Bain Capital unit discloses 17.4% Kailera Therapeutics (KLRA) stake

Rhea-AI Filing Summary

BCLS Fund IV Investments, L.P., an affiliate of Bain Capital Life Sciences, filed a Schedule 13D reporting a significant stake in Kailera Therapeutics, Inc.. The fund beneficially owns 22,583,268 shares of common stock, representing about 17.4% of the outstanding shares.

The position comes from preferred stock converting one-for-one into common stock at Kailera’s initial public offering and the purchase of 1,562,500 shares at $16.00 per share for $25,000,000. BCLS indicates investment purposes, plans to work actively with management and the board, and holds registration and lock-up rights under an Investor Rights Agreement and a 180-day Lock-Up Agreement.

Key Figures

Beneficial ownership: 22,583,268 shares Ownership percentage: 17.43% Shares outstanding: 129,537,314 shares +5 more

8 metrics

Beneficial ownership 22,583,268 shares Common stock directly held by BCLS Fund IV Investments, L.P.

Ownership percentage 17.43% Percent of Kailera common stock class represented by BCLS holdings

Shares outstanding 129,537,314 shares Kailera common stock issued and outstanding per IPO prospectus

IPO purchase size 1,562,500 shares Common shares purchased by BCLS from IPO underwriters

IPO purchase price $16.00 per share Price paid by BCLS in Kailera initial public offering

Total IPO purchase $25,000,000 Aggregate consideration for 1,562,500 IPO shares

Series A-1 preferred shares 16,875,000 shares Kailera Series A-1 Preferred Stock converted to common one-for-one

Series B preferred shares 4,145,768 shares Kailera Series B Preferred Stock converted to common one-for-one

Key Terms

Schedule 13D, beneficially owned, Investor Rights Agreement, Form S-1 Registration Rights, +2 more

6 terms

Schedule 13D regulatory

"If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this"

A Schedule 13D is a legal document that investors file with regulators when they buy a large enough stake in a company to potentially influence its management or decisions. It provides details about the investor’s intention, ownership stake, and plans, helping other investors understand who is gaining control and what their motives might be.

beneficially owned financial

"Aggregate amount beneficially owned by each reporting person 22,583,268.00"

Beneficially owned describes securities or assets where a person has the economic rights and control—such as the right to receive dividends and to direct voting—even if legal title is held in another name. Think of it like having the keys and using a car that’s registered to someone else: you get the benefits and make decisions. Investors care because beneficial ownership reveals who truly controls value and voting power, affecting corporate decisions and takeover dynamics.

Investor Rights Agreement regulatory

"The Reporting Person is party to the Amended and Restated Investor Rights Agreement (the "Investor Rights Agreement"), dated October 5, 2025"

A legally binding contract between a company and its investors that spells out investors’ core protections and privileges—such as voting rights, how and when shares can be sold, information access, and steps for resolving disputes. Think of it like a rulebook or homeowner association agreement for ownership: it clarifies who gets a say, how value can be realized, and what protections exist if things go wrong, making investment risks and expectations clearer for shareholders.

Form S-1 Registration Rights regulatory

"Form S-1 Registration Rights. If at any time beginning 180 days after the closing date of the Issuer's initial public offering"

Piggyback Registration Rights regulatory

"Piggyback Registration Rights. If, at any time after the Issuer's initial public offering, the Issuer proposes to register any shares"

A contractual right that lets existing shareholders join a company’s planned public sale of stock so they can sell their own shares at the same time under the same paperwork. It matters to investors because it gives insiders and early holders an easier, often faster way to convert shares to cash, while also potentially increasing the number of shares offered and affecting the share price — like catching a scheduled bus instead of hiring a private ride to get where you need to go.

Lock-Up Agreement regulatory

"In connection with the Issuer's initial public offering, the Reporting Person and Dr. Koppel each entered into a lock-up agreement (a "Lock-Up Agreement")"

A lock-up agreement is a contract that prevents company insiders and early investors from selling their shares for a fixed period after a stock sale, often after an initial public offering. It matters to investors because it temporarily limits the number of shares that can hit the market, which can keep the share price steadier; when the lock-up ends, a sudden increase in available shares can create extra volatility, revealing insiders’ confidence or lack thereof.

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SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934

Kailera Therapeutics, Inc.

(Name of Issuer)

Common Stock, $0.00001 par value per share

(Title of Class of Securities)

(CUSIP Number)

Bain Capital Life Sciences
Investors, LLC, 200 Clarendon Street
Boston, MA, 02116
617-516-2000

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)

04/16/2026

(Date of Event Which Requires Filing of This Statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§ 240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box.

The information required on the remainder of this cover page shall not be deemed to be "filed" for the purpose of Section 18 of the Securities Exchange Act of 1934 ("Act") or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

schemaVersion:

SCHEDULE 13D

CUSIP No.

1

Name of reporting person

BCLS Fund IV Investments, L.P.

