A co-culture apparatus and method for, among other things, converting a progenitor cell line into a target cell line. The apparatus comprises an exterior receptacle, a removable cartridge that fits into the exterior receptacle, and a closure member to seal the apparatus. The invention is also directed to a method for transforming a progenitor cell line into a target cell line. In one embodiment of the invention, the method comprises the steps of: establishing a progenitor cell line; establishing a support cell line; co-culturing said progenitor and support cell lines; establishing a transformation cell line; and co-culturing said progenitor and transformation cell lines, wherein the transformation cell line supports the transformation of the progenitor cell line into a target cell line.