REGULATED EXPRESSION OF ARTIFICIAL CHIMERIC GENES CONTAINED IN RETROVIRAL VECTORS - IMPLICATIONS FOR VIRUS-DIRECTED ENZYME PRODRUG THERAPY (VDEPT) AND OTHER GENE-THERAPY APPLICATIONS

Replication-defective retroviral vectors were created that contained c himeric genes composed of either the albumin (ALB) or the alpha-fetopr otein (AFP) transcriptional regulatory sequences linked to the coding domain of the thymidine kinase gene from Varicella tester virus (VZV T K). These viruses were used to infect the human hepatoblastoma cell li ne, HepG2. Subsequent to infection, the infected cells were single-cel l cloned. The level of expression of VZV TK from the chimeric genes co rrelated with the level of endogenous expression of ALB or AFP in most clones, indicating that the transcription of the chimeric VZV TK gene is controlled in a similar manner to the endogenous ALB or AFP genes, and that sites of viral integration are less important to overall gene expression. Most importantly, as the expression of the endogenous ALB gene was modified, so was expression of VZV TK from the ALB/VZV TK ch imeric gene. This demonstrates that retroviruses can deliver a chimeri c gene containing tissue-specific transcriptional regulatory sequences that can respond to endogenous cell regulatory signals resulting in r egulated gene expression.