Regulus Therapeutics (RGLS) 10-K 10 Mar 22 2021 FY Annual report Financial data

Cover

Cover - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Mar. 04, 2022	Jun. 30, 2021
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2021
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	4224 Campus Point Court, Suite 210
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	false
Entity Shell Company	false
Entity Public Float			$ 67.8
Entity Common Stock, Shares Outstanding		145,971,184
Documents Incorporated by Reference	Portions of the registrant’s definitive proxy statement to be filed with the Securities and Exchange Commission pursuant on Schedule 14A in connection with the registrant’s 2022 Annual Meeting of Stockholders, which will be filed subsequent to the date hereof, are incorporated by reference into Part III of this Form 10-K. Such proxy statement will be filed with the Securities and Exchange Commission no later than May 2, 2022.
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	FY
Entity Central Index Key	0001505512
Amendment Flag	false

Audit Information

Audit Information	12 Months Ended
	Dec. 31, 2021
Audit Information [Abstract]
Auditor Name	Ernst & Young LLP
Auditor Location	San Diego, California
Auditor Firm ID	42

Balance Sheets

Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 60,383	$ 31,087
Restricted cash	62	0
Contract and other receivables	0	503
Prepaid materials, net	3,010	3,314
Prepaid expenses and other current assets	1,780	1,826
Total current assets	65,235	36,730
Property and equipment, net	281	472
Intangibles, net	83	125
Right of use asset	2,564	253
Other assets	291	24
Total assets	68,454	37,604
Current liabilities:
Accounts payable	285	535
Accrued liabilities	821	581
Accrued research and development expenses	810	1,097
Accrued compensation	2,016	1,743
Current portion of term loan, less debt issuance costs	0	4,652
Other current liabilities	1,295	2,970
Total current liabilities	5,227	11,578
Operating lease liability, less current portion	2,417	0
Term loan, less current portion and debt issuance costs	4,673	0
Other long-term liabilities	1,179	0
Total liabilities	13,496	11,578
Stockholders’ equity (deficit):
Common stock, $0.001 par value; 400,000,000 shares authorized, 145,971,184 and 67,432,712 shares issued and outstanding at December 31, 2021 and 2020, respectively	146	67
Additional paid-in capital	509,660	453,002
Accumulated deficit	(454,853)	(427,045)
Total stockholders’ equity	54,958	26,026
Total liabilities and stockholders’ equity	68,454	37,604
Class A-1 Convertible Preferred Stock
Stockholders’ equity (deficit):
Convertible preferred stock	0	0
Class A-2 Convertible Preferred Stock
Stockholders’ equity (deficit):
Convertible preferred stock	1	1
Class A-3 Convertible Preferred Stock
Stockholders’ equity (deficit):
Convertible preferred stock	0	1
Class A-4 Convertible Preferred Stock
Stockholders’ equity (deficit):
Convertible preferred stock	$ 4	$ 0

Balance Sheets (Parenthetical)

Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2021	Dec. 31, 2020
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	400,000,000	400,000,000
Common stock, shares issued (shares)	145,971,184	67,432,712
Common stock, shares outstanding (in shares)	145,971,184	67,432,712
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
Preferred stock, shares issued (in shares)	256,700
Preferred stock, shares outstanding (in shares)	256,700	257,000
Class A-2 Convertible Preferred Stock
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	1,330,832	1,416,453
Preferred stock, shares issued (in shares)	1,330,832	1,416,453
Preferred stock, shares outstanding (in shares)	1,330,832	1,416,453
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
Preferred stock, shares issued (in shares)	258,707
Preferred stock, shares outstanding (in shares)	258,707	259,000
Class A-4 Convertible Preferred Stock
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	3,725,720	0
Preferred stock, shares issued (in shares)	3,725,720	0
Preferred stock, shares outstanding (in shares)	3,725,720	0

Statements of Operations and Co

Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Revenues:
Total revenues	$ 0	$ 10,006
Operating expenses:
Research and development	17,794	15,347
General and administrative	10,022	8,814
Total operating expenses	27,816	24,161
Loss from operations	(27,816)	(14,155)
Other income (expense):
Interest and other income	864	233
Interest and other expense	(855)	(1,808)
Loss before income taxes	(27,807)	(15,730)
Income tax expense	(1)	0
Net loss and comprehensive net loss	$ (27,808)	$ (15,730)
Net loss per share, basic (in dollars per share)	$ (0.32)	$ (0.45)
Net loss per share, diluted (in dollars per share)	$ (0.32)	$ (0.45)
Weighted average shares used to compute basic net loss per share (in shares)	85,704,535	34,977,378
Weighted average shares used to compute diluted net loss per share (in shares)	85,704,535	34,977,378
Revenue, Product and Service [Extensible Enumeration]	Revenue Under Collaborations [Member]	Revenue Under Collaborations [Member]

Statements of Stockholders' Equ

Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common stock	Additional paid-in capital	Accumulated deficit	Convertible Preferred StockPreferred stock
Beginning balance (in shares) at Dec. 31, 2019		21,018,663			3,704,288
Beginning 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	0	$ 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
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of options (in shares)		27,728
Issuance of common stock upon exercise of options	26		26
Issuance of common stock upon exercise of warrants (in shares)		2,668,681
Issuance of common stock upon exercise of warrants	832	$ 3	829
Issuance of common stock upon vesting of restricted stock units (in shares)		33,751
Issuance of common stock, preferred stock and warrants from private placement, net of offering costs (in shares)		58,923,352			3,725,720
Issuance of common stock, preferred stock and warrants from private placement, net of offering costs	32,360	$ 59	32,298		$ 3
Stock-based compensation expense	2,923		2,923
Issuance of common stock under Employee Stock Purchase Plan (in shares)		11,619
Issuance of common stock under Employee Stock Purchase Plan	$ 7		7
Issuance of common stock through ATM (in shares)	11,619	16,017,131
Issuance of common stock through ATM	$ 20,592	$ 16	20,576
Conversions of convertible preferred stock (in shares)		856,210			(85,621)
Conversions of convertible preferred stock		$ 1	(1)
Net loss	(27,808)			(27,808)
Ending balance (in shares) at Dec. 31, 2021		145,971,184			5,571,959
Ending balance at Dec. 31, 2021	$ 54,958	$ 146	$ 509,660	$ (454,853)	$ 5

Statements of Cash Flows

Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Operating activities
Net loss	$ (27,808)	$ (15,730)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation and amortization expense	459	467
Gain on PPP Loan forgiveness	(662)	0
Stock-based compensation	2,923	2,614
Other	46	154
Change in operating assets and liabilities:
Contracts and other receivables	503	638
Prepaid materials	304	610
Prepaid expenses and other assets	(221)	(605)
Accounts payable	(250)	(786)
Accrued liabilities	240	(188)
Accrued research and development expenses	(287)	949
Accrued compensation	273	66
Operating lease right-of-use assets and liabilities, net	279	(150)
Contract liabilities	0	(6)
Other liabilities	73	(569)
Net cash used in operating activities	(24,128)	(12,536)
Investing activities
Purchases of property and equipment	(251)	0
Acquisition of intangibles	0	(11)
Net cash used in investing activities	(251)	(11)
Financing activities
Proceeds from issuance of securities through private placement, net of issuance costs	32,360	18,166
Proceeds from issuance of common stock, net	21,431	957
Proceeds from borrowing under Paycheck Protection Program	0	662
Proceeds from exercise of common stock options	26	5
Payments on financing leases	(80)	(277)
Principal payments on term loan	0	(10,000)
Net cash provided by financing activities	53,737	9,513
Net increase (decrease) in cash, cash equivalents and restricted cash	29,358	(3,034)
Cash, cash equivalents and restricted cash at beginning of period	31,087	34,121
Cash, cash equivalents and restricted cash at end of period	60,445	31,087
Reconciliation of cash, cash equivalents and restricted cash
Cash and cash equivalents	60,383	31,087
Restricted cash	62	0
Total cash, cash equivalents and restricted cash	60,445	31,087
Supplemental disclosure of cash flow information
Interest paid	(729)	(1,356)
Income taxes paid	(1)	(1)
Supplemental disclosure of non-cash investing and financing activities
Paycheck Protection Program loan forgiveness	662	0
Unsettled sales of common stock through ATM	$ 0	$ 392

