P146 The use of surrogate crossmatching allows for the detection of a possible donor specific antibody to an HLA-DQ heterodimer

Aim The development of de novo donor-specific antibodies (DSA) post-transplant is an area of interest for the transplant community. There are several challenges in detecting DSA, including the use of recombinant HLA antigens vs. affinity-purified antigens from a phenotype, and the lack of donor typing at many loci. Herein, we describe a case where surrogate flow-cytometric crossmatch (FCXM) was used in conjunction with solid-phase immunoassays for the detection of DSA in a heart transplant recipient. Methods Post-transplant serum was tested by solid-phase immunoassays for the detection of DSA to the following donor antigens: A2,23; B7,8; Bw6; Cw7; DR15,17; DR52; DQ2,6. Confirmation of antibody specificity was obtained using FCXM using three surrogate donor cells. Results Initial testing by One Lambda LABScreen® PRA and Single Antigen assays provided negative results for HLA class I, and inconclusive results for HLA class II, suggesting possible reactivity to HLA-DQ2, HLA-DQA1∗05:01/DQB1∗02:01, or false-positive reactivity. In order to confirm the possible specificities obtained, surrogate crossmatching was performed utilizing pronased cells from donors with the following HLA types: Donor 1- DQB1∗02:XX, 03:XX (DQ9); DQA1∗02:01; Donor 2- DQB1∗02:01; DQA1∗05:01; Donor 3- DQB1∗02:01, 03:01 (DQ7); DQA1∗05:01, with recipient serum at dilutions of Neat, 1:2, 1:4, and 1:16. T cell crossmatch results at all dilutions were negative for each donor cell tested. Donor 1 tested B cell negative at all dilutions tested, while donor 2 tested positive at serum dilutions of Neat, 1:2, and 1:4, and donor 3 tested positive at serum dilutions of Neat and 1:2. This evidence allowed for us to assign a strong antibody, defined by our laboratory as predicted to yield a positive FCXM, to the DQA1∗05:01/DQB1∗02:01 heterodimer. Since donor HLA-DQA1 typing was not available, it is inconclusive whether the antibody detected should be considered donor-specific. Conclusion We conclude that while solid-phase immunoassays are useful tools for the detection of HLA antibodies, there are several challenges present which could require the use of additional assays for confirmation of test results. In addition, the lack of complete donor typing often makes it difficult for the laboratory to accurately interpret the findings of such results.