Allelic antibodies and their impact on organ allocation to highly sensitized patients

Abstract

Aim Based largely on the success of virtual crossmatching (vXM), the OPTN implemented a new kidney allocation process. Specifically, transplant candidates with cPRA values of 9899% and 100% now have priority for deceased donor (DD) kidneys. Recent studies revealed that the majority of these highly sensitized patients (HSPs) had HLA-DP antibodies, meaning that vXM was not possible unless the corresponding donor HLA-DP type was provided. A similar situation occurs if patients possess allele specific HLA antibodies and donors with the corresponding antigen are not allele level typed. Here again, vXM is not possible. In this study, we evaluated the distribution and frequency of allele specific HLA antibodies among HSPs. The allelic antibodies represented on SAB products are shown in the table below. Methods Luminex SAB assays were performed with sera from all listed kidney candidates with cPRA > 98% (n = 242). An antibody was considered positive when the MFI was > 2000. Results Of 189 black, 44 white and 9 Hispanic HSPs, 85% (n = 160), 89%(n = 39) and 78% (n = 11), respectively, had at least one allele specific antibody.The average number of allele specific antibodies per patient was 1.28 ± 0.71 (Class I) and 2.6 ± 1.59 (Class II). The most prominent allele specific antibodies are shown below (shaded). MFI values for the allele specific antibodies ranged from 2000– > 25000. Conclusions These data clearly show that allele specific HLA antibodies are common in HSPs. They are likely the tip of the iceberg since the only detectable allelic antibodies are those represented on the SAB panel. The “real” number of allelic antibodies is likely much greater. High resolution typing of DDs, at least for those alleles to which antibodies are commonly detected, needs to be provided in a timely fashion in order to perform accurate vXM for HSPs with allele specific antibodies. Download : Download full-size image