0001564590-22-010441 | 10-K | XBRL Viewer

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Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Cash flows from operating activities:
Consolidated net loss	$ (33,777)	$ (16,230)	$ (23,763)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	475	569	635
Stock-based compensation	1,614	1,465	1,783
Debt discount accretion and non-cash interest expense		346	707
Amortization (accretion) of premium (discount) of available-for-sale investment securities	366	110	(284)
Amortization of right-of-use assets	829	697	731
Loss (gain) on disposal of property and equipment	6	3	(28)
Changes in operating assets and liabilities:
Other receivables	1,604	(1,939)	58
Prepaid expenses and other assets	(3,378)	(1,122)	276
Accounts payable and accrued expenses	47	1,763	162
Contract liability		(208)	208
Operating lease liability	(861)	(755)	(498)
Net cash used in operating activities	(33,075)	(15,301)	(20,013)
Cash flows from investing activities:
Purchases of property and equipment	(192)	(202)	(79)
Purchases of available-for-sale investment securities	(126,506)	(21,066)	(40,647)
Maturities of available-for-sale investment securities	35,082	28,150	45,600
Proceeds from sale of property and equipment	50	18	51
Net cash (used in) provided by investing activities	(91,566)	6,900	4,925
Cash flows from financing activities:
Proceeds from issuance of common stock through option exercises	62
Proceeds from issuance of common stock through employee stock purchase plan	11	10	13
Proceeds from issuance of common stock from at-the-market offerings, net of offering costs	14,070	6,437	4,405
Proceeds from issuance of common stock from committed purchase agreement, net of offering costs	15,236
Proceeds from issuance of common stock from underwritten follow-on offering, net of offering costs	80,646	18,779
Proceeds from issuance of common stock through registered direct offering, net of offering costs			4,918
Repayments on borrowings		(9,083)	(8,000)
Net cash provided by financing activities	110,025	16,143	1,336
Net change in cash and cash equivalents	(14,616)	7,742	(13,752)
Cash and cash equivalents at beginning of period	16,952	9,210	22,962
Cash and cash equivalents at the end of period	$ 2,336	16,952	9,210
Supplemental disclosure of cash flow information:
Interest paid		308	$ 1,122
Purchase of fixed assets included in accounts payable		$ 17

Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Other Comprehensive Gain/(Loss) [Member]	Accumulated Deficit [Member]	Noncontrolling Interest [Member]	Convertible Preferred Stock Preferred Stock
Beginning balance at Dec. 31, 2018	$ 33,650	$ 2	$ 332,407	$ (60)	$ (298,701)		$ 2
Beginning balance, Shares at Dec. 31, 2018		2,186,389					2,285,952
Conversion of preferred stock to common stock, shares		229,283					(641,991)
Issuance of common stock upon release of restricted stock units, Shares		7,487
Issuance of common stock pursuant to employee stock purchase plan	13		13
Issuance of common stock pursuant to employee stock purchase plan, Shares		3,117
Issuance of common stock from at-the-market offerings, net of offering costs	4,405	$ 1	4,404
Issuance of common stock from at the market offerings, net of offering costs, Shares		805,357
Issuance of common stock from registered direct offering, net of offering costs	4,918	$ 1	4,917
Issuance of common stock from registered direct offering, net of offering costs, Shares		660,154
Stock-based compensation	1,783		1,783
Net unrealized gain (loss) on investments, net of tax	20			20
Net loss	(23,763)				(23,603)	$ (160)
Ending balance at Dec. 31, 2019	21,026	$ 4	343,524	(40)	(322,304)	(160)	$ 2
Ending balance, Shares at Dec. 31, 2019		3,891,787					1,643,961
Conversion of preferred stock to common stock		$ 1	1				$ (2)
Conversion of preferred stock to common stock, shares		587,444					(1,643,961)
Issuance of common stock from underwritten follow-on offering, net of offering costs	18,779	$ 4	18,775
Issuance of common stock from underwritten follow-on offering, net of offering costs, Shares		4,870,588
Issuance of common stock upon release of restricted stock units, Shares		8,678
Issuance of common stock pursuant to employee stock purchase plan	10		10
Issuance of common stock pursuant to employee stock purchase plan, Shares		3,382
Issuance of common stock from at-the-market offerings, net of offering costs	6,437	$ 2	6,435
Issuance of common stock from at the market offerings, net of offering costs, Shares		1,657,075
Stock-based compensation	1,465		1,465
Net unrealized gain (loss) on investments, net of tax	(3)			(3)
Net loss	(16,230)				(16,224)	(6)
Ending balance at Dec. 31, 2020	31,484	$ 11	370,210	(43)	(338,528)	(166)
Ending balance, Shares at Dec. 31, 2020		11,018,954
Issuance of common stock from underwritten follow-on offering, net of offering costs	80,646	$ 11	80,635
Issuance of common stock from underwritten follow-on offering, net of offering costs, Shares		10,781,250
Issuance of common stock upon release of restricted stock units, Shares		4,177
Issuance of common stock upon exercise of stock options	$ 62		62
Issuance of common stock upon exercise of stock options, Shares	10,751	10,751
Issuance of common stock pursuant to employee stock purchase plan	$ 11		11
Issuance of common stock pursuant to employee stock purchase plan, Shares		3,382
Issuance of common stock from at-the-market offerings, net of offering costs	14,070	$ 3	14,067
Issuance of common stock from at the market offerings, net of offering costs, Shares		2,974,521
Issuance of common stock from committed purchase agreement, net of offering costs	15,236	$ 3	15,233
Issuance of common stock from committed purchase agreement, net of offering costs, Shares		3,000,000
Stock-based compensation	1,614		1,614
Net unrealized gain (loss) on investments, net of tax	(220)			(220)
Net loss	(33,777)				(33,768)	(9)
Ending balance at Dec. 31, 2021	$ 109,126	$ 28	$ 481,832	$ (263)	$ (372,296)	$ (175)
Ending balance, Shares at Dec. 31, 2021		27,793,035

Summary of Significant Accounting Policies - Schedule of Potentially Dilutive Securities Not Included in Calculation of Diluted Net Loss Per Share (Detail) - shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities not included in calculation of diluted net loss per share	1,435,855	599,717	966,860
Class X Preferred Stock (if-converted to common stock) [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities not included in calculation of diluted net loss per share			587,445
Common Stock Warrants [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities not included in calculation of diluted net loss per share	13,760	13,904	13,904
Common Stock Options and Restricted Stock Units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities not included in calculation of diluted net loss per share	1,420,050	584,211	363,553
Employee Stock Purchase Plan [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities not included in calculation of diluted net loss per share	2,045	1,602	1,958

Income Tax - Schedule of Activity Related to Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Balance as of beginning of year	$ 21,707	$ 21,302	$ 19,643
Increase (decrease) related to prior year tax positions	(9)	3
Increase related to current year tax positions	534	402	1,659
Balance as of end of year	$ 22,232	$ 21,707	$ 21,302

Fair Value Measurements - Schedule of Available-for-sale Investments (Detail) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Schedule of Available-for-sale Securities [Line Items]
Gross Amortized Cost	$ 105,788	$ 14,730
Gross Unrealized Gains		7
Gross Unrealized Losses	(213)
Aggregate value of investment securities	105,575	14,737
Short-term Investments \| Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Amortized Cost	36,956	5,491
Gross Unrealized Gains		3
Gross Unrealized Losses	(35)
Aggregate value of investment securities	36,921	5,494
Short-term Investments \| Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Amortized Cost	12,973
Gross Unrealized Losses	(32)
Aggregate value of investment securities	12,941
Short-term Investments \| Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Amortized Cost	55,859	7,021
Gross Unrealized Gains		3
Gross Unrealized Losses	(146)
Aggregate value of investment securities	$ 55,713	7,024
Short-term Investments \| Asset-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Amortized Cost		2,218
Gross Unrealized Gains		1
Aggregate value of investment securities		$ 2,219

Stockholders' Equity - Summary of Stock Option Activity (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Outstanding Options, Beginning Balance	576,534
Number of Outstanding Options, Granted	892,239
Exercises	(10,751)
Number of Outstanding Options, Canceled/forfeited/expired	(45,472)
Number of Outstanding Options, Ending Balance	1,412,550
Number of Outstanding Options, Vested and Expected to Vest, Ending Balance	1,412,550
Number of Outstanding Options, Exercisable, Ending Balance	472,553
Weighted Average Exercise Price, Beginning Balance	$ 23.33
Weighted Average Exercise Price, Granted	5.08
Weighted Average Exercise Price, Exercises	5.78
Weighted Average Exercise Price, Canceled/forfeited/expired	22.38
Weighted Average Exercise Price, Ending Balance	12.01
Weighted Average Exercise Price, Options Vested and Expected to Vest, Ending Balance	12.01
Weighted Average Exercise Price, Options Exercisable, Ending Balance	$ 25.55
Weighted Average Contractual Term, Outstanding	8 years 5 months 15 days
Weighted Average Contractual Term, Options Vested and Expected to Vest	8 years 5 months 15 days
Weighted Average Contractual Term, Options Exercisable	7 years 1 month 6 days
Aggregate Intrinsic Value, Outstanding	$ 3,134,377
Aggregate Intrinsic Value, Options Vested and Expected to Vest	3,134,377
Aggregate Intrinsic Value, Options Exercisable	$ 763,461

Organization, Business and Basis of Presentation - Additional Information (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2021 USD ($) Segment	Dec. 31, 2020 USD ($)
Description Of Business [Line Items]
Accumulated deficit	$ 372,296	$ 338,528
Cash, cash equivalents and available-for-sale investments	107,900
Other receivables	$ 435	$ 2,039
Number of operating segment \| Segment	1
Pangu BioPharma [Member] \| Hong Kong [Member]
Description Of Business [Line Items]
Majority-owned subsidiary percentage	98.00%

- Definition

The cumulative amount of the reporting entity's undistributed earnings or deficit.

+ References + Details

Commitments and Contingencies - Schedule of Future Minimum Payments under Non-cancelable Operating Lease and Reconciliation to Operating Lease Liability (Detail) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Leases Operating [Abstract]
2022	$ 1,062
2023	404
Less: Amount representing interest	(88)
Present value of lease payments	1,378
Less: Current portion of operating lease liability	(980)	$ (861)
Long-term operating lease liability, net of current portion	$ 398	$ 1,378

Balance Sheet Details - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Property Plant And Equipment [Abstract]
Depreciation expense	$ 475	$ 569	$ 635

Fair Value Measurements

12 Months Ended

Dec. 31, 2021

Fair Value Disclosures [Abstract]

Fair Value Measurements

3. Fair Value Measurements

The carrying amounts of cash equivalents, prepaid and other assets, accounts payable and accrued liabilities are considered to be representative of their respective fair values because of the short-term nature of those instruments. Investment securities are recorded at fair value.

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

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

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

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

Financial assets measured at fair value on a recurring basis consist of investment securities. Investment securities are recorded at fair value, defined as the exit price in the principal market in which we would transact, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. Level 2 securities are valued using quoted market prices for similar instruments, non-binding market prices that are corroborated by observable market data, or discounted cash flow techniques and include our investments in asset-backed securities, commercial paper, corporate debt securities and municipal bonds. We have no financial liabilities measured at fair value on a recurring basis. None of our non-financial assets and liabilities are recorded at fair value on a non-recurring basis. No transfers between levels have occurred during the periods presented.

Assets measured at fair value on a recurring basis are as follows (in thousands):

			Fair Value Measurements Using
	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
As of December 31, 2021
Assets:
Current:
Cash equivalents	$	2,052	$	2,052	$	—	$	—
Available-for-sale investments:
Commercial paper		36,921		—		36,921		—
Corporate debt securities		55,713		—		55,713		—
Municipal bonds		12,941		—		12,941		—
Total available-for-sale investments		105,575		—		105,575		—
Total assets measured at fair value	$	107,627	$	2,052	$	105,575	$	—

			Fair Value Measurements Using
	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
As of December 31, 2020
Assets:
Current:
Cash equivalents	$	13,708	$	13,708	$	—	$	—
Available-for-sale investments:
Asset-backed securities		2,219		—		2,219		—
Commercial paper		5,494		—		5,494		—
Corporate debt securities		7,024		—		7,024		—
Total available-for-sale investments		14,737		—		14,737		—
Total assets measured at fair value	$	28,445	$	13,708	$	14,737	$	—

As of December 31, 2021 and 2020, available-for-sale investments are detailed as follows (in thousands):

		December 31, 2021
	Contractual Maturity	Gross Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Market Value
Available-for-sale investments:
Commercial paper	Within 1 year	$	36,956	$	—	$	(35	)	$	36,921
Corporate debt securities	1 to 2 years		55,859		—		(146	)		55,713
Municipal bonds	1 to 2 years		12,973		—		(32	)		12,941
		$	105,788	$	—	$	(213	)	$	105,575

		December 31, 2020
	Contractual Maturity	Gross Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Market Value
Available-for-sale investments:
Asset-backed securities	Within 1 year	$	2,218	$	1	$	—	$	2,219
Commercial paper	Within 1 year		5,491		3		—		5,494
Corporate debt securities	Within 1 year		7,021		3		—		7,024
		$	14,730	$	7	$	—	$	14,737

At each reporting date, we perform an evaluation of impairment to determine if the unrealized losses are other-than-temporary. Factors considered in determining whether a loss is other-than-temporary include the length of time and extent to which fair value has been less than the cost basis, the financial condition of the issuer, and our intent and ability to hold the investment until recovery of its amortized cost basis. Based on our evaluation, we determined that the unrealized losses were not other-than-temporary as of December 31, 2021.

