Kezar Life Sciences (KZR) 10-Q 6 Aug 20 2020 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2020	Aug. 04, 2020
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q2
Trading Symbol	KZR
Entity Registrant Name	Kezar Life Sciences, Inc.
Entity Central Index Key	0001645666
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Emerging Growth Company	true
Entity Small Business	true
Entity Ex Transition Period	true
Entity Common Stock, Shares Outstanding		46,256,284
Entity Current Reporting Status	Yes
Entity Shell Company	false
Entity File Number	001-38542
Entity Tax Identification Number	47-3366145
Entity Address, Address Line One	4000 Shoreline Court
Entity Address, Address Line Two	Suite 300
Entity Address, City or Town	South San Francisco
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94080
City Area Code	650
Local Phone Number	822-5600
Document Quarterly Report	true
Document Transition Report	false
Entity Interactive Data Current	Yes
Title of 12(b) Security	Common Stock, $0.001 par value
Security Exchange Name	NASDAQ
Entity Incorporation, State or Country Code	DE

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 17,296	$ 14,951
Marketable securities	140,175	63,255
Prepaid expenses	1,780	1,878
Other current assets	1,312	1,048
Total current assets	160,563	81,132
Property and equipment, net	3,902	4,282
Operating lease right-of-use asset	3,576	3,817
Other assets	282	282
Total assets	168,323	89,513
Current liabilities:
Accounts payable	1,007	823
Accrued liabilities	3,027	4,218
Operating lease liabilities, current	969	900
Other liabilities, current	42	62
Total current liabilities	5,045	6,003
Operating lease liabilities, noncurrent	4,960	5,464
Total liabilities	10,005	11,467
Stockholders' equity:
Common stock, $0.001 par value, 125,000,000 shares authorized as of June 30, 2020 (unaudited) and December 31, 2019; 45,826,798 and 19,208,077 shares issued and outstanding as of June 30, 2020 (unaudited) and December 31, 2019, respectively	46	19
Preferred stock, $0.001 par value, 10,000,000 shares authorized, zero shares issued and outstanding as of June 30, 2020 (unaudited) and December 31, 2019
Additional paid-in capital	262,041	162,505
Accumulated other comprehensive income(loss)	25	(196)
Accumulated deficit	(103,794)	(84,282)
Total stockholders' equity	158,318	78,046
Total liabilities and stockholders' equity	$ 168,323	$ 89,513

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Jun. 30, 2020	Dec. 31, 2019
Statement Of Financial Position [Abstract]
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	125,000,000	125,000,000
Common stock, shares issued	45,826,798	19,208,077
Common stock, shares outstanding	45,826,798	19,208,077
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Operating expenses:
Research and development	$ 7,148	$ 6,925	$ 14,605	$ 12,852
General and administrative	2,705	2,430	5,726	4,812
Total operating expenses	9,853	9,355	20,331	17,664
Loss from operations	(9,853)	(9,355)	(20,331)	(17,664)
Interest income	353	637	819	1,304
Net loss	$ (9,500)	$ (8,718)	$ (19,512)	$ (16,360)
Net loss per common share, basic and diluted	$ (0.22)	$ (0.46)	$ (0.51)	$ (0.86)
Weighted-average shares used to compute net loss per common share, basic and diluted	42,936,991	19,073,830	37,902,294	19,058,263

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (9,500)	$ (8,718)	$ (19,512)	$ (16,360)
Other comprehensive income (loss)
Foreign currency translation adjustments	97	(49)	(20)	(41)
Unrealized gain on marketable securities	50	23	241	88
Total other comprehensive income (loss), net of tax	147	(26)	221	47
Comprehensive loss	$ (9,353)	$ (8,744)	$ (19,291)	$ (16,313)

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Balance at Dec. 31, 2018	$ 108,797	$ 19	$ 158,176	$ (203)	$ (49,195)
Balance, shares at Dec. 31, 2018		19,114,421
Issuance of common stock under employee stock incentive plans	4		4
Issuance of common stock under employee stock incentive plans, shares		4,000
Vesting related to shares of common stock issued pursuant to early exercises	12		12
Stock-based compensation expense	901		901
Other comprehensive income (loss)	73			73
Net loss	(7,642)				(7,642)
Balance at Mar. 31, 2019	102,145	$ 19	159,093	(130)	(56,837)
Balance, shares at Mar. 31, 2019		19,118,421
Balance at Dec. 31, 2018	108,797	$ 19	158,176	(203)	(49,195)
Balance, shares at Dec. 31, 2018		19,114,421
Other comprehensive income (loss)	47
Net loss	(16,360)
Balance at Jun. 30, 2019	94,603	$ 19	160,295	(156)	(65,555)
Balance, shares at Jun. 30, 2019		19,132,645
Balance at Mar. 31, 2019	102,145	$ 19	159,093	(130)	(56,837)
Balance, shares at Mar. 31, 2019		19,118,421
Issuance of common stock under employee stock incentive plans	180		180
Issuance of common stock under employee stock incentive plans, shares		14,224
Vesting related to shares of common stock issued pursuant to early exercises	13		13
Stock-based compensation expense	1,009		1,009
Other comprehensive income (loss)	(26)			(26)
Net loss	(8,718)				(8,718)
Balance at Jun. 30, 2019	94,603	$ 19	160,295	(156)	(65,555)
Balance, shares at Jun. 30, 2019		19,132,645
Balance at Dec. 31, 2019	78,046	$ 19	162,505	(196)	(84,282)
Balance, shares at Dec. 31, 2019		19,208,077
Issuance of common stock and pre-funded warrants through underwritten offering	53,360	$ 19	53,341
Issuance of common stock and pre-funded warrants through underwritten offering, shares		18,965,385
Issuance of common stock under employee stock incentive plans	3		3
Issuance of common stock under employee stock incentive plans, shares		3,000
Vesting related to shares of common stock issued pursuant to early exercises	10		10
Stock-based compensation expense	1,173		1,173
Other comprehensive income (loss)	74			74
Net loss	(10,012)				(10,012)
Balance at Mar. 31, 2020	122,654	$ 38	217,032	(122)	(94,294)
Balance, shares at Mar. 31, 2020		38,176,462
Balance at Dec. 31, 2019	78,046	$ 19	162,505	(196)	(84,282)
Balance, shares at Dec. 31, 2019		19,208,077
Other comprehensive income (loss)	221
Net loss	(19,512)
Balance at Jun. 30, 2020	158,318	$ 46	262,041	25	(103,794)
Balance, shares at Jun. 30, 2020		45,826,798
Balance at Mar. 31, 2020	122,654	$ 38	217,032	(122)	(94,294)
Balance, shares at Mar. 31, 2020		38,176,462
Issuance of common stock and pre-funded warrants through underwritten offering	43,663	$ 8	43,655
Issuance of common stock and pre-funded warrants through underwritten offering, shares		7,590,909
Issuance of common stock under employee stock incentive plans	125		125
Issuance of common stock under employee stock incentive plans, shares		59,427
Vesting related to shares of common stock issued pursuant to early exercises	10		10
Stock-based compensation expense	1,219		1,219
Other comprehensive income (loss)	147			147
Net loss	(9,500)				(9,500)
Balance at Jun. 30, 2020	$ 158,318	$ 46	$ 262,041	$ 25	$ (103,794)
Balance, shares at Jun. 30, 2020		45,826,798

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Stockholders' Equity (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Jun. 30, 2020	Mar. 31, 2020
Statement Of Stockholders Equity [Abstract]
Issuance of common stock and pre-funded warrants through underwritten offerings, offering costs	$ 3,087	$ 3,447

Condensed Consolidated Statem_5

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Cash flows from operating activities:
Net loss	$ (19,512)	$ (16,360)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	731	628
Stock-based compensation	2,392	1,910
Amortization of premiums and discounts on marketable securities	(183)	(695)
Changes in operating assets and liabilities
Prepaid expenses, other current assets and other long-term assets	(166)	(440)
Accounts payable, accrued liabilities and other current liabilities	(1,219)	919
Operating lease liabilities	(435)	(374)
Net cash used in operating activities	(18,392)	(14,412)
Cash flows from investing activities:
Purchases of property and equipment	(110)	(523)
Purchases of marketable securities	(143,780)	(59,255)
Maturities of marketable securities	67,284	62,896
Net cash (used in) provided by investing activities	(76,606)	3,118
Cash flows from financing activities:
Proceeds from sale of common stock and pre-funded warrants in underwritten offerings, net of offering costs	97,235
Proceeds from issuance of common stock under employee stock incentive plans	128	184
Net cash provided by financing activities	97,363	184
Effect of exchange rate changes on cash and cash equivalents	(20)	(41)
Net increase (decrease) in cash and cash equivalents	2,345	(11,151)
Cash and cash equivalents at the beginning of period	14,951	24,182
Cash and cash equivalents at the end of period	17,296	13,031
Supplemental disclosures of noncash investing and financing information:
Reclassification of employee stock liability to equity upon vesting	20	25
Purchase of property and equipment in accounts payable		$ 23
Unpaid offering costs in accrued liabilities	$ 212

