The following table presents stock-based compensation expense as reflected in the Company's consolidated statements of operations and comprehensive loss (in thousands):


	Year Ended December 31,
	2021		2020
Research and development	$	4,759	$	1,674
General and administrative		7,752		3,589
Total stock-based compensation	$	12,511	$	5,263

The Plans are administered by the Board of Directors or, at the discretion of the Board of Directors, by a committee of the Board of Directors. The exercise prices, vesting and other restrictions are determined at the discretion of the Board of Directors, or its committee if so delegated, except that the exercise price per share of stock options may not be less than 100% of the fair market value of the share of common stock on the date of grant and the term of the stock option may not be greater than ten years. Incentive stock options granted to employees and restricted stock awards granted to employees, officers, members of the Board of Directors, advisors, and consultants of the Company typically vest over four years. Non-statutory options granted to employees, officers, members of the Board of Directors, advisors, and consultants of the Company typically vest over three or four years. Shares that are expired, terminated, surrendered or canceled under the Plans without having been fully exercised will be available for future awards. In addition, shares of common stock that are tendered to the Company by a participant to exercise an award are added to the number of shares of common stock available for the grant of awards.

In 2017, resTORbio adopted the 2017 Plan. In connection with resTORbio’s initial public offering completed in January 2018, the resTORbio Board adopted and resTORbio’s stockholders approved the 2018 Plan. The 2018 Plan provides that the number of shares reserved and available for issuance under the plan will automatically increase each January 1, beginning on January 1, 2019, by 4% of the outstanding number of shares of resTORbio’s common stock on the immediately preceding December 31 or such lesser number of shares as determined by the Board. On April 27, 2021, the stockholders approved an amendment and restatement of the 2018 Stock Option and Incentive Plan, to, among other things, increase the aggregate number of shares authorized for issuance under the 2018 Plan by 1,500,000 shares, plus on January 1, 2022 and each January 1, thereafter, the number of shares authorized for issuance shall be increased by the lesser of 5% of the number of shares of Common Stock issued and outstanding on the immediately preceding December 31, or such lesser number as determined by the compensation committee. On January 1, 2022, the number of shares reserved and available for issuance under the 2018 Plan automatically increased by 1,986,845 shares of Common Stock equal to 5% of the number of shares of Common Stock issued and outstanding on December 31, 2021.

Since the date of effectiveness of the 2018 Plan, resTORbio has not and the Company will not grant any further awards under the 2017 Plan. However, any shares of common stock subject to awards under the 2017 Plan that expire, terminate, or otherwise are surrendered, canceled, forfeited or repurchased without having been fully exercised or resulting in any common stock being issued will become available for issuance under the 2018 Plan. As of December 31, 2021, there are no outstanding options under the 2017 Plan.

As of December 31, 2021, the number of shares of common stock available for grant under the 2017 and 2018 Plan is 1,683,999. As of December 31, 2021, an aggregate of 2,574,170 shares of common stock were issuable upon the exercise of outstanding stock options under the 2017 Plan and 2018 Plans at a weighted average exercise price of $15.10 per share. In addition to this amount, as of December 31, 2021, 771,660 shares of common stock were issuable upon the vesting of 6,410 performance stock units (PSUs) granted in May 2021, 205,250 RSUs granted in August 2021, and 560,000 RSUs and PSUs granted in October 2021.

As of December 31, 2021, the number of shares of common stock available for grant under the 2014 and 2015 Plan is 277,339. As of December 31, 2021, an aggregate of 915,657 shares of common stock were issuable upon the exercise of outstanding stock options under the 2015 plan at a weighted average exercise price of $11.46 per share and an aggregate of 22,987 shares of common stock were issuable upon the exercise of outstanding stock options under the 2014 Plan at a weighted average exercise price of $1.61 per share.

Since the date of effectiveness of the Merger, the Company has not and will not grant any further awards under the 2014 Plan.

The 2018 ESPP provides that the number of shares reserved and available for issuance will automatically increase each January 1, beginning on January 1, 2019 and increasing each January 1 thereafter through January 1, 2028, by the least of (i) 1% of the outstanding number of shares of the Company’s common stock on the immediately preceding December 31; (ii) 77,703 shares or (iii) such number of shares as determined by the ESPP administrator.

On January 1, 2020, as a result of the foregoing evergreen provision, the number of shares of common stock available for issuance under the 2018 ESPP automatically increased from 79,369 to 131,432 shares. On January 1, 2021, as a result of the

foregoing evergreen provision, the number of shares of common stock available for issuance under the 2018 ESPP automatically increased from 131,432 to 524,775. During the 2021 Annual Meeting of the stockholders held on April 27, 2021, the stockholders approved an amendment and restatement of the Company's 2018 ESPP. As a result, the Company increased the shares available for issuance under the 2018 ESPP to 524,775 shares.

