Vaccines targeting SIV protease cleavage sites (PCSs) or full Gag and Env proteins.
(A) Diagram of the twelve protease cleavage sites (PCS1 through PCS12), located on three SIV polyproteins (Pr55Gag, Pr160Gag-Pol and Nef precursor), not drawn to scale. MA: matrix; CA: capsid; NC: nucleocapsid; TFP: transframe protein; PR: protease; RT: reverse transcriptase; and IN: integrase. (B) Peptide sequences of SIV immunogens in a conserved element vaccine targeting the PCSs (the PCS vaccine). Each sequence corresponds to -10 through +10 amino acid positions flanking each cleavage site. Slash (/) indicates the site of protease cleavage. These sequences were confirmed to be specific for SIV by NCBI protein BLAST and conserved among multiple SIV strains. The peptide immunogens were delivered as recombinant vesicular stomatitis viruses (rVSVpcs) and nanoparticles (NANOpcs). Peptide antigens with these sequences were also used in a Bio-Plex multiplexed assay to detect anti-PCS antibodies. (C) Sequences of three Gag or Env (non-PCS) peptides used in Bio-Plex to detect anti-Gag or Env antibodies, including one Gag peptide, named SIVgag, and two Env peptides, named SIVenv1 and SIVenv2. (D) Western blot analyses of protein expression from a full-length Gag and Env-based vaccine (the Gag/Env vaccine). VeroE6 cells were infected with recombinant vesicular stomatitis viruses (rVSVs) carrying full Gag or Env gene of SIVmac239 (rVSVgag/env) and the culture supernatants were analyzed by Western blot to detect Gag or Env protein expression using standard monoclonal antibodies (mAb, NIH AIDS Reagent Program) to Gag or Env. The full Gag and Env genes were also cloned into pVAX1 (a DNA vaccine vector), respectively, followed by NANO packaging (NANOgag/env). HEK293T cells were transfected with these DNA vaccines and analyzed by Western blot. (E) Vaccination scheme. Three groups (Control, PCS vaccine and Gag/Env vaccine) of eight female MCMs per group were primed and boosted on indicated weeks (wk). The Control group received empty rVSV virus and sterile water. One animal from the Gag/Env vaccine group was euthanized early due to severe health issues unrelated to vaccination, leaving seven animals in this group to complete the study. rVSV control vector (rVSV), rVSVpcs or rVSVgag/env was administered intramuscularly. NANO control vector (sterile water), NANOpcs or NANOgag/env was administered intranasally.