Organization and Description of

Organization and Description of the Business	6 Months Ended
	Jun. 30, 2020
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Organization and Description of the Business	1. Organization and Description of the Business Description of Business Kezar Life Sciences, Inc. (the “Company,” Liquidity Since commencing operations in mid-2015, substantially all of the Company’s efforts have been focused on research, development, and the advancement of the Company’s lead product candidate, KZR-616. The Company’s ultimate success depends on the outcome of the ongoing research and development activities. The Company has not yet generated product sales and as a result has experienced operating losses since inception and had an accumulated deficit of $103.8 million as of June 30, 2020. The Company expects to incur additional losses in the future to conduct research and development and will need to raise additional capital to fully implement management’s business plan. The Company intends to raise such capital through the issuance of additional equity, and potentially through borrowings, strategic alliances with partner companies and other licensing transactions. However, if such financing is not available at adequate levels, the Company may need to reevaluate its operating plans. Management believes that its existing cash, cash equivalents and marketable securities will be sufficient to fund the Company’s cash requirements for at least 12 months following the issuance of these financial statements. In July 2019, the Company entered into an Open Market Sale Agreement SM Accordingly, the $50.0 million of securities unsold pursuant to the ATM Agreement became available for issuance on the Company’s shelf registration statement on Form S-3 (File No. 333-232542). On February 4, 2020, the Company completed an underwritten public offering of 18,965,385 shares of its common stock, which includes the full exercise of the underwriters’ option to purchase additional shares of common stock, and, to certain investors in lieu thereof, pre-funded warrants to purchase 2,884,615 shares of its common stock at an exercise price of $0.001 per share (the “February Offering”). The public offering price of our common stock was $2.60 per share and the public offering price of each pre-funded warrant was $2.599 per underlying share. The net proceeds from the February offering were approximately $53.4 million, after deducting underwriting discounts and commissions and other offering expenses paid by us. The Company’s existing stockholder, Morningside Ventures Investments Ltd, together with its affiliate, and certain of the Company’s officers and directors purchased an aggregate of approximately $22.9 million of common stock in the offering. On June 11, 2020, the Company completed an underwritten public offering of 7,590,909 shares of its common stock and, to certain investors in lieu thereof, pre-funded warrants to purchase 909,091 shares of its common stock at an exercise price of $0.001 per share (the “June Offering”). The public offering price of our common stock was $5.50 per share and the public offering price of each pre-funded warrant was $5.499 per underlying share. The net proceeds from the June Offering were approximately $43.7 million, after deducting underwriting discounts and commissions and other offering expenses paid by us. In July 2020, the underwriters exercised an option to purchase an additional 427,707 shares of common stock, for net proceeds of approximately $2.2 million , after deducting underwriting discounts and commissions

Summary of Significant Accounti

Summary of Significant Accounting Policies	6 Months Ended
	Jun. 30, 2020
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Significant Accounting Policies The Company’s significant accounting policies are disclosed in the audited consolidated financial statements for the year ended December 31, 2019 and the notes thereto, which are included in the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2019, filed with the U.S. Securities and Exchange Commission (“SEC”) on March 12, 2020 (the “Annual Report”), and there ha ve been no material changes during the six months ended June 30, 2020. Basis of Presentation and Consolidation The condensed consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States (“GAAP”) and include the Company’s accounts and those of its wholly owned Australian subsidiary, The condensed consolidated balance sheet at December 31, 2019 has been derived from the audited consolidated financial statements at that date but does not include all information and footnotes required by GAAP for complete financial statements. These unaudited condensed consolidated financial statements should be read in conjunction with the audited financial statements included in the Annual Report. Unaudited Interim Condensed Consolidated Financial Statements The accompanying financial information as of June 30, 2020 is unaudited. The condensed consolidated financial statements included in this report reflect all adjustments (consisting only of normal recurring adjustments) that our management considers necessary for the fair statement of the results of operations for the interim periods covered and of our financial condition at the date of the interim balance sheet. The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with GAAP for interim financial information. Accordingly, they do not include all of the information and notes required by GAAP for complete financial statements. The results for interim periods are not necessarily indicative of the results for the entire year or any other interim period. The accompanying condensed consolidated financial statements and related financial information should be read in conjunction with the audited financial statements and the related notes thereto included in our Annual Report. Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting period. Significant items subject to such estimates and assumptions include the useful lives of fixed assets, stock-based compensation, and accrued research and development costs. Management bases its estimates on historical experience and on various other market-specific relevant assumptions that management believes to be reasonable under the circumstances. Actual results may differ from those estimates. We also anticipate that the COVID-19 pandemic will have an impact on the clinical and pre-clinical development timelines for our clinical and pre-clinical programs. Estimates and assumptions about future events and their effects cannot be determined with certainty and therefore require the exercise of judgment. As of the date of issuance of these financial statements, the Company is not aware of any specific event or circumstance that would require the Company to update its estimates, assumptions and judgments or revise the carrying value of its assets or liabilities. These estimates may change as new events occur and additional information is obtained and are recognized in the consolidated financial statements as soon as they become known. Actual results could differ from those estimates and any such differences may be material to the Company’s financial statements. Significant Risks and Uncertainties With the global spread of the ongoing COVID-19 pandemic in the first quarter of 2020, we have implemented business continuity plans designed to address and mitigate the impact of the COVID-19 pandemic on our business. The extent to which the COVID-19 pandemic impacts our business, our pre-clinical and clinical development and regulatory efforts, our corporate development objectives and the value of and market for our common stock, will depend on future developments that are highly uncertain and cannot be predicted with confidence at this time, such as the ultimate duration of the pandemic, travel restrictions, quarantines, social distancing and business closure requirements in the United States, Europe and other countries, and the effectiveness of actions taken globally to contain and treat the disease. The global economic slowdown, the overall disruption of global healthcare systems and the other risks and uncertainties associated with the pandemic could have a material adverse effect on our business, financial condition, results of operations and growth prospects. In addition, we are subject to other challenges and risks specific to our business and our ability to execute on our strategy, as well as risks and uncertainties common to companies in the biotechnology industry with development operations, including, without limitation, risks and uncertainties associated with: obtaining regulatory feedback regarding our product candidates; delays or problems in the supply of our product candidates; loss of single source suppliers or their failure to comply with manufacturing regulations; identifying, acquiring or in-licensing additional technologies or product candidates; clinical development and the inherent uncertainty of clinical success; the challenges of protecting and enhancing our intellectual property rights; and complying with applicable regulatory requirements. In addition, to the extent the ongoing COVID-19 pandemic adversely affects our business and results of operations, it may also have the effect of heightening many of the other risks and uncertainties discussed above. Cash and Cash Equivalents The Company considers all highly liquid investments with original maturities of three months or less at the time of purchase to be cash equivalents. Cash equivalents are stated at fair value. Marketable Securities All marketable securities have been classified as “available-for-sale” in accordance with the Company’s investment policy and cash management strategy. Short-term marketable securities mature within one-year from the balance sheet date. Investments in marketable securities are recorded at fair value, with any unrealized gains and losses reported within accumulated other comprehensive income as a separate component of stockholders’ deficit until realized or until a determination is made that an other-than-temporary decline in market value has occurred. If a credit loss does exist for available-for-sale debt securities and should be recognized, an allowance will be recorded rather than a write-down of the amortized cost basis. The amortized cost of debt securities is adjusted for amortization of premiums and accretion of discounts to maturity. Such amortization and accretion, together with interest on securities, are included in interest income on the Company’s condensed consolidated statements of operations. Leases At lease commencement, the Company records a lease liability based on the present value of lease payments over the expected lease term. The Company calculates the present value of lease payments using the discount rate implicit in the lease, unless that rate cannot be readily determined. In that case, the Company uses its incremental borrowing rate, which is the rate of interest that the Company would have to pay to borrow on a collateralized basis an amount equal to the lease payments over the expected lease term. The Company records a corresponding right-of-use (“ROU”) lease asset based on the lease liability, adjusted for any lease incentives received and any initial direct costs paid to the lessor prior to the lease commencement date. After lease commencement, the Company measures its leases as follows: (i) the lease liability based on the present value of the remaining lease payments using the discount rate determined at lease commencement; and (ii) the ROU lease asset based on the remeasured lease liability, adjusted for any unamortized lease incentives received, any unamortized initial direct costs and the cumulative difference between rent expense and amounts paid under the lease agreement. Any lease incentives received and any initial direct costs are amortized on a straight-line basis over the expected lease term. Rent expense is recorded on a straight-line basis over the expected lease term. The Company elected the short-term lease recognition exemption for all leases that qualify. This means, for those leases that qualify, the Company will not recognize ROU assets or lease liabilities, and this includes not recognizing ROU assets or lease liabilities for existing short-term leases of those assets in transition. The Company did not elect to apply the practical expedient to not separate lease and non-lease components for all of its leases. Accounting Pronouncements Adopted in 2020 In June 2016, the FASB issued ASU No. 2016-13 , Financial Instruments-Credit Losses (Topic 326) The Company adopted the new standard using the modified retrospective approach as of January 1, 2020 and the adoption In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework-Changes to the Disclosure Requirements for Fair Value Measurement The amendment of ASU No. 2018-13 removes disclosure requirements from Topic 820 in the areas of: (1) the amount of and reasons for transfers between Level 1 and Level 2 of the fair value hierarchy; (2) the policy for timing of transfers between levels; and (3) the valuation processes for Level 3 fair value measurements. In December 2019, the FASB issued ASU No. 2019-12, Income Taxes: Simplifying the Accounting for Income Taxes Income Taxes. As part of the simplification, along with other exceptions, it removes the exception to the incremental approach for intraperiod tax allocation in the event of a loss from continuing operations and income or a gain from other items. he adoption did not have a material impact on its

