Stem-cell research has been hyped in part because of its potential use for treating several degenerative disorders. The therapy may bring miracles; however, replacing diseased tissues with manufactured, healthy tissue is risky. Like many organ transplants, the introduced tissues may be rejected.
With the exception of twin donors, it is never a guarantee that a person's body will accept new tissues from another body. The immune system is merely doing its job of fighting foreign invaders, even those with good intent.
Interestingly, treatments for the brain have so far been well received by the host's immune system. In fact, over the last 10 years, there have been 250 human fetal tissue transplants to the brain worldwide.
\The brain is like an immunologically privileged site,"" said UW-Madison scientist Clive Svendsen. ""The immune system does not have the same access to the brain as it has to the rest of the body.""
These treatments also did not have to be custom-made for each patient.
""Pig brain cells put into the human brain will reject in the brain, but human to human won't,"" Svendsen said.
Chances are that the first human attempts in stem-cell therapy will be on patients with degenerative brain disorders, such as Alzheimer's and Parkinson's diseases.
As for the rest of the body, only time will tell how stem-cell therapy may get around transplant rejection'stem-cell research, after all, is still in its infancy. Karen Lebacqz, an ethicist from the Pacific School of Religion, sees both good and bad solutions to this problem in emerging technologies.
Adult stem-cell therapy may get around the body's foreign guards because adult stem cells can be obtained directly from the patient. Some opponents of embryonic stem-cell research already acknowledge the moral nature of adult stem-cell research and will certainly argue for the efficiency adult stem cells bring for therapy. But but the benefits of adult stem cells may deter its proponents from seeing the defects of this system.
Attention over the issue of derivation of stem cells has been distracting, Lebacqz pointed out. "" I think sometimes people assume that if we could just use adult stem cells, then there would be no ethical issues,"" she said.
According to Lebacqz, adult stem-cell research faces just as many questions as embryonic stem-cell research. Universal concerns include the sometimes ethically abusive research in the private arena, potential capabilities of stem-cell research in creating entire human beings and unequal distribution of stem cell's therapeutic benefits.
Announcements of cloned human embryos, Lebacqz said, has led many people to assume that it could be used to get immune system friendly tissues. To receive stem-cell therapy, a cloned embryo could be tailored for each patient.
Svendsen said he, at least with today's technology, that creating these individual clones will be impractical and expensive. ""To grow the cells alone, Jamie [Thompson, UW-Madison professor of anatomy] currently needs two technicians,"" Svendsen said.
Lebaqcz said she this method, with its need for a continuous reserve of human eggs, hampered with ""issues of justice,"" particularly for potential women donors. ""Where will we get all the eggs and embryos?"" she asked. ""Procedures for getting eggs from women are not without their own risks and discomfort and ethical issues. ?? what about the fate of the women involved?""
In Israel, Karl Skorecki, director of Rappaport Reasearch Institute looks into treatment of diabetes after coaxing human embryonic stem cells into insulin-producing cells. With these new cells, he is conducting trials in diabetic mice. To circumvent the tissue rejection, his team experiments with genetically immuno-suppressed mice.
The growing potential of genetic manipulation may solve tissue compatibility problems. One day, immuno-suppressed humans may be genetically manufactured. But Svendsen sees this as an enormous task.
""The immune system itself is evolved,"" said Svendsen. ""It will probably take a lot of genetic engineering to make such change.""
For now, immuno-suppressive drugs may be one way to conduct human stem-cell therapy. They have been used to persuade bodies to accept organ transplants. New and better drugs are routinely developed, but they are expensive and result in side effects like kidney failure and risk of cancer.
