CD38-cADPR axis mediated chronic Ca 2+signaling promotes the differentiation of TCF1 loterminal exhausted CD8 +T cells in tumor

Abstract

Abstract Preponderance of terminally exhausted CD8 +T cells (Tex term) at the tumor site is the major impediment for successful immunotherapy of cancer. Despite the recent understanding in epigenetic, transcriptomic and metabolic features of Tex term, the cellular pathway underpinning the differentiation of Tex termremains elusive. Upon assessing intratumoral CD8 +T cells from both clinical samples and pre-clinical mouse models, we observed that CD8 +T cells co-expressing CD38 and PD1 displayed the characteristic features of Tex term. Single cell RNA sequencing analysis from both murine tumor infiltrating CD8 +T cells and in vitrochronically stimulated human CD8 +T cells revealed that clusters co-expressing Cd38and Pdcd1diplayed the transcriptomic signature of Tex term. Most importantly, clusters expressing Cd38and Tcf7were found to be mutually exclusive. Further studies to decipher the role of CD38 showed that both pharmacological and genetic knockdown of CD38 maintained TCF1 expression in chronically exhausted CD8 +T cells and significantly improved their ability to control tumor growth upon adoptive transfer in B16–F10 melanoma bearing mice. Mechanistic studies revealed that CD38 expression on Tex termled to chronic elevation of intracellular Ca 2+levels through cADPR-RyR2 axis, which activated Akt signalling. Activation of Akt restrained the nuclear localization of Ezh2, which was found to be pivotal in maintaining TCF1 expression in Tex termand inhibition of which in CD8 +T cells resulted in poor anti-tumor response. Thus, our data suggests that CD38 could be a drugable target to improve the immunotherapeutic efficacy of CD8 +T cells in cancer. Supported by grants from IA/I/19/1/504277/WTDBT_/DBT-Wellcome Trust India Alliance/India CRG/2019/001334 SERB Extramural Fund CSIR Intramural Fund