INDUCIBLE HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 PACKAGING CELL-LINES

Packaging cell lines are important tools for transferring genes into e ukaryotic cells, Human immunodeficiency virus type 1 (HIV-1)-based pac kaging cell lines are difficult to obtain, in part owing to the proble m that some HIV-I proteins are cytotoxic in a variety of cells, To ove rcome this, we hale del:eloped an HIV-1-based packaging cell line whic h has an inducible expression system. The tetracycline-inducible expre ssion system was utilized to control the expression of the Rev regulat ory protein, which in turn controls the expression of the late protein s including Gag, Pol, and Env, Western blotting (immunoblotting) demon strated that the expression of p24(gag) and gp120(env) from the packag ing cells peaked on days 6 and 7 postinduction, Reverse transcriptase activity could be detected by day 4 after induction and also peaked on days 6 and 7, Defective vector virus could be propagated, yielding ti ters as high as 7 x 10(3) CFU/ml, while replication-competent virus aa s not detectable at any time, Thus, the cell fine should enable the tr ansfer of specific genes into CD4(+) cells and should be a useful tool for studying the biology of HIV-1, We have also established an induci ble HIV-1 Env-expressing cell line which could be used to propagate HI V-1 vectors that require only Env in trans. The env-minus vector virus titer produced from the Env-expressing cells reached 2 x 10(4) CFU/ml , The inducible HIV-1 Env-expressing cell line should be a useful tool for the study of HIV-1 Env as well.