Polyclonal antibody responses to HIV Env immunogens resolved using cryoEM

Here, the authors present cryoEMPEM, a method for high-resolution structural analysis of vaccine-elicited polyclonal antibody responses. They apply cryoEMPEM in combination with standard serology experiments to characterize the polyclonal antibody (pAb) responses elicited in rhesus macaques by HIV Env trimer immunogens and were able to determine up to 8 different polyclonal antibody structures in complex with their respective antigen from a single cryoEM dataset. Engineered ectodomain trimer immunogens based on BG505 envelope glycoprotein are widely utilized as components of HIV vaccine development platforms. In this study, we used rhesus macaques to evaluate the immunogenicity of several stabilized BG505 SOSIP constructs both as free trimers and presented on a nanoparticle. We applied a cryoEM-based method for high-resolution mapping of polyclonal antibody responses elicited in immunized animals (cryoEMPEM). Mutational analysis coupled with neutralization assays were used to probe the neutralization potential at each epitope. We demonstrate that cryoEMPEM data can be used for rapid, high-resolution analysis of polyclonal antibody responses without the need for monoclonal antibody isolation. This approach allowed to resolve structurally distinct classes of antibodies that bind overlapping sites. In addition to comprehensive mapping of commonly targeted neutralizing and non-neutralizing epitopes in BG505 SOSIP immunogens, our analysis revealed that epitopes comprising engineered stabilizing mutations and of partially occupied glycosylation sites can be immunogenic.

Automated summary

The authors proposed a method called cryoEMPEM for high-resolution structural analysis of vaccine-elicited polyclonal antibody responses. By applying this method in rhesus macaques, they were able to determine different polyclonal antibody structures and reveal new epitopes in the immune response.