A gene therapy model for retrovirus-induced disease with a viral env gene: expression-dependent resistance in immunosuppressed hosts.

At the initial stage of retroviral infection, virion envelope glycoprotein (env product) binds to cell surface receptors. Cells infected with retrovirus or into which the env gene was introduced, become resistant to superinfection by other retroviruses with the same receptor specificity, a phenomenon known as receptor interference. We have demonstrated previously that the introduction of an env gene from a truncated endogenous ecotropic murine leukemia virus (MuLV), the Fv-4 resistance (Fv-4r) gene, into the bone marrow hematopoietic cells of Fv-4 sensitive (Fv-4s) mice protected mice from ecotropic retrovirus-induced disease. Using the gene transfer system under the control of the retroviral vector and bone marrow transplantation (BMT), here we could show that the expression of an introduced Fv-4r gene in hematopoietic cells continued for more than 1 year after BMT. To determine the inhibitory mechanism of Fv-4r env gene expression against FLV-infection in this model system, peripheral blood mononuclear cells (PBMCs), or spleen cells from chimeras with various degrees of env-expression, were mixed with green fluorescence protein (GFP)-conjugated Friend MuLV envglycoprotein (GFP-Fr-ENV). The amount of GFP-Fr-ENV bound to these cells inversely correlated with the expression intensity of the transduced env gene indicating the receptor interference effect. Next, to see whether transduction of the Fv-4r gene would protect an immunosuppressed host from FLV-induced leukemogenesis, we generated immunocompromised chimeras by transplanting env-transduced bone marrow cells into a thymectomized host. These chimeras also resisted FLV-induced leukemogenesis, indicating that receptor interference-based gene therapy could become a therapeutic basis for immunodeficiency virus-induced diseases in vivo.