[144] Centessa Pharmaceuticals plc American SEC Filing

Rhea-AI Filing Summary

Atlas Venture funds have filed Amendment No. 1 to their Schedule 13D for ImageneBio, Inc. (formerly Ikena Oncology, Nasdaq: IKNA) to report dilution of their holdings after the 1-for-12 reverse stock split and completion of Ikena’s all-stock merger with Inmagene on 25 Jul 2025.

• Collectively, the reporting entities now own 418,179 post-split common shares, equal to 3.6 % of the 11.6 million shares outstanding.
• Breakdown: Fund X 241,800 shares (2.1 %), Fund XI 103,494 shares (0.9 %), Opportunity Fund I 72,885 shares (0.6 %).
• All voting and dispositive powers are shared among the respective limited partnerships and their general partners; no sole voting power is reported.
• The funds ceased to be 5 % beneficial owners on 25 Jul 2025; no purchases or sales occurred in the past 60 days.
• Purpose: administrative update reflecting dilution from the merger and reverse split; Atlas Venture continues to hold the same absolute number of economic shares pre-transaction but a lower percentage.

Atlas Venture disclaims group status among the reporting persons. A joint filing agreement is included as Exhibit 99.1.

Positive

• No insider selling: Atlas Venture did not dispose of any shares, signalling continued support for ImageneBio.
• Merger completion and reverse split finalized, providing corporate clarity after the Inmagene transaction.

Negative

• Ownership dilution: Atlas Venture’s combined stake falls below 5 %, slightly reducing insider alignment.
• Lower reporting threshold: Future 13D filings may cease unless ownership rises again, reducing visibility into a key holder’s changes.

Insights

Financial Analyst

TL;DR – Atlas Venture’s stake falls to 3.6 % due to merger-related dilution; no shares sold, impact on IKNA share supply already known.

The amendment is largely administrative. Atlas Venture’s absolute share count is unchanged, but the completed Inmagene merger and 1-for-12 reverse split expanded the denominator, cutting their ownership below the 5 % 13D threshold. The filing removes a potential overhang concern of insider selling, as none occurred. From a governance lens, the reduced concentration slightly broadens the float, but Atlas remains a meaningful holder. Market impact is likely minimal because the share count change was disclosed in the July 25 reverse-split announcement and already reflected in trading. Overall, neutral for valuation and liquidity.

Form 144 Filer Information	UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Form 144 NOTICE OF PROPOSED SALE OF SECURITIES PURSUANT TO RULE 144 UNDER THE SECURITIES ACT OF 1933
FORM 144

144: Filer Information

Filer CIK
Filer CCC
Is this a LIVE or TEST Filing?	LIVE TEST
Submission Contact Information
Name
Phone
E-Mail Address

144: Issuer Information

Name of Issuer

SEC File Number

Address of Issuer

Phone

Name of Person for Whose Account the Securities are To Be Sold

See the definition of "person" in paragraph (a) of Rule 144. Information is to be given not only as to the person for whose account the securities are to be sold but also as to all other persons included in that definition. In addition, information shall be given as to sales by all persons whose sales are required by paragraph (e) of Rule 144 to be aggregated with sales for the account of the person filing this notice.

Relationship to Issuer

144: Securities Information

Title of the Class of Securities To Be Sold	Name and Address of the Broker	Number of Shares or Other Units To Be Sold	Aggregate Market Value	Number of Shares or Other Units Outstanding	Approximate Date of Sale	Name the Securities Exchange
Common	UBS Financial Services, Inc Eleven Madison Avenue 4th Floor New York NY 10010	8322	127909.14	133618774	07/29/2025	Nasdaq

Furnish the following information with respect to the acquisition of the securities to be sold and with respect to the payment of all or any part of the purchase price or other consideration therefor:

144: Securities To Be Sold

Title of the Class	Date you Acquired	Nature of Acquisition Transaction	Name of Person from Whom Acquired	Is this a Gift?	Date Donor Acquired	Amount of Securities Acquired	Date of Payment	Nature of Payment *
Common	01/02/2020	Founders Shares	Issuer			5000	01/02/2020	NA
Common	05/01/2024	RSU Vest	Issuer			672	05/01/2025	NA
Common	06/30/2024	RSU Vest	Issuer			2650	06/30/2024	NA

* If the securities were purchased and full payment therefor was not made in cash at the time of purchase, explain in the table or in a note thereto the nature of the consideration given. If the consideration consisted of any note or other obligation, or if payment was made in installments describe the arrangement and state when the note or other obligation was discharged in full or the last installment paid.

Furnish the following information as to all securities of the issuer sold during the past 3 months by the person for whose account the securities are to be sold.

144: Securities Sold During The Past 3 Months

Name and Address of Seller	Title of Securities Sold	Date of Sale	Amount of Securities Sold	Gross Proceeds
Mario Alberto Accardi 3RD FLOOR 1 ASHLEY ROAD ALTRINCHAM, CHESHIRE X0 WA14 2DT	Common	06/24/2025	15000	210000.00

144: Remarks and Signature

Remarks

Date of Notice

Date of Plan Adoption or Giving of Instruction, If Relying on Rule 10b5-1

ATTENTION:

The person for whose account the securities to which this notice relates are to be sold hereby represents by signing this notice that he does not know any material adverse information in regard to the current and prospective operations of the Issuer of the securities to be sold which has not been publicly disclosed. If such person has adopted a written trading plan or given trading instructions to satisfy Rule 10b5-1 under the Exchange Act, by signing the form and indicating the date that the plan was adopted or the instruction given, that person makes such representation as of the plan adoption or instruction date.

Signature

ATTENTION: Intentional misstatements or omission of facts constitute Federal Criminal Violations (See 18 U.S.C. 1001)

FAQ

Why did Atlas Venture file an amended Schedule 13D for IKNA?

To report that its percentage ownership fell to 3.6 % after IKNA’s merger with Inmagene and a 1-for-12 reverse split on 25 Jul 2025.

How many IKNA shares does Atlas Venture now own?

Collectively 418,179 shares: Fund X 241,800; Fund XI 103,494; Opportunity Fund I 72,885.

Did Atlas Venture sell any IKNA shares?

No. The filing states no purchases or sales occurred in the past 60 days; dilution alone lowered the percentage.

What is IKNA’s new share count after the merger?

The filing references approximately 11.6 million common shares outstanding as of 25 Jul 2025.

Does Atlas Venture still have voting control over its IKNA shares?

Yes. Each fund and its general partners retain shared voting and dispositive power over their respective shares.