As filed with the Securities and Exchange Commission on March 23, 2023

Registration No. 333-

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, DC 20549

FORM S-8

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

CYTEIR THERAPEUTICS, INC.

(Exact name of registrant as specified in its charter)

Cyteir Therapeutics, Inc. 2021 Equity Incentive Plan

Cyteir Therapeutics, Inc. 2021 Employee Stock Purchase Plan

(Full titles of the plans)

Markus Renschler, M.D.

President and Chief Executive Officer

Cyteir Therapeutics, Inc.

128 Spring St, Building A, Suite 510

Lexington, MA 02421

(Name and address of agent for service)

(857) 285-4140

(Telephone number, including area code, of agent for service)

Please send copies of all communications to:

Marc A. Rubenstein, Esq.

Tara Fisher

Ropes & Gray LLP

Prudential Tower

800 Boylston Street

Boston, MA 02199-3600

617-951-7000

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company, or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer, “smaller reporting company,” and “emerging growth company” in Rule 12b-2 of the Exchange Act.

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 7(a)(2)(B) of the Securities Act. ☐

EXPLANATORY NOTE

This Registration Statement on Form S-8 registers additional shares of the Registrant’s common stock, par value $0.001 per share (the “Common Stock”), under the Registrant’s 2021 Equity Incentive Plan (the “2021 Plan”) and the Registrant's 2021 Employee Stock Purchase Plan ("2021 ESPP").

The number of shares of Common Stock reserved and available for issuance under the 2021 Plan is subject to an automatic annual increase on January 1 of each year by an amount equal to lesser of (i) five (5) percent of the number of shares of Common Stock outstanding as of such date and (ii) the number of shares of Common Stock determined by the Board on or prior to such date for such year. On January 1, 2023, the number of shares of Common Stock reserved and available for issuance under the 2021 Plan increased by 1,778,784 shares.

The number of shares of Common Stock reserved and available for issuance under the 2021 ESPP is subject to an automatic annual increase on January 1 of each year by an amount equal to one (1) percent of the number of shares of Common Stock issued and outstanding as of such date or such lesser number of shares of Common Stock as determined by the Board of Directors. On January 1, 2023, the number of shares of Common Stock reserved and available for issuance under the 2021 ESPP increased by 355,756 shares.

This Registration Statement on Form S-8 registers these additional 2,134,540 shares of Common Stock. The additional shares are of the same class as other securities relating to the plans for which the Registrant’s registration statement filed on Form S-8 (Registration No. 333-257920) on July 15, 2021 is effective. The information contained in the Registrant’s registration statement on Form S-8 (Registration No. 333-257920) is hereby incorporated by reference pursuant to General Instruction E.

PART II

Item 8. Exhibits.

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933, the Registrant certifies that it has reasonable grounds to believe that it meets all of the requirements for filing on Form S-8 and has duly caused this Registration Statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Lexington, Commonwealth of Massachusetts, on this 23rd day of March, 2023.

POWER OF ATTORNEY

Each person whose signature appears below constitutes and appoints Markus Renschler and Adam Veness, each of them acting singly, his or her true and lawful attorney-in-fact and agent with full power of substitution and resubstitution, for him or her and in his or her name, place and stead, in any and all capacities, to sign any and all amendments (including post-effective amendments) to this Registration Statement on Form S-8 to be filed by Cyteir Therapeutics, Inc., and to file the same, with all exhibits thereto, and other documents in connection therewith, with the Securities and Exchange Commission, granting unto said attorneys-in-fact and agents full power and authority to be done in and about the premises, as fully to all intents and purposes as he or she might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents, or their substitutes, may lawfully do or cause to be done by virtue hereof.

* * * *

Pursuant to the requirements of the Securities Act of 1933, this Registration Statement has been signed by the following persons in the capacities and on the dates indicated: