Construction and characterization of recombinant VLPs and semliki-forest virus live vectors for comparative evaluation in the SHIV monkey model

For testing of recombinant virus-like particles (VLPs) in the SHIV monkey m odel, SIV(mac)239 Pr56(gag) precursor-based pseudovirions were modified by HIV-1 gp160 derived peptides. First, well-characterized epitopes from the H IV-1 envelope glycoprotein were inserted into the Pr56(gag) precursor by re placing defined regions that were shown to be dispensable for virus particl e formation. Expression of these chimeric proteins in a baculovirus express ion system resulted in efficient assembly and release of non-infectious, hy brid VLPs. In a second approach the HIV-1(IIIB) external glycoprotein gp120 was covalently linked to an Epstein-Barr virus derived transmembrane domai n. Coexpression of the hybrid envelope derivative with the Pr56(gag) precur sor yielded recombinant SIV derived Pr56(gag) particles with the HIV-1 gp12 0 firmly anchored on the VLP surface. Immunization of rhesus monkeys with e ither naked VLPs or VLPs adsorbed to alum induced substantial serum antibod y titers and promoted both T helper cell and cytotoxic T lymphocyte respons es. Furthermore, priming macaques with the corresponding set of recombinant Semliki-Forest viruses tended to enhance the immunological outcome. Challe nge of the immunized monkeys with chimeric SHIV resulted in a clearly accel erated reduction of the plasma viremia as compared to control animals.