Vaccination with DNA is an attractive strategy for induction of pathogen-specific T cells and
antibodies. Studies in humans have shown that DNA vaccines are safe, but their immuno-
genicity needs further improvement. As a step towards this goal, we have previously dem-
onstrated that immunogenicity is increased with the use of an alphavirus DNA-launched
replicon (DREP) vector compared to conventional DNA vaccines. In this study, we investi-
gated the effect of varying the dose and number of administrations of DREP when given as
a prime prior to a heterologous boost with poxvirus vector (MVA) and/or HIV gp140 protein
formulated in glucopyranosyl lipid A (GLA-AF) adjuvant. The DREP and MVA vaccine con-
structs encoded Env and a Gag-Pol-Nef fusion protein from HIV clade C. One to three ad-
ministrations of 0.2
μ
g DREP induced lower HIV-specific T cell and IgG responses than the
equivalent number of immunizations with 10
μ
g DREP. However, the two doses were equal-
ly efficient as a priming component in a heterologous prime-boost regimen. The magnitude
of immune responses depended on the number of priming immunizations rather than the
dose. A single low dose of DREP prior to a heterologous boost resulted in greatly increased
immune responses compared to MVA or protein antigen alone, demonstrating that a mere
0.2
μ
g DREP was sufficient for priming immune responses. Following a DREP prime, T cell
responses were expanded greatly by an MVA boost, and IgG responses were also expand-
ed when boosted with protein antigen. When MVA and protein were administered simulta-
neously following multiple DREP primes, responses were slightly compromised compared
to administering them sequentially. In conclusion, we have demonstrated efficient priming
of HIV-specific T cell and IgG responses with a low dose of DREP, and shown that the prim-
ing effect depends on number of primes administered rather than dose.