Aktis Oncology (AKTS) MPM funds disclose initial insider stakes holdings

Rhea-AI Filing Summary

Aktis Oncology, Inc. had several MPM-affiliated investment vehicles file an initial Form 3 to report their beneficial ownership as of 01/08/2026. The group reports indirect ownership of 341,709 shares of common stock and indirect holdings of Series Seed, Series A and Series B Redeemable Convertible Preferred Stock, which are each convertible into common stock on a 3.8044-for-1 basis. The preferred shares will convert into common stock upon the closing of Aktis Oncology’s initial public offering and have no expiration date. The reporting persons state that they disclaim beneficial ownership of these securities except to the extent of their pecuniary interest, and the shares are held through various MPM-managed funds and entities.

SEC Form 3

FORM 3

UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

INITIAL STATEMENT OF BENEFICIAL OWNERSHIP OF SECURITIES

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934
or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person^*

MPM BIOVENTURES 2018, L.P.

(Last) (First) (Middle)

C/O MPM BIOIMPACT LLC

399 BOYLSTON STREET, SUITE 1100

(Street)

BOSTON MA 02116

(City) (State) (Zip)

2. Date of Event Requiring Statement (Month/Day/Year)
01/08/2026

3. Issuer Name and Ticker or Trading Symbol
Aktis Oncology, Inc. [ AKTS ]

4. Relationship of Reporting Person(s) to Issuer
(Check all applicable)

	Director	X	10% Owner
	Officer (give title below)		Other (specify below)

5. If Amendment, Date of Original Filed (Month/Day/Year)

6. Individual or Joint/Group Filing (Check Applicable Line)

	Form filed by One Reporting Person
X	Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Beneficially Owned
1. Title of Security (Instr. 4)	2. Amount of Securities Beneficially Owned (Instr. 4)	3. Ownership Form: Direct (D) or Indirect (I) (Instr. 5)	4. Nature of Indirect Beneficial Ownership (Instr. 5)
Common Stock	341,709	I	See Footnote(1)(2)

Table II - Derivative Securities Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 4)	2. Date Exercisable and Expiration Date (Month/Day/Year)		3. Title and Amount of Securities Underlying Derivative Security (Instr. 4)		4. Conversion or Exercise Price of Derivative Security	5. Ownership Form: Direct (D) or Indirect (I) (Instr. 5)	6. Nature of Indirect Beneficial Ownership (Instr. 5)
	Date Exercisable	Expiration Date	Title	Amount or Number of Shares
Series Seed Redeemable Convertible Preferred Stock	(3)	(3)	Common Stock	1,314,262	$0(3)	I	See Footnote(1)(4)
Series A Redeemable Convertible Preferred Stock	(3)	(3)	Common Stock	5,914,197	$0(3)	I	See Footnote(1)(5)
Series B Redeemable Convertible Preferred Stock	(3)	(3)	Common Stock	1,577,119	$0(3)	I	See Footnote(1)(6)

1. Name and Address of Reporting Person^*

MPM BIOVENTURES 2018, L.P.

(Last) (First) (Middle)

C/O MPM BIOIMPACT LLC

399 BOYLSTON STREET, SUITE 1100

(Street)

BOSTON MA 02116

(City) (State) (Zip)

Relationship of Reporting Person(s) to Issuer

	Director	X	10% Owner
	Officer (give title below)		Other (specify below)

1. Name and Address of Reporting Person^*

MPM BIOVENTURES 2018 (B), L.P.

