A scanning electron micrograph of a melanoma cell

Science Photo Library/Alamy

A personalised mRNA vaccine for melanoma, the deadliest form of skin cancer, is expected to be approved for use in the US, Europe and the UK next year. The vaccine is designed to stimulate immune responses against genetic mutations that are unique to an individual’s cancer. When used alongside standard treatment in a late-stage trial, it substantially cut the risk of cancer recurrence or death within the next two years.

“I think approval could be quick, and next year sounds reasonable,” says Alan Melcher at the Institute of Cancer Research in London, who wasn’t involved in the trial.

“It is a huge deal,” says Rebecca Lee at the University of Manchester, UK, who also wasn’t involved. Thousands of people in the UK alone could benefit from this, based on the trial’s patient population, she says. “It’s highly likely the US and Europe [including the UK] will approve it next year.” However, producing the vaccine is very expensive, and it may not be deemed cost-effective for use on the UK’s National Health Services (NHS), she says.

In August, drug-maker Moderna announced that the vaccine had positive results in a late-stage trial. More specific findings have now been released.

The trial recruited more than 1100 adults who had surgery to remove high-risk melanomas that were likely to recur or spread to distant sites. In the UK, 19,400 melanoma cases are diagnosed annually, of which about 25 per cent are deemed high risk.

Two-thirds of the participants were randomly assigned to receive a bespoke vaccine on top of standard immunotherapy, called pembrolizumab, which helps the immune system find and destroy cancer. Both were delivered every three weeks for up to a year. The remaining participants received placebo injections plus pembrolizumab.

The vaccine is made by genetically sequencing a small sample of a person’s cancer and comparing that sequence with the DNA in the individual’s healthy blood cells. This enables researchers to pinpoint mutations specific to the cancer.

Based on the same technology used in covid-19 vaccines, the cancer vaccine contains mRNA molecules that encode for proteins with up to 34 of those mutations. “The jab contains a fingerprint of proteins specifically associated with the cancer,” says Lee. “This helps [immune] T-cells recognise the cancer better, and then pembrolizumab prevents those T-cells from becoming exhausted once they’ve started attacking the cancer cells.”

About two years after the start of treatment, 82 per cent of the participants who received the vaccine plus pembrolizumab were alive without their cancer recurring, on average, compared with 70 per cent among those on pembrolizumab alone. “It’s a really exciting result,” says Lee. Side effects were similar between the two groups.

The results combine cancer recurrence and death rates into one figure, but since a treated cancer has to recur for it to cause death, this combined measure should be interpreted mostly as a sign of the vaccine reducing recurrence, says Melcher. The participants haven’t been tracked for long enough to robustly determine whether the vaccine improves survival rates. These results should be available within a few years, says Lee.

But because the vaccine has to be tailored to and manufactured for each individual, it is expected to be very costly, which could affect NHS access. “If it was a cheap drug, I’d definitely say it will get approved [for NHS use], but it’s going to be expensive,” says Lee. In January, a report by Reuters suggested it would cost around $200,000 per treatment. Moderna and Merck (also known as MSD), which was also involved in the vaccine’s development, did not respond to a request about its cost.

Further research is needed to better understand who is mostly likely to benefit from the vaccine, says Melcher. Some people may have mutations included in their vaccine that fail to stimulate anti-cancer immunity as predicted, or pembrolizumab could work so well that the vaccine can’t lead to further improvement. “If we can find immune markers in the blood or tumour that predict patient responses, we could use those to determine who to give the jab to,” says Melcher.

James Larkin, also at the Institute of Cancer Research, says personalised vaccines could also work for other types of cancer, such as those affecting the lungs, bladder and kidneys, which are also routinely treated with immunotherapy. Further research is needed to verify this and explore whether the vaccines could work as standalone treatments.