FAS and autoimmune lymphoproliferative syndrome: The discovery of humans with a similar lymphoproliferative phenotype and harboring heterozygous loss-of-function FAS mutations, dubbed Autoimmune Lymphoproliferative Syndrome (ALPS), further solidified FAS-induced apoptosis as a critical player in maintaining lymphocyte homeostasis (Sneller et al., 1992; Fisher et al., 1995; Rieux-Laucat et al., 1995).