A Major Step Toward Overcoming Immunotherapy Resistance in Melanoma: The RP1 Oncolytic Virus Vaccine

The Importance of Advanced Melanoma

Melanoma is an aggressive subtype accounting for around 5% of all skin cancers. 

Although the chance of recovery is high with early diagnosis, treatment options narrow and outcomes worsen as the disease progresses. Immunotherapies have revolutionized the fight against melanoma in recent years, but many patients either fail to respond from the outset or develop resistance over time. Resistance remains one of the greatest challenges facing clinicians. This is precisely where an innovative approach, oncolytic virus therapy, is attracting attention and opening a new door for patients.

RP1 and Nivolumab: Two Powerful Immunotherapies Join Forces

Recent research shows promising results with the combination of RP1 (vusolimogene oderparepvec) and nivolumab in melanoma patients resistant to immunotherapies.

RP1 (Vusolimogene Oderparepvec): An Engineered Virus Targeting Cancer

RP1 is a therapeutic, genetically modified Herpes Simplex Virus Type 1 (HSV-1)-based oncolytic virus vaccine. This specially programmed virus targets and infects only cancer cells, replicating inside them and causing them to rupture. This breakdown releases tumor-specific proteins and molecules that activate the immune system. The immune system is thus effectively stimulated against the tumor, generating a broad immune response.

Nivolumab: A Modern Immunotherapy That Releases Immunity’s Chains

Nivolumab is an immunotherapy targeting the PD-1 protein. Normally, PD-1 protects the immune system from excessive reactions. Cancer cells, however, use this mechanism to escape immune attack. By blocking PD-1, Nivolumab reactivates immune cells’ ability to fight cancer.

Combining these treatments launches a powerful, two-pronged attack on cancer cells, acting both directly and by activating the immune system.

IGNYTE Trial: An Effective Combination Against Resistant Melanoma

The IGNYTE clinical trial investigated the efficacy and safety of RP1 plus nivolumab in advanced melanoma patients resistant to immunotherapy. Updated results appeared on July 8, 2025, in the Journal of Clinical Oncology .

Profile of the Patients Enrolled

• A total of 140 patients participated.

• Nearly half of patients (48.6%) had the most advanced stage of melanoma (IVM1b/c/d).

• 65.7% had never responded to previous anti-PD-1 treatment.

• More than half (56.4%) were PD-L1-negative, a group less responsive to immunotherapy.

• 46.4% had previously received both anti-PD-1 and anti-CTLA-4 treatment.

How the Study Was Conducted

• RP1 was injected directly into tumors.

• Each patient received a maximum of 8 doses of RP1, with additional doses given when necessary.

• Patients received Nivolumab at regular intervals for 2 years.

• Treatment responses were assessed by an independent review committee using RECIST 1.1 criteria.

Study Results and Clinical Significance

• A Notable Response Rate: 32.9% of patients had an objective response, and 15% of these achieved complete recovery.

• Durable Responses: Among responders, the average response duration reached approximately 34 months, demonstrating that responses were not temporary.

• Effects Throughout the Body: Responses occurred even in distant tumors not injected with RP1. This indicates that treatment generates a systemic immune response.

• Manageable Side Effects: Serious treatment-related side effects were uncommon (12.9%); effects were generally mild (77.1%).

• A Strong Increase in Immune Response: Treated tumor sites showed substantial increases in immune cells and PD-L1 expression.

Next Steps and FDA Review

The FDA granted this promising combination “Priority Review” status as of January 2025. Phase III IGNYTE-3 studies were launched to confirm efficacy in larger patient populations.

The Rise of Oncolytic Virus Therapies

Oncolytic virus therapies are not entirely new. T-VEC (Talimogene Laherparepvec), the first oncolytic virus therapy approved by the FDA in 2015, was an important milestone. RP1 is emerging as a much more advanced and powerful version of this approach.

Conclusion: Renewed Hope for Melanoma Patients

The combination of RP1 and nivolumab offers new hope to melanoma patients with immunotherapy resistance. It has the potential to reach broader patient groups in the future, improving quality of life and survival. This new step in oncology brings hope that even diseases previously considered untreatable may be managed.