Genetic susceptibility to Multisystem Inflammatory Syndrome in Children (MIS-C) SARS-CoV-2 SOCS1 XIAP CYBB Asymptomatic MIS-C inflammation Monogenic variants in: No genetic risk factors XIAP, X-linked inhibitor of apoptosis CYBB, Cytochrome b(-245), beta subunit SOCS1, Suppressor of cytokine signaling 1

Background: The tumor TNF receptor family member 4-1BB (CD137) is encoded by TNFRSF9 and expressed on activated T cells. 4-1BB provides a costimulatory signal that enhances CD8 1 T-cell survival, cytotoxicity, and mitochondrial activity, thereby promoting immunity against viruses and tumors. The ligand for 4-1BB is expressed on antigen-presenting cells and EBV-transformed B cells. Objective: We investigated the genetic basis of recurrent sinopulmonary infections, persistent EBV viremia, and EBVinduced lymphoproliferation in 2 unrelated patients. Methods: Whole-exome sequencing, immunoblotting, immunophenotyping, and in vitro assays of lymphocyte and mitochondrial function were performed. Results: The 2 patients shared a homozygous G109S missense mutation in 4-1BB that abolished protein expression and ligand binding. The patients' CD8 1 T cells had reduced proliferation, impaired expression of IFN-g and perforin, and diminished cytotoxicity against allogeneic and HLA-matched EBV-B cells. Mitochondrial biogenesis, membrane potential, and function were significantly reduced in the patients' activated T cells. An inhibitory antibody against 4-1BB recapitulated the patients' defective CD8 1 Tcell activation and cytotoxicity against EBV-infected B cells in vitro. Conclusion: This novel immunodeficiency demonstrates the critical role of 4-1BB costimulation in host immunity against EBV infection.

Distinct and shared roles of beta-arrestin-1 and beta-arrestin-2 on the regulation of C3a receptor signaling in human mast cells.