Abstract: The subject invention is directed to a mixed cell composition to generate a therapeutic protein at a target site by providing a first population of mammalian cells transfected or transduced with a gene that is sought to be expressed, and a second population of mammalian cells that have not been transfected or transduced with the gene, wherein endogenously existing forms of the second population of mammalian cells are decreased at the target site, and wherein generation of the therapeutic protein by the first population of mammalian cells at the target site stimulates the second population cells to induce a therapeutic effect.