David
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Engineered Herpes Virus used to eliminate cancer
Researchers are investigating a novel cancer treatment that uses a carefully engineered virus based on herpes simplex virus type 1 (HSV-1). This experimental therapy, known as RP1, has been designed to interact specifically with tumor cells, and early clinical trials are showing encouraging outcomes.
RP1 is injected directly into tumors, where it reproduces mainly inside cancer cells. During this process, it releases immune-signalling proteins that help the body better identify cancer. RP1 also affects CTLA-4, a pathway tumors often use to reduce immune attention, supporting a more balanced immune response. These combined actions may help the immune system respond not only at the injection site but also in other areas of the body.
In a clinical study involving 140 patients with advanced melanoma, many of whom had not benefited from previous immunotherapies, around one third experienced noticeable tumor reduction. Nearly 15% showed complete disappearance of detectable tumors. Some tumors that were not directly treated also reduced in size, suggesting a broader immune effect.
The therapy was given alongside nivolumab, an immune checkpoint treatment. Patients received RP1 injections every two weeks for several cycles, followed by nivolumab alone. Side effects were generally mild, most commonly fatigue and temporary fever. The modified virus does not cause typical herpes infections.
RP1 is part of an emerging group of treatments known as oncolytic virus therapies, which use modified viruses to support the immune system’s ability to recognize cancer. Larger trials are now underway to explore its potential in additional cancer types.
Study reference:
“Cancer-fighting herpes virus shown to be an effective treatment for some advanced melanoma.”
Keck Medicine of USC, 2025.
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