Fair Value Measurements

Fair Value Measurements	6 Months Ended
	Jun. 30, 2020
Fair Value Disclosures [Abstract]
Fair Value Measurements	3. Fair Value Measurements Financial assets and liabilities are recorded at fair value. The carrying amount of certain financial instruments, including cash and cash equivalents, marketable securities, other current assets, accounts payable and accrued liabilities, approximate fair value due to their relatively short maturities. Assets and liabilities recorded at fair value on a recurring basis in the condensed consolidated balance sheets are categorized based upon the level of judgment associated with the inputs used to measure their fair values. Fair value is defined as the exchange price that would be received for an asset or an exit price that would be paid to transfer a liability in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. The authoritative guidance on fair value measurements establishes a three-tier fair value hierarchy for disclosure of fair value measurements as follows: Level 1 : Quoted prices in active markets for identical assets or liabilities. Level 2 : Observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities, quoted prices in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3 : Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. Assets and liabilities measured at fair value are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. The Company’s assessment of the significance of a particular input to the fair value measurement in its entirety requires management to make judgments and consider factors specific to the asset or liability. The Company applies fair value accounting for all financial assets and liabilities and nonfinancial assets and liabilities that are required to be recognized or disclosed at fair value in the financial statements. The Company determines the fair value of Level 1 assets using quoted prices in active markets for identical assets. The Company reviews trading activity and pricing for Level 2 investments as of each measurement date. Level 2 inputs, which are obtained from various third-party data providers, represent quoted prices for similar assets in active markets and were derived from observable market data, or, if not directly observable, were derived from or corroborated by other observable market data. In certain cases, where there is limited activity or less transparency around inputs to valuation, securities are classified as Level 3 within the valuation hierarchy. The Company does not have any assets or liabilities measured using Level 3 inputs as of June 30, 2020 or December 31, 2019. The following table summarizes the Company’s financial assets measured at fair value on a recurring basis and classified under the appropriate level of the fair value hierarchy as described above (in thousands): June 30, 2020 Total Level 1 Level 2 Level 3 Financial Assets: Money market funds $ 17,100 $ 17,100 $ — $ — U.S. Treasury securities 75,788 75,788 — — Commercial paper 30,906 — 30,906 — Corporate debt securities 14,056 — 14,056 — U.S. agency bonds 19,425 — 19,425 — Total $ 157,275 $ 92,888 $ 64,387 $ — December 31, 2019 Total Level 1 Level 2 Level 3 Financial Assets: Money market funds $ 14,731 $ 14,731 $ — $ — U.S. Treasury securities 5,285 5,285 — — Commercial paper 15,186 — 15,186 — Corporate debt securities 17,171 — 17,171 — U.S. agency bonds 25,613 — 25,613 — Total $ 77,986 $ 20,016 $ 57,970 $ —

Available-for-Sale Securities

Available-for-Sale Securities	6 Months Ended
	Jun. 30, 2020
Investments Debt And Equity Securities [Abstract]
Available-for-Sale Securities	4. Available-for-Sale Securities The following table is a summary of available-for-sale securities recorded in cash and cash equivalents or marketable securities in the Company’s condensed consolidated balance sheets (in thousands): June 30, 2020 Amortized Cost Unrealized Gains Unrealized Losses Fair Value Financial Assets Money market funds $ 17,100 $ — $ — $ 17,100 U.S. Treasury securities 75,761 28 (1 ) 75,788 Commercial paper 30,791 115 — 30,906 Corporate debt securities 13,965 91 — 14,056 U.S. agency bonds 19,385 40 — 19,425 Total $ 157,002 $ 274 $ (1 ) $ 157,275 December 31, 2019 Amortized Cost Unrealized Gains Unrealized Losses Fair Value Financial Assets Money market funds $ 14,731 $ — $ — $ 14,731 U.S. Treasury securities 5,285 1 (1 ) 5,285 Commercial paper 15,174 12 — 15,186 Corporate debt securities 17,168 3 — 17,171 U.S. agency bonds 25,597 16 — 25,613 Total $ 77,955 $ 32 $ (1 ) $ 77,986 As of June 30, 2020 and December 31, 2019, the Company has not recognized an allowance for credit losses on any securities in an unrealized loss position. The following table displays additional information regarding gross unrealized losses and fair value by major security type for available-for-sale securities in an unrealized loss position as of June 30, 2020 and December 31, 2019 (in thousands): June 30, 2020 December 31, 2019 Less than 12 consecutive months Less than 12 consecutive months Fair Value Unrealized Losses Fair Value Unrealized Losses U.S. Treasury securities $ 8,117 $ (1 ) $ 4,535 $ (1 ) Total $ 8,117 $ (1 ) $ 4,535 $ (1 ) The Company currently does not intend to sell these securities prior to maturity and does not consider these investments to be other-than-temporarily impaired at June 30, 2020. There were no sales of available-for-sale securities in any of the periods presented. As of June 30, 2020, the amortized cost and estimated fair value of the Company’s available-for-sale securities by contractual maturity are shown below (in thousands): Amortized Estimated Cost Fair Value Available-for-sale securities maturing: In one year or less $ 157,002 $ 157,275 Total available-for-sale securities $ 157,002 $ 157,275

Balance Sheet Components

Balance Sheet Components	6 Months Ended
	Jun. 30, 2020
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Balance Sheet Components	5. Balance Sheet Components Property and Equipment, Net Property and equipment consisted of the following (in thousands): June 30, 2020 December 31, 2019 Leasehold improvements $ 3,268 $ 3,268 Furniture, laboratory and office equipment 2,666 2,578 Computer equipment 275 253 Total property and equipment 6,209 6,099 Less accumulated depreciation and amortization (2,307 ) (1,817 ) Property and equipment, net $ 3,902 $ 4,282 Depreciation expense was $0.3 million and $0.5 million for the three and six months ended June 30, 2020, respectively, compared to $0.2 million and $0.4 million for the three and six months ended June 30, 2019, respectively. Accrued Liabilities Accrued liabilities consisted of the following (in thousands): June 30, 2020 December 31, 2019 Accrued preclinical and research costs $ 759 $ 1,687 Accrued clinical costs 825 1,027 Accrued employee-related costs 973 1,293 Accrued professional services 296 53 Other 174 158 Total accrued liabilities $ 3,027 $ 4,218

Lease

Lease	6 Months Ended
	Jun. 30, 2020
Leases [Abstract]
Lease	6. Lease In August 2017, the Company entered into a lease agreement to lease 24,357 square feet of combination laboratory and office space in South San Francisco, California. This lease expires in February 2025 The contractually specified minimum rent and annual rent increases for the operating lease are included in the measurement of the ROU asset and related lease liabilities. Under the lease arrangement, we may be required to pay directly, or reimburse the lessor for real estate taxes, insurance, utilities, maintenance and other operating costs. Such amounts are generally variable and therefore not included in the measurement of the ROU asset and related lease liability but are instead recognized as variable lease expense in our Condensed Consolidated Statements of Operations when they are incurred. The operating lease agreement has one option to extend the lease term for a period of five years at the fair market rate at the time of the extension. The option to extend the lease was not recognized as part of the Company’s lease liability and ROU asset as the Company determined the renewal rent costs are uncertain and the option is not reasonably certain to be exercised. Because the rate implicit in the lease is not readily determinable, the Company uses its incremental borrowing rate to determine the present value of the lease payments. The Company recorded lease liabilities and ROU asset for its office lease based on the present value of lease payments over the expected lease term. As of June 30, 2020, the weighted average remaining lease term was 4.67 years and the weighted average discount rate used to determine the operating lease liability was 10.0%. Information related to the Company’s ROU asset and related lease liabilities were as follows (in thousands): Three months ended June 30, 2020 Six months ended June 30, 2020 Cash paid for operating lease liabilities $ 224 $ 435 Operating lease costs 275 550 Variable lease costs 81 212 Maturities of lease liabilities as of June 30, 2020 were as follows for the years ending December 31: 2020 $ 752 2021 1,542 2022 1,588 2023 1,635 2024 1,684 Thereafter 282 Total undiscounted lease payments 7,483 Less: imputed interest (1,554 ) Total lease liabilities $ 5,929 Operating lease liabilities, current 969 Operating lease liabilities, noncurrent 4,960 Total operating lease liabilities $ 5,929

