A new study has suggested that injecting tumors with commercially available flu vaccines could have potential as an immunotherapy approach in cancer.

The research, published in Proceedings of the National Academy of Sciences, used both mouse cancer models and patient-derived xenografts in mice to show how the flu shot was able to stimulate an antitumoral immune response.

“We first saw this phenomenon in a mouse model, where we put a tumor in the lung and gave an influenza infection [in the lung] and we wanted to then see if this same antitumor benefit happened in patients too,” said Andrew Zloza, MD, PhD, lead author of the work and assistant professor in the department of internal medicine at Rush Medical College in Chicago, Illinois.

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The team interrogated data from the Surveillance, Epidemiology, and End Results (SEER)-Medicare database of over 30,000 individuals with lung cancer and found that those whom had at least 1 instance of influenza during their cancer had decreased mortality compared with patients who didn’t have influenza.

The receipt of clearly activated influenza is not a practical therapeutic strategy for most people, so the team moved to also test inactivated flu vaccines to see whether these could stimulate a similar antitumor response.

The team used immunocompetent mice and injected them intravenously with a melanoma cell line to create lung tumors. The mice were then treated with flu virus or various types of inactivated flu vaccine with and without adjuvants. Active influenza infection and intratumoral injection of the flu vaccine — but not intramuscular injection — generated an antitumor response in the mice, as well as the expected resistance to flu.

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“Even if we spark that response in the tumor, we still see a systemic effect, but the effect has to start in the tumor. If you can do a biopsy to check if its cancer, you can reach it well enough to inject something into it. I think it can be used in many accessible tumor types, but it has to be intratumoral injection,” said Dr Zloza.

Currently, the majority of viral therapies are oncolytic viruses, which are viruses that directly infect and lyse tumor cells. Only one is currently approved, T-VEC for the treatment of advanced melanoma, but several are in development and at various stages of clinical trials.

If these early results from using the flu vaccine as an immune-priming agent hold up in human trials, the process for its approval by the US Food and Drug Administration (FDA) in cancer could be expedited.