Stem cells have the remarkable potential to develop into many different cell types in the body during early life and growth. In addition, in many tissues they serve as a sort of internal repair system, dividing essentially without limit to replenish other cells as long as the person or animal is still alive. When a stem cell divides, each new cell has the potential either to remain a stem cell or become another type of cell with a more specialized function, such as a muscle cell, a red blood cell, or a brain cell.
There are two types of stem cells:
- Embryonic stem cells that are derived from an embryo that has not yet been implanted in a woman’s uterus.
- Adult stem cells, a relatively rare undifferentiated cell found in many organs and differentiated tissues with a limited capacity for both self renewal (in the laboratory) and differentiation.
The use of embryonic stems cells has generated much debate because of the ethical concerns perceived by many in the destruction of a living embryo. The use of adult stem cells is much less controversial.
Recent Research Reports: Negative Findings
Two recent studies of promising uses of stem cells, one on the use of stem cell transplants, the other on the use of retinal stem cells to treat Parkinson’s, had discouraging findings.
- Stem cell transplants: Hopes for treating life-threatening diseases with cells taken from patients’ own bodies have suffered a setback after research showed they might trigger severe immune reactions.The surprise finding will be a hurdle for scientists working on induced pluripotent stem (iPS) cells, a variety of cell that holds promise for treating conditions as diverse as muscular dystrophy, Parkinson’s and heart disease. A study done at the University of California, San Diego, found that iPS cell triggered immune reactions when transplanted into mice, in some cases completely destroying the animal’s immune system. Although the studies were done in rodents, the findings raise doubts about the use of iPS cells in human therapies.[But see the good news at the end of this post.]
- Retinal cell transplants to treat Parkinson’s Since retinal calls also produce L-dopa, transplanting these cells into the brain of people with Parkinson’s, it was hoped, might turn out to work better than oral administration of L-dopa. Researchers tried to assess the safety, tolerability, and efficacy of transplanting these cells into people with advanced Parkinson’s. Around 650,000 cells were injected into the brain of each patient.Each person’s symptoms were assessed after a year but it was found that the treatment made no difference at all. Instead, it caused some adverse effects, mostly neurological or psychiatric.
But now for some good news
Researchers involved in a study using iPS stem cells to treat Parkinson’s in a mouse model have concluded that protein-based iPS stem cells might well be able to treat humans with PD.
Stem cells are considered by many to be promising candidate sources of cells to reverse nerve cell loss in individuals with Parkinson disease through their ability to regenerate and repair diseased tissues. As noted in the “stem cell primer” at the outset of this post, there are two types of stem cells with potential for therapy — embryonic and adult (iPS) cells. In turn, there are two types of iPS cells:
- Protein-based iPS cells in which reprogramming proteins are transferred directly into the cells, and
- Virus-based iPS cells in which viruses are used to deliver the necessary genetic information directly to the cells.
Researchers found several problems with cells derived from virus-based human iPS cells that precluded their use in the Parkinson disease model but found that nerve cells derived from protein-based human iPS cells reversed disease when transplanted into the brain of rats modeling Parkinson disease. They therefore conclude that protein-based human iPS cells could be used in the treatment of individuals with Parkinson disease.
But, as with all mouse-based research, there’s no guarantee that what works with mice will work with humans.
And, saving the best for last, what may be the best news of all
A report released just a week ago (on my 82nd birthday!) Stanford University scientists report being able to turn human skin cells directly into neuron cells. Skins cells into brain cells — sounds like science fiction but it’s reported in the May issue of Nature.
Human skin cells can be converted directly into functional neurons in a period of four to five weeks with the addition of just four proteins, according to the study. The finding is significant because it bypasses the need to first create induced pluripotent stem cells, and may make it much easier to generate patient- or disease-specific neurons for study in a laboratory dish.
It may also circumvent the potential problem with iPS cells, reported in the first bad news entry above, in which laboratory mice rejected genetically identical iPS cells — seemingly on the basis of the proteins used to render them pluripotent.
The new research parallels that of the same Stanford group in 2010, which showed it was possible to change mouse skin cells directly into neurons with a similar combination of proteins.“We are now much closer to being able to mimic brain or neurological diseases in the laboratory,” said Marius Wernig, assistant professor of pathology at Stanford and a member of it’s Institute for Stem Cell Biology and Regenerative Medicine. “We may perhaps even be able to one day use these cells for human therapies.”
Yes, very good news. But also very preliminary. It’ll probably be a few years before you can order a new brain on amazon.com.