Bacteria-based cancer therapy reactivates vaccines you've already had

Vaccines against cancer are somewhat of a holy grail for medicine – but what if you could repurpose a vaccine you’ve already had? Scientists have demonstrated in mice a way to trick the immune system into attacking tumors by mistaking them for a pathogen it’s already developed a response against.

Generally, vaccines work by stimulating the immune system to mount a response against a particular antigen associated with a virus, bacteria or other pathogen, up to and including cancer. Of course, a vaccine is usually given its target before it’s administered to a patient, but for the new study, researchers at the University of Massachusetts Amherst investigated how to reactivate an existing immune response to target cancer.

“The idea is that everybody is vaccinated with a whole bunch of things, and if you could take that immunization and target it towards a cancer, you could use it to eliminate the cancer,” said Neil Forbes, senior author of the study. “But cancers obviously aren’t going to display viral molecules on their surface. So the question was, could we take a molecule inside the cancer cell using Salmonella and then have the immune system attack that cancer cell as if it was an invading virus?”

The team genetically engineered a strain of Salmonella bacteria to seek out cancer cells, and once there, deliver a particular protein – in this case ovalbumin, which is found in chicken eggs. This protein disperses throughout the fluid inside the cancer cells.

This bacterial therapy was administered to mice that had pancreatic cancer and, importantly, had previously been vaccinated against ovalbumin. As the protein spread through the cellular fluid, it caught the attention of the previously primed immune system, which mounted a response against the tumors.

Image source: James Gathany / CDC, Wikimedia Commons.