Hematopoietic cytokine-inducible gene expression from retroviral vectors.

Retroviral vectors capable of cytokine-inducible gene expression will be useful for a number of gene therapy applications. We explored one mechanism whereby cytokine inducibility may be imparted to the retroviral U3 promoter/enhancer by utilizing the JAK-STAT signal transduction pathway that is activated by a number of hematopoietic cytokines. We used PCR mutagenesis to insert a consensus binding site for the ubiquitous transcription factor Sp1 into the Moloney murine leukemia virus U3 followed by the insertion of multimers of a STAT-binding oligonucleotide with the core sequence 5'-TTCCCGGAA. After insertion of the modified U3s into a retroviral vector expressing the luciferase reporter gene and transduction of the HepG2 cell line, luciferase expression was induced with recombinant human IFN-gamma. The level of induction reached a maximum of 9.9-fold higher than the uninduced vector when the Sp1-U3 contained four STAT oligos. When this optimal vector was compared with the wild-type and Sp1 vectors, respective values of 17.9- and 16.7-fold higher expression were achieved with IFN-gamma treatment. Retroviral vectors incorporating these cytokine-inducible U3s will be useful for gene therapy in a number of situations involving gene transfer to hematopoietic, hepatic and other cytokine-responsive cell types.