Replimune's RP1 Melanoma Drug Gets Second Chance with FDA

Replimune, a biotechnology company focused on oncolytic immunotherapies, has received a surprising boost as the U.S. Food and Drug Administration (FDA) accepted a resubmission for its advanced melanoma drug, RP1. This development comes just a month after the company had suggested that alignment with the FDA on the drug's future had not been reached.

FDA Reversal Breathes New Life into RP1

RP1, also known as vusolimogene oderparepvec, is an engineered strain of the herpes simplex virus designed to replicate in tumors and enhance immune response. The therapy is intended for use in combination with Bristol Myers Squibb's checkpoint inhibitor Opdivo (nivolumab) for the treatment of advanced melanoma.

In July, the FDA rejected Replimune's initial biologics license application (BLA) for RP1, citing concerns about the adequacy of the Phase III IGNYTE trial. This decision led to a significant drop in investor confidence, with Replimune's shares plummeting 40% following the announcement of unsuccessful discussions with the FDA in September.

However, in a dramatic turn of events, Replimune announced on Monday that the FDA has accepted a resubmission of the BLA for RP1. The agency has set a target action date of April 26, 2026, based on a Class II resubmission timeline. This news sparked a remarkable recovery in Replimune's stock, which surged approximately 93% to $8.69 per share.

Controversy and Scientific Support

The initial rejection of RP1 was met with surprise and controversy within the scientific community. In August, 22 scientists involved in the design and execution of the IGNYTE trial penned an open letter to the FDA, addressing concerns raised in the Complete Response Letter (CRL) and urging the agency to reconsider its decision.

Adding to the complexity of the situation, reports emerged suggesting that Richard Pazdur, director of the FDA's Oncology Center of Excellence (OCE) and acting director of the Office of Oncologic Diseases, had personally intervened in the decision-making process. An unnamed FDA official claimed that the Center for Biologics Evaluation and Research had mishandled the RP1 review from the beginning, necessitating involvement from Pazdur and his team.

A Potential Path Forward

Replimune CEO Sushil Patel expressed satisfaction with the FDA's acceptance of the resubmission, stating, "We are pleased the agency has accepted the resubmission of our BLA for RP1. RP1 plus nivolumab offers a strong risk benefit profile where there are few options for patients with advanced melanoma, who have progressed on PD-1 based therapy."

The resubmission includes additional information, data, and analyses that will be part of the BLA review. While the specific details of these new elements have not been disclosed, they appear to have been sufficient to warrant reconsideration by the FDA.

As the pharmaceutical industry watches closely, the outcome of this resubmission could have significant implications not only for Replimune and patients with advanced melanoma but also for the broader landscape of oncolytic immunotherapies and the regulatory process for innovative cancer treatments.