TNFRSF13B Variant-Induced TACI Dysregulation Underlies CAEBV Pathogenesis

The tumor necrosis factor (TNF) receptor superfamily member, transmembrane activator and CAML interactor (TACI) encoded by TNFRSF13B, are extensively involved in immune responses. In our previous work, TNFRSF13B exon 2 variants were recurrently identified in chronic active Epstein-Barr virus disease (CAEBV). Here we aim to reveal the roles of TNFRSF13B variants in CAEBV, and investigate the feasibility of targeting TNFRSF13B/TACI as a new approach to control EBV infection. The lymphoblastoid cell lines (LCL) models carrying homozygous TNFRSF13B exon 2 frameshift mutations were constructed using CRISPR/Cas9. Immunological assays, transcriptomic analysis, and gene silencing experiments were performed on LCL models to measure the effect of TNFRSF13B exon 2 variants and explore the underlying mechanisms. TACI ligands and a TLR9 agonist were applied to modulate TACI signaling and EBV activities. Frameshift mutations in exon 2 of TNFRSF13B significantly up-regulated the short isoforms of TACI (TACI-S) at the expense of its long isoforms (TACI-L) in LCLs. The up-regulated TACI-S induced more intense activation of NF-κB, MAPK, and Rho signaling pathways, leading to the switch of EBV activities to lytic reactivation. The subsequent increased viral load and viral IL-10 provide a rational for the susceptibility of variant carriers to CAEBV. The BAFF trimer, an indirect TACI-signaling inhibitor, also significantly suppressed the EBV lytic program. Gene silencing experiments indicated that XBP-1 might be involved in the TACI-mediated regulation of EBV lytic activities in EBV-immortalized B cells. This study underscores the impact of TNFRSF13B variants on EBV infection and host immune responses, offering insights into CAEBV pathogenesis and potential therapeutic strategies.