Divergent role of CD8 T cells with distinct metabolic phenotypes during curative radio-immunotherapy in hot versus cold tumors

Immunotherapy has potential for impactful cancer cures by empowering patients’ own immune cells. We developed a radio-immunotherapy regimen that can cure large immunologically hot and cold murine tumors. Here we explored the divergent role of CD8 T cells during this radio-immunotherapy in contrasting hot colon carcinoma versus cold melanoma models. We introduced an immunocompetent mouse model with mCherry expressing CD8 T cells to provide immune cell tracking in vivo . We investigated single-cell function, metabolism, and gene expression changes with temporal context using flow cytometry, in vivo multiphoton imaging, single-cell RNA sequencing, and multiplexed immunofluorescence to determine the underlying mechanisms. We found that in contrast to the hot colon carcinoma model, CD8 T cells from the cold melanoma model do not drive tumor cures, despite getting activated, possibly due to a static oxidative metabolism and exhausted phenotype as well as down regulation of tumor MHC-I expression. These findings have implications for improving immunotherapy response in immunologically cold cancers.