RP1 FDA Review Accepted
FDA Accepts Replimune's Resubmitted RP1 BLA for Advanced Melanoma, Setting August 2 PDUFA Date
Key Points
IGNYTE enrolled 140 patients with advanced melanoma who progressed after anti-PD-1 therapy; RP1 plus nivolumab delivered a 34% overall response rate with a median duration of response of 24.8 months, and median progression‑free survival of 30.6 months on RP1 plus nivolumab versus 4.4 months on the prior anti-PD-1 regimen.
This appears to be the third BLA submission for RP1, following an initial complete response letter in July 2025 and a second one in April 2026; the June 2026 resubmission was accepted as a complete, class 1 response with an August 2, 2026 PDUFA date, and an advisory committee meeting is expected in late July.
Market reaction to RP1’s regulatory developments has been swift, with the stock rising roughly 80% on news of the planned third BLA submission in May 2026.
In the immediate aftermath of the FDA update, Replimune shares were down more than 7% in pre-market trading, after closing at about $11.13 on the prior session.
RP1 is described as an oncolytic immunotherapy based on an attenuated herpes simplex virus (HSV-1) engineered with a fusogenic protein and a cell-stimulating factor to enhance tumor antigen presentation and stimulate anti-tumor immunity.
The FDA has accepted Replimune's resubmitted drug application for RP1 in combination with nivolumab, setting an action date of August 2, 2026 for the advanced melanoma treatment, according to OncLive. The agency classified the filing as a Class 1 response — meaning a two-month review — and plans to hold an advisory committee meeting in late July 2026 before making its final call.
This is Replimune's third attempt at approval. The FDA had previously rejected the application twice. Despite that rocky road, Replimune CEO Sushil Patel called the Class 1 acceptance a sign of "urgent unmet need" for patients who have run out of anti-PD-1 options.
Three Strikes, One More Chance: The RP1 Approval Timeline
Replimune first submitted its BLA for RP1 in late 2024. The FDA rejected it in July 2025, citing manufacturing problems and a need for more mature data, Dermatology Times reported. A second rejection came in April 2026, this time over questions about how nivolumab was timed during the IGNYTE trial. Both letters were called "complete response letters" — industry shorthand for a formal rejection.
Replimune held a Type A meeting with the FDA in May 2026 — a high-priority, structured sit-down to resolve disputes. That meeting went well. Replimune announced plans for a third submission on May 15, 2026, and the stock jumped roughly 80%, according to Nasdaq. The company officially resubmitted on June 20, 2026, and the FDA accepted it six days later.
IGNYTE Trial Data: What RP1 Actually Did for Patients
The approval bid rests on the IGNYTE Phase 3 trial. It enrolled 140 patients with advanced melanoma who had already failed anti-PD-1 therapy — drugs like pembrolizumab or nivolumab that are usually the first line of defense. These are patients with few options left. RP1 plus nivolumab produced a 34% overall response rate. That compares to a typical 10–15% response rate for other treatments in this setting, according to Investing.com.
The durability numbers stand out most. The median duration of response hit 24.8 months. More striking: patients on RP1 plus nivolumab had a median progression-free survival of 30.6 months. On their prior anti-PD-1 regimen, that number was just 4.4 months. The complete response rate — meaning tumors disappeared entirely — was 15%.
How RP1 Works: An Engineered Virus That Attacks Tumors
RP1 is built on a modified herpes simplex virus (HSV-1). Scientists stripped out the harmful parts and added two key tools. The first is a fusogenic protein called GALV-GP R-, which makes cancer cells fuse together and burst. The second is GM-CSF, a cytokine that signals the immune system to attack the dying tumor cells. The goal is to turn a cold tumor — one the immune system ignores — into a hot one it can target, according to TipRanks.
This approach differs from Amgen's Imlygic (T-VEC), the only oncolytic virus currently approved in the U.S. RP1 is designed to be more potent at triggering an immune response. The combination with nivolumab, which removes a "brake" on immune cells, is the core bet: virus destroys tumor, immune system finishes the job.
Stock Drops 7% as AdCom Creates Uncertainty Before August Vote
Replimune shares fell more than 7% in pre-market trading on June 26, the day the FDA acceptance was announced. The stock had closed the prior session at $11.13. The dip looks like profit-taking after the 80% May surge, but analysts see a real concern underneath: the advisory committee meeting in late July, according to Nasdaq.
An AdCom is not required for every drug. When the FDA calls one, it usually means the agency still has questions. Analysts at Cantor Fitzgerald noted the Class 1 timing is the "best-case scenario" but warned that the AdCom signals the FDA wants outside expert input on whether the IGNYTE data — based on a single-arm trial without a randomized control group — is strong enough for full accelerated approval. A strong AdCom vote in July would nearly guarantee an approval on August 2. A split vote would rattle the stock.
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