(Last) (First) (Middle)

C/O MPM BIOIMPACT LLC

399 BOYLSTON STREET, SUITE 1100

(Street)

BOSTON MA 02116

(City) (State) (Zip)

Relationship of Reporting Person(s) to Issuer

	Director	X	10% Owner
	Officer (give title below)		Other (specify below)

1. Name and Address of Reporting Person^*

MPM ASSET MANAGEMENT INVESTORS BV2018 LLC

(Last) (First) (Middle)

C/O MPM BIOIMPACT LLC

399 BOYLSTON STREET, SUITE 1100

(Street)

BOSTON MA 02116

(City) (State) (Zip)

Relationship of Reporting Person(s) to Issuer

	Director	X	10% Owner
	Officer (give title below)		Other (specify below)

1. Name and Address of Reporting Person^*

MPM BioVentures 2018 GP LLC

(Last) (First) (Middle)

C/O MPM BIOIMPACT LLC

399 BOYLSTON STREET, SUITE 1100

(Street)

BOSTON MA 02116

(City) (State) (Zip)

Relationship of Reporting Person(s) to Issuer

	Director	X	10% Owner
	Officer (give title below)		Other (specify below)

1. Name and Address of Reporting Person^*

MPM BioVentures 2018 LLC

(Last) (First) (Middle)

C/O MPM BIOIMPACT LLC

399 BOYLSTON STREET, SUITE 1100

(Street)

BOSTON MA 02116

(City) (State) (Zip)

Relationship of Reporting Person(s) to Issuer

	Director	X	10% Owner
	Officer (give title below)		Other (specify below)

1. Name and Address of Reporting Person^*

MPM ONCOLOGY INNOVATIONS FUND LP

(Last) (First) (Middle)

C/O MPM BIOIMPACT LLC

399 BOYLSTON STREET, SUITE 1100

(Street)

BOSTON MA 02116

(City) (State) (Zip)

Relationship of Reporting Person(s) to Issuer

	Director	X	10% Owner
	Officer (give title below)		Other (specify below)

1. Name and Address of Reporting Person^*

MPM Oncology Innovations Fund GP LLC

(Last) (First) (Middle)

C/O MPM BIOIMPACT LLC

399 BOYLSTON STREET, SUITE 1100

(Street)

BOSTON MA 02116

(City) (State) (Zip)

Relationship of Reporting Person(s) to Issuer

	Director	X	10% Owner
	Officer (give title below)		Other (specify below)

1. Name and Address of Reporting Person^*

EVNIN LUKE

(Last) (First) (Middle)

C/O MPM BIOIMPACT LLC

399 BOYLSTON STREET, SUITE 1100

(Street)

BOSTON MA 02116

(City) (State) (Zip)

Relationship of Reporting Person(s) to Issuer

	Director	X	10% Owner
	Officer (give title below)		Other (specify below)

Explanation of Responses:

1. The Reporting Persons disclaim beneficial ownership of the securities except to the extent of his or its pecuniary interest therein.

2. The shares are held by MPM Asset Management LLC, of which Dr. Gadicke is the manager.

3. Each share of Series Seed Redeemable Convertible Preferred Stock, Series A Redeemable Convertible Preferred Stock and Series B Redeemable Convertible Preferred Stock is convertible into shares of the Issuer's Common Stock on a 3.8044-for-1 basis. Upon the closing of the Issuer's initial public offering, all shares of Series Seed Redeemable Convertible Preferred Stock, Series A Redeemable Convertible Preferred Stock and Series B Redeemable Convertible Preferred Stock will convert into shares of Common Stock of the Issuer. The Series Seed Redeemable Convertible Preferred Stock, Series A Redeemable Convertible Preferred Stock and Series B Redeemable Convertible Preferred Stock have no expiration date.

4. The shares are held as follows: 556,810 by MPM BioVentures 2018, L.P. ("BV 2018"), 29,593 by MPM BioVentures 2018 (B), L.P. ("BV 2018(B)"), 10,988 by MPM Asset Management Investors BV2018 LLC ("AM BV2018"), 119,478 by MPM Oncology Innovations Fund, L.P. ("MPM Oncology") and 597,393 by Oncology Impact Private Investment Fund 2, L.P. ("MPM Oncology Impact"). MPM BioVentures 2018 GP LLC and MPM BioVentures 2018 LLC ("BV2018 LLC") are the direct and indirect general partners of BV 2018 and BV 2018(B). BV 2018 LLC is the manager of AM BV2018. Drs. Evnin and Gadicke are managing directors of BV 2018 LLC and managers of MPM Oncology Innovations Fund GP LLC, which is the general partner of MPM Oncology. Dr. Gadicke is the managing member of MPM Oncology Investments 2 LLC, which is the general partner of MPM Oncology Impact.

