P138 Clinical characteristics of patients who manifest unexplained crossmatch results for solid organ transplantation

Abstract

Aim The flow cytometric crossmatch (FCXM) and the virtual crossmatch (VCXM) assess compatibility between solid organ donors and recipients. Theoretically, both methods should give the same results. Realistically, however, they can be discrepant due to limitations of assays used to detect alloantibodies, non-HLA alloantibodies, autoantibodies, and non-specific reactivity. We sought to identify clinical features of patients who manifest such discrepancies, hypothesizing an association with female gender, autoimmune disease, and potential heart recipients. Methods We retrospectively evaluated all living and deceased donor FCXMs (performed using BD FacsCanto flow cytometer, BD Biosciences, San Jose, CA) for solid organ transplant offers for patients at University of California San Diego from 2015 to 2017. Based on previous validation studies, a positive FCXM was coded as ”expected” when a single donor-specific HLA antibody (detected using LABScreen single antigen assay, One Lambda, Canoga Park, CA) demonstrated a mean fluorescent intensity of 3,000 or higher, or when the sum of multiple antibodies reached that threshold. Deceased donor typing was performed using LinkSeq real-time polymerase chain reaction kit (Linkage Biosciences, South San Francisco, CA). Living donor HLA genotyping was performed by SSO or NGS-based methods. FCXMs with unexpected positive results were investigated. Results 1594 FCXMs (1369 for kidney, 139 for heart, 47 for lung, and 39 for multiple organs) for 967 potential recipients (621 males, 346 females) were analyzed. Unexpected positive results occurred in 109 T cell FCXMs in 81 patients (8%) and 40 B cell FCXMs in 23 patients (2%). Analysis by both crossmatch and patient demonstrated correlations with female gender (T cell p Conclusions Unexpected positive FCXMs correlate with female gender, but not with transplant organ. In 5 cases with persistent unexpected positive FCXMs, we have successfully transplanted patients using the VCXM.