If you believe some celebrities and politicians, stem cells, cells that are “unassigned” and can become a working cell in any tissue of the body, can save the world, if we only let them. If you believe others, stem cell research and therapy represent the slippery slope to a world where human life is expendable. But what do the scientists think? What are the reasonable expectations for stem cell therapy according to the scientific world?
Professor Jane Johnston believes that stem cell therapy is promising, but only in certain cases. Parkinson’s Disease is often cited as a disease that would be particularly receptive to treatment with stem cells because it affects a small specific part of the brain that produces the neurotransmitter dopamine, as opposed to the broad complicated effects of a disease like Alzheimer’s. Dr. Johnston agrees, but she described an adult Parkinsonian brain that received dopamine-producing stem cells to replace the damaged cells. “Changes that occur in a Parkinsonian brain cannot support dopamine-producing cells,” she said. “The healthy cells created from the stem cells die off.”
For Dr. Johnston, then, the question is what is the aging brain? How and why do aging and disease change the brain? “You’ve got to understand the environment,” Dr. Johnston asserted. Apparently, you can’t put infant cells in a geriatric brain and expect them to get along.
The good news is that there are many potential treatments for degenerative diseases beyond human embryonic stem cells. Dr. Johnston has taken progenitor cells, a more developed type of stem cell, from rodents and grown them in the lab to screen for their response to various treatments. She prefers progenitor cells to stem cells because the problem is the adult brain, not the pediatric brain, and these cells can be isolated from adult human tissue, addressing the issues of a system stressed by age.
Alternatively, scientists are exploring ways to trigger an aging brain to act in a more youthful manner. “Nerve cells grow during development,” she said, “because they are signaled to grow. When we become adults, those signals are restricted. Some progenitor cells, however, remain within brain tissue and one strategy employed by scientists is to try to reactivate them, enabling them to divide into a supply of new cells.” In other words, for stem cell therapy or any regeneration therapy to be successful, scientists will need to learn how to “trick” the brain into thinking it is 2-years-old again to recreate the environment of a growing, adapting nervous system. Otherwise, the new stem cells are in hostile foreign territory – an old brain.
Dr. Johnston seems to feel a mixture of hope and frustration when she talks about cell therapy. “Politicians and celebrities, in focusing on stem cell research, are putting the focus on replacing what is lost rather than on developing treatments that will address the underlying cause of the disease. We know we are many steps away from putting viable stem cells into diseased tissue. Unless we fully understand the nature of the disease, putting new cells in old tissue will never be more than a temporary fix.”
Instead, Dr. Johnston sees significant promise in cell therapies that involve disease tissue created in dishes in the lab. Genetic material isolated from the fibroblasts (skin cells) of an Alzheimer’s patient could be transferred into a stem or progenitor cell source in the lab, creating a personalized model of the patient, and then screened with therapeutic drugs in the search for a beneficial reaction. Such cell models will have enormous potential as tools for researchers and for the development of new effective medicines.
There is still so much that we do not know about even the most simple disease process, and Dr. Johnston believes that stem cells are important in helping scientists understand the way cells develop and react. But even if stem cell therapy is not a panacea, human ingenuity just might be.
