Viral protein R (Vpr) is a 14kD, 96 amino acid accessory protein of the HIV virion that has been demonstrated to have important functions in the viral replication cycle including, among others, the induction of cell cycle arrest and apoptosis in rapidly proliferating cells, which results in immune dysfunction in infected individuals. Several investigators have studied the potential use of the apoptosis inducing and cell cycle arrest effect of Vpr as an anti-tumor therapeutic. In vitro studies have indicated that Vpr is cytotoxic against a large number of different tumor cell types including a number that are p53 independent. Likewise, some in vivo tumor studies using different delivery platforms/methods have indicated an anti-cancer effect mediated by Vpr. Our group has used the aggressive and poorly immunogenic murine melanoma tumor line B16.F10 as a model to deliver, through in vivo electroporation, Vpr expressing plasmids to established tumors and have demonstrated that this treatment regimen can induce growth attenuation and tumor regression in a proportion of the treated mice and appears to be associated with the induction of intratumoral apoptosis. Overall, to date, the data from a number of research groups, including our own, have indicated that Vpr has biological activity against a number of tumors in both in vivo and in vitro models and, as such, may be a potential candidate for testing in human clinical trials. In this report, we summarize the evidence supporting this hypothesis.

Summary Nucleic acid immunization is an important vaccination strategy which delivers DNA constructs encoding for a specific immunogen into the host. These expression cassettes transfect the host cells, which become the in vivo protein source for the production of antigen. This antigen then is the focus of the resulting immune response. This vaccination technique is being explored as an immunization strategy against a variety of infectious diseases as well as cancer. The first generation DNA immunization experiments have shown that the DNA vaccines' ability to elicit humoral and cellular responses in vivo in a safe and well-tolerated manner in various model systems, including humans. As we explore the next generation of DNA vaccines, our goal is to refine the current strategy to elicit more clinically efficacious immune responses. A more clinically effective vaccine may need to elicit a more specific immune response against the targeted pathogen. It would be a distinct advantage to design immunization strategies which can be "focused" according to the correlates of protection known for the particular pathogen. In order to focus the immune responses induced from DNA immunization, we have investigated the co-delivery of genes for immunologically important molecules, such as costimulatory molecules and cytokines which play critical regulatory and signaling roles in immunity. We and others have shown that the use of these molecular adjuvants could enhance and modulate immune responses induced by DNA immunogens. Co-administration of costimulatory molecules (CD80 and CD86), proinflammatory cytokines (IL-1 , TNF- , and TNF- ), Th1 cytokines (IL-2, IL-12, IL-15, and IL-18), Th2 cytokine (IL-4, IL-5 and IL-10), and GM-CSF with DNA vaccine constructs led to modulation of the magnitude and direction (humoral or cellular) of the immune responses. These studies demonstrate the potential utility of molecular adjuvant strategy as an important tool for the development of more rationally designed vaccines.

Nucleic acid immunization has been investigated as immunotherapy for infectious diseases as well as for treating specific types of cancers. In this approach, nucleic acid expression cassettes are directly inoculated into the host, whose transfected cells become the production source of novel and possibly immunologically foreign protein. We have developed a DNA vaccine construct which encodes for PSA by cloning a cDNA for PSA into a mammalian expression vector under control of a CMV promoter. We investigated and characterized the immunogenicity of PSA DNA expression cassettes in mice. PSA-specific immune responses induced in vivo by immunization were characterized by enzyme-linked immunosorbent assay (ELISA), T helper proliferation cytotoxic T lymphocyte (CTL), and flow cytometry assays. We observed a strong and persistent antibody response against PSA for at least 180 days following immunization. In addition, a significant T helper cell proliferation was observed against PSA protein. Using synthetic peptides spanning the PSA open frame, we identified four dominant T helper epitopes of PSA. Furthermore, immunization with PSA plasmid induced MHC Class I CD8+ T cell-restricted cytotoxic T lymphocyte response against tumor cell targets expressing PSA. The prostate represents a very specific functional organ critical for reproduction but not for the health and survival of the individual. Understanding the immunogenicity of PSA DNA immunization cassettes offers insight into the possible use of this tumor-associated antigen as a target for immunotherapy. These results demonstrate the ability of the genetic PSA to serve as a specific immune target capable of generating both humoral and cellular immune responses in vivo.

The human immunodeficiency virus-1 (HIV-1) is a retrovirus which preferentially infects and kills CD4+ T cells and macrophages, ultimately resulting in immune system failure and multi-pathogen infections. Recent breakthroughs in combination therapy using three different anti-retroviral agents have generated optimism regarding the ability to control viral replication in vivo [46]. However, this therapeutic regimen is costly, and it is too early to tell whether this approach can eradicate established infection [26, 46]. The costs and the stringent administration regimen requirements of these pharmaceutical agents make it clear that these drugs will only be effectively utilized in a limited part of the world population. Therefore, to address the worldwide problem of HIV-1 infection, there remains a need for a prophylactic vaccination strategy designed to control the epidemic through mass immunization campaigns [115].