Synthesis and Immunological Evaluation of Pentamannose-Based HIV-1 Vaccine Candidates

Abstract

Dense glycosylation and the trimeric conformation of the human immunodeficiency virus-1 (HIV-1) envelope protein limit the accessibility of some cellular glycan processing enzymes and end up with high-mannose-type N-linked glycans on the envelope spike, among which the Man 5 GlcNAc 2 structure occupies a certain proportion. The Man 5 GlcNAc 2 glycan composes the binding sites of some potent broadly neutralizing antibodies, and some lectins that can bind Man 5 GlcNAc 2 show HIV-neutralizing activity. Therefore, Man 5 GlcNAc 2 is a potential target for HIV-1 vaccine development. Herein, a highly convergent and effective strategy was developed for the synthesis of Man 5 and its monofluoromodified, trifluoro-modified, and S-linked analogues. We coupled these haptens to carrier protein CRM197 and evaluated the immunogenicity of the glycoconjugates in mice. The serological assays showed that the native Man 5 conjugates failed to induce Man 5 -specific antibodies in vivo, while the modified analogue conjugates induced stronger antibody responses. However, these antibodies could not bind the native gp120 antigen. These results demonstrated that the immune tolerance mechanism suppressed the immune responses to Man 5 -related structures and the conformation of glycan epitopes on the synthesized glycoconjugates was distinct from that of native glycan epitopes on gp120.

Synthesis and Immunological Study of N-Glycan-Bacteriophage Qβ Conjugates Reveal Dominant Antibody Responses to the Conserved Chitobiose Core

“…In a related study, Krauss and co-workers have shown that 2G12 epitope mimics consisting of oligomannose glycopeptide conjugates, which lack the chitobiose core, elicit antibodies targeting the glycan core instead of the external mannose moieties. , The immune response to the mannose core is attributed partially to the fact that endogenous α-mannosidases trim the outer mannose residues in the immunogens during the immunization. , More recently, Ye and co-workers have reported the synthesis and mouse immunization of the CRM197 conjugates of the Man5 core and its fluorinated derivatives that lack the chitobiose core . They have shown that the Man5-CRM197 conjugate failed to raise any measurable glycan-specific antibody responses; the fluorinated Man5-CRM197 conjugates stimulate moderate Man5-dependent antibody responses, but they do not show any cross-reactivity toward native HIV-1 gp120 expressing natural Man5GlcNAc2 epitope.…”

“…45,46 More recently, Ye and co-workers have reported the synthesis and mouse immunization of the CRM197 conjugates of the Man5 core and its fluorinated derivatives that lack the chitobiose core. 68 They have shown that the Man5-CRM197 conjugate failed to raise any measurable glycan-specific antibody responses; the fluorinated Man5-CRM197 conjugates stimulate moderate Man5-dependent antibody responses, but they do not show any crossreactivity toward native HIV-1 gp120 expressing natural Man5GlcNAc2 epitope. The immune dominance of the chitobiose core as well as the immune tolerance of the extended N-glycan structures, as observed in the present and other related studies, poses a challenge to raise N-glycanspecific antibodies through conventional glycoconjugate vaccine design and immunization.…”

Drug Discovery Based on Fluorine-Containing Glycomimetics

“…Studies have shown that inoculating different mixtures of immunogens with the same epitope can improve the antibody’s affinity toward antigen epitopes. Based on this, our research group developed a highly convergent and effective synthesis strategy for Man5 and its monofluoro-modified, trifluoro-modified, and S-linked analogs, which could be combined with CRM197 to develop an anti-HIV vaccine candidate [ 166 ]. The results revealed that the modified analogs elicited strong antibody responses.…”