RELEASE OF VIRUS-LIKE PARTICLES FROM CELLS INFECTED WITH POLIOVIRUS REPLICONS WHICH EXPRESS HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 GAG

The effectiveness of attenuated poliovirus vaccines when given orally to induce both systemic and mucosal immune responses against polioviru s has resulted in an effort to develop poliovirus-based vectors to exp ress foreign proteins. We have previously described the construction o f poliovirus genomes (referred to as replicons) in which the complete human immunodeficiency virus type 1 (HIV-1) gag gene was substituted f or the capsid gene (P1) (D. C. Porter, D. C. Ansardi, and C. D. Morrow , J. Virol. 69:1548-1555, 1995). Infection of cells with encapsidated replicons resulted in the expression of a 55-kDa protein. To further c haracterize the biological features of the HIV-1 Gag proteins expresse d in cells infected with encapsidated replicons, we utilized biochemic al analysis and electron microscopy. Expression of tbe 55-kDa protein in cells infected with encapsidated replicons resulted in myristylatio n of the pr55(gag) protein. The Gag precursor protein was released fro m infected cells; analysis on sucrose density gradients revealed that the precursor sedimented at a density consistent with that of an HIV-1 virus-like particle. Analysis of replicon-infected cells by electron microscopy demonstrated the presence of condensed structures at the pl asma membrane and the release of virus-like particles. These studies d emonstrate that poliovirus-based vectors can be used to express foreig n proteins which require posttranslational modifications, such as myri stylation, and assemble into higher-order structures, providing a foun dation for the future use of poliovirus replicons as vaccine vectors.