Priming with plasmid DNAs expressing interleukin-12 and simian immunodeficiency virus gag enhances the immunogenicity and efficacy of an experimental AIDS vaccine based on recombinant vesicular stomatitis virus.

Of the various approaches being developed as prophylactic HIV vaccines, those based on a heterologous plasmid DNA prime, live vector boost vaccination regimen appear especially promising in the nonhuman primate/simian-human immunodeficiency virus (SHIV) challenge model. In this study, we sought to determine whether a series of intramuscular priming immunizations with a plasmid DNA vaccine expressing SIVgag p39, in combination with plasmid expressed rhesus IL-12, could effectively enhance the immunogenicity and postchallenge efficacy of two intranasal doses of recombinant vesicular stomatitis virus (rVSV)-based vectors expressing HIV-1 env 89.6P gp160 and SIVmac239 gag p55 in rhesus macaques. In macaques receiving the combination plasmid DNA prime, rVSV boost vaccination regimen we observed significantly increased SIVgag- specific cell-mediated and humoral immune responses and significantly lower viral loads postintravenous SHIV89.6P challenge relative to macaques receiving only the rVSV vectored immunizations. In addition, the plasmid DNA prime, rVSV boost vaccination regimen also tended to increase the preservation of peripheral blood CD4+ cells and reduce the morbidity and mortality associated with SHIV89.6P infection. An analysis of immune correlates of protection after SHIV89.6P challenge revealed that the prechallenge SHIV-specific IFN-gamma ELISpot response elicited by vaccination and the ability of the host to mount a virus-specific neutralizing antibody response postchallenge correlated with postchallenge clinical outcome. The correlation between vaccine-elicited cell-mediated immune responses and an improved clinical outcome after SHIV challenge provides strong justification for the continued development of a cytokine-enhanced plasmid DNA prime, rVSV vector boost immunization regimen for the prevention of HIV infection.

Immunogenicity of attenuated vesicular stomatitis virus vectors expressing HIV type 1 Env and SIV Gag proteins: comparison of intranasal and intramuscular vaccination routes.

An experimental AIDS vaccine based on attenuated, recombinant vesicular stomatitis virus (rVSV), when administered by a combination of parenteral and mucosal routes, has proven effective at preventing AIDS in a rhesus macaque model (Rose NF, et al.: Cell 2001;106:539-549). In an effort to determine the optimal route of vaccine administration we evaluated the ability of rVSV-based vaccine vectors expressing HIV-1 Env and SIV Gag proteins, when given either intramuscularly (i.m.) or intranasally (i.n.), to elicit antigen-specific cellular and humoral immune responses, and to protect from a subsequent vaginal challenge with simian-human immunodeficiency virus (SHIV89.6P). Our results demonstrate that macaques vaccinated by the i.n. route developed significantly higher antigen-specific cellular immune responses as determined by MHC class I tetramer staining, IFN-gamma ELISPOT, and cytotoxic T cell assays. However, systemic and mucosal humoral immune responses did not vary significantly with the route of vaccine administration. Given the importance of cell-mediated immune responses in slowing AIDS progression, intranasal delivery of a VSV-based AIDS vaccine may be an optimal as well as practical route for vaccination and should be considered in design of clinical trials.

Comparative ability of plasmid IL-12 and IL-15 to enhance cellular and humoral immune responses elicited by a SIVgag plasmid DNA vaccine and alter disease progression following SHIV(89.6P) challenge in rhesus macaques.

Plasmid-based IL-12 has been demonstrated to successfully enhance the immunogenicity of DNA vaccines, thus enabling a reduction of the amount of DNA required for immunization. IL-15 is thought to affect the maintenance and enhance effector function of CD8(+) memory T cells. Since the ability to elicit a long-term memory response is a desirable attribute of a prophylactic vaccine, we sought to evaluate the ability of these plasmid-based cytokines to serve as vaccine adjuvants in rhesus macaques. Macaques were immunized with plasmid DNA encoding SIVgag in combination with plasmid IL-12, IL-15, or a combination of IL-12 and IL-15. The plasmid-based cytokines were monitored for their ability to augment SIVgag-specific cellular and humoral immune responses and to alter the clinical outcome following pathogenic SHIV(89.6P) challenge. Macaques receiving SIVgag pDNA in combination with plasmid IL-12 alone, or in combination with plasmid IL-12 and IL-15, demonstrated significantly elevated cell-mediated and humoral immune responses resulting in an improved clinical outcome following virus challenge compared to macaques receiving SIVgag pDNA alone. Macaques receiving SIVgag pDNA in combination with plasmid IL-15 alone demonstrated minor increases in cell-mediated and humoral immune responses, however, the clinical outcome following virus challenge was not improved. These results have important implications for the continued development of plasmid DNA vaccines for the prevention of HIV-1 infection.

