Ronal M. Peralta

Abstract CD8 + T cells are critical mediators of antitumor immunity but differentiate into a dysfunctional state, known as T cell exhaustion, after persistent T cell receptor stimulation in the tumor microenvironment (TME). Exhausted T (T ex ) cells are characterized by upregulation of coinhibitory molecules and reduced polyfunctionality. T cells in the TME experience an immunosuppressive metabolic environment via reduced levels of nutrients and oxygen and a buildup of lactic acid. Here we show that terminally T ex cells uniquely upregulate Slc16a11 , which encodes monocarboxylate transporter 11 (MCT11). Conditional deletion of MCT11 in T cells reduced lactic acid uptake by T ex cells and improved their effector function. Targeting MCT11 with an antibody reduced lactate uptake specifically in T ex cells, which, when used therapeutically in tumor-bearing mice, resulted in reduced tumor growth. These data support a model in which T ex cells upregulate MCT11, rendering them sensitive to lactic acid present at high levels in the TME.

Response rates to immunotherapy in solid tumors remain low due in part to the elevated prevalence of terminally exhausted T cells, a hypofunctional differentiation state induced through persistent antigen and stress signaling. However, the mechanisms promoting progression to terminal exhaustion in the tumor remain undefined. Using the low-input chromatin immunoprecipitation sequencing method CUT&RUN, we profiled the histone modification landscape of tumor-infiltrating CD8 + T cells throughout differentiation. We found that terminally exhausted T cells had unexpected chromatin features that limit their transcriptional potential. Terminally exhausted T cells had a substantial fraction of active chromatin, including active enhancers enriched for bZIP/AP-1 transcription factor motifs that lacked correlated gene expression, which was restored by immunotherapeutic costimulatory signaling. Reduced transcriptional potential was also driven by an increase in histone bivalency, which we linked directly to hypoxia exposure. Enforced expression of the hypoxia-insensitive histone demethylase Kdm6b was sufficient to overcome hypoxia, increase function, and promote antitumor immunity. Our study reveals the specific epigenetic changes mediated by histone modifications during T cell differentiation that support exhaustion in cancer, highlighting that their altered function is driven by improper costimulatory signals and environmental factors. These data suggest that even terminally exhausted T cells may remain competent for transcription in settings of increased costimulatory signaling and reduced hypoxia.