Molecular and biological characterization of simian-human immunodeficiency virus-like particles produced by recombinant fowlpox viruses

Virus-like particles (VLPs) mimicking the simian-human immunodeficiency virus SHIV 89.6P (VLP SHIV) were produced by co-infection of Vero cells with fowlpox SIV gag/ pol (FP gag/ pol SIV) and fowlpox HIV-1 env 89.6P (FP env 89.6P) recombinant viruses. As a necessary prerequisite for a more efficient vaccine approach, ultrastructural, functional and molecular characterizations of VLP SHIV were performed in the SHIV-macaque model to verify the similarity of these particles to SHIV 89.6P. Here we show that VLP SHIV can infect T cells by fusion without replication, as demonstrated by the absence of new viral progeny in VLP SHIV-infected C8166 cells. Biochemical characterization showed identical protein profiles of VLP SHIV and SHIV 89.6P, and ultrastructural analysis of Vero cells releasing VLP SHIV also confirmed the morphological similarity of these pseudovirions to SHIV 89.6P particles. Viral mRNAs were also found packaged inside the core of VLP SHIV by RT-PCR and reverse transcriptase assays.