The cancer-fighting version of herpes holds promise in early human studies

Illustration of the herpes simplex virus.

Illustration of the herpes simplex virus.
Illustration: Shutterstock (Shutterstock)

Scientists may be able to turn the long-standing enemy of germs into an ally in the fight against cancer, new research from this week suggests. In preliminary data from a Phase I trial, a genetically modified version of the herpes virus showed promise in the treatment of difficult-to-remove tumors, with one patient experiencing complete remission for 15 months. However, much more research is needed to confirm early treatment success.

The viral treatment is known as RP2, and is a genetically modified strain of herpes simplex 1, the virus responsible for most cases of oral herpes in humans, as well as some cases of genital herpes. Developed by Replimune, the RP2 is designed to work on two fronts. When injected directly into the tumor, the virus is expected to selectively infect and kill specific cancer cells. But it also blocks the expression of a protein known as CTLA-4 produced by these cells and hijacks their machinery to produce another molecule called GM-CSF. As a result of these cellular changes, the tumor’s ability to hide from and fight back from the immune system is weakened.

In a Phase I study by researchers at The Institute of Cancer Research and The Royal Marsden NHS Foundation Trust in the UK, RP2 was given as the only treatment to nine patients with advanced cancer that had not responded to other treatments; it was also administered in combination with another immunotherapeutic drug to 30 patients. Three patients treated with RP2 alone appeared to respond to the treatment, meaning their tumors shrank or stopped growing, and seven patients treated with combination therapy also responded. In particular, one patient with a form of cancer along the salivary gland showed no signs of cancer for at least 15 months following treatment with RP2 alone. No life-threatening adverse events were reported in the study, and the most common post-treatment symptoms were fever, chills and other flu-like illnesses.

Finds, presented this week at the Congress of the European Society for Medical Oncology in 2022 (ESMO) are preliminary as they have not yet been verified in a formal peer-review process. They also rely on a very small sample, which means any results should be treated with care. But Phase I trials aren’t about to show that the therapy is effective, it’s that it is safe enough for humans. So the fact that some people with seemingly incurable cancers seem to be already responding to RP2, the team argues, is a very good sign that it can live up to its potential.

“Our study shows that a genetically modified cancer-killing virus can do two blows to tumors – directly destroying cancer cells from within while triggering the immune system against them,” said lead author Kevin Harrington, professor of Biological Cancer Therapies at the Institute of Cancer Research in the years statement from the organization.

The scientists were full of hope about cancer-fighting viruses for a long time. But only recently did this hope finally pay off. In 2015, the first viral therapy was approved in the USA, in some advanced cases of melanoma. In May, researchers in California began a Phase I clinical trial for the anti-cancer virus called Vaxinia. Other companies develop their own candidates, either alone or in combination with other treatments. And Replimune is developing two other candidates based on their modified herpes virus.

While many experimental therapies ultimately do not cross the finish line and do not reach the public, it is possible that at least some of these viruses may one day become the new standard cancer treatment.

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