Selective depletion of ABO-responsive B cells by T-cell-engaging bispecific antibody conjugates for ABOi transplantation

Abstract

Organ transplantation is a pivotal treatment for patients with organ failure. ABOincompatible (ABOi) transplantation, developed to expand the donor pool, presents significant clinical challenges due to preexisting antibodies targeting ABO antigens on donor organs. Current therapies using broad B-cell depletion, such as rituximab, effectively reduce antibody-mediated rejection but increase infection risks. Therefore, there is a critical need for targeted methods to specifically eliminate ABO-responsive B cells. Here, we developed a novel bispecific antibody-ligand conjugate (BiALC) platform designed to selectively target ABO-responsive B cells. Using synthetic trisaccharide A antigens conjugated to T-cell-recruiting Fab fragments, our optimized hexameric construct, (A3-peg)2-alpha CD3, demonstrated enhanced affinity and potent cytotoxicity specifically against type A antigen-responsive B cells. Notably, BiALC maintained robust efficacy even in the presence of circulating anti-A antibodies. In murine models, (A3-peg)2-alpha CD3 selectively depleted A-responsive B cells without broadly affecting total immunoglobulin M-positive (IgM+) and IgG+ B-cell populations, preserving overall immune competence. Similarly, the human-compatible BiALC, (A3-peg)2-alpha hCD3, effectively and selectively depleted type A-responsive B cells from human peripheral blood mononuclear cells, with potency comparable with that of rituximab, while sparing total antibody-secreting cells. Overall, the BiALC strategy offers a promising antigen-specific approach to reduce rejection risks in ABOi transplantation without inducing broad immunosuppression through nonspecific pan-B-cell depletion, supporting its potential for clinical translation.