An effective HIV vaccine capable of inducing broadly neutralizing antibodies remains a significant goal in combating the HIV/AIDS epidemic. Recent discovery of a new class of glycan-reactive broadly neutralizing antibodies (bNAbs), represented by PG9, PG16, PGT121, and PGT128, has shed light on design of novel epitope-based vaccine. These bNAbs neutralize primary HIV-1 strains with remarkable breadth and potency and appear to target glycopeptide epitopes located in the variable domains (V1/V2 or V3) of HIV-1 gp120. Mutational, biochemical and structural studies suggest that the epitopes of PG9 and PG16 are glycopeptides consist of two N-glycans (at the N160 and N156/N173 glycosylation sites) and a patch of peptide in the V1/V2 domain, while the epitopes of PGT128 appear to involve the N-glycans at the N332 and N301 sites. However, further characterization of the glycan specificity was complicated by the heterogeneity in glycosylation of gp120. We used a synthetic approach to constructing homogeneous V1V2 and V3 glycopeptides carrying defined glycans for further defining the glycan specificity, which led to the identification of a cyclic glycopeptide epitope carrying a Man5GlcNAc2 glycan at N160 and a sialylated N-glycan at N156/N173 site as the minimal epitopes for PG9/PG16. We also designed and synthesized cyclic V3 glycopeptides that confirm the essence of a Man9/Man8GlcNAc2 glycan at the N332 site for PGT128 recognition. With the ability to reconstitute these glycopeptide epitopes via synthesis, we propose to design novel immunogens and hypothesize that displaying the glycopeptide epitopes on bacteriophage Qb (a well-characterized virus-like particle) in a highly ordered repetitive pattern will lead to immunogens capable of eliciting glycopeptide-specific neutralizing antibodies. We will test this hypothesis through pursuing three specific aims.
Aim 1 is to design and synthesize Qb-based immunogens carrying polyvalent V1V2 and V3 glycopeptide epitopes. Construction of the immunogens includes chemoenzymatic synthesis of alkyne-glycopeptides and their subsequent conjugation with azide-tagged Qb via the copper-catalyzed azide-alkyne cycloaddition (CuAAC) click reaction;
Aim 2 is to evaluate the antigenicity of the synthetic immunogens by antibody binding studies;
and Aim 3 is to evaluate the immunogenicity of the synthetic vaccines in rabbits. The anti-sera from immunized rabbits are analyzed by ELISAs and viral neutralization assays. These experiments will assess the magnitude, breadth and duration of neutralizing antibody responses from immunizations with the glycopeptide epitope-based immunogens. This study is likely to yield important new insights in the design of a truly effective HIV-1 vaccine.

Public Health Relevance

A truly effective vaccine is the best hope to combat the global HIV/AIDS epidemic that threatens human health and social stability. The proposed research aims to design and test novel immunogens based on the newly identified glycopeptide epitopes of broadly neutralizing antibodies, which will provide important new information to speed up HIV vaccine development.

Agency
National Institute of Health (NIH)
Institute
National Institute of Allergy and Infectious Diseases (NIAID)
Type
Research Project (R01)
Project #
5R01AI113896-03
Application #
9097520
Study Section
Special Emphasis Panel (ZAI1)
Program Officer
Singh, Anjali
Project Start
2014-07-11
Project End
2019-06-30
Budget Start
2016-07-01
Budget End
2017-06-30
Support Year
3
Fiscal Year
2016
Total Cost
Indirect Cost
Name
University of Maryland College Park
Department
Type
DUNS #
790934285
City
College Park
State
MD
Country
United States
Zip Code
20742
Cai, Hui; Zhang, Rou-Shu; Orwenyo, Jared et al. (2018) Synthetic HIV V3 Glycopeptide Immunogen Carrying a N334 N-Glycan Induces Glycan-Dependent Antibodies with Promiscuous Site Recognition. J Med Chem 61:10116-10125
Li, Chao; Wang, Lai-Xi (2018) Chemoenzymatic Methods for the Synthesis of Glycoproteins. Chem Rev 118:8359-8413
Toonstra, Christian; Wu, Lisa; Li, Chao et al. (2018) Top-Down Chemoenzymatic Approach to Synthesizing Diverse High-Mannose N-Glycans and Related Neoglycoproteins for Carbohydrate Microarray Analysis. Bioconjug Chem 29:1911-1921
Cai, Hui; Orwenyo, Jared; Giddens, John P et al. (2017) Synthetic Three-Component HIV-1 V3 Glycopeptide Immunogens Induce Glycan-Dependent Antibody Responses. Cell Chem Biol 24:1513-1522.e4
Cai, Hui; Orwenyo, Jared; Guenaga, Javier et al. (2017) Synthetic multivalent V3 glycopeptides display enhanced recognition by glycan-dependent HIV-1 broadly neutralizing antibodies. Chem Commun (Camb) 53:5453-5456
Freund, Natalia T; Wang, Haoqing; Scharf, Louise et al. (2017) Coexistence of potent HIV-1 broadly neutralizing antibodies and antibody-sensitive viruses in a viremic controller. Sci Transl Med 9:
Yang, Mingjun; Huang, Jing; Simon, Raphael et al. (2017) Conformational Heterogeneity of the HIV Envelope Glycan Shield. Sci Rep 7:4435
Orwenyo, Jared; Cai, Hui; Giddens, John et al. (2017) Systematic Synthesis and Binding Study of HIV V3 Glycopeptides Reveal the Fine Epitopes of Several Broadly Neutralizing Antibodies. ACS Chem Biol 12:1566-1575
Toonstra, Christian; Amin, Mohammed N; Wang, Lai-Xi (2016) Site-Selective Chemoenzymatic Glycosylation of an HIV-1 Polypeptide Antigen with Two Distinct N-Glycans via an Orthogonal Protecting Group Strategy. J Org Chem 81:6176-85
Wang, Denong; Tang, Jin; Tang, Jiulai et al. (2015) Targeting N-glycan cryptic sugar moieties for broad-spectrum virus neutralization: progress in identifying conserved molecular targets in viruses of distinct phylogenetic origins. Molecules 20:4610-22