According to the researchers, patients who received an RNA vaccine before their treatment with immunotherapy saw their life expectancy increase by several months or even years. A hypothesis that is still cautious, but considered “credible” by some experts.
Prolonged survival observed in two types of cancer
Researchers analyzed more than 1,000 medical records of patients treated between 2019 and 2023 for non-small cell lung cancer or metastatic melanoma.
Among the 884 patients with advanced lung cancer treated with immune checkpoint inhibitors, 180 received an anti-Covid mRNA vaccine within 100 days of starting treatment. Their average survival was 37 months, compared to 20 months for the unvaccinated.
Among the 210 melanoma patients, 43 had also received an injection within the same time frame. Their survival time reached 30 to 40 months, compared to 27 months for the unvaccinated.
The researchers specify that, since several vaccinated people were still alive at the time of the analysis, their actual life expectancy could be higher than these estimates.
Promising statistical analyzes and preclinical trials
Led by Dr. Steven Lin of MD Anderson Cancer Center (University of Texas), the team also used various statistical tools to minimize bias.
“We explored as many statistical approaches as possible.” specifies Adam Grippin, immunotherapy researcher at MD Anderson, who presented the results. Even after adjustment, the link between vaccination and better survival remained significant.
Notably, traditional vaccines, such as those against influenza or pneumonia, have not produced the same effect, suggesting that messenger RNA technology plays a specific role in the immune response.
How the mRNA vaccine works on the immune system
To test their hypothesis, the researchers carried out experiments on mice with tumors last July. These showed that the anti-Covid mRNA vaccine could make cancers more sensitive to immunotherapy, slowing tumor growth.
“One of the mechanisms by which this works is that when you give an mRNA vaccine, it acts as a surge that moves all these immune cells from the bad areas like the tumor to the right areas, for example the lymph nodes where they stimulate other cells to launch a targeted attack” explains Dr Elias Sayour, co-author of the study.
A “booster” effect to be confirmed
According to the researchers, mRNA vaccines could therefore act as a real “immune alarm”. They trigger the release of cytokines, including type 1 interferon, which activates immune cells within tumors. These then migrate to the lymph nodes, where they push other cells to attack the cancer cells.
Tumors, to defend themselves, produce proteins capable of inhibiting the immune system. Drugs called “checkpoint inhibitors” block this strategy, allowing natural defenses to continue their action against cancer.
The combination of these treatments with an mRNA vaccine could therefore strengthen this response.
Adjuvants that stimulate… and worry
Dr. Ivan Pourmir, oncologist and immunotherapy researcher, provides a complementary explanation. “Most vaccines contain adjuvants, which are molecules that will excite the immune system, with a non-specific response.. These adjuvants would be used to “mimic the presence of a virus or bacteria in order to educate the immune system“.
In the present case, mRNA vaccines developed by Pfizer or Moderna, which use lipid nanoparticles and modified RNA, could serve as adjuvants and therefore “boost a reaction against cancer”.
But this mechanism is not without risk. “What we can fear is that the adjuvant also restarts an autoimmune reaction“, underlines Dr Pourmir, recalling that this type of effect had already been observed with certain influenza vaccines or certain checkpoint inhibitor drugs.
“In lung cancer or melanoma, the immune response is spontaneous at first, but it turns off. The checkpoint inhibitor drugs given to patients are antibodies that target signaling molecules on the surface of white blood cells. The problem is that this process can also reactivate autoimmune white blood cells against our own organs and patients can then trigger autoimmune diseases that were previously latent and unexpressed.
Can RNA vaccines prove to be valuable allies against cancer or, on the contrary, promote autoimmune diseases? “All these known hypotheses are plausible, but they must be confirmed by more in-depth clinical studies” insists Dr. Pourmir. “The idea that vaccines may have improved the survival of these patients also remains to be confirmed beyond observational studies, because nothing at the moment excludes potential confirmation bias.” he concludes.
If these results are confirmed, messenger RNA vaccines – initially developed to counter Covid-19 – could become a new tool in the fight against cancer. But for scientists, caution remains in order: only in-depth clinical studies will make it possible to validate this possible medical turning point.