Broad and potent cellular and humoral immune responses after a second late HIV-modified vaccinia virus ankara vaccination in HIV-DNA-primed and HIV-modified vaccinia virus ankara-boosted swedish vaccinees

We have previously shown that an HIV vaccine regimen including three HIV-DNA immunizations and a single HIV-modified vaccinia virus Ankara (MVA) boost was safe and highly immunogenic in Swedish volunteers. A median 38 months after the first HIV-MVA vaccination, 24 volunteers received 10⁸ plaque-forming units of HIV-MVA. The vaccine was well tolerated. Two weeks after this HIV-MVA vaccination, 18 (82%) of 22 evaluable vaccinees were interferon (IFN)-γ enzyme-linked immunospot (ELISpot) reactive: 18 to Gag and 10 (45%) to Env. A median minimal epitope count of 4 to Gag or Env was found in a subset of 10 vaccinees. Intracellular cytokine staining revealed CD4⁺ and/or CD8⁺ T cell responses in 23 (95%) of 24 vaccinees, 19 to Gag and 19 to Env. The frequency of HIV-specific CD4⁺ and CD8⁺ T cell responses was equally high (75%). A high proportion of CD4⁺ and CD8⁺ T cell responses to Gag was polyfunctional with production of three or more cytokines (40% and 60%, respectively). Of the Env-specific CD4⁺ T cells 40% were polyfunctional. Strong lymphoproliferative responses to Aldrithiol-2 (AT-2)-treated subtype A, B, C, and A-E virus were demonstrable in 21 (95%) of 22 vaccinees. All vaccinees developed binding antibodies to Env and Gag. Neutralizing antibodies were detected in a peripheral blood mononuclear cell (PBMC)-based assay against subtype B and CRF01-AE viruses. The neutralizing antibody response rates were influenced by the vaccine dose and/or mode of delivery used at the previous HIV-MVA vaccination. Thus, a second late HIV-MVA boost induced strong and broad cellular immune responses and improved antibody responses. The data support further exploration of this vaccine concept.