Introduction: Broad spectrum neutralizing antibodies against HIV-1 are essential for the development of a humoral anti-AIDS vaccine. We used fusion complexes and CD4-independent gp120 as new immunogens to induce neutralizing antibodies blocking the infectivity of different primary isolates of HIV-1.
Methods: Spleen cells from mice immunized with fusion complexes were used to prepare murine hybridomas. Secreted antibodies were screened for their neutralizing activity using the pseudovirus standard neutralization assay. In parallel, the immunogenicity of CD4-independent Env, on which conserved epitopes might be exposed, has been tested.
Results: Among antibodies secreted by hybridoma clones, 8% showed a neutralizing activity higher than 40% (1 μg/ml), and the best ones showed neutralization levels as high as 80% against the pseudovirus B panel, reaching neutralization levels similar or higher than the Tri-mAb control. 10 hybridoma clones showing 80% or higher neutralization levels were selected and re-cloned by limiting dilutions. Panel C evaluation is ongoing. Preliminary results using a 1:1000 sera dilution from mice immunized with CD4-independent Env showed a neutralizing activity of 40-60% and, as expected, a 2-3 folds neutralization increase in the presence of sCD4.
Conclusions: Monoclonal antibodies obtained by immunizing with fusion complexes showed a broad spectrum neutralizing activity against all panel B pseudoviruses, as well as against a group of selected laboratory isolates. Sera from mice immunized with CD4-independent Env showed neutralizing activity against heterologous Envs that increases in the presence of sCD4, suggesting the elicitation of antibodies against the conserved coreceptor binding site. In conclusion, fusion complexes and CD4-independent Env represent potential new immunogens that can induce neutralizing antibodies with activity against a wide panel of HIV-1 isolates.