Evalution of electronic dp epitype profiling to determine dp donor-specific antibodies during virtual crossmatch

Abstract

Our aim is to evaluate the utility of incorporating epitype analysis into the computerized virtual crossmatch (vXM) workflow for donors with DP alleles that are not covered by a recipient’s HLA antibody screening and identification assay. Our lab has used vXM to select deceased donors for transplantations for more than ten years. If the donor DP antigens are covered by the assay, the DSA can be determined directly by vXM. If the donor antigen is not included in the assay but is covered by an epitype (EDP) group which includes a DP antigen covered by the assay, the DSA can be determined based on the positivity of the EDP antigen using manual epitype profiling. A new epitype profiling system was deployed by informatics vendor HLA Data Systems, developers of the mTilda Lab Management System and VxMatch, to ensure that DP alleles not covered by HLA antibody tests are incorporated into an electronic vXM workflow. The epitype profiling system contains a data table of the highly polymorphic DP hypervariable regions (HVR) for DPB1 alleles. There are a total of six HVR regions (HVR-A, B, C, D, E, F) containing the unique amino acid profile per allele and 291 epitype groups determined so far which correspond to alleles belonging to the same HVR motif. The system returns the HVR motifs for donor and alleles of the recipient antibodies and then sorts alleles of recipient antibodies by increasing reactivity. Total negative and positive HVR matches are based on a configurable positivity cutoff value. Matches are color-coded for investigation of possible DSA when there is a positive match that is accompanied by zero negative matches. If a DP antigen bead is negative, presence of antibodies to polymorphic motifs carried by the DP antigen can be excluded. The computerized epitype profiling system was validated against our manual process for donors with alleles not contained within the assay, DPB1*16:01 and DPB1*85:01, and HVR motif profiling performed without error. With the increasing discovery of DP alleles, the system can cross-reference G-groups to determine HVR motifs for new alleles and can be configured to profile other HLA genes. Our evaluation suggests that extending vXM to include computerized epitype profiling is an efficient and reliable means to evaluate DP alleles not covered by antibody assays.