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Blocking CCL2 nitration in tumors promoted CD8+ influx and reduced tumor growth and prolonged survival in mice when combined with adoptive cell therapy.

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SUMMARY Effective cancer immunotherapy requires overcoming immunosuppressive tumor microenvironments. We found that local nitric oxide (NO) production by tumor-infiltrating myeloid cells is important for adoptively transferred CD8+ cytotoxic T cells to destroy tumors. These myeloid cells are phenotypically similar to inducible nitric oxide synthase (NOS2)- and tumor necrosis factor (TNF)-producing dendritic cells (DC), or Tip-DCs. Depletion of immunosuppressive, colony stimulating factor 1 receptor (CSF-1R)-dependent arginase 1+ myeloid cells enhanced NO-dependent tumor killing. Tumor elimination via NOS2 required the CD40-CD40L pathway. We also uncovered a strong correlation between survival of colorectal cancer patients and NOS2, CD40 and TNF expression in their tumors. Our results identify a network of pro-tumor factors that can be targeted to boost cancer immunotherapies.