In January 2021, we adopted the Dynavax Technologies Corporation 2021 Inducement Award Plan (“2021 Inducement Plan”), pursuant to which we reserved 1,500,000 shares of common stock for issuance under the plan to be used exclusively for grants of awards to individuals who were not previously our employees or directors. In June 2021, we amended the 2021 Inducement Plan (“Amended 2021 Inducement Plan”) to increase the number of shares of common stock reserved under the 2021 Inducement Plan to 3,250,000. The Amended 2021 Inducement Plan was terminated effective as of April 3, 2022 and, therefore, there are no shares of our common stock available for grant.

In May 2022, our stockholders approved the amendment and restatement of our 2018 Equity Incentive Plan (the “Amended 2018 EIP”) to, among other things, increase the authorized number of shares of common stock by 15,000,000. The maximum number of shares of common stock that may be issued under the Amended 2018 EIP, will not exceed 32,600,000 shares of common stock. As of December 31, 2023, the Amended 2018 EIP and the Amended and Restated 2014 Employee Stock Purchase Plan are our active plans (the "Plans").

The Amended 2018 EIP is administered by our Board of Directors, or a designated committee of the Board of Directors, and awards granted under the Amended 2018 EIP have a term of 7 years unless earlier terminated by the Board of Directors. As of December 31, 2023, there were 9,388,428 shares of common stock reserved for issuance under the Amended 2018 EIP.

Under our Amended 2018 EIP, we may grant stock options, RSUs, performance-based awards, and other awards that are settled in shares of our common stock. Our equity awards generally vest over a three-year period contingent upon continuous service and unless exercised, expire seven or ten years from the date of grant (or earlier upon termination of continuous service). Activity under our stock plans is set forth below:

The following table summarizes the activity of stock options for the year ended December 31, 2023:


	Shares Underlying Outstanding Options (in thousands)			Weighted-Average Exercise Price Per Share		Weighted-Average Remaining Contractual Term (years)		Aggregate Intrinsic Value (in thousands)
Balance at December 31, 2022		9,339		$	10.70		4.61	$	16,291
Options granted		1,982			11.17
Options exercised		(850	)		7.48
Options cancelled:
Options forfeited (unvested)		(90	)		10.93
Options expired (vested)		(261	)		21.39
Balance at December 31, 2023		10,120		$	10.78		4.18	$	37,388
Vested and expected to vest at December 31, 2023		9,976		$	10.77		4.15	$	37,024
Exercisable at December 31, 2023		7,014		$	10.40		3.50	$	29,613

Stock-based compensation expense related to options was approximately $18.7 million, $17.2 million and $11.1 million for the years ended December 31, 2023, 2022 and 2021, respectively. The total intrinsic value of stock options exercised during the years ended December 31, 2023, 2022 and 2021 was $5.0 million, $7.7 million, and $7.9 million, respectively. The total intrinsic value of exercised stock options is calculated based on the difference between the exercise price and the quoted market price of our common stock as of the close of the exercise date.

The total fair value of stock options vested during the years ended December 31, 2023, 2022 and 2021 was $19.5 million, $17.5 million and $9.0 million, respectively.

The following table summarizes the activity of RSUs for the year ended December 31, 2023:


	Number of Shares (In thousands)			Weighted-Average Grant-Date Fair Value
Non-vested as of December 31, 2022		3,479		$	11.00
Granted		2,748			11.48
Vested (1)		(1,515	)		10.13
Forfeited		(267	)		11.45
Non-vested as of December 31, 2023		4,445		$	11.57

(1) Inclusive of approximately 600,145 RSUs for the year ended December 31, 2023, which were not converted into shares due to net share settlement in order to cover the required amount of employee withholding taxes. The value of the withheld shares was classified as a reduction to additional paid-in capital.

Stock-based compensation expense related to RSUs was approximately $20.4 million, $13.2 million and $7.9 million for the years ended December 31, 2023, 2022 and 2021, respectively. The aggregate fair value of the RSUs outstanding as of December 31, 2023, 2022 and 2021, based on our stock price on that date, was $62.2 million, $37.0 million and $37.3 million, respectively.

The total fair value of RSUs vested during the years ended December 31, 2023, 2022 and 2021 was $16.1 million, $15.7 million and $4.7 million, respectively.

