Pre-clinical development of a multi-CTL epitope-based DNA prime MVA boost vaccine for AIDS

Reliable and effective methods for induction of cytotoxic T-lymphocytes (CTL) are constantly persued. Central to this search is work in animal models, which allow to test novel vaccine strategies and ultimately lead to a more efficient planning of clinical trials. Here, human immunodeficiency virus (HIV) vaccine candidates were constructed as a string of partially overlapping CTL epitopes (20 human, 3 macaque and 1 mouse) delivered and expressed using plasmid DNA and modified virus Ankara (MVA; an attenuated vaccinia virus), which are both vaccine vehicles acceptable for use in humans. In mice, these vaccines were shown to induce virus-specific interferon-gamma-producing and cytolytic CD8+ T-cells after a single intramuscular needle injection. When immunization protocols were sought which would improve the level of induced HIV-specific T-cells, DNA priming-MVA boosting was found to be the most potent protocol. The multi-epitope DNA also elicited CTL when delivered intradermally using the Accell gene delivery device (gene gun). Finally, a combined intradermal gene gun DNA-MVA vaccination regimen induced in macaques high frequencies of circulating CTL, which were comparable to those observed in simian immunodeficiency virus (SIV)-infected monkeys. Further optimization of this method in non-human primates is under way. Thus, a vaccination regimen for an effective elicitation of CTL has been developed which might facilitate evaluation of the role(s) that these lymphocytes play in the control of SIV and HIV infections.