P124 : PREDICTION OF NEGATIVE FLOW CYTOMETRY CROSS MATCH BASED ON ALLELE/HLA EPITOPE ANALYSIS: A CASE REPORT

Abstract

Patient C.A’s pre-transplant sera was found to be negative for antibodies against HLA Class I but strongly positive for antibodies against HLA Class II. The Class II specificities of the patient’s anti HLA antibodies were DR1, DR4, DR7 and DR10, DR17, DR18. The highest bead, DRB1∗01:02 was about10,000 MFI. In the single antigen bead kit used at our center, four DR4 beads were present: DRB1∗04:01, DRB1∗04:02, DRB1∗04:03, and DRB1∗04:05. Of the four, three were positive. The DRB1∗O4:02 bead was not reactive. In the past year, the patient was eligible for a deceased donor transplant. The deceased donor’s HLA type was HLA A2, A24, B7, B41, DR4, DR11, DQ7, DQ8. A flow cross match (FCXM) was performed. Though the donor’s HLA type was DR4, the B cell FCXM was negative, as well as the T cell FCXM. A possible explanation for the negative FCXM in the DR4 positive donor is that the donor’s HLA DR4 allele was DRB1∗04:02. In order for this explanation to be plausible, an epitope must be present on DRB1∗04:01, DRB1∗04:03, and DRB1∗04:05 (positive beads) but not on DRB1∗04:02 (negative bead). In real time, we searched the HLA epitope registry http://epregistry.ufpi.br/index/index for evidence of such an epitope. Epitope 70QA was present on the following Luminex alleles: DRB1∗01:01, DRB1∗01:02, DRB1∗04:01, DRB1∗04:03, DRB1∗04:04, DRB1∗04:05, DRB1∗14:02, DRB1∗15:01, DRB1∗15:02, DRB1∗15:03, DRB5∗02:02. We noted that this epitope excluded the DRB1∗04:02 allele. To further substantiate the reactivity of the patient’s sera, a FCXM was performed between the sera of the recipient against the B and T cells of a subject known to have the DRB1∗04:01 allele. The B cell FCXM was strongly positive, whereas the T cell FCXM was negative. It is a policy of our center not to transplant potential transplant patients with a positive B cell FCXM this particular case, the above referenced patient would be eligible to receive a kidney transplant from a donor with a DRB1∗04:02 type. Unfortunately, the current UNOS registry does not permit transplant centers to enter allele specific and/or epitope specific unacceptable antigen information. If the input of allele or epitope specific antigen data was initiated by UNOS, it would be extremely beneficial for transplant candidates who develop such allele specific antibodies. A.J. Norin: Speaker’s Bureau; Company/Organization; Immucor-Lifecodes. Scientific/Medical Advisor; Company/Organization; ICON CL.