We granted PSUs to certain executives. These PSUs vest upon a specified market condition. The summary of PSU activities for the year ended December 31, 2023 is as follows:

Stock-based compensation expense related to PSUs was approximately $2.5 million, $0.8 million and $1.8 million for the years ended December 31, 2023, 2022 and 2021, respectively. The aggregate intrinsic value of the PSUs outstanding as of December 31, 2023, 2022 and 2021, based on our stock price on that date, was $7.8 million, $2.1 million and $3.3 million, respectively.

As of December 31, 2023, approximately 36,000 shares underlying performance-based options were outstanding.

The fair value of each time-based option is estimated on the date of grant using the Black-Scholes option valuation model. The fair value of each RSU is determined at the date of grant using our closing stock price. The fair value of each PSU is estimated using the Monte Carlo simulation method on the date of grant. The weighted-average assumptions used in the calculations of these fair value measurements are as follows:


	Stock Options									Market-Based Performance Stock Units								Employee Stock Purchase Plan
	Year Ended December 31,									Year Ended December 31,								Year Ended December 31,
	2023			2022			2021			2023			2022			2021		2023			2022			2021
Weighted-average fair value	$	7.32		$	7.95		$	7.17		$	18.25		$	11.62		$	8.40	$	5.35		$	7.37		$	6.48
Risk-free interest rate		4.0	%		2.0	%		0.7	%		4.3	%		1.7	%	From 0.03% to 1.92%			4.9	%		2.1	%		0.1	%
Expected life (in years)		4.5			4.5			4.5			2.9			2.9			2.9		1.3			1.3			1.2
Expected volatility		0.8			0.8			0.9			0.9			0.9			0.9		0.7			1.0			1.0

Expected volatility is based on historical volatility of our stock price. The expected life of options granted is estimated based on historical option exercise and employee termination data. Our senior management, who hold a majority of the options outstanding, and other employees were grouped and considered separately for valuation purposes. The risk-free rate for periods within the contractual life of the option is based on the U.S. treasury yield curve in effect at the time of grant. Forfeiture estimates are based on historical employee turnover. The dividend yield is zero percent for all years and is based on our history and expectation of dividend payouts.

Compensation expense is based on awards ultimately expected to vest and reflects estimated forfeitures. For equity awards with time-based vesting, the fair value is amortized to expense on a straight-line basis over the vesting periods.

We have also granted performance-based equity awards to certain of our employees. For equity awards with performance-based vesting criteria, the fair value is amortized to expense when the achievement of the vesting criteria becomes probable.

The following table summarizes stock-based compensation expense recorded in each component of operating expenses in our consolidated statements of operations, and amounts capitalized to our inventories (in thousands):


	Year Ended December 31,
	2023		2022		2021
Employees and directors stock-based compensation expense	$	42,592	$	32,915	$	21,285

	Year Ended December 31,
	2023		2022		2021
Research and development	$	9,285	$	5,954	$	3,818
Selling, general and administrative		29,069		23,118		14,894
Cost of sales - product		1,839		1,123		553
Inventories		2,399		2,720		2,020
Total	$	42,592	$	32,915	$	21,285

As of December 31, 2023, the total unrecognized compensation cost related to non-vested stock options and RSUs deemed probable of vesting, including all stock options with time-based vesting, net of estimated forfeitures, amounted to $46.1 million, which is expected to be recognized over the remaining weighted-average vesting period of 1.6 years. As of December 31, 2023, the total unrecognized compensation cost related to PSUs amounted to $5.5 million.

The Amended and Restated 2014 Employee Stock Purchase Plan (the “Employee Stock Purchase Plan”) provides for the purchase of common stock by eligible employees. In May 2021, our stockholders approved the amendment and restatement of the Employee Stock Purchase Plan to increase the authorized number of shares of common stock by 1,000,000. The maximum number of shares of common stock that may be issued under the Employee Stock Purchase Plan will not exceed 1,850,000 shares of common stock.

The purchase price per share is the lesser of (i) 85% of the fair market value of the common stock on the commencement of the two-year offer period (generally, the sixteenth day in February or August) or (ii) 85% of the fair market value of the common stock on the exercise date, which is the last day of a purchase period (generally, the fifteenth day in February or August). For the year ended December 31, 2023, employees have acquired approximately 161,000 shares of our common stock under the Employee Stock Purchase Plan and approximately 722,000 shares of our common stock remained available for future purchases under the Employee Stock Purchase Plan.

As of December 31, 2023, the total unrecognized compensation cost related to shares of our common stock under the Employee Stock Purchase Plan amounted to $1.0 million, which is expected to be recognized over the remaining weighted-average vesting period of 1.2 years.