According to their capacity to replicate in vitro, human immunodeficiency virus (HIV) isolates can be divided into two major groups, rapid/high and slow/low. Rapid/high viruses can easily be transmitted to a variety of cell lines of T-lymphoid (CEM, H9, and Jurkat) and monocytoid (U937) origin. In contrast, slow/low viruses replicate transiently, if at all, in these cell lines. Except for a few isolates, the great majority of slow/low viruses replicate in peripheral blood mononuclear cells and Jurkat-tatIII cells constitutively expressing the tatlIl gene of HIV-1. The viruses able to replicate efficiently cause syncytium formation and are regularly isolated from immunodeficient patients. Poorly replicating HIV isolates, often obtained from individuals with no or mild disease, show syncytium formation and single-cell killing simultaneously or, with some isolates, cell killing only.

We have previously shown that macaques vaccinated with DNA vectors expressing SIVmac239 antigens developed potent immune responses able to reduce viremia upon high-dose SIVmac251 challenge. To further improve vaccine-induced immunity and protection, we combined the SIVmac239 DNA vaccine with protein immunization using inactivated SIVmac239 viral particles as protein source. Twenty-six weeks after the last vaccination, the animals were challenged intrarectally at weekly intervals with a titrated dose of the heterologous SIVsmE660. Two of DNA-protein coimmunized macaques did not become infected after 14 challenges, but all controls were infected by 11 challenges. Vaccinated macaques showed modest protection from SIVsmE660 acquisition compared with naïve controls (P = 0.050; stratified for TRIM5α genotype). Vaccinees had significantly lower peak (1.6 log, P = 0.0048) and chronic phase viremia (P = 0.044), with 73% of the vaccinees suppressing viral replication to levels below assay detection during the 40-wk follow-up. Vaccine-induced immune responses associated significantly with virus control: binding antibody titers and the presence of rectal IgG to SIVsmE660 Env correlated with delayed SIVsmE660 acquisition; SIV-specific cytotoxic T cells, prechallenge CD4 + effector memory, and postchallenge CD8 + transitional memory cells correlated with control of viremia. Thus, SIVmac239 DNA and proteinbased vaccine protocols were able to achieve high, persistent, broad, and effective cellular and humoral immune responses able to delay heterologous SIVsmE660 infection and to provide long-term control of viremia. These studies support a role of DNA and protein-based vaccines for development of an efficacious HIV/AIDS vaccine.T he use of a combination vaccine consisting of the recombinant Canarypox ALVAC-HIV (vCP1521; containing Gag, PR, and Env) together with gp120 Env protein (AIDSVAX B/E) resulted in modest, but statistically significant protection from infection in the RV144 vaccine trial conducted in Thailand (1). The limited efficacy and the fact that the vaccine-induced responses waned over time suggest that improved vaccine designs are needed to achieve long-lasting cross-clade-specific immune responses able to prevent infection. Rhesus macaque simian immunodeficiency virus (SIV) challenge models provide an excellent system to test different vaccine modalities and to compare efficacy using different challenge viruses and infection routes.DNA as priming immunization together with boosting by recombinant viral vectors is a vaccine platform widely used in the HIV/SIV field. DNA as the only vaccine component has been considered poorly immunogenic in humans, although recent results showed that in vivo DNA electroporation (EP) results in more efficient vaccine delivery, a higher frequency of responders, and higher, longer-lasting immunity than needle/syringe delivery (2). Similarly, the inclusion of DNA encoding the cytokine IL-12 as molecular adjuvant has been shown to be advantageous (3). These recent data suggest that DN...

We have tested the efficacy of DNA immunization as a single vaccination modality for rhesus macaques followed by highly pathogenic SIVmac251 challenge. To further improve immunogenicity of the native proteins, we generated expression vectors producing fusion of the proteins Gag and Env to the secreted chemokine MCP3, targeting the viral proteins to the secretory pathway and to a ␤-catenin (

Intramuscular injection of macaques with an IL-12 expression plasmid (0.1 or 0.4 mg DNA/animal) optimized for high level of expression and delivered using in vivo electroporation, resulted in the detection of systemic IL-12 cytokine in the plasma. Peak levels obtained by day 4-5 post injection were paralleled by a rapid increase of IFN-γ, indicating bioactivity of the IL-12 cytokine. Both plasma IL-12 and IFN-γ levels were reduced to basal levels by day 14, indicating a short presence of elevated levels of the bioactive IL-12. The effect of IL-12 as adjuvant together with an SIVmac239 DNA vaccine was further examined comparing two groups of rhesus macaques vaccinated in the presence or absence of IL-12 DNA. The IL-12 DNA-adjuvanted group developed significantly higher SIV-specific cellular immune responses, including IFN-γ (+) Granzyme B (+) T cells, demonstrating increased levels of vaccine-induced T cells with cytotoxic potential, and this difference persisted for 6 mo after the last vaccination. Coinjection of IL-12 DNA led to increases in Gag-specific CD4 (+) and CD4 (+) CD8 (+) double-positive memory T cell subsets, whereas the Env-specific increases were mainly mediated by the CD8 (+) and CD4 (+) CD8 (+) double-positive memory T cell subsets. The IL-12 DNA-adjuvanted vaccine group developed higher binding antibody titers to Gag and mac251 Env, and showed higher and more durable neutralizing antibodies to heterologous SIVsmE660. Therefore, co-delivery of IL-12 DNA with the SIV DNA vaccine enhanced the magnitude and breadth of immune responses in immunized rhesus macaques, and supports the inclusion of IL-12 DNA as vaccine adjuvant.

We used optimized DNA expression vectors to compare two gene delivery methodologies in rhesus macaques, namely direct DNA injection and in vivo adaptive constant-current electroporation via the intramuscular route. The use of in vivo electroporation increased levels of gene expression and immune responses. We used an optimized HIV gag expression plasmid to show the development of new cellular immune responses in SIV-infected animals controlling viremia. Furthermore, after vaccination with SIV expression plasmids the recall responses to the SIV antigens were very high, indicating that DNA is a strong boost in the presence of antiretroviral treatment in SIV-infected animals. There was substantial animal-to-animal variability in DNA expression, revealed by plasma measurements of IL-15 produced by co-injected IL-15 DNA. IL-15 expression levels correlated with peak immune responses. Electroporation led to an expansion of antigen-specific CD4+ and CD8+ T cells of both central and effector memory phenotype. These results indicate that improved gene delivery and expression by electroporation dramatically increases immunogenicity of DNA vaccines. Electroporation is thus an important method to improve the effectiveness of DNA vaccination.