A Triumph for Stem Cell Research
Although the potential applications of stem cell therapy are numerous, right now some of its most promising conceivable uses are in the treatment of degenerative brain disorders, such as Alzheimer’s disease (AD) or Parkinson’s disease (PD). In both of these afflictions, essential brain regions deteriorate, leading to notoriously debilitating symptoms. In AD, cholinergic neurons are depleted, while a loss of dopaminergic neurons is responsible for the effects of PD. Some scientists see disorders like these as ideal cases for stem cell treatment. For, in theory, if cholinergic or dopaminergic neurons are deteriorating, one could implant stem cells into the brain of the patient that could then be prodded to form new neurons. This could offset the atrophy caused by the disease.
Thus far, attempts to do this in laboratory animals have had mixed results. Sometimes a slight improvement can be seen, lending credence to the potential validity of the procedure. But failure for a diseased animal to get better after stem cell injection is more common, indicating there are problems with the technique. It is thought that those problems may have to do with the genetic compatibility of the stem cells being implanted into the subject’s brain and the subject's immune system. Perhaps the immune system is recognizing the stem cells as foreign and initiating a response to destroy them. This could be responsible for the animal’s lack of improvement.
Any scientists in training might want to pause for a moment before reading on and try to think about a logical solution to this problem. If a mouse’s immune system is rejecting stem cells from another mouse, what is a way to get around this?
The answer is: use stem cells genetically identical to the subject mouse’s cells. A group of researchers at Memorial Sloan-Kettering Cancer Center induced PD in mice by injecting them with a toxin. They then took skin cells from the tails of the mice and did a little DNA switcheroo. They took the DNA out of the skin cells and transferred it into mouse egg cells that had already had their own DNA extracted from them. The group then prodded the egg cells to divide, eventually producing stem cells as a part of normal embryonic development. The researchers added the appropriate growth factors to the stem cells to cause them to differentiate into brain cells.
They then injected the newly formed brain cells into the PD mice. The immune systems of the mice recognized the brain cells as “self”, since they were genetically identical. Thus, no immune response was mounted, and the mice showed significant neurological improvement. Out of about 100,000 genetically similar brain cells injected into each PD mouse, approximately 20,000 cells survived to function in each brain. Of course the study also had a group for comparison that received genetically dissimilar cells, and these mice did not get healthier. Only a few hundred of the genetically different cells survived in the brains of the mice in this group (of the same number injected).
This is what stem cell researchers have been waiting for: the use of somatic cell nuclear transfer (cloning) technology to make replacement cells for the body, resulting in clear evidence that it can lead to significant recovery from degenerative disorders. It is vindication for those who have been proclaiming the limitless possibilities of stem cells.
It, however, does not get around the fundamental problem stem cell advocates face. It requires the use of embryonic cells to create the stem cells. Thus, despite the potential it has, it will continue to face harsh political opposition. One has to hope, however, that as these procedures become perfected in organisms like mice, opponents will have to adopt a more utilitarian perspective. Perhaps using some of the half a million frozen embryos that are collecting dust in the in vitro fertilization clinics across the country would be considered a little more in depth if their ability to alleviate the suffering of living PD sufferers, which number over a million in the U.S. alone, had been demonstrated repeatedly in animal studies.
For other posts from me on stem cells, go here or here.