Multiplex bead immunoassay in ABO-A2-incompatible kidney transplantation.

Kidney transplantation from ABO-A2 donors into ABO-O and -B recipients can alleviate inequitable transplant access created by ABO demographics. ABO-A2-incompatible eligibility is determined by anti-A hemagglutination titres. However, titres do not distinguish antibodies specific for A-II glycans, the sole A-antigen subtype in vascular endothelium, from other anti-A antibodies. We examined whether reliance on anti-A titres unnecessarily limited ABO-A2-incompatible transplants for candidates with low anti-A-II levels. We created a single-antigen-bead immunoassay for ABO antibodies, confirmed the specificity and reproducibility, and demonstrated the ability to detect anti-A and -B glycan-subtype-specific antibodies in healthy control sera. We then measured subtype-specific anti-A antibodies in original sera from ABO-B and -O candidates who had been previously evaluated for ABO-A2-incompatible eligibility. Anti-A-II levels in candidates who had been deemed ineligible (anti-A titres >4) were compared to eligible candidates (anti-A titres ≤4) who had subsequently received ABO-A2-incompatible kidneys. Of 141 candidates, 75(53%) were ineligible; 66(47%) were eligible and received ABO-A2 kidneys. Re-testing original sera, 55%(41/75) of ineligible candidates had anti-A-II levels comparable to eligible candidates. Anti-A titres did not reflect anti-A-II levels. Our ABO antibody assay reproducibly measures graft-specific anti-A-II antibodies, providing information beyond anti-A titres that may increase transplant access for ABO-B and -O candidates.