FDA weighs Replimune's melanoma immunotherapy RP1

Overview

Patients with advanced melanoma that keeps growing after standard immunotherapy have almost nothing left to try. Replimune wants to sell them a virus that is injected straight into tumors. On July 30, an FDA expert panel voted on whether the company's trial data are solid enough to prove the drug works.

The stakes are narrow but real. FDA staff said the study cannot show whether the drug itself helped or whether patients improved for other reasons. The panel's vote is only advice. The agency's binding decision lands August 2.

Why it matters

If approved, patients out of options gain a new melanoma therapy. If rejected, they wait years for a fresh trial to finish.

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Key Indicators

34%

Tumor response rate

Share of anti-PD-1-failed melanoma patients whose tumors shrank on RP1 plus nivolumab in the IGNYTE trial.

24.8 months

Median duration of response

How long tumor shrinkage lasted, on average, for patients who responded.

~30%

Replimune single-day share drop

Stock fall after the FDA released briefing documents questioning the data.

Aug 2, 2026

FDA decision deadline

The binding date by which the agency must rule on the application.

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People Involved

Sushil Patel

Leading the company through its third attempt at FDA approval

Robert Coffin

Advisory and board role; original designer of the RP1 virus

Organizations Involved

Replimune Group

Biotechnology company

Seeking first-ever product approval for RP1

A Massachusetts biotech developing tumor-injected virus therapies for cancer.

FDA Cellular, Tissue, and Gene Therapies Advisory Committee

Federal advisory panel

Voted July 30 on whether the data support approval

An outside panel of experts that advises the FDA on cell and gene therapy products.

Timeline

January 2025 July 2026

6 events Latest: Today

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July 2026
Advisory panel votes on RP1's evidence
Today Advisory Vote

The FDA's Cellular, Tissue, and Gene Therapies Advisory Committee meets to vote on whether the data reliably support approval of RP1 plus nivolumab. The vote is advice, not a final ruling.
Today
FDA briefing documents call the data uninterpretable
Statement

FDA staff publish concerns that the trial cannot separate RP1's effect from nivolumab's or from patient differences. Replimune shares fall about 30% in a day.
2 days ago
June 2026
FDA accepts a third resubmission
Regulatory

The agency takes up the application again and sets a fresh decision date of August 2, 2026, and signals an advisory committee meeting.
June 26th, 2026
October 2025
FDA accepts a resubmission
Regulatory

Replimune refiles and the FDA sets a new decision date of April 10, 2026, under a standard resubmission timeline.
October 20th, 2025
July 2025
FDA rejects the first application
Legal

The agency issues a Complete Response Letter, saying the single-arm IGNYTE trial is not adequate and well-controlled and cannot be interpreted because patients differed too much. No safety problems are raised.
July 22nd, 2025
January 2025
FDA accepts RP1 filing with priority review
Regulatory

The FDA takes up Replimune's application for RP1 plus nivolumab and sets a decision date of July 22, 2025. The drug carries breakthrough therapy designation.
January 21st, 2025

Historical Context

3 moments from history that rhyme with this story — and how they unfolded.

October 2015

T-VEC (Imlygic) approval (2015)

The FDA approved talimogene laherparepvec, the first oncolytic virus therapy, for melanoma lesions in the skin and lymph nodes. Robert Coffin, who later founded Replimune, developed it. An advisory panel had backed it 22-1.

Then

Doctors gained a virus injected directly into melanoma tumors, though its effect on survival was modest.

Now

It proved oncolytic viruses could reach market and set the scientific template Replimune built RP1 on.

Why this matters now

RP1 is the next-generation version of the same idea, from the same scientist. It shows the approach can win approval, but also that the FDA scrutinizes how much the virus itself adds.

April 2023

Covis Therapeutics' Makena withdrawal (2023)

The FDA pulled the preterm-birth drug Makena after a confirmatory trial failed to show benefit. It had reached market through accelerated approval based on weaker early data years earlier.

Then

The drug came off the market and patients lost access.

Now

The case hardened FDA insistence that accelerated approvals rest on trials that can actually confirm benefit.

Why this matters now

It explains why FDA reviewers press Replimune on the missing control arm. The agency has been burned when single-arm data did not hold up.

March 2007 to April 2010

Provenge (sipuleucel-T) advisory fight (2007-2010)

An FDA panel backed Dendreon's prostate cancer immunotherapy, but the agency demanded more data and delayed approval. Provenge finally cleared in 2010 after a survival trial.

Then

Patients and investors endured a three-year limbo while the company ran more trials.

Now

The drug reached market but struggled commercially, and Dendreon later went bankrupt.

Why this matters now

It shows how a novel immunotherapy can survive FDA doubts yet face a long, costly path, a plausible outcome for RP1 if approval slips to the confirmatory trial.