Krystal Halts Melanoma Trial After FDA Rejection of Similar Therapy

Krystal Biotech has discontinued its Phase I/II trial of KB707, an intratumoral immunotherapy for melanoma, following the FDA's unexpected rejection of a similar therapy, Replimune's RP1. Both therapies utilize modified herpes simplex virus vectors to stimulate immune responses against tumors, but the FDA raised concerns about trial design and patient population heterogeneity in Replimune's application. This regulatory decision created uncertainty around accelerated approval pathways, prompting Krystal to suspend enrollment while continuing to monitor existing patients and consider future development plans. Despite halting the melanoma trial, Krystal is advancing the development of inhaled KB707 for non-small cell lung cancer, citing promising efficacy and safety data. The controversy highlights ongoing challenges in regulatory approval processes for novel viral immunotherapies targeting solid tumors. Experts in the field have urged the FDA to reconsider its stance, emphasizing the real-world relevance of heterogeneous patient populations in clinical trials.