On November 18, 2015, the Company’s Board of Directors adopted and approved the 2015 Equity Incentive Plan (the 2015 Plan), which authorized the Company to grant up to 14,895 ordinary shares in the form of incentive share options, nonstatutory share options, share appreciation rights, restricted share awards, restricted share units and other share awards. The types of share-based awards, including the rights amount, terms, and exercisability provisions of grants are determined by the Company’s Board of Directors. The purpose of the 2015 Plan was to provide the Company with the flexibility to issue share-based awards as part of an overall compensation package to attract and retain qualified personnel. On May 18, 2017, the Company amended the 2015 Plan to increase the number of ordinary shares available for issuance under the 2015 Plan by 14,640 shares to 29,535 shares.

On March 14, 2018, the Company’s Board of Directors adopted and approved the 2018 Equity Incentive Plan (the 2018 Plan), which became effective upon the execution and delivery of the underwriting agreement related to the Company’s IPO in May 2018. Since adopting the 2018 Plan, no further grants will be made under the 2015 Plan. The ordinary shares underlying any options that are forfeited, canceled, repurchased or are otherwise terminated by the Company under the 2015 Plan will not be added back to the ordinary shares available for issuance.

The 2018 Plan originally authorized the Company to grant up to 67,897 ordinary shares in the form of incentive share options, nonstatutory share options, share appreciation rights, restricted share awards, restricted share units, performance share awards,

performance cash awards and other share awards. The types of share-based awards, including the amount, terms, and exercisability provisions of grants are determined by the Company’s Board of Directors. The ordinary shares underlying any options that are forfeited, canceled, repurchased or are otherwise terminated by the Company under the 2018 Plan are added back to the ordinary shares available for issuance under the 2018 Plan.

On December 5, 2018, pursuant to powers delegated to it by the Board of Directors of the Company, the Compensation Committee approved an increase in the number of ordinary shares available to be granted pursuant to the 2018 Plan by 4% of the total number of shares of the Company’s issued share capital on December 31, 2018, being 38,272 ordinary shares.

On February 14, 2020, pursuant to powers delegated to it by the Board of Directors of the Company, the Compensation Committee approved, by written resolution, an increase of 39,650 ordinary shares to the number of ordinary shares available to be granted pursuant to the 2018 Plan, being just under 4% of the total number of the Company’s ordinary shares outstanding on December 31, 2019, in accordance with the terms of the 2018 Plan.

On June 10, 2020, at the Company’s annual general meeting of shareholders, the shareholders approved and adopted an amended and restated 2018 Plan which, among other things included an increase of 150,000 ordinary shares to the number of ordinary shares reserved for issuance under the 2018 Plan.

On June 23, 2021, at the Company’s annual general meeting of shareholders, the shareholders approved an amendment to the amended and restated 2018 Plan to increase the number of ordinary shares reserved for issuance under the amended and restated 2018 Plan by 1,000,000 ordinary shares to 1,295,819 ordinary shares.

On November 24, 2021, the Company’s Board of Directors adopted and approved the 2021 Inducement Equity Incentive Plan (the 2021 Inducement Plan) reserving 333,333 of its ordinary shares to be used exclusively for grants of awards to individuals that were not previously employees or directors of the Company (or following such individuals’ bona fide period of non-employment with the company), as a material inducement to such individuals’ entry into employment with the company within the meaning of Rule 5635(c)(4) of the Nasdaq Listing Rules. The terms and conditions of the 2021 Inducement Plan are substantially similar to the 2018 Plan.

Share Options

Unless specified otherwise in an individual option agreement, share options granted under the 2015 Plan, the 2018 Plan and the 2021 Inducement Plan generally have a ten year term and a four year vesting period for employees and a one year vesting period for directors. The vesting requirement is conditioned upon a grantee’s continued service with the Company during the vesting period. Once vested, all awards are exercisable from the date of grant until they expire. The option grants are non-transferable. Vested options generally remain exercisable for 90 days subsequent to the termination of the option holder’s service with the Company. In the event of an option holder’s disability or death while employed by or providing service to the Company, the exercisable period extends to twelve months or eighteen months, respectively.