2

Check the appropriate box if a member of a Group (See Instructions)

(a)
(b)

3

SEC use only

4

Source of funds (See Instructions)

WC

5

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

6

Citizenship or place of organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 0.00
8	Shared Voting Power 22,583,268.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 22,583,268.00

11

Aggregate amount beneficially owned by each reporting person

22,583,268.00

12

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

13

Percent of class represented by amount in Row (11)

17.43 %

14

Type of Reporting Person (See Instructions)

PN

SCHEDULE 13D

Item 1.	Security and Issuer
(a)	Title of Class of Securities: Common Stock, $0.00001 par value per share
(b)	Name of Issuer: Kailera Therapeutics, Inc.
(c)	Address of Issuer's Principal Executive Offices: 180 Third Avenue, 4th Floor, Waltham, MASSACHUSETTS , 02451.
Item 2.	Identity and Background
(a)	This Schedule 13D is filed by BCLS Fund IV Investments, L.P., a Delaware limited partnership (the "Reporting Person"). Bain Capital Life Sciences Investors, LLC, a Delaware limited liability company ("BCLSI"), is the manager of Bain Capital Life Sciences IV General Partner, LLC, a Delaware limited liability company ("BCLS Fund IV GP"), which is the general partner of Bain Capital Life Sciences Fund IV, L.P., a Delaware limited partnership ("BCLS Fund IV"), which is the managing member of BCLS Fund IV Investments GP, LLC, a Delaware limited liability company ("BCLS Fund IV Investments GP" and, together with the Reporting Person, BCLSI, BCLS Fund IV GP and BCLS Fund IV, the "Bain Capital Life Sciences Entities"), which is the general partner of the Reporting Person. As a result, BCLSI may be deemed to share voting and dispositive power with respect to the securities held by the Reporting Person. Voting and investment decisions with respect to the securities held by the Reporting Person are made by the Partners of BCLSI.
(b)	c/o Bain Capital Life Sciences Investors, LLC, 200 Clarendon Street, Boston, Massachusetts 02116.
(c)	Investment in securities.
(d)	During the last five years, none of the Bain Capital Life Sciences Entities have been convicted in a criminal proceeding (excluding traffic violations or similar misdemeanors).
(e)	During the last five years, none of the Bain Capital Life Sciences Entities have been a party to a civil proceeding of a judicial or administrative body of competent jurisdiction and as a result of such proceeding was or is subject to a judgment, decree or final order enjoining future violations of, or prohibiting or mandating activities subject to, federal or state securities laws or finding any violation with respect to such laws.
(f)	See Item 2(a) hereof.
Item 3.	Source and Amount of Funds or Other Consideration
	Prior to the Issuer's initial public offering, the Reporting Person held 16,875,000 shares of the Issuer's Series A-1 Preferred Stock and 4,145,768 shares of the Issuer's Series B Preferred Stock. Upon the closing of the Issuer's initial public offering, each share of the Issuer's Series A-1 Preferred Stock and Series B Preferred Stock automatically converted into one share of Common Stock. As a result, following the conversion, the Reporting Person held 21,020,768 shares of Common Stock. On April 20, 2026, the Reporting Person purchased 1,562,500 shares of Common Stock from the underwriters in the Issuer's initial public offering at a price of $16.00 per share for a total purchase price of $25,000,000. The Reporting Person used its own working capital to acquire all of the foregoing equity securities of the Issuer.
Item 4.	Purpose of Transaction
	The information set forth in Item 3 of this Schedule 13D is incorporated by reference in its entirety into this Item 4. Adam Koppel, a Partner of BCLSI, is a member of the Issuer's board of directors (the "Board"). The Reporting Person acquired the securities reported herein for investment purposes. In its capacity as a significant stockholder of the Issuer, the Reporting Person intends to take an active role in working with the Issuer's management and the Board on operational, financial and strategic initiatives. The Reporting Person reviews and intends to continue to review, on an ongoing and continuing basis, their investment in the Issuer. Depending upon the factors discussed below and subject to applicable law, the Reporting Person may from time to time acquire additional securities of the Issuer or sell or otherwise dispose of some or all of their securities of the Issuer. Any transactions that the Reporting Persons may pursue may be made at any time and from time to time without prior notice and will depend upon a variety of factors, including, without limitation, current and anticipated future trading prices of the securities of the Issuer, the financial condition, results of operations and prospects of the Issuer, general economic, financial market and industry conditions, other investment and business opportunities avialable to the Reporting Person, tax considerations and other factors.
Item 5.	Interest in Securities of the Issuer
(a)	The information set forth in Items 2 and 3 and on the cover pages of this Schedule 13D is incorporated by reference in its entirety into this Item 5. As of the date hereof the Reporting Person directly holds 22,583,268 shares of Common Stock, representing approximately 17.4% of the outstanding shares of Common Stock. The percentage of the outstanding shares of Common Stock held by the Reporting Person is based on 129,537,314 shares of Common Stock issued and outstanding, as reported by the Issuer in its prospectus relating to its initial public offering (after giving effect to the full exercise of the underwriters' option to purchase additional shares), filed with the Securities and Exchange Commission pursuant to Rule 424(b) under the Securities Act of 1933, as amended, on April 17, 2026.
(b)	See Item 5(a) hereof.
(c)	See Item 3 hereof.
(d)	Except as otherwise described in this Item 5, no one other than the Reporting Person has the right to receive, or the power to direct the receipt of, dividends from, or the proceeds from the sale of, any of the shares of Common Stock beneficially owned by the Reporting Person as described in this Item 5.
(e)	Not applicable.
Item 6.	Contracts, Arrangements, Understandings or Relationships With Respect to Securities of the Issuer
	The information set forth in Item 3 of this Schedule 13D is incorporated by reference in its entirety into this Item 6. Investor Rights Agreement. The Reporting Person is party to the Amended and Restated Investor Rights Agreement (the "Investor Rights Agreement"), dated October 5, 2025, with the Issuer and certain other stockholders of the Issuer. The Investor Rights Agreement provides the Reporting Person with the following rights with respect to the registration of its shares of Common Stock: Form S-1 Registration Rights. If at any time beginning 180 days after the closing date of the Issuer's initial public offering the holders of the majority of the registrable securities request in writing that the Issuer effect a registration with respect to all or part of such registrable securities then outstanding and having an anticipated aggregate offering price that would exceed $25,000,000, net of expenses, the Issuer may be required to register their shares. The Issuer is obligated to effect at most two registrations in response to these demand registration rights. Piggyback Registration Rights. If, at any time after the Issuer's initial public offering, the Issuer proposes to register any shares of its Common Stock under the Securities Act of 1933, as amended, subject to certain exceptions, the holders of registrable securities will be entitled to notice of the registration and to include their shares of registrable securities in the registration. Form S-3 Registration. If, at any time after the Issuer becomes entitled under the Securities Act of 1933, as amended, to register its shares on a registration statement on Form S-3, the holders of at least 25% of the registrable securities request in writing that the Issuer effect a registration with respect to registrable securities at an aggregate price to the public in the offering of at least $10,000,000, the Issuer will be required to effect such registration. Lock-Up Agreement. In connection with the Issuer's initial public offering, the Reporting Person and Dr. Koppel each entered into a lock-up agreement (a "Lock-Up Agreement") with the representatives of the several underwriters. Pursuant to the Lock-Up Agreement, the Reporting Person and Dr. Koppel each agreed, subject to certain exceptions, not to sell or otherwise transfer any shares of the Issuer's Common Stock or securities convertible into or exercisable or exchangeable for, shares of Common Stock for 180 days after the date of the prospectus relating to the Issuer's initial public offering without the prior written consent of the representatives. The foregoing summaries of the Investor Rights Agreement and Lock-Up Agreement do not purport to be complete and are qualified in their entirety by reference to the Investor Rights Agreement and Lock-Up Agreement, each of which is filed as an exhibit hereto and incorporated by reference herein.
Item 7.	Material to be Filed as Exhibits.
	Exhibit A. Investor Rights Agreement (incorporated by reference from Exhibit 10.11 to the Issuer's Registration Statement on Form S-1 (File No. 333-294690). Exhibit B. Lock-Up Agreement.

