A cancer-fighting version of herpes shows promise in early human trial

An illustration of a herpes simplex virus.

An illustration of a herpes simplex virus.
Illustration: Shutterstock (Shutterstock)

Scientists may be able to turn an ancient germ enemy into a cancer-fighting ally, new research suggests this week. In preliminary data from a Phase I trial, a genetically modified version of the herpes virus has shown promise in treating difficult-to-eradicate tumors, with one patient having experienced complete remission for 15 months so far. However, much more research will be needed to confirm the early success of the treatment.

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

In a Phase I study conducted by scientists at The Institute of Cancer Research and The Royal Marsden NHS Foundation Trust in the UK, RP2 was given as the sole treatment to nine patients with advanced cancers who had failed to respond to other therapies; it was also given in combination with another immunotherapy drug to 30 patients. Three patients who received RP2 alone appeared to respond to the treatment, meaning their cancers regressed or stopped growing, and seven patients on the combination therapy also responded. One patient in particular, with a form of carcinoma along his salivary gland, showed no signs of cancer for at least 15 months after treatment with RP2 alone. No life-threatening side effects were reported in the study, with the most common post-treatment symptoms being fever, chills and other flu-like illnesses.

The findings, presented this week at the European Society for Medical Oncology Congress (ESMO) in 2022, are tentative, as they have yet to be vetted through the formal peer review process. They are also based on a very small sample size, meaning any results should be taken with caution. But Phase I trials aren’t meant to show that a treatment is effective, just that it’s safe enough for people to take. So the fact that some people with seemingly incurable cancers already seem to be responding to RP2, the team says, is a very good sign that it can live up to its potential.

“Our study shows that a genetically engineered, cancer-killing virus can deliver a one-two punch against tumors — destroying cancer cells directly from the inside while turning on the immune system against them,” said lead author Kevin Harrington, professor of Biological Cancer Therapies at The Institute of Cancer Research. , in a pronunciation from within the organisation.

Scientists have been hopeful long on cancer-fighting viruses. But it is only recently that these hopes have finally begun to bear fruit. In 2015, the first viral therapy was: approved in the US for certain advanced cases of melanoma. In May, scientists in California launched a Phase I clinical trial of their anticancer virus called Vaxinia. Other businesses develop their own candidates, 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 fail to make it to the finish line and reach the public, it’s possible that at least some of these viruses could one day become a new standard cancer treatment.

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