As of December 31, 2021, all available-for-sale investments were in a gross unrealized loss position and have been in such position for less than twelve months. As of December 31, 2020, available-for-sale investments were in a gross unrealized gain position.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Income Tax - Additional Information (Detail) - USD ($)	12 Months Ended
Income Tax - Additional Information (Detail) - USD ($)	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Tax [Line Items]
Income tax (benefit) provision	$ 0	$ 0	$ 0
Valuation allowance	$ 84,112,000	74,646,000
Period of change in ownership	3 years
Percentage of change in ownership	50.00%
Unrecognized tax benefits, income tax penalties and interest accrued	$ 0	$ 0	$ 0
Change in unrecognized tax benefits	0
Federal [Member]
Income Tax [Line Items]
NOLs carryforwards	204,500,000
NOLs carryforwards not subject to expiration	92,000,000.0
NOLs carryforwards subject to expiration	$ 112,500,000
NOLs carryforwards expiration year	2025
Research and development credit carryforward	$ 6,500,000
Research and development credit carryforward expiration year	2026
Federal [Member] \| Orphan Drug Credits [Member]
Income Tax [Line Items]
Research and development credit carryforward	$ 12,500,000
Research and development credit carryforward expiration year	2035
State [Member]
Income Tax [Line Items]
NOLs carryforwards subject to expiration	$ 192,000,000.0
NOLs carryforwards expiration year	2021
Research and development credit carryforward	$ 4,800,000
Foreign [Member]
Income Tax [Line Items]
NOLs carryforwards not subject to expiration	$ 8,700,000

Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Statement Of Income And Comprehensive Income [Abstract]
Consolidated net loss	$ (33,777)	$ (16,230)	$ (23,763)
Other comprehensive loss:
Change in unrealized gain (loss) on available-for-sale investments, net of tax	(220)	(3)	20
Comprehensive loss	(33,997)	(16,233)	(23,743)
Comprehensive loss attributable to noncontrolling interest in Pangu BioPharma Limited	9	6	160
Comprehensive loss attributable to aTyr Pharma, Inc. common stockholders	$ (33,988)	$ (16,227)	$ (23,583)

- Definition

Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income (loss) and other comprehensive income (loss), attributable to noncontrolling interests. Excludes changes in equity resulting from investments by owners and distributions to owners.

+ References + Details

- Definition

Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income and other comprehensive income. Excludes changes in equity resulting from investments by owners and distributions to owners.

+ References + Details

- Definition

The consolidated profit or loss for the period, net of income taxes, including the portion attributable to the noncontrolling interest.

+ References

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+ Details

Balance Sheet Details - Summary of Property and Equipment (Detail) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Property Plant And Equipment [Line Items]
Property and equipment, Gross	$ 6,700	$ 7,523
Less accumulated depreciation and amortization	(6,157)	(6,624)
Property and equipment, Net	543	899
Computer and Office Equipment [Member]
Property Plant And Equipment [Line Items]
Property and equipment, Gross	616	552
Scientific and Laboratory Equipment [Member]
Property Plant And Equipment [Line Items]
Property and equipment, Gross	4,383	5,270
Tenant Improvements [Member]
Property Plant And Equipment [Line Items]
Property and equipment, Gross	$ 1,701	$ 1,701

Summary of Significant Accounting Policies - Summary of Net Loss Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Numerator:
Net loss attributable to aTyr Pharma, Inc.	$ (33,768)	$ (16,224)	$ (23,603)
Denominator:
Shares used in computing net loss per share, basic and diluted	19,080,878	9,160,269	3,355,600
Net loss per share - basic and diluted	$ (1.77)	$ (1.77)	$ (7.03)

- Definition

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

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+ Details

Income Tax (Tables)

12 Months Ended

Dec. 31, 2021

Income Tax Disclosure [Abstract]

Schedule of Pretax Losses for Domestic and Foreign Operations

Pretax losses were generated by both domestic and foreign operations as follows (in thousands):

	Years Ended December 31,
	2021			2020			2019
United States	$	(33,316	)	$	(15,950	)	$	(23,315	)
Foreign		(458	)		(280	)		(448	)
Worldwide pre-tax loss	$	(33,774	)	$	(16,230	)	$	(23,763	)

Schedule of Reconciliations of the Expected Statutory Federal Income Tax

A reconciliation of the expected statutory federal income tax provision to the actual income tax provision is summarized as follows (in thousands):

	Years Ended December 31,
	2021			2020			2019
Expected income taxes benefit at federal statutory rate	$	(7,093	)	$	(3,408	)	$	(4,990	)
State income taxes, net of federal benefit		(2,313	)		(12	)		(19	)
Permanent items and other		592			169			49
Stock compensation		90			804			701
Research credits		(1,253	)		(835	)		(817	)
Unrecognized tax benefits		500			334			327
Foreign rate differential		21			13			20
Change in tax rate		52			(7	)		(49	)
Change in valuation allowance		9,404			2,942			4,778
Income tax (benefit) expense	$	—		$	—		$	—

Schedule of Significant Components of Deferred Tax Assets

Significant components of our deferred tax assets are summarized as follows (in thousands):

	December 31,
	2021			2020
Deferred tax assets:
Net operating loss carryforwards	$	48,833		$	41,203
Capitalized research and development expenses		18,086			17,007
Research credits and other state credits		13,695			12,954
Intangible assets		1,465			1,655
Reserve and accruals		641			544
Share-based compensation expense		1,369			1,253
Lease liability		290			472
Valuation allowance		(84,112	)		(74,646	)
Total deferred tax assets	$	267		$	442
Deferred tax liabilities:
Right of use lease assets		(267	)		(442	)
Total deferred tax liabilities		(267	)		(442	)
Net deferred tax assets	$	—		$	—

Schedule of Activity Related to Unrecognized Tax Benefits

The activity related to our unrecognized tax benefits is summarized as follows (in thousands):

	December 31,
	2021			2020		2019
Balance as of beginning of year	$	21,707		$	21,302	$	19,643
Increase (decrease) related to prior year tax positions		(9	)		3		—
Increase related to current year tax positions		534			402		1,659
Balance as of end of year	$	22,232		$	21,707	$	21,302

Stockholders' Equity - Summary of Warrants Outstanding (Detail)	12 Months Ended
	Dec. 31, 2021 $ / shares shares
Warrant One [Member]
Class Of Warrant Or Right [Line Items]
Number Outstanding	1,066
Exercise Price Per Share \| $ / shares	$ 281.50
Expiration Date	2023-07
Warrant Two [Member]
Class Of Warrant Or Right [Line Items]
Number Outstanding	6,830
Exercise Price Per Share \| $ / shares	$ 43.93
Expiration Date	2023-11
Warrant Three [Member]
Class Of Warrant Or Right [Line Items]
Number Outstanding	2,978
Exercise Price Per Share \| $ / shares	$ 50.37
Expiration Date	2024-06
Warrant Four [Member]
Class Of Warrant Or Right [Line Items]
Number Outstanding	2,886
Exercise Price Per Share \| $ / shares	$ 51.98
Expiration Date	2024-12
Warrant Five [Member]
Class Of Warrant Or Right [Line Items]
Number Outstanding	13,760

Commitments and Contingencies - Additional Information (Detail) $ in Millions	1 Months Ended	12 Months Ended
	Jul. 31, 2018 ft²	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Debt Instrument [Line Items]
Lease extended maturity date	May 31, 2023
Lease, option to extend	false
Operating lease expense \| $		$ 1.0	$ 1.0	$ 1.0
Operating lease, weighted average remaining lease term		1 year 4 months 24 days	2 years 4 months 24 days
Operating lease, weighted average discount rate		9.60%	9.60%
Maximum [Member]
Debt Instrument [Line Items]
Lease space	24,494
Minimum [Member]
Debt Instrument [Line Items]
Lease space	20,508

Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2021

Fair Value Disclosures [Abstract]

Schedule of Assets Measured at Fair Value on Recurring Basis

Assets measured at fair value on a recurring basis are as follows (in thousands):

			Fair Value Measurements Using
	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
As of December 31, 2021
Assets:
Current:
Cash equivalents	$	2,052	$	2,052	$	—	$	—
Available-for-sale investments:
Commercial paper		36,921		—		36,921		—
Corporate debt securities		55,713		—		55,713		—
Municipal bonds		12,941		—		12,941		—
Total available-for-sale investments		105,575		—		105,575		—
Total assets measured at fair value	$	107,627	$	2,052	$	105,575	$	—

			Fair Value Measurements Using
	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
As of December 31, 2020
Assets:
Current:
Cash equivalents	$	13,708	$	13,708	$	—	$	—
Available-for-sale investments:
Asset-backed securities		2,219		—		2,219		—
Commercial paper		5,494		—		5,494		—
Corporate debt securities		7,024		—		7,024		—
Total available-for-sale investments		14,737		—		14,737		—
Total assets measured at fair value	$	28,445	$	13,708	$	14,737	$	—

Schedule of Available-for-sale Investments

As of December 31, 2021 and 2020, available-for-sale investments are detailed as follows (in thousands):

		December 31, 2021
	Contractual Maturity	Gross Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Market Value
Available-for-sale investments:
Commercial paper	Within 1 year	$	36,956	$	—	$	(35	)	$	36,921
Corporate debt securities	1 to 2 years		55,859		—		(146	)		55,713
Municipal bonds	1 to 2 years		12,973		—		(32	)		12,941
		$	105,788	$	—	$	(213	)	$	105,575

		December 31, 2020
	Contractual Maturity	Gross Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Market Value
Available-for-sale investments:
Asset-backed securities	Within 1 year	$	2,218	$	1	$	—	$	2,219
Commercial paper	Within 1 year		5,491		3		—		5,494
Corporate debt securities	Within 1 year		7,021		3		—		7,024
		$	14,730	$	7	$	—	$	14,737

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2021

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Cash and Cash Equivalents

Cash and cash equivalents consist primarily of readily available checking, money market accounts and money market funds. We consider all highly liquid investments that mature in three months or less when purchased to be cash equivalents.

Investment Securities

Investment securities primarily consist of investment grade corporate debt securities, municipal bond securities and commercial paper. We classify all investment securities as available-for-sale. Investment securities are carried at fair value, with the unrealized gains and losses, if any, reported as a component of other comprehensive income (loss) in stockholders’ equity until realized. Realized gains and losses from the sale of investment securities, if any, are determined on a specific identification basis. A decline in the market

value of any investment security below cost that is determined to be other than temporary will result in an impairment charge to earnings and a new cost basis for the security is established. No such impairment charges were recorded for any period presented. Premiums and discounts are amortized or accreted over the life of the related security as an adjustment to yield using the straight-line method and are included in interest income. Interest income is recognized when earned. As of December 31, 2021, we held an aggregate total of $105.6 million of investment securities which consisted of corporate debt securities, municipal bonds, and commercial paper all of which will mature in less than two years, and there was an unrealized loss of approximately $0.2 million between the amortized cost and fair value of these investment securities. As of December 31, 2020, we held $14.7 million of corporate debt securities, asset-backed securities and commercial paper, all of which mature in less than one year, and there was an unrealized loss of approximately $3,000 between the amortized cost and fair value of these investment securities.

Concentration of Credit Risk

Financial instruments that potentially subject us to significant concentration of credit risk consist primarily of cash, cash equivalents and investment securities. We have established guidelines regarding diversification of investments and their maturities, which are designed to maintain principal and maximize liquidity. We maintain deposits in federally insured financial institutions in excess of federally insured limits. We have not experienced any losses in such accounts and we believe that we are not exposed to significant credit risk due to the financial position of the depository institutions in which those deposits are held.

Property and Equipment

Property and equipment are stated at cost and depreciated on a straight-line basis over the estimated useful life of the related assets (generally three to seven years). Leasehold improvements are stated at cost and amortized on a straight-line basis over the lesser of the remaining term of the related lease or the estimated useful life of the leasehold improvements. Repairs and maintenance costs are charged to expense as incurred.

Impairment of Long-Lived Assets

Long-lived assets consist primarily of property and equipment. An impairment loss is recorded if and when events and circumstances indicate that assets might be impaired and the undiscounted cash flows estimated to be generated by those assets are less than the carrying amount of those assets. While our current and historical operating losses are indicators of impairment, we believe that future cash flows to be received support the carrying value of our long-lived assets and, accordingly, have not recognized any impairment losses since inception.

