Development of Methods for Somatic Cell Gene Therapy Directed Against Viral Diseases,Using Retroviral Vectors Carrying the Murine or Human Interferon-β Coding Sequence: Establishment of the Antiviral State in Human Cells

We are developing methods for somatic cell gene therapy directed against chronic and fatal virus infections, such as acquired immunodeficiency (AIDS), by transforming cells with a constitutively expressed interferon (IFN) coding sequence. Previous work from our laboratory has shown that stable antiviral expression (SAVE) can be obtained in murine BALB/c 3T3 cells and human U937 cells transformed with plasmids carrying either the murine or the human IFN-β coding sequence placed under the expression control of a 0.6-kb Xho II–Nru I promoter region of the murine H-2K^b major histocompatibility complex (MHC) gene (Macé et al., 1991; Seif et al., 1991). In the present paper, we report the construction of murine (Mu) and human (Hu) IFN-β-expressing retroviral vectors (pMPZen-MuIFNβ, pHMB-K^bMuIFNβ) and the problems encountered. Because of the murine origin of commonly used packaging cells and the species specificity of IFN, it was evident that placing the murine IFN-β sequence under constitutive expression control could result in the production of Mu IFN in the murine packaging system, and thereby lead to decreased vector production and also to enhanced resistance of target cells. Using a packaging cell line that releases a β-galactosidase-expressing vector, we show that, as expected, Mu IFN-α/β decreases vector production of murine packaging cells and also inhibits the transformation of target NIH-3T3 cells with this vector, but the presence of anti-Mu IFN antibodies rescues the viral titer of the packaging cells and restores the sensitivity of target cells to virus transformation. However, the same antibody treatment is unable to rescue the viral titer of ψ-2 packaging cells producing autocrine Mu IFN-β encoded by the pMPZen-MuIFNβ and pHMB-K^bMuIFNβ vectors. Because of the species specificity of IFN, this problem is circumvented with the pMFG-HuIFNβ vector carrying the human IFN-β sequence. In spite of the production of Hu IFN, murine ψ-CRIP packaging cells are able to release retroviral vectors expressing Hu IFN-β, and these amphotropic vectors can transform human MRC-5 cells and confer to these cells an enhanced resistance to vesicular stomatitis virus (VSV) infection.

Overview summary

We are developing methods for somatic cell gene therapy directed against chronic and fatal virus diseases, such as AIDS, by transforming viral target cells with IFN-expressing retroviral vectors. We report here our failure to produce retroviral vectors expressing murine IFN-β by murine ψ-2 packagingcells, due to their very high sensitivity to the autocrine murine IFN-β encoded by the vector. In contradistinction, because of the insensitivity of murine ψ-CRIP packaging cells to human IFN-β, we have obtained retroviral vectors expressing human IFN-β, which are able to confer to human cells an enhanced resistance to viral infection.