Commensal Microbiota and Cancer Immunotherapy: Harnessing Commensal Bacteria for Cancer

Cancer is one of the leading causes of death worldwide and the number of cancer patients is expected to continuously increase in the future. Traditional cancer therapies focus on inhibiting cancer growth while largely ignoring the contribution of the immune system in eliminating cancer cells. Recently, better understanding of immunological mechanisms pertaining to cancer progress has led to development of several immunotherapies, which revolutionized cancer treatment. Nonetheless, only a small proportion of cancer patients respond to immunotherapy and maintain a durable response. Among multiple factors contributing to the variability of immunotherapy response rates, commensal microbiota inhabiting patients have been identified as one of the most critical factors determining the success of immunotherapy. The functional diversity of microbiota differentially affects the host immune system and controls the efficacy of immunotherapy in individual cancer patients. Moreover, clinical studies have demonstrated that changing the gut microbiota composition by fecal microbiota transplantation in patients who failed a previous immunotherapy converts them to responders of the same therapy. Consequently, both academic and industrial researchers are putting extensive efforts to identify and develop specific bacteria or bacteria mixtures for cancer immunotherapy. In this review, we will summarize the immunological roles of commensal microbiota in cancer treatment and give specific examples of bacteria that show anticancer effect when administered as a monotherapy or as an adjuvant agent for immunotherapy. We will also list ongoing clinical trials testing the anticancer effect of commensal bacteria.

Automated summary

Cancer is a leading cause of death globally, and the number of cancer patients is expected to continue increasing. Traditional cancer therapies have largely ignored the role of the immune system in eliminating cancer cells, but recent understanding of immunological mechanisms has led to the development of immunotherapies that have revolutionized cancer treatment. However, only a small proportion of patients respond to immunotherapy, and one critical factor in determining the success of immunotherapy is the commensal microbiota inhabiting patients. The functional diversity of the microbiota can differentially affect the host immune system and control the efficacy of immunotherapy in individual cancer patients. Clinical studies have shown that changing the gut microbiota composition through fecal microbiota transplantation can convert non-responders to responders of the same therapy. Therefore, extensive efforts are being made to identify and develop specific bacteria or bacteria mixtures for cancer immunotherapy.