Not all stem cells are controversial
New discoveries, particularly during the 21st century, have opened up possibilities for exciting disease breakthroughs. This scientific progress has not come without controversy, particularly in the area of stem cell research. For the vast majority of diseases and disorders that involve damaged body tissues and aging, the use of stem cells seems to offer hope as impressive as the mystical fountain of youth. Controversy arises, however, because stem cells are hard to come by and harvesting some types of stem cells involves ethical issues.
Biologists the world over are taking a closer look at these “master” cells that can both renew indefinitely and differentiate into any kind of specialized cells, such as blood, bone, muscle, nerve, organ, skin, and more. These unique properties place them apart from other “set” cells. Other cells – once their nature is determined during embryonic development – can only divide and reproduce after their own kind. This inability to change is a good thing, because it means that your body is not going to morph on you, and that your skin stays on the outside of your body and your heart remains a heart. However, there are distinct advantages that stem cells might offer in treating disease.
Scientists believe that stem cells are the “source” cells from which all other cells are offspring. Once formed, our bodies retain a finite number of stem cell reserves in various organs, which activate as needed to repair and replace injured or diseased tissues. As these wonder cells deplete, the aging process accelerates. Stem cells stored in adulthood are not as malleable as embryonic stem cells but they are still remarkable.
In normal human development, the cells in most specialized tissues are continually lost and then replaced by new cells in the same form. This turnover of cells is enormous, such that during a human lifespan, the number of cells in the body that form and die is more than 100 times the number found in the body at any given point. Your body consists of around 10 trillion cells that reproduce in two ways:
- Meiosis: The formation of sperm and eggs, which we will not discuss in this article, and
- Mitosis: The growth and division of cells
During normal mitosis, DNA in differentiated (non-stem) cells replicates within the “parent” cell then it divides in two, creating two genetically identical “daughter” cells. Depending on the cell type, this dividing cycle can last from hours to years. For example, bacterial cells can divide as frequently as every 30 minutes, skin cells divide about every 12 hours, while liver cells divide about every 2 years.
Stem (non-differentiated) cells act differently during mitosis. Stem cells have two properties on division that distinguish them from other cells: they self-renew and can differentiate to specific mature cells. This means they are cells of pure potential. When a stem cell divides, it continues to renew itself because one of the daughter cells remains as a stem cell while the other goes on to become a differentiated cell, such as a bone or skin cell. Because one cell in the dividing process stays undefined, the supply of stem cells remains constant.
To shine a light on the controversy of using stem cells to treat disease, it is important to discuss the various types. Some may be more ethically acceptable for use than others and knowing these differences will help you decide whether you support their use or not.
Most Flexible Stem Cells
Embryonic stem cells, derived from early embryos, (from conception to 8 weeks gestation) have unlimited potential to differentiate into any of the over 200 cell types within the body. These are the most flexible of all stem cells because they do not trigger rejection when transplanted into another person, but are controversial because they are products of elective abortions, often resulting from unwanted multiple conceptions that occur during fertility treatments. While debate rages about what constitutes “human life”, there is also concern that embryos will become a commodity, and fear about where this might lead. However, not all research uses this type of stem cell.
Somewhat Flexible Stem Cells
In human development, once past the embryonic stage, stem cells lose some of their potential to differentiate. Even into adulthood, some of the reserve stem cells are stored in the liver and bone marrow. They appear to have a limited range but still can differentiate into a number of cell types. Since these cells are flexible, but not as flexible as the embryonic stem cells, research to push these cells past their apparent limited threshold is ongoing. These cells tend to be flexible only within certain boundaries, for example, those found in the liver may differentiate into blood and liver cells but not skin or bone cells. All adult stem cells are extremely rare and their identification and isolation represent great research challenges.
The richest source of adult stem cells is bone marrow. Regrettably, harvesting bone marrow involves surgically inserting a needle into the pelvis – a painful procedure – and typically the donor needs four to six weeks to fully regenerate marrow tissue. The bloodstream also contains adult stem cells, referred to as peripheral blood stem cells, but their concentration is significantly lower than in bone marrow, making harvesting them a slow process. Recent advances, however, have made the procedure more efficient and it is becoming more common. Medical scientists also extract “adult” stem cells from cord blood collected at birth (with the mother’s prior permission) but usually, the number of cells obtained from this process is too few to treat an adult patient adequately.
Stem cells derived from adult bone marrow, the blood stream, or cord blood, may also pose a number of problems in the person receiving the transplanted cells, such as disease and genetic mutation transfer. Stem cells derived from bone marrow, adult blood, and cord blood may have therapeutic potential only when given to the individual from whom they were derived, called “autologous” transplantation; or from an immunologically matched donor, called “allogenic” transplantation.
Least Flexible Stem Cells
Lastly, some stem cells have very limited potential as they can only generate specialized cell types within any particular tissue. These are useful to the body’s repair process but hold little interest for exploration in disease research.
The most obvious possibilities for biomedical research and clinical medicine lie in the area of regenerative medicine. Research is taking place for a diverse array of medical conditions including age-related wasting of muscle tissue, Parkinson’s disease, diabetes, AIDS, certain types of senile dementia, and Crohn’s disease. An ability to create stem cells that are committed to specific tissue lineages should allow the reversal of these otherwise progressive degenerative diseases.
Depending on the disease and type of research, scientists experiment with different types of stem cells. In the case of Crohn’s disease, researchers are looking at the least controversial type; transplanting stem cells from within the patient’s own blood (autologous) to adjust the immune system. While initial small-scale studies show remission is possible, skeptics do not believe this method will succeed over the long-term since Crohn’s seems to be a systemic disease. It could be that transplanting stem cells from a matched donor (allogeneic) who does not have Crohn’s might be the best approach researchers will look at. Before widespread use of stem cells for treatment of Crohn’s disease, researchers must also address treatment side effects.
The promising potential of stem cell therapy has given rise to initially encouraging clinical results. While doctors in North America and Western Europe continue to study stem cell therapy, rigorously evaluating its potential benefits, necessity triggered application of this science in clinical practice in Ukraine almost twenty years ago. Nearly a million people in the Kiev area alone experienced adverse health effects when radioactive dust settled across Ukraine following the nuclear reactor explosion at Chernobyl in April 1986. Faced with treating patients suffering from conditions ranging from diabetes to blood anemia and cancer, the Ukrainian government began funding new research into repairing tissue and blood cells that would produce results quickly. Doctors turned to adult stem cell therapy, and they claim to have been successfully treating patients there since the Chernobyl disaster. Scientists in other countries are skeptical about this success because there are no published random clinical trials – the gold standard of medical research – regarding the positive or negative effects of stem cell therapy. Many countries have banned some forms of stem cell research, while scientists in other countries strive to become leaders in this controversial area of exploration. Recently, this enthusiasm has lead to a troubling disclosure by Dr. Woo Suk Hwang, of Korea, who announced he had falsified results from his lab that showed, during 2004 and 2005, significant progress in cloning human embryonic stem cells. Despite his admission, most researchers believe that stem cells will eventually yield revolutionary medical treatments.
Undeniably, the potential for using stem cells as disease therapy is opening a vast, entirely new area of biomedical research. While it is clear that opportunities abound for developing new and dramatic therapeutic applications, numerous obstacles stand in the way of progress. Ethical debate must continue and scientists must solve the basic science of applying stem cells to treat disease in order to design and implement effectual stem cell therapies. Only with ethical and scientific support, will the potential of using stem cell research to treat disease advance to actuality.