Advancing Antibody Titer Assessment in ABO-Incompatible Transplantation

Background: The accurate evaluation of anti-ABO antibodies is essential for risk stratification in ABO-incompatible (ABOi) transplantation. Historically, hemaggluti-nation-based titration has been the cornerstone of such an assessment; however, dif-ferent tools are being evaluated in this context. In recent years, several novel methods have been reported. Methods: A narrative review was conducted using PubMed, Scopus, and Google Scholar, focusing on recent studies evaluating anti-ABO antibody measurement tech-niques in the context of ABOi organ transplantation. Results: In addition to the conventional tube method, techniques such as column ag-glutination technology, flow cytometry, and enzyme-linked immunosorbent assay are utilized for anti-ABO antibody assessment. However, any particular technique, sig-nificant interinstitutional and interoperator variabilities have been reported due to differences in the detailed protocols and the inherently subjective nature of some techniques. Moreover, these assays are based on the antibody binding to ABO anti-gens expressed on red blood cells, which might not accurately reflect the clinical con-text of organ transplantation. In recent years, technological advances have enabled the development of novel assays evaluating antibody responses specifically against the ABO antigens expressed on vascular endothelial cells. These include glycan mi-croarrays, which differentiate responses by ABO antigen subtypes, and CD31-based microarrays, wherein recombinant CD31 proteins expressing ABO antigens are im-mobilized. These approaches are applied to assess clinically relevant anti-ABO anti-bodies in the context of ABOi organ transplantation. Conclusions: The objective evaluation of antibody titers against ABO antigens on vascular endothelial cells might not only enable a more accurate risk assessment but also facilitate meaningful comparisons between institutions.