Broad and potent immune responses to a low dose intradermal HIV-1 DNA boosted with HIV-1 recombinant MVA among healthy adults in Tanzania

Abstract

Background: We conducted a phase I/II randomized placebo-controlled trial with the aim of exploring whether priming with a low intradermal dose of a multiclade, multigene HIV-1 DNA vaccine could improve the immunogenicity of the same vaccine given intramuscularly prior to boosting with a heterologous HIV-1 MVA among healthy adults in Dar es Salaam, Tanzania.

Methods: Sixty HIV-uninfected volunteers were randomized to receive DNA plasmid vaccine 1mg intradermally (id), n=20, or 3.8mg intramuscularly (im), n=20, or placebo, n=20, using a needle-free injection device. DNA plasmids encoding HIV-1 genes gp160 subtype A, B, C; rev B; p17/p24 gag A, B and Rtmut B were given at weeks 0, 4 and 12. Recombinant MVA (10(8)pfu) expressing HIV-1 Env, Gag, Pol of CRF01_AE or placebo was administered im at month 9 and 21.

Results: The vaccines were well tolerated. Two weeks after the third HIV-DNA injection, 22/38 (58%) vaccinees had IFN-γ ELISpot responses to Gag. Two weeks after the first HIV-MVA boost all 35 (100%) vaccinees responded to Gag and 31 (89%) to Env. Two to four weeks after the second HIV-MVA boost, 28/29 (97%) vaccinees had IFN-γ ELISpot responses, 27 (93%) to Gag and 23 (79%) to Env. The id-primed recipients had significantly higher responses to Env than im recipients. Intracellular cytokine staining for Gag-specific IFN-γ/IL-2 production showed both CD8(+) and CD4(+) T cell responses. All vaccinees had HIV-specific lymphoproliferative responses. All vaccinees reacted in diagnostic HIV serological tests and 26/29 (90%) had antibodies against gp160 after the second HIV-MVA boost. Furthermore, while all of 29 vaccinee sera were negative for neutralizing antibodies against clade B, C and CRF01_AE pseudoviruses in the TZM-bl neutralization assay, in a PBMC assay, the response rate ranged from 31% to 83% positives, depending upon the clade B or CRF01_AE virus tested.

Conclusions: This vaccine approach is safe and highly immunogenic. Low dose, id HIV-DNA priming elicited higher and broader cell-mediated immune responses to Env after HIV-MVA boost compared to a higher HIV-DNA priming dose given im. Three HIV-DNA priming immunizations followed by two HIV-MVA boosts efficiently induced Env-antibody responses.

Fig. 1

Profile of trial participants showing 258 who attended pre-screening sessions, 162 screened to obtain 60 enrolled, 59 who received three HIV-DNA/placebo vaccinations, 50 who received the first HIV-MVA/placebo vaccinations and 42 who received the second HIV-MVA/placebo vaccinations.

Fig. 2

HIV-specific interferon-γ ELISpot responses in responders (cut-off SFC was >55 spots/10⁶ peripheral blood mononuclear cells and 4 times the background and the baseline value): (a) two weeks after three HIV-DNA injections by id group; (b) two weeks after three HIV-DNA injections by im group; (c) two weeks after the first HIV-MVA boost in the DNA id-primed group and (d) two weeks after the first HIV-MVA boost in the DNA im-primed group; (e) two to four weeks after the second HIV-MVA boost in the DNA id-primed group and (f) two to four weeks after the second HIV-MVA boost in the DNA im-primed group.

Fig. 3

Lymphoproliferation (LPA) against AT-2 inactivated HIV-1 antigen measured by the [³H]-thymidine uptake assay (cut-off ≥ 6 SI) in HIVIS03 vaccinees at baseline, two weeks after three HIV-DNA vaccinations, two weeks after the first HIV-MVA boost and two weeks after the second HIV-MVA boost.

Fig. 4

Correlation between Gag WR reactivity in IFN-γ ELISpot and HIV CM responses in LPA in 50 HIVIS03 volunteers two weeks after the first HIV-MVA immunization (r² = 0.414, p < 0.001).

Fig. 5

Magnitude of HIV-specific CD4⁺ and CD8⁺ T cell responses to Gag assessed by a 4-colour IFN-γ/IL-2 ICS assay four weeks after the second HIV-MVA boost in samples from vaccinees primed with HIV-DNA id or im.