Effect of ABO incompatibility on T-cell flow cytometry cross-match results prior to living donor kidney transplantation

Background. Due to its high sensitivity, the flow cytometry crossmatch (FCXM) has been described as valuable tool for identifying an optimal donor. We here focused on the impact of ABO incompatibility on FCXM results. Methods. We analyzed 29 ABO incompatible and 89 ABO compatible donor-recipient pairs (73 and 175 data sets, respectively) prior to living donor kidney transplantation. In all patients, lymphocytotoxic crossmatches for B and T cells were negative. Results. Recipients with blood group O (A to O and B to O) displayed significantly (P < 0.05) higher T-FCXM results than those with blood group A and B (A to B, B to A and AB to A), respectively. Donor-specific T-FCXM responses (Δ MFI values) were significantly higher (P < 0.05) in ABO incompatible vs. compatible pairs (ABO incompatible recipients with blood group O: 32 ± 6; with blood group A: 19 ± 7; with blood group B: 7 ± 4; recipients with ABO compatibility: 3 ± 2, respectively, data represent mean ± SEM). Consistent with the T-FCXM results donor-specific isohemagglutinins (IgG titers) were significantly higher in recipients with blood group O vs. A, both prior to rituximab treatment and plasmapheresis/immune adsorption (P = 0.004) and immediately prior to transplantation, i.e., after rituximab and antibody-depleting therapies (P = 0.04). Conclusions. ABO incompatibility was associated with higher T-FCXM responses, especially in recipients with blood group O. This finding has major impact on the interpretation of flow crossmatch results. Current cut-off values need to be reassessed in the ABO incompatible setting. This article is protected by copyright. All rights reserved.