Thursday, November 21, 2024
11/21/2024
Elicitation of cross-neutralizing Abs (cNAbs) to inhibit entry of diverse clinical HIV isolates following Env vaccination remains a high priority to develop a broadly effective vaccine, but the elicitation of cNAbs against cross-conserved Env determinants has been elusive. However, very recently we accomplished an important initial step in this process. We primed rabbits with immunization of native flexibly linked (NFL) trimer-liposomes containing targeted N-glycan deletions proximal to the highly conserved CD4 binding site (CD4bs) to better activate B cell responses to this region. The engineered gaps in the N-glycan shield were gradually restored by heterologous sequential boosting. We elicited cross-neutralizing activity in the serum and purified IgG of selected animals and, subsequently, cloned two cNAbs. The cNAb most relevant to this proposal, E70, provides proof-of- principle for a fundamentally different approach. The CD4bs-directed E70 is relatively potent against multiple tier 2 isolates and, importantly, recognizes approximately 50% of N-glycan as part of its epitope as well as adjacent conserved polypeptide that is part of the CD4bs. (The 2nd mAb, 1C2, is a broadly neutralizing antibody (bNAb), neutralizing 80% of a 40 isolate panel and is directed to the gp41:gp120 interface.) The high-resolution cryoEM structure of the E70 epitope on the NFL native-like trimer provides critical preliminary data on how to train the immune system to recognize other N-glycans proximal to the conserved protein surface of the CD4bs to mediate cross-neutralization of tier 2 isolates. We call this approach “N-glycan baiting”. For this approach, we will leave one selected N-glycan proximal to the CD4bs intact as “the bait” while removing all other proximal N- glycans on the initial priming immunogens. The priming will be performed at 6 individual N-glycan sites that ring the conserved CD4bs protein surface. This allows a given cell receptor to recognize chimeric epitopes comprised of the “anchor glycan” and surrounding conserved polypeptide. With boosting, all N-glycans are eventually restored in a step-wise manner, limiting angles of approach to a given N-glycan bait to regenerate the intact N- glycan shield while still driving a subset of B cells directed to the original anchor glycan and protein as a chimeric, non-self-epitope. This strategy fundamentally differs from our original approach in targeting the receptor binding site by full deletion of all proximal N-glycans. Accordingly, the major objective of this grant is to generate novel HIV trimeric Env immunogens by structure-based design, containing N-glycan deletions at the CD4bs but to retain individual “anchor glycans”. We will first characterize the N-glycan-anchored priming immunogens by state-of-the-art biophysical methods (Aim 1). Next, we will determine immunogenicity in small animals in Aims 2 and 3, including neonates. Following targeting of the N-glycan shield in small animals, we will perform non- human primate (NHP) immunogenicity and challenge (Aim 4). If we are successful at N-glycan baiting at the CD4bs, we can apply this approach to other sites on the HIV Env, essentially turning the protective N-glycan shield against the virus as a target of neutralization as is often done by the remarkable HIV-elicited bNAbs.
HHS’ Tracking Accountability in Government Grants System (TAGGS) website provides access to detailed descriptions of grants, loans, aggregated direct payments and other types of financial assistance awarded by the HHS Operating Divisions (OPDIVs) and the Office of the Secretary Staff Divisions (STAFFDIVs).