The Business, Basis of Presenta

The Business, Basis of Presentation and Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2021
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 clinical-stage biopharmaceutical company focused on discovering and developing first-in-class drugs targeting micro RNAs to treat dise ases with significant unmet medical need. 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. Liquidity 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 $538.0 million. As of December 31, 2021, we had approximately $60.4 million of cash and cash equivalents. 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. 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. Additionally, the impact of the COVID-19 pandemic to our business and operating results presents additional uncertainty. 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 invested our excess cash primarily in money market funds. 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. 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, 2021 or 2020. 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 right of use assets ("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 a lease term of 12 months or less at inception 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. Fair Value of Financial Instruments We follow ASC 820-10 issued by the FASB with respect to fair value reporting for financial assets and liabilities. The guidance defines fair value, provides guidance for measuring fair value and requires certain disclosures. The guidance does not apply to measurements related to share-based payments. The guidance discusses valuation techniques such as the market approach (comparable market prices), the income approach (present value of future income or cash flow), and the cost approach (cost to replace the service capacity of an asset or replacement cost). The guidance establishes a fair value hierarchy that prioritizes the inputs to valuation techniques used to measure fair value into three broad levels. Our financial instruments consist of cash and cash equivalents, contract and other receivables, accounts payable, accrued liabilities, and our Term Loan. Fair value estimates of these instruments are made at each reporting period end based on relevant market information. These estimates may be subjective in nature and involve uncertainties and matters of significant judgment and therefore cannot be determined with precision. The carrying amount of cash and cash equivalents, contract and other receivables, accounts payable, and accrued liabilities are generally considered to be representative of their respective fair values because of the short-term nature of those instruments. We believe that the fair value of the Term Loan approximates its carrying value. 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, an d 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 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 relationships entered into or evaluated, after December 31, 2022. We are assessing the impact this standard will have on our financial statements and disclosures. In August 2020, the FASB issued ASU 2020-06, Debt—Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging—Contracts in Entity’s Own Equity (Subtopic 815-40): Accounting for Convertible Instruments and Contracts in an Entity’s Own Equity, which simplifies accounting for convertible instruments by removing major separation models required under current GAAP. This standard removes certain settlement conditions that are required for equity contracts to qualify for the derivative scope exception and it also simplifies the diluted earnings per share calculation in certain areas. This standard is effective for fiscal years beginning after December 15, 2021, including interim periods within those fiscal years. Early adoption is permitted, but no earlier than fiscal years beginning after December 15, 2020 and adoption must be as of the beginning of the Company’s annual fiscal year. The adoption of this standard on January 1, 2021 did not impact our financial statements or disclosures.

Net Loss Per Share

Net Loss Per Share	12 Months Ended
	Dec. 31, 2021
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, warrants 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) 92,556,717 shares for the year ended December 31, 2021, consisting of convertible preferred stock, warrants, stock options and restricted stock units, and 70,751,812 shares for the year ended December 31, 2020, consisting of convertible preferred stock, warrants, stock options and restricted stock units.

Investments

Investments	12 Months Ended
	Dec. 31, 2021
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 to maturity and do not sell our investments before we have recovered our amortized cost basis. As of December 31, 2021 and 2020, 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, 2021
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, 2021 and 2020 (in thousands): Fair value as of December 31, 2021 Total Level 1 Level 2 Level 3 Assets: Cash equivalents (money market funds) $ 57,905 $ 57,905 $ — $ — $ 57,905 $ 57,905 $ — $ — 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 $ — $ —

Collaborations

Collaborations	12 Months Ended
	Dec. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Collaborations	Collaborations Revenue recognized from our strategic collaborations was zero for the year ended December 31, 2021 and $10.0 million for the year ended December 31, 2020. 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. 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 February 2014, we and Sanofi entered into a second amended and restated collaboration and license agreement (the “2014 Sanofi Amendment”) 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. 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. In 2019, we completed the performance obligations under the 2018 Sanofi Amendment and recognized revenue for the $6.8 million in Upfront Amendment Payments. 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, 2021, the $25.0 million in development milestone payments (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, 2021
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, 2021 2020 Laboratory equipment $ 4,215 $ 4,967 Computer equipment and software 265 281 Furniture and fixtures — — Leasehold improvements 115 83 4,595 5,331 Less accumulated depreciation and amortization (4,314) (4,859) Property and equipment, net $ 281 $ 472 Depreciation and amortization of property and equipment of $0.4 million and $0.5 million was recorded for the years ended December 31, 2021 and 2020, respectively.

Intangible Assets, net

Intangible Assets, net	12 Months Ended
	Dec. 31, 2021
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, 2021 2020 Patents $ 189 $ 219 Accumulated amortization - Patents (106) (94) Intangibles, net $ 83 $ 125 Intangible asset amortization of less than $0.1 million was recorded for the years ended December 31, 2021 and 2020. 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, 2021 is expected to be recognized is approximately 11.8 years.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2021
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. Litigation From time to time, we may be involved in various lawsuits, legal proceedings, or claims that arise in the ordinary course of business. We believe there are no claims or actions pending against us at December 31, 2021 which will have, individually, or in the aggregate, a material adverse effect on our business, liquidity, financial position or results of operations. Litigation, however, is subject to inherent uncertainties, and an adverse result in such matters may arise from time to time that may harm our business.

Debt

Debt	12 Months Ended
	Dec. 31, 2021
Debt Disclosure [Abstract]
Debt	Debt On June 17, 2016, we entered into a loan and security agreement ("Loan Agreement") with Oxford Finance, LLC, (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, 2024 (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. The Loan Agreement was amended eight times between October 2017 through May 2019. 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 Loan Agreement (the "Tenth Amendment"). Pursuant to the terms of the Tenth Amendment, we were eligible for up to an additional seven months of interest only payments in the event we paid down $10.0 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 occurred 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 5) 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 prepaym ents to the Lender. As the Principal Paydown Event occurred by April 30, 2021, we received an additional seven months of interest only payment extension and were not obligated to make principal payments on the Term Loan until January 1, 2022. On December 31, 2021, we entered into an eleventh amendment to the Loan Agreement (the "Eleventh Amendment"). Under the terms of the Eleventh Amendment, our required monthly payments to the Lender are to be comprised of interest only through and including (i) December 1, 2022, if the 2022 Equity Event (as defined below) does not occur or (ii) December 1, 2023 if the 2022 Equity Event occurs. The “2022 Equity Event” means the receipt by us, during the calendar year 2022, of unrestricted net cash proceeds of at least $20.0 million from the sale and issuance of our equity securities. In addition, the maturity date for the Term Loan was extended to May 1, 2024. If the 2022 Equity Event does not occur, then commencing on January 1, 2023 and continuing on each successive payment date thereafter through and including the maturity date of May 1, 2024, we will be required to make consecutive equal monthly payments of principal, together with applicable interest, in arrears, to the Lender. If the 2022 Equity Event does occur, then commencing on January 1, 2024 and continuing on each successive payment date thereafter through and including the maturity date of May 1, 2024, we will be required to make consecutive equal monthly payments of principal, together with applicable interest, in arrears, to the Lender. The Eleventh Amendment also provides that we are required to maintain a minimum cash balance of $5.0 million. As consideration for the Lender’s entry into the Eleventh Amendment, we made a payment of $0.3 million to the Lender. 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 the Lender currently has a positive lien. 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 first quarter of 2021, we received a waiver from the Lender with respect to noncompliance with a covenant under the Loan Agreement. We are in compliance with all Loan Agreement covenants as of the date of the filing of this Form 10-K. As of December 31, 2021, $4.7 million was outstanding under the Term Loan. An additional $1.3 million is also payable at the conclusion of the Term Loan (the related $1.2 million accreted liability balance is presented in other long-term liabilities on our balance sheet at December 31, 2021) . We had less than $0.1 million of debt issuance costs outstanding as of December 31, 2021, 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, 2021, future principal payments for the Term Loan due under the Loan Agreement are as follows (in thousands): 2022 — 2023 3,304 2024 1,377 $ 4,681 Paycheck Protection Program Loan On April 23, 2020, we received 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 was set to mature on April 23, 2022 and bore interest at a rate of 1.0% per annum. The PPP Loan was evidenced by a promissory note dated April 23, 2020, which contained customary events of default relating to, among other things, payment defaults and breaches of representations and warranties. The PPP Loan was prepayable by us at any time prior to maturity with no prepayment penalties. 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 during the 24 week period beginning on the date of loan disbursement. For purposes of the PPP, payroll costs exclude compensation of an individual employee in excess of $100,000, annualized, prorated for the covered period. Not more than 40% of the forgiven amount may be for non-payroll costs. Forgiveness is reduced if full-time headcount declines during the covered period as compared to specified reference periods, or if salaries and wages for employees with salaries of $100,000 or less annually are reduced by more than 25%, unless certain safe harbors are satisfied. In the event the PPP Loan, or any portion thereof, is forgiven pursuant to the PPP, the amount forgiven is applied to outstanding principal and includes accrued interest. We used all proceeds from the PPP Loan to retain employees, maintain payroll and make lease and utility payments, and we sought forgiveness in accordance with the program. We received full forgiveness of our PPP Loan in the second quarter of 2021. We accounted for the full forgiveness of our PPP Loan by recording a gain in interest and other income for the year ended December 31, 2021.

