The Ten-Eleven-Translocation (TET) enzymes belong to a family of oxygenases that are dependent on 2-oxoglutarate and Fe (II) and are able to oxidize methylcytosines. This may represent a step toward DNA demethylation and as such these proteins are involved in the epigenetic control of transcription. Acquired TET2 loss-of-function mutations have been reported in about 20% of human myeloid malignancies.Analysis of two Tet2-deficiency mouse models shows that Tet2 controls hydroxymethylation and homeostasis in the hematopoietic compartment. Tet2 deficiency results in pleiotropic abnormalities of both early and late steps of hematopoiesis and leads to the development of myeloid disorders. The sequencing of TET2 in a large series of patients with mature lymphoproliferations identifies TET2 mutations in 12% of T-cell lymphoma. They are significantly associated with DNMT3A mutations and are more frequently observed in two subtypes, the angioimmunoblastic T-cell lymphoma and the peripheral T-cell lymphoma, not other specified. Analysis of flow-sorted populations shows the presence of TET2 and DNMT3A alterations in hematopoietic progenitors in some patients. In summary, TET2 mutations may affect early progenitors, confer a selective advantage compared with controls progenitors and result in a clonal hematopoiesis. Some additional genetic events are likely required to the myeloid or lymphoid transformation. Both diseases could therefore arise from a common alteration of the hematopoietic stem cell compartment.
