TET proteins regulate the lineage specification and TCR-mediated expansion of iNKT cells

Abstract

TET proteins oxidize 5-methylcytosine in DNA to 5-hydroxymethylcytosine and other oxidation products. We found that simultaneous deletion of Tet2 and Tet3 in mouse CD4+CD8+ double-positive thymocytes resulted in dysregulated development and proliferation of invariant natural killer T cells (iNKT cells). Tet2-Tet3 double-knockout (DKO) iNKT cells displayed pronounced skewing toward the NKT17 lineage, with increased DNA methylation and impaired expression of genes encoding the key lineage-specifying factors T-bet and ThPOK. Transfer of purified Tet2-Tet3 DKO iNKT cells into immunocompetent recipient mice resulted in an uncontrolled expansion that was dependent on the nonclassical major histocompatibility complex (MHC) protein CD1d, which presents lipid antigens to iNKT cells. Our data indicate that TET proteins regulate iNKT cell fate by ensuring their proper development and maturation and by suppressing aberrant proliferation mediated by the T cell antigen receptor (TCR).

5-Hydroxymethylcytosine (5hmC), or How to Identify Your Favorite Cell

“…This is the case for Tet2 (and to a lesser degree Tet3), which is consistently reported in murine models [39,40,43,[45][46][47]49] and human cells [37,38,42,[50][51][52]. Of note, the role of Tet2 in mast cell differentiation described above [40] is partially independent of 5hmC, as rescuing mast cell developmental changes upon Tet2 knockout was only possible by the re-expression of Tet2 independently of its catalytic activity, which assumes that Tet2 possibly interacts with other complexes (something similar has been shown between TET1 and the SIN3A co-repressor complex [53]).…”

“…In line with this, 5hmC changes are overrepresented in highly transcribed genes. For example, chromatin-accessible-regions are associated with T cell [36,44] and induced natural killers (iNK) T cell development [45], Treg FoxP3 activation [46,47], B cell identity genes [39,41], or Bcl6 binding sites in T follicular helper (Tfh) cells [48] (Figure 2 and Table 1). During mast cell development, it was shown that Tet2 knockout caused differential 5hmC levels in genes enriched with leukocyte differentiation and proliferation, malignant transformation, and mast cell-related processes [40].…”

“…Moreover, 5hmC was suggested to mark long-range interactions between enhancers and other regulatory regions at the transition points of T-cell development. More recently, using Tet2-Tet3 double knock-out (DKO) mice, the same group showed that TET proteins are essential for maturation of invariant natural killer T cells (iNKT), and its absence generates a T cell antigen receptor (TCR)-mediated expansion of these cells and a lethal lymphocytic infiltrate in lung and liver [45]. Transcriptomic evaluation identified a characteristic profile of natural killer NKT17 cells (expressing RAR-related orphan receptor γ (RORγt) and Interleukin 17) and genes related with malignant transformation.…”

CMML: Clinical and molecular aspects

“…TET2 mutations can be present in T cells in CMML [35] and are frequent in cases with AID (Itzykson et al unpublished observation). TET enzymes have been involved in normal innate and adaptive immunity [36,37], but how TET2 mutations affect the function of normal T cells remains unclear.…”

TET proteins in natural and induced differentiation

“…After deletion of Tet2 and Tet3 genes broadly in all T cells, a subset of innate-like and glycolipid-CD1d specific T cells called NKT cells displayed an altered differentiation pattern and were expanded and could transfer lymphoma-like disease [15•]. NKT subset specific transcription factor expression was altered in these mice and the population of NKT cells was biased to a normally rare RORγt-dependent subset called NKT17 [15•]. This phenotype was associated with reduced chromatin accessibility at distal regulatory elements that were normally enriched for 5hmC in wild-type NKT cells [15•].…”