Accrued Expenses

Accrued expenses include salaries, wages, benefits costs, consulting fees, legal and research and development costs. Accrued clinical studies costs of $1.0 million and $1.1 million as of December 31, 2021 and 2020, respectively, included clinical studies and product manufacturing costs. We have entered into contractual arrangements related to our clinical studies with clinical research organizations (CROs) and contracted development and manufacturing organizations (CDMOs) and recognize expense based on work completed and efforts expended pursuant to our contractual arrangements. We make estimates of our accrued CRO costs as of each balance sheet date based on facts and circumstances known at the time and include total trial management costs, sites activated, patients enrolled and number of patient visits. We estimate the time period over which services will be performed and the level of effort to be expended in each period. There may be instances in which payments made to our service providers including CROs and CDMOs, will temporarily exceed the level of services provided and result in a prepayment of the expense. If the actual timing of the performance of services or the level of effort varies from our estimate, we adjust the accrual or prepaid expense balance accordingly. Historically, our estimated accrued liabilities have materially approximated actual expenses incurred.

Leases

We determine if an arrangement is a lease at inception. Short-term leases with an initial term of 12 months or less are not recorded on the balance sheet. For long-term operating leases with an initial term of greater than 12 months, we recognized an operating right-of-use asset (ROU) and a lease liability based on the present value of future lease payments using an estimated rate of interest that we would pay to borrow equivalent funds on a collateralized basis at the lease commencement date. We determine the lease term at the commencement date by considering whether renewal options and termination options are reasonably assured of exercise. Rent expense for the operating lease is recognized on a straight-line basis over the lease term and is included in operating expenses in our consolidated statements of operations.

If a lease is modified, the modified contract is evaluated to determine whether it is or contains a lease. If a lease continues to exist, the lease modification is determined to be a separate contract when the modification grants the lessee an additional ROU that is not included in the original lease and the lease payments increase commensurate with the standalone price for the additional ROU. A lease modification that results in a separate contract will be accounted for in the same manner as a new lease. For a modification that is not a separate contract, we reassess the lease classification using the modified terms and conditions and the facts and circumstances

as of the effective date of the modification and recognize the amount of the remeasurement of the lease liability for the modified lease as an adjustment to the corresponding operating lease ROU asset.

Our right-of-use assets consist of an operating lease for our facility headquarters. We have a noncancelable operating lease that includes certain tenant improvement allowances and is subject to base lease payments, which escalate over the term of the lease, additional charges for common area maintenance and other costs. We currently do not have any finance leases.

We do not separate lease and non-lease components for our long-term leases.

Rent expense for the operating lease is recognized on a straight-line basis over the lease term and is included in our consolidated statement of operations. Variable lease payments, including lease operating expenses, are recorded as incurred.

Revenue Recognition

We evaluate our agreements under ASC Topic 606, Revenue from Contracts with Customers and ASC Topic 808, Collaborative Arrangements. 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. In determining the appropriate amount of revenue to be recognized as we fulfill our obligations under our agreement, we perform the following steps: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations; and (v) recognition of revenue when (or as) we satisfy each performance obligation. As part of the accounting for these arrangements, we must develop assumptions that require judgment to determine the stand-alone selling price for each performance obligation identified in the contract. We use key assumptions to determine the stand-alone selling price, which may include forecasted revenues, development timelines, reimbursement rates for personnel costs, discount rates and probabilities of technical and regulatory success.

We recognize revenue in one of two ways, over time or at a point in time. We recognize revenue over time when we are executing on our performance obligation over time and our partner receives benefit over time. For example, we recognize revenue over time when we provide research and development services. We recognize revenue at a point in time when we transfer control of a distinct performance obligation to our partner. For example, 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.

Research and Development Costs

Research and development costs are expensed as incurred. Research and development costs include: salaries and employee-related expenses, including stock-based compensation and benefits for personnel in research and product development functions; costs associated with conducting our preclinical, development and regulatory activities, including fees paid to third-party professional consultants, service providers and our scientific, therapeutic and clinical advisors; costs to acquire, develop and manufacture preclinical study and clinical trial materials; costs incurred under clinical trial agreements with clinical research organizations and investigative sites; costs for laboratory supplies; payments related to licensed products and technologies; allocated facilities and information technology costs; and depreciation.

Patent Costs

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

Stock-Based Compensation

Stock-based compensation expense represents the grant date fair value of employee stock option grants recognized as expense over the requisite service period of the awards (usually the vesting period) on a straight-line basis. We estimate fair value of stock option grants using the Black-Scholes option pricing model. We estimate the fair value using assumptions, including the risk-free interest rate, the expected volatility of a peer group of similar companies, the expected term of the awards and the expected dividend yield. These estimates involve inherent uncertainties and the application of management’s judgment. If factors change and different assumptions are used, our stock-based compensation expense could be materially different in the future. We follow ASC Topic 718, Compensation – Stock Compensation as guidance for accounting modification.

Income Taxes

We account for income taxes under the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the financial statements. Under this method, deferred tax assets and liabilities are determined on the basis of the differences between the financial statements and tax basis of assets

and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. The effect of a change in tax rates on deferred tax assets and liabilities is recognized as income in the period that includes the enactment date.

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

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

Net Loss Per Share

Basic net loss per share is calculated by dividing the net loss attributable to common stockholders by the weighted average number of common shares outstanding for the period, without consideration for common stock equivalents. Diluted net loss per share attributable to common stockholders is calculated by dividing the net loss attributable to common stockholders by the weighted average number of common stock and common stock equivalents outstanding for the period determined using the treasury-stock method. Dilutive common stock equivalents are comprised of convertible preferred stock, warrants for common stock, options and restricted stock units outstanding under our stock option plan and estimated shares to be purchased under our employee stock purchase plan. For all periods presented, there is no difference in the number of shares used to calculate basic and diluted shares outstanding due to our net loss position.

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

	Years Ended December 31,
	2021		2020		2019
Class X preferred stock (if-converted to common stock)		—		—		587,445
Common stock warrants		13,760		13,904		13,904
Common stock options and restricted stock units		1,420,050		584,211		363,553
Employee stock purchase plan		2,045		1,602		1,958
Total		1,435,855		599,717		966,860

The following table summarizes our net loss per share (in thousands, except per share data):

	Years Ended December 31,
	2021			2020			2019
Numerator:
Net loss attributable to aTyr Pharma, Inc.	$	(33,768	)	$	(16,224	)	$	(23,603	)

Denominator:
Shares used in computing net loss per share, basic and diluted		19,080,878			9,160,269			3,355,600

Net loss per share - basic and diluted	$	(1.77	)	$	(1.77	)	$	(7.03	)

Recent Accounting Pronouncements

In June 2016, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2016-13, Financial Instruments – Credit Losses (Topic 326), to provide financial statement users with more decision-useful information about the expected credit losses on financial instruments and other commitments to extend credit held by a reporting entity at each reporting date. To achieve this objective, the amendments in Topic 326 replace the incurred loss impairment methodology in current GAAP with a methodology that reflects expected credit losses and requires consideration of a broader range of reasonable and supportable information to inform credit loss estimates. Topic 326 is effective for fiscal years beginning after December 15, 2022, including interim periods within those fiscal years for smaller reporting companies. We expect the adoption of the amendments in Topic 326 to have an immaterial effect on our consolidated financial position or the results of its operations when such amendment is adopted.

In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740), Simplifying the Accounting for Income Taxes to identify, evaluate, and improve areas of GAAP for which costs and complexity can be reduced while maintaining or improving the usefulness of the information provided to users of financial statements. The amendments for Topic 740 simplify the accounting for income taxes by removing certain exceptions to the general principles in Topic 740. The amendments also improve consistent application of and simplify GAAP for other areas of Topic 740 by clarifying and amending existing guidance. Topic 740 is effective for fiscal years beginning after December 15, 2020 which we adopted prospectively on January 1, 2021. The adoption did not have a material effect on our consolidated financial position or results of operations.

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Significant Accounting Policies [Line Items]
Impairment charges on investment securities	$ 0
Aggregate value of investment securities	105,575,000	$ 14,737,000
Unrealized gain between amortized cost and fair value of investment securities	0.2	3,000
Impairment of long lived assets	0
Accrued clinical studies costs	$ 1,004,000	$ 1,089,000
Maximum [Member]
Significant Accounting Policies [Line Items]
Maturity period of investment securities	2 years	1 year
Estimated useful life of property and equipment	7 years
Minimum [Member]
Significant Accounting Policies [Line Items]
Estimated useful life of property and equipment	3 years
Percentage of tax benefit to be realized upon settlement	50.00%

License, Collaboration and Other Agreements - Additional Information (Detail) - USD ($)	1 Months Ended				12 Months Ended
	Jan. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jan. 31, 2020	Dec. 31, 2021	Dec. 31, 2020
Research And Development Arrangement Contract To Perform For Others [Line Items]
Upfront payment received				$ 8,000,000.0
Milestone payments received	$ 2,000,000.0
Other receivables					$ 435,000	$ 2,039,000
Hong Kong University of Science and Technology [Member]
Research And Development Arrangement Contract To Perform For Others [Line Items]
Collaborative agreement, funding received			$ 750,000
Funding of project cost, description			The ITC funded approximately 50% of the total estimated project cost, with aTyr contributing the remaining 50%. The research grant agreement between Pangu BioPharma, HKUST and the Government of the Hong Kong Special Administration Region was effective April 1, 2020.
Expenses					$ 400,000	$ 200,000
Development Regulatory And Sales Milestones [Member] \| Kyorin Pharmaceutical Co Ltd [Member]
Research And Development Arrangement Contract To Perform For Others [Line Items]
Remaining receivable based on achievement of research milestones				165,000,000.0
Development Regulatory And Sales Milestones [Member] \| Kyorin Pharmaceutical Co Ltd [Member] \| Collaboration Revenue [Member]
Research And Development Arrangement Contract To Perform For Others [Line Items]
Stand-alone selling price of license		$ 100,000		$ 7,900,000

Income Tax - Schedule of Significant Components of Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Deferred tax assets:
Net operating loss carryforwards	$ 48,833	$ 41,203
Capitalized research and development expenses	18,086	17,007
Research credits and other state credits	13,695	12,954
Intangible assets	1,465	1,655
Reserve and accruals	641	544
Share-based compensation expense	1,369	1,253
Lease liability	290	472
Valuation allowance	(84,112)	(74,646)
Total deferred tax assets	267	442
Deferred tax liabilities:
Right of use lease assets	(267)	(442)
Total deferred tax liabilities	$ (267)	$ (442)

Stockholders' Equity

12 Months Ended

Dec. 31, 2021

Equity [Abstract]

Stockholders' Equity

7. Stockholders’ Equity

Underwritten Follow-On Public Offerings

In September 2021, we completed an underwritten follow-on public offering of 10,781,250 shares of our common stock, including the full exercise of the underwriters’ option to purchase additional shares, at a price to the public of $8.00 per share. The total net proceeds from the offering were approximately $80.6 million, after deducting underwriting discounts, commissions and offering expenses payable by us.

In February 2020, we completed an underwritten follow-on public offering of 4,235,294 shares of our common stock at a price to the public of $4.25 per share. In March 2020, the underwriters fully exercised their over-allotment option for the issuance of an additional 635,294 shares of common stock. The total net proceeds from the offering were approximately $18.8 million, after deducting underwriting discounts, commissions and offering expenses payable by us.

At-the-Market Offering Program

In March 2021, we entered into a Capital on Demand^TM Sales Agreement with JonesTrading Institutional Services LLC (JonesTrading) for an at-the-market offering (ATM Offering Program), pursuant to which we can sell from time to time, at our option, up to an aggregate of $25.0 million of shares of our common stock through JonesTrading, as sales agent or principal. JonesTrading is entitled to a commission at a fixed rate equal of up to 3% of the gross proceeds. For the year ended December 31, 2021, we sold an aggregate of 986,267 shares of common stock at an average price of $4.75 per share for net proceeds of $4.4 million under the JonesTrading ATM Offering Program.

In May 2019, we entered into a sales agreement with H.C. Wainwright & Co., LLC (Wainwright) with respect to an ATM Offering Program under which we could offer and sell shares of our common stock having an aggregate offering price of up to $10.0 million. Wainwright was entitled to a commission at a fixed rate equal to 3% of the gross proceeds. In November 2020, we amended our sales agreement with Wainwright to increase the amount of the ATM Offering Program up to $20.0 million. In March 2021, the ATM Offering Program with Wainwright automatically terminated upon the issuance and sale of all of the shares of common stock having an aggregate offering price of $20.0 million. Under the ATM Offering Program with Wainwright, during 2020, we sold an aggregate of 1,657,075 shares of common stock at an average price of $4.07 per share for net proceeds of $6.4 million. Prior to the termination of the sales agreement with Wainwright, in 2021, we sold an aggregate of 1,988,254 shares of common stock at an average price of $4.99 per share for net proceeds of $9.6 million under the Wainwright ATM Offering Program.

