Bambusa Therapeutics: RA funds hold preferred stock

The preferred-stock holdings convert into common shares on a one-for-one basis before Bambusa’s initial public offering closes.

Accepted by SEC EDGAR 10/29/2026 - 04:33 PM EDT Learn about SEC filing dates

Rhea-AI Filing Summary

Bambusa Therapeutics, Inc. reports that RA Capital Healthcare Fund, L.P. holds Series A-1 and A-2 Preferred Stock convertible into 2,844,910 and 299,948 common shares, respectively; RA Capital Nexus Fund III, L.P. holds the corresponding series convertible into 1,278,148 and 52,932 common shares. All preferred stock automatically converts one-for-one before the issuer’s initial public offering closes. The funds, their adviser RA Capital Management, L.P., its general partner RA Capital Management GP, LLC, Peter Kolchinsky and Rajeev M. Shah disclaim beneficial ownership except to the extent of their respective pecuniary interests. Kolchinsky and Shah are the general partner’s managing members and are identified as directors and ten-percent owners; Dr. Derek DiRocco, a Partner of the Adviser, serves on Bambusa’s board.

Insider Trade Summary

Holdings reported, no transactions

Holdings

Insider RA CAPITAL MANAGEMENT, L.P., RA Capital Healthcare Fund LP, RA Capital Nexus Fund III, L.P., Kolchinsky Peter, Shah Rajeev M.

Role Director, 10% Owner | Director | Director | Director, 10% Owner | Director, 10% Owner

Type	Security	Shares	Price	Value
Holding	Series A-1 Preferred Stock F1, F2, F3	--	--	--
Holding	Series A-1 Preferred Stock F1, F2, F4	--	--	--
Holding	Series A-2 Preferred Stock F1, F2, F3	--	--	--
Holding	Series A-2 Preferred Stock F1, F2, F4	--	--	--

Holdings: Series A-1 Preferred Stock — 4,123,058 contracts (Indirect, See Footnotes); Series A-2 Preferred Stock — 352,880 contracts (Indirect, See footnotes)

Footnotes (4)

1. F1. All shares of the preferred stock, par value $0.00001 per share, of the Issuer will automatically be converted on a one-for-one basis to shares of the Issuer's common stock, par value $0.00001 per share ("Common Stock") prior to the closing of the Issuer's initial public offering of its Common Stock.
2. F2. RA Capital Management, L.P. (the "Adviser") is the investment manager for RA Capital Healthcare Fund, L.P. (the "Fund") and RA Capital Nexus Fund III, L.P. (the "Nexus Fund III"). The general partner of the Adviser is RA Capital Management GP, LLC (the "Adviser GP"), of which Dr. Peter Kolchinsky and Mr. Rajeev Shah are the managing members. Each of the Adviser, the Adviser GP, the Fund, the Nexus Fund III, Dr. Kolchinsky and Mr. Shah disclaims beneficial ownership of any of the reported securities, except to the extent of its or his respective pecuniary interest therein.
3. F3. Held directly by the Fund.
4. F4. Held directly by the Nexus Fund III.

Key Figures

Series A-1 conversion shares — RA Capital Healthcare Fund, L.P.: 2,844,910 common shares Series A-2 conversion shares — RA Capital Healthcare Fund, L.P.: 299,948 common shares Series A-1 conversion shares — RA Capital Nexus Fund III, L.P.: 1,278,148 common shares +2 more

5 metrics

Series A-1 conversion shares — RA Capital Healthcare Fund, L.P. 2,844,910 common shares Underlying common shares from preferred stock conversion

Series A-2 conversion shares — RA Capital Healthcare Fund, L.P. 299,948 common shares Underlying common shares from preferred stock conversion

Series A-1 conversion shares — RA Capital Nexus Fund III, L.P. 1,278,148 common shares Underlying common shares from preferred stock conversion

Series A-2 conversion shares — RA Capital Nexus Fund III, L.P. 52,932 common shares Underlying common shares from preferred stock conversion

Preferred-stock conversion ratio 1 preferred share to 1 common share Automatic conversion before the initial public offering closes

Key Terms

Series A-1 Preferred Stock, Series A-2 Preferred Stock, beneficial ownership, pecuniary interest, +1 more

5 terms

Series A-1 Preferred Stock financial

"All shares of the preferred stock"

Series A-1 preferred stock is a specific class of company shares created in an early financing round that typically gives its holders priority over common shareholders for dividends and money if the company is sold or liquidates. Think of it as a special ticket with upfront privileges — often convertible into ordinary shares and sometimes carrying voting or protective rights — so investors use it to reduce risk and preserve control compared with ordinary stock.

Series A-2 Preferred Stock financial

"Series A-2 Preferred Stock"

Series A-2 preferred stock is a specific class of shares created during a funding round that gives its holders stronger financial protections and priority over common shareholders, such as getting paid first if the company is sold or winding down. Investors care because these shares behave like a hybrid between a loan and regular stock: they often offer fixed payouts or conversion rights and a better claim on assets, making them lower risk and shaping potential returns.

beneficial ownership regulatory

"disclaims beneficial ownership of any of the reported securities"

Beneficial ownership means the person or entity that actually enjoys the benefits of owning shares or other assets — such as receiving dividends, voting rights, or price gains — even if the legal title is held in another name. For investors it matters because knowing who truly controls and profits from a company reveals who can influence decisions, exposes potential conflicts of interest or hidden concentration of power, and affects transparency and risk in the stock.

pecuniary interest financial

"except to the extent of its or his respective pecuniary interest therein"

one-for-one basis technical

"automatically be converted on a one-for-one basis"

FAQ

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

How many BBTX common shares are represented by RA Capital’s preferred stock?

