8 Months Ended

12 Months Ended

Oct. 31, 2020USD ($)

Sep. 30, 2020USD ($)

Aug. 31, 2020USD ($)

Mar. 31, 2019USD ($)

Nov. 30, 2018USD ($)

Feb. 28, 2014USD ($)$ / sharesshares

Jul. 31, 2013USD ($)

Jul. 31, 2012target

Dec. 31, 2020USD ($)shares

Sep. 30, 2020USD ($)

Jun. 30, 2020USD ($)

Mar. 31, 2020USD ($)

Dec. 31, 2019USD ($)shares

Sep. 30, 2019USD ($)

Jun. 30, 2019USD ($)

Mar. 31, 2019USD ($)

Jan. 31, 2014USD ($)

Dec. 31, 2020USD ($)shares

Dec. 31, 2019USD ($)shares

Nov. 30, 2020USD ($)

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Revenue

$ 5,000,000

$ 5,000,000

$ 0

$ 6,000

$ 18,000

$ 18,000

$ 18,000

$ 6,778,000

$ 10,006,000

$ 6,832,000

Common stock, shares issued (shares) | shares

67,432,712

21,018,663

67,432,712

21,018,663

Common stock value

$ 67,000

$ 21,000

$ 67,000

$ 21,000

Upfront payment received

$ 1,800,000

$ 2,500,000

Contract with customer, asset

$ 5,000,000

Development Milestones

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Expected revenue through milestone payments

$ 25,000,000

Materials Sold

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Expected revenue through milestone payments

4,000,000

Achievement of Enrollment Milestone

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Expected revenue through milestone payments

5,000,000

Strategic Alliances and Collaborations

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Revenue

10,000,000

6,800,000

Sanofi

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Number of collaborative areas granted | target

4

Initial upfront option payment

$ 4,000,000

$ 1,000,000

1,000,000

Milestone payments, earned

$ 6,800,000

Upfront payment received

$ 400,000

Expected revenue through milestone payments

$ 6,800,000

Agreement period

24 months

Enrollment milestone

$ 10,000,000

Development milestone not achievable

25,000,000

25,000,000

Sanofi | Private Placement

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Common stock, shares issued (shares) | shares

108,648

Price per share (in dollars per share) | $ / shares

$ 92.04

Common stock value

$ 10,000,000

Restriction period in which Alliances could not sell, transfer, make any short sale of, or grant any option for the sale of any common stock

12 months

Sanofi | Development Commercialization And License Agreement

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Initial upfront option payment

$ 2,500,000

$ 2,500,000

Deferred revenue creditable against future milestones

$ 1,250,000

$ 1,250,000

$ 1,250,000

Milestone payments, earned

$ 1,250,000

Sanofi | Minimum | United States

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Royalties based on percentage of net sales

1000.00%

Sanofi | Minimum | Outside of the US

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Royalties based on percentage of net sales

1000.00%

Sanofi | Maximum | United States

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Royalties based on percentage of net sales

20.00%

Sanofi | Maximum | Outside of the US

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Royalties based on percentage of net sales

20.00%

Sanofi | Development Milestones

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Expected revenue through milestone payments

$ 40,000,000

Sanofi | Proof-of-Concept Trial

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Expected revenue through milestone payments

38,800,000

$ 38,800,000

Sanofi | Clinical

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Expected revenue through milestone payments

25,000,000

25,000,000

Sanofi | Regulatory and Commercialization Milestones

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Expected revenue through milestone payments

$ 130,000,000

$ 130,000,000

Sanofi | Enrollment Milestone

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Expected revenue through milestone payments

$ 10,000,000

Property and Equipment, net (De

Property and Equipment, net (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 5,331	$ 5,331
Less accumulated depreciation and amortization	(4,859)	(4,410)
Property and equipment, net	472	921
Depreciation and amortization expense	467	931
Laboratory equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	4,967	4,967
Computer equipment and software
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	281	281
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	0	0
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 83	$ 83

Intangible Assets, net (Details

Intangible Assets, net (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Intangible asset amortization (2020, less than)	$ 100
Finite-lived intangible assets, amortization expense, next 12 months (less than $1 million)	100
Finite-lived intangible assets, amortization expense, year two (less than $1 million)	100
Finite-lived intangible assets, amortization expense, year three (less than $1 million)	100
Finite-lived intangible assets, amortization expense, year four (less than $1 million)	100
Finite-lived intangible assets, amortization expense, year five (less than $1 million)	$ 100
Remaining amortization period	13 years 10 months 24 days
Patents
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross	$ 219	$ 465
Accumulated amortization - Patents	(94)	(199)
Intangibles, net	$ 125	$ 266

