System for simultaneous tissue-specific and disease-specific regulation of therapeutic gene expression

Gene therapy has been proposed as an alternative strategy for treating nongenetic disorders, such as cancer and coronary artery disease. However, for many of these types of diseases, the therapeutic genes must be tightly regulated, as extensive toxicity and pathology can result if their expression is not adequately controlled. Toward this end, we have developed a regulatory system in which the expression of a therapeutic transgene is controlled simultaneously by both a tissue-specific promoter and a disease-specific promoter. Thus, the transgene of interest will be expressed in a given cell only if both of these promoters are active. Unlike many other transgene-regulatory systems that have been previously developed, this system does not require the persistent expression of any foreign genes that could provoke an immune response or lead to toxicity. As proof of concept, we synthesized a construct harboring the lacZ transgene that is under the control of both the hepatocyte-specific human alpha(1)-antitrypsin promoter and the zinc-inducible mouse metallothionein promoter. We show that reporter gene expression from this construct is regulated in both a hepatocyte-specific and zinc-regulated manner, as reporter gene expression occurs only in hepatocyte-derived cells that have been exposed to zinc. The improved regulation offered by our system would facilitate the targeting of transgene expression to sites of disease in the body and spare healthy tissue, thereby considerably enhancing the therapeutic window of gene therapy.