Company: PRME
Filing Date: 2025-05-19
Form Type: DEFA14A
Source: 0001193125-25-122158
Chunk: 8

Company: Prime Medicine, Inc.
Filing Date: 2025-05-19
Form: DEFA14A
Chunk 8
---
 reported are from the first adult patient treated in the trial.

The
first patient was treated with a single dose of PM359, administered by intravenous infusion. NADPH oxidase activity was measured by the DHR assay at baseline, Day 15 and Day 30. Treatment with PM359 led to complete restoration of NADPH oxidase
activity in 58% of neutrophils by Day 15 and 66% of neutrophils by Day 30, significantly exceeding the anticipated minimum threshold for clinical benefit of 20%. Additionally, the patient experienced rapid engraftment of his autologous transplant
following myeloablative conditioning. Engraftment was confirmed in neutrophils on Day 14 and in platelets on Day 19. Of note, this is nearly two-times faster than approved gene editing technologies, where
median engraftment has been reported to occur on Days 27 and 35 across these same measures.

Treatment with PM359 was generally well-tolerated, with an
acceptable safety profile. Adverse events (“AEs”) were generally consistent with AEs otherwise observed during myeloablative conditioning with busulfan. No serious AEs related to PM359 were reported as of the data cutoff.

Beam Arbitration

The Company is currently engaged in
arbitration proceedings with Beam Therapeutics, Inc. regarding the parties’ collaboration and license agreement and the Company’s development of a product for the treatment of AATD. The arbitration remains in an early stage.

Cautionary Note Regarding Forward Looking Statements

This Current Report on Form 8-K contains forward-looking statements within the meaning of the
Private Securities Litigation Reform Act of 1995, as amended, including, without limitation, the Company’s expectations regarding: the continued development and advancement of its AATD and Wilson’s Disease programs, including the timing of
the filing of IND and/or CTA applications in mid-2026 and the first half of 2026, respectively, and the timing of initial data for both programs in 2027; the initiation, timing, progress, and results of its
research and development programs, preclinical studies and future clinical trials, and the release of data related thereto; the collaboration with Bristol Myers Squibb and the intended and potential benefits thereof, including the receipt of
potential milestone and royalty payments from commercial product sales, if any; the potential of Prime Editing to correct the causative mutations of diseases, including of AATD, Wilson’s