Debt (Details)

Debt (Details)

Nov. 30, 2020USD ($)

Oct. 08, 2020USD ($)

Sep. 30, 2020USD ($)

Aug. 25, 2020

May 03, 2019USD ($)

Apr. 09, 2019USD ($)

Jun. 22, 2016USD ($)

Jun. 17, 2016number_of_payment

Mar. 31, 2019USD ($)

Nov. 30, 2018USD ($)

Dec. 31, 2020USD ($)

Sep. 30, 2020USD ($)

Jun. 30, 2020USD ($)

Mar. 31, 2020USD ($)

Dec. 31, 2019USD ($)

Sep. 30, 2019USD ($)

Jun. 30, 2019USD ($)

Mar. 31, 2019USD ($)

Dec. 31, 2020USD ($)

Dec. 31, 2019USD ($)

May 01, 2020USD ($)

Apr. 23, 2020USD ($)

May 07, 2019USD ($)

Nov. 05, 2018USD ($)

Debt Instrument [Line Items]

Upfront payment received

$ 1,800,000

$ 2,500,000

Forgiveness amount threshold for PPP loan

$ 500,000

Total revenues

$ 5,000,000

$ 5,000,000

$ 0

$ 6,000

$ 18,000

$ 18,000

$ 18,000

$ 6,778,000

$ 10,006,000

$ 6,832,000

Strategic Alliances and Collaborations

Debt Instrument [Line Items]

Total revenues

$ 10,000,000

$ 6,800,000

Strategic Alliances and Collaborations | Sanofi

Debt Instrument [Line Items]

Total revenues

$ 5,000,000

$ 4,000,000

$ 1,000,000

Term Loan

Debt Instrument [Line Items]

Proceeds from borrowing under term loan

$ 20,000,000

Stated interest rate, percentage

8.51%

Number of monthly payments | number_of_payment

24

Payment fee

5.50%

5.50%

Repayments of debt

$ 5,000,000

$ 4,000,000

$ 1,000,000

$ 10,000,000

Additional extension for interest only payments

7 months

Long-term debt

$ 4,681,000

$ 4,681,000

Deferred finance costs

$ 100,000

$ 100,000

Debt instrument effective rate

8.98%

8.98%

Term Loan | Other Current Liabilities

Debt Instrument [Line Items]

Fee amount

$ 1,300,000

$ 1,300,000

Term Loan | London Interbank Offered Rate (LIBOR)

Debt Instrument [Line Items]

Basis spread on variable rate, percentage

0.44%

Fourth Amendment

Debt Instrument [Line Items]

Written note for prepayment

10 days

Prepayment requirement of loan from license fees

25.00%

Expected revenue through milestone payments

$ 10,000,000

Prepayment requirement of loan from license fees, amount

$ 400,000

$ 600,000

Payment fee

5.50%

Seventh Amendment

Debt Instrument [Line Items]

Minimum cash, debt covenant

$ 10,000,000

Debt covenant cash amount, condition one

10,000,000

Debt covenant cash amount, condition two

5,000,000

Debt covenant cash amount, condition three

0

Eight Amendment

Debt Instrument [Line Items]

Minimum cash, debt covenant

$ 20,000,000

Interest only payment fee

$ 100,000

Maturity extension fee

$ 700,000

Eight Amendment - Milestone Payment

Debt Instrument [Line Items]

Minimum cash, debt covenant

$ 10,000,000

PPP Loan

Debt Instrument [Line Items]

Debt instrument, face amount

$ 700,000

Tenth Amendment

Debt Instrument [Line Items]

Interest only payment extension

7 months

Prepayment requirement

1000000000.00%

1000000000.00%

Minimum | Seventh Amendment

Debt Instrument [Line Items]

Prepayment requirement of loan from license fees

25.00%

Prepayment requirement of loan from license fees, amount

$ 5,000,000

Minimum | Eight Amendment

Debt Instrument [Line Items]

Prepayment requirement of loan from license fees

75.00%

Maximum | Seventh Amendment

Debt Instrument [Line Items]