For the year ended December 31, 2021 the Company issued a total of 15,667 shares under the 2018 ESPP. Expense related to the issuance of such shares was less than $0.1 million. No shares were issued under the 2018 ESPP during the year ended December 31, 2020.

A summary of stock option activity is set forth below (in thousands, except share and per share data):


	Outstanding Awards
	Number of Shares Underlying Outstanding Options			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value
Outstanding, December 31, 2020		3,706,945		$	10.90		7.98	$	15,126
Options authorized		—
Options granted		2,161,472		$	14.37
Options exercised		(1,125,339	)	$	4.17
Options forfeited or cancelled		(867,761	)	$	14.06
Outstanding, December 31, 2021		3,875,317		$	14.08		8.85	$	13,212
Options exercisable December 31, 2021		991,847		$	13.42		8.46	$	4,033
Vested and expected to vest, December 31, 2021		3,875,317		$	14.08		8.85	$	13,212

The fair value of each stock option was estimated at the date of grant using a Black-Scholes option-pricing model using the following assumptions:


	Year Ended December 31,
	2021		2020
Expected volatility	77.2% - 79.8%		72.6% - 96.3%
Risk-free interest rate	0.1% - 1.4%		0.1% - 1.7%
Dividend yield		—		—
Expected term	0.90 - 6.08 years		1.00 - 6.08 years

The Company will continue to use judgment in evaluating the expected volatility, risk-free interest rates, dividend yield and expected term, utilized for stock-based compensation on a prospective basis.

The aggregate intrinsic value is calculated as the difference between the exercise price of the underlying stock options and the fair value of the Company’s common stock for stock options that were in-the-money at December 31, 2021 and 2020. The aggregate intrinsic value of stock options exercised during the years ended on December 31, 2021 and 2020 was $10.1 million and $2.5 million, respectively.

The total fair value of options that vested during the years ended December 31, 2021 and 2020 was $2.3 million and $2.4 million, respectively. The options granted during the years ended December 31, 2021 and 2020 had a weighted-average per share grant-date fair value of $9.68 per share and $9.96 per share, respectively.

As of December 31, 2021, the total unrecognized stock-based compensation expense related to unvested stock options was $24.8 million, which is expected to be recognized over the remaining weighted-average vesting period of 2.8 years.

The following table presents a summary of the Company's RSU activity and related information:


	Number of Units Outstanding			Weighted- Average Grant Date Fair Value
Outstanding, December 31, 2020		—
RSUs granted (including performance-based RSUs)		777,160		$	7.84
RSUs Vested		—
RSUs forfeited		(5,500	)	$	7.12
Outstanding, December 31, 2021		771,660		$	7.85

In May 2021, the Company granted 6,410 RSUs with service and performance conditions to an employee, none of which vested during the year ending December 31, 2021. Vesting of these awards is contingent on the occurrence of certain milestone events and fulfilment of any remaining service condition. As a result, the related compensation cost is recognized as an expense when achievement of the milestone is considered probable. The expense recognized for these awards is based on the grant date fair value of the Company's common stock multiplied by the number of units granted. The Company recognized less than $0.1 million of related expense during the year ended December 31, 2021.

In October 2021, the Company granted 560,000 RSUs with service and performance conditions to certain employees, none of which vested during the year ended December 31, 2021. Vesting of these awards is contingent on the occurrence of certain milestone events and fulfilment of any remaining service condition. As a result, the related compensation cost is recognized as an expense when achievement of the milestone is considered probable. The expense recognized for these awards is based on the grant date fair value of the Company's common stock multiplied by the number of units granted. The Company recognized $1.6 million of related expense during the year ended December 31, 2021.

The weighted-average grant date fair value of RSUs granted during the year ended December 31, 2021 was $7.84. There was no RSU activity during the year ended December 31, 2020. Additionally, no RSUs vested during the year ended December 31, 2021.

As of December 31, 2021, there was approximately $4.1 million of unrecognized compensation cost related to unvested RSUs that the Company expects to recognize over a remaining weighted-average period of approximately 1.3 years.

The following table presents stock-based compensation expense by type of award (in thousands):


	Year Ended December 31,
	2021		2020
Stock Options		10,511		5,263
Restricted stock units (including performance-based RSUs)		1,944		—
Employee Stock Purchase Plan		56		—
Total	$	12,511	$	5,263