Recent experiments in mouse models have shown that injecting an inactivated flu virus into cancer tumors makes them shrink and boosts the effectiveness of immunotherapy.

doctor delivering flu shot
Is the flu shot the next step in fighting cancer?

When it comes to cancer tumors, many factors influence whether or not they will respond to treatment. One of these is whether the tumors are “hot” or “cold.” What does this mean?

In recent years, a new type of anticancer therapy has been gaining in popularity: immunotherapy. This form of therapy works by boosting the body’s own immune response to cancer tumors.

However, for the therapy to have a higher chance of working, the tumors have to be “hot” tumors — that is, they must contain immune cells. If a tumor does not contain (enough) immune cells, or contains immunosuppressant cells, it is called a “cold” tumor.

One question that researchers have been trying hard to answer is: How do we turn cold tumors into hot tumors that will respond to immunotherapy?

A team of investigators from the Rush University Medical Center in Chicago, IL, may now have found an effective way of doing just that by using inactivated flu viruses — essentially, flu vaccines — in mouse model experiments.

The researchers explain their process, as well as their findings, in a study paper that now features in the journal PNAS.

New approach shrinks tumors in mice

The researchers got the idea for their new study by looking at data from the National Cancer Institute. The data indicated that people with lung cancer who had also been in the hospital with influenza-related lung infections tended to live longer than those with lung cancer who had not had a flu virus.

When they recreated this scenario in mouse models, the researchers confirmed that those with cancer tumors and influenza-related infections tended to live longer.

Going forward, the team wants “to understand how our strong immune responses against pathogens like influenza and their components could improve our much weaker immune response against some tumors,” says senior study author Dr. Andrew Zloza.

“However,” he adds, “there are many factors we do not understand about live infections, and this effect does not repeat in tumors where influenza infections do not naturally occur, like skin.”

So, the researchers injected an inactivated influenza virus into melanoma tumors in mouse models.

They found that this “vaccine” turned tumors from cold to hot by increasing the concentration of dendritic cells in the tumors. These cells can stimulate an immune response, and indeed, they led to an increase in CD8+ T cells. These can recognize and destroy cancer cells.

As a result, the mice’s melanoma tumors either grew at a slower rate or started shrinking.

Also, the researchers saw that delivering the flu vaccine into a melanoma tumor on one side of a mouse’s body led to the reduction not just of the growth of the injected tumor, but also to the slower growth of another tumor, on a different side of the body, which they had not injected.

The researchers saw similar results when delivering the flu vaccine to tumors of metastatic triple-negative breast cancer in mouse models.