P125 HLA allele specific antibodies: What should be entered in Unet, antigen, allele or epitope (case report)?

Aim Identification of donor-specific antibodies (DSA) represents one of the major functions of the HLA laboratory. Pre-existing DSAs are known to be important in organ allocation, while de novo developed DSA contribute to antibody (Ab) mediated rejection. Advances in solid-phase antibody analysis (SAA) now allow for the detection of HLA allele-specific Ab. The aim of this study was to examine HLA-A locus specific Ab in a kidney transplant candidate (TC). Methods A 64-yo male patient (typed A∗02:xx, 26:xx) was evaluated for a deceased donor kidney transplant. Two previous heart transplant (in 1986 and 2005) donors typed A1, A31 and A3, A31. HLA-A locus low and high resolution typing was performed using PCR-SSOP method (One Lambda Inc.), and sequence based typing (SBT) (GeneDX), respectively. Ab analysis was performed using SAA (One Lambda Inc.). Epitope analysis of HLA to which TC had Ab was conducted using HLAMatchmaker computer algorithm. Results Ab reactivity and antigen epitope analysis are presented in Table 1. Notably, TC had strongly reactive Ab against A∗26:01. Subsequent SBT of TC at A locus revealed presence of A∗02:01 and A∗26:09 alleles. The latter has a very low frequency in the US population. An epitope analysis of HLA-A locus Ab revealed that all positively-reactive HLA-A locus alleles share epitope 163R. Thus, we faced two questions. First, how should the TC’s typing at A locus be entered in Unet? Second, what antigens/alleles should be listed as unacceptable?. Conclusions The TC’s A locus typing was entered in Unet as A∗02:01/02:01 (considering changing A locus typing of the recipient to A2/A26 after kidney transplantation), and the list of unacceptable antigens included A1, A43, A25, A∗66:01, A∗11:01, A∗11:02, A26 (considering that all A26 donors will most likely have A∗26:01 allele). The results of this study present a new insight in organ allocation and post-transplant Ab monitoring, i.e. entering epitopes/eplets shared between unacceptable alleles (in this case 163R) instead of unacceptable UNOS antigens.