Side effects and other clinical issues will need to be addressed as adult stem cell research progresses and more human trials are launched. Those studies will go a long way to eventually determining the real medical potential of these remarkable cells. But for now, the future of adult stem cells remains closely linked to the political and ethical debates surrounding their embryonic cousins.Among many researchers, it has become almost politically incorrect to speak with unguarded enthusiasm about adult stem cell research-not because the research isn’t exciting, but because such praise has inevitably provided ammunition to opponents of embryonic stem cell research. U.S. senator Sam Brownback of Kansas, for example, used recent results from Prockop’s group at Tulane and Edwin M. Horwitz’s group at St. Jude’s Children’s Research Hospital in Memphis, TN, to argue that adult stem cells are so potent and versatile that there’s no need to destroy embryos to get their stem cells, and thus no need for the government to provide funding for embryonic-stem-cell research. But Prockop reflects the views of most scientists when he says, “We can learn from both groups of cells. We have too much to learn to stop any of this work.”
There are, in fact, substantive scientific questions remaining to be answered before the relative merits of embryonic and adult stem cells can be determined. Some scientists claim embryonic stem cells are easier to grow in culture, and they are unquestionably capable of more cellular fates, but they also pose a small but theoretical risk of developing into cancerous tissues. Adult stem cells may not be as potent as embryonic stem cells, but preliminary clinical results suggest they are safe in humans. Yet they have many academic critics. Stanford biologist Irving Weissman argues that, almost without exception, adult cells have not been characterized rigorously enough, and he dismisses the politicians and religious figures who tout the virtues of adult stem cells, saying, “Those who have made the claim that human adult stem cells can do everything and anything that we want seem to know something that the experts don’t know.”
Nonetheless, virtually all the researchers who’ve laid their hands on adult and embryonic stem cells see them ushering in a new kind of medicine in the 21st century, where the healing wisdom of these powerful biological agents provides a kind of in situ doctoring, where repair and regeneration are startlingly real possibilities, where the drugstore of the future is as likely to dispense bags of cells as bottles of pills. The question, as much political as scientific, is how quickly we are going to get there.