Antigen and eplet coverage by representative solid-phase immunoassays for anti-HLA antibody screen

Solid-phase immunoassays (SPIs) are the current standard of care for detecting and identifying anti-HLA antibodies in transplantation. However, whether SPIs with different configurations provide comprehensive antigen and eplet coverage has not been documented in the literature. We systematically compared four commercial SPI panels - Mixed, PRA (Panel Reactive Antibody), SAB (Single Antigen Bead), and ExPlex - to assess their coverage of antigens and eplets cataloged in the HLA Eplet Registry. Our results show overlapping and variable antigen and eplet representation across these assays. Out of a total of 252 class I and 260 class II eplets in the HLA Eplet Registry, 251 (99.6 %) and 260 (100 %) were covered by one or more assays; 209 (82.9 %) class I and 189 (72.7 %) of class II eplets were covered by all four assays. All antibody-verified eplets in Class I antigens are represented in three or more assays, whereas two Class II eplets were exclusive to SAB. Although ExPlex did not significantly increase the number of eplets represented beyond the SAB panel, it expanded the diversity of eplets within unique antigenic contexts. We also examined the relationship between eplet dose per bead and antibody reactivity in the PRA assay. Positive correlations were observed between bead-level eplet numbers and mean fluorescence intensity (MFI) in a collection of sera with 82LR (Bw4) or 80 N (Bw6) eplet patterns. Our findings indicate broad coverage of HLA eplets by current SPIs, which offer acceptable antigenic coverage for pre-transplant immune risk screening. We also share the R script to enable ongoing analyses and monitoring of antigen and eplet coverage in future screening reagents.