Inhibition of diacylglycerol kinase alpha restores restimulation-induced cell death and reduces immunopathology in XLP-1

X-linked lymphoproliferative disease (XLP-1) is an often-fatal primary immunodeficiency associated with the exuberant expansion of activated CD8+ T cells after Epstein-Barr virus (EBV) infection. XLP-1 is caused by defects in signaling lymphocytic activation molecule (SLAM)–associated protein (SAP), an adaptor protein that modulates T cell receptor (TCR)–induced signaling. SAP-deficient T cells exhibit impaired TCR restimulation-induced cell death (RICD) and diminished TCR-induced inhibition of diacylglycerol kinase a (DGKa), leading to increased diacylglycerol metabolism and decreased signaling through Ras and PKCq (protein kinase Cq). We show that down-regulation of DGKa activity in SAP-deficient T cells restores diacylglycerol signaling at the immune synapse and rescues RICD via induction of the proapoptotic proteins NUR77 and NOR1. Pharmacological inhibition of DGKa prevents the exces sive CD8+ T cell expansion and interferon-g production that occur in SAP-deficient mice after lymphocytic choriomeningitis virus infection without impairing lytic activity. Collectively, these data highlight DGKa as a viable therapeutic target to reverse the life-threatening EBV-associated immunopathology that occurs in XLP-1 patients.