A potential advantage of using stem cells from an adult is that the patient's own cells could be expanded in culture and then reintroduced into the patient. The use of the patient's own adult stem cells would mean that the cells would not be rejected by the immune system. This represents a significant advantage, as immune rejection is a difficult problem that can only be circumvented with immunosuppressive drugs.
Scientists in many laboratories are trying to find ways to grow adult stem cells in cell culture and manipulate them to generate specific cell types so they can be used to treat injury or disease. Some examples of potential treatments include replacing the dopamine-producing cells in the brains of Parkinson's patients, developing insulin-producing cells for type I diabetes and repairing damaged heart muscle following a heart attack with cardiac muscle cells.
The first potential applications of human embryonic stem cell technology may be in the area of drug discovery. The ability to grow pure populations of specific cell types offers a proving ground for chemical compounds that may have medical importance. Treating specific cell types with chemicals and measuring their response offers a short cut to sort out chemicals that can be used to treat the diseases that involve those specific cell types. Stem cell technology, therefore, would permit the rapid screening of hundreds of thousands of chemicals that must now be tested through much more time-consuming processes.
The study of human development also benefits from embryonic stem cell research. The earliest stages of human development have been difficult or impossible to study. Human embryonic stem cells offer insights into developmental events that cannot be studied directly in humans in utero or fully understood through the use of animal models. Understanding the events that occur at the first stages of development has potential clinical significance for preventing or treating birth defects, infertility and pregnancy loss. A thorough knowledge of normal development could ultimately allow the prevention or treatment of abnormal human development. For instance, screening drugs by testing them on cultured human embryonic stem cells could help reduce the risk of drug-related birth defects.
Stem cell research has shown benefits in many areas of health, but most of the studies have only been done on lab animals. Some examples are improved stroke recovery shown in rats embryonic stem cells were used to treat a Parkinson's-like condition in mice and rats.
Canadian and Italian scientists transplanted adult stem cells from the brains of mice into the bone marrow of other rodents. The stem cells changed behaviour and began making blood cells. Movement was restored in paralysed mice and rats by injecting stem cells into the spinal fluid
In one of the few stem cell studies done involving humans, some people who failed to benefit from cataract surgery improved when they received corneal stem cell transplants.
Stem cells represent hope for millions of Americans. They have the potential to treat or cure a myriad of diseases, including Parkinson's, Alzheimer's, diabetes, heart disease, stroke, spinal cord injuries and burns.
This extraordinary research is still in its infancy and practical application will only be possible with additional study. Scientists need to understand what leads cells to specialization in order to direct cells to become particular types of tissue.
For example, islet cells control insulin production in the pancreas, which is disrupted in people with diabetes. If an individual with diabetes is to be cured, the stem cells used for treatment must develop into new insulin-producing islet cells, not heart tissue or other cells. Research is required to determine how to control the differentiation of stem cells so they will be therapeutically effective. Research is also necessary to study the potential of immune rejection of the cells, and how to overcome that problem.
The ability to grow human tissue of all kinds opens the door to treating a range of cell-based diseases and to growing medically important tissues that can be used for transplantation purposes. For example, diseases like juvenile onset diabetes mellitus and Parkinson's disease occur because of defects in one of just a few cells types. Replacing faulty cells with healthy ones offers hope of lifelong treatment. Similarly, injecting healthy cells to replace damaged or diseased cells could shore failing hearts and other organs, in theory, up.
Human embryonic and adult stem cells each have advantages and disadvantages regarding potential use for cell-based regenerative therapies. Of course, adult and embryonic stem cells differ in the number and type of differentiated cells types they can become. Embryonic stem cells can become all cell types of the body because they are pluripotent. Adult stem cells are generally limited to differentiating into different cell types of their tissue of origin. However, some evidence suggests that adult stem cell plasticity may exist, increasing the number of cell types a given adult stem cell can become.
Large numbers of embryonic stem cells can be relatively easily grown in culture, while adult stem cells are rare in mature tissues and methods for expanding their numbers in cell culture have not yet been worked out. This is an important distinction, as large numbers of cells are needed for stem cell replacement therapies.
There are many ways in which human stem cells can be used in basic research and in clinical research. However, there are many technical hurdles between the promise of stem cells and the realisation of these uses, which will only be overcome by continued intensive stem cell research. A better understanding of the genetic and molecular controls of the processes may yield information about how diseases arise and suggests new strategies for therapy.
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