5. The shares are held as follows: 2,505,648 by BV 2018, 133,170 by BV 2018(B), 49,452 by AM BV2018, 537,654 by MPM Oncology and 2,688,273 by MPM Oncology Impact.

6. The shares are held as follows: 668,173 by BV 2018, 35,512 by BV 2018(B), 13,187 by AM BV2018, 143,374 by MPM Oncology and 716,873 by MPM Oncology Impact.

Remarks:

This filing is 1 of 2 identical filings due to limitations on number of Reporting Persons. See Form 3 filed by Ansbert Gadicke.

	/s/ Luke Evnin	01/08/2026
	/s/ Ansbert Gadicke, managing director of MPM BioVentures 2018 LLC, the managing member of MPM BioVentures 2018 GP LLC, the GP of MPM BioVentures 2018 (B), L.P.	01/08/2026
	/s/ Ansbert Gadicke, managing director of MPM BioVentures 2018 LLC	01/08/2026
	/s/ Ansbert Gadicke, managing director of MPM BioVentures 2018 LLC, the managing member of MPM BioVentures 2018 GP LLC	01/08/2026
	/s/ Ansbert Gadicke, managing director of MPM BioVentures 2018 LLC, the managing member of MPM BioVentures 2018 GP LLC, the GP of MPM BioVentures 2018, L.P.	01/08/2026
	/s/ Ansbert Gadicke, managing director of MPM BioVentures 2018 LLC, the manager of MPM Asset Management Investors BV2018 LLC	01/08/2026
	/s/ Ansbert Gadicke, manager of MPM Oncology Innovations Fund GP LLC	01/08/2026
	/s/ Ansbert Gadicke, manager of MPM Oncology Innovations Fund GP LLC, the general partner of MPM Oncology Innovations Fund, L.P.	01/08/2026
	** Signature of Reporting Person	Date
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
* If the form is filed by more than one reporting person, see Instruction 5 (b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
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FAQ

What does the Form 3 filing for Aktis Oncology (AKTS) disclose?

The Form 3 discloses that multiple MPM-affiliated funds and entities report indirect beneficial ownership of 341,709 shares of Aktis Oncology common stock plus several series of redeemable convertible preferred stock.

Who are the reporting persons in the Aktis Oncology (AKTS) Form 3?

The reporting persons are MPM BioVentures 2018, L.P., related MPM BioVentures and MPM Asset Management entities, MPM Oncology Innovations funds, and associated general partners, along with Luke Evnin, all reporting as 10% owners.

How many Aktis Oncology (AKTS) common shares are reported as beneficially owned?

The filing reports 341,709 shares of common stock as indirectly beneficially owned, with indirect ownership described in the footnotes through various MPM-managed investment vehicles.

What preferred stock holdings related to Aktis Oncology (AKTS) are reported?

The Form 3 reports indirect holdings of Series Seed, Series A and Series B Redeemable Convertible Preferred Stock, with underlying amounts of 1,314,262, 5,914,197 and 1,577,119 shares respectively, each convertible into common stock.

What is the conversion ratio for Aktis Oncology (AKTS) preferred stock in this filing?

Each share of Series Seed, Series A and Series B Redeemable Convertible Preferred Stock is convertible into Aktis Oncology common stock on a 3.8044-for-1 basis, as stated in the footnotes.

When will the Aktis Oncology (AKTS) preferred shares convert into common stock?

The filing states that all shares of Series Seed, Series A and Series B Redeemable Convertible Preferred Stock will convert into common stock upon the closing of Aktis Oncology’s initial public offering.

Do the reporting persons fully claim ownership of the Aktis Oncology (AKTS) securities?

No. The reporting persons disclaim beneficial ownership of the securities except to the extent of their pecuniary interest, as disclosed in the Explanation of Responses.