Purchase Agreement

In September 2020, we entered into a common stock purchase agreement (Purchase Agreement) with Aspire Capital Fund, LLC (Aspire Capital), which provides that, upon the terms and subject to the conditions and limitations set forth therein, Aspire Capital is committed to purchase up to an aggregate of $20.0 million of shares of our common stock at our request from time to time during the 30 month term of the Purchase Agreement. Concurrently with entering into the Purchase Agreement, we also entered into a registration rights agreement with Aspire Capital, in which we agreed to file one or more registration statements, as permissible and necessary to register under the Securities Act of 1933, as amended, for the resale of the shares of our common stock that have been and may be issued to Aspire Capital under the Purchase Agreement. For the year ended December 31, 2021, we sold an aggregate of 3,000,000 shares of common stock at an average price of $5.09 per share for net proceeds of $15.2 million under this Purchase Agreement. We did not sell any shares of common stock to Aspire Capital under this Purchase Agreement for the year ended December 31, 2020.

2014 Stock Plan

We adopted a stock option plan in 2007 (the 2007 Plan), which was subsequently amended, restated and renamed in July 2014 (the 2014 Plan) to provide for the incentive stock options, nonstatutory stock options, stock and rights to purchase restricted stock to eligible recipients. Recipients of incentive stock options are eligible to purchase shares of our common stock at an exercise price equal to no less than the estimated fair market value of such stock on the date of grant. The maximum term of options under the 2014 Plan is ten years. Options granted generally vest over four years. Shares underlying any awards under the 2014 Plan that are forfeited, canceled, reacquired by us prior to vesting, satisfied without the issuance of stock or otherwise terminated (other than by exercise) will be added to shares available for issuance under the 2015 Plan.

2015 Stock Plan

In April 2015, our board of directors adopted, and our stockholders approved, the 2015 Stock Plan (the 2015 Plan). The 2015 Plan became effective on May 6, 2015 and we ceased granting any new awards under our 2014 Plan. Awards granted under the 2014 Plan prior to our IPO that are forfeited, canceled, reacquired by us prior to vesting satisfied without the issuance of stock or otherwise terminated (other than by exercise) will be added to shares available for issuance under the 2015 Plan. At our 2020 Annual Meeting of Stockholders and at our 2021 Annual Meeting of Stockholders, our stockholders approved an amendment to increase the number of shares of common stock reserved under the 2015 Plan by 350,000 shares and 750,000 shares, respectively. Total shares available for issuance under the 2015 Plan as of December 31, 2021 were 420,896. Shares underlying any awards under the 2015 Plan that are forfeited, canceled, reacquired by us prior to vesting, satisfied without the issuance of stock or otherwise terminated (other than by exercise) will be added to shares available for issuance under the 2015 Plan.

The maximum term of options granted under 2015 Plan is ten years. For an initial grant to an employee, 25% of the options generally vest on the first anniversary of the original vesting date, with the balance vesting monthly over the remaining three years. For subsequent grants to an employee, the options generally vest monthly over a four-year term.

Inducement Grants

Options under inducement grants vest over a period of four years, with 25% vesting on the one year anniversary of the grant date and the remaining 75% vesting on a monthly basis over three years thereafter, subject to continuous employment. These options were inducement grants issued outside of the 2015 Plan in accordance with Nasdaq Listing Rule 5635(c)(4). In addition, from time to time, we may make inducement grants of stock options to new employees.

In October 2021, we granted a non-qualified option to purchase 70,000 shares of our common stock at an exercise price of $8.73 per share as an inducement award in connection with the hiring of our Vice President, Regulatory Affairs, and in December 2021, we granted a non-qualified option to purchase 70,000 shares of our common stock at an exercise price of $7.77 per share as an inducement award in connection with the hiring of our Vice President, Human Resources.

We intend to file a registration statement on Form S-8 to register the shares of common stock underlying the options granted under the inducement grants prior to the time at which this option becomes exercisable.

Employee Stock Purchase Plan

In April 2015, our board of directors adopted, and our stockholders approved, our 2015 Employee Stock Purchase Plan (the 2015 ESPP). The 2015 ESPP became effective on May 6, 2015. As of December 31, 2021, total shares reserved for issuance under the 2015 ESPP were 71,933.

Stock-based Compensation

Stock Options

Stock option activity is summarized as follows:

	Number of Outstanding Stock Options			Weighted Average Exercise Price		Weighted Remaining Contractual Term		Aggregate Intrinsic Value
Outstanding as of December 31, 2020		576,534		$	23.33
Granted		892,239		$	5.08
Exercises		(10,751	)	$	5.78
Canceled/forfeited/expired		(45,472	)	$	22.38
Outstanding as of December 31, 2021		1,412,550		$	12.01		8.46	$	3,134,377
Options vested and expected to vest as of December 31, 2021		1,412,550		$	12.01		8.46	$	3,134,377
Options exercisable as of December 31, 2021		472,553		$	25.55		7.10	$	763,461

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

Years Ended December 31,

2021

2020

2019

Expected term (in years)

5.50 – 6.08

5.51 – 6.07

Risk-free interest rate

0.6% – 1.3%

0.3% – 1.5%

1.4% – 2.6%

Expected volatility

86.3% – 104.8%

102.2% – 109.7%

97.2% – 105.4%

Expected dividend yield

0.0%

The assumptions used in the Black-Scholes option pricing model to determine the fair value of the ESPP offering were as follows:

	Years Ended December 31,
	2021		2020		2019
Expected term (in years)		0.50		0.50		0.50
Risk-free interest rate	0.04% – 0.12%		0.1% – 1.6%		1.6% – 2.5%
Expected volatility	89.7% – 108.12%		89.7% – 143.2%		99.7% – 141.7%
Expected dividend yield		0.0%		0.0%		0.0%

Expected term. The expected term represents the period of time that options are expected to be outstanding. Because we do not have sufficient history of exercise behavior, we determine the expected life assumption using the simplified method, which is an average of the contractual term of the option and its vesting period.

Risk-free interest rate. We base the risk-free interest rate assumption on the U.S. Treasury’s rates for U.S. Treasury zero-coupon bonds with maturities similar to those of the expected term of the award being valued.

Expected volatility. The expected volatility assumption is based on our historical volatility as well as the volatilities of a peer group of similar companies whose share prices are publicly available. The peer group was developed based on companies in the biotechnology industry.

Expected dividend yield. We base the expected dividend yield assumption on the fact that we have never paid cash dividends and have no present intention to pay cash dividends.

Restricted Stock Units

Occasionally, we grant restricted stock units to employees. The fair value of restricted stock is determined by the closing price of the Company's common stock reported on the Nasdaq Global Select Market on the date of grant. Restricted stock unit activity is summarized as follows:

	Number of Outstanding Restricted Stock Units			Weighted Average Grant Date Fair Value
Balance as of December 31, 2020		7,677		$	5.32
Granted		4,000		$	3.89
Released		(4,177	)	$	6.18
Balance as of December 31, 2021		7,500		$	4.08

The allocation of stock-based compensation for all options, including performance options with market condition and restricted stock units is as follows (in thousands):

	Years Ended December 31,
	2021		2020		2019
Research and development	$	295	$	254	$	354
General and administrative		1,319		1,211		1,429
Total stock-based compensation expense	$	1,614	$	1,465	$	1,783

The weighted-average grant date fair value per share of stock options granted by us, during the years ended December 31, 2021, 2020 and 2019 was $3.82, $3.39 and $5.67, respectively. The total grant date fair value of restricted stock units granted by us during the years ended December 31, 2021, 2020, and 2019 was approximately $16,000, $21,000 and $39,000, respectively. The aggregate intrinsic value of stock options exercised during the year ended December 31, 2021 was approximately $80,000. We did not have any options exercised during the years ended December 31, 2020 and 2019. The aggregate intrinsic value of restricted stock units released during the years ended December 31, 2021, 2020 and 2019 was approximately $31,000, $34,000 and $31,000, respectively. As of December 31, 2021, total unrecognized share-based compensation expense related to unvested stock options and restricted stock units was approximately $3.5 million and $20,000, respectively. These unrecognized costs for options and restricted stock units are expected to be recognized ratably over a weighted-average period of approximately 3.0 years and 2.6 years, respectively.

Warrants

Warrants outstanding for the purchase of common stock as of December 31, 2021 were as follows:

Number		Exercise Price		Expiration
Outstanding		Per Share		Date
	1,066	$	281.50	July 2023
	6,830	$	43.93	November 2023
	2,978	$	50.37	June 2024
	2,886	$	51.98	December 2024
	13,760

Common Stock Reserved for Future Issuance

Common stock reserved for future issuance was as follows:

	December 31, 2021
Common stock warrants		13,760
Common stock options and restricted stock units		1,420,050
Shares available under the 2015 equity incentive plan		420,896
Shares available under the employee stock purchase plan		71,933
		1,926,639

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2021

Accounting Policies [Abstract]

Organization and Business

We were incorporated in the state of Delaware on September 8, 2005. We are focused on the discovery and development of innovative medicines based on novel immunological pathways.

Principles of Consolidation

Our consolidated financial statements include our accounts and our 98% majority-owned subsidiary in Hong Kong, Pangu BioPharma Limited (Pangu BioPharma). All intercompany transactions and balances are eliminated in consolidation.

Liquidity and Financial Condition

We have incurred losses and negative cash flows from operations since our inception. As of December 31, 2021, we had an accumulated deficit of $372.3 million and we expect to continue to incur net losses for the foreseeable future. As of December 31, 2021, our cash, cash equivalents and available-for-sale investments were $107.9 million. We believe that our current cash, cash equivalents and available-for-sale investments, will be sufficient to meet our anticipated cash requirements for a period of at least one year from the date of this Annual Report.

We do not expect to generate any revenues from product sales unless and until we successfully complete development and obtain regulatory approval for one or more of our product candidates, which we expect will take a number of years at a minimum. If we obtain regulatory approval for any of our product candidates, we expect to incur significant commercialization expenses related to product sales, marketing, manufacturing and distribution. Accordingly, we will need to raise substantial additional capital to fund our operations. The amount and timing of our future funding requirements will depend on many factors, including the pace and results of our preclinical and clinical development efforts and the timing and nature of the regulatory approval process for our product candidates. We anticipate that we will seek to fund our operations through equity offerings, grant funding, collaborations, strategic partnerships and/or licensing arrangements, and when we are closer to commercialization of our product candidates potentially through debt financings. However, we may be unable to raise additional capital or enter into such arrangements when needed on favorable terms or at all. Our failure to raise capital or enter into such arrangements when needed would have a negative impact on our financial condition and ability to develop our product candidates.

Use of Estimates

Our consolidated financial statements are prepared in accordance with generally accepted accounting principles (GAAP). The preparation of our consolidated financial statements requires us to make estimates and assumptions that impact the reported amounts of assets, liabilities and expenses and the disclosure for these items in our consolidated financial statements and accompanying notes. The most significant estimates in our consolidated financial statements relate to the fair value of equity issuances and awards, and clinical trial and research and development expenses. Although these estimates are based on our knowledge of current events and actions we may undertake in the future, actual results may ultimately differ materially from these estimates and assumptions.

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. We view our operations and manage our business in one operating segment.

Cash and Cash Equivalents

Investment Securities

Concentration of Credit Risk

Property and Equipment

Impairment of Long-Lived Assets

Accrued Expenses

Leases

We do not separate lease and non-lease components for our long-term leases.

