CD4 and common variable immunodeficiency: Whereas in CVID, T cell abnormalities, such as deficiencies in naïve T CD4+ or regulatory T cells, and expansion of T CD8+ cells have been observed, somatic variants in STAT5B and TET2 might also be linked to the disease pathophysiology and increased susceptibility to autoimmune diseases, lymphoproliferative disorders [59,60], and malignant transformation [61].