Mitochondrial potential reflects T cell fitness and function during cancer immunotherapy.

Checkpoint inhibitors have transformed cancer treatment, yet predicting responses remains challenging. Mitochondrial quality decreases in tumor infiltrating lymphocytes and correlates with impaired antitumor immunity in animal models. Mitochondrial membrane potential (MMP) increases with T cell activation and may also indicate cellular dysfunction. Here, we assessed the MMP of tumor-associated T cells as an indicator of cell phenotypes and immunotherapy responses in non-small cell lung carcinoma and clear cell renal cell carcinoma patients. Primary tumors were collected followed by analysis of peripheral blood mononuclear cells prior to and after 3 wk on treatment with immune checkpoint inhibitors (ICIs). Peripheral blood mononuclear T cells were analyzed for MMP using tetramethylrhodamine ethyl ester (TMRE) and sorted into high and low populations. TCRβ and single-cell RNA sequencing of primary tumors identified and characterized peripheral blood T cell clones associated with the tumor microenvironment. As anticipated, ICI therapy increased the frequency of effector T cells in patients who experienced clinical benefit. TMREhigh peripheral blood T cells with tumor-matching TCRβ sequences had elevated oxidative phosphorylation gene signatures. Gene signatures of stress and exhaustion, such as Tigit and Cmc1, were also elevated in the TMREhigh CD8 T cell populations, while gene expression patterns in TMRElow cells suggested mitochondrial fitness and cell longevity. Importantly, clinical benefit from ICIs was negatively correlated with the TMREhigh CD8 T cell gene expression signature. These findings highlight a T cell population characterized by elevated MMP that correlates with exhaustion-like transcriptional states and poor response to immunotherapy.