Engineered live attenuated bacteria producing 5-hydroxyindole remodels heterogeneous tumor microenvironment and promotes antitumor immunity

Abstract The highly immunosuppressive tumor microenvironment (TME) stimulates cancer cells resistance to immunotherapy. We have previously shown that a live-attenuated Brucella melitensisΔ vjbR(BmΔ vjbR) bacterial strain, breaks cancer cell resistance to immunotherapy by remodeling the TME and facilitating infiltration of cytotoxic CD8 +T cells (CTLs) into the tumor. As a result, there was shrinkage of tumor size and significant improvement in survival of these mice. However, BmΔ vjbRwas efficient in only controlling colorectal tumors, but was rendered ineffective in B16 melanoma. In this study, we sought to improve the efficacy of BmΔ vjbRin controlling different cancers by engineering it to augment the production of 5-hydroxyindole (HI), i.e., BmΔ vjbR-HI. The effect of BmΔ vjbR-HI in modulating the function and activity of CTLs was assessed by flowcytometry in in vitroassays. The tumor modulating activity of the BmΔ vjbR-HI was also assessed by intravenous injection of this bacteria followed by adoptive CTL therapy in colon carcinoma, melanoma and pancreatic orthotropic murine tumors. We found that BmΔ vjbR-HI increased inflammatory cytokines in CD8 +T cells. The granzyme-B production and cytotoxicity of CD8 +T cells was also enhanced on treatment with the bacteria. BmΔ vjbR-HI remodeled the TME and ameliorated MC32-CEA colorectal cancer, B16-OVA melanoma and Panc-02 orthotropic pancreatic tumors. Moreover, the BmΔ vjbR-HI homed into the TME by uptake in myeloid derived suppressor cells. Overall, our findings demonstrate that BmΔ vjbR-HI remodels heterogeneous TMEs of different cancers to promote CTL-mediated antitumor immunity. These findings have significant translational potential in antitumor microbial immunotherapy. Jugal Das and Jianxun Song are recipients of Careers in Immunology Fellowship 2022.