Autosomal homozygous TET2 missense or nonsense in humans results in immunodeficiency, growth impairment and autoimmune lymphoproliferative syndrome (ALPS) like phenotypes of raised proportion of double negative (CD4-CD8-) T-cells (DNTs), raised soluble Fas ligand level, lymphadenopathy, hepatosplenomegaly, autoimmunity and remarkable predisposition to lymphoma, which is reminiscent of phenotypes of TET2 deficient mice (24). This evidence concerns the gene TET2 and immunodeficiency disease.