Vehicles for genetic vaccines against human immunodeficiency virus: induction of T cell-mediated immune responses.

Success of a candidate vaccine against human immunodeficiency virus (HIV) depends on the type, site, strength, longevity and specificity of the immune responses it induces. The specificity of a vaccine is determined by the HIV-derived immunogens it employs in its formulation. Central to the other features is a correct and efficient delivery of the immunogens to the relevant cells of the immune system, which leads to orchestrated actions of millions of cells of several types and functions at multiple sites in the body. Thus, for elicitation of cytotoxic T lymphocyte responses, immunogens have to be delivered to the so called 'professional' antigen-presenting cells in a way that leads to a specific activation and expansion of naïve or precursor T cells, subsequent maturation of effector functions and, importantly, generation of a potent immunological memory. Many aspects of theseprocesses are currently unknown. However, it is very likely that the immunogenicities of genetic vaccines, i.e. vaccines delivering genes coding for immunogens rather than purified possibly adjuvanted proteins or peptides themselves, are in great part determined by the choice of vaccine vehicles and route of administration. In addition, vaccine immunogenicities can be augmented semi-rationally by immunogen engineering and co-delivering immunomodulatory molecules, and empirically by combining different vehicles expressing the same immunogen in heterologous prime-boost protocols. In any case, a successful vaccination strategy against HIV as well as other chronic viral infections has to elicit better immune responses than the natural infections do.