Toward defining the immunogenicity of HLA epitopes: Impact of HLA class I eplets on antibody formation during pregnancy

Abstract

Eplets are functional units of structural epitopes on donor HLA, potentially recognized by complementarity‐determining regions of the paratope of the recipients' B‐cell receptors or antibodies (Ab). Their individual immunogenicity is poorly described, yet this feature would be of clinical importance for pretransplant risk assessment. The aim of this study was to determine the relative immunogenicity of HLA class I eplets in the pregnancy setting, where mismatched eplets are present on paternal HLA antigens of the unborn child. One hundred fifty‐nine predominantly Caucasian mothers giving birth at the University Hospital Basel and their first newborns were HLA‐typed at high‐resolution by next‐generation sequencing (NGS) (NGSgo Workflow and NGSengine from GenDx; sequencing with a Miseq from Illumina) and eplets were determined using HLAMatchmaker. HLA class I specific IgG Ab was assessed in maternal sera drawn immediately after full‐term delivery, by OneLambda LABScreen single antigen ibeads. The Ab profile was subsequently evaluated for eplet‐associated patterns. All 72 currently Ab‐verified HLA class I eplets were examined for their immunogenicity according to the frequency of child‐specific HLA Ab (CSA) directed against their structures. Four hundred twelve of 477 (86.4%) paternal HLA‐A, ‐B or ‐C alleles were mismatched. CSA were present in 46 mothers (28.9%), directed against 80 (19.4%) of these mismatches. The 10 most immunogenic eplets were 62GK, 145KHA, 144TKH, 62GE, 107W, 80I, 82LR, 41T, 127K, 45KE with immunogenicity rates between 45.8% and 27.3%. This pregnancy study also identified five non‐reactive eplets: 62RR, 76ESN, 80TLR, 156DA, 163RW. Based on our results, immunogenic hot and cold spots on the surface of HLA class I molecules were localized and visualized on 3D models. This study strengthens the presumption that different eplets represent different immunogenic potentials. Validation of these results in the clinical transplant setting is an essential next step in identifying those eplets representing a particularly high‐risk potential.

Development of an immunogenicity score for HLA‐DQ eplets: A conceptual study

“…So far, most investigators either reduced the complexity by focusing only on antibody-verified eplets or selected the putative target based on the simplest eplet combination, which was regarded as the most likely one. 9,23,24 Therefore, such approaches have inherent biases. In this study, we aimed to explore the immunogenicity of all HLA-DQ eplets in an unbiased manner.…”

“…Indeed, it is very challenging to clearly determine the targeted eplet based on an antibody reaction pattern. So far, most investigators either reduced the complexity by focusing only on antibody‐verified eplets or selected the putative target based on the simplest eplet combination, which was regarded as the most likely one 9,23,24 . Therefore, such approaches have inherent biases.…”

Matchmaker, matchmaker make me a match: Opportunities and challenges in optimizing compatibility of HLA eplets in transplantation

“…Eplet incompatibility predicts the potential for immune‐mediated injuries, and efforts are underway to identify the most immunogenic eplets (Hönger et al., 2020). Risk of immune‐mediated injuries may be accentuated with re‐exposure to similar HLA eplets.…”

Memory B Cells in Pregnancy Sensitization

“…Subsequent studies which relied on cytotoxic assays later determined the prevalence and timing of pregnancyinduced anti-HLA antibody (4)(5)(6). The advent of singleantigen bead technology has greatly improved detection methods and revealed that pregnancy elicits a paternal HLAreactive antibody response in 50-84% of mothers in the first year after pregnancy that may have HLA epitope bias (6)(7)(8)(9)(10)(11)(12). As in other types of immune exposures, the number of times that a woman is exposed to fetal alloantigen matters, as multiparous females have a higher incidence of paternal HLA-reactive antibodies (7) with strong binding to HLA epitopes (13).…”