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2021
Equity [Abstract]
Stockholders’ Equity	Stockholders’ Equity Common Stock As of December 31, 2021, there were 145,971,184 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 Incentive Plan (the "2019 Plan"). The 2019 Plan is the successor to and continuation of the Company's 2012 Equity Incentive Plan. 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 (defined below) of the May 2019 SPA (defined below). 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. As of December 31, 2021, 1,964,112 shares of common stock were available for new equity award grants under the 2019 Plan and 9,061,885 shares of common stock were reserved for issuance pursuant to equity awards outstanding as of December 31, 2021. Private Placements of Common Stock, Non-Voting Preferred Stock and Warrants On May 3, 2019, we entered into a securities purchase agreement (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 resolved 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 made a public announcement of our plan to recommence the Phase 1 Trial (the “Public Announcement”), we would sell and the Purchasers would 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 $0.7464 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. On November 24, 2021, we entered into a Securities Purchase Agreement (the "November 2021 SPA") with certain institutional and other accredited investors, including certain directors, executive officers and employees of the Company (the “2021 Purchasers”), pursuant to which we agreed to sell and issue shares of our common stock and shares of newly designated non-voting convertible preferred stock (the “2021 PIPE”). At the closing under the November 2021 SPA that occurred on November 30, 2021 (the “2021 Closing”), we sold and issued to the 2021 Purchasers (i) 58,923,352 shares of common stock at a purchase price of $0.36 per share, and (ii) 3,725,720 shares of non-voting Class A-4 convertible preferred stock, in lieu of shares of common stock, at a price of $3.60 per share. Total gross proceeds from the 2021 Closing were approximately $34.6 million. Each share of non-voting Class A-4 convertible preferred stock is convertible into 10 shares of common stock, subject to certain beneficial ownership conversion limitations. An aggregate of 2,222,222 shares of common stock were purchased for $0.8 million by a director of the Company at the 2021 Closing. We evaluated the non-voting Class A-4 convertible preferred stock sold in the 2021 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 May 2019 SPA, the December 2020 SPA and the November 2021 SPA for the years ended December 31, 2021 and 2020 (in thousands): Class A-1 Convertible Preferred Stock Class A-2 Convertible Preferred Stock Class A-3 Convertible Preferred Stock Class A-4 Convertible Preferred Stock Warrants Common Stock Balance at December 31, 2019 416 3,288 — — 46,774 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 2021 Closing — — — 3,726 — 58,923 Conversions/Exercises — (85) — — (4,170) 3,525 Balance at December 31, 2021 257 1,331 259 3,726 61,868 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 that 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 16,017,131 shares were sold and settled for proceeds of $20.7 million (net of $0.7 million in offering costs) under the Stock Sales Agreement during the year ended December 31, 2021. A total of 492,268 shares were sold for proceeds of $0.3 million (net of less than $0.1 million in offering costs) under the Stock Sales Agreement during the year ended December 31, 2020. On August 10, 2021, we increased the amount of common stock available for sale in the ATM Offering under the Stock Sales Agreement to $50.0 million. At December 31, 2021, $50.0 million remained eligible to be sold in the ATM Offering. Shares Reserved for Future Issuance The following shares of common stock were reserved for future issuance as of December 31, 2021 (in thousands): Class A-1 convertible preferred stock outstanding (as-converted) 2,567 Class A-2 convertible preferred stock outstanding (as-converted) 13,308 Class A-3 convertible preferred stock outstanding (as-converted) 2,587 Class A-4 convertible preferred stock outstanding (as-converted) 37,257 2019 PIPE Initial Closing warrants 12,778 2019 PIPE Milestone Closing warrants 30,595 2020 PIPE warrants 18,495 Common stock options outstanding 8,661 RSUs outstanding 401 Common stock available for future grant under the 2019 Equity Incentive Plan 2,164 Common stock available for future grant under the Inducement Plan 1,800 Employee Stock Purchase Plan 259 Total common shares reserved for future issuance 130,872 The following table summarizes our stock option activity under all equity incentive plans for the year ended December 31, 2021 (shares and aggregate intrinsic value in thousands): Number of Weighted Weighted average remaining contractual term Aggregate intrinsic value Options outstanding at December 31, 2020 6,813 $ 1.10 Granted 3,351 $ 1.40 Exercised (28) $ 0.96 Canceled/forfeited/expired (1,475) $ 1.36 Options outstanding at December 31, 2021 8,661 $ 1.17 8.24 $ — Vested and exercisable at December 31, 2021 3,494 $ 1.22 7.93 $ — The weighted average grant date fair value per share of employee stock options granted during the years ended December 31, 2021 and 2020 was $1.07 and $0.91, respectively. The total intrinsic value of stock options exercised was less than $0.1 million for the years ended December 31, 2021 and 2020. Cash received from the exercise of stock options was less than $0.1 million for the years ended December 31, 2021 and 2020. The total compensation cost related to stock options not yet recognized was $2.1 million as of December 31, 2021. The weighted-average period over which this expense is expected to be recognized is approximately 1.6 years. The following table summarizes our RSU activity under all equity incentive plans for the year ended December 31, 2021 (shares and aggregate intrinsic value in thousands): Number of Weighted Weighted average remaining contractual term Aggregate intrinsic value RSUs outstanding at December 31, 2020 34 $ 1.50 Granted 446 $ 0.95 Vested (34) $ 1.50 Canceled/forfeited/expired (45) $ 0.96 RSUs outstanding at December 31, 2021 401 $ 0.95 0.39 $ 126 The total compensation cost related to non-vested RSUs not yet recognized was $0.2 million as of December 31, 2021. The weighted-average period over which this expense is expected to be recognized is approximately 0.4 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, 2021 Inducement Plan and the shares purchasable under our Employee Stock Purchase Plan during the periods presented: Year ended December 31, 2021 2020 Stock options Risk-free interest rate 1.0 % 1.1 % Volatility 95.8 % 95.4 % Dividend yield — — Expected term (years) 6.1 6.1 Performance stock options Risk-free interest rate 1.0 % 1.4 % Volatility 95.7 % 95.4 % Dividend yield — — Expected term (years) 6.1 6.1 Employee stock purchase plan shares Risk-free interest rate 0.1 % 0.6 % Volatility 101.2 % 98.0 % 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, 2021 2020 Research and development $ 821 $ 693 General and administrative 2,102 1,921 Total $ 2,923 $ 2,614 Employee Stock Purchase Plan In October 2012, we adopted the 2012 Employee Stock Purchase Plan (“2012 Purchase Plan”), which enables participants to contribute up to 15% of such participant’s eligible compensation during a defined six-month period to purchase our common stock. The purchase price of common stock under the 2012 Purchase Plan will be the lesser of: (i) 85% of the fair market value of our common stock at the inception of the enrollment period or (ii) 85% of the fair market value of our common stock at the applicable purchase date. As of December 31, 2021, 108,565 shares of our common stock had been issued under the 2012 Purchase Plan, with 11,619 shares of common stock issued for the year ended December 31, 2021. Under the 2012 Purchase Plan, 259,402 shares of our common stock were reserved for future issuance and have been authorized for purchase as of December 31, 2021. Inducement Plan On November 23, 2021, our Board of Directors adopted the 2021 Inducement Plan (the “Inducement Plan”), which became effective immediately. Stockholder approval of the Inducement Plan was not required pursuant to Rule 5635(c)(4) of the Nasdaq Listing Rules. The Inducement Plan initially reserved 2,000,000 shares of common stock and provides for the grant of NSOs that was used exclusively for grants to individuals that were not previously employees or directors of the Company, as an inducement material to the individual’s entry into employment with the Company. Under the Inducement Plan, options were granted with varying vesting terms, but typically vested over four years, with 25% of the total grant vesting on the first anniversary of the effective date of the option grant and the remaining grant vesting monthly thereafter over the following 36 months. As of December 31, 2021, 1,800,000 shares were reserved for future issuance under the Inducement Plan.

