[S-8 POS] IGM Biosciences, Inc. SEC Filing

Rhea-AI Filing Summary

IGM Biosciences completed a merger and is removing unsold securities from registration. On August 14, 2025 the company merged with Concentra Merger Sub V, Inc., becoming a wholly owned subsidiary of Concentra Biosciences, LLC. Each outstanding public share (other than treasury shares, shares owned by Parent/Merger Sub, and any shares subject to valid appraisal rights) was converted into $1.247 cash per share plus one non-transferable contractual contingent value right per share.

As a result of the Merger and the termination of the company’s offerings, IGM is filing post-effective amendments to withdraw and remove any unissued and unsold securities previously registered on multiple Form S-8 registration statements and to terminate those registration statements.

Positive

• Merger completed with Concentra Biosciences, LLC, creating a wholly owned subsidiary status
• Cash consideration per share specified: $1.247 paid for each eligible share
• Contingent value rights issued—one non-transferable right per share, providing a potential future claim

Negative

• Termination of public offerings and removal of all unissued and unsold securities from multiple Form S-8 registration statements
• Company ceased to be publicly independent—now a wholly owned subsidiary, which ends ongoing securities registrations and related public liquidity

Insights

M&A Specialist

TL;DR: IGM completed a definitive merger; public shares were cashed out at $1.247 plus contingent rights and registration statements were terminated.

The filing documents a completed acquisition structure where Merger Sub merged into IGM and IGM survived as a wholly owned subsidiary of the private acquirer. The cash consideration of $1.247 per share and issuance of non-transferable contingent value rights are explicit transaction terms. The post-effective amendments serve a regulatory cleanup purpose: removing unsold securities from multiple Form S-8 registrations and terminating those filings following the cessation of public offerings. This is a routine post-closing compliance step triggered by the change in ownership.

Corporate Governance Expert

TL;DR: Governance changes confirmed by merger; public registration terminated and company converted to a private subsidiary.

The filing confirms that shares held in treasury and by the acquirer were excluded from the cash-out conversion, and appraisal rights were preserved for eligible dissenting stockholders. Terminating the Form S-8 effectiveness aligns the company’s disclosure and registration obligations with its new ownership status. The document contains specific, actionable corporate event facts without forward-looking projections or additional financial statements.

As filed with the Securities and Exchange Commission on August 14, 2025

Registration No. 333-233826

Registration No. 333-237411

Registration No. 333-248111

Registration No. 333-254877

Registration No. 333-263927

Registration No. 333-270991

Registration No. 333-277744

Registration No. 333-285602

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

POST-EFFECTIVE AMENDMENT NO. 1 TO FORM S-8 REGISTRATION STATEMENT NO. 333-233826

POST-EFFECTIVE AMENDMENT NO. 1 TO FORM S-8 REGISTRATION STATEMENT NO. 333-237411

POST-EFFECTIVE AMENDMENT NO. 1 TO FORM S-8 REGISTRATION STATEMENT NO. 333-248111

POST-EFFECTIVE AMENDMENT NO. 1 TO FORM S-8 REGISTRATION STATEMENT NO. 333-254877

POST-EFFECTIVE AMENDMENT NO. 1 TO FORM S-8 REGISTRATION STATEMENT NO. 333-263927

POST-EFFECTIVE AMENDMENT NO. 1 TO FORM S-8 REGISTRATION STATEMENT NO. 333-270991

POST-EFFECTIVE AMENDMENT NO. 1 TO FORM S-8 REGISTRATION STATEMENT NO. 333-277744

POST-EFFECTIVE AMENDMENT NO. 1 TO FORM S-8 REGISTRATION STATEMENT NO. 333-285602

FORM S-8

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

IGM BIOSCIENCES, INC.

(Exact name of registrant as specified in its charter)

Delaware		77-0349194
(State or other jurisdiction of incorporation or organization)		(IRS employer identification number)

4747 Executive Drive, Suite 210

San Diego, California 92121

(Address of Principal Executive Offices, including Zip Code)

Amended and Restated 2018 Omnibus Incentive Plan

Amended and Restated 2019 Employee Stock Purchase Plan

Amended and Restated 2010 Stock Plan

(Full title of the Plans)

Michael Hearne

Chief Financial Officer

IGM Biosciences, Inc.

4747 Executive Drive, Suite 210

San Diego, California 92121

(858) 281-5372

(Name, Address and Telephone Number, including Area Code, of Agent for Service)

Copies to:

Ryan A. Murr

Gibson, Dunn & Crutcher LLP

One Embarcadero Center Suite 2600

San Francisco, California 94111

(415) 393-8200

Tony Jeffries

Robert T. Ishii

Jennifer Knapp

Ethan Lutske

Wilson Sonsini Goodrich & Rosati, P.C.

650 Page Mill Road

Palo Alto, California 94304

(650) 493-9300

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 definitions of “large accelerated filer, “accelerated filer,” “smaller reporting company,” and “emerging growth company” in Rule 12b-2 of the Exchange Act.

