174-P: VIRTUAL CROSSMATCH IN A PATIENT WITH HLA ALLELE SPECIFIC ANTIBODY

Abstract

Aim HLA typing at low/intermediate resolution levels is acceptable for the characterization of HLA genes of solid organ recipients and donors. However, the interpretation of virtual crossmatch may be problematic for transplant candidates with allele specific antibodies. We present here a case report and a possible strategy to alleviate this problem. Methods HLA typing was performed using SSO for low/intermediate resolution and SSP for high resolution. One Lambda Single Antigen Bead assay was used for the detection and identification of serum HLA antibodies. Crossmatch was performed using CDC and flow cytometry. Results The patient is a 52-year old Caucasian male, previously sensitized to HLA antigens, listed for heart transplantation. Due to the urgency of the transplant, an organ offer from a 28-year old donor was accepted even though the patient displayed an allele specific, potentially donor specific antibody (DSA) directed to DRB1∗13:03 antigen ( Table 1 ). [table1] The available donor HLA class II type was: DR13, DR15, DQ6. This donor was accepted based on the known frequency of HLA-DR13 alleles (13:03 allele is 5-fold less frequent than 13:01) and the presumed decreased risk of anti-HLA class II DSA compared to class I DSA in heart transplantation. CDC and flow cytometry crossmatches were performed at the time of transplant and yielded negative results. Extended typing of the donor revealed that the donor carried the HLA-DRB1∗13:01 gene. Thus, the allele specific DRB1∗13:03 antibody was not a DSA. Post-transplant outcome was favorable. C4d staining was negative in serial allograft biopsies. Conclusions In patients with allele specific antibodies, the frequency of related HLA alleles may guide the interpretation of the virtual crossmatch. Whenever possible, extended HLA typing of the donor should be performed to confirm the presence or absence of DSA.