The other stem cells
Like children, human embryonic stem cells are filled with potential but difficult to control. Since they were first isolated in 1998 from human embryos only a few days old, these primordial cells have achieved both fame and notoriety. Removed from their tightly programmed life as an embryo, they can multiply indefinitely in the lab in primitive form or they can be coaxed to differentiate into virtually any cell in the body--a nest of beating heart cells, for example. But inject them into intact animals, and they are just as likely to be rejected by the immune system or turned into a deadly tumor filled with teeth, hair, and random cells.
These untamed primitive cells are important because they're a potential inroad to cures for devastating diseases like Parkinson's, diabetes, heart failure, and Alzheimer's. Their promise has stirred the imagination of the public, ignited the fervor of Nancy Reagan and others wounded by such illnesses, and attracted piles of money from government, commercial investors, and philanthropists. And the view that embryonic stem cells per se are forbidden fruit--as argued by abortion opponents--may be softening. Just last week, over 250 members of Congress, including avowed "pro-lifers," came out in support of using taxpayer money on the estimated 400,000 frozen spare embryos, stored in fertility clinics, that might otherwise be destroyed.
But all this hoopla fails to confront the real issue, which is not about using spare embryos. Rather it's about giving scientists license to make living human embryos from scratch--through IVF or human cloning--that is part and parcel of the long-term pursuit of therapeutically usable embryonic stem cells. This is the hidden but ever so hot issue on which there is no consensus, either in Congress or among the states. California has a voter referendum in November to issue a $3 billion bond to support stem-cell research, including therapeutic cloning. Other states have outlawed this approach entirely. Even the European Parliament and the United Nations have failed to agree whether therapeutic cloning is blessed or sinful.
What may be saving embryonic stem cells from the political quagmire are their increasingly compelling distant cousins, adult stem cells, which are quickly making regenerative medicine a dramatic reality. Until recently these cells have been largely ignored because they were thought to have limited regenerative value. But that has changed, in part because of the fuss and money surrounding embryo research. These less primitive but more stable cells exist in small quantities in all body organs. They won't be rejected and won't cause uncontrolled cell growth, and are therefore preferred for patient therapy. Of particular interest are the ones that nest in the bone marrow; they have the ability to transform into almost any tissue in the body.
Network. We are just learning that in the body, adult stem cells are players in a highly disciplined ballet. Indeed, they are key elements in a repair network in which wounded tissue sends out molecular SOS signals that mobilize stem cells in the affected organ and at the same time recruit bone marrow stem cells to home into the injury site. This may lead to a slow but natural replacement of tissues over time. Just last month a study in Lancet from the University of Florida reported that women who had had bone-marrow transplants from male donors were found--at autopsy months to years later--to have low levels of neurons of male origin, i.e., brain cells with Y chromosomes. Similar findings in both humans and animals suggest that stem cells may be replenishing other organs as well. A critical research question is whether or not these self-replenishing powers can be made to work faster and better, perhaps through drugs that stimulate stem-cell multiplication. Research already has some promising results.