Bacteria inside tumors contribute to immunotherapy resistance

In the first paper, the researchers analyzed the genetic profiles of tumors and showed that it is the increased total number of bacteria – and not specific types – that weakens the immune response. Laboratory models confirmed the results: using antibiotics shrank tumors and boosted the immune response, while adding bacteria made immunotherapy treatments less effective. In addition, the team collaborated with doctors from the Cancer Center. M.D. Anderson to study how bacteria levels relate to treatment response in head and neck cancer patients participating in clinical trials.

In the second paper, the team analyzed data from the Javelin HN100 phase III clinical trial, which assessed whether adding PD-L1-targeted immunotherapy to standard chemoradiotherapy could improve outcomes for patients with head and neck squamous cell carcinoma. It turned out that patients with high levels of bacteria in the tumor had worse results from immunotherapy than those who received only chemoradiotherapy. The study involved specialists from Memorial Sloan-Kettering Cancer Center and the Dana-Farber Cancer Institute.

Overall, both studies showed that excess bacteria in tumors attracts neutrophils, immune system cells that normally protect the body from infections. However, in cancer, these cells can conversely suppress the antitumor immune response, making immunotherapy less effective. These findings pave the way for further research into why bacteria accumulate in tumors and how this process can be modified to improve treatment outcomes.