Enhanced simian immunodeficiency virus-specific immune responses in macaques induced by priming with recombinant Semliki Forest virus and boosting with modified vaccinia virus Ankara

The immunogenicity of two vector-based vaccines, either given alone or in a prime-boost regimen, was investigated. Cynomolgus macaques were immunised with modified vaccinia virus Ankara (MVA) expressing simian immunodeficiency virus (SIV)macJ5 env, gag–pol, nef, rev, and tat genes (MVA–SIVmac) or pr... Full description

The immunogenicity of two vector-based vaccines, either given alone or in a prime-boost regimen, was investigated. Cynomolgus macaques were immunised with modified vaccinia virus Ankara (MVA) expressing simian immunodeficiency virus (SIV)macJ5 env, gag–pol, nef, rev, and tat genes (MVA–SIVmac) or primed with a Semliki forest virus (SFV) vaccine expressing the same genes (SFV–SIVmac) and boosted with MVA–SIVmac. Generally, antibody responses, T-cell proliferative responses and cytotoxic T-cell responses remained low or undetectable in vaccinees receiving MVA–SIVmac or SFV–SIVmac alone. In contrast, monkeys who first received SFV–SIVmac twice and then were boosted with MVA–SIVmac showed increased antibody responses as well as high T-cell proliferative responses. Three of these vaccinees had cytotoxic T-lymphocytes directed against three or four of the gene products. No evidence of protection was seen against an intrarectal heterologous SIVsm challenge given 3 months after the last immunisation. The study demonstrates a prime-boost strategy that efficiently induces both humoral and cellular immune responses.