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Equity Incentive Plans and Stock-Based Compensation (Tables)
 6 Months Ended
Jun. 30, 2022
Share-Based Payment Arrangement [Abstract]  
Summary of Restricted Stock Activity
The following table summarizes restricted stock activity during the six months ended June 30, 2022:
  Number
of
Shares		Weighted-
Average
Grant Date
fair value
Outstanding and unvested, as of December 31, 202121,841 $2.16 
Issued— $— 
Vested(21,841)$2.16 
Repurchases— $— 
Outstanding and unvested, as of June 30, 2022— $— 
Summary of Black-Scholes Option Pricing Model to Estimate Stock-based Compensation Expense for Stock Option Awards
The Company used Black-Scholes option pricing model to estimate stock-based compensation expense for stock option awards with the following assumptions:
  Six Months Ended
June 30,
 20222021
Expected volatility
73.78% - 75.17%
74.95% - 76.31%
Risk-free interest rate
1.64% - 3.39%
0.61% - 1.07%
Expected dividend——
Expected term (in years)
5.33 - 6.08
5.44 - 6.08
Underlying common stock fair value
4.92 - 12.68
26.13 - 38.23
Summary of Option Activity Under the 2015 Plan and 2020 Plan
A summary of option activity under the 2015 Plan and the 2020 Plan is as follows:
  Number
of
Options		Weighted-
Average Exercise
Price per Share		Weighted-
Average
Remaining
Contractual
Term (in Years)		Aggregate
Intrinsic
Value
Outstanding as of December 31, 20213,620,180 $14.56 8.25$16,735 
Granted2,114,870 $10.80 
Exercised(25,727)$4.07 
Forfeited(289,059)$13.19 
Outstanding as of June 30, 20225,420,264 $12.99 8.33$6,796 
Exercisable as of June 30, 20221,999,005 $11.48 7.28$4,666 
Vested and expected to vest as of June 30, 20225,420,264 $12.99 8.33$6,796 
Summary of Components and Classification of Stock-based Compensation Expense for Stock-based Awards
The following table presents the components and classification of stock-based compensation expense for the Company’s stock-based awards for the three and six months ended June 30, 2022 and 2021 (in thousands):
Three Months Ended
June 30,		Six Months Ended
June 30,
2022202120222021
Restricted stock awards$7 $51 $36 $102 
Stock options and ESPP3,396 2,229 6,898 4,756 
Total stock-based compensation expense$3,403 $2,280 $6,934 $4,858 
Research and development expenses$1,761 $868 $3,675 $2,038 
General and administrative expenses$1,642 $1,412 $3,259 $2,820 
Summary of Black-Scholes Option Pricing Model to Estimate Stock-based Compensation Expense for 2020 Employee Stock Purchase Plan The Company used Black-Scholes option pricing model to estimate stock-based compensation expense for the 2020 ESPP with the following assumptions:
 Six Months Ended
June 30,
 20222021
Risk-free interest rate
0.60%
0.07%
Expected term of options (in years)
0.50
0.50
Expected stock price volatility
63.17%
89.51%
Expected dividends
—
—