Defined Contribution Plan

Defined Contribution Plan	12 Months Ended
	Dec. 31, 2021
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, 2021 and 2020.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2021
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, 2021 2020 Current: Federal $ — $ (13) State 1 1 1 (12) Deferred: Federal — 12 State — — — 12 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, 2021 2020 Expected income tax benefit at federal statutory tax rate $ (5,840) $ (3,309) State income taxes, net of federal benefit 1 (927) Tax credits (1,180) (1,216) Change in valuation allowance 6,659 2,606 Return to provision adjustments 80 (14) Stock compensation 243 1,644 Reserve for uncertain tax positions 176 1,179 Other (138) 37 Income tax expense $ 1 $ — The following table summarizes the significant components of our deferred tax assets and liabilities (in thousands): December 31, 2021 2020 Deferred tax assets: Net operating loss carryovers $ 87,877 $ 82,747 Research and development and other tax credits 35,344 34,337 Intangibles and property and equipment basis difference 607 715 Stock compensation expense 587 283 Lease liability 631 88 Other 564 281 Total deferred tax assets 125,610 118,451 Total deferred tax liabilities (782) (282) Net deferred tax asset 124,828 118,169 Valuation allowance (124,828) (118,169) Net deferred tax asset $ — $ — 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 $124.8 million. As of December 31, 2021, we had NOL carryforwards for U.S. federal and California state tax purposes of $366.8 million and $276.0 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 $103.4 million will carry forward indefinitely, but may only offset 80% of our taxable income. As of December 31, 2021, we also had federal and California research and development tax credit carryforwards of $33.0 million and $9.7 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, 2021 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, 2021 2020 Beginning balance of unrecognized tax benefits $ 17,939 $ 16,573 Decrease for prior year tax positions (1,174) (1) Increase for current year tax positions 188 1,367 Total $ 16,953 $ 17,939 Included in unrecognized tax benefits of $17.0 million at December 31, 2021 was $13.7 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, 2021 and 2020, we have not recognized any interest or penalties related to income taxes.

Leases

Leases	12 Months Ended
	Dec. 31, 2021
Leases [Abstract]
Leases	Leases On June 19, 2019, we entered into a lease agreement (the “Prior Lease”) with ARE SD Region No.44 LLC ("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 “Prior Premises”). The commencement date of the Prior Lease was July 1, 2019 (the “Prior Commencement Date”). We used the Prior Premises as our principal executive offices and as a laboratory for research and development and other related uses. The term of the Prior Lease (the “Prior Initial Term”) was two years, six months, ending December 31, 2021. The base rent payments due for the Prior Premises were $0.4 million in 2020 and $0.4 million in 2021, net of certain rent abatement terms. We were also 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 July 1, 2019, we recorded a $0.8 million lease liability for the Prior Lease, which was calculated as the present value of future lease payments to be made under the Prior 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 operating lease agreement with Landlord dated February 25, 2019. On February 11, 2021, we entered into a lease agreement (the "Campus Point Lease") with ARE-SD Region No. 61, LLC (as successor in interest to 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 was April 15, 2021. However, for accounting purposes the lease commencement date was February 11, 2021. We are using the Campus Point Premises as our new principal executive offices and as a laboratory for research and development. The term of the Campus Point Lease (“Campus Point Initial Term”) is 60 months, ending April 30, 2026. The aggregate base rent due over the initial term of the Campus Point Lease is approximately $3.8 million. We are also 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. On February 11, 2021, concurrently with entry into the Campus Point Lease, we entered into an Assignment and Assumption of Lease (the “Assignment Agreement”) with Turning Point Therapeutics, Inc. (“Assignee”) and a Consent to Assignment (the "Consent") with Landlord. Pursuant to the Assignment Agreement, we assigned all rights, title, and interest under the Prior Lease to Assignee and delivered the Prior Premises to Assignee on April 22, 202 1. Pursuant to the Assignment Agreement, Assignee paid us $60,000 in non-refundable assignment consideration. Additionally, the Consent stipulates that we were not required to pay a fee pursuant to the Prior Lease in connection with the assignment. The execution of the Campus Point Lease, Consent, and Assignment Agreement resulted in a modification which was not accounted for as a separate contract. Rather, we accounted for the three contracts with Campus Point 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 $0.2 million reduction in the lease liability for the Prior Lease as a deferred credit that is amortized as a reduction to rent expense over the term of the Campus Point Lease. A lease liability of less than $0.1 million and ROU asset of less than $0.1 million remained with respect to the Prior Lease and was fully amortized as of April 30, 2021. On February 11, 2021, we recorded a $3.2 million lease liability for the Campus Point Lease, which was calculated as the present value of future lease payments to be made under the Campus Point Lease. A $3.0 million ROU asset was also recorded on February 11, 2021, which represents the difference between the lease liability and the $0.2 million deferred credit for the reduction of the lease liability under the Prior Lease. The table below summarizes our lease liabilities and corresponding ROU assets as of December 31, 2021 and 2020 (in thousands): Year Ended December 31, 2021 2020 Assets Operating $ 2,564 $ 253 Financing — 288 Total ROU assets $ 2,564 $ 541 Liabilities Current: Operating $ 589 $ 417 Financing — 56 Long-term: Operating 2,417 — Financing — — Total lease liabilities $ 3,006 $ 473 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, 2021 and 2020 (in thousands): Year Ended December 31, 2021 2020 Lease cost: Operating lease cost $ 746 $ 278 Finance lease cost: Amortization of right-of-use assets 29 178 Interest expense on lease liabilities 1 10 Total finance lease cost $ 30 $ 188 Cash payment information: Operating cash used for operating leases $ 468 $ 429 Operating cash used for finance leases 1 10 Financing cash used for finance leases 80 277 Total cash paid for amounts included in the measurement of lease liabilities $ 549 $ 716 The table below summarizes other non-cash information under our operating and financing lease obligations as of December 31, 2021 and 2020 (in thousands, except years and rates): Year Ended December 31, 2021 2020 Supplemental non-cash information: Operating lease liabilities arising from obtaining right-of-use assets $ 3,006 $ — Weighted-average remaining lease term (years) - operating leases 4.3 1.0 Weighted-average remaining lease term (years) - finance leases 0 0.2 Weighted-average discount rate - operating leases 6.0 % 10.9 % Weighted-average discount rate - finance leases — 4.9 % Our future lease payments under our operating lease at December 31, 2021 are as follows (in thousands): Operating Leases 2022 $ 754 2023 776 2024 800 2025 824 2026 277 Total operating lease payments 3,431 Less: amount representing interest (425) Present value of obligations under operating lease 3,006 Less: current portion (589) Long-term operating lease obligations $ 2,417

