Tissue-specific and ectopic expression of genes introduced into transgenic mice by retroviruses

Recombinant retroviruses containing the complete genomic human beta globin gene (under the control of its own promoter) and the bacterial neomycin phosphotransferase gene (under the control of the normal or enhancerless viral promoter) were used to derive transgenic mouse strains by infection of preimplantation embryos. Expression of the beta globin gene in hematopoietic tissues was observed in all transgenic strains. In addition, one strain showed ectopic expression of beta globin in the same tissues that also expressed high levels of RNA from the viral promoter. It is likely that expression from the long terminal repeat (LTR), in contrast to expression from the internal promoter, is dependent on the site of integration. Thus, retroviral vectors can be used for tissue-specific expression of foreign genes in transgenic mice, as well as for the identification of loci that allow developmental activation of a provirus.     

Implantation of vascular grafts lined with genetically modified endothelial cells

The possibility of using the vascular endothelial cell as a target for gene replacement therapy was explored. Recombinant retroviruses were used to transduce the lacZ gene into endothelial cells harvested from mongrel dogs. Prosthetic vascular grafts seeded with the genetically modified cells were implanted as carotid interposition grafts into the dogs from which the original cells were harvested. Analysis of the graft 5 weeks after implantation revealed genetically modified endothelial cells lining the luminal surface of the graft. This technology could be used in the treatment of atherosclerosis disease and the design of new drug delivery systems.     

Expression of a bacterial gene in mammalian cells

Transfection of cultured monkey kidney cells with recombinant DNA constructed with a cloned Escherichia coli gene that codes for xanthine-guanine phosphoribosyltransferase and several different SV40 DNA-based vectors, results in the synthesis of readily measurable quantities of the bacterial enzyme. Moreover, the physiological defect in purine nucleotide synthesis characteristic of human Lesch-Nyhan cells can be overcome by the introduction of the bacterial gene into these cells.