Abstract
Tryptophan (Trp) metabolites have emerged as key regulators of host tumor immunity and cancer patient response to immunotherapy. However, the function of and mechanism underlying Trp in tumor-activated CTLs in the tumor microenvironment are incompletely understood. Using a defined co-culture system of tumor-specific CTLs and cognate antigen-expressing tumor cells, we performed a genome-wide metabolomics screening and observed that Trp level is elevated in the tumor cell-activated CTLs. Parallel genome-wide RNA-Sequencing and ATAC-Sequencing analysis determined that tumor-specific CTLs respond to tumor cells by transcriptionally activating Slc7a5 expression. Pharmacological inhibition of Slc7a5 decreased Trp uptake in tumor-activated CTLs and suppressed CTL lytic activity in killing tumor cells in vitro. Mice with Slc7a5 deficiency only in T cells exhibited diminished level of tumor-infiltrating T cells and increased tumor growth and metastasis. scRNA-sequencing analysis revealed that Slc7a5 deficiency resulted in decreased activation of the aryl hydrocarbon receptor (AhR) pathway and repressed FasL expression in tumor-infiltrating T cells. Chromatin immunoprecipitation determined that AhR binds to Faslg promoter in tumor-infiltrating T cells. FasL blockade therapy promotes tumor growth and metastasis in tumor-bearing mice. In human cancer patients, AhR expression correlates with FasL expression in tumor-infiltrating T cells. Furthermore, FasL expression is correlated with patient response to pembrolizumab and survival time. Our finding determines that the Slc7a5-Trp metabolic pathway activates AhR to up-regulate FasL expression in tumor-infiltrating T cells to sustain CTL anti-tumor immunity. Targeting CAR-T cells to up-regulate Slc7a5 to maintain T cell proliferation and function therefore could be a promising direction in cancer immunotherapy.