EXPRESSION OF HIV-1 ENVELOPE GLYCOPROTEINS BY SEMLIKI FOREST VIRUS VECTORS

We have used Semliki Forest virus (SFV) vectors to express both the hu man immunodeficiency virus type 1 (HIV-1) envelope precursor gp160 and the cleaved external portion gp120. Expression of the foreign gene in this system is by transfection of recombinant SFV RNA, or by infectio n with a recombinant SFV virus that has a wide host range. pSFV1-gp120 or pSFV1-gp160 were expressed in baby hamster kidney (BHK) cells and two human cell lines: HeLa cervical carcinoma and MOLT-4 CD4+ T cells. After SFV1-gp120 infection of HeLa cells, 3.3 mug of gp120 was secret ed into the media by 1 million cells in a 24-hr period. The secreted e nvelope glycoprotein was recognized by anti-gp120 monoclonal antibodie s directed against both linear and conformation-dependent epitopes in different regions of the molecule. The recombinant gp120 also bound to a soluble form of the CD4 receptor. Syncytium formation was observed when MOLT-4 cells were infected with SFV1-gp160. The gp160 expressed b y BHK cells induced syncytia during cocultivation with C8166 CD4+ T ce lls. These data indicate that SFV vectors can be used to produce the H IV-1 envelope glycoproteins to high levels, and that these proteins ar e correctly processed, folded, and transported to the cell surface. Fu rthermore, they exhibit functional activity as indicated by their abil ity to bind to soluble receptor and induce cell-to-cell fusion.