Human cDC1 enhance cytotoxic function of CD226+ terminally exhausted tumor-infiltrating lymphocytes.

Prevention or reversal of T cell exhaustion is a major objective of cancer immunotherapy. However, few models exist to generate, characterize and modulate exhausted human T cells, particularly within solid tumors in vivo, which likely hampers the discovery and translation of novel therapeutics. In this study we describe a humanized mouse model where functional human CD8+ T cells specific for the tumor antigen NY-ESO-1 develop in vivo from human CD34+ hematopoietic stem cells genetically modified to express a HLA-A *0201-restricted NY-ESO-1 specific T cell receptor (TCR). HLA-A *0201+ NY-ESO-1+ expressing A375 melanoma tumors engrafted in these mice and were refractory to treatment with anti-PD-1 despite being infiltrated with NY-ESO-1 specific T cells. Tumor-Infiltrating Lymphocytes (TIL) upregulated tissue resident memory (TRM) markers CD103 and CD69 along with exhaustion markers PD-1, TIGIT, and CD39 relative to T cells from other organs. Further, TILs failed to secrete cytokines TNF and IFNγ following in vitro stimulation with conventional Type I Dendritic Cells (cDC1), indicative of terminal exhaustion. However, cDC1 stimulation of the terminally exhausted NY-ESO-1 specific TILs led to enhanced tumor killing that was associated with increased CD107a and Granzyme B expression that was restricted to a subset of CD226+ NY-ESO-1 specific TILs. These findings establish a novel platform to investigate T cell exhaustion in human tumors and suggest a role for cDC1 in enhancing terminally exhausted TIL cytotoxic function.