title: Selectable bicistronic vectors in skin gene therapy.
abstract: Bicistronic vectors (BCV) are important tools for gene therapy applications allowing selection for increased expression of a desired gene by linking it to a selectable gene, such as the multi-drug resistance (MDR) gene. However, both the design of the BCV and the cell type to be transduced can have a strong impact on the vector performance in the target cells. To analyze which factors might influence the efficiency of BCV in achieving high gene expression levels in skin and to determine the best suited BCV for cutaneous transduction, both keratinocytes (KC) and fibroblasts (FB) were transduced with different BCV constructs, BGIM, BMIG and QGIM. In BGIM, expression of the BCV cassette encompassing the green fluorescent protein (GFP) gene connected to the MDR gene was driven by a retroviral LTR-promoter. In BMIG, the order of the two genes was reversed, while in QGIM the GFP- and MDR-gene were arranged similar as in BGIM, but expressed by a CMV- instead of an LTR-promoter. FACS-analysis revealed that the percentage of genetically modified cells varied substantially with 47.9% QGIM-, 35.5% BMIG- and 17.9% BGIM-transduced KC expressing both genes. For FB the numbers were 56.7% (QGIM), 38.4% (BMIG) and 8.3% (BGIM). Furthermore, the choice of BCV determined the intensity of GFP-expression with the highest levels measured in BGIM-, followed by QGIM- and then BMIG-transduced cells. Interestingly, highly efficient enrichment through colchicine selection was possible for QGIM- (up to 97.1% KC, 97.8% FB) and BMIG- (85.0% KC and 98.0% FB) but not BGIM- (29.9% KC and 18.6% FB) transduced cells. Finally, immunohistochemistry and FACS-analysis demonstrated, that colchicine selection of QGIM-transduced skin equivalents led to increased numbers of GFP-expressing KC (from 51.2% up to 72.3%) and enhanced GFP-intensity in the skin. These results show that BCV present a promising vector system to enhance the expression of a desired gene in skin but important parameters taken into account when employing a selectable BCV for skin gene therapy applications are the retroviral vector backbone, the order in which the genes are arranged, and the target cells to be transduced and selected.
authors.affiliation: Department of Dermatology and Allergology, University of Munich, Munich, Germany.
authors.forename: Frank
authors.initials: F
authors.lastname: Scheidemann
authors.forename: Jean-Philippe
authors.initials: JP
authors.lastname: Therrien
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Pfützner
mesh_terms: D002478:Cells, Cultured; D003078:Colchicine / Q000494:pharmacology; D005347:Fibroblasts / Q000378:metabolism; D015316:Genetic Therapy / Q000379:methods*; D005822:Genetic Vectors; D049452:Green Fluorescent Proteins / Q000235:genetics; D006801:Humans; D015603:Keratinocytes / Q000378:metabolism; D012871:Skin Diseases / Q000628:therapy*; D014161:Transduction, Genetic
chemical_list: D049452:Green Fluorescent Proteins; D003078:Colchicine