Pre-Funded Warrants

Pre-Funded Warrants	6 Months Ended
	Jun. 30, 2020
Equity [Abstract]
Pre-Funded Warrants	7. Pre-Funded Warrants On February 4, 2020, the Company completed an underwritten public offering of 18,965,385 shares of its common stock including the full exercise of the underwriters’ option to purchase additional shares of common stock, and pre-funded warrants to purchase 2,884,615 shares of its common stock. The public offering price of the common stock was $2.60 per share and the public offering price of the pre-funded warrants was $2.599 per underlying share. The net proceeds from the public offering were approximately $53.4 million, after deducting underwriting discounts and commissions and other offering expenses paid by the Company. On June 11, 2020, the Company completed an underwritten public offering of 7,590,909 shares of its common stock and pre-funded warrants to purchase 909,091 shares of its common stock. The public offering price of the common stock was $5.50 per share and the public offering price of the pre-funded warrants was $5.499 per underlying share. The net proceeds from the public offering were approximately $43.7 million after deducting underwriting discounts and commissions and other offering expenses paid by the Company. Each pre-funded warrant entitles the holder to purchase shares of common stock at an exercise price of $0.001 per share and expires 20 years from the date of issuance. These warrants were recorded as a component of stockholders’ equity within additional paid-in capital. Per the terms of the warrant agreement, a holder of the outstanding warrant is not entitled to exercise any portion of the pre-funded warrant if, upon exercise of such portion of the warrant, the holder’s ownership of our common stock (together with its affiliates) or the combined voting power of our securities beneficially owned by such holder (together with its affiliates) would exceed 9.99% after giving effect to the exercise (“Maximum Ownership Percentage”). Upon at least 61 days’ prior notice to us by the warrant holder, any warrant holder may increase or decrease the Maximum Ownership Percentage to any other percentage not to exceed 19.99%. As of June 30, 2020, no shares underlying the pre-funded warrants have been exercised. The following table represents a summary of the pre-funded warrants outstanding as of the date identified. Issue Date Classification Exercise Price Expiration Date Number of shares underlying warrants as of June 30, 2020 February 4, 2020 Equity $ 0.001 February 4, 2040 2,884,615 June 11, 2020 Equity $ 0.001 June 11, 2040 909,091 Total Outstanding 3,793,706

Stock-Based Compensation

Stock-Based Compensation	6 Months Ended
	Jun. 30, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation	8. Stock-Based Compensation Stock Incentive Plans 2018 Equity Incentive Plan In June 2018, the Company’s board of directors adopted and its stockholders approved the 2018 Equity Incentive Plan (the “2018 Plan”), which became effective as of June 20, 2018, at which point no further grants could be made under the 2015 Equity Incentive Plan (the “2015 Plan”) described below. Under the 2018 Plan, the Company may grant incentive stock options (“ISOs”), nonstatutory stock options (“NSOs”), stock appreciation rights, restricted stock awards, restricted stock units and other stock-based awards. As of June 30, 2020, options to purchase 2,648,968 shares of common stock were outstanding and 1,348,693 shares were available for future issuance under the 2018 Plan. Initially, subject to adjustment as provided in the 2018 Plan, the aggregate number of shares of the Company’s common stock authorized for issuance pursuant to stock awards under the 2018 Plan was 4,000,000 shares, which is the sum of (i) 1,600,692 shares plus (ii) the number of shares reserved and available for issuance under the 2015 Plan at the time the 2018 Plan became effective and (iii) the number of shares subject to stock options or other stock awards granted under the 2015 Plan that expire, terminate are forfeited or otherwise not issued, or are withheld to satisfy a tax withholding obligation in connection with an award or to satisfy a purchase or exercise price of an award (such as upon the expiration or termination of a stock award prior to vesting). The number of shares of the Company’s common stock reserved for issuance under the 2018 Plan automatically increases on January 1 of each year, beginning on January 1, 2019 and continuing through and including January 1, 2028, by 5% of the total number of shares of capital stock outstanding on December 31 of the preceding calendar year, or a lesser number of shares determined by the Company’s board of directors prior to such increase. The maximum number of shares that may be issued upon the exercise of ISOs under the 2018 Plan is 12,500,000 shares. 2015 Equity Incentive Plan The Company’s 2015 Plan provided for the granting of ISOs and NSOs to employees, directors and consultants at the discretion of its board of directors. The 2015 Plan was terminated as to future awards in June 2018, although it continues to govern the terms of options that remain outstanding under the 2015 Plan. No additional stock awards will be granted under the 2015 Plan, and all outstanding stock awards granted under the 2015 Plan that are repurchased, forfeited, expire or are cancelled will become available for grant under the 2018 Plan in accordance with its terms. Options granted under the 2015 Plan expire no later than 10 years from the date of grant. Options granted under the 2015 Plan vest over periods determined by the Company’s board of directors, generally over four years. The 2015 Plan allows for early exercise of certain options prior to vesting. Upon termination of employment, the unvested shares are subject to repurchase at the original exercise price. As of June 30, 2020 options to purchase 1,829,074 shares of common stock were outstanding under the 2015 Plan. 2018 Employee Stock Purchase Plan In June 2018, the Company’s board of directors adopted and its stockholders approved the 2018 Employee Stock Purchase Plan (the “ESPP”), which became effective as of June 20, 2018. The ESPP is intended to qualify as an “employee stock purchase plan” within the meaning of Section 423 of the U.S. Internal Revenue Code of 1986, as amended. The number of shares of common stock initially reserved for issuance under the ESPP was 200,000 shares. The ESPP provides for an annual increase on January 1 of each year, beginning on January 1, 2019 and continuing through and including January 1, 2028, equal to the lesser of (i) 1% of the shares of common stock outstanding on the last day of the prior fiscal year or (ii) 375,000 shares, or a lesser number of shares determined by the Company’s board of directors prior to such increase. As of June 30, 2020, 83,083 shares of common stock had been issued under the ESPP and 500,141 shares remained available for future issuance under the ESPP. The price per share of common stock to be paid by an ESPP participant on the applicable purchase date of an offering period shall be equal to 85% of the lesser of the fair market value of a share of common stock on (i) the applicable offering date or (ii) the applicable purchase date. The Company’s board of directors authorized an initial six-month offering period beginning on November 16, 2018 and ending on May 15, 2019. The Company’s board of directors has subsequently authorized additional six-month offering periods, with the most recent offering period beginning on May 16, 2020. Stock Option Activity The following table summarizes activity under the Company’s stock option plans and related information (in thousands, except share and per share amounts): Number of Options Outstanding Weighted Average Exercise Price Weighted Average Remaining Contractual Term (Years) Aggregate Intrinsic Value Outstanding at December 31, 2019 3,107,066 $ 7.19 8.2 $ 3,151 Options granted 1,389,476 $ 3.76 Options exercised (6,000 ) $ 0.90 $ 22 Options cancelled (12,500 ) $ 22.85 Outstanding at June 30, 2020 4,478,042 $ 6.09 8.3 $ 7,229 Vested and exercisable at June 30, 2020 1,950,185 $ 5.26 7.3 $ 4,066 The weighted average grant date fair value of options granted during the six months ended June 30, 2020 was $2.68 per share. The aggregate intrinsic value of exercised stock options during the three and six months ended June 30, 2020 was $12,000 and $22,000, respectively. The aggregate intrinsic value is calculated as the difference between the exercise price and the estimated fair value of the Company’s common stock at the date of exercise. Stock-Based Compensation Expense Total stock-based compensation expense recognized by function was as follows (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2020 2019 2020 2019 Research and development $ 518 $ 470 $ 982 $ 917 General and administrative 701 539 1,410 993 Total stock-based compensation expense $ 1,219 $ 1,009 $ 2,392 $ 1,910 As of June 30, 2020, the unrecognized stock-based compensation cost was $11.7 million with an estimated weighted average amortization period of 2.7 years The fair value of the stock options granted is calculated using the Black-Scholes option-pricing model with the following range of assumptions: Three Months Ended June 30, Six Months Ended June 30, 2020 2019 2020 2019 Expected term (years) 5.5 - 6.0 5.9 5.0 - 6.0 5.9 Expected volatility 88.1 - 90.8 % 78.7 - 81.3 % 83.8 - 90.8 % 78.7 - 81.9 % Risk-free interest rate 0.4 - 0.5 % 1.9 - 2.4 % 0.4 - 1.6 % 1.9 - 2.6 % Expected dividend yield — — — —

Income Taxes

Income Taxes	6 Months Ended
	Jun. 30, 2020
Income Tax Disclosure [Abstract]
Income Taxes	9. Income Taxes No provision for income taxes was recorded for the three and six months ended June 30, 2020 and 2019, respectively. Deferred tax assets generated from the Company’s net operating losses have been fully reserved, as the Company believes it is not more likely than not that the benefit will be realized. In December 2015, the Protecting Americans from Tax Hikes Act of 2015 (the “PATH Act”) was signed into law, which created several new research and development (“R&D”) tax credit provisions, including allowing qualified small businesses to utilize the R&D credit against the employer’s portion of payroll tax up to a maximum of $250,000 per year. The Company qualified as a small business under the PATH Act for 2016, 2017, 2018 and 2019. During the three and six months ended June 30, 2020, the Company utilized $108,000 and $264,000, respectively, of R&D tax credits as a reduction of payroll expenses to offset its payroll tax liabilities, compared to $79,000 and $172,000 for the three and six months ended June 30, 2019, respectively. The remaining R&D tax credits available for future payroll tax liabilities have been recorded as deferred tax assets with a full valuation allowance.

