P117 Limitation of donor specific antibody mean florescent intensity values in predicting transplant compatibility: The saga continues

Abstract

Aim A positive flow cytometry crossmatch (FCXM) can be predicted when the presence of strong donor specific antibody (DSA) is detected by Luminex single antigen bead (SAB) assays. We present the case of a 23 year-old Hispanic male kidney transplant candidate with a strong HLA-B45 DSA to his potential living donor and consistent negative crossmatches. Methods DDT-treated sera was tested to detect HLA antibodies using LABScreen PRA beads and LABScreen Single Antigen beads (One Lambda, Inc.). Acid treatment of the SAB was used to denature the HLA Class I antigens. The sera was also tested using SAB from a different manufacturer (Immucor, Inc.). FCXM was performed with pronase-treated peripheral blood lymphocytes isolated by negative selection using the RoboSep Automated Cell Separator (StemCell Technologies). FCXM were performed with 3 surrogate HLA-B45-positive cells. CDC crossmatch was performed with potential donor. Results Strong HLA-B45 DSA (MFI = 5052) gave consistent negative crossmatch results with all HLA-B45-positive cells ( n = 3). The strong HLA-B45 antibody disappeared upon testing with acid-treated SAB (One Lambda, Inc.), implying presence of a true DSA. Testing with PRA beads (One Lambda, Inc.) gave positive results. Additional testing with the SAB from a different vendor (Immucor, Inc.) demonstrated the presence of a weak HLA-B45 DSA (MFI = 1426) that correlated better with the negative crossmatch results. Conclusions Relying on MFI values from a single vendor to predict a positive virtual crossmatch and influence clinical decision making may unnecessarily disadvantage the patient. This study indicates that the use of the LABScreen SAB assay as the sole method for unacceptable antigen determination can lead to a significant disadvantage for selected patients. The use of 2 different SAB platforms or 2 different bead assays (PRA and SAB) in the HLA antibody testing algorithm would prevent selected patients displaying high reactivity to certain specificities from being inappropriately excluded from receiving an organ due to aberrantly highly positive SAB results. Moreover, this case highlights the necessity to perform prospective crossmatches to confirm strong antibody specificities detected on SAB.