Prepayment requirement of loan from license fees

75.00%

Maximum | Eight Amendment

Debt Instrument [Line Items]

Prepayment requirement of loan from license fees

100.00%

Debt - Future Principal Payment

Debt - Future Principal Payments (Details) - Term Loan $ in Thousands	Dec. 31, 2020USD ($)
Debt Instrument [Line Items]
2021	$ 0
2022	4,681
Long-term debt	$ 4,681

Debt - PPP Loan (Details)

Debt - PPP Loan (Details) - PPP Loan - USD ($) $ in Millions	Dec. 31, 2020	Apr. 23, 2020
Debt Instrument [Line Items]
Debt instrument, face amount		$ 0.7
Other Current Liabilities
Debt Instrument [Line Items]
Long-term debt, gross	$ 0.7

Stockholders' Equity - Common S

Stockholders' Equity - Common Stock and Private Placements (Details) $ / shares in Units, $ in Millions	Dec. 04, 2020USD ($)$ / sharesshares	Jan. 22, 2020shares	Dec. 24, 2019USD ($)$ / sharesshares	May 07, 2019USD ($)$ / sharesshares	May 03, 2019USD ($)shares	Dec. 12, 2018USD ($)shares	Dec. 31, 2020USD ($)voteshares	Dec. 31, 2019shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, shares issued (shares)							67,432,712	21,018,663
Common stock voting rights per share | vote							1
Common shares reserved for future issuance (in shares)							93,260,000
Private Placement
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares issued (in shares)	24,341,607				9,730,534
Number of securities called by warrants (in shares)	18,256,204			9,730,534
Sale of stock (usd per share) | $ / shares	$ 0.7464			$ 1.205
Consideration received on transaction | $	$ 19.4				$ 16.7
Convertible preferred stock, shares issued upon conversion (in shares)	10			10
Warrant exercise period					5 years
Warrant exercise price (usd per share) | $ / shares				$ 1.08
Milestone Closing
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Consideration received on transaction | $			$ 24.6
At The Moment
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares issued (in shares)						1,903,880	492,268
Consideration received on transaction | $						$ 2.1	$ 0.3
Class A-1 Convertible Preferred Stock | Private Placement
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of securities called by warrants (in shares)				4,158,980
Sale of stock (usd per share) | $ / shares				$ 10.80
Nonvoting convertible preferred stock issued (in shares)				415,898
Class A-1 Convertible Preferred Stock | Private Placement | Warrant
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Sale of stock (usd per share) | $ / shares				$ 0.125
Class A-2 Convertible Preferred Stock | Milestone Closing
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares issued (in shares)			3,288,390
Number of securities called by warrants (in shares)			32,883,900
Consideration received on transaction | $			$ 26
Convertible preferred stock, shares issued upon conversion (in shares)			10
Warrant exercise price (usd per share) | $ / shares			$ 0.666
Warrants, term			5 years
Class A-3 Convertible Preferred Stock | Private Placement
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of securities called by warrants (in shares)	2,047,276
Sale of stock (usd per share) | $ / shares	$ 6.22
Nonvoting convertible preferred stock issued (in shares)	272,970
Warrant exercise price (usd per share) | $ / shares	$ 0.622
Warrants, term	5 years
Class A-3 Convertible Preferred Stock | Private Placement | Warrant
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Sale of stock (usd per share) | $ / shares	$ 0.125
Directors, Executive Officers and Employees | Private Placement
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares issued (in shares)	833,208				526,083
Directors, Executive Officers and Employees | Class A-1 Convertible Preferred Stock | Private Placement
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of securities called by warrants (in shares)				526,083
Proceeds from issuance of preferred warrants | $				$ 0.6
Directors, Executive Officers and Employees | Class A-3 Convertible Preferred Stock | Private Placement
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of securities called by warrants (in shares)	624,906
Proceeds from issuance of preferred warrants | $	$ 0.6
Certain Directors and Executive Officers | Class A-2 Convertible Preferred Stock | Milestone Closing
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares issued (in shares)			121,581
Number of securities called by warrants (in shares)			1,215,810
Consideration received on transaction | $			$ 1
2019 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for future grant (in shares)							868,432
Common shares reserved for future issuance (in shares)							6,847,361
Additional shares available (in shares)		4,166,860
Yearly authorized increase		5.00%

