The Use of Retroviral Vectors for tet-Regulated Gene Expression in Cell Populations

Today the treatment of inherited diseases holds a major field in gene therapy, and γ -retroviral vectors are often the preferred tool for stable introduction of the therapeutic gene(s) into the host cell genome. In many cases, the newly introduced gene has to be constitutively expressed, since enzyme function often is required at all times. However, in some cases gene function might be demanded only transiently, making a strict control of gene expression necessary. For more than a decade, the tet-system has proven to facilitate such strict control by tightly regulating gene expression, thereby assuring high expression levels in almost all organs and tissues. Yet, most of these results were obtained from the analysis of either selected cell clones or transgenic animals. On the contrary, in case of conditional gene expression, as necessary for gene therapy approaches, the use of genetically modified cell populations, where the majority of cells display similar regulatory properties, is required. Therefore, great effort has been undertaken to design viral vectors carrying the response unit that enables homogenous regulation of gene expression in transduced cell populations. This article summarizes critical points that have to be considered for the conditional regulation of gene expression in cell populations mediated by the tet-system. Examples of the required vector elements and tet-system components as well as advice on the handling of the system are given. These tools have been specifically developed to improve population-based gene regulation.