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Equity Incentive Plans and Stock-Based Compensation (Tables)
 3 Months Ended
Mar. 31, 2022
Share-based Payment Arrangement [Abstract]  
Summary of Restricted Stock Activity
The following table summarizes restricted stock activity during the three months ended March 31, 2022:
  Number
of
Shares		Weighted-
Average
Grant Date
fair value
Outstanding and unvested, as of December 31, 202121,841 $2.16 
Issued— $— 
Vested(15,606)$2.11 
Repurchases— $— 
Outstanding and unvested, as of March 31, 20226,235 $2.29 
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:
  Three Months Ended
March 31,
 20222021
Expected volatility
74.48% - 75.01%
74.95% - 75.72%
Risk-free interest rate
1.64% - 2.13%
0.61% - 1.06%
Expected dividend——
Expected term (in years)
6.02 - 6.08
5.77 - 6.08
Underlying common stock fair value
7.56 - 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 
Granted1,691,370 $11.88 
Exercised(12,124)$4.63 
Forfeited(102,557)$11.19 
Outstanding as of March 31, 20225,196,869 $13.62 8.42$4,445 
Exercisable as of March 31, 20221,660,467 $10.65 7.51$3,152 
Vested and expected to vest as of March 31, 20225,196,869 $13.62 8.42$4,445 
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 months ended March 31, 2022 and 2021 (in thousands):
Three Months Ended
March 31,
20222021
Restricted stock awards$29 $51 
Stock options and ESPP3,502 2,527 
Total stock-based compensation expense$3,531 $2,578 
Research and development expenses$1,914 $1,170 
General and administrative expenses$1,617 $1,408 
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:
 Three Months Ended
March 31,
 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
—
—