Net Loss per Share

Net Loss per Share	6 Months Ended
	Jun. 30, 2020
Earnings Per Share [Abstract]
Net Loss Per Share	10. Net Loss Per Share Net Loss Per Share The following table sets forth the calculation of basic and diluted net loss per share during the periods presented (in thousands, except share and per share data): Three Months Ended June 30, Six Months Ended June 30, 2020 2019 2020 2019 Numerator: Net loss $ (9,500 ) $ (8,718 ) $ (19,512 ) $ (16,360 ) Denominator: Weighted-average shares of common stock outstanding 42,936,991 19,073,830 37,902,294 19,058,263 Net loss per share, basic and diluted $ (0.22 ) $ (0.46 ) $ (0.51 ) $ (0.86 ) Basic net loss per common share is calculated by dividing net loss by the weighted-average number of shares of common stock and pre-funded warrants outstanding during the period, without consideration of common share equivalents. Diluted net loss per common share is computed by dividing net loss by the weighted-average number of shares of common stock, pre-funded warrants and common share equivalents outstanding for the period. The pre-funded warrants are included in the computation of basic and diluted net loss per common share as the exercise price is negligible and the pre-funded warrants are fully vested and exercisable. Common share equivalents are only included in the calculation of diluted net loss per common share when their effect is dilutive. Potential dilutive securities, which include, vested and unvested options to purchase common stock and unvested common stock outstanding that were exercised early The following outstanding shares of common stock equivalents were excluded from the computation of the diluted net loss per share for the periods presented because their effect would have been anti-dilutive: Three and Six Months Ended June 30, 2020 2019 Stock options to purchase common stock 4,478,042 2,875,446 Common stock subject to future vesting 19,441 45,287 Total 4,497,483 2,920,733

Subsequent Events

Subsequent Events	6 Months Ended
	Jun. 30, 2020
Subsequent Events [Abstract]
Subsequent Event	11. Subsequent Event In July 2020, the Company issued an additional 427,707 shares of common stock, pursuant to the exercise by the underwriters of their option to purchase additional shares of common stock in the June Offering, for net proceeds of approximately $2.2 million, after deducting underwriting discounts and commissions and other offering expenses paid by us.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2020
Accounting Policies [Abstract]
Basis of presentation and consolidation	Basis of Presentation and Consolidation The condensed consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States (“GAAP”) and include the Company’s accounts and those of its wholly owned Australian subsidiary, The condensed consolidated balance sheet at December 31, 2019 has been derived from the audited consolidated financial statements at that date but does not include all information and footnotes required by GAAP for complete financial statements. These unaudited condensed consolidated financial statements should be read in conjunction with the audited financial statements included in the Annual Report.
Unaudited Interim Condensed Consolidated Financial Statements	Unaudited Interim Condensed Consolidated Financial Statements The accompanying financial information as of June 30, 2020 is unaudited. The condensed consolidated financial statements included in this report reflect all adjustments (consisting only of normal recurring adjustments) that our management considers necessary for the fair statement of the results of operations for the interim periods covered and of our financial condition at the date of the interim balance sheet. The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with GAAP for interim financial information. Accordingly, they do not include all of the information and notes required by GAAP for complete financial statements. The results for interim periods are not necessarily indicative of the results for the entire year or any other interim period. The accompanying condensed consolidated financial statements and related financial information should be read in conjunction with the audited financial statements and the related notes thereto included in our Annual Report.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting period. Significant items subject to such estimates and assumptions include the useful lives of fixed assets, stock-based compensation, and accrued research and development costs. Management bases its estimates on historical experience and on various other market-specific relevant assumptions that management believes to be reasonable under the circumstances. Actual results may differ from those estimates. We also anticipate that the COVID-19 pandemic will have an impact on the clinical and pre-clinical development timelines for our clinical and pre-clinical programs. Estimates and assumptions about future events and their effects cannot be determined with certainty and therefore require the exercise of judgment. As of the date of issuance of these financial statements, the Company is not aware of any specific event or circumstance that would require the Company to update its estimates, assumptions and judgments or revise the carrying value of its assets or liabilities. These estimates may change as new events occur and additional information is obtained and are recognized in the consolidated financial statements as soon as they become known. Actual results could differ from those estimates and any such differences may be material to the Company’s financial statements.
Significant Risks and Uncertainties	Significant Risks and Uncertainties With the global spread of the ongoing COVID-19 pandemic in the first quarter of 2020, we have implemented business continuity plans designed to address and mitigate the impact of the COVID-19 pandemic on our business. The extent to which the COVID-19 pandemic impacts our business, our pre-clinical and clinical development and regulatory efforts, our corporate development objectives and the value of and market for our common stock, will depend on future developments that are highly uncertain and cannot be predicted with confidence at this time, such as the ultimate duration of the pandemic, travel restrictions, quarantines, social distancing and business closure requirements in the United States, Europe and other countries, and the effectiveness of actions taken globally to contain and treat the disease. The global economic slowdown, the overall disruption of global healthcare systems and the other risks and uncertainties associated with the pandemic could have a material adverse effect on our business, financial condition, results of operations and growth prospects. In addition, we are subject to other challenges and risks specific to our business and our ability to execute on our strategy, as well as risks and uncertainties common to companies in the biotechnology industry with development operations, including, without limitation, risks and uncertainties associated with: obtaining regulatory feedback regarding our product candidates; delays or problems in the supply of our product candidates; loss of single source suppliers or their failure to comply with manufacturing regulations; identifying, acquiring or in-licensing additional technologies or product candidates; clinical development and the inherent uncertainty of clinical success; the challenges of protecting and enhancing our intellectual property rights; and complying with applicable regulatory requirements. In addition, to the extent the ongoing COVID-19 pandemic adversely affects our business and results of operations, it may also have the effect of heightening many of the other risks and uncertainties discussed above.
Cash and Cash Equivalents	Cash and Cash Equivalents The Company considers all highly liquid investments with original maturities of three months or less at the time of purchase to be cash equivalents. Cash equivalents are stated at fair value.
Marketable Securities	Marketable Securities All marketable securities have been classified as “available-for-sale” in accordance with the Company’s investment policy and cash management strategy. Short-term marketable securities mature within one-year from the balance sheet date. Investments in marketable securities are recorded at fair value, with any unrealized gains and losses reported within accumulated other comprehensive income as a separate component of stockholders’ deficit until realized or until a determination is made that an other-than-temporary decline in market value has occurred. If a credit loss does exist for available-for-sale debt securities and should be recognized, an allowance will be recorded rather than a write-down of the amortized cost basis. The amortized cost of debt securities is adjusted for amortization of premiums and accretion of discounts to maturity. Such amortization and accretion, together with interest on securities, are included in interest income on the Company’s condensed consolidated statements of operations.
Leases	Leases At lease commencement, the Company records a lease liability based on the present value of lease payments over the expected lease term. The Company calculates the present value of lease payments using the discount rate implicit in the lease, unless that rate cannot be readily determined. In that case, the Company uses its incremental borrowing rate, which is the rate of interest that the Company would have to pay to borrow on a collateralized basis an amount equal to the lease payments over the expected lease term. The Company records a corresponding right-of-use (“ROU”) lease asset based on the lease liability, adjusted for any lease incentives received and any initial direct costs paid to the lessor prior to the lease commencement date. After lease commencement, the Company measures its leases as follows: (i) the lease liability based on the present value of the remaining lease payments using the discount rate determined at lease commencement; and (ii) the ROU lease asset based on the remeasured lease liability, adjusted for any unamortized lease incentives received, any unamortized initial direct costs and the cumulative difference between rent expense and amounts paid under the lease agreement. Any lease incentives received and any initial direct costs are amortized on a straight-line basis over the expected lease term. Rent expense is recorded on a straight-line basis over the expected lease term. The Company elected the short-term lease recognition exemption for all leases that qualify. This means, for those leases that qualify, the Company will not recognize ROU assets or lease liabilities, and this includes not recognizing ROU assets or lease liabilities for existing short-term leases of those assets in transition. The Company did not elect to apply the practical expedient to not separate lease and non-lease components for all of its leases.
Accounting Pronouncements Adopted in 2020	Accounting Pronouncements Adopted in 2020 In June 2016, the FASB issued ASU No. 2016-13 , Financial Instruments-Credit Losses (Topic 326) The Company adopted the new standard using the modified retrospective approach as of January 1, 2020 and the adoption In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework-Changes to the Disclosure Requirements for Fair Value Measurement The amendment of ASU No. 2018-13 removes disclosure requirements from Topic 820 in the areas of: (1) the amount of and reasons for transfers between Level 1 and Level 2 of the fair value hierarchy; (2) the policy for timing of transfers between levels; and (3) the valuation processes for Level 3 fair value measurements. In December 2019, the FASB issued ASU No. 2019-12, Income Taxes: Simplifying the Accounting for Income Taxes Income Taxes. As part of the simplification, along with other exceptions, it removes the exception to the incremental approach for intraperiod tax allocation in the event of a loss from continuing operations and income or a gain from other items. he adoption did not have a material impact on its
Fair Value Measurements	Financial assets and liabilities are recorded at fair value. The carrying amount of certain financial instruments, including cash and cash equivalents, marketable securities, other current assets, accounts payable and accrued liabilities, approximate fair value due to their relatively short maturities. Assets and liabilities recorded at fair value on a recurring basis in the condensed consolidated balance sheets are categorized based upon the level of judgment associated with the inputs used to measure their fair values. Fair value is defined as the exchange price that would be received for an asset or an exit price that would be paid to transfer a liability in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. The authoritative guidance on fair value measurements establishes a three-tier fair value hierarchy for disclosure of fair value measurements as follows: Level 1 : Quoted prices in active markets for identical assets or liabilities. Level 2 : Observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities, quoted prices in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3 : Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. Assets and liabilities measured at fair value are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. The Company’s assessment of the significance of a particular input to the fair value measurement in its entirety requires management to make judgments and consider factors specific to the asset or liability. The Company applies fair value accounting for all financial assets and liabilities and nonfinancial assets and liabilities that are required to be recognized or disclosed at fair value in the financial statements. The Company determines the fair value of Level 1 assets using quoted prices in active markets for identical assets. The Company reviews trading activity and pricing for Level 2 investments as of each measurement date. Level 2 inputs, which are obtained from various third-party data providers, represent quoted prices for similar assets in active markets and were derived from observable market data, or, if not directly observable, were derived from or corroborated by other observable market data.