Stockholders' Equity - Share Ac

Stockholders' Equity - Share Activity (Details) - shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Activity of Shares [Roll Forward]
Common stock, shares outstanding (in shares)	21,018,663
Common stock, shares outstanding (in shares)	67,432,712	21,018,663
Class A-1 Convertible Preferred Stock
Activity of Shares [Roll Forward]
Preferred stock, shares outstanding (in shares)	415,898
Preferred stock, shares outstanding (in shares)	256,700	415,898
Class A-1 Convertible Preferred Stock | 2019 Plan
Activity of Shares [Roll Forward]
Preferred stock, shares outstanding (in shares)	416,000	0
Conversions of convertible preferred stock (in shares)		0
Preferred stock, shares outstanding (in shares)		416,000
Class A-1 Convertible Preferred Stock | 2019 Plan | Initial Closing
Activity of Shares [Roll Forward]
Shares issued (in shares)		416,000
Class A-1 Convertible Preferred Stock | 2019 Plan | Milestone Closing
Activity of Shares [Roll Forward]
Shares issued (in shares)		0
Class A-1 Convertible Preferred Stock | 2020 Plan
Activity of Shares [Roll Forward]
Conversions of convertible preferred stock (in shares)	(159,000)
Preferred stock, shares outstanding (in shares)	257,000
Class A-1 Convertible Preferred Stock | 2020 Plan | 2020 Closing
Activity of Shares [Roll Forward]
Shares issued (in shares)	0
Class A-2 Convertible Preferred Stock
Activity of Shares [Roll Forward]
Preferred stock, shares outstanding (in shares)	3,288,390
Preferred stock, shares outstanding (in shares)	1,416,453	3,288,390
Class A-2 Convertible Preferred Stock | 2019 Plan
Activity of Shares [Roll Forward]
Preferred stock, shares outstanding (in shares)	3,288,000	0
Conversions of convertible preferred stock (in shares)		0
Preferred stock, shares outstanding (in shares)		3,288,000
Class A-2 Convertible Preferred Stock | 2019 Plan | Initial Closing
Activity of Shares [Roll Forward]
Shares issued (in shares)		0
Class A-2 Convertible Preferred Stock | 2019 Plan | Milestone Closing
Activity of Shares [Roll Forward]
Shares issued (in shares)		3,288,000
Class A-2 Convertible Preferred Stock | 2020 Plan
Activity of Shares [Roll Forward]
Conversions of convertible preferred stock (in shares)	(1,872,000)
Preferred stock, shares outstanding (in shares)	1,416,000
Class A-2 Convertible Preferred Stock | 2020 Plan | 2020 Closing
Activity of Shares [Roll Forward]
Shares issued (in shares)	0
Class A-3 Convertible Preferred Stock
Activity of Shares [Roll Forward]
Preferred stock, shares outstanding (in shares)	0
Preferred stock, shares outstanding (in shares)	258,707	0
Class A-3 Convertible Preferred Stock | 2019 Plan
Activity of Shares [Roll Forward]
Preferred stock, shares outstanding (in shares)	0	0
Conversions of convertible preferred stock (in shares)		0
Preferred stock, shares outstanding (in shares)		0
Class A-3 Convertible Preferred Stock | 2019 Plan | Initial Closing
Activity of Shares [Roll Forward]
Shares issued (in shares)		0
Class A-3 Convertible Preferred Stock | 2019 Plan | Milestone Closing
Activity of Shares [Roll Forward]
Shares issued (in shares)		0
Class A-3 Convertible Preferred Stock | 2020 Plan
Activity of Shares [Roll Forward]
Conversions of convertible preferred stock (in shares)	(14,000)
Preferred stock, shares outstanding (in shares)	259,000
Class A-3 Convertible Preferred Stock | 2020 Plan | 2020 Closing
Activity of Shares [Roll Forward]
Shares issued (in shares)	273,000
Warrant | 2019 Plan
Activity of Shares [Roll Forward]
Warrants outstanding (in shares)	46,774,000	0
Conversions of convertible preferred stock (in shares)		0
Warrants outstanding (in shares)		46,774,000
Warrant | 2019 Plan | Initial Closing
Activity of Shares [Roll Forward]
Warrants issued (in shares)		13,890,000
Warrant | 2019 Plan | Milestone Closing
Activity of Shares [Roll Forward]
Warrants issued (in shares)		32,884,000
Warrant | 2020 Plan
Activity of Shares [Roll Forward]
Conversions of convertible preferred stock (in shares)	(1,039,000)
Warrants outstanding (in shares)	66,038,000
Warrant | 2020 Plan | 2020 Closing
Activity of Shares [Roll Forward]
Warrants issued (in shares)	20,303,000
Common stock | 2019 Plan
Activity of Shares [Roll Forward]
Common stock, shares outstanding (in shares)	9,731,000	0
Common stock, shares outstanding (in shares)		9,731,000
Common stock | 2019 Plan | Initial Closing
Activity of Shares [Roll Forward]
Shares issued (in shares)		9,731,000
Common stock | 2019 Plan | Milestone Closing
Activity of Shares [Roll Forward]
Shares issued (in shares)		0
Common stock | 2020 Plan
Activity of Shares [Roll Forward]
Conversions of convertible preferred stock (in shares)	(21,493,000)	0
Common stock, shares outstanding (in shares)	55,566,000
Common stock | 2020 Plan | 2020 Closing
Activity of Shares [Roll Forward]
Shares issued (in shares)	24,342,000