Revenue Recognition

Research and Development Costs

Patent Costs

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

Stock-Based Compensation

Income Taxes

Net Loss Per Share

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

	Years Ended December 31,
	2021		2020		2019
Class X preferred stock (if-converted to common stock)		—		—		587,445
Common stock warrants		13,760		13,904		13,904
Common stock options and restricted stock units		1,420,050		584,211		363,553
Employee stock purchase plan		2,045		1,602		1,958
Total		1,435,855		599,717		966,860

The following table summarizes our net loss per share (in thousands, except per share data):

	Years Ended December 31,
	2021			2020			2019
Numerator:
Net loss attributable to aTyr Pharma, Inc.	$	(33,768	)	$	(16,224	)	$	(23,603	)

Denominator:
Shares used in computing net loss per share, basic and diluted		19,080,878			9,160,269			3,355,600

Net loss per share - basic and diluted	$	(1.77	)	$	(1.77	)	$	(7.03	)

Recent Accounting Pronouncements

Fair Value Measurements - Schedule of Assets Measured at Fair Value on Recurring Basis (Detail) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	$ 2,052	$ 13,708
Total assets measured at fair value	107,627	28,445
Available-for-sale [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	105,575	14,737
Available-for-sale [Member] \| Short-term Investments \| Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	36,921	5,494
Available-for-sale [Member] \| Short-term Investments \| Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	55,713	7,024
Available-for-sale [Member] \| Short-term Investments \| Municipal Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	12,941
Available-for-sale [Member] \| Short-term Investments \| Asset-backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value		2,219
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	2,052	13,708
Total assets measured at fair value	2,052	13,708
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value	105,575	14,737
Significant Other Observable Inputs (Level 2) [Member] \| Available-for-sale [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	105,575	14,737
Significant Other Observable Inputs (Level 2) [Member] \| Available-for-sale [Member] \| Short-term Investments \| Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	36,921	5,494
Significant Other Observable Inputs (Level 2) [Member] \| Available-for-sale [Member] \| Short-term Investments \| Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	55,713	7,024
Significant Other Observable Inputs (Level 2) [Member] \| Available-for-sale [Member] \| Short-term Investments \| Municipal Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	$ 12,941
Significant Other Observable Inputs (Level 2) [Member] \| Available-for-sale [Member] \| Short-term Investments \| Asset-backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value		$ 2,219

Balance Sheet Details

12 Months Ended

Dec. 31, 2021

Balance Sheet Details [Abstract]

Balance Sheet Details

5. Balance Sheet Details

Prepaid expenses consist of the following (in thousands):

	December 31,
	2021		2020
Prepaid clinical and research expense	$	557	$	583
Prepaid manufacturing expenses (1)		4,188		513
Other prepaid expenses		478		707
	$	5,223	$	1,803

(1)

Prepaid manufacturing expenses of $3.7 million incurred in 2021 included a reservation fee and raw materials for manufacturing of efzofitimod clinical trial materials planned to occur in the second half of 2022.

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

	December 31,
	2021			2020
Computer and office equipment	$	616		$	552
Scientific and laboratory equipment		4,383			5,270
Tenant improvements		1,701			1,701
		6,700			7,523
Less accumulated depreciation and amortization		(6,157	)		(6,624	)
	$	543		$	899

As of December 31, 2021, 2020 and 2019, depreciation expense was $0.5 million, $0.6 million and $0.6 million, respectively.

Accrued expenses consist of the following (in thousands):

	December 31,
	2021		2020
Accrued salaries, wages and benefits	$	2,326	$	1,809
Accrued clinical studies costs	$	1,004	$	1,089
Other accrued expenses		672		674
	$	4,002	$	3,572

Commitments and Contingencies

12 Months Ended

Dec. 31, 2021

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

6. Commitments and Contingencies

Facility Lease

We have a non-cancelable facility lease that is subject to base lease payments, which escalate over the term of the lease, additional charges for common area maintenance and other costs. In July 2018, we entered into a lease amendment that reduced the space we lease from 24,494 square feet to 20,508 square feet and extended the lease term to May 2023. With the lease amendment, we do not have an option to extend the lease.

Operating lease expense for each of the years ended December 31, 2021, 2020 and 2019 was $1.0 million. As of December 31, 2021 and 2020, the weighted average remaining lease term was 1.4 years and 2.4 years, respectively, and the weighted average discount rate for each year was 9.6%.

Future minimum payments under the non-cancelable facility lease and reconciliation to the operating lease liability as of December 31, 2021 were as follows (in thousands):

	Operating Lease
2022	$	1,062
2023		404
Less: Amount representing interest		(88	)
Present value of lease payments		1,378
Less: Current portion of operating lease liability		(980	)
Long-term operating lease liability, net of current portion	$	398

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 2,336	$ 16,952
Available-for-sale investments	105,575	14,737
Other receivables	435	2,039
Prepaid expenses	5,223	1,803
Total current assets	113,569	35,531
Property and equipment, net	543	899
Right-of-use assets	1,267	2,083
Other assets	158	213
Total assets	115,537	38,726
Current liabilities:
Accounts payable	1,031	1,431
Accrued expenses	4,002	3,572
Current portion of operating lease liability	980	861
Total current liabilities	6,013	5,864
Long-term operating lease liability, net of current portion	398	1,378
Commitments and contingencies (Note 6)
Stockholders’ equity:
Preferred stock, $0.001 par value per share; 5,000,000 undesignated authorized shares; Class X Convertible Preferred Stock issued and outstanding shares – 0 as of December 31, 2021 and 2020, respectively
Common stock, $0.001 par value per share; 42,500,000 and 21,425,000 authorized shares as of December 31, 2021 and 2020, respectively; issued and outstanding shares – 27,793,035 and 11,018,954 as of December 31, 2021 and 2020, respectively	28	11
Additional paid-in capital	481,832	370,210
Accumulated other comprehensive loss	(263)	(43)
Accumulated deficit	(372,296)	(338,528)
Total aTyr Pharma stockholders’ equity	109,301	31,650
Noncontrolling interest in Pangu BioPharma Limited	(175)	(166)
Total stockholders' equity	109,126	31,484
Total liabilities and stockholders’ equity	$ 115,537	$ 38,726

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2021	Dec. 31, 2020
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	5,000,000	5,000,000
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	42,500,000	21,425,000
Common stock, shares issued	27,793,035	11,018,954
Common stock, shares outstanding	27,793,035	11,018,954
Class X Convertible Preferred Stock [Member]
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0

Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Revenues:
Total revenues		$ 10,455	$ 422
Operating expenses:
Research and development	$ 23,264	17,291	14,048
General and administrative	10,751	9,075	9,352
Total operating expenses	34,015	26,366	23,400
Loss from operations	(34,015)	(15,911)	(22,978)
Total other income (expense), net	238	(319)	(785)
Consolidated net loss	(33,777)	(16,230)	(23,763)
Net loss attributable to noncontrolling interest in Pangu BioPharma Limited	9	6	160
Net loss attributable to aTyr Pharma, Inc.	$ (33,768)	$ (16,224)	$ (23,603)
Net loss per share, basic and diluted	$ (1.77)	$ (1.77)	$ (7.03)
Shares used in computing net loss per share, basic and diluted	19,080,878	9,160,269	3,355,600
License Revenues [Member]
Revenues:
Total revenues		$ 10,455	$ 422

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2021

Accounting Policies [Abstract]

Schedule of Potentially Dilutive Securities Not Included in Calculation of Diluted Net Loss Per Share

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

	Years Ended December 31,
	2021		2020		2019
Class X preferred stock (if-converted to common stock)		—		—		587,445
Common stock warrants		13,760		13,904		13,904
Common stock options and restricted stock units		1,420,050		584,211		363,553
Employee stock purchase plan		2,045		1,602		1,958
Total		1,435,855		599,717		966,860

Summary of Net Loss Per Share

The following table summarizes our net loss per share (in thousands, except per share data):

	Years Ended December 31,
	2021			2020			2019
Numerator:
Net loss attributable to aTyr Pharma, Inc.	$	(33,768	)	$	(16,224	)	$	(23,603	)

Denominator:
Shares used in computing net loss per share, basic and diluted		19,080,878			9,160,269			3,355,600

Net loss per share - basic and diluted	$	(1.77	)	$	(1.77	)	$	(7.03	)

Stockholders' Equity - Schedule of Restricted Stock Unit Activity (Detail) - Restricted Stock Unit [Member]	12 Months Ended
	Dec. 31, 2021 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Number of Outstanding Restricted Stock Units, Beginning Balance \| shares	7,677
Number of Outstanding Restricted Stock Units, Granted \| shares	4,000
Number of Outstanding Restricted Stock Units, Released \| shares	(4,177)
Number of Outstanding Restricted Stock Units, Ending Balance \| shares	7,500
Weighted Average Grant Date Fair Value, Beginning Balance \| $ / shares	$ 5.32
Weighted Average Grant Date Fair Value, Granted \| $ / shares	3.89
Weighted Average Grant Date Fair Value, Released \| $ / shares	6.18
Weighted Average Grant Date Fair Value, Ending Balance \| $ / shares	$ 4.08

Balance Sheet Details (Tables)

12 Months Ended

Dec. 31, 2021

Balance Sheet Details [Abstract]

Schedule of Prepaid Expenses

Prepaid expenses consist of the following (in thousands):

	December 31,
	2021		2020
Prepaid clinical and research expense	$	557	$	583
Prepaid manufacturing expenses (1)		4,188		513
Other prepaid expenses		478		707
	$	5,223	$	1,803

Summary of Property and Equipment

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

	December 31,
	2021			2020
Computer and office equipment	$	616		$	552
Scientific and laboratory equipment		4,383			5,270
Tenant improvements		1,701			1,701
		6,700			7,523
Less accumulated depreciation and amortization		(6,157	)		(6,624	)
	$	543		$	899

Summary of Accrued Expenses

Accrued expenses consist of the following (in thousands):

	December 31,
	2021		2020
Accrued salaries, wages and benefits	$	2,326	$	1,809
Accrued clinical studies costs	$	1,004	$	1,089
Other accrued expenses		672		674
	$	4,002	$	3,572

Balance Sheet Details - Parenthetical (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2021 USD ($)
Prepaid Manufacturing Expenses [Member]
Prepaid Expenses [Line Items]
Reservation fees and raw materials	$ 3.7

Stockholders' Equity - Additional Information (Detail) - USD ($)	1 Months Ended					9 Months Ended	12 Months Ended
	Dec. 31, 2021	Oct. 31, 2021	Sep. 30, 2020	Feb. 29, 2020	Apr. 30, 2015	Sep. 30, 2021	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Mar. 31, 2021	Nov. 30, 2020	Mar. 31, 2020	May 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Commission Rate Equal To Gross Proceeds1										3.00%
Number of common stock shares reserved for issuance	1,926,639						1,926,639
Stock options granted							892,239
Weighted average exercise price, granted							$ 5.08
Weighted average grant date fair value of options granted							$ 3.82	$ 3.39	$ 5.67
Total grant date fair value of restricted stock units vested							$ 16,000	$ 21,000	$ 39,000
Aggregate intrinsic value of stock options exercised							80,000	0	0
Aggregate intrinsic value of restricted stock units	$ 31,000						31,000	$ 34,000	$ 31,000
Unrecognized share based compensation expense related to unvested stock options	3,500,000						3,500,000
Unrecognized share based compensation expense related to restricted stock units	$ 20,000						$ 20,000
Employee Stock Option [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized cost expected to be recognized over a weighted average period							3 years
Restricted Stock Unit [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized cost expected to be recognized over a weighted average period							2 years 7 months 6 days
2014 Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Maximum term for stock option plan grant							10 years
Options vesting period							4 years
2015 Stock Option and Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Maximum term for stock option plan grant					10 years
Options vesting period					4 years
Options vesting period, description							For an initial grant to an employee, 25% of the options generally vest on the first anniversary of the original vesting date, with the balance vesting monthly over the remaining three years. For subsequent grants to an employee, the options generally vest monthly over a four-year term.
2015 Stock Option and Incentive Plan [Member] \| One Year Anniversary [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Option vesting percentage					25.00%
2015 Employee Stock Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of common stock shares reserved for issuance	71,933						71,933
Aspire Capital [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares issued and sold							3,000,000	0
Shares Issued, Price Per Share	$ 5.09						$ 5.09
Proceeds from Issuance of Common Stock							$ 15,200,000
Commitment to purchase shares			$ 20,000,000.0
Long-term purchase commitment, period			30 months
Long-term purchase commitment, description			upon the terms and subject to the conditions and limitations set forth therein, Aspire Capital is committed to purchase up to an aggregate of $20.0 million of shares of our common stock at our request from time to time during the 30 month term of the Purchase Agreement.
Common Stock [Member] \| Inducement Pool Non Qualified Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options vesting period							4 years
Stock options granted	70,000	70,000
Weighted average exercise price, granted	$ 7.77	$ 8.73
Common Stock [Member] \| One Year Anniversary [Member] \| Inducement Pool Non Qualified Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options vesting period							1 year
Option vesting percentage							25.00%
Common Stock [Member] \| Share-based Payment Arrangement, Tranche Two \| Inducement Pool Non Qualified Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options vesting period							3 years
Option vesting percentage							75.00%
Public Offerings
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Proceeds from Issuance of Common Stock				$ 18,800,000		$ 80,600,000
Public Offerings \| Common Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares issued and sold				4,235,294		10,781,250
Shares Issued, Price Per Share				$ 4.25		$ 8.00
Shares issued, price per share												635,294
ATM Offering Program [Member] \| Cowen Company, LLC (Cowen) [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Proceeds from Issuance of Common Stock							$ 4,400,000
ATM Offering Program [Member] \| Cowen Company, LLC (Cowen) [Member] \| Sale Agreement [Member] \| Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Agreed upon value of sale of common stock per transaction										$ 25,000,000.0
ATM Offering Program [Member] \| Common Stock [Member] \| Cowen Company, LLC (Cowen) [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares issued and sold							986,267
Shares Issued, Price Per Share	4.75						$ 4.75
ATM Offering Program [Member] \| H.C. Wainwright & Co., LLC [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Proceeds from Issuance of Common Stock							$ 9,600,000	$ 6,400,000
Commission rate equal to gross proceeds													3.00%
ATM Offering Program [Member] \| H.C. Wainwright & Co., LLC [Member] \| Sale Agreement [Member] \| Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Agreed upon value of sale of common stock per transaction											$ 20,000,000.0		$ 10,000,000.0
ATM Offering Program [Member] \| Common Stock [Member] \| H.C. Wainwright & Co., LLC [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares issued and sold							1,988,254	1,657,075
Shares Issued, Price Per Share	$ 4.99						$ 4.99	$ 4.07		$ 20.0
IPO [Member] \| 2015 Stock Option and Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Effective date of plan							May 06, 2015
Number of common stock shares reserved for issuance	420,896						420,896
Additional number of common stock shares reserved for issuance	750,000						750,000	350,000
IPO [Member] \| 2015 Employee Stock Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Effective date of plan							May 06, 2015
Number of common stock shares reserved for issuance	71,933						71,933

