文摘
DPA1 antibodies were shown to be a risk of antibody-mediated rejection (AMR). We present a case showing high MFI DPA1 donor-specific antibodies (DSA) causing +ve CDC crossmatch (CxM), but -ve flow xM (FxM). At the time of deceased donor offer, we perform prospective FxM if the intended candidate displays strong DP DSA. This particular case received first kidney transplant in 2004 from a 8/10 mismatched donor. Luminex single antigen bead assay (One Lambda) revealed strong antibodies to all mismatched donor’s HLA and CREG, and thus had 100% CPRA. The patient also displayed strong antibodies to several DPs including to the alpha chains, DPA1∗01 and DPA1∗03. The patient received a deceased donor offer in May 2015. Virtual xM (VxM) identified 3 strong DSAs directed to DPA1∗01(MFI = 16282), DPA1∗03(MFI = 13167) and DPB1∗04(MFI = 19568), and predicted positive B FxM. Contrary to the prediction, the donor-specific FxM was -ve (T cell MCS = 29; B cell MCS = 110). Kidney offer was declined because of multiple high MFI DSAs. To have better insights on our failed VxM prediction, we performed pronase as well as CxMs. The pronase B FxM was weakly +ve with a MCS = 209 (+ve cutoff >120 MCS), which is within the range relates to -ve CxM. Unexpectedly, the B CxM with and without DTT-treated sera were turned to be strongly +ve. Additional xMs with a surrogate donor cells expressing a single target DPA1∗01:03 also produced similar results, i.e., +ve pronase B FxM with MCS=178 and +ve B CxM. We confirmed DP antibodies assignment using Immucor single antigen beads, and typed previous donor and patient for DPA1 and DPB1 loci. These results ruled out DPB1∗04:01 antibody, but cannot confirm DPB1∗04:02, because DPB1∗04:02 beads in both venders’ systems were paired with DQA1∗01:03. It is more likely the patient has only DPA1∗01 and DPA1∗03 antibodies. Unambiguous assignment of DPA1 antibodies will remain challenging until the single antigen bead array includes multiple DP antigen series with different alpha and beta chain pairs. In conclusion, comprehensive antibody analyses by single antigen beads, and high-resolution typing of DPB1 and DPA1 of donor and recipient are necessary to define DPA1 antibodies. CDC xM is a critical test to determine the risk of hyper acute AMR in patients having strong DPA1 DSAs, and FxM may yield false negative results in these cases.
