T cell cancer therapy requires CD40-CD40L activation of TNFα-iNOS-producing dendritic cells. Mus musculus

The effectiveness of new cancer therapies such as checkpoint blockade and adoptive cell transfer of activated anti-tumor T cells requires overcoming immunosuppressive tumor microenvironments. We found that the activation of tumor-infiltrating myeloid cells to produce local nitric oxide is a prerequisite for adoptively transferred CD8+ cytotoxic T cells to destroy tumors. These myeloid cells are phenotypically similar to ‘Tip-DCs’ or nitric oxide- and TNFα-producing dendritic cells. The nitric oxide-dependent killing was tempered by coincident arginase 1 expression, which competes with iNOS for arginine, the substrate for nitric oxide production. Depletion of immunosuppressive CSF-1R-dependent arginase 1+ myeloid cells enhanced nitric oxide-dependent tumor killing. Tumor killing via iNOS was independent of the microbiota but dependent on the CD40-CD40L pathway and, in part, lymphotoxin alpha. We extended our findings in mice to uncover a strong correlation between iNOS, CD40 and TNF expression and survival in colorectal cancer patients. Our results identify a network of anti-tumor targets to boost the efficacy of cancer immunotherapies. Overall design: EG7 tumor was injected in C57BL/6 and after 7 days of tumor growth mice were treated with adoptive CD8+ T cells specific to recognize OVA antigen. After 3 days mice were sacrified and tumor masses used to isolate cells.CD11b+NO+Ly6C+Ly6G- live cells were FACS sorted from tumor masses pooled from 12 mice for each sample. 3 samples from 3 different experiments were obtained.