The Business, Basis of Presen_2

The Business, Basis of Presentation and Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2021
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. Additionally, the impact of the COVID-19 pandemic to our business and operating results presents additional uncertainty.
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
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 invested our excess cash primarily in money market funds. 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 we 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.
Leases	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 right of use assets ("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 a lease term of 12 months or less at inception 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.
Fair Value of Financial Instruments	Fair Value of Financial Instruments We follow ASC 820-10 issued by the FASB with respect to fair value reporting for financial assets and liabilities. The guidance defines fair value, provides guidance for measuring fair value and requires certain disclosures. The guidance does not apply to measurements related to share-based payments. The guidance discusses valuation techniques such as the market approach (comparable market prices), the income approach (present value of future income or cash flow), and the cost approach (cost to replace the service capacity of an asset or replacement cost). The guidance establishes a fair value hierarchy that prioritizes the inputs to valuation techniques used to measure fair value into three broad levels. Our financial instruments consist of cash and cash equivalents, contract and other receivables, accounts payable, accrued liabilities, and our Term Loan. Fair value estimates of these instruments are made at each reporting period end based on relevant market information. These estimates may be subjective in nature and involve uncertainties and matters of significant judgment and therefore cannot be determined with precision. The carrying amount of cash and cash equivalents, contract and other receivables, accounts payable, and accrued liabilities are generally considered to be representative of their respective fair values because of the short-term nature of those instruments. We believe that the fair value of the Term Loan approximates its carrying value.
Recent Accounting Pronouncements	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, an d 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 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 relationships entered into or evaluated, after December 31, 2022. We are assessing the impact this standard will have on our financial statements and disclosures. In August 2020, the FASB issued ASU 2020-06, Debt—Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging—Contracts in Entity’s Own Equity (Subtopic 815-40): Accounting for Convertible Instruments and Contracts in an Entity’s Own Equity, which simplifies accounting for convertible instruments by removing major separation models required under current GAAP. This standard removes certain settlement conditions that are required for equity contracts to qualify for the derivative scope exception and it also simplifies the diluted earnings per share calculation in certain areas. This standard is effective for fiscal years beginning after December 15, 2021, including interim periods within those fiscal years. Early adoption is permitted, but no earlier than fiscal years beginning after December 15, 2020 and adoption must be as of the beginning of the Company’s annual fiscal year. The adoption of this standard on January 1, 2021 did not impact our financial statements or disclosures.
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, 2021
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, 2021 and 2020 (in thousands): Fair value as of December 31, 2021 Total Level 1 Level 2 Level 3 Assets: Cash equivalents (money market funds) $ 57,905 $ 57,905 $ — $ — $ 57,905 $ 57,905 $ — $ — 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 $ — $ —

Property and Equipment, net (Ta

Property and Equipment, net (Tables)	12 Months Ended
	Dec. 31, 2021
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment	The following table summarizes our major classes of property and equipment (in thousands): December 31, 2021 2020 Laboratory equipment $ 4,215 $ 4,967 Computer equipment and software 265 281 Furniture and fixtures — — Leasehold improvements 115 83 4,595 5,331 Less accumulated depreciation and amortization (4,314) (4,859) Property and equipment, net $ 281 $ 472

Intangible Assets, net (Tables)

Intangible Assets, net (Tables)	12 Months Ended
	Dec. 31, 2021
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, 2021 2020 Patents $ 189 $ 219 Accumulated amortization - Patents (106) (94) Intangibles, net $ 83 $ 125

Debt (Tables)

Debt (Tables)	12 Months Ended
	Dec. 31, 2021
Debt Disclosure [Abstract]
Schedule of Future Principal Payments	As of December 31, 2021, future principal payments for the Term Loan due under the Loan Agreement are as follows (in thousands): 2022 — 2023 3,304 2024 1,377 $ 4,681

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2021
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 May 2019 SPA, the December 2020 SPA and the November 2021 SPA for the years ended December 31, 2021 and 2020 (in thousands): Class A-1 Convertible Preferred Stock Class A-2 Convertible Preferred Stock Class A-3 Convertible Preferred Stock Class A-4 Convertible Preferred Stock Warrants Common Stock Balance at December 31, 2019 416 3,288 — — 46,774 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 2021 Closing — — — 3,726 — 58,923 Conversions/Exercises — (85) — — (4,170) 3,525 Balance at December 31, 2021 257 1,331 259 3,726 61,868
Common Stock Reserved for Future Issuance	The following shares of common stock were reserved for future issuance as of December 31, 2021 (in thousands): Class A-1 convertible preferred stock outstanding (as-converted) 2,567 Class A-2 convertible preferred stock outstanding (as-converted) 13,308 Class A-3 convertible preferred stock outstanding (as-converted) 2,587 Class A-4 convertible preferred stock outstanding (as-converted) 37,257 2019 PIPE Initial Closing warrants 12,778 2019 PIPE Milestone Closing warrants 30,595 2020 PIPE warrants 18,495 Common stock options outstanding 8,661 RSUs outstanding 401 Common stock available for future grant under the 2019 Equity Incentive Plan 2,164 Common stock available for future grant under the Inducement Plan 1,800 Employee Stock Purchase Plan 259 Total common shares reserved for future issuance 130,872
Stock Option Activity	The following table summarizes our stock option activity under all equity incentive plans for the year ended December 31, 2021 (shares and aggregate intrinsic value in thousands): Number of Weighted Weighted average remaining contractual term Aggregate intrinsic value Options outstanding at December 31, 2020 6,813 $ 1.10 Granted 3,351 $ 1.40 Exercised (28) $ 0.96 Canceled/forfeited/expired (1,475) $ 1.36 Options outstanding at December 31, 2021 8,661 $ 1.17 8.24 $ — Vested and exercisable at December 31, 2021 3,494 $ 1.22 7.93 $ —
Schedule of Restricted Stock Units Activity	The following table summarizes our RSU activity under all equity incentive plans for the year ended December 31, 2021 (shares and aggregate intrinsic value in thousands): Number of Weighted Weighted average remaining contractual term Aggregate intrinsic value RSUs outstanding at December 31, 2020 34 $ 1.50 Granted 446 $ 0.95 Vested (34) $ 1.50 Canceled/forfeited/expired (45) $ 0.96 RSUs outstanding at December 31, 2021 401 $ 0.95 0.39 $ 126
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, 2021 Inducement Plan and the shares purchasable under our Employee Stock Purchase Plan during the periods presented: Year ended December 31, 2021 2020 Stock options Risk-free interest rate 1.0 % 1.1 % Volatility 95.8 % 95.4 % Dividend yield — — Expected term (years) 6.1 6.1 Performance stock options Risk-free interest rate 1.0 % 1.4 % Volatility 95.7 % 95.4 % Dividend yield — — Expected term (years) 6.1 6.1 Employee stock purchase plan shares Risk-free interest rate 0.1 % 0.6 % Volatility 101.2 % 98.0 % 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, 2021 2020 Research and development $ 821 $ 693 General and administrative 2,102 1,921 Total $ 2,923 $ 2,614

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2021
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, 2021 2020 Current: Federal $ — $ (13) State 1 1 1 (12) Deferred: Federal — 12 State — — — 12 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, 2021 2020 Expected income tax benefit at federal statutory tax rate $ (5,840) $ (3,309) State income taxes, net of federal benefit 1 (927) Tax credits (1,180) (1,216) Change in valuation allowance 6,659 2,606 Return to provision adjustments 80 (14) Stock compensation 243 1,644 Reserve for uncertain tax positions 176 1,179 Other (138) 37 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, 2021 2020 Deferred tax assets: Net operating loss carryovers $ 87,877 $ 82,747 Research and development and other tax credits 35,344 34,337 Intangibles and property and equipment basis difference 607 715 Stock compensation expense 587 283 Lease liability 631 88 Other 564 281 Total deferred tax assets 125,610 118,451 Total deferred tax liabilities (782) (282) Net deferred tax asset 124,828 118,169 Valuation allowance (124,828) (118,169) Net deferred tax asset $ — $ —
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, 2021 2020 Beginning balance of unrecognized tax benefits $ 17,939 $ 16,573 Decrease for prior year tax positions (1,174) (1) Increase for current year tax positions 188 1,367 Total $ 16,953 $ 17,939

