Development of gene therapy model of retrovirus-induced disease

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Fv-4 is a mouse gene that dominantly confers resistance to infection by ecotropic murine leukemia virus (MuLV). Fv-4 resistant (Fv-4^r) gene product was expressed in hematopoietic cells and a part of glandular organs of Fv-4^r-bearing mice. Immunoelectron microscopically, this antigen was expressed on the cell surface and a part of endoplasmic reticulum. Flowcytometric analysis revealed that the Fv-4^r antigen was expressed in erythroid cells, granulocytic cells, T cells and B cells with almost the same intensity. Immunoprecipitaion followed by Western blotting revealed that Fv-4^r gene product existed in the serum of Fv-4^r-bearing mice. The soluble Fv-4^r antigen had a molecular weight of about 80 kDa. The serum Fv-4^r antigen binds to ecotropic MuLV receptors, shown by specific binding to transfectant mink cells expressing ecotropic MuLV receptor, but not to parental mink cells. C3H thymocytes or spleen cells that had ecotropic MuLV receptor and had been preincubated with soluble Fv-4^r antigen were mixed with Friend leukemia virus (FLV). C3H cells treated with Fv-4^r antigen became refractory to binding by FLV.These results provide evidence that the Fv-4^r antigen is released from cells of Fv-4^r-bearing mice in vivo and binds to cells expressing surface receptors for ecotropic MuLV,thereby protecting them from infection with FLV.Next, the implication of these findings for gene therapy of retrovirus-induced disease was examined. Fv-4^r gene was first transduced to leukemia cell line of C3H mouse origin and the cells successfully expressed Fv-4^r antigen. Then, the bone marrow cells of C3H mice were transduced with Fv-4^r gene and transplanted to lethally irradiated C3H mice. The resulting chimera mice expressed Fv-4^r antigen in hematopoietic cells.