Mitochondrial potential as a biomarker of T cell fitness and function in cancer immunotherapy

Checkpoint inhibitors have transformed cancer treatment, yet predicting responses remains challenging. Mitochondrial quality decreases in tumor infiltrating lymphocytes and correlates with impaired anti-tumor immunity in animal models. Mitochondrial membrane potential (MMP) increases with T cell activation but 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 Carinoma and clear cell Renal Cell Carcinoma patients. Primary tumors were collected followed by analysis of peripheral blood mononuclear cells (PBMC) prior to and after three weeks on treatment with immune checkpoint inhibition (ICI). PBMC 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 ICI was negatively correlated with the TMREhigh CD8 T cell gene expression signature. These findings highlight the presence of a T cell population of with elevated MMP that correlates with T cell exhaustion-like states and failed response to immunotherapy.