Label-free metabolic imaging of tumor-induced T cell exhaustion

Antitumor activity of T cells often determines treatment efficacy for immunotherapy and radiotherapy. Due to the immunosuppressive tumor microenvironment, tumor-infiltrating T cells often exhibit a hypofunctional exhausted phenotype. Current methods to evaluate T cell exhaustion use flow cytometry or cytokine production measurements that are either destructive to the sample or cannot capture single-cell heterogeneity, respectively. Here, we used fluorescence lifetime imaging of the metabolic co-enzyme NAD(P)H to evaluate T cell metabolism during exhaustion. Exhausted T cells have significantly different NAD(P)H lifetimes compared to functional T cells. This study demonstrates a label-free method to monitor T cell exhaustion in tumors.