Selection and Analysis of HIV-1 Envelope Epitopes for Design of Vaccines that can Induce Broadly Neutralizing Antibodies
HIV-1 vaccines are designed to mimic the structure and contextual elements of viral epitopes that have the potential to induce broadly neutralizing antibodies (bnAbs) in vivo. The structure of gp41 membrane proximal external region (MPER), targeted by three bnAbs, is poorly defined. The goal of this study is to select epitopes with enhanced binding to MPER bnAbs, to identify neutralization-competent structures by characterizing the function of epitope-specific antibodies in vivo and to determine if these selected MPER epitopes can be used to broaden the immune response as potential vaccines.MPER epitopes were selected by biopanning with phage-displayed peptide libraries against bnAbs 4E10, 2F5 and Z13. Epitopes were screened in antigen competition binding assays where M13-displayed epitopes competed with HIV-1 envelope peptides or infectious HIV-1 particles for antibody binding. In vivo response to MPER was assessed by M13 immunoprecipitation and neutralization competition assays using HIV-positive plasma. Immunogenicity of select epitopes was determined by immunization of mice and elicited cellular and humoral immune responses were assessed.Unique 4E10, and known 2F5 and Z13, epitopes were selected from M13 phage display libraries, which were able to compete with envelope peptide and HIV-1 for antibody binding. 4E10 and 2F5 epitopes were found to be immunogenic during HIV-1 infection; of the twelve HIV+ patient plasma tested, 100% and 58% reacted with phage-displayed 4E10 and 2F5 MPER epitopes, respectively. 4E10-epitopes were capable of absorbing MPER-specific neutralizing antibodies in HIV+ plasma. Mouse immunization with selected, neutralization-competent MPER epitopes elicited HIV-1 specific cellular and humoral immune responses and boosted the neutralizing activity of a gp145 protein subunit vaccine.Unique 4E10 epitopes, that represent functional HIV-1 envelope trimers, were identified. Chronically HIV-infected individuals generate neutralizing antibodies to a subset of the selected MPER-variant epitopes. These M13-displayed 4E10 epitopes have the potential to elicit HIV-1 neutralizing antibodies in mice. Increasing the range of antibody recognition to MPER, potentially by vaccination with multiple MPER variant epitopes, will be the key to improve HIV-1 vaccine design.
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