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Embryonic Stem Cell Questions1. What is an embryonic stem cell? 1. What is an embryonic stem cell? Embryonic stem cells (ESCs) only exist at the earliest stage of embryonic development -- from four days through 14 days after the egg is fertilized. At this point the embryo is a microscopic hollow ball of about 150 cells called a blastocyst. Between 30 and 50 of the cells inside that ball are stem cells that are pluripotent, meaning they have the ability to develop into any of the more than 200 types of cells in our bodies. Embryonic stem cells are unspecialized cells that become specialized. That means that when the proper conditions occur in the body or in a laboratory, like a blank computer microchip, embryonic stem cells can be programmed to develop into specific tissues. 2. What is the source of embryonic stem cells? Embryonic stem cells, as their name suggests, are derived from embryos. But those used for research are generated in a laboratory dish, not derived from eggs fertilized in a woman's body. For people who have problems with fertility, an egg is fertilized by sperm in a laboratory dish at an in vitro fertilization clinic. Some blastocysts are not used for fertility treatment because they are unhealthy, damaged or in excess of what is needed for family-building. Thousands are routinely discarded as medical waste by fertility clinics, and the ESCs removed from these damaged or surplus embryos –- with the donors’ written permission – are used for embryonic stem cell research. Under proper conditions, the embryonic stem cells retain the ability to divide and make copies of themselves, apparently indefinitely. After they have duplicated for many months without changing, they are called a stem cell line. 3. How are embryonic stem cells developed? Growing cells in the laboratory is known as cell culture. Human embryonic stem cells are isolated by transferring the inner cell mass into a plastic laboratory culture dish that contains a nutrient broth known as culture medium. The cells divide and spread over the surface of the dish. The inner surface of the culture dish is typically coated with connective tissue cells that have been treated so they will not divide. This coating layer of cells is called a feeder layer because these cells release nutrients into the culture medium. Over the course of several days, the stem cells from the inner cell mass proliferate (divide or duplicate) and begin to crowd the culture dish. When this occurs, they are removed gently and plated into several fresh culture dishes. The process of distributing the cells to additional plates is repeated many times and for many months, and is called subculturing. After six months or more, the original 30 stem cells yield millions of embryonic stem cells. Embryonic stem cells from a single embryo that have proliferated in cell culture for many months without differentiating and appear genetically normal are referred to as an embryonic stem cell line. Once cell lines are established batches can be frozen and shipped to other laboratories for further culture and experimentation [Source: National Institutes of Health]. 4. How many unused embryos are there? According to a survey conducted by Rand Health in 2003, there are approximately 400,000 such embryos in storage in the United States. (Source: Hoffman, D.I., et al. 2003. Cryopreserved Embryos in the United States And Their Availability for Research. Fertility and Sterility 79: 1063-1069.) Most of these embryos will never be used for fertility treatment either because the parents are successful in having the children they want or because treatment is unsuccessful. In addition to donating unused embryos for research, discarding them or leaving them frozen, there is one more alternative: According to the Rand study, about 2 percent of excess embryos are offered by the parents for adoption to create pregnancies in biologically unrelated mothers. But many parents are uncomfortable and unwilling to offer their excess embryos for adoption. The bottom line is that there is no conflict between the adoption of embryos and the use of embryos for medical research. There are more than enough embryos for both purposes. 5. Are there any drawbacks to using these embryonic cells? One possible drawback to using differentiated embryonic stem cells in stem cell therapies is that embryonic stem cells from one person might be rejected by the immune system as a foreign object when placed into another person, because the proteins on the embryonic stem cell surfaces might be recognize as foreign by the recipient's immune system. The potential for the rejection of cells from unrelated donors applies equally to adult stem cells and embryonic stem cells. However, while adult stem cells can sometimes be isolated from a patient and then transplanted into the same patient, embryonic stem cells would always be from an unrelated donor, unless they can be derived by therapeutic cloning. Therapeutic cloning is a way of making embryonic stem cells that are genetically identical to a particular patient (see “Cloning: Therapeutic vs. Reproductive” section). There is hope that eventually the problems within the iPS process will be eliminated and it will be possible to use iPS cell-based therapies for treatments. But we are not yet at that point. Scientists continue to investigate this approach to develop ways of minimizing the rejection of adult stem cells and embryonic stem cells from unrelated donors. 6. Why are doctors and scientists so excited about embryonic stem cells? We are at the very earliest stages of stem cell research and still have a great deal to learn. Embryonic stem cell research provides insight into the origin of disease and may lead to new, more effective treatments for serious human ailments such as juvenile diabetes, Parkinson's disease, ALS, cancer, heart failure and spinal cord injuries. Scientists believe research using these cells may answer fundamental questions about how specialized cells develop in an embryo, and how they communicate and work together to form all the tissues and organs in the body. In addition, stem cell lines will be useful for testing the safety and effectiveness of new drugs on human tissue, so they are optimized before reaching the open market. Another potential application of stem cells is making cells and tissues for medical therapies. Today, donated organs and tissues are often used to replace those that are diseased or destroyed. Unfortunately, the number of people needing a transplant far exceeds the number of organs available for transplantation. Through stem cell research, scientists may be able to generate healthy heart muscle cells in the laboratory and then transplant those cells into patients with chronic heart disease. Pluripotent stem cells offer the possibility of a renewable source of replacement cells and tissues. In January 2009, the FDA approved the first-ever human clinical trials using therapies derived from human embryonic stem cells. California based Geron will test a new treatment for recent spinal cord injuries. Another, using ESCs to repair retinal damage, is pending approval. |
Basic Questions
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Copyright © 2006, 2009 Michigan Citizens For Stem Cell Research & Cures