(503) Identification of an Unrecognized A*02:94n Allele at the Time of Organ Allocation

Body: Many CIWD null alleles are not readily identified by qPCR, one of the most common methods currently used to HLA type deceased donors. While they may be listed in the ambiguity string which often contains both null and expressed alleles, in many cases an expressed allele is selected as the correct typing for organ allocation. The lack of proper identification of null alleles at the time of organ allocation greatly disadvantages highly sensitized patients. We recently identified an HLA-A*02:94N allele in a deceased donor, post-allocation, using a sequence based high resolution typing method. The donor was typed as HLA-A*02,33 using qPCR and match runs for allocation were performed using what qPCR identified as the most probable allele which was an A*02 expressed allele. The A*02:94N allele was present in the ambiguity string however, an expressed A*02 allele was selected as the most probable allele and the donor was entered in UNET as having an HLA-A2 antigen. HLA-A2 is the most common HLA-A antigen, consequently, patients who are not HLA-A2 and are sensitized by pregnancy, transfusion, or a previous transplant have a high chance of being sensitized by exposure to HLA-A2 antigens. For many high reactors, improper identification of an HLA-A2 null allele in a deceased donor prevents them from receiving an organ offer from an otherwise antigen-matched or compatible donor. Surrogate donor crossmatches were performed using serum from two sensitized patients with strong HLA-A2 antibodies and HLA-A*02:94N donor cells. Both crossmatches were negative. Organs from this donor could have been transplanted in patients with HLA-A2 antibodies. Unfortunately, due to the inability of the qPCR typing method to identify all CIWD null alleles, patients with HLA-A2 antibodies were ruled out at the time of the UNET match run.

Conclusion: This case highlights the need to properly identify CIWD null allele prior to the UNET match run in order to provide greater access to transplant for highly sensitized patients.