Stockholders' Equity - ATM Offe

Stockholders' Equity - ATM Offerring (Details) - USD ($) $ in Thousands	Dec. 12, 2018	Mar. 08, 2021	Dec. 31, 2020	Dec. 31, 2019
Class of Stock [Line Items]
Amount eligible to be drawn down under the ATM			$ 7,100
Contract and other receivables			503	$ 1,141
Other current liabilities			$ 2,970	$ 3,047
At The Moment
Class of Stock [Line Items]
Commission fee rate	3.00%
Number of shares issued (in shares)	1,903,880		492,268
Consideration received on transaction	$ 2,100		$ 300
Payments for commissions	$ 100		$ 100
At The Moment | Subsequent Event
Class of Stock [Line Items]
Number of shares issued (in shares)		3,096,003
Consideration received on transaction		$ 4,400
Payments for commissions		$ 100
ATM Not Settled in 2020
Class of Stock [Line Items]
Number of shares issued (in shares)			309,485
Consideration received on transaction			$ 400
Payments for commissions			$ 100

Stockholders' Equity - Shares R

Stockholders' Equity - Shares Reserved for Future Issuance (Details) shares in Thousands	Dec. 31, 2020shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock options outstanding (in shares)	6,813
Total common shares reserved for future issuance (in shares)	93,260
Common stock available for future grant under the 2019 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for future grant (in shares)	868
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for future grant (in shares)	188
RSUs outstanding
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
RSUs outstanding (in shares)	34
Class A-1 convertible preferred stock outstanding (as-converted)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Preferred stock, shares outstanding (in shares)	2,567
Class A-2 convertible preferred stock outstanding (as-converted)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Preferred stock, shares outstanding (in shares)	14,165
Class A-3 convertible preferred stock outstanding (as-converted)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Preferred stock, shares outstanding (in shares)	2,587
2019 PIPE Initial Closing warrants
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Warrants outstanding (in shares)	13,890
2019 PIPE Milestone Closing warrants
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Warrants outstanding (in shares)	31,845
2020 PIPE warrants
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Warrants outstanding (in shares)	20,303

Stockholders' Equity - Stock Op

Stockholders' Equity - Stock Option Activity (Details) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020USD ($)$ / sharesshares
Number of options
End number of options (in shares), outstanding	6,813
Stock options
Number of options
Beginning number of options (in shares), outstanding	3,098
Number of options, Granted (in shares)	3,889
Number of options, Exercised (in shares)	(7)
Number of options, Canceled/forfeited/expired (in shares)	(167)
End number of options (in shares), outstanding	6,813
Number of options, Exercisable (in shares)	1,953
Weighted average exercise price
Beginning, Weighted average exercise price, Options outstanding (in dollars per share) | $ / shares	$ 1.17
Weighted average exercise price, Granted (in dollars per share) | $ / shares	1.19
Weighted average exercise price, Exercised (in dollars per share) | $ / shares	0.70
Weighted average exercise price, Canceled/forfeited/expired (in dollars per share) | $ / shares	4.63
Ending, Weighted average exercise price, Options outstanding (in dollars per share) | $ / shares	1.10
Weighted average exercise price, Exercisable (in dollars per share) | $ / shares	$ 1.33
Weighted average remaining contractual term
Weighted average remaining contractual term, Options outstanding	8 years 6 months 25 days
Weighted average remaining contractual term, Exercisable	7 years 6 months 3 days
Aggregate intrinsic value
Aggregate intrinsic value, Options outstanding | $	$ 2,662
Aggregate intrinsic value, Exercisable | $	$ 971

