In April 2014, the Company adopted the Corbus Pharmaceuticals Holdings, Inc. 2014 Equity Incentive Plan (the “2014 Plan”). Pursuant to the 2014 Plan, the Company’s Board may grant incentive and nonqualified stock options and restricted stock to employees, officers, directors, consultants and advisors.

Pursuant to the terms of an annual evergreen provision in the 2014 Plan, the number of shares of common stock available for issuance under the 2014 Plan shall automatically increase on January 1 of each year by at least seven percent (7%) of the total number of shares of common stock outstanding on December 31st of the preceding calendar year, or, pursuant to the terms of the 2014 Plan, in any year, the Board may determine that such increase will provide for a lesser number of shares.

In accordance with the terms of the 2014 Plan, and pursuant to the annual evergreen provision contained in the 2014 Plan, effective as of January 1, 2022, the number of shares of common stock available for issuance under the 2014 Plan increased by 292,205 shares, which was seven percent (7%) of the outstanding shares of common stock on December 31, 2021. As of January 1, 2022 there was a total reserve of 1,144,567 shares and 558,671 shares available for future grants. As of March 31, 2022 there were 426,486 shares available for future grants.

In accordance with the terms of the 2014 Plan, and pursuant to the annual evergreen provision contained in the 2014 Plan, effective as of January 1, 2023, the number of shares of common stock available for issuance under the 2014 Plan increased by 291,991 shares, which was seven percent (7%) of the outstanding shares of common stock on December 31, 2022. As of January 1, 2023, there was a total reserve of 1,436,558 shares and 741,870 shares available for future grants. As of March 31, 2023 there were 510,671 shares available for future grants.

In connection with all stock-based payment awards, total stock-based compensation expense, net of estimated forfeitures, recognized in the condensed consolidated statements of operations and comprehensive loss was as follows:


	Three Months Ended March 31,
	2023		2022

Research and development expenses	$	93,922	$	176,218
General and administrative expenses		932,457		1,415,528
Total stock-based compensation	$	1,026,379	$	1,591,746

The total stock-based compensation expense recognized by award type was as follows:


	Three Months Ended March 31,
	2023		2022

Stock Options	$	1,023,741	$	1,591,746
Restricted Stock Units		2,638		—
Total stock-based compensation	$	1,026,379	$	1,591,746

The fair value of each option award is estimated on the date of grant using the Black-Scholes option pricing model that uses the assumptions noted in the following table. The Company uses historical data, as well as subsequent events occurring prior to the issuance of the financial statements, to estimate option exercises and employee terminations in order to estimate its forfeiture rate. The expected term of options granted under the 2014 Plan, all of which qualify as “plain vanilla” per SEC Staff Accounting Bulletin 107, is determined based on the simplified method due to the Company’s limited operating history, and is 6.25 years based on the average between the vesting period and the contractual life of the option. For non-employee options, the expected term is the contractual term. The risk-free rate is based on the yield of a U.S. Treasury security with a term consistent with the option.

The weighted average assumptions used principally in determining the fair value of options granted to employees were as follows:


	Three Months Ended March 31,
	2023			2022
Risk free interest rate		3.85	%		1.70	%
Expected dividend yield	0%				0	%
Expected term in years	6.25				6.25
Expected volatility		100.13	%		97.49	%
Estimated forfeiture rate		17.64	%		13.00	%

A summary of option activity for the three months ended March 31, 2023 and is presented below:


Options	Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term in Years		Aggregate Intrinsic Value
Outstanding at December 31, 2022		617,996		$	88.99
Granted		246,967			4.22
Exercised		(43,836	)		0.85
Forfeited or Canceled		(15,768	)		55.23
Outstanding at March 31, 2023		805,359		$	68.23		7.35	$	21,943,617
Vested at March 31, 2023		406,396		$	113.92		5.56	$	5,049,321
Vested and expected to vest at March 31, 2023		715,248		$	75.45		7.08	$	17,485,170

The weighted average grant-date fair value of options granted during the three months ended March 31, 2023 and 2022 was $3.44 and $11.10 per share, respectively. The aggregate intrinsic value of options exercised during the three months ended March 31, 2023 and 2022 was approximately $92,689 and $0, respectively. As of March 31, 2023, there was approximately $5,733,215 of total unrecognized compensation expense, related to non-vested share-based option compensation arrangements. The unrecognized compensation expense is estimated to be recognized over a period of 2.02 years as of March 31, 2023.

A RSU represents the right to receive one share of our common stock upon vesting of the RSU. The fair value of each RSU is based on the closing price of our common stock on the date of grant. We grant RSUs with service conditions that vest in four equal annual installments provided that the employee remains employed with us on the vesting date.

A summary of RSU activity for the three months ended March 31, 2023 and is presented below:


RSU's	Number of Shares Underlying RSUs		Weighted Average Grant Date Fair Value
Unvested at December 31, 2022		—	$	—
Granted		23,990		4.26
Forfeited		—		—
Vested		—		—
Unvested at March 31, 2023		23,990	$	4.26

As of March 31, 2023, there was $81,163 of unrecognized compensation costs related to unvested RSUs, which are expected to be recognized over a weighted-average period of 3.87 years.