Author: Hoi See Tsao
Institution: Wellesley College
Date: November 2006
Stem cells were first isolated by scientists at the University of Wisconsin and Johns Hopkins University on 5 November 1998. In less than a decade, we hear about them everywhere on television, in the newspaper and even in presidential elections. However, what exactly are stem cells and why are they causing so much hype?
Stem cells are characterized by three properties. First, they are unspecialized, meaning that a stem cell does not have any particular job or role to perform in the body, such as pumping blood or transporting molecules such as oxygen around the body. This function gives stem cells their name, as every body cell "stems" from stem cells. Second, they can divide and renew themselves for long periods of time in a process called proliferation. If the resulting cells from proliferation continue to be unspecialized like the original stem cells, the cells are said to be capable of long-term self-renewal. Third, stem cells can become specialized cells through a process called differentiation due to a series of internal and external signals.
There are two main types of stem cells embryonic stem cells and adult stem cells. Embryonic stem cells are derived from embryos that develop from eggs that have been fertilized artificially in vitro or outside of the living organism. Adult stem cells are undifferentiated cells that are found amongst differentiated cells such as in tissues or organs. The main role of adult stem cells is the repair and maintenance of tissue. A major difference between embryonic stem cells and adult stem cells is in the types of tissue that they can differentiate into - embryonic stem cells can become any cell type in the body while adult stem cells are usually limited to differentiating into the cell types of the tissue that they are found in. Embryonic stem cells also tend to be easily grown while the methods for growing adult stem cells are still not worked out. This leads to differences in their application such as in cell replacement therapies, where large numbers of cells are needed.
Applications of Stem Cells
One important function of stem cells is to help scientists find out about the process of cell differentiation. At present, the signals that turn particular genes on and off and affect stem cell differentiation are not fully understood. Through stem cell research, scientists may be able to gain a greater understanding of human development and many diseases that arise from abnormal cell division and differentiation, such as cancer and birth defects. This will hopefully enable the development of new therapeutic strategies for these diseases.
In addition, new medications and drugs could be tested on differentiated human stem cells. One exciting project currently underway is the testing of cancer cell lines with potential anti-tumor medications. However, there is one obstacle to the effectiveness of drug testing using stem cells: the conditions of the differentiated human stem cells must be identical for each drug testing to allow for the comparison of drug effectiveness. Since our knowledge of the signals that control cell differentiation is still incomplete, it is often very difficult to consistently produce identical differentiated cells for each drug being tested.
Nonetheless, one of the most important and exciting applications of human stem cells is their ability to generate new cells and tissues that could potentially be used to replace ailing or destroyed tissue through a technique called cell-based therapy. At the moment, the demand for transplantable tissues and organs is much greater than the supply that can be generated from human stem cells. However, their potential as a source of replacement cells or tissues gives hope in the treatment of many diseases such as Parkinson's disease, Alzheimer's disease, spinal cord injury, severe skin burns, stroke, diabetes and arthritis.
For example, in type I diabetes patients, the pancreatic cells that normally produce insulin are destroyed by the patients' immune systems. Without insulin, the patient is unable to transport sugar from the blood to the cells, depriving the cells of energy needed for daily functioning. Recent studies demonstrate the potential for human embryonic stem cells to differentiate and become insulin-producing cells. If successful, these cells could be transplanted and used to treat diabetics in the future.
The Future of Stem Cells
At the moment, scientists are still struggling to precisely control stem cells during differentiation, transplantation and engraftment (the insertion of tissue or an organ into the body to replace damaged or defective tissue). In addition, scientists are working to avoid the problem of immune rejection by experimenting with various ways of generating tissues that will not be rejected by the body. Apart from technical obstacles, scientists also face ethical issues, such as whether embryonic stem cells have human life and whether stem cells should be created through embryos produced through in vitro fertilization.
"There are many ethical issues. Someone needs to set some guidelines and make sure people are staying within reasonable bounds. The question is: Who should do it? We shouldn't avoid doing the research just because it's difficult to figure out how to deal with the ethical issues," says Professor Heather Tavernier, a Chemistry professor teaching at Wellesley College, "I think that there are some things that most people would agree are reasonable, and some things that most people would agree are not reasonable. To start with, we should stick with the first category of research, and slowly work on figuring out other types of stem cell research that are ethically acceptable."
Similarly, Gary Yau, a first-year student at the University of Hong Kong, argues that "I think that the government should support stem cell research because it has the potential for researchers to find ways to cure many diseases. [However,] some people also argue that using embryonic stem cells is unethical. It's like killing a human being, although it depends on how we define a human-being."
There is still a long way to go until stem cells can be safely used to cure many debilitating diseases. However, that does not mean that we can simply sit back and let other people decide whether stem cell research should go ahead. Instead, we need to fully understand the importance and applications of stem cell research. By doing so, we will be able to make informed decisions about stem cell research which may influence the government's support of stem cells.
"It would probably be safest to stay away from embryonic stem cell research to start with. There are plenty of stem cells available from umbilical cord blood of babies. I think that the field needs to establish itself as a reasonable, ethical field, using cord blood cells for acceptable research goals," suggests Professor Tavernier, "Stem cell research is important, and people who go too far will just jeopardize the entire field."
Unless otherwise stated, all information was obtained from the National Institute of Health stem cell information website:
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