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

BCLS Fund IV Investments, L.P.

Signature:	/s/ Adam Koppel
Name/Title:	Adam Koppel, Partner of Bain Capital Life Sciences Investors, LLC
Date:	04/23/2026

FAQ

How large is BCLS Fund IV Investments’ stake in Kailera Therapeutics (KLRA)?

BCLS Fund IV Investments beneficially owns 22,583,268 shares of Kailera Therapeutics common stock, representing about 17.4% of the outstanding shares. This percentage is based on 129,537,314 shares outstanding, as disclosed in Kailera’s IPO prospectus referenced in the Schedule 13D filing.

How did BCLS Fund IV Investments acquire its KLRA shares?

BCLS initially held Series A-1 and Series B preferred stock that converted one-for-one into 21,020,768 common shares at Kailera’s IPO. It then bought an additional 1,562,500 common shares from the IPO underwriters at $16.00 per share, totaling $25,000,000, using its working capital.

What is the Investor Rights Agreement mentioned for Kailera Therapeutics (KLRA)?

BCLS is party to an Amended and Restated Investor Rights Agreement granting registration rights for its Kailera shares. These include Form S-1 demand registrations above $25,000,000, piggyback rights on company offerings, and Form S-3 registrations for offerings of at least $10,000,000 once Form S-3 becomes available.

What lock-up restrictions apply to BCLS and Adam Koppel regarding KLRA shares?

In connection with Kailera’s IPO, BCLS and Dr. Adam Koppel each signed a Lock-Up Agreement with the underwriters. They agreed, subject to exceptions, not to sell or transfer Kailera common stock or related securities for 180 days after the IPO prospectus date without underwriter consent.

What role does Bain Capital Life Sciences play in Kailera Therapeutics (KLRA)?

Bain Capital Life Sciences Investors, LLC manages entities that ultimately control BCLS Fund IV Investments. Partner Adam Koppel serves on Kailera’s board of directors. The Schedule 13D states BCLS intends to take an active role with Kailera’s management and board on operational, financial, and strategic initiatives.