Mutations in the SH2D1A gene resulting in X-linked lymphoproliferative disease (XLP) are associated with impaired iNKT cell development as well as defective immune cell activities, such as NK and CD8+ T cell cytotoxicity, T cell cytokine production, activation-induced cell death, and germinal center formation [81]; defects that are recapitulated in Sap−/− mice [119,120,121]. Here, CD8A is linked to X-linked lymphoproliferative disease.