Stockholders' Equity - Schedule of Allocation of Stock-Based Compensation for All Options Including Performance Options with Market Condition and Restricted Stock Units (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 1,614	$ 1,465	$ 1,783
Research and Development Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	295	254	354
General and Administrative Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 1,319	$ 1,211	$ 1,429

Income Tax - Schedule of Reconciliations of the Expected Statutory Federal Income Tax (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Expected income taxes benefit at federal statutory rate	$ (7,093,000)	$ (3,408,000)	$ (4,990,000)
State income taxes, net of federal benefit	(2,313,000)	(12,000)	(19,000)
Permanent items and other	592,000	169,000	49,000
Stock compensation	90,000	804,000	701,000
Research credits	(1,253,000)	(835,000)	(817,000)
Unrecognized tax benefits	500,000	334,000	327,000
Foreign rate differential	21,000	13,000	20,000
Change in tax rate	52,000	(7,000)	(49,000)
Change in valuation allowance	9,404,000	2,942,000	4,778,000
Income tax (benefit) expense	$ 0	$ 0	$ 0

Commitments and Contingencies (Tables)	12 Months Ended
Commitments and Contingencies (Tables)	Dec. 31, 2021
Debt Instruments [Abstract]
Schedule of Future Minimum Payments under Non-cancelable Operating Lease and Reconciliation to Operating Lease Liability	<p style="text-align:justify;margin-top:12pt;margin-bottom:0pt;text-indent:5%;font-family:Times New Roman;font-size:10pt;font-weight:normal;font-style:normal;text-transform:none;font-variant: normal;">Future minimum payments under the non-cancelable facility lease and reconciliation to the operating lease liability as of December 31, 2021 were as follows (in thousands):</p> <p style="text-align:justify;margin-bottom:0pt;margin-top:0pt;text-indent:0%;font-family:Times New Roman;font-size:10pt;"> </p> <div> <table border="0" cellpadding="0" cellspacing="0" style="margin:auto;border-collapse:collapse; width:60%;"> <tr> <td style="background-color:#FFFFFF;padding-left:0pt;padding-Right:0.75pt;padding-Top:0.75pt;width:80.3%; border-bottom:solid 0.75pt transparent;" valign="bottom"> <p style="text-align:center;margin-bottom:0pt;margin-top:0pt;margin-left:0pt;;text-indent:0pt;;font-family:Times New Roman;font-size:10pt;font-weight:normal;font-style:normal;text-transform:none;font-variant: normal;"> </p></td> <td style="background-color:#FFFFFF;padding-left:0pt;padding-Right:0.75pt;padding-Top:0.75pt;width:1.88%; border-bottom:solid 0.75pt transparent;" valign="bottom"> <p style="margin-bottom:0pt;margin-top:0pt;margin-left:0pt;;text-indent:0pt;;font-weight:bold;color:#000000;font-family:Times New Roman;font-size:10pt;font-style:normal;text-transform:none;font-variant: normal;"> </p></td> <td colspan="2" style="background-color:#FFFFFF;padding-left:0pt;padding-Right:0.75pt;padding-Top:0.75pt;padding-Bottom:0pt;width:16.8%; border-bottom:solid 0.75pt #000000;" valign="bottom"> <p style="text-align:center;margin-bottom:0pt;margin-top:0pt;margin-left:0pt;;text-indent:0pt;;font-weight:bold;color:#000000;font-family:Times New Roman;font-size:10pt;font-style:normal;text-transform:none;font-variant: normal;">Operating Lease</p></td> <td style="background-color:#FFFFFF;padding-left:0pt;padding-Right:0.75pt;padding-Top:0.75pt;width:1%;white-space:nowrap;" valign="bottom"> <p style="margin-bottom:0pt;margin-top:0pt;margin-left:0pt;;text-indent:0pt;;font-weight:bold;color:#000000;font-family:Times New Roman;font-size:10pt;font-style:normal;text-transform:none;font-variant: normal;"> </p></td> </tr> <tr> <td style="background-color:#CFF0FC;padding-left:0pt;padding-Right:0.75pt;padding-Top:0.75pt;padding-Bottom:0pt;width:80.3%;" valign="bottom"> <p style="margin-bottom:0pt;margin-top:0pt;margin-left:0pt;;text-indent:0pt;;color:#000000;font-family:Times New Roman;font-size:10pt;font-weight:normal;font-style:normal;text-transform:none;font-variant: normal;">2022</p></td> <td style="background-color:#CFF0FC;padding-left:0pt;padding-Right:0.75pt;padding-Top:0.75pt;padding-Bottom:0pt;width:1.88%;" valign="bottom"> <p style="margin-bottom:0pt;margin-top:0pt;margin-left:0pt;;text-indent:0pt;;color:#000000;font-family:Times New Roman;font-size:10pt;font-weight:normal;font-style:normal;text-transform:none;font-variant: normal;"> </p></td> <td style="background-color:#CFF0FC;padding-left:0pt;padding-Right:0.75pt;padding-Top:0.75pt;padding-Bottom:0pt;width:1%; border-top:solid 0.75pt #000000;white-space:nowrap;" valign="bottom"> <p style="margin-bottom:0pt;margin-top:0pt;margin-left:0pt;;text-indent:0pt;;color:#000000;font-family:Times New Roman;font-size:10pt;font-weight:normal;font-style:normal;text-transform:none;font-variant: normal;">$</p></td> <td style="background-color:#CFF0FC;padding-left:0pt;padding-Right:0.75pt;padding-Top:0.75pt;padding-Bottom:0pt;width:15.8%; border-top:solid 0.75pt #000000;white-space:nowrap;" valign="bottom"> <p style="text-align:right;margin-bottom:0pt;margin-top:0pt;margin-left:0pt;;text-indent:0pt;;color:#000000;font-family:Times New Roman;font-size:10pt;font-weight:normal;font-style:normal;text-transform:none;font-variant: normal;">1,062</p></td> <td style="background-color:#CFF0FC;padding-left:0pt;padding-Right:0.75pt;padding-Top:0.75pt;padding-Bottom:0pt;width:1%;white-space:nowrap;" valign="bottom"> <p style="margin-bottom:0pt;margin-top:0pt;margin-left:0pt;;text-indent:0pt;;color:#000000;font-family:Times New Roman;font-size:10pt;font-weight:normal;font-style:normal;text-transform:none;font-variant: normal;"> </p></td> </tr> <tr> <td style="background-color:#FFFFFF;padding-left:0pt;padding-Right:0.75pt;padding-Top:0.75pt;padding-Bottom:0pt;width:80.3%;" valign="bottom"> <p style="margin-bottom:0pt;margin-top:0pt;margin-left:0pt;;text-indent:0pt;;color:#000000;font-family:Times New Roman;font-size:10pt;font-weight:normal;font-style:normal;text-transform:none;font-variant: normal;">2023</p></td> <td style="background-color:#FFFFFF;padding-left:0pt;padding-Right:0.75pt;padding-Top:0.75pt;padding-Bottom:0pt;width:1.88%;" valign="bottom"> <p style="margin-bottom:0pt;margin-top:0pt;margin-left:0pt;;text-indent:0pt;;color:#000000;font-family:Times New Roman;font-size:10pt;font-weight:normal;font-style:normal;text-transform:none;font-variant: normal;"> </p></td> <td style="background-color:#FFFFFF;padding-left:0pt;padding-Right:0.75pt;padding-Top:0.75pt;padding-Bottom:0pt;width:1%;white-space:nowrap;" valign="bottom"> <p style="margin-bottom:0pt;margin-top:0pt;margin-left:0pt;;text-indent:0pt;;color:#000000;font-family:Times New Roman;font-size:10pt;font-weight:normal;font-style:normal;text-transform:none;font-variant: normal;"> </p></td> <td style="background-color:#FFFFFF;padding-left:0pt;padding-Right:0.75pt;padding-Top:0.75pt;padding-Bottom:0pt;width:15.8%;white-space:nowrap;" valign="bottom"> <p style="text-align:right;margin-bottom:0pt;margin-top:0pt;margin-left:0pt;;text-indent:0pt;;color:#000000;font-family:Times New Roman;font-size:10pt;font-weight:normal;font-style:normal;text-transform:none;font-variant: normal;">404</p></td> <td style="background-color:#FFFFFF;padding-left:0pt;padding-Right:0.75pt;padding-Top:0.75pt;padding-Bottom:0pt;width:1%;white-space:nowrap;" valign="bottom"> <p style="margin-bottom:0pt;margin-top:0pt;margin-left:0pt;;text-indent:0pt;;color:#000000;font-family:Times New Roman;font-size:10pt;font-weight:normal;font-style:normal;text-transform:none;font-variant: normal;"> </p></td> </tr> <tr> <td style="background-color:#CFF0FC;padding-left:0pt;padding-Right:0.75pt;padding-Top:0.75pt;width:80.3%; border-bottom:solid 0.75pt transparent;" valign="bottom"> <p style="margin-bottom:0pt;margin-top:0pt;margin-left:0pt;;text-indent:0pt;;color:#000000;font-family:Times New Roman;font-size:10pt;font-weight:normal;font-style:normal;text-transform:none;font-variant: normal;">Less: Amount representing interest</p></td> <td style="background-color:#CFF0FC;padding-left:0pt;padding-Right:0.75pt;padding-Top:0.75pt;width:1.88%; border-bottom:solid 0.75pt transparent;" valign="bottom"> <p style="margin-bottom:0pt;margin-top:0pt;margin-left:0pt;;text-indent:0pt;;color:#000000;font-family:Times New Roman;font-size:10pt;font-weight:normal;font-style:normal;text-transform:none;font-variant: normal;"> </p></td> <td style="background-color:#CFF0FC;padding-left:0pt;padding-Right:0.75pt;padding-Top:0.75pt;padding-Bottom:0pt;width:1%; border-bottom:solid 0.75pt #000000;white-space:nowrap;" valign="bottom"> <p style="margin-bottom:0pt;margin-top:0pt;margin-left:0pt;;text-indent:0pt;;color:#000000;font-family:Times New Roman;font-size:10pt;font-weight:normal;font-style:normal;text-transform:none;font-variant: normal;"> </p></td> <td style="background-color:#CFF0FC;padding-left:0pt;padding-Right:0.75pt;padding-Top:0.75pt;padding-Bottom:0pt;width:15.8%; border-bottom:solid 0.75pt #000000;white-space:nowrap;" valign="bottom"> <p style="text-align:right;margin-bottom:0pt;margin-top:0pt;margin-left:0pt;;text-indent:0pt;;color:#000000;font-family:Times New Roman;font-size:10pt;font-weight:normal;font-style:normal;text-transform:none;font-variant: normal;">(88</p></td> <td style="background-color:#CFF0FC;padding-left:0pt;padding-Right:0.75pt;padding-Top:0.75pt;width:1%; border-bottom:solid 0.75pt transparent;white-space:nowrap;" valign="bottom"> <p style="margin-bottom:0pt;margin-top:0pt;margin-left:0pt;;text-indent:0pt;;color:#000000;font-family:Times New Roman;font-size:10pt;font-weight:normal;font-style:normal;text-transform:none;font-variant: normal;">)</p></td> </tr> <tr> <td style="background-color:#FFFFFF;padding-left:0pt;padding-Right:0.75pt;padding-Top:0.75pt;padding-Bottom:0pt;width:80.3%;" valign="bottom"> <p style="margin-bottom:0pt;margin-top:0pt;margin-left:0pt;;text-indent:0pt;;color:#000000;font-family:Times New Roman;font-size:10pt;font-weight:normal;font-style:normal;text-transform:none;font-variant: normal;">Present value of lease payments</p></td> <td style="background-color:#FFFFFF;padding-left:0pt;padding-Right:0.75pt;padding-Top:0.75pt;padding-Bottom:0pt;width:1.88%;" valign="bottom"> <p style="margin-bottom:0pt;margin-top:0pt;margin-left:0pt;;text-indent:0pt;;color:#000000;font-family:Times New Roman;font-size:10pt;font-weight:normal;font-style:normal;text-transform:none;font-variant: normal;"> </p></td> <td style="background-color:#FFFFFF;padding-left:0pt;padding-Right:0.75pt;padding-Top:0.75pt;padding-Bottom:0pt;width:1%; border-top:solid 0.75pt #000000;white-space:nowrap;" valign="bottom"> <p style="margin-bottom:0pt;margin-top:0pt;margin-left:0pt;;text-indent:0pt;;color:#000000;font-family:Times New Roman;font-size:10pt;font-weight:normal;font-style:normal;text-transform:none;font-variant: normal;"> </p></td> <td style="background-color:#FFFFFF;padding-left:0pt;padding-Right:0.75pt;padding-Top:0.75pt;padding-Bottom:0pt;width:15.8%; border-top:solid 0.75pt #000000;white-space:nowrap;" valign="bottom"> <p style="text-align:right;margin-bottom:0pt;margin-top:0pt;margin-left:0pt;;text-indent:0pt;;color:#000000;font-family:Times New Roman;font-size:10pt;font-weight:normal;font-style:normal;text-transform:none;font-variant: normal;">1,378</p></td> <td style="background-color:#FFFFFF;padding-left:0pt;padding-Right:0.75pt;padding-Top:0.75pt;padding-Bottom:0pt;width:1%;white-space:nowrap;" valign="bottom"> <p style="margin-bottom:0pt;margin-top:0pt;margin-left:0pt;;text-indent:0pt;;color:#000000;font-family:Times New Roman;font-size:10pt;font-weight:normal;font-style:normal;text-transform:none;font-variant: normal;"> </p></td> </tr> <tr> <td style="background-color:#CFF0FC;padding-left:0pt;padding-Right:0.75pt;padding-Top:0.75pt;width:80.3%; border-bottom:solid 0.75pt transparent;" valign="bottom"> <p style="margin-bottom:0pt;margin-top:0pt;margin-left:0pt;;text-indent:0pt;;color:#000000;font-family:Times New Roman;font-size:10pt;font-weight:normal;font-style:normal;text-transform:none;font-variant: normal;">Less: Current portion of operating lease liability</p></td> <td style="background-color:#CFF0FC;padding-left:0pt;padding-Right:0.75pt;padding-Top:0.75pt;width:1.88%; border-bottom:solid 0.75pt transparent;" valign="bottom"> <p style="margin-bottom:0pt;margin-top:0pt;margin-left:0pt;;text-indent:0pt;;color:#000000;font-family:Times New Roman;font-size:10pt;font-weight:normal;font-style:normal;text-transform:none;font-variant: normal;"> </p></td> <td style="background-color:#CFF0FC;padding-left:0pt;padding-Right:0.75pt;padding-Top:0.75pt;padding-Bottom:0pt;width:1%; border-bottom:solid 0.75pt #000000;white-space:nowrap;" valign="bottom"> <p style="margin-bottom:0pt;margin-top:0pt;margin-left:0pt;;text-indent:0pt;;color:#000000;font-family:Times New Roman;font-size:10pt;font-weight:normal;font-style:normal;text-transform:none;font-variant: normal;"> </p></td> <td style="background-color:#CFF0FC;padding-left:0pt;padding-Right:0.75pt;padding-Top:0.75pt;padding-Bottom:0pt;width:15.8%; border-bottom:solid 0.75pt #000000;white-space:nowrap;" valign="bottom"> <p style="text-align:right;margin-bottom:0pt;margin-top:0pt;margin-left:0pt;;text-indent:0pt;;color:#000000;font-family:Times New Roman;font-size:10pt;font-weight:normal;font-style:normal;text-transform:none;font-variant: normal;">(980</p></td> <td style="background-color:#CFF0FC;padding-left:0pt;padding-Right:0.75pt;padding-Top:0.75pt;width:1%; border-bottom:solid 0.75pt transparent;white-space:nowrap;" valign="bottom"> <p style="margin-bottom:0pt;margin-top:0pt;margin-left:0pt;;text-indent:0pt;;color:#000000;font-family:Times New Roman;font-size:10pt;font-weight:normal;font-style:normal;text-transform:none;font-variant: normal;">)</p></td> </tr> <tr> <td style="background-color:#FFFFFF;padding-left:0pt;padding-Right:0.75pt;padding-Top:0.75pt;width:80.3%; border-bottom:double 2.5pt transparent;" valign="bottom"> <p style="margin-bottom:0pt;margin-top:0pt;margin-left:0pt;;text-indent:0pt;;color:#000000;font-family:Times New Roman;font-size:10pt;font-weight:normal;font-style:normal;text-transform:none;font-variant: normal;">Long-term operating lease liability, net of current portion</p></td> <td style="background-color:#FFFFFF;padding-left:0pt;padding-Right:0.75pt;padding-Top:0.75pt;width:1.88%; border-bottom:double 2.5pt transparent;" valign="bottom"> <p style="margin-bottom:0pt;margin-top:0pt;margin-left:0pt;;text-indent:0pt;;color:#000000;font-size:11pt;font-family:Calibri;font-weight:normal;font-style:normal;text-transform:none;font-variant: normal;"> </p></td> <td style="background-color:#FFFFFF;padding-left:0pt;padding-Right:0.75pt;padding-Top:0.75pt;padding-Bottom:0pt;width:1%; border-top:solid 0.75pt #000000; border-bottom:double 2.5pt #000000;white-space:nowrap;" valign="bottom"> <p style="margin-bottom:0pt;margin-top:0pt;margin-left:0pt;;text-indent:0pt;;color:#000000;font-family:Times New Roman;font-size:10pt;font-weight:normal;font-style:normal;text-transform:none;font-variant: normal;">$</p></td> <td style="background-color:#FFFFFF;padding-left:0pt;padding-Right:0.75pt;padding-Top:0.75pt;padding-Bottom:0pt;width:15.8%; border-top:solid 0.75pt #000000; border-bottom:double 2.5pt #000000;white-space:nowrap;" valign="bottom"> <p style="text-align:right;margin-bottom:0pt;margin-top:0pt;margin-left:0pt;;text-indent:0pt;;color:#000000;font-family:Times New Roman;font-size:10pt;font-weight:normal;font-style:normal;text-transform:none;font-variant: normal;">398</p></td> <td style="background-color:#FFFFFF;padding-left:0pt;padding-Right:0.75pt;padding-Top:0.75pt;width:1%; border-bottom:double 2.5pt transparent;white-space:nowrap;" valign="bottom"> <p style="margin-bottom:0pt;margin-top:0pt;margin-left:0pt;;text-indent:0pt;;color:#000000;font-size:1pt;font-family:Times New Roman;font-weight:normal;font-style:normal;text-transform:none;font-variant: normal;"> </p></td> </tr> </table></div>

