Published: July 12, 2025, 10:56 PM
In a groundbreaking development, scientists at the University of Southern California have turned the herpes simplex virus type 1 (HSV-1) - best known for causing cold sores - into a powerful tool against cancer. By genetically modifying the virus, researchers created a therapy called RP1, which, when combined with the cancer drug nivolumab, has shown remarkable results in treating advanced melanoma.
Melanoma, a severe form of skin cancer, becomes particularly hard to treat once it spreads to organs like the liver or brain. But in a recent study, RP1 therapy shrank tumors in one-third of patients who had run out of other treatment options. Even more remarkably, about 16% of participants experienced a complete disappearance of their tumors.
Dr. Gino Kim In, a medical oncologist at Keck Medicine of USC, highlighted the significance of the results: “About half of all advanced melanoma cases cannot be managed with currently available immunotherapy treatments. This new therapy offers hope to patients who may have run out of options.”
RP1 works by directly injecting the modified herpes virus into tumors, where it selectively infects and destroys cancer cells while leaving healthy tissue unharmed. The drug nivolumab, given alongside, helps the immune system recognize and attack the cancer more effectively.
Perhaps the most fascinating outcome of the study is that even tumors which weren’t directly injected began to shrink, indicating a system-wide immune response triggered by the therapy. Patients received injections every two weeks, and if the treatment showed results, they continued with monthly nivolumab infusions for up to two years.
Importantly, the treatment was well-tolerated and did not cause serious side effects. Full study findings were published in the Journal of Clinical Oncology and presented at the American Society of Clinical Oncology’s annual meeting.