Synthesis and assembly of chimeric human immunodeficiency virus gag pseudovirions.

Expression of the HIV Gag precursor in insect cells by recombinant baculoviruses results in the assembly and budding of noninfectious pseudovirions that resemble immature virus. Three strategies for packaging additional viral epitopes into pseudovirions were examined: coinfection of insect cells with individual baculoviruses encoding separate Gag and Env structural genes, inframe Gag-Env fusion proteins, and Gag-frameshift-Env fusion proteins. Electron microscopy and Western blot analysis indicated that neither the coinfection nor the inframe fusion strategies reliably produced large quantities of structurally stable chimeric pseudovirions. The frameshift fusion method utilized the retroviral Gag-Pol ribosomal frameshift mechanism for the coexpression of Gag and Gag-frameshift-Env fusion proteins. Large quantities of pseudovirions containing both the Gag and Env epitopes were produced in insect cells. Mice inoculated with the Gag-frameshift-Env pseudovirions developed cytotoxic lymphocyte responses to both HIV Gag and Env epitopes. Vaccine and immunotherapeutic applications of chimeric pseudovirions are discussed.