P040 : THREE METHODS TO IDENTIFY CYTOTOXIC ANTIBODIES; ONE METHOD IS NOT ENOUGH

Abstract

Background Donor HLA specific complement dependent cytotoxic (CDC) antibodies (abs) have been associated with hyperacute rejection and are a detriment to solid organ transplantation. The Luminex single antigen (LSA)-C1q binding assay has been introduced to detect CDC+ abs. In a study of 190 patients (pts) sera tested by CDC and LSA-C1q, LSA-C1q was more sensitive than CDC in detecting 85% of class I and 75% of class II abs. 15–25% of abs detected by CDC were negative by the LSA-C1q assay. Aim: The aim of our study was to determine the appropriate methods to identify unacceptable antigens (UAs) for the virtual crossmatch by comparing the ability of a third assay, LSA-C3d binding, to detect CDC+ abs not detected by LSA-C1q. Methods Sera from 25 pts from the original cohort of 190 pts with positive LSA, CDC and negative C1q assay results were tested by the LSA-C3d assay. Results In 59% of the cases, the results of LSA-C3d were also negative and consistent with C1q data. 19% of the abs detected by CDC that were LSA-C1q neg were LSA-C3d pos. 9% of the abs detected by CDC were C1q pos and C3d neg. 13% of the abs showed no correlative patterns for CDC, LSA-C1q and LSA-C3d. The LSA-C3d assay appears to give false pos results for class I abs to rare alleles and HLA-C locus antigens. Both solid phase assays have non-specific background binding issues for some sera that make interpretation difficult. Conclusions In most cases LSA-C1q and LSA-C3d results are consistent with each other and identify more cytotoxic abs than the CDC assay. Although both solid phase assays are more sensitive than CDC in detecting the majority of cytotoxic pos abs. In 15–20% of the cases, the CDC assay is required to resolve the discrepancies and high background issues. A systematic analysis of LSA, CDC, LSA-C1q, and LSA-C3d results is needed to identify clinically relevant abs for the assignment of UAS.