Abstract: The invention provides a method of culturing mononuclear cells, comprising isolating mononuclear cells from the blood or cell-containing fluids of the body of a mammal; culturing the cells in a culture medium comprising one or more of gangliosides, phospholipids, glycolipids and growth factors for endothelial cells. These cells are useful, for example, for the endothelialization of injured vessels. The invention also provides a method of making cells capable of expressing a biologically active protein, comprising isolating mononuclear cells from the blood or cell-containing fluids of the body of a mammal; culturing the cells in a culture medium comprising one or more of gangliosides, phospholipids, glycolipids and growth factors for endothelial cells; optionally, before or after culturing the cells, immortalizing the cells; and transfecting the cells with a nucleic acid construct comprising a gene for the biologically active protein.