RA Capital Healthcare Fund, L.P.’s Series A-1 and A-2 Preferred Stock are convertible into 2,844,910 and 299,948 common shares, respectively; RA Capital Nexus Fund III, L.P.’s corresponding holdings are convertible into 1,278,148 and 52,932 common shares.

Who disclaims beneficial ownership of BBTX preferred stock?

RA Capital Management, L.P., RA Capital Management GP, LLC, the two RA Capital funds, Peter Kolchinsky and Rajeev M. Shah disclaim beneficial ownership except to the extent of their respective pecuniary interests.

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

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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

OMB APPROVAL

OMB Number:			3235-0104
Estimated average burden
hours per response:			0.5

1. Name and Address of Reporting Person^*

RA CAPITAL MANAGEMENT, L.P.

(Last) (First) (Middle)

200 BERKELEY STREET, 18TH FLOOR

(Street)

BOSTON MASSACHUSETTS 02116

(City) (State) (Zip)

UNITED STATES

(Country)

2. Date of Event Requiring Statement (Month/Day/Year)
10/29/2026

3. Issuer Name and Ticker or Trading Symbol
Bambusa Therapeutics, Inc. [ BBTX ]

3a. Foreign Trading Symbol

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

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

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

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)

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 A-1 Preferred Stock	(1)	(1)	Common Stock	2,844,910	(1)	I	See Footnotes(2)(3)
Series A-1 Preferred Stock	(1)	(1)	Common Stock	1,278,148	(1)	I	See Footnotes(2)(4)
Series A-2 Preferred Stock	(1)	(1)	Common Stock	299,948	(1)	I	See footnotes(2)(3)
Series A-2 Preferred Stock	(1)	(1)	Common Stock	52,932	(1)	I	See footnotes(2)(4)

1. Name and Address of Reporting Person^*

RA CAPITAL MANAGEMENT, L.P.

(Last) (First) (Middle)

200 BERKELEY STREET, 18TH FLOOR

(Street)

BOSTON MASSACHUSETTS 02116

(City) (State) (Zip)

UNITED STATES

(Country)

Relationship of Reporting Person(s) to Issuer

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

1. Name and Address of Reporting Person^*

RA Capital Healthcare Fund LP

(Last) (First) (Middle)

C/O RA CAPITAL MANAGEMENT, L.P.

200 BERKELEY STREET, 18TH FLOOR

(Street)

BOSTON MASSACHUSETTS 02116

(City) (State) (Zip)

UNITED STATES

(Country)

Relationship of Reporting Person(s) to Issuer

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

1. Name and Address of Reporting Person^*

RA Capital Nexus Fund III, L.P.

(Last) (First) (Middle)

C/O RA CAPITAL MANAGEMENT, L.P.

200 BERKELEY STREET, 18TH FLOOR

(Street)

BOSTON MASSACHUSETTS 02116

(City) (State) (Zip)

UNITED STATES

(Country)

Relationship of Reporting Person(s) to Issuer

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

1. Name and Address of Reporting Person^*

Kolchinsky Peter

(Last) (First) (Middle)

C/O RA CAPITAL MANAGEMENT, L.P.

200 BERKELEY STREET, 18TH FLOOR

(Street)

BOSTON MASSACHUSETTS 02116

(City) (State) (Zip)

UNITED STATES

(Country)

Relationship of Reporting Person(s) to Issuer

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

1. Name and Address of Reporting Person^*

Shah Rajeev M.

(Last) (First) (Middle)

C/O RA CAPITAL MANAGEMENT, L.P.

200 BERKELEY STREET, 18TH FLOOR

(Street)

BOSTON MASSACHUSETTS 02116

(City) (State) (Zip)

UNITED STATES

(Country)

Relationship of Reporting Person(s) to Issuer

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

Explanation of Responses:

1. All shares of the preferred stock, par value $0.00001 per share, of the Issuer will automatically be converted on a one-for-one basis to shares of the Issuer's common stock, par value $0.00001 per share ("Common Stock") prior to the closing of the Issuer's initial public offering of its Common Stock.

2. RA Capital Management, L.P. (the "Adviser") is the investment manager for RA Capital Healthcare Fund, L.P. (the "Fund") and RA Capital Nexus Fund III, L.P. (the "Nexus Fund III"). The general partner of the Adviser is RA Capital Management GP, LLC (the "Adviser GP"), of which Dr. Peter Kolchinsky and Mr. Rajeev Shah are the managing members. Each of the Adviser, the Adviser GP, the Fund, the Nexus Fund III, Dr. Kolchinsky and Mr. Shah disclaims beneficial ownership of any of the reported securities, except to the extent of its or his respective pecuniary interest therein.

3. Held directly by the Fund.

4. Held directly by the Nexus Fund III.

Remarks:

Dr. Derek DiRocco, a Partner of the Adviser, serves on the Issuer's board of directors.

	/s/ Peter Kolchinsky, Manager of RA Capital Management, L.P.	10/29/2026
	/s/ Peter Kolchinsky, Manager of RA Capital Healthcare Fund GP, LLC, the General Partner of RA Capital Healthcare Fund, L.P.	10/29/2026
	/s/ Peter Kolchinsky, Manager of RA Capital Nexus Fund III GP, LLC, the General Partner of RA Capital Nexus Fund III, L.P.	10/29/2026
	/s/ Peter Kolchinsky, individually	10/29/2026
	/s/ Rajeev Shah, individually	10/29/2026
	** 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).
Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.
* Form 3: SEC 1473 (03-26)