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Immunogenicity of native and CD4 liganded monomeric and trimeric envelope glycoproteins based on HIV-1 Subtype C consensus Founder virus sequences
Retrovirologyvolume 9, Article number: P21 (2012)
The ability to induce a broadly neutralizing antibody (bNAb) response following vaccination is regarded as a crucial aspect in developing an effective HIV-1 vaccine. This study describes the design and construction of a subtype C founder virus consensus Env immunogen derived from newly transmitted/founder virus sequences, and its immunogenicity testing in the presence or absence of liganded CD4, in small animals.
Monomeric (gp120), dimeric (gp120GCN4) and trimeric (gp140GCN4 +/-) founder virus conformations were expressed in mammalian cell culture. Unliganded or 2dCD4S60C liganded Env glycoproteins were purified by lectin affinity chromatography, followed by conformation and complex purification using size exclusion chromatography. Immunogens/immune complexes were evaluated by ELISA, SDS-PAGE, Native PAGE and Surface Plasmon Resonance. Immunogenicity of each conformation alone or complexed to 2dCD4S60C was evaluated in rabbits. Breadth and potency of the rabbit sera was tested against 12 pseudoviruses (Tiers 1-3), derived from HIV-1 subtype B and C Env, using the PhenoSense Neutralizing antibody assay (Monogram Bioscience Inc.).
Minimal neutralizing breadth was obtained from animals immunized exclusively with Env conformations. However, animals that received the Env/2dCD4S60C complex showed extensive neutralizing capacity against all 12 viruses tested, including the tier 2 and 3 virus strains. End-point ELISA titre results revealed that the rabbits that were immunized with Env/2dCD4S60C produced both Env and 2dCD4 specific titres, but those directed towards 2dCD4 were on average 10x lower than the 2dCD4 control group. This implies a proportion of the neutralizing antibody activity is directed towards conserved epitopes exposed on the Env/2dCD4S60C immunogens.
The ability to induce bNAb activity in previous immunization studies utilizing Env/CD4 complexes was attributed to the induction of high anti-CD4 titres. By contrast, in our study the relatively low anti-CD4 titres compared to anti-Env titres and neutralization profiles suggest an alternative mechanism of neutralization other than a response directed to CD4 alone.