Stockholders' Equity - Share _2

Stockholders' Equity - Share Activity and Employee Stock Purchase Plan Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	12 Months Ended		87 Months Ended
	Oct. 31, 2012	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2019
Class of Stock [Line Items]
Proceeds from stock options exercised		$ 5	$ 3
Stock options
Class of Stock [Line Items]
Weighted average grant date fair value of employee stock options (in dollars per share)		$ 0.91	$ 0.52
Total intrinsic value of stock options exercised		$ 100	$ 100
Proceeds from stock options exercised		100	$ 100
Compensation cost related to non-vested awards not yet recognized		$ 1,800
Weighted-average recognition period of compensation cost related to non-vested awards not yet recognized		2 years 1 month 6 days
RSUs outstanding
Class of Stock [Line Items]
Compensation cost related to non-vested awards not yet recognized		$ 100
Weighted-average recognition period of compensation cost related to non-vested awards not yet recognized		3 months 18 days
Employee Stock Purchase Plan 2012
Class of Stock [Line Items]
Percentage of participants eligible compensation	15.00%
Shares issued (in shares)		4,998		96,946
Common stock shares reserved for future issuance and authorized for purchase (in shares)		187,689
Option One - at inception of enrollment period
Class of Stock [Line Items]
Percentage of fair market value of common stock	85.00%
Option Two - at applicable purchase date
Class of Stock [Line Items]
Percentage of fair market value of common stock	85.00%

Stockholders' Equity - RSU Acti

Stockholders' Equity - RSU Activity (Details) - RSUs outstanding - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding [Roll Forward]
RSUs outstanding, beginning balance (in shares)	129
Granted (in shares)	0
Vested (in shares)	(76)
Canceled/forfeited/expired (in shares)	(19)
RSUs outstanding, ending balance (in shares)	34
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
RSUs outstanding, beginning balance (usd per share)	$ 1.50
Granted (usd per share)	0
Vested (usd per share)	1.50
Forfeited (usd per share)	1.50
RSUs outstanding, ending balance (usd per share)	$ 1.50	$ 1.50
Weighted average remaining contractual term	3 months
Aggregate intrinsic value		$ 46

Stockholders' Equity - Assumpti

Stockholders' Equity - Assumptions Used to Estimate Fair Value of Stock Options and Performance Stock and Employee Stock Purchase Plan (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Stock options
Weighted average assumptions
Risk-free interest rate	1.10%	1.70%
Volatility	95.40%	94.60%
Dividend yield	0.00%	0.00%
Expected term (years)	6 years 1 month 6 days	6 years 1 month 6 days
Performance stock options
Weighted average assumptions
Risk-free interest rate	1.40%	2.60%
Volatility	95.40%	93.80%
Dividend yield	0.00%	0.00%
Expected term (years)	6 years 1 month 6 days	6 years 1 month 6 days
Employee Stock Purchase Plan
Weighted average assumptions
Risk-free interest rate	0.60%	2.30%
Volatility	98.00%	110.50%
Dividend yield	0.00%	0.00%
Expected term (years)	6 months	6 months

Stockholders' Equity - Schedule

Stockholders' Equity - Schedule of Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expenses	$ 2,614	$ 2,288
Research and development
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expenses	693	309
General and administrative
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expenses	$ 1,921	$ 1,979

Defined Contribution Plan (Deta

Defined Contribution Plan (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Retirement Benefits [Abstract]
Defined contribution minimum age requirement of eligible employees	18 years
Maximum 401 (K) plan contribution rates as percentage of employees compensation	50.00%
Rate of contribution to 401(K) plan as a percentage of employees contribution	50.00%
Percentage of employee's earnings the company may contribute to the 401(k) plan	6.00%
Employer contribution to 401(k) plan	$ 0.1	$ 0.1

Income Taxes - Components of In

Income Taxes - Components of Income Tax (Benefit) Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Current:
Federal	$ (13)	$ (13)
State	1	1
Current income tax expense (benefit), total	(12)	(12)
Deferred:
Federal	12	13
State	0	0
Deferred income tax expense (benefit), total	12	13
Income tax expense	$ 0	$ 1