The fair value of options granted are estimated using the Black-Scholes option-pricing model. The inputs for the Black-Scholes model require significant management assumptions. The risk-free interest rate is based on a normalized estimate of the 7-year U.S. treasury yield. The Company has estimated the expected term utilizing the “simplified” method for awards that qualify as “plain vanilla”. The Company does not have sufficient company-specific historical and implied volatility information and it therefore estimates its expected share volatility based on historical volatility information of reasonably comparable guideline public companies and itself. The Company expects to continue to do so until such time as it has adequate historical data regarding the volatility of its own traded share price. Expected dividend yield is based on the fact that the Company has never paid cash dividends and the Company’s future ability to pay cash dividends on its shares may be limited by the terms of any future debt or preferred securities. The Company has elected to account for forfeitures as they occur.

The Company granted 197,085, 1,028,090 and 4,322 share options to employees and directors during the years ended December 31, 2022, 2021 and 2020, respectively. There were 296,199, 1,033,820 and 17,778 unvested employee and director options outstanding as of December 31, 2022, December 31, 2021 and December 31, 2020, respectively. Total expense recognized related to the employee and director share options was $3,580, $3,779, and $1,136, for the years ended December 31, 2022, 2021 and 2020, respectively. Total unamortized compensation expense related to employee and director share options was $929, $21,521 and $970 as of December 31, 2022, December 31, 2021 and December 31, 2020, respectively, expected to be recognized over a remaining weighted average vesting period of 1.41 years, 3.49 years and 1.47 years as of December 31, 2022, December 31, 2021 and December 31, 2020, respectively.

On July 7, 2022, certain of the Company's executive officers and employees agreed to the surrender and cancellation of certain previously granted share options for an aggregate of 906,800 ordinary shares in order to make additional shares available under the

2018 Plan. Total expense recognized in connection with the cancellation of these employee share options was $17,350 for the year ended December 31, 2022, and was recorded in other income and expense as Cancellation of Share Options.

The following table summarizes total stock option activity for all Company plans:

The weighted average grant-date fair value per share of share options granted during the years ended December 31, 2022, 2021 and 2020 was $2.39, $23.67 and $19.17, respectively.

Restricted Share Units (RSUs)

The Company granted 66,398 RSUs to directors during the year ended December 31, 2022 and 123,017 RSUs to employees and directors during the year ended December 31, 2021. No RSUs were granted to employees or directors during the year ended December 31, 2020.

The fair value of the RSUs is determined on the date of grant based on the market price of the Company’s ordinary shares on that date. The fair value of RSUs is expensed ratably over the vesting period, which is generally one year for directors and two years for employees under our 2018 Plan and four years for employees under our 2021 Inducement Plan. Total expense recognized related to the RSUs was $1,178, $960 and $63 for the years ended December 31, 2022, 2021 and 2020, respectively. Total unamortized compensation expense related to the RSUs was $434 and $1,416 as of December 31, 2022 and December 31, 2021, respectively, and is expected to be recognized over a remaining average vesting period of 0.88 years and 1.89 years as of December 31, 2022 and December 31, 2021, respectively.

No RSUs, which are subject to certain performance-based vesting conditions (Performance RSUs), were awarded during the years ended December 31, 2022 and 2021. The Company awarded 71,927 RSUs to certain employees during the year ended December 31, 2020 which were subject to certain vesting conditions (Performance RSUs).

The weighted average grant date fair value of Performance RSUs with a market condition was determined using the Monte Carlo simulation model. The fair value of Performance RSUs is expensed ratably over the vesting period. Due to the expiration of Performance RSUs, a credit of $0 was recognized for the year ended December 31, 2021. Total expense recognized related to Performance RSUs was $1,560 for the year ended December 31, 2020. All Performance RSUs were fully expensed as of December 31, 2021. Total unamortized compensation expense related to Performance RSUs was $152 for the year ended December 31, 2020, expected to be recognized over a remaining average vesting period of 0.20 years as of December 31, 2020.

There was a total of $1,363, $22,937 and $1,122 unamortized share-based compensation expense for share options, restricted share units and performance restricted share units as of December 31, 2022, December 31, 2021 and December 31, 2020, respectively, expected to be recognized over a remaining average vesting period of 1.28 years, 3.32 years and 0.80 years as of December 31, 2022, December 31, 2021 and December 31, 2020, respectively.