| abstract |
The present invention features packaging cell lines and recombinant retroviral particles produced thereby, particularly pseudotyped retroviral particles. Preferably, the packaging cell lines are derived from HeLa, Cf2Th, D17, MDCK, or BHK cells, most preferably from Cf2Th cells. Retroviral particles are produced by inducibly expressing an envelope protein of interest (e.g., a retroviral envelope or the envelope protein of vesicular stomatitis virus (VSV G)). Inducible expression of the envelope protein is accomplished by operably linking an envelope protein-encoding nucleotide sequence to an inducible promoter (e.g., a promoter composed of a minimal promoter linked to multiple copies of tetO, the binding site for the tetracycline repressor (tetR) of the Escherichia coli tetracycline resistance operon Tn10). Expression from the inducible promoter is regulated by a multi-chimeric transactivating factor, composed of a first ligand-binding domain that negatively regulates transcription from the inducible promoter (e.g., a prokaryotic tetracycline repressor polypeptide (tetR)), a transcriptional activation domain, and a second ligand-binding domain (e.g., a ligand-binding domain of a steroid receptor, preferably an estrogen receptor (ER)). |