Large accelerated filer		☐		Accelerated filer		☐
Non-accelerated filer		☒		Smaller reporting company		☒
				Emerging growth company		☐

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

DEREGISTRATION OF UNSOLD SECURITIES

These Post-Effective Amendments (the “Post-Effective Amendments”) filed by IGM Biosciences, Inc., a Delaware corporation (the “Registrant”), to deregister all shares of the Registrant’s common stock, $0.01 par value per share (the “Shares”), remaining unissued under the following Registration Statements on Form S-8 (each, a “Registration Statement”, and collectively, the “Registration Statements”) filed by the Registrant with the U.S. Securities and Exchange Commission (the “Commission”).

• Registration Statement on Form S-8 (No. 333-233826) pertaining to the registration of (i) 4,372,807 Shares issuable under the Amended and Restated 2018 Omnibus Incentive Plan (the “2018 Plan”), (ii) 280,000 Shares issuable under the Amended and Restated 2019 Employee Stock Purchase Plan (the “ESPP”) and (iii) 595,832 Shares issuable under the Amended and Restated 2010 Stock Plan.

• Registration Statement on Form S-8 (No. 333-237411) pertaining to the registration of (i) 964,487 Shares issuable under the 2018 Plan and (ii) 241,121 Shares issuable under the ESPP.

• Registration Statement on Form S-8 (No. 333-248111) pertaining to the registration of (i) 257,248 Shares issuable under the 2018 Plan and (ii) 64,312 Shares issuable under the ESPP.

• Registration Statement on Form S-8 (No. 333-254877) pertaining to the registration of (i) 1,278,965 Shares issuable under the 2018 Plan and (ii) 319,741 Shares issuable under the ESPP.

• Registration Statement on Form S-8 (No. 333-263927) pertaining to the registration of (i) 1,299,920 Shares issuable under the 2018 Plan and (ii) 324,980 Shares issuable under the ESPP.

• Registration Statement on Form S-8 (No. 333-270991) pertaining to the registration of (i) 1,723,292 Shares issuable under the 2018 Plan and (ii) 430,823 Shares issuable under the ESPP.

• Registration Statement on Form S-8 (No. 333-277744) pertaining to the registration of (i) 4,507,245 Shares issuable under the 2018 Plan and (ii) 560,000 Shares issuable under the ESPP.

• Registration Statement on Form S-8 (No. 333-285602) pertaining to the registration of (i) 2,385,497 Shares issuable under the 2018 Plan and (ii) 560,000 Shares issuable under the ESPP.

The Registrant is filing these Post-Effective Amendments to withdraw and remove any unissued and unsold securities issuable by Registration pursuant to the above-referenced Registration Statements.

On July 1, 2025, the Registrant entered into an Agreement and Plan of Merger (the “Merger Agreement”) with Concentra Biosciences, LLC, a Delaware limited liability company (“Parent”), and Concentra Merger Sub V, Inc., a Delaware corporation and wholly owned subsidiary of Parent (“Merger Sub”). Pursuant to the Merger Agreement, on August 14, 2025, Merger Sub was merged with and into the Registrant with the Registrant surviving as a wholly owned subsidiary of Parent (the “Merger”). In the Merger, each share of Common Stock (the “Shares”) (other than (i) Shares owned or held in the Company’s treasury immediately prior to the Effective Time, (ii) Shares owned directly or indirectly by Parent or Merger Sub immediately prior to the Effective Time and (iii) Shares held by any stockholder of the Registrant who properly exercised appraisal rights under Delaware law) was converted into the right to receive (i) $1.247 per Share in cash and (ii) one non-transferable contractual contingent value right for each Share.

As a result of the Merger, the Registrant has terminated all offerings of its securities pursuant to the Registration Statements. In accordance with an undertaking made by the Registrant in each of the Registration Statements to remove from registration, by means of a post-effective amendment, any of the securities that had been registered for issuance that remain unsold at the termination of the offerings, the Registrant hereby removes from registration all such securities registered under the Registration Statements that remain unsold as of the date hereof and terminates the effectiveness of the Registration Statements.

SIGNATURE

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 these Post-Effective Amendments to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of San Diego, State of California, on August 14, 2025. No other person is required to sign these Post-Effective Amendment to the Registration Statements in reliance on Rule 478 of the Securities Act of 1933, as amended.

IGM BIOSCIENCES, INC.

By: /s/ Michael Hearne

Name: Michael Hearne

Title: Chief Financial Officer

FAQ

What did IGM Biosciences (IGMS) shareholders receive in the merger?

Each eligible share was converted into $1.247 in cash plus one non-transferable contractual contingent value right per share.

When was the merger of IGM Biosciences completed?

The Merger was effected on August 14, 2025, when Merger Sub merged with and into IGM, with IGM surviving as a subsidiary.

Why is IGM filing post-effective amendments to its Form S-8 registrations?

Per the registration undertakings, the company is removing from registration any unissued and unsold securities remaining after termination of the offerings due to the Merger and terminating those registration statements.

Were any shares excluded from the cash conversion?

Yes. Excluded were shares held in treasury, shares owned directly or indirectly by Parent or Merger Sub prior to the Effective Time, and shares held by stockholders who properly exercised appraisal rights under Delaware law.

Does the filing disclose any forward-looking financial guidance or earnings?

No. The filing is a post-effective amendment describing the Merger and the withdrawal of unsold registered securities; it does not provide earnings or forward-looking financial guidance.