1α,25(OH) 2 D 3 Decreases Expression of Immune Checkpoint Receptors and Enhances Anti-Tumor Immunity of Human Cytotoxic T Cells

Epidemiological surveys have revealed that low serum vitamin D level was correlated with increased risk of tumors. Dysfunctional T cells in tumor patients are characterized as exhausted with high levels of immune checkpoint receptors (ICRs). However, whether the reduced level of vitamin D in cancer patients correlates with cytotoxic T cell exhaustion is unknown. Here, we show that serum level of vitamin D is negatively correlated with expression of PD-1, TIGIT, and Tim-3, but positively correlated with CD28 expression on CD8+ and Vγ9Vδ2+ T cells in patients with non-small cell lung cancer (NSCLC). 1α,25(OH)2D3, the active form of vitamin D, promotes the nuclear translocation of vitamin D receptor (VDR), which binds to the promoter region of Pdcd1, Tim3, Tigit genes and inhibits their expression. Besides, 1α,25(OH)2D3 pretreatment also promotes the methylation of CpG island in promoter region of Pdcd1 gene and increases H3K27 acetylation at promoter region of Cd28 gene, which leads to surface PD-1 down-regulation and CD28 up-regulation respectively. We further reveal that VDR-mediated Ca2+ influx enhanced expression of Th1 cytokines via T cell receptor activation. Functionally, 1α,25(OH)2D3 pretreated CD8+ T cells or Vγ9Vδ2+ T cells showed increased Th1 cytokines production and enhanced anti-tumor immunity. Finally, oral 1α,25(OH)2D3 could also decrease expression of PD-1, Tim-3, TIGIT and increase expression of CD28, resulting in cytokine production (associated with antitumor immunity) by cytotoxic T cells of patients with NSCLC. Collectively, our findings uncover the pleiotropic effects of 1α,25(OH)2D3 in rescuing exhausted phenotype of human cytotoxic T cells in tumor patients and promoting their anti-tumor immunity.