Studies of a prophylactic HIV-1 vaccine candidate based on modified vaccinia virus Ankara (MVA) with and without DNA priming: Effects of dosage and route on safety and immunogenicity

BackgroundTwo parallel studies evaluated safety and immunogenicity of a prophylactic HIV-1 vaccine in 192 HIV-seronegative, low-risk volunteers. Modified vaccinia virus Ankara (MVA) and plasmid DNA (pTHr) expressed HIV-1 clade A gag p24 and p17 fused to a string of 25 overlapping CD8+ T cell epitopes (HIVA).MethodsThese studies compared intramuscular, subcutaneous, and intradermal MVA at dosage levels ranging from 5 × 106–2.5 × 108 pfu. In Study IAVI-010, DNA vaccine was given as a prime at months 0 and 1, followed by MVA as a boost at months 5 and 8. In Study IAVI-011, MVA alone was given at months 0 and 2. Regular safety monitoring was performed. Immunogenicity was measured by the interferon (IFN)-γ ELISPOT assay on peripheral blood mononuclear cells (PBMC).ResultsNo serious adverse events were attributed to either vaccine; most adverse events were mild or moderate, although MVA resulted in some severe local reactions. Five vaccine recipients had at least one positive IFN-γ ELISPOT response, but none were sustained.ConclusionThis HIV-1 vaccine candidate was in general safe and well-tolerated. Local reactions were common, but tolerable. Detectable immune responses were infrequent.