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2021
Leases [Abstract]
Schedule of Lease Liabilities and ROU Assets	The table below summarizes our lease liabilities and corresponding ROU assets as of December 31, 2021 and 2020 (in thousands): Year Ended December 31, 2021 2020 Assets Operating $ 2,564 $ 253 Financing — 288 Total ROU assets $ 2,564 $ 541 Liabilities Current: Operating $ 589 $ 417 Financing — 56 Long-term: Operating 2,417 — Financing — — Total lease liabilities $ 3,006 $ 473
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, 2021 and 2020 (in thousands): Year Ended December 31, 2021 2020 Lease cost: Operating lease cost $ 746 $ 278 Finance lease cost: Amortization of right-of-use assets 29 178 Interest expense on lease liabilities 1 10 Total finance lease cost $ 30 $ 188 Cash payment information: Operating cash used for operating leases $ 468 $ 429 Operating cash used for finance leases 1 10 Financing cash used for finance leases 80 277 Total cash paid for amounts included in the measurement of lease liabilities $ 549 $ 716 The table below summarizes other non-cash information under our operating and financing lease obligations as of December 31, 2021 and 2020 (in thousands, except years and rates): Year Ended December 31, 2021 2020 Supplemental non-cash information: Operating lease liabilities arising from obtaining right-of-use assets $ 3,006 $ — Weighted-average remaining lease term (years) - operating leases 4.3 1.0 Weighted-average remaining lease term (years) - finance leases 0 0.2 Weighted-average discount rate - operating leases 6.0 % 10.9 % Weighted-average discount rate - finance leases — 4.9 %
Schedule of Operating Lease, Liability, Maturity	Our future lease payments under our operating lease at December 31, 2021 are as follows (in thousands): Operating Leases 2022 $ 754 2023 776 2024 800 2025 824 2026 277 Total operating lease payments 3,431 Less: amount representing interest (425) Present value of obligations under operating lease 3,006 Less: current portion (589) Long-term operating lease obligations $ 2,417

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, 2021	Dec. 31, 2020
Accounting Policies [Abstract]
Financing from sale proceeds, debt, and agreement revenues	$ 538,000
Cash and cash equivalents	$ 60,383	$ 31,087

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, 2021
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, 2021	Dec. 31, 2020
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, 2021segment
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, 2021	Dec. 31, 2020
Earnings Per Share [Abstract]
Potentially dilutive securities not included in calculation of diluted net loss per share (in shares)	92,556,717	70,751,812

Investments (Details)

Investments (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
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, 2021	Dec. 31, 2020
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, fair value disclosure	$ 57,905	$ 26,901
Cash equivalents (money market funds)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, fair value disclosure	57,905	26,901
Fair Value, Inputs, Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, fair value disclosure	57,905	26,901
Fair Value, Inputs, Level 1 | Cash equivalents (money market funds)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, fair value disclosure	57,905	26,901
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						12 Months Ended
	Oct. 31, 2020USD ($)	Sep. 30, 2020USD ($)	Aug. 31, 2020USD ($)	Nov. 30, 2018USD ($)	Feb. 28, 2014USD ($)	Jul. 31, 2012target	Dec. 31, 2021USD ($)	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Nov. 30, 2020USD ($)
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Revenue							$ 0	$ 10,006,000
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							0	$ 10,000,000
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
Expected revenue through milestone payments				$ 6,800,000
Agreement period				24 months
Milestone payments, earned									$ 6,800,000
Enrollment milestone			$ 10,000,000
Development milestone not achievable							25,000,000
Sanofi | Development Commercialization And License Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Deferred revenue creditable against future milestones					$ 1,250,000		1,250,000
Initial upfront option payment					$ 2,500,000
Sanofi | Proof-of-Concept Trial
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Expected revenue through milestone payments							38,800,000
Sanofi | Clinical
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Expected revenue through milestone payments							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
Sanofi | Development Milestones
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Expected revenue through milestone payments				$ 40,000,000
Sanofi | Enrollment Milestone
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Expected revenue through milestone payments				$ 10,000,000
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%

Property and Equipment, net - M

Property and Equipment, net - Major Classes of Property and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 4,595	$ 5,331
Less accumulated depreciation and amortization	(4,314)	(4,859)
Property and equipment, net	281	472
Laboratory equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	4,215	4,967
Computer equipment and software
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	265	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	$ 115	$ 83

Property and Equipment, net - N

Property and Equipment, net - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Property, Plant and Equipment [Abstract]
Depreciation and amortization expense	$ 459	$ 467

Intangible Assets, net - Major

Intangible Assets, net - Major Classes of Intangible Assets (Details) - Patents - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross	$ 189	$ 219
Accumulated amortization - Patents	(106)	(94)
Intangibles, net	$ 83	$ 125

Intangible Assets, net - Narrat

Intangible Assets, net - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Goodwill and Intangible Assets Disclosure [Abstract]
Intangible asset amortization (less than)	$ 0.1	$ 0.1
Finite-lived intangible assets, amortization expense, next 12 months (less than $0.1 million)	0.1
Finite-lived intangible assets, amortization expense, year two (less than $0.1 million)	0.1
Finite-lived intangible assets, amortization expense, year three (less than $0.1 million)	0.1
Finite-lived intangible assets, amortization expense, year four (less than $0.1 million)	0.1
Finite-lived intangible assets, amortization expense, year five (less than $0.1 million)	$ 0.1
Remaining amortization period	11 years 9 months 18 days

Debt - Narrative (Details)

Debt - Narrative (Details)

Nov. 30, 2020USD ($)

Oct. 08, 2020USD ($)

Sep. 30, 2020USD ($)

Aug. 25, 2020

Jun. 22, 2016USD ($)

Jun. 17, 2016payment

Dec. 31, 2022USD ($)

Dec. 31, 2021USD ($)prepayment

Dec. 31, 2020USD ($)

May 31, 2019amendment

May 01, 2020USD ($)

Apr. 23, 2020USD ($)

Debt Instrument [Line Items]

Number of times agreement was amended | amendment

8

Forgiveness amount threshold for PPP loan (not less than)

$ 500,000

Total revenues

$ 0

$ 10,006,000

Other long-term liabilities

1,179,000

0

Strategic Alliances and Collaborations

Debt Instrument [Line Items]

Total revenues

0

$ 10,000,000

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 | payment

24

Repayments of debt

$ 5,000,000

$ 4,000,000

$ 1,000,000

$ 10,000,000

Payment fee

5.50%

Number of times agreement was amended | prepayment

3

Additional extension for interest only payments

7 months

Long-term debt

$ 4,681,000

Other long-term liabilities

1,200,000

Deferred finance costs

$ 100,000

Debt instrument effective rate

8.98%

Term Loan | Other Current Liabilities

Debt Instrument [Line Items]

Fee amount

$ 1,300,000

Term Loan | London Interbank Offered Rate (LIBOR)

Debt Instrument [Line Items]

Basis spread on variable rate, percentage

0.44%

PPP Loan

Debt Instrument [Line Items]

Debt instrument, face amount

$ 700,000

$ 700,000

Tenth Amendment

Debt Instrument [Line Items]

Interest only payment extension

7 months

Prepayment requirement

1000000000.00%

Eleventh Amendment

Debt Instrument [Line Items]

Cash collateral for borrowed securities

5,000,000

Fee amount

$ 300,000

Eleventh Amendment | Forecast

Debt Instrument [Line Items]

Unrestricted net cash proceeds amount

$ 20,000,000

Debt - Future Principal Payment

Debt - Future Principal Payments (Details) - Term Loan $ in Thousands	Dec. 31, 2021USD ($)
Debt Instrument [Line Items]
2022	$ 0
2023	3,304
2024	1,377
Long-term debt	$ 4,681

