In vivo electroporation in DNA-VLP prime-boost preferentially enhances HIV-1 envelope-specific IgG2a, neutralizing antibody and CD8 T cell responses.

Although in vivo electroporation (EP) has been utilized to improve immunogenicity in DNA vaccines alone or in prime-boost regimens with both proteins and viral-vectors, no studies on in vivo EP in DNA-VLP prime-boost regimens against HIV-1 have been reported. Previously we developed stably transfected Drosophila S2 clones to produce HIV-1 virus-like particles (VLP) and demonstrated that priming mice twice with DNA plasmids encoding HIV-1 gp120 and gag and boosting twice with HIV-1 VLP (i.e. DDVV immunization) elicited both envelope-specific antibody and envelope and gag-specific CD8 T cell responses. However, the potency and the breadth of immunogenicity still need to be improved. In this study we tested the effect of in vivo EP during DNA priming on immunogenicity of this DNA-VLP prime-boost regimen. Here we report that although both DDVV and DDVV+EP elicited gp120-specific ELISA-binding antibody responses, average EC50 values of gp120-specific ELISA-binding total IgG, IgG2a, but not IgG1, antibody responses were significantly higher in DDVV+EP than in DDVV. Moreover, while DDVV elicited neutralizing antibody responses against autologous, but not other five, strains tested, DDVV+EP not only elicited significantly higher anti-autologous neutralizing antibody responses, but also cross-neutralizes four of five other HIV-1 strains tested, including two tier 2 strains. Finally, although CD4 and CD8 T cells from both DDVV and DDVV+EP immunizations secreted IFN-γ, IL-2, TNF-α upon HIV-1 envelope peptide stimulation, average HIV-1 envelope-specific CD8 T cells that secreted IFN-γ, IL-2 and/or TNF-α were significantly higher in DDVV+EP than in DDVV. Thus we conclude that DDVV+EP immunization preferentially increases HIV-1 envelope-specific TH1 cytokine-mediated IgG2a responses and significantly enhances the potency and the breadth of neutralizing antibody responses including tier 2 viruses. Further study on this heterologous regimen in large animals is warranted.