Abstract
Heterologous protein scaffolds engrafted with structurally defined HIV Env epitopes recognized by broadly neutralizing monoclonal antibodies (MAbs) represent a promising strategy to elicit broad neutralizing antibodies. In such regards, a protein scaffold based on the HIV p24 CA protein is a highly attractive approach, providing also Gag epitopes for eliciting HIV non-neutralizing protective antibodies and specific CD4+ and CD8+ T cell responses. In the present study, computational techniques were employed to verify the presence of acceptor sites for conformational HIV Env epitopes and, as proof of concept, the analysis of HIV p24 CA-based scaffolds using a complete V3 loop in a MAb-bound conformation is presented. The V3-p24 epitope-scaffold proteins show the formation of capsomers made of hexamers similarly to the p24 wild type protein. Moreover, the conformational V3 loop presented on p24 scaffold is recognized by a panel of anti-V3 MAbs. The results suggest that HIV p24 CA protein has suitable acceptor sites for engrafting foreign epitopes, without disrupting the formation of capsomer hexamer structures, and that the V3 epitope does retain its antibody-bound conformation. This strongly support the feasibility of developing a scaffolding strategy based on p24 CA proteins displaying conformational minimal structural, antigenic HIV Env epitopes.
Highlights
Efforts to elicit protective immunity to HIV has resulted in unsatisfactory results [1]
Besides the presentation of relevant Env neutralizing epitopes, it would provide Gag epitopes for eliciting HIV non-neutralizing protective antibodies and specific CD4+ and CD8+ T cell responses
Three different monoclonal antibodies (MAbs) specific for the V3 loop sequence have been used in a titration from 10 pg to 10 ng/ml and the results show a clear binding by all three MAbs to the three p24:V3 chimera proteins coated at a concentration of 0.1 mg/ml, suggesting that the V3 loop inserted on the p24 scaffold is was sufficiently exposed and retained the ability to bind to anti-V3 mAbs
Summary
Efforts to elicit protective immunity to HIV has resulted in unsatisfactory results [1]. Strategies to elicit or expand such HIV broadly reactive and cross-clade NAbs are currently pursued by several groups, aiming at focusing the immune response on specific epitopes which can be either immunorecessive, cryptic or transiently exposed To this goal, one of the optimal experimental strategies appears to be the selection of the minimal structural and antigenic epitopes, in order to isolate them from all other potential and confounding B-cell epitopes as well as from the shielding N-linked glycans within the whole HIV envelope glycoprotein [18,19,20,21].
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