The technique of stripping cells from a donor organ and repopulating the extracellular matrix with a patient's own cells is moving ahead, as illustrated by this article: "Spain, a world leader in human organ transplants, is now also a pioneer in the creation of bioartificial organs with stem cells implanted into patients after the opening on Tuesday in Madrid of the first laboratory in the world dedicated to the growth of artificial organs for human transplant. The laboratory will 'empty' human hearts or other human organs unsuitable for transplantation and recolonize their cell content with the patient's stem cells, allowing the organs to grow anew, ready for tranplant back into the new body ... Transplantation of such organs could a daily reality in 'between five and ten years' ... So far, the cardiology unit of the Gregorio Maranon has 'applied the elimination of cells' to eight hearts that have succesfully become viable organs using the patient's stem cells. And by late 2010 they want to install a heart from a donor using regenerated cells. Moreover, 'as it advances, [we could also use] animal organs.'" The downside of decellularization as a technology is that it does still require a donor organ - it is essentially a way of working around the present inability to build a suitably structured framework for an artificial organ. Since replacing all of the cells largely eliminates immune rejection issues in a transplant procedure, there is no reason not to use animal organs, however. They should be just as effective.