Gut Bacteria Transplants Boost Cancer Immunotherapy Success Rates to 75-80%

Cancer immunotherapy has revolutionized treatment but fails in over half of patients due to primary resistance. This phase 2 clinical trial investigated whether fecal microbiota transplantation could overcome this limitation by optimizing the gut microbiome before treatment.

Researchers enrolled 40 patients with either non-small cell lung cancer or melanoma who had never received immunotherapy. Each patient received a single dose of freeze-dried stool from healthy donors via oral capsules before starting immune checkpoint inhibitors. The study tracked treatment responses and analyzed gut bacteria changes using advanced sequencing.

Results exceeded expectations: 80% of lung cancer patients and 75% of melanoma patients responded to treatment, compared to typical response rates of 20-45%. Surprisingly, success wasn't linked to acquiring specific beneficial bacteria from donors. Instead, responders consistently lost harmful bacterial species, particularly Enterocloster citroniae, E. lavalensis, and Clostridium innocuum. When researchers transplanted post-FMT stool from successful patients into tumor-bearing mice, the cancer-fighting effects disappeared if they reintroduced the eliminated bacteria.

These findings suggest that certain gut bacteria actively sabotage immune responses against cancer. For longevity and health optimization, this highlights the critical importance of gut microbiome composition in immune function. The treatment was generally safe, with serious side effects only in melanoma patients receiving more intensive immunotherapy combinations. This research opens new possibilities for enhancing cancer treatment through targeted microbiome interventions.