Stem Cell Therapy and Therapeutic Cloning

Paralysed rats have been enabled to walk again, by transplanting nerve cells derived from human embryonic stem cells into the animals. The findings add to a growing number of studies that suggest that embryonic stem cells could have a valuable role to play in treating spinal injuries. The researchers say trials on people using this technique could start in about two years time. Researchers are exploring a number of approaches to enable recovery from spinal-cord injury, including drugs that overcome spinal cells' reluctance to re-grow, ways of bridging the gap between severed nerves, and transplants of various tissues, including adult stem-cells derived from bone marrow, and nerve cells from the nose. Human trials of some treatments, such as that using nose cells, have already begun. But the first stem-call trials will be on patients
with recent spinal cord injuries and localised damage; treating people who have been paralysed for years, or who suffer from degenerative nerve diseases, is more difficult.
Ways will also have to be found to prevent people rejecting the stem cells. One possible alternative to immunosuppressant drugs would be to first give the patient bone-marrow stem cells from the same source as the nerve cells. This might trick the patient’s immune system into developing tolerance.

But adult cells have serious limitations as a mass-market treatment, because not many cells can be grown from a single source. That is not a problem with embryonic stem cells (ESCs). "One cell bank derived from a single embryo produces enough neurons to treat 10 million Parkinson's disease patients", says Thomas Okarma of the Geron company in California. What is more, adult stem cells may not be as versatile. "At this moment, there is very little hard evidence that a bone marrow stem cell can turn into anything but blood, or that a skin stem cell can become anything but skin", he says. ESCs, on the other hand, have the potential to develop into practically any type of tissue.But there is nevertheless a serious problem with ESCs. "Undifferentiated human embryonic stem cells have a very high probability of forming tumours," says Hans Keirstead at the University of California, Irvine, whose team has performed the latest research. To prevent this, his team turned ESCs into specialised cells before transplanting them. They transformed the ESCs into oligodendrocytes, the cells that form the insulating layer of myelin that is vital for conducting nerve impulses. Keirstead's team transplanted the oligodendrocytes into rats with "bruised" spines. After nine weeks, the rats fully regained the ability to walk, he says, whereas rats given no therapy remained paralysed. The team repeated the experiment on three separate occasions, with the same results. Analysis of the rats' spinal cords revealed that the transplanted oligodendrocytes had wrapped themselves around neurons and formed new myelin sheaths. The transplanted cells also secreted growth factors that appear to have stimulated the formation of new neurons.While many promising spinal repair experiments have proved hard to reproduce, researchers at Johns Hopkins University in Baltimore, Maryland, also announced similar results last week. The team injected undifferentiated human ESCs into rats with injured spinal cords. After 24 weeks, the treated rats could support their own weight. Team leader Douglas Kerr thinks the animals' recovery was not due to the growth of new cells, but to the secretion of two growth factors (TGF-alpha and BDNF), which protected damaged neurons and helped them to re-establish connections with other neurons. "The stem cells' magic was really their ability to get into the area of injury and snuggle up to those neurons teetering on the brink of death," says Kerr, whose results will appear in the Journal of Neuroscience.
" Umbilical cord blood stem cells are used as a part of the therapy regimen for nearly 50 diseases today. One of the challenges in developing additional cellular therapies is the need to multiply and preserve large quantities of these powerful umbilical cord blood stem cells for use in treating an even broader range of diseases. These important studies indicate that we can substantially increase the number of these valuable cells and freeze them for later use", says Jan Visser of ViaCell.

Okarma hopes the results will help persuade policy makers in Washington not to ban therapeutic cloning, which is one way of obtaining human ESCs, and increase funding for ESC research. "The promise of this technology is beginning to be realised", he says. "That's why we think this battle is worth fighting."