Regulated lentiviral packaging cell line devoid of most viral cis-acting sequences.

Packaging cell lines derived from human immunodeficiency virus-1 (HIV-1) are promising tools for in vivo somatic cell gene therapy protocols due to the ability of lentiviruses to infect nondividing cells. We describe here the generation of a safe, stable HIV-1 packaging cell line capable of expressing all of the HIV-1 structural, enzymatic, and regulatory proteins but lacking majority of the cis-acting sequences. The use of an inducible expression system circumvented the cytotoxic and cytostatic effects associated with the expression of some of the HIV-1 viral proteins. Reverse transcriptase activity was detectable in the supernatant from the stable packaging line 1 day after induction, while vector titers peaked 5 days postinduction. Vector titers of up to 3.5 x 10(4) infectious units/ml (IU/ml) were maintained through 8 months following the establishment of the cell line. Lineage-specific gene delivery can be achieved from this established cell line as viral stocks obtained specifically infect CD4(+) target cells. Moreover, this cell line provides a safe and easy to use system for screening of drugs that inhibit HIV-1 replication.