Background:  Delivery of HIV genes within recombinant adeno-associated virus (rAAV) protein capsid is a potent inducer of both antibodies and T-cell responses in animal studies. A rAAV-based vaccine (tgAAC09), consisting of single-stranded DNA from clade C HIV-1 genes for the gag, protease, and part of the reverse transcriptase proteins enclosed within a rAAV serotype 2 protein capsid, was developed as 1 potential component of a multi-component HIV vaccine. Our objective was to evaluate the safety and immunogenicity of tgAAC09 in healthy, HIV-seronegative volunteers with low HIV risk.

Methods:  In this dose-escalation study, 80 healthy, HIV-uninfected volunteers (50 in Europe, 30 in India) received a single intra-muscular injection of tgAAC09 at different doses:  3x10⁹ DRP (n = 16), 3x10¹⁰ DRP (n = 23), 3x10¹¹ DRP (n = 25), or placebo (n = 16). In addition, 21 of 50 volunteers in Europe received a boost vaccination of tgAAC09 at a dose of 3x10¹¹ DRP or placebo. T-cell responses were assessed by interferon-gamma (IFN-γ) ELISpot assay, anti-AAV2 neutralizing titers by a cell-based assay, and vaccine shedding by polymerase chain reaction (PCR).

Results:  The vaccine appears to be well tolerated after both initial and boost vaccination. Mild to moderate local and systemic reactogenicity was experienced by approximately 15 to 20% of volunteers. No serious vaccine-related adverse events were reported. The proportion of reactogenicity and adverse events were evenly distributed among the different dose groups and placebo. There was no evidence of vaccine shedding in different anatomical compartments (blood, urine, saliva, semen, vaginal fluid). At baseline, 48% of European volunteers and 95% of Indian volunteers had detectable neutralizing titres against AAV2. The proportion of volunteers with a ≥4-fold rise in anti-AAV2 NT increased with higher doses and after boost vaccination. Dose-dependent HIV-specific T-cell responses were detected in 7 of 64 vaccinees; with 20% (5 of 25) of volunteers in the highest-dose group responding. All responses were to gag epitopes and the magnitude was moderate (39-385 SFC/10⁶ peripheral blood mononuclear cells). No induction of antibody to HIV was observed.

Conclusions:  Vaccination with tgAAC09 appears to be safe and well-tolerated. Immunogenicity data indicated a modest response, which was dose dependent, weak in magnitude, and directed to gag, as expected. Future clinical trials will focus on higher doses of tgAAC09, determining the optimal interval for boost vaccination and effect of pre-existing immunity to AAV2.

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