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	6 Months Ended
	Jun. 30, 2020
Fair Value Disclosures [Abstract]
Summary of Financial Assets Measured at Fair Value on a Recurring Basis	The following table summarizes the Company’s financial assets measured at fair value on a recurring basis and classified under the appropriate level of the fair value hierarchy as described above (in thousands): June 30, 2020 Total Level 1 Level 2 Level 3 Financial Assets: Money market funds $ 17,100 $ 17,100 $ — $ — U.S. Treasury securities 75,788 75,788 — — Commercial paper 30,906 — 30,906 — Corporate debt securities 14,056 — 14,056 — U.S. agency bonds 19,425 — 19,425 — Total $ 157,275 $ 92,888 $ 64,387 $ — December 31, 2019 Total Level 1 Level 2 Level 3 Financial Assets: Money market funds $ 14,731 $ 14,731 $ — $ — U.S. Treasury securities 5,285 5,285 — — Commercial paper 15,186 — 15,186 — Corporate debt securities 17,171 — 17,171 — U.S. agency bonds 25,613 — 25,613 — Total $ 77,986 $ 20,016 $ 57,970 $ —

Available-for-Sale Securities (

Available-for-Sale Securities (Tables)	6 Months Ended
	Jun. 30, 2020
Investments Debt And Equity Securities [Abstract]
Summary of Available-For-Sale Securities Recorded in Cash and Cash Equivalents or Marketable Securities	The following table is a summary of available-for-sale securities recorded in cash and cash equivalents or marketable securities in the Company’s condensed consolidated balance sheets (in thousands): June 30, 2020 Amortized Cost Unrealized Gains Unrealized Losses Fair Value Financial Assets Money market funds $ 17,100 $ — $ — $ 17,100 U.S. Treasury securities 75,761 28 (1 ) 75,788 Commercial paper 30,791 115 — 30,906 Corporate debt securities 13,965 91 — 14,056 U.S. agency bonds 19,385 40 — 19,425 Total $ 157,002 $ 274 $ (1 ) $ 157,275 December 31, 2019 Amortized Cost Unrealized Gains Unrealized Losses Fair Value Financial Assets Money market funds $ 14,731 $ — $ — $ 14,731 U.S. Treasury securities 5,285 1 (1 ) 5,285 Commercial paper 15,174 12 — 15,186 Corporate debt securities 17,168 3 — 17,171 U.S. agency bonds 25,597 16 — 25,613 Total $ 77,955 $ 32 $ (1 ) $ 77,986
Summary of Gross Unrealized Losses and Fair Value by Major Security Type for Available-For-Sale Securities in Unrealized Loss Position	The following table displays additional information regarding gross unrealized losses and fair value by major security type for available-for-sale securities in an unrealized loss position as of June 30, 2020 and December 31, 2019 (in thousands): June 30, 2020 December 31, 2019 Less than 12 consecutive months Less than 12 consecutive months Fair Value Unrealized Losses Fair Value Unrealized Losses U.S. Treasury securities $ 8,117 $ (1 ) $ 4,535 $ (1 ) Total $ 8,117 $ (1 ) $ 4,535 $ (1 )
Summary of Amortized Cost and Estimated Fair Value of Available-for-sale Securities by Contractual Maturity	As of June 30, 2020, the amortized cost and estimated fair value of the Company’s available-for-sale securities by contractual maturity are shown below (in thousands): Amortized Estimated Cost Fair Value Available-for-sale securities maturing: In one year or less $ 157,002 $ 157,275 Total available-for-sale securities $ 157,002 $ 157,275

Balance Sheet Components (Table

Balance Sheet Components (Tables)	6 Months Ended
	Jun. 30, 2020
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Property and Equipment	Property and equipment consisted of the following (in thousands): June 30, 2020 December 31, 2019 Leasehold improvements $ 3,268 $ 3,268 Furniture, laboratory and office equipment 2,666 2,578 Computer equipment 275 253 Total property and equipment 6,209 6,099 Less accumulated depreciation and amortization (2,307 ) (1,817 ) Property and equipment, net $ 3,902 $ 4,282
Accrued Liabilities	Accrued liabilities consisted of the following (in thousands): June 30, 2020 December 31, 2019 Accrued preclinical and research costs $ 759 $ 1,687 Accrued clinical costs 825 1,027 Accrued employee-related costs 973 1,293 Accrued professional services 296 53 Other 174 158 Total accrued liabilities $ 3,027 $ 4,218

Lease (Tables)

Lease (Tables)	6 Months Ended
	Jun. 30, 2020
Leases [Abstract]
Details of Right-of-Use Assets and Lease Liabilities	Information related to the Company’s ROU asset and related lease liabilities were as follows (in thousands): Three months ended June 30, 2020 Six months ended June 30, 2020 Cash paid for operating lease liabilities $ 224 $ 435 Operating lease costs 275 550 Variable lease costs 81 212 Maturities of lease liabilities as of June 30, 2020 were as follows for the years ending December 31: 2020 $ 752 2021 1,542 2022 1,588 2023 1,635 2024 1,684 Thereafter 282 Total undiscounted lease payments 7,483 Less: imputed interest (1,554 ) Total lease liabilities $ 5,929 Operating lease liabilities, current 969 Operating lease liabilities, noncurrent 4,960 Total operating lease liabilities $ 5,929

Pre-Funded Warrants (Tables)

Pre-Funded Warrants (Tables)	6 Months Ended
	Jun. 30, 2020
Equity [Abstract]
Summary of Pre-Funded Warrants Outstanding	The following table represents a summary of the pre-funded warrants outstanding as of the date identified. Issue Date Classification Exercise Price Expiration Date Number of shares underlying warrants as of June 30, 2020 February 4, 2020 Equity $ 0.001 February 4, 2040 2,884,615 June 11, 2020 Equity $ 0.001 June 11, 2040 909,091 Total Outstanding 3,793,706

