Antigen reactivity defines tissue-resident memory and exhausted T cells in tumours.

CD8 + T cells are a key weapon in the therapeutic armamentarium against cancer. While CD8 + CD103 + T cells with a tissue-resident memory T (T RM ) cell phenotype have been favourably correlated with patient prognoses 1-6 , the tumour microenvironment also contains dysfunctional exhausted T (T EX ) cells that exhibit a myriad of T RM -like features, leading to conflation of these two populations. Here, we deconvolute T RM and T EX cells within the intratumoural CD8 + CD103 + T cell pool across human cancers, ascribing markers and gene signatures that distinguish these CD8 + populations and enable their functional distinction. We found that while T RM cells exhibit superior functionality and are associated with long-term survival post-tumour resection, they are not associated with responsiveness to immune checkpoint blockade. Deconvolution of the two populations showed that tumour-associated T EX and T RM cells are clonally distinct, with the latter comprising both tumour-independent bystanders and tumour-specific cells segregated from their cognate antigen. Intratumoural T RM cells can be forced towards an exhausted fate when chronic antigen stimulation occurs, arguing that the presence or absence of continuous antigen exposure within the microenvironment is the key distinction between respective tumour-associated T EX and T RM populations. These results suggest unique roles for T RM and T EX cells in tumour control, underscoring the need for distinct strategies to harness these T cell populations in novel cancer therapies.