RA Capital Management, L.P. and affiliated reporting persons filed a Form 4 with the SEC on November 3, 2026, disclosing a series of open-market purchases and preferred-stock conversions in Bambusa Therapeutics, Inc. (NASDAQ:BBTX) occurring on October 30 and November 2, 2026.

Key Highlights

  • Open-market purchase on October 30: RA Capital Healthcare Fund, L.P. acquired 189,909 shares of common stock at a weighted average price of $14.23, with individual transaction prices ranging from $13.61 to $14.58.
  • Second October 30 purchase: An additional 263,911 shares were acquired at a weighted average price of $14.92, with prices ranging from $14.65 to $15.00.
  • Preferred stock conversions on November 2: Series A-1 and Series A-2 Preferred Stock automatically converted on a one-for-one basis into common stock prior to the closing of Bambusa Therapeutics' initial public offering, adding 3,144,858 shares to the Fund and 1,331,080 shares to Nexus Fund III.
  • November 2 open-market purchases: The Fund acquired 2,335,109 shares and Nexus Fund III acquired 164,891 shares, both at $16 per share.
  • Post-transaction beneficial ownership: Following all reported transactions, the Fund held 5,933,787 shares and Nexus Fund III held 1,495,971 shares, each held indirectly.
  • Multiple reporting persons: The filing was made jointly by RA Capital Management, L.P., RA Capital Healthcare Fund, L.P., RA Capital Nexus Fund III, L.P., Peter Kolchinsky, and Rajeev Shah, all of 200 Berkeley Street, 18th Floor, Boston, Massachusetts 02116.

RA Capital Discloses IPO-Era Share Acquisitions in Bambusa Therapeutics

According to the filing, RA Capital Management, L.P. serves as investment manager for RA Capital Healthcare Fund, L.P. and RA Capital Nexus Fund III, L.P. The general partner of the Adviser is RA Capital Management GP, LLC, of which Peter Kolchinsky and Rajeev Shah are the managing members. The filing notes that Dr. Derek DiRocco, a Partner of the Adviser, serves on the Bambusa Therapeutics board of directors. Each of the reporting persons is identified as a Director and, where applicable, a 10% owner of the issuer.

The October 30, 2026 transactions consisted of two separate open-market purchase blocks. The first, totaling 189,909 shares, carried a weighted average price of $14.23 per share. The second block of 263,911 shares carried a weighted average price of $14.92. The filing states the reporting persons will provide full per-transaction price details upon request to the issuer, any security holder, or SEC staff.

On November 2, 2026, all preferred stock, par value $0.00001 per share, automatically converted to common stock, par value $0.00001 per share, on a one-for-one basis prior to the closing of Bambusa Therapeutics' initial public offering of its common stock, as described in the filing. Series A-1 Preferred Stock contributed 2,844,910 shares to the Fund and 1,278,148 shares to Nexus Fund III; Series A-2 Preferred Stock added 299,948 shares to the Fund and 52,932 shares to Nexus Fund III. The filing states that each reporting person "disclaims beneficial ownership of any of the reported securities, except to the extent of its or his respective pecuniary interest therein."

What Was Disclosed

The filing disclosed six common stock transactions and four derivative-security conversions by RA Capital Management and affiliated entities in Bambusa Therapeutics, covering open-market purchases on October 30 and November 2, 2026, and automatic preferred-stock-to-common-stock conversions coinciding with the company's initial public offering.