Replimune is making a third attempt at FDA approval for its melanoma therapy RP1, following what the company described as “productive” discussions with the agency. The treatment, a modified oncolytic herpes simplex virus, had been rejected twice before, with the second refusal in 2024 seen as one of the FDA’s more controversial decisions. The resignation of former commissioner Marty Makary appears to have opened a window for reconsideration.
RP1 is being developed as an intratumoral therapy for patients with advanced melanoma who have progressed on prior anti-PD-1 treatments. Clinical data from a Phase 2 trial showed a durable response rate of approximately 30% in a heavily pretreated population, with some patients maintaining responses beyond 12 months. The safety profile has been manageable, with common adverse events including fatigue, fever, and injection-site reactions.
The company now plans to submit a biologics license application by mid-2025, aiming for a standard 12-month FDA review cycle. A priority review designation remains possible but has not yet been granted. Replimune’s regulatory pathway will also require a post-marketing commitment to confirm the durable benefit in a larger Phase 3 trial.
News of the resubmission sent shares up 12% in after-hours trading, adding roughly $150 million to Replimune’s market capitalization. The melanoma immunotherapy market is projected to reach $9 billion by 2030, with competition from checkpoint inhibitors and personalized neoantigen vaccines. RP1’s oncolytic mechanism offers a differentiated approach, though commercial adoption may be limited by the need for repeated intratumoral injections.
If approved, RP1 could become the second oncolytic virus therapy on the U.S. market after Amgen’s Imlygic, offering a new option for patients with limited alternatives. However, some analysts caution that the FDA’s recent leadership turmoil could slow the review process, and that RP1’s modest response rate may not justify broad use in a rapidly evolving melanoma landscape.