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	6 Months Ended
	Jun. 30, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Summary of Activity under Stock Option Plans and Related Information	The following table summarizes activity under the Company’s stock option plans and related information (in thousands, except share and per share amounts): Number of Options Outstanding Weighted Average Exercise Price Weighted Average Remaining Contractual Term (Years) Aggregate Intrinsic Value Outstanding at December 31, 2019 3,107,066 $ 7.19 8.2 $ 3,151 Options granted 1,389,476 $ 3.76 Options exercised (6,000 ) $ 0.90 $ 22 Options cancelled (12,500 ) $ 22.85 Outstanding at June 30, 2020 4,478,042 $ 6.09 8.3 $ 7,229 Vested and exercisable at June 30, 2020 1,950,185 $ 5.26 7.3 $ 4,066
Stock-Based Compensation Expense Recognized	Total stock-based compensation expense recognized by function was as follows (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2020 2019 2020 2019 Research and development $ 518 $ 470 $ 982 $ 917 General and administrative 701 539 1,410 993 Total stock-based compensation expense $ 1,219 $ 1,009 $ 2,392 $ 1,910
Fair Value of Employee Stock Options Granted is Calculated Using Black Scholes Option Pricing Model with Range of Assumptions	The fair value of the stock options granted is calculated using the Black-Scholes option-pricing model with the following range of assumptions: Three Months Ended June 30, Six Months Ended June 30, 2020 2019 2020 2019 Expected term (years) 5.5 - 6.0 5.9 5.0 - 6.0 5.9 Expected volatility 88.1 - 90.8 % 78.7 - 81.3 % 83.8 - 90.8 % 78.7 - 81.9 % Risk-free interest rate 0.4 - 0.5 % 1.9 - 2.4 % 0.4 - 1.6 % 1.9 - 2.6 % Expected dividend yield — — — —

Net Loss per Share (Tables)

Net Loss per Share (Tables)	6 Months Ended
	Jun. 30, 2020
Earnings Per Share [Abstract]
Calculation of Basic and Diluted Net Loss per Share	The following table sets forth the calculation of basic and diluted net loss per share during the periods presented (in thousands, except share and per share data): Three Months Ended June 30, Six Months Ended June 30, 2020 2019 2020 2019 Numerator: Net loss $ (9,500 ) $ (8,718 ) $ (19,512 ) $ (16,360 ) Denominator: Weighted-average shares of common stock outstanding 42,936,991 19,073,830 37,902,294 19,058,263 Net loss per share, basic and diluted $ (0.22 ) $ (0.46 ) $ (0.51 ) $ (0.86 )
Anti-dilutive Outstanding Shares of Common Stock Equivalents Excluded from Computation of Diluted Net Loss per Share	The following outstanding shares of common stock equivalents were excluded from the computation of the diluted net loss per share for the periods presented because their effect would have been anti-dilutive: Three and Six Months Ended June 30, 2020 2019 Stock options to purchase common stock 4,478,042 2,875,446 Common stock subject to future vesting 19,441 45,287 Total 4,497,483 2,920,733

Organization and Description _2

Organization and Description of the Business - Additional Information (Details)	Jun. 11, 2020USD ($)$ / sharesshares	May 31, 2020USD ($)shares	Feb. 04, 2020USD ($)$ / sharesshares	Jul. 31, 2020USD ($)shares	Jul. 31, 2019USD ($)	Jun. 30, 2020USD ($)Segment$ / sharesshares	Dec. 31, 2019USD ($)
Organization And Description Of Business [Line Items]
Number of operating segments | Segment						1
Accumulated deficit						$ 103,794,000	$ 84,282,000
Pre funded warrants to purchase shares of common stock | shares	909,091		2,884,615			3,793,706
Pre funded warrants exercise price | $ / shares	$ 0.001		$ 0.001			$ 0.001
Underwritten Public Offering
Organization And Description Of Business [Line Items]
Issuance of common stock | shares	7,590,909		18,965,385
Pre funded warrants to purchase shares of common stock | shares	909,091		2,884,615
Pre funded warrants exercise price | $ / shares	$ 0.001		$ 0.001
Common stock, shares issued, price per share | $ / shares	5.50		2.60
Warrant issue price per share | $ / shares	$ 5.499		$ 2.599
Net proceeds from the public offering	$ 43,700,000		$ 53,400,000
Underwritten Public Offering | Subsequent Event
Organization And Description Of Business [Line Items]
Issuance of common stock | shares				427,707
Net proceeds from the public offering				$ 2,200,000
Underwritten Public Offering | Existing Stockholder, Morningside Ventures and certain officers and directors
Organization And Description Of Business [Line Items]
Net proceeds from the public offering			$ 22,900,000
Underwritten Public Offering | Existing Stockholder, Equal Talent Investments Limited, and one of the Directors
Organization And Description Of Business [Line Items]
Net proceeds from the public offering	$ 8,500,000
ATM Agreement | Jefferies, LLC
Organization And Description Of Business [Line Items]
Issuance of common stock | shares		0
Securities unsold and available for issuance		$ 50,000,000
Minimum
Organization And Description Of Business [Line Items]
Sufficient cash and cash equivalents available period term						12 months
Maximum | ATM Agreement | Jefferies, LLC
Organization And Description Of Business [Line Items]
Common stock aggregate offering price					$ 50,000,000

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Financial Assets Measured at Fair Value on Recurring Basis (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	$ 157,275	$ 77,986
Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	92,888	20,016
Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	64,387	57,970
Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	17,100	14,731
Money Market Funds | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	17,100	14,731
U.S. Treasury Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	75,788	5,285
U.S. Treasury Securities | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	75,788	5,285
Commercial paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	30,906	15,186
Commercial paper | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	30,906	15,186
Corporate debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	14,056	17,171
Corporate debt securities | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	14,056	17,171
U.S. agency bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	19,425	25,613
U.S. agency bonds | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	$ 19,425	$ 25,613

Available-for-Sale Securities -

Available-for-Sale Securities - Summary of Available-For-Sale Securities Recorded in Cash and Cash Equivalents or Marketable Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	$ 157,002
Fair Value	157,275
Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	157,002	$ 77,955
Unrealized Gains	274	32
Unrealized Losses	(1)	(1)
Fair Value	157,275	77,986
Fair Value, Measurements, Recurring | Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	17,100	14,731
Fair Value	17,100	14,731
Fair Value, Measurements, Recurring | U.S. Treasury Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	75,761	5,285
Unrealized Gains	28	1
Unrealized Losses	(1)	(1)
Fair Value	75,788	5,285
Fair Value, Measurements, Recurring | Commercial paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	30,791	15,174
Unrealized Gains	115	12
Fair Value	30,906	15,186
Fair Value, Measurements, Recurring | Corporate debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	13,965	17,168
Unrealized Gains	91	3
Fair Value	14,056	17,171
Fair Value, Measurements, Recurring | U.S. agency bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	19,385	25,597
Unrealized Gains	40	16
Fair Value	$ 19,425	$ 25,613

Available-for-Sale Securities_2

Available-for-Sale Securities - Additional Information (Details) - USD ($)	6 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Investments Debt And Equity Securities [Abstract]
Allowance for credit losses on securities in unrealized loss position	$ 0	$ 0
Sale of available-for-sale securities	$ 0

Available-for-Sale Securities_3

Available-for-Sale Securities - Summary of Gross Unrealized Losses and Fair Value by Major Security Type for Available-For-Sale Securities in Unrealized Loss Position (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair Value	$ 8,117	$ 4,535
Unrealized Losses	(1)	(1)
U.S. Treasury Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair Value	8,117	4,535
Unrealized Losses	$ (1)	$ (1)

Available-for-Sale Securities_4

Available-for-Sale Securities - Summary of Amortized Cost and Estimated Fair Value of Available-for-sale Securities by Contractual Maturity (Details) $ in Thousands	Jun. 30, 2020USD ($)
Available-for-sale securities maturing, Amortized Cost
In one year or less, Amortized Cost	$ 157,002
Amortized Cost	157,002
Available-for-sale securities maturing, Estimated Fair Value:
In one year or less, Estimated Fair Value	157,275
Total available-for-sale securities, Estimated Fair Value	$ 157,275

Balance Sheet Components - Prop

Balance Sheet Components - Property and Equipment (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Property Plant And Equipment [Line Items]
Total property and equipment	$ 6,209	$ 6,099
Less accumulated depreciation and amortization	(2,307)	(1,817)
Property and equipment, net	3,902	4,282
Leasehold Improvements
Property Plant And Equipment [Line Items]
Total property and equipment	3,268	3,268
Furniture, Laboratory and Office Equipment
Property Plant And Equipment [Line Items]
Total property and equipment	2,666	2,578
Computer Equipment
Property Plant And Equipment [Line Items]
Total property and equipment	$ 275	$ 253

Balance Sheet Components - Addi

Balance Sheet Components - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Depreciation expense	$ 0.3	$ 0.2	$ 0.5	$ 0.4

Balance Sheet Components - Accr

Balance Sheet Components - Accrued Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Accrued preclinical and research costs	$ 759	$ 1,687
Accrued clinical costs	825	1,027
Accrued employee-related costs	973	1,293
Accrued professional services	296	53
Other	174	158
Total accrued liabilities	$ 3,027	$ 4,218

Lease - Additional Information

Lease - Additional Information (Details)	6 Months Ended
	Jun. 30, 2020ft²
Operating lease existence of option to extend [true false]	true
Operating lease, option to extend	The operating lease agreement has one option to extend the lease term for a period of five years at the fair market rate at the time of the extension.
Operating lease, renewal term	5 years
Weighted average remaining lease term	4 years 8 months 1 day
Operating lease liability, weighted average discount rate	10.00%
South San Francisco, California [Member]
Area of lease	24,357
Lease expiration date	Feb. 28, 2025

