Immunogenicity and safety of the vaccinia virus LC16m8Δ vector expressing SIV Gag under a strong or moderate promoter in a recombinant BCG prime-recombinant vaccinia virus boost protocol

We compared the effect of the very strong pSFJ1-10 and moderately strong p7.5 promoters on the immunogenicity and pathogenicity of the replication-competent vaccinia virus (VV) LC16m8Δ (m8Δ) vector harboring the SIV gag gene in a vaccination regimen consisting of a recombinant BCG-SIVGag (rBCG-SIVGag) prime followed by a recombinant vaccinia boost. m8Δ/pSFJ/SIVGag synthesized more Gag protein than m8Δ/p7.5/SIVGag but replicated less efficiently in vitro. In addition, m8Δ/pSFJ/SIVGag was less pathogenic and elicited Gag-specific IFN-γ+, CD107a+, CD8+ cells more efficiently than m8Δ/p7.5/SIVGag. Vaccination by this regimen elicited long-lasting Gag-specific CD8+ T cells, the majority of which showed a CCR7− phenotype at over 8 weeks post-boost. Tetramer staining analyses revealed maintenance of Gag specific tetramer+, CD62L−, CD8+ T cells for long time in vaccinated mice. However, Gag expression increased the neurotoxicity of the vaccinia vector, indicating the necessity of safety testing for each recombinant VV. We propose that this recombinant BCG prime-m8Δ/pSFJ/HIVGag boost regimen would be a promising vaccination procedure for preventing HIV infection.