Redirecting antibody epitope specificity with HIV-1 ENV-based immunization

The National Institute of Allergy and Infectious Diseases awarded The Wistar Institute of Anatomy and Biology $887,239 on May 1, 2026, under the Allergy and Infectious Diseases Research program (CFDA 93.855) to investigate epitope switching in HIV-1 antibody responses and optimize vaccine design strategies that redirect antibody specificity toward broadly neutralizing targets.

The research addresses a major barrier to HIV-1 vaccine development: the immunodominance of non-neutralizing antibodies targeting the GP41 base of envelope (Env) trimers, which fail to neutralize virus because the base is occluded on the viral surface. Wistar's preliminary data show that antibody lineages can switch epitope specificity through somatic hypermutation—V3-glycan broadly neutralizing antibody lineages can lose track to become base-targeting antibodies, and conversely, base antibodies can be redirected to neutralizing V3-glycan epitopes. The project will characterize "derailed" and "rescued" antibodies, investigate mechanisms driving on-target-to-off-target and off-target-to-on-target switches, and use these findings to design vaccine approaches that prevent antibody derailment and recycle non-neutralizing responses into broadly neutralizing antibodies.

Performance runs through April 30, 2031, at Philadelphia, PA. Swarthmore College serves as sub-recipient, with Dr. Fera providing structural characterization of HIV-1 Env-antibody interactions using cryo-electron microscopy and X-ray crystallography, training personnel, designing and supervising experiments, and directing the structural research components. In years 3 and 4, Swarthmore will support Dr. Fera's sabbatical leave to dedicate full effort to research, with NIH funding covering the second semester of salary and benefits.

Abstract

The main barrier to developing an efficacious HIV-1 vaccine is the requirement of eliciting broadly neutralizing antibodies (BNABS) targeting neutralization-sensitive epitopes of the envelope (ENV) glycoprotein. A major problem is the frequent and overwhelming induction of non-neutralizing antibody responses directed to the GP41 base of ENV when using soluble ENV trimers as immunogens. These off-target antibodies fail to neutralize HIV- 1, as the ENV base is occluded by the viral surface and not accessible for antibody recognition in HIV-1 virions. The base of soluble ENV immunogens has been shown to be immunodominant in preclinical animal models and humans, where base antibodies have derailed multiple clinical trials. Despite numerous attempts to occlude the ENV base using glycans, membrane-bound ENV and nanoparticle scaffolds, the immunodominance of the base persists. Interestingly, our preliminary studies show that the specificity of anti-ENV antibody lineages is not fixed, instead, antibody lineages can switch their epitope specificity through somatic hypermutation in response to immunization with ENV. In particular, we show that V3-glycan bnab lineages can lose track to become base antibodies and that base antibodies can be redirected to target the neutralizing V3-glycan epitope. Thus, we hypothesize that bnab precursors can be derailed from maturing into BNABS and that non-neutralizing antibodies can be rescued to mature into BNABS through immunization. Here, we will investigate this phenomenon of epitope switching from on-target to off-target epitopes and vice versa through characterization of "derailed" and "rescued" antibodies. We will investigate the on-target to off- target switch to inform vaccine design strategies that prevent antibody switching towards the ENV base. We will investigate the off-target to on-target switch to design vaccine approaches that recycle base responses to induce BNABS. In aim 1, we will investigate the mechanisms of epitope switching from the neutralizing V3-glycan epitope of ENV to the base using mouse models. In aim 2, we will investigate the mechanism of epitope switching from the base to the neutralizing V3-glycan epitope and the potential of "rescued" antibodies to mature into BNABS in mouse models. In aim 3, we will investigate whether other bnab lineages and other off-target antibodies can undergo epitope switching too. We have produced nine new humanized and rhesus-ized mouse models and innovative AI-generated immunogens that we will leverage for these specific aims. Structural approaches will be used to characterize the molecular mechanisms of epitope switching. These aims will inform immunogen design strategies to keep bnab lineages on track after initial activation and to "rescue" off-target responses. Collectively, this proposal will investigate previously overlooked challenges for HIV-vaccine design and will bring new opportunities not only for HIV vaccines but for vaccine design in general.