Prime Medicine — Third Quarter 2026 Earnings Summary

Financial Performance:

• Total revenue for the three months ended September 30, 2026, was $4.2 million, compared to $1.2 million in the same period of 2025, driven by collaboration revenue from a related party of $4.2 million versus $1.2 million in the prior year.
• Research and development (R&D) expenses were $34.1 million for the quarter, a decrease from $44.0 million in the prior year period, attributed to lower facility costs for lab equipment repair and maintenance and the absence of restricted stock unit issuances present in 2025.
• General and administrative (G&A) expenses were $10.0 million for the quarter, down from $11.2 million in the prior year, primarily due to lower corporate legal fees.
• Net loss was $39.0 million for the quarter, an improvement from $50.6 million in the prior year period.
• Net loss per share (basic and diluted) was $0.22 for the quarter, compared to $0.32 in the prior year.
• Cash, cash equivalents, investments, and restricted cash were $74.8 million as of September 30, 2026, down from $191.4 million as of December 31, 2025.
• Total assets were $213.9 million as of September 30, 2026, compared to $342.7 million as of December 31, 2025.
• Total stockholders' equity was $8.4 million as of September 30, 2026, compared to $120.9 million as of December 31, 2025.

Guidance and Future Outlook:

• The company expects its cash position as of September 30, 2026, combined with $134.7 million in net proceeds from a November 2026 public offering, to fund operating expenses and capital requirements through 2027.
• Initial clinical data for both PM577a (Wilson disease) and PM647 (Alpha-1 Antitrypsin Deficiency) are expected in 2027.
• A Biologics License Application (BLA) submission for PM359 (Chronic Granulomatous Disease) is planned for the first half of 2027.
• Management anticipates 2027 will be a meaningful year for patient communities, with the FDA's draft guidance on individualized genome editing potentially creating opportunities to extend Prime Editing therapies to additional diseases if finalized.

Business Segments and Product Lines:

• Wilson Disease (PM577a): The first patient was dosed in October 2026 in a global Phase 1/2 clinical trial; the FDA granted Rare Pediatric Disease designation to PM577 for this indication. PM577a targets the ATP7B H1069Q mutation. A follow-on candidate, PM577b, targeting the R778L mutation, is in preclinical development.
• Alpha-1 Antitrypsin Deficiency (PM647): The FDA cleared the Investigational New Drug (IND) application in September 2026. The Phase 1/2 trial will initially enroll adults with lung-only manifestations, potentially expanding to those with significant liver disease. The clearance followed the resolution of an arbitration dispute with Beam Therapeutics in July 2026.
• Chronic Granulomatous Disease (PM359): The program holds Regenerative Medicine Advanced Therapy, Fast Track, Orphan Drug, and Rare Pediatric Disease designations.
• Cystic Fibrosis (CF): The in vivo CF program is advancing with support from the Cystic Fibrosis Foundation.
• Oncology and Immunology: Prime Medicine is advancing Prime Edited ex vivo CAR-T products in partnership with Bristol Myers Squibb, combining Prime Medicine's Prime Editing and PASSIGE technologies with BMS's cell therapy expertise.

Market and Competitive Landscape:

• The company views Wilson disease and AATD as the foundation of a liver franchise built on a shared technology platform and development strategy.
• The PM647 IND clearance enables clinical study in the U.S., where approximately 100,000 people carry the PiZZ genotype targeted by the therapy.
• The resolution of the arbitration with Beam Therapeutics confirmed PM647 is within Prime Medicine's "Field" as defined by their 2019 Collaboration and License Agreement.

Risks and Challenges:

• Forward-looking statements highlight risks including uncertainties related to product candidates entering clinical trials, regulatory approvals, and the results of preclinical or clinical studies not being predictive of future results.
• Risks include the scope of intellectual property protection, the ability to identify and enter future license agreements, and the potential impact of general economic and industry conditions.
• The company notes that actual events or results may differ materially from forward-looking statements due to various uncertainties and important factors.

Management Commentary and Tone:

• CEO Allan Reine, M.D., stated the company made significant progress, highlighting the dosing of the first patient in the PM577a trial as the first clinical study of an in vivo Prime Editing therapy.
• Management emphasized the versatility of the universal liver LNP platform, noting that two wholly owned liver programs have moved into or been cleared for clinical development in just months.
• Dr. Reine expressed encouragement regarding the FDA's draft guidance on individualized genome editing and confidence in the platform's ability to translate scientific innovation into clinical programs.

Other Key Points:

• Prime Medicine closed an underwritten public offering in November 2026, including the full exercise of the underwriters' option, raising $143.7 million in gross proceeds and $134.7 million in net proceeds.
• The company reported pro-forma cash, cash equivalents, investments, and restricted cash of approximately $209.5 million following the offering.
• The PM577a trial (NCT07748403) is an open-label, global, first-in-human study designed to evaluate safety, tolerability, and preliminary clinical efficacy in adults and adolescents with Wilson disease.
• The PM647 Phase 1/2 trial will be a global, single-arm, open-label, first-in-human study evaluating a one-time intravenous infusion.