HIV-1 Vaccine Development:  Constrained Peptide Immunogens Show Improved Binding to the Anti-HIV-1 gp41 MAb

Abstract

The human immunodeficiency virus type I (HIV-1) transmembrane glycoprotein gp41 mediates viral entry through fusion of the target cellular and viral membranes. A segment of gp41 containing the sequence Glu-Leu-Asp-Lys-Trp-Ala has previously been identified as the epitope of the HIV-1 neutralizing human monoclonal antibody 2F5 (MAb 2F5). The 2F5 epitope is highly conserved among HIV-1 envelope glycoproteins. Antibodies directed at the 2F5 epitope have neutralizing effects on a broad range of laboratory-adapted HIV-1 variants and primary isolates. Recently, a crystal structure of the epitope bound to the Fab fragment of MAb 2F5 has shown that the 2F5 peptide adopts a beta-turn conformation [Pai, E. F., Klein, M. H., Chong, P., and Pedyczak, A. (2000) World Intellectual Property Organization Patent WO-00/61618]. We have designed cyclic peptides to adopt beta-turn conformations by the incorporation of a side-chain to side-chain lactam bridge between the i and i + 4 residues containing the Asp-Lys-Trp segment. Synthesis of extended, nonconstrained peptides encompassing the 2F5 epitope revealed that the 13 amino acid sequence, Glu-Leu-Leu-Glu-Leu-Asp-Lys-Trp-Ala-Ser-Leu-Trp-Asn, maximized MAb 2F5 binding. Constrained analogues of this sequence were explored to optimize 2F5 binding affinity. The solution conformations of the constrained peptides have been characterized by NMR spectroscopy and molecular modeling techniques. The results presented here demonstrate that both inclusion of the lactam constraint and extension of the 2F5 segment are necessary to elicit optimal antibody binding activity. The ability of these peptide immunogens to stimulate a high titer, peptide-specific immune response incapable of viral neutralization is discussed in regard to developing an HIV-1 vaccine designed to elicit a 2F5-like immune response.

An oligosaccharide-based HIV-1 2G12 mimotope vaccine induces carbohydrate-specific antibodies that fail to neutralize HIV-1 virions

“…A more plausible cause is that conformational f lexibility in the oligomannan arms is still high, and the immune response is ''diluted'' by recognition of improper structures within the chemical space. This complicating factor has been proposed as a reason for the inability to mimic the broad neutralizing characteristics of other HIV-1-directed mAbs (4,10,33).…”

“…For several of these mAbs, identification and extensive characterization of the neutralizing epitopes have been realized (4)(5)(6)(7). This structural knowledge has been used to design antigens intended to direct the primary immune response toward the neutralizing epitope (8)(9)(10). However, in all immunization studies performed to date these vaccine candidates have failed to elicit broadly neutralizing antibodies.…”

Immunogenicity of recombinant human immunodeficiency virus type 1-like particles expressing gp41 derivatives in a pre-fusion state

“…In addition to simple linear or structurally constrained peptide immunogens, recombinant protein immunogens including displays of constrained 2F5 epitope in the contexts of various protein scaffolds have been also pursued [28][29][30][31][32][33][34][35][36][37]. While inducing high antibody titers against the primary amino acid sequence of the epitope, these immunogens have failed to elicit NAbs against primary HIV-1.…”

Quaternary protein mimetics of gp41 elicit neutralizing antibodies against HIV fusion‐active intermediate state

“…10,20,[23][24][25][26] First, synthetic peptide antigens representing monomeric gp41 peptides are conformationally unstable. Since stability and bioactive conformation are intimately associated with trimeric quaternary structure, they are difficult to duplicate using monomeric peptides.…”

“…Consequently, attempts to exploit these peptides as immunogens, alone or with additional variable regions, have been unsuccessful. [23][24][25][26] Golding et al 10 and Louis et al 20 showed that antibodies gp41 Protein Mimetics Elicit Neutralizing Antibodies 321 generated against complexed peptides or engineered trimeric peptides based on the N-HR or C-HR domains possess viral neutralizing activity. These results suggest that targeting the bioactive conformations of the N-HR or C-HR domains is a viable vaccine design strategy.…”