Stockholders' Equity (Tables)

12 Months Ended

Dec. 31, 2021

Summary of Stock Option Activity

Stock option activity is summarized as follows:

	Number of Outstanding Stock Options			Weighted Average Exercise Price		Weighted Remaining Contractual Term		Aggregate Intrinsic Value
Outstanding as of December 31, 2020		576,534		$	23.33
Granted		892,239		$	5.08
Exercises		(10,751	)	$	5.78
Canceled/forfeited/expired		(45,472	)	$	22.38
Outstanding as of December 31, 2021		1,412,550		$	12.01		8.46	$	3,134,377
Options vested and expected to vest as of December 31, 2021		1,412,550		$	12.01		8.46	$	3,134,377
Options exercisable as of December 31, 2021		472,553		$	25.55		7.10	$	763,461

Summary of Assumptions Used to Determine Fair Value of Employee Stock Purchase Plan

The assumptions used in the Black-Scholes option pricing model to determine the fair value of the ESPP offering were as follows:

	Years Ended December 31,
	2021		2020		2019
Expected term (in years)		0.50		0.50		0.50
Risk-free interest rate	0.04% – 0.12%		0.1% – 1.6%		1.6% – 2.5%
Expected volatility	89.7% – 108.12%		89.7% – 143.2%		99.7% – 141.7%
Expected dividend yield		0.0%		0.0%		0.0%

Schedule of Restricted Stock Units Activity

	Number of Outstanding Restricted Stock Units			Weighted Average Grant Date Fair Value
Balance as of December 31, 2020		7,677		$	5.32
Granted		4,000		$	3.89
Released		(4,177	)	$	6.18
Balance as of December 31, 2021		7,500		$	4.08

Schedule of Allocation of Stock-Based Compensation for All Options Including Performance Options with Market Condition and Restricted Stock Units

The allocation of stock-based compensation for all options, including performance options with market condition and restricted stock units is as follows (in thousands):

	Years Ended December 31,
	2021		2020		2019
Research and development	$	295	$	254	$	354
General and administrative		1,319		1,211		1,429
Total stock-based compensation expense	$	1,614	$	1,465	$	1,783

Summary of Warrants Outstanding

Warrants outstanding for the purchase of common stock as of December 31, 2021 were as follows:

Number		Exercise Price		Expiration
Outstanding		Per Share		Date
	1,066	$	281.50	July 2023
	6,830	$	43.93	November 2023
	2,978	$	50.37	June 2024
	2,886	$	51.98	December 2024
	13,760

Summary of Common Stock Reserved for Future Issuance

Common stock reserved for future issuance was as follows:

	December 31, 2021
Common stock warrants		13,760
Common stock options and restricted stock units		1,420,050
Shares available under the 2015 equity incentive plan		420,896
Shares available under the employee stock purchase plan		71,933
		1,926,639

Employee Stock Option [Member]

Summary of Assumptions Used to Determine Fair Value of Employee Stock Option Grants and Performance Options with Market Condition

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

Years Ended December 31,

2021

2020

2019

Expected term (in years)

5.50 – 6.08

5.51 – 6.07

Risk-free interest rate

0.6% – 1.3%

0.3% – 1.5%

1.4% – 2.6%

Expected volatility

86.3% – 104.8%

102.2% – 109.7%

97.2% – 105.4%

Expected dividend yield

0.0%

Stockholders' Equity - Summary of Common Stock Reserved for Future Issuance (Detail)	Dec. 31, 2021 shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance	1,926,639
Common Stock Warrants [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance	13,760
Common Stock Options and Restricted Stock Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance	1,420,050
Shares Available Under the 2015 Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance	420,896
2015 Employee Stock Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance	71,933

Income Tax

12 Months Ended

Dec. 31, 2021

Income Tax Disclosure [Abstract]

Income Tax

8. Income Tax

Pretax losses were generated by both domestic and foreign operations as follows (in thousands):

	Years Ended December 31,
	2021			2020			2019
United States	$	(33,316	)	$	(15,950	)	$	(23,315	)
Foreign		(458	)		(280	)		(448	)
Worldwide pre-tax loss	$	(33,774	)	$	(16,230	)	$	(23,763	)

For the years ended December 31, 2021, 2020, and 2019, we did not record a provision for income taxes due to a full valuation allowance against our deferred taxes. A reconciliation of the expected statutory federal income tax provision to the actual income tax provision is summarized as follows (in thousands):

	Years Ended December 31,
	2021			2020			2019
Expected income taxes benefit at federal statutory rate	$	(7,093	)	$	(3,408	)	$	(4,990	)
State income taxes, net of federal benefit		(2,313	)		(12	)		(19	)
Permanent items and other		592			169			49
Stock compensation		90			804			701
Research credits		(1,253	)		(835	)		(817	)
Unrecognized tax benefits		500			334			327
Foreign rate differential		21			13			20
Change in tax rate		52			(7	)		(49	)
Change in valuation allowance		9,404			2,942			4,778
Income tax (benefit) expense	$	—		$	—		$	—

Deferred income taxes are provided for temporary differences in recognizing certain income and expense items for financial and tax reporting purposes. The deferred tax assets consisted primarily of the income tax benefits from net operating loss (NOL) carryforwards, research and development credits and capitalized research and development expenses, along with other accruals and reserves. Valuation allowances of $84.1 million and $74.6 million as of December 31, 2021 and 2020, respectively, have been recorded to offset deferred tax assets as realization of such assets does not meet the more-likely-than-not threshold under ASC 740, Accounting for Income Taxes.

Significant components of our deferred tax assets are summarized as follows (in thousands):

	December 31,
	2021			2020
Deferred tax assets:
Net operating loss carryforwards	$	48,833		$	41,203
Capitalized research and development expenses		18,086			17,007
Research credits and other state credits		13,695			12,954
Intangible assets		1,465			1,655
Reserve and accruals		641			544
Share-based compensation expense		1,369			1,253
Lease liability		290			472
Valuation allowance		(84,112	)		(74,646	)
Total deferred tax assets	$	267		$	442
Deferred tax liabilities:
Right of use lease assets		(267	)		(442	)
Total deferred tax liabilities		(267	)		(442	)
Net deferred tax assets	$	—		$	—

As of December 31, 2021, we had federal NOL carryforwards of approximately $204.5 million, with $92.0 million of NOLs generated after December 31, 2017 carrying forward indefinitely and $112.5 million of NOLs that will begin to expire in 2025. NOLs generated after January 1, 2018 are subject to an 80% of taxable income limitation when utilized after December 31, 2020 in accordance with the Tax Cuts and Jobs Act of 2017 as modified by the Coronavirus Aid, Relief and Economic Security Act (CARES Act). We had state net operating loss carryforwards of approximately $192.0 million, and foreign net operating loss carryforwards of $8.7 million. The state net operating losses will begin to expire in 2021. The foreign net operating losses carry over indefinitely.

