Evaluation in rabbits of different anti‐SHIV vaccine strategies based on DNA/fowlpox priming and virus‐like particle boosting

Two different prime‐boost immunization protocols were tested in rabbits and their immune response was evaluated and compared with the final aim of defining a vaccine strategy that might be able to protect non‐human primates from infection with the pathogenic simian/human immunodeficiency virus, SHIV 89.6P . The two regimens were based on three priming immunizations with either an expression plasmid plus a fowlpox (FP) recombinant vector or with two FP recombinant vectors, each one expressing either the SIV mac239 gag / pol or the HIV‐1 env 89.6P genes. In both protocols, priming immunizations were followed by two boosts with SHIV‐mimicking virus‐like particles (VLP). A complete SHIV‐specific response was observed in all animals. Interestingly, the DNA vaccine was three to 10 times more efficient than the FP recombinant in inducing an anti‐ gag humoral response. Real‐time PCR confirmed the memory effect on T‐cell subsets secreting interleukin‐4 and interferon‐γ, as a consequence of stimulation of both arms of the immune system. Although both protocols were almost equally effective in eliciting homologous neutralizing antibodies and highlighted the efficacy of VLP administration for boosting, protocol A seemed to be more effective in promoting a balanced T‐cell memory immune response and appears more promising for vaccine purposes.