Modifications of HIV-1 retrovirus-like particles to enhance safety and immunogenicity

HIV-1 retrovirus-like particles can be produced in VERO cells that have bee n transfected with an expression construct encoding HIV-1 structural protei ns. The particles are entirely non-infectious although structurally they re semble infectious virus particles. This makes them a promising candidate fo r use as an HIV-1 vaccine. In order to ensure their safety and enhance thei r immunogenicity, the retrovirus-like particles were modified in a number o f ways. A large deletion in the HIV-1 pol gene has eliminated reverse trans criptase and integrase activities. Deletion of RNA packaging signals in the RNA untranslated leader sequence and in Gag reduced packaged RNA to 5% of that in HIV-1 virus. Replacement of the existing HIV-1(LAI) envelope protei n with that of HIV-1(MN) has ensured that immune responses to the particles are relevant to those against the majority of HIV-1 clade B isolates. In a ddition to these changes in particle composition, yields of the modified pa rticles were increased using a superior method of inducing the expression c onstruct promoter, and an effective scheme for particle purification was de veloped. Immunization of non-human primates demonstrated that the particles were capable of generating anti-HIV-1 neutralizing antibodies. The technol ogical refinements reported here will permit retrovirus-like particles to b e tested safely in humans, and the change in envelope proteins should allow a more realistic evaluation of the immunogenicity of these particles. Expe rience gained in engineering these refinements will greatly facilitate othe r modifications that may be required to achieve maximum efficacy as a vacci ne against HIV-1. (C) 1998 The International Association of Biological Stan dardization.