As of December 31, 2021, we had federal and state research and development credit carryforwards of approximately $6.5 million and $4.8 million, respectively, which begin to expire in 2026 for federal purposes and carry over indefinitely for state purposes. We had $12.5 million of federal Orphan Drug Credits as of December 31, 2021, which will begin to expire in 2035.

Utilization of the domestic NOL and research and development credit carryforwards may be subject to a substantial annual limitation due to ownership change limitations that may have occurred or that could occur in the future, as required by Sections 382 and 383 of the Internal Revenue Code of 1986, as amended (the Code), as well as similar state and foreign provisions. These ownership changes may limit the amount of NOL and research and development credit carryforwards that can be utilized annually to offset future taxable income and tax, respectively. In general, an “ownership change” as defined by Section 382 of the Code results from a transaction or series of transactions over a three-year period resulting in an ownership change of more than 50 percentage points of the outstanding stock of a company by certain stockholders. Since the Company’s formation, we raised capital through the issuance of capital stock on several occasions which on its own or combined with the purchasing stockholders’ subsequent disposition of those shares, has resulted in such an ownership change, and could result in an ownership change in the future.

Upon the occurrence of an ownership change under Section 382 as outlined above, utilization of the NOL and research and development credit carryforwards become subject to an annual limitation under Section 382 of the Code, which is determined by first multiplying the value of our stock at the time of the ownership change by the applicable long-term, tax-exempt rate, which could be subject to additional adjustments. Any limitation may result in expiration of a portion of our NOL or research and development credit carryforwards before utilization. Due to the existence of the valuation allowance, any impact to the NOL and research and development tax credit carryforwards from Section 382 analysis will be offset by a corresponding adjustment to valuation allowance, resulting in no tax provision impact.

We recognize a tax benefit from an uncertain tax position when it is more likely than not that the position will be sustained upon examination, including resolutions of any related appeals or litigation processes, based on the technical merits. Income tax positions must meet a more-likely-than-not recognition threshold to be recognized.

Our practice is to recognize interest and penalties related to income tax matters in income tax expense. We had no accrual for interest and penalties on our balance sheet and had not recognized interest or penalties in the consolidated statements of operations for the years ended December 31, 2021, 2020 and 2019.

Due to the existence of the valuation allowance, future changes in unrecognized tax benefits will not impact our effective tax rate.

Uncertain tax positions are evaluated based upon the facts and circumstances that exist at each reporting period. Subsequent changes in judgment based upon new information may lead to changes in recognition, derecognition, and measurement. Adjustments may result, for example, upon resolution of an issue with the taxing authorities, or expiration of a statute of limitations barring an assessment for an issue.

The activity related to our unrecognized tax benefits is summarized as follows (in thousands):

	December 31,
	2021			2020		2019
Balance as of beginning of year	$	21,707		$	21,302	$	19,643
Increase (decrease) related to prior year tax positions		(9	)		3		—
Increase related to current year tax positions		534			402		1,659
Balance as of end of year	$	22,232		$	21,707	$	21,302

We do not anticipate that the amount of unrecognized tax benefits as of December 31, 2021 will change within the next twelve months.

We are subject to taxation in the United States, Hong Kong and state jurisdictions. Our tax years from inception are subject to examination by the United States, Hong Kong and California authorities due to carry forward of unutilized NOLs and research and development credits.

- Definition

The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 21
-URI http://asc.fasb.org/extlink&oid=121826272&loc=d3e32857-109319

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
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-Paragraph 2
-Subparagraph (SAB Topic 11.C)
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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-Section 50
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-Subparagraph (b)
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section S99
-Paragraph 1
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-URI http://asc.fasb.org/extlink&oid=122134291&loc=d3e330036-122817

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=121826272&loc=d3e32705-109319

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-URI http://asc.fasb.org/topic&trid=2144680

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
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-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6424122&loc=d3e41874-109331

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-Paragraph 1
-Subparagraph (SX 210.4-08(h)(2))
-URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690

+ Details

Stockholders' Equity - Summary of Assumptions Used to Determine Fair Value of Employee Stock Option Grants, Employee Stock Purchase Plan and Performance Options with Market Condition (Detail)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
ESPP [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	6 months	6 months	6 months
Risk-free interest rate, minimum	0.04%	0.10%	1.60%
Risk-free interest rate, maximum	0.12%	1.60%	2.50%
Expected volatility, minimum	89.70%	89.70%	99.70%
Expected volatility, maximum	108.12%	143.20%	141.70%
Expected dividend yield	0.00%	0.00%	0.00%
Employee Stock Option [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate, minimum	0.60%	0.30%	1.40%
Risk-free interest rate, maximum	1.30%	1.50%	2.60%
Expected volatility, minimum	86.30%	102.20%	97.20%
Expected volatility, maximum	104.80%	109.70%	105.40%
Expected dividend yield	0.00%	0.00%	0.00%
Employee Stock Option [Member] \| Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	5 years 6 months	5 years 6 months	5 years 6 months 3 days
Employee Stock Option [Member] \| Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	6 years 29 days	6 years 29 days	6 years 25 days

Fair Value Measurements - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2021
Maximum [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments effective maturity period	12 months

Balance Sheet Details - Summary of Accrued Expenses (Detail) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Accrued Liabilities Current [Abstract]
Accrued salaries, wages and benefits	$ 2,326	$ 1,809
Accrued clinical studies costs	1,004	1,089
Other accrued expenses	672	674
Accrued expenses	$ 4,002	$ 3,572

License, Collaboration and Other Agreements

12 Months Ended

Dec. 31, 2021

License Agreement [Abstract]

License, Collaboration and Other Agreements

4. License, Collaboration and Other Agreements

Kyorin Pharmaceutical Co., Ltd.

In January 2020, we entered into a collaboration and license agreement with Kyorin Pharmaceutical Co., Ltd. (Kyorin) for the development and commercialization of efzofitimod (the non-proprietary name for our lead therapeutic candidate ATYR1923) for interstitial lung diseases (ILD) in Japan. Under the agreement (the Kyorin Agreement), Kyorin received an exclusive right to develop and commercialize efzofitimod in Japan for all forms of ILD. Under the terms of the Kyorin Agreement, Kyorin is obligated to fund all research, development, regulatory, marketing and commercialization activities in Japan. In September 2020, Kyorin began dosing

patients in a Phase 1 clinical trial of efzofitimod (known as KRP-R120 in Japan) and completed the last subject visit in December 2020. The Phase 1 clinical trial, which was conducted and funded by Kyorin, is a placebo-controlled study to evaluate the safety, pharmacokinetics and immunogenicity of efzofitimod. Efzofitimod was observed to be generally well-tolerated with no drug-related serious adverse events and pharmacokinetics findings were consistent with previous studies of efzofitimod. We received an $8.0 million upfront payment in January 2020 and a $2.0 milestone payment in January 2021 upon completion of enrollment in the Phase 1 clinical trial in December 2020, and we are eligible to receive up to an additional $165.0 million in the aggregate upon achievement of certain development, regulatory and sales milestones, as well as tiered royalties ranging from the mid-single digits to mid-teens on net sales in Japan.

Either party may terminate the Kyorin Agreement in the event that the other party breaches the agreement and fails to cure the breach, becomes insolvent or challenges certain of the intellectual property rights licensed under the agreement.

We assessed our license and collaboration with Kyorin in accordance with Topic 606 and concluded that Kyorin is a customer. We identified the following performance obligations under the Kyorin Agreement: 1) the license of efzofitimod for ILD in Japan; and 2) free clinical trial material for Kyorin’s Phase 1 clinical trial. The $8.0 million upfront payment received from Kyorin is non-refundable and non-creditable and is considered fixed consideration. We determined that the relative stand-alone selling price was $7.9 million when the license was delivered to Kyorin in January 2020. We determined that the relative standalone selling price was $0.1 million for the free clinical trial material delivered to Kyorin in June 2020, using the “expected cost plus a margin” approach. In December 2020, Kyorin completed the last subject visit in its Phase 1 trial of efzofitimod. This achievement triggered a $2.0 million milestone payment, which we received in January 2021.

The remaining milestones and royalty payments under the Kyorin Agreement are variable consideration. Since the milestone payments are binary in nature, we will use the “most-likely” method to evaluate whether the milestones should be included as revenue. We will constrain these amounts until the milestone is probable of being achieved. The royalties are dependent on future sales by Kyorin which are at the full discretion of Kyorin. Accordingly, we will apply a constraint to these amounts until the future sale sales have occurred.

Hong Kong University of Science and Technology

In March 2020, our subsidiary, Pangu BioPharma, together with the Hong Kong University of Science and Technology (HKUST) was awarded a grant of approximately $750,000 to build a high-throughput platform for the development of bi-specific antibodies. The project is being funded by the Hong Kong Government’s Innovation and Technology Commission (ITC) under the Partnership Research Program (PRP). The PRP aims to support research and development projects undertaken by companies in collaboration with local universities and public research institutions. The ITC funded approximately 50% of the total estimated project cost, with aTyr contributing the remaining 50%. The research grant agreement between Pangu BioPharma, HKUST and the Government of the Hong Kong Special Administration Region was effective April 1, 2020. The term of the project was initially for two years and in December 2021, due to the ongoing COVID-19 pandemic, was extended for an additional six months with no additional cost.

All the contributions provided by the ITC are paid to HKUST and we record expenses incurred related to this grant award when incurred. Expenses for the years ended December 31, 2021 and 2020 were $0.4 million and $0.2 million, respectively.

Balance Sheet Details - Summary of Prepaid Expenses (Detail) - USD ($)
$ in Thousands

Dec. 31, 2021

Dec. 31, 2020

Prepaid Expenses [Line Items]

Prepaid expenses

$ 5,223

$ 1,803

Prepaid Clinical and Research Expense [Member]

Prepaid Expenses [Line Items]

Prepaid expenses

557

583

Prepaid Manufacturing Expenses [Member]

Prepaid Expenses [Line Items]

Prepaid expenses

^[1]

4,188

513

Other Prepaid Expenses [Member]

Prepaid Expenses [Line Items]

Prepaid expenses

$ 478

$ 707

[1]	Prepaid manufacturing expenses of $3.7 million incurred in 2021 included a reservation fee and raw materials for manufacturing of efzofitimod clinical trial materials planned to occur in the second half of 2022

Income Tax - Schedule of Pretax Losses for Domestic and Foreign Operations (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
United States	$ (33,316)	$ (15,950)	$ (23,315)
Foreign	(458)	(280)	(448)
Worldwide pre-tax loss	$ (33,774)	$ (16,230)	$ (23,763)

- Definition

Amount of income (loss) from continuing operations, including income (loss) from equity method investments, before deduction of income tax expense (benefit), and income (loss) attributable to noncontrolling interest.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 32
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=123359005&loc=d3e8933-108599

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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-Name Accounting Standards Codification
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-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-05(b)(2))
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Reference 9: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
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-Name Accounting Standards Codification
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-Subparagraph (SX 210.9-04(15))
-URI http://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260

+ Details

Employee Benefits - Additional Information (Detail) - 401 (k) Plan [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Defined Contribution Plan Disclosure [Line Items]
Policy approved month and year	2015-04
Date of Policy beginning	Jun. 01, 2015
Percentage of match employee contribution	50.00%
Percentage of participants's annual salary	6.00%
Discretionary contribution	$ 0.2	$ 0.2	$ 0.2

Organization, Business and Basis of Presentation

12 Months Ended

Dec. 31, 2021

Accounting Policies [Abstract]

Organization, Business and Basis of Presentation

1. Organization, Business and Basis of Presentation

Organization and Business

We were incorporated in the state of Delaware on September 8, 2005. We are focused on the discovery and development of innovative medicines based on novel immunological pathways.

Principles of Consolidation

Liquidity and Financial Condition

Use of Estimates

Segment Reporting

Employee Benefits

12 Months Ended

Dec. 31, 2021

Compensation And Retirement Disclosure [Abstract]

Employee Benefits

9. Employee Benefits

401(k) Plan

We maintain a defined contribution 401(k) plan available to eligible employees. Employee contributions are voluntary and are determined on an individual basis, limited to the maximum amount allowable under federal tax regulations. In April 2015, our Board of Directors approved a policy, beginning on June 1, 2015, to match employee contributions equal to 50% of the participant’s contribution of up to a maximum of 6% of the participant’s annual salary. We made discretionary contributions totaling $0.2 million during each of the years ended December 31, 2021, 2020 and 2019.