D-Template Assembled Trimeric Peptide Mimetics of the HIV-1 gp41 Pre-Hairpin Intermediate Induce D5-like Neutralizing Antibody Responses
Chengwei Wu
Scientist, Merck Research Laboratories
Efforts to develop an HIV-1 vaccine have focused on conserved structural elements that are the target of broadly neutralizing monoclonal antibodies (bnMab). The drug Fuzeon® validates the pre-hairpin intermediate (PHI) as an effective therapeutic target in humans. Mab D5, which binds to a highly conserved hydrophobic pocket on the N-Heptad Repeat (NHR) coiled-coil, demonstrates that antibodies directed against the pre-hairpin can be neutralizing. Proceeding from knowledge of the crystal structure of D5 bound to its epitope, peptide immunogens, displayed as highly structured coiled-coil trimers, have evolved from presentation of the minimal epitope sequence (N17) to extended sequences encompassing larger portions of the NHR (N36). Direct comparison of covalently constrained N17 and N36 trimers in rodent immunogenicity studies showed that the longer peptide elicited higher titers of functional neutralizing antibodies, suggesting that neutralizing epitopes outside of the D5 pocket may exist.
Herein, we present work focuses on efforts to further extend coverage of the gp41 NHR region by engineering and testing 51-residue peptides (N51) in the context of covalently stabilized trimers to determine whether increased neutralization potency is realized in animals vaccinated with these constructs. We report the synthesis of six stabilized trimers in which three copies of N51 are covalently attached to a 3-fold symmetric template. We evaluate the peptides in rodent and primate immunogenicity studies and demonstrate their abilities to elicit high peptide-specific antibody responses which neutralize the D5 hypersensitive V570A virus, as well as other clinical HIV-1 clades. We show antiviral potency results for the trimer based on an in vitro viral entry inhibition assay and confirm the ability of D5 to recognize these structures.