Single-Cell RNA Analysis Reveals Reduced Frequency and Activity of CXCR5+ Atypical Memory B Cells in Islet Xenotransplantation Treated With Clinically Applicable Immunosuppressants Including Belimumab.

Background: Porcine-to-human islet xenotransplantation offers a promising solution to type 1 diabetes. This study investigates the use of Belimumab, a human monoclonal antibody that inhibits B cell activating factor (BAFF) as part of an immunosuppressive regimen in porcine-to-non-human primate xenotransplantation.

Methods: Porcine islets were transplanted into Rhesus monkeys with an immunosuppressant regimen. Blood samples were collected from the monkeys pre- and post-treatment, and single-cell RNA sequencing was performed to investigate immune cell landscape changes, focusing on B cells.

Results: UMAP clustering of B cells identified five distinct subsets. Notably, Belimumab treatment significantly reduced the proportion of both CXCR5⁺ and CXCR5^- atypical memory B cells, which possess the potential to differentiate into antibody-secreting cells. Furthermore, differentially expressed gene (DEG) analysis revealed a comprehensive functional impairment, along with significant downregulation of activation markers such as CD69 and CD83, across all B cell subsets.

Conclusions: Our study elucidates the mechanism of action of Belimumab in non-human primate models, serving as preclinical subjects for B-cell-targeted therapy research in a xenotransplantation context. Significantly, our data indicate that Belimumab not only reduces the proportion of antibody-secreting atypical memory B cells but also induces functional impairment across all B cell subsets. Given the potential pathogenic roles of atypical memory B cells in autoimmunity and other related settings, their reduction by Belimumab could play a crucial role in regulating B-cell-mediated immune responses in pig-to-non-human primate pancreatic islet xenotransplantation. Thus, our findings highlight the prospective utility of Belimumab as a B cell suppressant in future clinical xenotransplantation applications.