IGM Biosciences merger closes: $1.247 cash + CVR per share disclosed

IGM Biosciences, Inc. filed post-effective amendments to multiple Form S-8 registration statements to withdraw and remove any unissued and unsold securities after the company completed a merger.

Accepted by SEC EDGAR 08/14/2025 - 04:11 PM EDT Learn about SEC filing dates

Rhea-AI Filing Summary

IGM Biosciences, Inc. filed post-effective amendments to multiple Form S-8 registration statements to withdraw and remove any unissued and unsold securities after the company completed a merger. The company entered into a Merger Agreement on July 1, 2025, and on August 14, 2025 the merger closed with Concentra Merger Sub V, Inc. merging into IGM and IGM surviving as a wholly owned subsidiary of Concentra Biosciences, LLC. As part of the merger, each outstanding share of IGM common stock (subject to limited exceptions) was converted into $1.247 in cash per share and one non-transferable contractual contingent value right (CVR) per share. Because the company is now a wholly owned subsidiary, it has terminated all offerings of its securities under the listed registration statements and removed from registration all unsold securities covered by those statements.

Positive

• Registered securities removed and offerings terminated, aligning the company’s registration status with its post-merger ownership structure
• Per-share cash consideration disclosed at $1.247 per share, providing a clear, documented cash component of merger consideration
• Contingent value right (CVR) granted for each share, preserving potential contingent upside for former shareholders

Negative

• Company is now a wholly owned subsidiary of Concentra Biosciences, LLC, ending IGM’s status as an independent public company
• All offerings under the listed Form S-8 registration statements terminated, which ends previously registered equity issuance programs for employees and the ESPP

Insights

M&A Specialist

TL;DR: The filing documents a completed merger that converted public equity into cash plus CVRs and ends the company's registered equity offerings.

The filing confirms closing mechanics rather than financial performance: IGM entered a Merger Agreement on July 1, 2025, and the merger became effective August 14, 2025, with IGM surviving as a wholly owned subsidiary of Parent. The post-effective amendments withdraw unissued and unsold shares from multiple Form S-8 registration statements, consistent with the undertaking to remove remaining registered securities at termination. The record of per-share consideration ($1.247 cash and one CVR) is material to equity holders' realized value and future potential contingent payments.

Corporate Governance Expert

TL;DR: Governance changes are implicit—IGM is now a private subsidiary and its prior equity registration programs are closed out.

The post-effective amendments are administrative steps that follow the Merger: terminating prior employee and ESPP registration statements and removing unsold registered securities. The filing documents that treasury-held shares and shares owned by Parent/Merger Sub were excluded from conversion, and that appraisal rights were preserved for eligible stockholders. This formalizes the end of public registrant disclosures tied to those S-8 offerings.

FAQ

AI-generated questions and answers. How Rhea-AI works. Not financial advice.

What happened to IGM Biosciences (IGMS) shares in the merger?

Each outstanding share (subject to limited exceptions) was converted into $1.247 in cash and one non-transferable contractual contingent value right (CVR) per share.

When did the IGM merger agreement and merger close?

The company entered the Merger Agreement on July 1, 2025, and the merger closed with effectiveness on August 14, 2025.

What happened to IGM’s Form S-8 registration statements?

IGM filed post-effective amendments to withdraw and remove any unissued and unsold securities and terminated the effectiveness of the listed Form S-8 registration statements.

Were any shares excluded from conversion in the merger?

Yes. Excluded were (i) shares 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 stockholders who properly exercised appraisal rights under Delaware law.

Who is the parent following the merger?

Following the merger, IGM is a wholly owned subsidiary of Concentra Biosciences, LLC.

AI-generated analysis. How Rhea-AI works. Not financial advice.

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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