Prime Medicine Announced New England Journal Of Medicine Publication Of PM359 Clinical Data For Two Patients For Treatment Of Chronic Granulomatous Disease

Prime Medicine, Inc. (NASDAQ:PRME), a biotechnology company committed to delivering a new class of differentiated one-time curative genetic therapies, today announced the publication of Phase 1/2 clinical data with PM359, the Company's investigational autologous hematopoietic stem cell product for p47 phox chronic granulomatous disease (CGD) in the New England Journal of Medicine (NEJM). The data will also be presented in a poster session at the 67th American Society of Hematology (ASH) Annual Meeting, December 6-9, 2025 in Orlando, Florida.

Both patients enrolled in the study had a history of prior CGD-defining complications, including CGD-associated colitis (CAC), and skin and soft tissue infections, and both were maintained on long-term prophylactic therapy. Both patients experienced rapid neutrophil engraftment, achieving 69% and 83% dihydrorhodamine-positive (DHR+) neutrophils by Day 30, respectively, far in excess of the 20% projected minimum threshold for clinical benefit. DHR activity remained stable over time in both patients, suggesting that gene correction occurred in the long-term repopulating hematopoietic stem cells (HSCs) of the bone marrow. Both patients remain free of new CGD-related complications or significant intercurrent illnesses post-infusion; additionally, Patient 1 stopped his mesalamine treatment and has not experienced a flare of CAC, and Patient 2's levels of fecal calprotectin have decreased substantially, and his chronic CAC symptoms have abated. No clinically significant adverse events attributable to PM359 occurred in either patient, and all observed toxicities were consistent with busulfan-based conditioning