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	Jun. 15, 2019shares	May 07, 2019USD ($)$ / sharesshares	Nov. 30, 2021USD ($)$ / sharesshares	Dec. 31, 2021voteshares	Dec. 31, 2020shares	May 03, 2019closing
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, shares issued (shares)							145,971,184	67,432,712
Common stock voting rights per share | vote							1
Number of years for increase of authorized shares		10 years
Common shares reserved for future issuance (in shares)							130,872,000
Number of closings (up to) | closing									2
Private Placement
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares issued (in shares)					9,730,534
Number of securities called by warrants (in shares)					9,730,534
Sale of stock (usd per share) | $ / shares					$ 1.205
Consideration received on transaction | $					$ 16.7
Convertible preferred stock, shares issued upon conversion (in shares)					10
Warrant exercise period					5 years
Warrant exercise price (usd per share) | $ / shares					$ 1.08
Private Placement | Directors, Executive Officers and Employees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares issued (in shares)					526,083
Private Placement | Class A-1 Convertible Preferred Stock
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
Private Placement | Class A-1 Convertible Preferred Stock | Directors, Executive Officers and Employees
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
Private Placement | Class A-1 Convertible Preferred Stock | Warrants
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Sale of stock (usd per share) | $ / shares					$ 0.125
Milestone Closing
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Consideration received on transaction | $			$ 24.6
Milestone Closing | Class A-2 Convertible Preferred Stock
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
Milestone Closing | Class A-2 Convertible Preferred Stock | Certain Directors and Executive Officers
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
2020 Closing
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares issued (in shares)	24,341,607
Number of securities called by warrants (in shares)	18,256,204
Sale of stock (usd per share) | $ / shares	$ 0.7464
Consideration received on transaction | $	$ 19.4
Convertible preferred stock, shares issued upon conversion (in shares)	10
2020 Closing | Directors, Executive Officers and Employees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares issued (in shares)	833,208
2020 Closing | Class A-3 Convertible Preferred Stock
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	$ 0.7464
Warrants, term	5 years
2020 Closing | Class A-3 Convertible Preferred Stock | Directors, Executive Officers and Employees
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
2020 Closing | Class A-3 Convertible Preferred Stock | Warrants
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Sale of stock (usd per share) | $ / shares	$ 0.125
2021 Closing
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares issued (in shares)						58,923,352
Sale of stock (usd per share) | $ / shares						$ 0.36
Consideration received on transaction | $						$ 34.6
Convertible preferred stock, shares issued upon conversion (in shares)						10
2021 Closing | Directors, Executive Officers and Employees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares issued (in shares)						2,222,222
2021 Closing | Class A-4 Convertible Preferred Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Sale of stock (usd per share) | $ / shares						$ 3.60
Nonvoting convertible preferred stock issued (in shares)						3,725,720
2021 Closing | Class A-4 Convertible Preferred Stock | Directors, Executive Officers and Employees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Proceeds from issuance of preferred warrants | $						$ 0.8
2019 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Additional shares available (in shares)		4,166,860
Yearly authorized increase		5.00%
Shares available for future grant (in shares)							1,964,112
Common shares reserved for future issuance (in shares)							9,061,885
Prior Plans
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares)				0

Stockholders' Equity - Share Ac

Stockholders' Equity - Share Activity (Details) - shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Activity of Shares [Roll Forward]
Common stock, shares outstanding (in shares)	67,432,712
Shares issued (in shares)	11,619
Common stock, shares outstanding (in shares)	145,971,184	67,432,712
Class A-1 Convertible Preferred Stock
Activity of Shares [Roll Forward]
Preferred stock, shares outstanding (in shares)	257,000	416,000
Conversions of convertible preferred stock (in shares)	0	(159,000)
Preferred stock, shares outstanding (in shares)	256,700	257,000
Class A-1 Convertible Preferred Stock | 2020 Closing
Activity of Shares [Roll Forward]
Shares issued (in shares)		0
Class A-1 Convertible Preferred Stock | 2021 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)	1,416,453	3,288,000
Conversions of convertible preferred stock (in shares)	(85,000)	(1,872,000)
Preferred stock, shares outstanding (in shares)	1,330,832	1,416,453
Class A-2 Convertible Preferred Stock | 2020 Closing
Activity of Shares [Roll Forward]
Shares issued (in shares)		0
Class A-2 Convertible Preferred Stock | 2021 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)	259,000	0
Conversions of convertible preferred stock (in shares)	0	(14,000)
Preferred stock, shares outstanding (in shares)	258,707	259,000
Class A-3 Convertible Preferred Stock | 2020 Closing
Activity of Shares [Roll Forward]
Shares issued (in shares)		273,000
Class A-3 Convertible Preferred Stock | 2021 Closing
Activity of Shares [Roll Forward]
Shares issued (in shares)	0
Class A-4 Convertible Preferred Stock
Activity of Shares [Roll Forward]
Preferred stock, shares outstanding (in shares)	0	0
Conversions of convertible preferred stock (in shares)	0	0
Preferred stock, shares outstanding (in shares)	3,725,720	0
Class A-4 Convertible Preferred Stock | 2020 Closing
Activity of Shares [Roll Forward]
Shares issued (in shares)		0
Class A-4 Convertible Preferred Stock | 2021 Closing
Activity of Shares [Roll Forward]
Shares issued (in shares)	3,726,000
Warrants
Activity of Shares [Roll Forward]
Warrants outstanding (in shares)	66,038,000	46,774,000
Conversions of convertible preferred stock (in shares)	(4,170,000)	(1,039,000)
Warrants outstanding (in shares)	61,868,000	66,038,000
Warrants | 2020 Closing
Activity of Shares [Roll Forward]
Warrants issued (in shares)		20,303,000
Warrants | 2021 Closing
Activity of Shares [Roll Forward]
Warrants issued (in shares)	0
Common stock
Activity of Shares [Roll Forward]
Common stock, shares outstanding (in shares)
Conversions of convertible preferred stock (in shares)	(3,525,000)	(21,493,000)
Common stock, shares outstanding (in shares)
Common stock | 2020 Closing
Activity of Shares [Roll Forward]
Shares issued (in shares)		24,342,000
Common stock | 2021 Closing
Activity of Shares [Roll Forward]
Shares issued (in shares)	58,923,000

Stockholders' Equity - ATM Offe

Stockholders' Equity - ATM Offerring (Details) - At The Moment - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Aug. 10, 2021	Dec. 12, 2018
Class of Stock [Line Items]
Commission fee rate				3.00%
Number of shares issued (in shares)	16,017,131	492,268
Consideration received on transaction	$ 20.7	$ 0.3
Payments for commissions	0.7	$ 0.1
Amount eligible to be drawn down under the ATM	$ 50		$ 50

Stockholders' Equity - Shares R

Stockholders' Equity - Shares Reserved for Future Issuance (Details) - shares	Dec. 31, 2021	Nov. 23, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock options outstanding (in shares)	8,661,000
Total common shares reserved for future issuance (in shares)	130,872,000
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)	2,164,000
Common stock available for future grant under the Inducement Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for future grant (in shares)	1,800,000
Total common shares reserved for future issuance (in shares)		2,000,000
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for future grant (in shares)	259,000
RSUs outstanding
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
RSUs outstanding (in shares)	401,000
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)	2,567,000
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)	13,308,000
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)	2,587,000
Class A-4 Convertible Preferred Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Preferred stock, shares outstanding (in shares)	37,257,000
2019 PIPE Initial Closing warrants
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Warrants outstanding (in shares)	12,778,000
2019 PIPE Milestone Closing warrants
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Warrants outstanding (in shares)	30,595,000
2020 PIPE warrants
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Warrants outstanding (in shares)	18,495,000

Stockholders' Equity - Stock Op

Stockholders' Equity - Stock Option Activity (Details) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2021USD ($)$ / sharesshares
Number of options
Options outstanding, ending period (in shares)	8,661
Stock options
Number of options
Options outstanding, beginning period (in shares)	6,813
Granted (in shares)	3,351
Exercised (in shares)	(28)
Canceled/forfeited/expired (in shares)	(1,475)
Options outstanding, ending period (in shares)	8,661
Vested and Exercisable (in shares)	3,494
Weighted average exercise price
Options outstanding, beginning period (in dollars per share) | $ / shares	$ 1.10
Granted (in dollars per share) | $ / shares	1.40
Exercised (in dollars per share) | $ / shares	0.96
Canceled/forfeited/expired (in dollars per share) | $ / shares	1.36
Options outstanding, ending period (in dollars per share) | $ / shares	1.17
Exercisable (in dollars per share) | $ / shares	$ 1.22
Weighted average remaining contractual term
Options outstanding	8 years 2 months 26 days
Exercisable	7 years 11 months 4 days
Aggregate intrinsic value
Options outstanding | $	$ 0
Exercisable | $	$ 0

Stockholders' Equity - Share _2

Stockholders' Equity - Share Activity and Employee Stock Purchase Plan Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Class of Stock [Line Items]
Proceeds from stock options exercised	$ 26	$ 5
Shares issued (in shares)	11,619
Stock options
Class of Stock [Line Items]
Weighted average grant date fair value of employee stock options (in dollars per share)	$ 1.07	$ 0.91
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	$ 2,100
Weighted-average recognition period of compensation cost related to non-vested awards not yet recognized	1 year 7 months 6 days
RSUs outstanding
Class of Stock [Line Items]
Compensation cost related to non-vested awards not yet recognized	$ 200
Weighted-average recognition period of compensation cost related to non-vested awards not yet recognized	4 months 24 days
Employee Stock Purchase Plan 2012
Class of Stock [Line Items]
Shares issued (in shares)	108,565
Common stock shares reserved for future issuance and authorized for purchase (in shares)	259,402
Employee Stock Purchase Plan | 2012 Purchase Plan
Class of Stock [Line Items]
Discount rate from fair value on purchase date that participants pay for shares	15.00%
Offering period	6 months
Percentage of fair market value of common stock	85.00%