A dose sparing effect by plasmid encoded IL-12 adjuvant on a SIVgag-plasmid DNA vaccine in rhesus macaques.

An experimental pDNA vaccine adjuvant expressing IL-12 was evaluated for its ability to augment the humoral and cellular immune responses elicited by a SIVmac239 gag p39 expressing pDNA vaccine. To determine the effect of vaccine dose on the immune response, rhesus macaques were immunized with 1.5 mg or 5.0 mg of SIVmac239 gag pDNA, with or without co-immunization of IL-12 pDNA at 1.5 mg and 5.0 mg, respectively. Serum antibody responses to simian immunodeficiency virus (SIV) gag were increased 10-fold (p=0.044, 0.002) in macaques receiving IL-12 pDNA. Cellular immune responses, monitored by SIV gag-specific IFN-gamma ELISpot assay, were also significantly higher (p=0.007, 0.019) when the pDNA vaccine was co-immunized with IL-12 pDNA at high and low doses. There was no statistical difference between the immune responses elicited by the high and low dose of IL-12 pDNA (p=0.221, 0.917), a finding which could allow a dose reduction of vaccine without the concomitant loss of imunogenicity. Furthermore, analysis of the breadth of the T-cell response during the vaccination schedule, using overlapping peptides to SIV gag, demonstrated a significant correlation (p=0.0002) between the magnitude and breadth of the immune responses in the vaccines. These results have important implications for the continuing development of an effective, safe low dose pDNA vaccine adjuvant suitable for human use.

A comparative evaluation of nasal and parenteral vaccine adjuvants to elicit systemic and mucosal HIV-1 peptide-specific humoral immune responses in cynomolgus macaques.

Cynomolgus macaques were immunized by either the intramuscular (i.m.) or intranasal (i.n.) route with a HIV-1 peptide-based immunogen (C4-V3 89.6P) alone, or formulated with novel adjuvants to evaluate the ability of the adjuvants to augment peptide-specific systemic and mucosal immune responses. A mutant cholera toxin, CT-E29H, or the combination of recombinant human IL-1alpha (rhIL-1alpha) protein and recombinant human GM-CSF (rhGM-CSF) protein were tested as adjuvants for i.n. immunization, while a stable emulsion of a synthetic monophosphoryl lipid A (MPL) analogue (RC529-SE) plus rhGM-CSF protein was tested as an adjuvant for i.m. immunization. Macaques immunized i.n. with peptide alone failed to elicit an anti-C4-V3 89.6P antibody response in serum. In contrast, all the tested peptide/adjuvant formulations elicited peptide-specific immune responses. RC529-SE/rhGM-CSF elicited the highest peak anti-peptide IgG geometric mean titer in serum (1:32,768 at week 25) followed by rhIL-1alpha/rhGM-CSF (1:1217 at week 10) and CT-E29H (1:256 at week 25). Measurable SHIV neutralizing antibody responses were detectable in only one macaque immunized i.m. with peptide formulated with RC529-SE/rhGM-CSF. Macaques immunized by the i.n. route with peptide in combination with CT-E29H failed to elicit measurable antibody responses at nasal or genital mucosal surfaces. In contrast, antibody responses at the nasal and genital mucosa were detected in macaques immunized by the i.n. route with peptide in combination with rhIL-1alpha/rhGM-CSF. However, antibody responses at the nasal and genital mucosa were highest in macaques immunized parenterally with peptide in combination with the adjuvants RC529-SE/rhGM-CSF. These results suggest that parenteral vaccine administration in combination with the appropriate adjuvant formulation can elicit vaccine-specific humoral immune responses in both systemic and mucosal compartments.