Stem Cells: The Hope And The Hype

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THE HUNT FOR NEW SOLUTIONS

To get around political roadblocks, scientists are searching for another source of cells that is less ethically troublesome, ideally one that involves no embryo destruction at all. One approach is "altered nuclear transfer," in which a gene, known as CDX2, would be removed before the cell is fused with the egg. That would ensure that the embryo lives only long enough to produce stem cells and then dies. That strategy, promoted by Dr. William Hurlbut, a member of the President's Council on Bioethics, has its critics. Dr. Robert Lanza of biotech firm Advanced Cell Technology considers it unethical to deliberately create a crippled human embryo "not for a scientific or medical reason, but purely to address a religious issue." The most exciting new possibility doesn't go near embryos at all. Dr. Shinya Yamanaka of Kyoto University reported tantalizing success in taking an adult skin cell, exposing it to four growth factors in a petri dish and transforming it into an embryo-like entity that could produce stem cells--potentially sidestepping the entire debate over means and ends.

Even if scientists discover an ideal source of healthy cell lines, there is still much to learn about how to coax them into turning into the desired kind of tissue. Parkinson's patients suffering from tremors caused by damaged nerves could benefit from replacement neurons, while diabetics who can't produce insulin could control their blood sugar with new pancreatic islet cells. But so far, no human ESCs have been differentiated reliably enough that they could be safely transplanted into people, although animal studies with human cells are under way. Not surprisingly, the groups closest to human trials are in the biotech industry, which operates without government funds. Geron claims it is close to filing for permission to conduct the first human trials relying on ESC-based therapy. It is using stem cells to create oligodendroglial progenitor cells, which produce neurons and provide myelin insulation for the long fingers that extend out from the body of a nerve cell. Lanza's group is also close to filing for FDA permission to begin clinical trials on three cell-based therapies: one for macular degeneration, one for repairing heart muscle and another for regenerating damaged skin. Not to to be outdone, the academic groups are just a few steps behind. Lorenz Studer at Memorial Sloan-Kettering Cancer Center in New York City has been able to differentiate ESCs into just about every cell type affected by Parkinson's disease and has transplanted them into rats and improved their mobility. Next, he plans to inject the cells into monkeys.

THE RISKS ON THE NEW FRONTIER

But the closer scientists come to human trials, the more concerned the FDA will be with ensuring patient safety. The government will look at how the cells were grown and whether there would be risk of contamination from animal products used in the process. Regulators want data on how the cells will behave in the human body. Stem cells have shown a dismaying talent for turning into tumors. Will they migrate into unwanted areas? No one knows. You can't find out for sure until you test in humans, but it's hard to test in humans until you can be reasonably sure you won't harm them in the process.