Stockholders' Equity - RSU Acti

Stockholders' Equity - RSU Activity (Details) - RSUs outstanding $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2021USD ($)$ / sharesshares
Number of options
RSUs outstanding, beginning balance (in shares) | shares	34
Granted (in shares) | shares	446
Vested (in shares) | shares	(34)
Canceled/forfeited/expired (in shares) | shares	(45)
RSUs outstanding, ending balance (in shares) | shares	401
Weighted average grant date fair value
RSUs outstanding, beginning balance (usd per share) | $ / shares	$ 1.50
Granted (usd per share) | $ / shares	0.95
Vested (usd per share) | $ / shares	1.50
Forfeited (usd per share) | $ / shares	0.96
RSUs outstanding, ending balance (usd per share) | $ / shares	$ 0.95
Weighted average remaining contractual term	4 months 20 days
Aggregate intrinsic value | $	$ 126

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, 2021	Dec. 31, 2020
Stock options
Weighted average assumptions
Risk-free interest rate	1.00%	1.10%
Volatility	95.80%	95.40%
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	1.00%	1.40%
Volatility	95.70%	95.40%
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	0.10%	0.60%
Volatility	101.20%	98.00%
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, 2021	Dec. 31, 2020
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expenses	$ 2,923	$ 2,614
Research and development
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expenses	821	693
General and administrative
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expenses	$ 2,102	$ 1,921

Stockholders' Equity - Induceme

Stockholders' Equity - Inducement Plan (Details) - shares	Nov. 23, 2021	Dec. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common shares reserved for future issuance (in shares)		130,872,000
Inducement Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common shares reserved for future issuance (in shares)	2,000,000
Vesting period	4 years
Shares available for future grant (in shares)		1,800,000
Inducement Plan | First anniversary of the effective date
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting percentage	25.00%
Inducement Plan | Remaining 75%, vesting monthly
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period for remaining vesting rights	36 months

Defined Contribution Plan (Deta

Defined Contribution Plan (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
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, 2021	Dec. 31, 2020
Current:
Federal	$ 0	$ (13)
State	1	1
Current income tax expense (benefit), total	1	(12)
Deferred:
Federal	0	12
State	0	0
Deferred income tax expense (benefit), total	0	12
Income tax expense	$ 1	$ 0

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, 2021	Dec. 31, 2020
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Expected income tax benefit at federal statutory tax rate	$ (5,840)	$ (3,309)
State income taxes, net of federal benefit	1	(927)
Tax credits	(1,180)	(1,216)
Change in valuation allowance	6,659	2,606
Return to provision adjustments	80	(14)
Stock compensation	243	1,644
Reserve for uncertain tax positions	176	1,179
Other	(138)	37
Income tax expense	$ 1	$ 0

Income Taxes - Components of De

Income Taxes - Components of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Deferred tax assets:
Net operating loss carryovers	$ 87,877	$ 82,747
Research and development and other tax credits	35,344	34,337
Intangibles and property and equipment basis difference	607	715
Stock compensation expense	587	283
Lease liability	631	88
Other	564	281
Total deferred tax assets	125,610	118,451
Total deferred tax liabilities	(782)	(282)
Net deferred tax asset	124,828	118,169
Valuation allowance	(124,828)	(118,169)
Net deferred tax asset	$ 0	$ 0

Income Taxes - Narrative (Detai

Income Taxes - Narrative (Details) - USD ($)	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Operating Loss Carryforwards [Line Items]
Valuation allowance	$ 124,828,000	$ 118,169,000
Net operating loss carryovers	87,877,000	82,747,000
Unrecognized tax benefits	16,953,000	17,939,000	$ 16,573,000
Unrecognized tax benefits that would impact effective tax rate	13,700,000
Income tax penalties and interest accrued	0	0
Internal Revenue Service (IRS)
Operating Loss Carryforwards [Line Items]
Net operating loss carryovers		366,800,000
Internal Revenue Service (IRS) | Research Tax Credit Carryforward
Operating Loss Carryforwards [Line Items]
Research and development tax credits carryforward		33,000,000
California
Operating Loss Carryforwards [Line Items]
Net operating loss carryovers		276,000,000
California | Research Tax Credit Carryforward
Operating Loss Carryforwards [Line Items]
Research and development tax credits carryforward		$ 9,700,000
After 2017, No Expiration | Internal Revenue Service (IRS)
Operating Loss Carryforwards [Line Items]
Net operating loss carryovers	$ 103,400,000

Income Taxes - Changes in Amoun

Income Taxes - Changes in Amount of Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Beginning balance of unrecognized tax benefits	$ 17,939	$ 16,573
Decrease for prior year tax positions	(1,174)	(1)
Increase for current year tax positions	188	1,367
Total	$ 16,953	$ 17,939

Leases - Narrative (Details)

Leases - Narrative (Details) $ in Thousands	Feb. 11, 2021USD ($)ft²contract	Dec. 31, 2021USD ($)	Apr. 30, 2021USD ($)	Dec. 31, 2020USD ($)	Jul. 01, 2019USD ($)	Jun. 19, 2019USD ($)ft²
Lessee, Lease, Description [Line Items]
Liability to be paid		$ 754
Operating lease, liability, payments, due year two		776
Operating lease, right-of-use asset		2,564		$ 253
Operating lease payments due		$ 3,431
Prior Premises
Lessee, Lease, Description [Line Items]
Net rentable area | ft²						8,727
Term of lease						2 years 6 months
Liability to be paid						$ 400
Operating lease, liability, payments, due year two						$ 400
Initial direct cost liability					$ 800
Operating lease, right-of-use asset					600
Deferred credit, operating lease liability					$ 200
Campus Point Lease
Lessee, Lease, Description [Line Items]
Term of lease	60 months
Initial direct cost liability	$ 3,200		$ 100
Operating lease, right-of-use asset	3,000		100
Deferred credit, operating lease liability	$ 200
Rented area | ft²	13,438
Operating lease payments due	$ 3,800
Nonrefundable lease cost for assignment of lease	$ 60
Number of operating lease contracts | contract	3
Deferred cost of liability			$ 200

Leases - Lease Asset and Liabil

Leases - Lease Asset and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Assets
Operating	$ 2,564	$ 253
Financing	0	288
Total ROU assets	2,564	541
Current:
Operating	589	417
Financing	0	56
Long-term:
Operating	2,417	0
Financing	0	0
Total lease liabilities	$ 3,006	$ 473
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	Other assets	Other assets
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	Property and equipment, net	Property and equipment, net
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	Other current liabilities	Other current liabilities
Finance Lease, Liability, Current, Statement of Financial Position [Extensible List]	Other current liabilities	Other current liabilities
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	Operating	Operating
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	Operating	Operating

Leases - Lease Cost (Details)

Leases - Lease Cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Leases [Abstract]
Operating lease cost	$ 746	$ 278
Finance lease cost:
Amortization of right-of-use assets	29	178
Interest expense on lease liabilities	1	10
Total finance lease cost	30	188
Cash payment information:
Cash payment information:	468	429
Operating cash used for finance leases	1	10
Financing cash used for finance leases	80	277
Total cash paid for amounts included in the measurement of lease liabilities	549	716
Operating lease liabilities arising from obtaining right-of-use assets	$ 3,006	$ 0
Weighted-average remaining lease term (years) - operating leases	4 years 3 months 18 days	1 year
Weighted-average remaining lease term (years) - finance leases	0 years	2 months 12 days
Weighted-average discount rate - operating leases	6.00%	10.90%
Weighted-average discount rate - finance leases	0.00%	4.90%

Leases - Future Lease Payments

Leases - Future Lease Payments Under Operating and Finance Leases (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Operating Leases
2022	$ 754
2023	776
2024	800
2025	824
2026	277
Total operating lease payments	3,431
Less: amount representing interest	(425)
Present value of obligations under operating lease	3,006
Less: current portion	(589)	$ (417)
Long-term operating lease obligations	$ 2,417	$ 0