Seasonal Flu Vaccine Slows Tumor Growth In Mice By Kicking Immune System Into Gear

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When it comes to treating cancer, immunotherapies – treatments that activate a patient’s own immune system – are becoming ever more promising. Now, scientists have used the humble flu vaccine to boost the cancer-fighting capabilities of mice by injecting it directly into the site of tumors.

Immunotherapy treatments are particularly effective when tumors are “hot” as opposed to “cold”. Immune cells in cold tumors aren’t very active as they’re focused on not killing the body’s healthy cells, which can be hard to differentiate from cancerous ones. However, in hot tumors, the immune system is raring to go, burning with the desire to stop the tumor in its tracks.

So, to successfully treat a tumor using immunotherapy, we ideally want a hot tumor, but only a minority are found in this state. The solution? Find a way to make cold tumors hot, revving up the immune system so that it can purge cancerous cells.

Publishing their findings in the Proceedings of the National Academy of Sciences, a team from Rutgers University attempted to do just this using mice as their test subjects and the flu vaccine as an immune system activator.

The team injected the seasonal flu vaccine (minus its synthetic adjuvants – compounds that boost the immune response) straight into the lungs of mice, which contained melanoma cancer, with hopes immune cells would rush to the tumor site and make it “hot”. They then monitored the sensitivity of the tumors to the body’s immune system.

The researchers found that the cold tumors that had received a flu shot appeared to become hot; they experienced systematic immune responses and were sensitive to treatments that block the tumors’ anti-immune defenses.

The team was inspired to test out the seasonal flu jab after they discovered a deactivated version of the flu virus had a positive effect. Their suspicions were confirmed when the vaccine reduced tumor growth in addition to providing immunity to the virus.

Melanoma cells – usually associated with malignant skin cancers in people – were used because they cannot be directly infected by the flu virus. Therefore, the results suggest that the virus doesn’t actually need to infect tumor cells to have an effect, it simply boosts the body’s immune response at the site of the tumor. Strangely, only the adjuvant-free vaccine worked; the vaccine containing immune-boosting adjuvants failed to reduce tumor growth, although it did provide immunity to the flu.

It’s important to remember that the study was conducted on mice, so the same effect might not be seen in people. However, the researchers did look at data on 30,000 people receiving treatment for lung cancer and found that those who had suffered from a flu infection appeared to have improved survival rates.     

Still, if the flu vaccine proves to be an effective way to aid cancer immunotherapies in humans, real-life use of it in patients is a long way off. And the vaccine isn’t perfect. Although it proved successful when administered straight into the lung, it failed to achieve the same effect when injected into skin affected by melanoma.

Nevertheless, the study provides intriguing evidence that viruses can activate the immune system to create an “immunologically inflamed hot microenvironment” at the site of cancer.

“Patients receiving intratumoral seasonal influenza vaccination may experience multiple clinical benefits and that seasonal influenza vaccination is a crucial public health tool that may be utilized as both a preventive measure against infection and an immunotherapy for cancer,” the researchers write.

  

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