Unlike other viruses for which effective vaccines have been developed, HIV-1 has evolved mechanisms to evade immune control over virus replication. These mechanisms include the extraordinary genetic diversity of the virus, viral latency, and targeting of the immune system. Evolutional variations of the envelope gene have not only resulted in the development of different groups (M, N, and O) and subgroups (clades) in diverse geographic regions of the world, but also significant genomic variations within clades. These clade variants of HIV will require novel vaccine approaches to elicit population-based protective immunity. Viral latency is the ability of the virus to remain dormant for long periods through integrating its viral DNA into the host genome. Viral latency requires vaccines to produce immune response that are robust enough to kill the virus and that can be maintained over extended periods of time to produce lasting immunity. Finally, HIV-1 targets CD4 cells and thus compromises the immune surveillance mechanisms critical to maintaining both cellular and humoral immunity to HIV-1. Therefore, an effective vaccine against HIV-1 must bolster the development of broadly reactive neutralizing antibodies against genetic variants of HIV-1, as well as induce an effective HIV-specific CTL response to eliminate virus-infected cells. The ideal vaccine approach will produce long-term responses within these arms of host immunity. This study is designed to evaluate the safety, tolerability, and immunogenicity of a novel prophylactic vaccine consisting of DNA priming followed by a protein boost.

The first vaccine component administered in this study is a DNA vaccination; the second component is a recombinant protein vaccination. This combination will be used to determine whether the vaccine strategy can induce a balanced humoral and cell mediated immune responses to HIV-1.

Two HIV antigens, Gag and Env, are included in this study's vaccine formulation. Studies have shown that HIV-1 Gag is a potent inducer of cell mediated immune responses, while Env is the target of neutralizing antibody responses. The vaccine used in this study contains a 5-valent Env design (Env derived from one of 5 clades of HIV) in order to examine if a polyvalent Env formulation may expand the breadth of neutralizing antibody responses induced in human volunteers. For both DNA priming and protein boosting, a set of Env antigens from clades A, B, C, and E of HIV-1 M group will be produced (2 Env antigens from clade B and 1 Env each from the other three clades). All 5 Env antigens are selected from the primary HIV-1 viral isolates with the hope of producing broad antibody responses against the primary viruses circulating in the worldwide human population.

Thirty-six healthy volunteers will be randomized to one of five groups. Groups 1, 2, and 3 will receive different doses of the vaccine to determine the optimal dose. Groups 4 and 5 will receive the vaccine through either intradermal or intramuscular administration. Each group will receive 3 doses of DNA vaccination at weeks 0, 4, and 12, and 2 doses of protein vaccination at weeks 20 and 28. Blood sampling throughout the duration of the study will provide an assessment of the safety and immunogenicity of the vaccine in healthy volunteers. It is expected that volunteers will be enrolled in this study for 1 year.