Novel Immune Checkpoint Deficiency and Susceptibility to EBV-Associated Lymphoma

Background: Understanding genetic predisposition to cancer is of paramount importance to tailor therapeutic strategies. Several defects in immune checkpoint regulators have been discovered in patients with EBV-induced lymphoma (e.g. CD27, PRKCD, RASGRP1, MAGT1, SH2D1A, ITK). Here, we describe the clinical and immune phenotype of 2 unrelated patients from consanguineous families presenting with a primary immune deficiency (PID) and EBV-associated lymphoproliferation due to biallelic mutations in CD137 (TNFRSF9/4-1BB). Methods: One patient of Turkish origin (P1) and Palestinian origin (P2), respectively were evaluated. Genetic analysis using whole exome sequencing was conducted. Immunological and biochemical assays were performed on primary patient material. Results: Clinical findings included recurrent sinopulmonary and herpes virus infections from childhood on. One patient suffered from auto-immunity (AIHA and auto-immune thrombocytopenia). Abnormal immunoglobulin levels were documented (IgG 413-1670, IgM 105-714, IgA 49-68 mg/dL). Both patients developed EBV-associated lymphoproliferative disorders: P1 developed Burkitt lymphoma and was treated according to NHL-BFM2000 regimen in combination with rituximab. He is currently in remission. P2 had monoclonal EBV-positive lymphoproliferation and was successfully treated with immunosuppressive therapy (e.g. cellcept, glucocorticoids). To shed light on the underlying genetic etiology, we performed whole exome sequencing. A large homozygous deletion in CD137 (c.1_545+1716del) was identified for P1, while P2 harbored a homozygous missense mutation (c.C452T, p.Thr151Met). Impaired anti-CD3 T cell lymphocyte activation and proliferation were observed, amenable to correction upon addition of anti-CD28 monoclonal antibodies. In an attempt to provide definitive proof that the CD137 gene variant causes the activation defect of T-cells, we designed a genetic rescue experiment in patient T cells. Upon retrovirus-mediated recombinant expression of WT CD137, proliferation and activation defects in T cells were restored. Conclusions: In sum, we here show that a genetic defect in the immune checkpoint molecule CD137 causes a new primary immunodeficiency disorder with susceptibility to EBV-induced lymphomagenesis. Disclosures No relevant conflicts of interest to declare.