Insights into the Absence of Lymphoma Despite Fulminant Epstein-Barr Virus Infection in Patients with XIAP Deficiency.

Unlabelled: X-linked Lymphoproliferative Syndromes (XLP), which arise from mutations in the or genes, are characterized by the inability to control Epstein-Barr Virus (EBV) infection. While primary EBV infection triggers severe diseases in each, lymphomas occur at high rates with XLP-1 but not with XLP-2. Why XLP-2 patients are apparently protected from EBV-driven lymphomagenesis, in contrast to all other described congenital conditions that result in heightened susceptibility to EBV, remains a key open question. To gain insights, we cross-compared newly EBV infected versus immune stimulated B-cells from XLP-2 patients or upon XIAP CRISPR knockout, relative to healthy controls. XIAP perturbation impeded outgrowth of newly EBV-infected primary human B-cells, though had no impact on proliferation of B-cells stimulated by CD40 ligand and interleukin-21 or upon established EBV-immortalized lymphoblastoid cell lines (LCLs). B-cells from XLP-2 patients or in which XIAP was depleted by CRISPR editing exhibited a markedly lower EBV transformation efficiency than healthy control B-cells. Mechanistically, nascent EBV infection activated p53-mediated apoptosis signaling, whose effects on transforming B-cell death were counteracted by XIAP. In the absence of XIAP, EBV infection triggered high rates of apoptosis, not seen with CD40L/IL-21 stimulation. Moreover, inflammatory cytokines are present at high levels in XLP-2 patient serum with fulminant EBV infection, which heightened apoptosis induction in newly EBV-infected cells. These findings highlight the crucial role of XIAP in supporting early stages of EBV-driven B-cell immortalization and provide insights into the absence of EBV+ lymphoma in XLP-2 patients.

Key Points: XIAP loss-of-function markedly impairs EBV+ B-cells outgrowth over the first week post-infection, particularly in the presence of IFN-γ.XIAP mutation impedes EBV-driven B-cell transformation by potentiating p53-driven caspase activation and apoptosis.