Live biotherapeutic enterococcus lactis MNC-168 promotes the efficacy of immune checkpoint blockade in cancer therapy by activating STING pathway via bacterial membrane vesicles

The gut microbiome has the potential to influence tumor development and affect the efficacy of cancer therapeutics, particularly immunotherapy. However, the specific species and strains rather than all microbes that promote antitumor immunity by modulating the function of systemic immunity or tumor-infiltrating lymphocytes (TILs) in tumor environments remain to be elucidated. In this study, we analyzed the microbiome composition of responders and non-responders to PD-1 blockade therapy from a clinical cohort and found that Enterococcus spp. were abundant in the responders. Through in vitro screening, we identified Enterococcus lactis MNC-168, a commensal bacterium isolated from a healthy individual, which significantly inhibited tumor growth and enhanced the efficacy of anti-PD-1 treatment by promoting antitumor immunity. Mechanistically, MNC-168 activates innate immunity through a STING-IFN-I (stimulator of interferon genes-type I interferons) dependent pathway by releasing bacterial membrane vesicles (MVs), and targeting tumor tissue, thereby augmenting the antitumor immune response. Furthermore, we have confirmed the safety profile of MNC-168 and its enhancing effect on Anti-PD-1 activity across multiple preclinical models, as well as its potential clinical relevance to Anti-PD-1 therapy. These findings suggest that MNC-168 could represent a promising strategy for cancer therapy and has the potential to improve the efficacy of current immunotherapies.