Immunodeficiency and EBV-induced lymphoproliferation caused by 4-1BB deficiency

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 + 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 EBV-induced 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 + T cells had reduced proliferation, impaired expression of IFN-γ 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 + T-cell 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.