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Expected Statutory Federal Income Tax Provision to Actual Income Tax Provision (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Expected income tax benefit at federal statutory tax rate	$ (3,309)	$ (3,904)
State income taxes, net of federal benefit	(927)	(1,390)
Tax credits	(1,216)	(374)
Change in valuation allowance	2,606	603
Return to provision adjustments	(14)	(358)
Stock compensation	1,644	3,934
Reserve for uncertain tax positions	1,179	1,444
Other	37	46
Income tax expense	$ 0	$ 1

Income Taxes - Components of De

Income Taxes - Components of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred tax assets:
Net operating loss carryovers	$ 82,747	$ 79,675
Research and development and other tax credits	34,337	33,429
Deferred revenue	0	1
Intangibles and property and equipment basis difference	715	782
Stock compensation expense	283	1,389
Lease liability	88	164
Other	281	461
Total deferred tax assets	118,451	115,901
Total deferred tax liabilities	(282)	(325)
Net deferred tax asset	118,169	115,576
Valuation allowance	(118,169)	(115,564)
Net deferred tax asset	$ 0	$ 12

Income Taxes - Narrative (Detai

Income Taxes - Narrative (Details) - USD ($)	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating Loss Carryforwards [Line Items]
Valuation allowance	$ 118,169,000	$ 115,564,000
Net operating loss carryovers	82,747,000	79,675,000
Unrecognized tax benefits	17,939,000	16,573,000	$ 14,700,000
Unrecognized tax benefits that would impact effective tax rate	14,500,000
Income tax penalties and interest accrued	0	$ 0
Internal Revenue Service (IRS)
Operating Loss Carryforwards [Line Items]
Net operating loss carryovers	342,400,000
Internal Revenue Service (IRS) | Research Tax Credit Carryforward
Operating Loss Carryforwards [Line Items]
Research and development tax credits carryforward	32,100,000
California
Operating Loss Carryforwards [Line Items]
Net operating loss carryovers	289,200,000
California | Research Tax Credit Carryforward
Operating Loss Carryforwards [Line Items]
Research and development tax credits carryforward	9,400,000
After 2017, No Expiration | Internal Revenue Service (IRS)
Operating Loss Carryforwards [Line Items]
Net operating loss carryovers	$ 79,000,000

Income Taxes - Changes in Amoun

Income Taxes - Changes in Amount of Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Beginning balance of unrecognized tax benefits	$ 16,573	$ 14,700
Decrease for prior year tax positions	(1)	(7)
Increase for current year tax positions	1,367	1,880
Total	$ 17,939	$ 16,573

Leases (Details)

Leases (Details)	Feb. 19, 2019USD ($)	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Jul. 01, 2019USD ($)	Jun. 19, 2019USD ($)ft²	Apr. 01, 2019USD ($)	Feb. 25, 2019USD ($)ft²	Dec. 31, 2017USD ($)	Aug. 31, 2015USD ($)	Jul. 31, 2015ft²
Lessee, Lease, Description [Line Items]
Net rentable area | ft²										59,248
Term of lease										96 months
Tenant incentive									$ 1,400,000
Tenant improvement allowance used								$ 8,200,000
Lease expense extinguished from prior lease							$ 14,400,000
Total lease payments		$ 442,000
Lessee, operating lease, liability, payments		442,000
Noncash leasehold improvements		5,600,000
Deferred costs accumulated amortization		900,000
Termination of lease		(1,600,000)
Operating lease, right-of-use asset		253,000	$ 464,000
Reduction of lease liability		1,300,000
Operating lease, liability		417,000
February Lease
Lessee, Lease, Description [Line Items]
Net rentable area | ft²							24,562
Term of lease							51 months
Total lease payments							$ 4,800,000
Lessee, operating lease, liability, payments		600,000
Operating lease, liability, payments, due year two		1,200,000
Operating lease, liability, payments, due year three		1,200,000
Operating lease, liability, payments, due year four		1,200,000
Operating lease, liability, payments, due year five		600,000
New Premises
Lessee, Lease, Description [Line Items]
Net rentable area | ft²					8,727
Term of lease					2 years 6 months
Lessee, operating lease, liability, payments		100,000
Operating lease, liability, payments, due year two		400,000
Operating lease, liability, payments, due year three		400,000
Deferred costs accumulated amortization		200,000
Initial direct cost liability				$ 800,000
Operating lease, right-of-use asset				600,000
Deferred credit, operating lease liability				$ 200,000
Lease payments eliminated					$ 4,800,000
Reduction of lease liability		500,000
Operating lease, liability		0
Nitto
Lessee, Lease, Description [Line Items]
Relocation assistance payment	$ 100,000
Difference between the security deposits under the Prior Lease and Nitto’s prior lease	200,000
Rent reimbursement	$ 1,300,000
Lease modification impact		$ 400,000
Initial direct cost liability						$ 3,800,000
Operating lease, right-of-use asset						2,900,000
Deferred credit, operating lease liability						$ 900,000

