Medical researchers have developed a new cancer vaccine that, when used in combination with another drug, was able to eliminate melanoma in mice with 100 percent success. The therapy could potentially be employed alongside other therapies to treat particularly aggressive tumors.

As reported in the Proceedings of the National Academy of Sciences, the team added a molecule called Diprovocim to a vaccine that can draw cancer-fighting cells to tumor sites. Diprovocim is an adjuvant, a substance that enhances the body's immune response. The team has shown that it also prompts the immune system to be ready to fight cancer cells if they ever return. This is particularly important as it could prevent cancer recurrence.

"This co-therapy produced a complete response – a curative response – in the treatment of melanoma," study co-leader Professor Dale Boger, from the Scripps Research Institute, said in a statement. "Just as a vaccine can train the body to fight off external pathogens, this vaccine trains the immune system to go after the tumor."

The test involved 24 mice with a particularly aggressive form of melanoma all being treated with the anti-cancer therapy anti-PD-L1. The mice were split into three equal-sized groups. One group was given the cancer vaccine with Diprovocim, one was given the vaccine with an alternative adjuvant called alum, and the remaining group was only given the vaccine.

The vaccine doesn’t have to be administered directly into the tumor. It was given to the mice in two intramuscular injections seven days apart. After 54 days, the researchers observed a 100 percent survival rate for mice that received both the vaccine and the Diprovocim, 25 percent for mice administered the vaccine and alum, and 0 percent in those that only received the vaccine.

The strength of Diprovocim, developed by Boger and study co-leader Nobel laureate Bruce Beutler, comes from how it interacts with the immune system. In the latest study, using the molecule as an adjuvant in the vaccine cocktail stimulated the formation of tumor-infiltrating white blood cells. The immune system was given a way to fight the tumor from the get-go. Attempts at re-establishing the melanoma in the first group were unsuccessful.

"It wouldn't take," Boger added. "The animal is already vaccinated against it."

The team is now designing further pre-clinical tests for this vaccine, trying to establish how it works in combination with other anti-cancer drugs. If the further tests are as successful, human trials may soon begin.