As the prenatal lethality of Stat5a/b−/− mice was connected to severe combined immunodeficiency, erythroid defects, and subsequent anemia [52,64,65], it was somehow surprising that hematopoietic-specific STAT5A/B deletion led to anemia and lymphopenia, but did not influence survival [60,61]. This evidence concerns the gene STAT5A and Immunodeficiency.