Inhibition of Diacylglycerol kinase alpha restores TCR-induced diacylglycerol signaling and restimulation-induced cell death in XLP1 T lymphocytes

X‐linked lymphoproliferative disease (XLP1) is a rare primary immunodeficiency associated with an unconstrained, life‐threatening expansion of CD8+ T cells following Epstein‐Barr virus (EBV) infection. XLP1 is caused by mutations in SAP, an adaptor protein that mediates signaling through the SLAM family receptors. SAP‐deficient cells exhibit impaired T cell receptor (TCR) restimulation‐ induced cell death (RICD), a key physiological process in maintaining lymphocyte homeostasis. We previously showed that SAP has a critical role in TCR‐induced inhibition of diacylglycerol kinase alpha (DGKα), which phosphorylates diacylglycerol (DAG) to phosphatidic acid, acting as a major regulator of T cell signaling. Here, we show that in SAP‐deficient Jurkat cells, DGKα activity impairs immune synapse (IS) formation, MTOC reorientation and affects the integrity of DAG gradient. By taking advantage of confocal live‐cell imaging, we found that RNAi‐mediated silencing or pharmacological inhibition of DGKα in SAP‐deficient cells rescues both immune synapse formation and MTOC repositioning, and the subsequent DAG accumulation at the IS. Inhibition/silencing of DGKα was also sufficient to restore PKCand RasGRP1 recruitment at the immune synapse, as well as ERK1/2 activation and IL‐2 production/IL‐2 receptor membrane exposure in SAP knockdown primary T cells. Notably, DGKα blockade specifically reestablished RICD in both SAP‐ silenced cells and XLP1 patients’ T cells by restoring RSK‐mediated induction and phosphorylation of the pro‐apoptotic genes Nur77 and Nor1. Furthermore, in vivo inhibition of DGKα prevented aberrant CD8+ T cell expansion, TNFand IFNproduction as well as tissue infiltration in Lymphocytic Choriomeningitis Virus‐infected SAP KO mice, a mouse model of XLP1. Altogether, these data demonstrates that DGKα inhibition, by increasing localized DAG signaling at the IS, restores RICD in SAP deficient cells. In vivo, this limits the CD8+ T cell expansion and tissue damage that characterize XLP1. Collectively, these data highlight the key role for the SAP‐mediated DGKα inhibition in regulating T lymphocyte homeostasis and highlight DGKas an attractive therapeutic target in XLP1 patients.