Lease - Details of Right-of-Use

Lease - Details of Right-of-Use Assets and Lease Liabilities (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Lessee Disclosure [Abstract]
Cash paid for operating lease liabilities	$ 224	$ 435	$ 374
Operating lease costs	275	550
Variable lease costs	81	212
2020	752	752
2021	1,542	1,542
2022	1,588	1,588
2023	1,635	1,635
2024	1,684	1,684
Thereafter	282	282
Total undiscounted lease payments	7,483	7,483
Less: imputed interest	(1,554)	(1,554)
Total lease liabilities	5,929	5,929
Operating lease liabilities, current	969	969		$ 900
Operating lease liabilities, noncurrent	4,960	4,960		$ 5,464
Total operating lease liabilities	$ 5,929	$ 5,929

Pre-Funded Warrants - Additiona

Pre-Funded Warrants - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	Jun. 11, 2020	Feb. 04, 2020	Jun. 30, 2020
Class Of Warrant Or Right [Line Items]
Pre funded warrants to purchase shares of common stock	909,091	2,884,615	3,793,706
Pre funded warrants exercise price	$ 0.001	$ 0.001	$ 0.001
Maximum ownership percentage, not to exceed upon exercise of warrants			9.99%
Maximum ownership percentage, increase or decrease upon prior notice			19.99%
Pre-funded warrants exercised			0
Underwritten Public Offering
Class Of Warrant Or Right [Line Items]
Issuance of common stock	7,590,909	18,965,385
Pre funded warrants to purchase shares of common stock	909,091	2,884,615
Common stock, shares issued, price per share	$ 5.50	$ 2.60
Warrant issue price per share	$ 5.499	$ 2.599
Net proceeds from the public offering	$ 43.7	$ 53.4
Pre funded warrants exercise price	$ 0.001	$ 0.001

Pre-Funded Warrants - Summary o

Pre-Funded Warrants - Summary of Pre-Funded Warrants Outstanding (Details) - $ / shares	Jun. 11, 2020	Feb. 04, 2020	Jun. 30, 2020
Equity [Abstract]
Issue Date	Jun. 11, 2020	Feb. 4, 2020
Exercise Price	$ 0.001	$ 0.001	$ 0.001
Expiration Date	Jun. 11, 2040	Feb. 4, 2040
Number of shares underlying warrants	909,091	2,884,615	3,793,706

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Details) - USD ($)	3 Months Ended	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options shares outstanding	4,478,042	4,478,042	3,107,066
Common stock, shares issued	45,826,798	45,826,798	19,208,077
Aggregate intrinsic value of exercised stock options		$ 22,000
Employee options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized stock-based compensation cost	$ 11,700,000	$ 11,700,000
Estimated weighted average amortization period		2 years 8 months 12 days
2018 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares available for future issuance	1,348,693	1,348,693
Number of shares will increase automatically through every year on specified date		--01-01
Number of shares increase automatically continuing through maximum period		beginning on January 1, 2019 and continuing through and including January 1, 2028
Weighted average grant date fair value of options granted		$ 2.68
2018 Equity Incentive Plan | Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Maximum number of shares authorized available for issuance				1,600,692
Increase in number of shares reserved for issuance as percentage of total number of shares of capital stock outstanding on last date of preceding calendar year		5.00%
2018 Equity Incentive Plan | Maximum | Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Maximum number of shares authorized available for issuance				4,000,000
2018 Equity Incentive Plan | Employee options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options shares outstanding	2,648,968	2,648,968
2018 Equity Incentive Plan | Incentive Stock Options | Maximum | Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Maximum number of shares issued upon exercise of incentive stock options	12,500,000	12,500,000
2015 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period		4 years
Options to purchase of common stock outstanding	1,829,074	1,829,074
Aggregate intrinsic value of exercised stock options	$ 12,000	$ 22,000
2015 Equity Incentive Plan | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options granted expiry period		10 years
2018 Employee Stock Purchase Plan | Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares available for future issuance	500,141	500,141		200,000
Common stock, shares issued	83,083	83,083
Authorized an offering beginning period		Nov. 16, 2018
Authorized an offering ending period		May 15, 2019
Authorized an additional offering beginning period		May 16, 2020
2018 Employee Stock Purchase Plan | Maximum | Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of annual increase in number of common stock shares		1.00%
Annual increase in number of common stock shares		375,000
Option price per share of common stock at fair market value		85.00%

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Activity under Stock Option Plans and Related Information (Details) $ / shares in Units, $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2020USD ($)$ / sharesshares	Dec. 31, 2019USD ($)$ / sharesshares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of options outstanding, Outstanding, Beginning balance | shares	3,107,066
Number of options outstanding, Options granted | shares	1,389,476
Number of options outstanding, Options exercised | shares	(6,000)
Number of options outstanding, Options cancelled | shares	(12,500)
Number of options outstanding, Outstanding, Ending balance | shares	4,478,042	3,107,066
Number of options outstanding, options vested and exercisable | shares	1,950,185
Weighted average exercise price, Outstanding, Beginning balance | $ / shares	$ 7.19
Weighted average exercise price, Options granted | $ / shares	3.76
Weighted average exercise price, Options exercised | $ / shares	0.90
Weighted average exercise price, Options cancelled | $ / shares	22.85
Weighted average exercise price, Outstanding, Ending balance | $ / shares	6.09	$ 7.19
Weighted average exercise price, options vested and exercisable | $ / shares	$ 5.26
Weighted average remaining contractual term, (Years) Outstanding, Beginning balance	8 years 3 months 18 days	8 years 2 months 12 days
Weighted average remaining contractual term, (Years) options vested and exercisable	7 years 3 months 18 days
Aggregate intrinsic value, Outstanding, Beginning balance | $	$ 3,151
Aggregate intrinsic value, Options exercised | $	22
Aggregate intrinsic value, Outstanding, Ending balance | $	7,229	$ 3,151
Aggregate intrinsic value, options vested and exercisable | $	$ 4,066

Stock-Based Compensation - Stoc

Stock-Based Compensation - Stock-Based Compensation Expense Recognized (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 1,219	$ 1,009	$ 2,392	$ 1,910
Research and Development Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	518	470	982	917
General and Administrative Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 701	$ 539	$ 1,410	$ 993

Stock-Based Compensation - Fair

Stock-Based Compensation - Fair Value of Stock Options Granted is Calculated Using Black Scholes Option Pricing Model with Range of Assumptions (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)		5 years 10 months 24 days		5 years 10 months 24 days
Expected volatility, Minimum	88.10%	78.70%	83.80%	78.70%
Expected volatility, Maximum	90.80%	81.30%	90.80%	81.90%
Risk-free interest rate, Minimum	0.40%	1.90%	0.40%	1.90%
Risk-free interest rate, Maximum	0.50%	2.40%	1.60%	2.60%
Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)	5 years 6 months		5 years
Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)	6 years		6 years

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	1 Months Ended	3 Months Ended		6 Months Ended
	Dec. 31, 2015	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Income Tax Disclosure [Abstract]
Provision for income taxes		$ 0	$ 0	$ 0	$ 0
Research and development tax credit utilized as reduction of payroll expenses		$ 108,000	$ 79,000	$ 264,000	$ 172,000
Research and development tax credit utilized against employer's portion of payroll tax	$ 250,000

Net Loss Per Share - Calculatio

Net Loss Per Share - Calculation of Basic and Diluted Net Loss per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Numerator:
Net loss	$ (9,500)	$ (10,012)	$ (8,718)	$ (7,642)	$ (19,512)	$ (16,360)
Denominator:
Weighted-average shares of common stock outstanding	42,936,991		19,073,830		37,902,294	19,058,263
Net loss per common share, basic and diluted	$ (0.22)		$ (0.46)		$ (0.51)	$ (0.86)

Net Loss Per Share - Anti-dilut

Net Loss Per Share - Anti-dilutive Outstanding Shares of Common Stock Equivalents Excluded from Computation of Diluted Net Loss per Share (Details) - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share	4,497,483	2,920,733	4,497,483	2,920,733
Stock Options to Purchase Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share	4,478,042	2,875,446	4,478,042	2,875,446
Common stock subject to future vesting [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share	19,441	45,287	19,441	45,287

Subsequent Event - Additional I

Subsequent Event - Additional Information (Details) - Underwritten Public Offering - USD ($) $ in Millions	Jun. 11, 2020	Feb. 04, 2020	Jul. 31, 2020
Subsequent Event [Line Items]
Issuance of common stock	7,590,909	18,965,385
Net proceeds from the public offering	$ 43.7	$ 53.4
Subsequent Event
Subsequent Event [Line Items]
Issuance of common stock			427,707
Net proceeds from the public offering			$ 2.2