Inhibition of TET (Ten-Eleven Translocation) enzymes enhances systemic anti-tumor immune responses in T cells

Abstract

Abstract TET enzymes facilitate DNA demethylation by oxidizing 5-methylcytosine to 5-hydroxymethylcytosine and other oxidation products in DNA. Loss-of-function mutations in TET enzymes are associated with increased proliferation and increased stem cell function in many cellular lineages. Moreover, there are several hints that inhibition of TET enzymes in tumor-infiltrating T cells might enhance anti tumor immune responses in solid tumors. For instance, TET2 deficiency in mouse T cells increased the number of CD8+ central memory T cells, and TET deficiency human CD8 chimeric antigen receptor (CAR) T cells increased their antigen-specific proliferation and capacity to reject tumor cells in a patient with chronic lymphocytic leukemia. Furthermore, we previously showed that TET deficiency in regulatory T cells decreased the stability of Foxp3 expression; hence TET deficiency would be expected to counter the ability of regulatory T cells to suppress anti-tumor responses. In this study, we found that TET loss of function in CD8 TILs indeed slowed tumor growth and promoted anti tumor responses in a mouse CAR T cell model. The function of TET proteins and other Fe(II) and a-ketoglutarate dependent dioxygenases is inhibited by L-2-Hydroxyglutarate (L2HG), which is normally kept at low levels by the enzyme L-2HG dehydrogenase (L2HGDH). We found that when CAR T cells were rendered low in TET activity in any one of three ways: (i) deficiency of the TET enzymes, (ii) depletion of L2HGDH and (iii) pretreatment of L2HG, they showed decreased expression of inhibitory receptors as well as increased secretion of inflammatory cytokines. Based on these results, we suggest that TET inhibition in T cells might be a promising general approach in cancer immunotherapy.