v3.22.4
Stockholders’ Equity and Stock-Based Compensation (Tables)
12 Months Ended
Dec. 31, 2022
Equity [Abstract]  
Schedule of Warrant Activity A summary of the Company’s warrant activity for the year ended December 31, 2022 was as follows:
Shares of Stock under WarrantsWeighted-
Average
Exercise
Price
Weighted-
Average
Remaining
Contractual
Term
Aggregate
Intrinsic
Value
Outstanding at January 1, 2021
15,174,000 $2.34 3.76$26,841,000 
Granted— — — 
Exercised(10,794,000)0.88 58,191,000 
Canceled(24,000)3.29 — 
Outstanding at December 31, 2021
4,356,000 $5.96 1.76$785,000 
Granted— — — 
Exercised— — — 
Canceled— — — 
Outstanding at December 31, 2022
4,356,000 $5.96 0.76$273,000 
Summary of Stock Option Activity Under 2018 Plan and 2006 Plan
A summary of the Company’s stock option activity is as follows:   
Shares of Stock under Stock Options
Weighted-
Average
Exercise
Price
 
Weighted-
Average
Remaining
Contractual
Term
 
Aggregate
Intrinsic
Value
 
Outstanding at January 1, 2022
12,765,000$4.97 8.9$7,891,000 
Granted16,148,0002.12 
Exercised(467,000)0.74 580,000 
Canceled(4,424,000)4.18 
Outstanding at December 31, 2022
24,022,0003.288.52,068,000 
Vested and exercisable at December 31, 2022
7,791,000$3.79 7.5$1,513,000 
Share-based Payment Arrangement, Restricted Stock Unit, Activity
Restricted stock activity was as follows:
Stock UnitsWeighted- Average Grant Date Fair Value per Share
Outstanding at January 1, 2022
361,000$4.74 
Granted
Released(265,000)4.74
Forfeited— 
Outstanding at December 31, 2022
96,000$4.74
Performance stock activity was as follows:
Stock UnitsWeighted- Average Grant Date Fair Value per Share
Outstanding at January 1, 2022
290,000$4.74 
Granted
Released
Forfeited
Outstanding at December 31, 2022
290,000$4.74
Summary of Recognized Stock-Based Compensation Expense
The Company recognized stock-based compensation expense for the years ended December 31, 2022 and 2021 was as follows: 
Years Ended December 31,
20222021
Research and development$13,402,000 $3,531,000 
General and administrative9,015,000 6,188,000 
Total stock-based compensation expense$22,417,000 $9,719,000 
Schedule of Weighted-Average Assumptions in Black -Scholes Option Pricing Model
The weighted-average assumptions used in the Black-Scholes-Merton option pricing model to determine the fair value of the employee stock option grants were as follows:
Years Ended December 31,
20222021
Risk-free interest rate2.4%1.1%
Expected volatility68.0%76.2%
Expected term (in years)5.86.0
Expected dividend yield0.0%0.0%