Not all Mismatches Were Created Equal: Empirical Identification of Regions Within HLA-DQ Molecules That Harbor the Highest Immunogenicity.

Abstract

<h4>Background</h4>HLA-DQ mismatches between donor and recipient confer the highest risk for generation of donor-specific antibodies leading to poor allograft survival. Therefore, understanding hierarchical immunogenicity of HLA-DQ mismatches is needed to guide risk stratification.<h4>Methods</h4>Adsorption/elution experiments were optimized using homozygous cell lines as targets. Serum samples from transplant recipients studied herein were limited to those obtained at first documentation of de novo HLA-DQ donor-specific antibodies.<h4>Results</h4>The use of different HLA-DQ targets in optimized adsorption/elution experiments allowed for separation of sera exhibiting polyclonal antibody reactivity into individual antibodies recognizing epitopes with monospecificity. Our heterogeneous cohort demonstrated only a small repertoire of amino acids, or regions of interest, associated with the initial HLA-DQ humoral response. Most of the mismatches listed in the HLA Eplet Registry did not participate in these first-tier responses. Adsorption/elution studies were instrumental in documenting epitope spreading in patients with broadening of HLA-DQ antibody repertoire, highlighting the occurence of a first-tier response before triggering additional immune responses. Finally, first-tier regions of interest correlate with first-field (low-resolution) HLA typing, namely conventional serologic HLA-DQ antigen families, enriched with DQα chains specificity.<h4>Conclusions</h4>These findings clearly demonstrate that some "molecular mismatches" are more immunogenic than others. They further support our previous observations documenting increased risk of HLA-DQα*05 heterodimer mismatches and provide a tool to continue interrogating differential immunogenicity. Finally, we provide guidance to identify high- and low-risk HLA-DQ mismatches. Taken together, our study supports a different conceptual and experimental framework to study HLA-DQ immunogenicity, and an immunological rationale to guide risk stratification.