Leases (Lease Asset and Liabili

Leases (Lease Asset and Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Assets
Operating	$ 253	$ 464
Financing	288	466
Total ROU assets	541	930
Current:
Operating	417	361
Financing	56	277
Long-term:
Operating	0	417
Financing	0	56
Total lease liabilities	$ 473	$ 1,111
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:OtherLiabilitiesCurrent	us-gaap:OtherLiabilitiesCurrent
Finance Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:OtherLiabilitiesCurrent	us-gaap:OtherLiabilitiesCurrent
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	us-gaap:OtherAssetsNoncurrent	us-gaap:OtherAssetsNoncurrent
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	us-gaap:PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization	us-gaap:PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	us-gaap:OtherLiabilitiesNoncurrent	us-gaap:OtherLiabilitiesNoncurrent
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	us-gaap:OtherLiabilitiesNoncurrent	us-gaap:OtherLiabilitiesNoncurrent

Leases (Lease Cost) (Details)

Leases (Lease Cost) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Leases [Abstract]
Operating lease cost	$ 278	$ 715
Finance lease cost:
Amortization of right-of-use assets	178	182
Interest expense on lease liabilities	10	5
Total finance lease cost	188	187
Cash payment information:
Cash payment information:	429	756
Operating cash used for finance leases	10	24
Financing cash used for finance leases	277	263
Total cash paid for amounts included in the measurement of lease liabilities	716	1,043
Operating lease liabilities arising from obtaining right-of-use assets	$ 0	$ 778
Weighted-average remaining lease term (years) - operating leases	1 year	2 years
Weighted-average remaining lease term (years) - finance leases	2 months 12 days	1 year 2 months 12 days
Weighted-average discount rate - operating leases	10.90%	10.90%
Weighted-average discount rate - finance leases	4.90%	4.90%

Leases (Future Lease Payments U

Leases (Future Lease Payments Under Operating and Finance Leases) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Operating Leases
2021	$ 442
Total lease payments	442
Less: amount representing interest	(25)
Present value of obligations under leases	417
Less: current portion	(417)	$ (361)
Long-term lease obligations	0	417
Finance Leases
2021	56
Total lease payments	56
Less: amount representing interest	0
Present value of obligations under leases	56
Less: current portion	(56)	(277)
Long-term lease obligations	$ 0	$ 56

Selected Quarterly Financial _3

Selected Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019
Quarterly Financial Information Disclosure [Abstract]
Total revenues	$ 5,000	$ 5,000	$ 0	$ 6	$ 18	$ 18	$ 18	$ 6,778	$ 10,006	$ 6,832
Total operating expenses	(6,028)	(6,095)	(6,496)	(5,541)	(4,453)	(5,011)	(4,686)	(9,516)	(24,161)	(23,666)
Net loss	$ (1,322)	$ (1,524)	$ (6,947)	$ (5,937)	$ (4,893)	$ (5,423)	$ (5,016)	$ (3,260)	$ (15,730)	$ (18,592)
Basic and diluted net loss per share (dollars per share)	$ (0.03)	$ (0.04)	$ (0.23)	$ (0.25)	$ (0.23)	$ (0.26)	$ (0.30)	$ (0.31)	$ (0.45)	$ (1.08)

Subsequent Events (Details)

Subsequent Events (Details) $ in Thousands	Feb. 11, 2021USD ($)ft²	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Apr. 15, 2026USD ($)	Jul. 31, 2015
Subsequent Event [Line Items]
Term of lease					96 months
Operating lease cost		$ 278	$ 715
Subsequent Event
Subsequent Event [Line Items]
Rented area | ft²	13,438
Term of lease	60 months
Operating lease cost				$ 3,800
Nonrefundable lease cost for assignment of lease	$ 60