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

Organ transplantation is a pivotal treatment for patients with organ failure. ABO-incompatible (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-αCD3, 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-αCD3 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-αhCD3, 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.