Signatures of recent activation identify a circulating T cell compartment containing tumor-specific antigen receptors with high avidity

T cell receptor (TCR) avidity is assumed to be a major determinant of the spatiotemporal fate and protective capacity of tumor-specific T cells. However, monitoring polyclonal T cell responses with known TCR avidities in vivo over space and time remains challenging. Here, we investigated the fate and functionality of tumor neoantigen-specific T cells with TCRs of distinct avidities in a well-established, reductionist preclinical tumor model and human melanoma patients. Surprisingly, we found that both high- and low-avidity T cells are similarly abundant within the tumor and adopt concordant phenotypic signs of exhaustion. Outside the tumor, high-avidity TCR T cells were also not generally overrepresented, but instead selectively enriched in T cell populations with intermediate PD-1 protein expression or corresponding RNA and surface protein signatures of recent activation. Tumor-reactive TCRs with high protective capacity circulating in peripheral blood are therefore characterized by a signature of recent activation. scRNA sequencing data for antigen specific cells before and after TIL infusion and from the infusion product of melanoma patients