Abstract
SummaryCharacterizing polyclonal antibody responses via currently available methods is inherently complex and difficult. Mapping epitopes in an immune response is typically incomplete, which creates a barrier to fully understanding the humoral response to antigens and hinders rational vaccine design efforts. Here, we describe a method of characterizing polyclonal responses by using electron microscopy, and we applied this method to the immunization of rabbits with an HIV-1 envelope glycoprotein vaccine candidate, BG505 SOSIP.664. We detected known epitopes within the polyclonal sera and revealed how antibody responses evolved during the prime-boosting strategy to ultimately result in a neutralizing antibody response. We uncovered previously unidentified epitopes, including an epitope proximal to one recognized by human broadly neutralizing antibodies as well as potentially distracting non-neutralizing epitopes. Our method provides an efficient and semiquantitative map of epitopes that are targeted in a polyclonal antibody response and should be of widespread utility in vaccine and infection studies.
Highlights
Vaccines are composed of killed or attenuated pathogens or protein subunits derived from the pathogen surface
The target for HIV broadly neutralizing antibodies (bnAbs) is the metastable envelope (Env) antigen, which consists of the two glycoproteins gp120 and gp41 arranged in a3(gp41)3 trimeric assembly and sits on the surface of the viral particle
Stabilization is required for the generation of a recombinant molecule (SOSIP) that mimics the native trimer on the virus, and these recombinant trimers bind bnAbs and are antigenically native (Binley et al, 2000; Sanders et al, 2002, 2013)
Summary
Vaccines are composed of killed or attenuated pathogens or protein subunits derived from the pathogen surface. Most successful vaccines are based on these approaches, highly antigenically variable pathogens, such as HIV, and pathogens that circulate in the population as a large number of serotypes have proven less tractable. A different approach based on isolating functional antibodies to the pathogen by studying their interaction with their targets and designing vaccine candidates has been described (Burton, 2002, 2017; McLellan et al, 2013; Rappuoli and De Gregorio, 2016; Walker et al, 2009). The target for HIV bnAbs is the metastable envelope (Env) antigen, which consists of the two glycoproteins gp120 and gp arranged in a (gp120)3(gp41) trimeric assembly and sits on the surface of the viral particle. Engineered proteins have been designed to stimulate the precursor B cells of bnAbs (Briney et al, 2016; Escolano et al, 2016; Jardine et al, 2015; Medina-Ramırez et al, 2017; Sok et al, 2016; Steichen et al, 2016) and help advance structureguided vaccine development against HIV according to the use of sequential immunogens (Escolano et al, 2016)
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