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Stem Cell Science Frequently Asked Questions
What is a cell?
Cells are the structural and functional units of all living organisms. Some organisms, such as bacteria, are unicellular, consisting of a single cell. Other organisms are multicellular and may have many cells. Humans have an estimated 100,000,000,000,000 (one hundred trillion) cells and more than 200 different types of cells (liver cells, skin cells, muscle cells, etc.). ∗
What is a stem cell?
Stem cells have the remarkable potential to develop into many different cell types in the body. They can divide without limit to replenish other cells, serving as a sort of repair system for the body. When a stem cell divides, each new cell has the potential to either remain a stem cell or become another type of cell with a more specialized function, such as a muscle cell, a red blood cell, or a brain cell. ∗
Are all stem cells the same?
No. Stem cells isolated from different sources and tissues are distinct in that they have varying degrees of potency (see next question) and give rise to differing mature cell types. Additionally, as each person differs slightly at the genetic level (their DNA sequence), the stem cells derived from each individual are likewise different.
What is the difference between totipotent, pluripotent, and multipotent?
Totipotent cells can form all the cell types in a body, plus the extraembryonic, or placental, cells. Embryonic cells within the first couple of cell divisions after fertilization are the only cells that are totipotent. Pluripotent cells can give rise to all of the cell types that make up the body; embryonic stem cells are considered pluripotent. Multipotent cells can develop into more than one cell type, but are more limited than pluripotent cells; adult stem cells and cord blood stem cells are considered multipotent.
How do embryonic stem cells, somatic stem cells, and cord blood stem cells differ?
Embryonic stem cells (ESCs) are derived from the embryo and have the potential to become all the different cell types of the body (pluripotency). Somatic stem cells, sometimes called adult stem cells, are found in organs or tissues, can self-renew and yield the differentiated cell types comprising that organ or tissue (multipotency), and are important for maintenance and repair of the organ or tissue. Cord blood stem cells can be isolated from the umbilical cord of newborn infants and are less mature than adult stem cells. Cord blood stem cells are a type of somatic stem cell. Somatic stem cells are restricted in the types of cells they can produce in the lab.
How are embryonic stem cell lines made (in the lab)?
Embryonic stem cells are usually derived from the inner cell mass of preimplantation embryos, corresponding to 5-9 days after fertilization in humans and 3-4 days in mice. Embryos used to generate human ESCs come from several sources. The first human ESCs were derived from donated embryos left after in vitro fertilization (IVF). IVF embryos analyzed by preimplantation genetic diagnosis can also be used to generate ESCs. An alteration of this technique allows generation of ESCs from single cells removed from embryos in a process similar to preimplantation genetic testing. ESCs can be derived from eggs that have been parthenogenetically activated; that is, the eggs are induced to divide without being fertilized by sperm. Somatic cell nuclear transfer (SCNT) can be used to produce embryos from somatic or adult cells using donated enucleated eggs, and then ESCs can be generated from the resulting embryos.
Where do embryos come from to make new ESC lines?
When embryos are used to generate human ESC lines, they come from donations after in vitro fertilization cycles by individuals who have given written informed written consent. Alternatively, hESC lines can be derived from donated eggs that are activated to begin development without fertilization by sperm, or from SCNT embryos.
What are induced pluripotent stem (iPS) cells?
iPS cells are somatic cells that were manipulated to exhibit properties of embryonic stem cells. Introduction of a set of four factors into somatic cells, along with specific culture conditions, alters each cell's epigenetic signature, resetting the cell to a pluripotent ESC-like state. This process is termed "reprogramming." Like ES cells, iPS cells can be differentiated into many different cell types in the lab, and mouse iPS cells have passed even the most stringent tests for pluripotency. iPS cells have been derived from patients affected by a number of diseases, allowing scientists to develop new models of these diseases and screen potential therapeutic agents. iPS cells, therefore, have great potential to contribute to the search for new therapies. Although ES cells remain the gold standard for pluripotency, the scientific community is actively investigating the potential of iPS cells to fulfill many of the research purposes of ESCs. Moreover, if significant safety concerns can be overcome, iPS cells could eventually be valuable to the development of cell-based therapies.
Is it true that some somatic stem cells in our bodies can be the source of common cancers?
So-called cancer stem cells are cancer cells that have stem cell-like properties, i.e., they can self-renew and differentiate into other cell types. They are associated with some, but not all, types of cancers. Data suggest that recurrence of some cancers is caused by a failure of current therapies to target and kill these cancer stem cells. However, the relationship between cancer stem cells and somatic stem cells is unclear. Somatic stem cells can become cancerous, but cancer stem cells do not necessarily come from somatic stem cells.
How are stem cells currently used to treat disease?
Somatic stem cells, such as blood-forming stem cells in bone marrow (called hematopoietic stem cells, or HSCs), are currently the only type of stem cell commonly used to treat human diseases. Doctors have been transferring HSCs in bone marrow transplants for over 40 years. More advanced techniques for collecting, or "harvesting," HSCs are now used in order to treat leukemia, lymphoma and several inherited blood disorders. The clinical potential of somatic stem cells has also been demonstrated in the treatment of other human diseases that include diabetes and advanced kidney cancer. However, these newer uses involved studies with a very limited number of patients. ∗
What are the potential benefits of stem cell research?
The National Institutes of Health indicates that approximately 1.1 million Americans suffer a heart attack each year, and together cardiovascular diseases and cancers are the top two causes of death according to the CDC, with each killing over half a million Americans each year. Regenerative medicine holds the promise of new ways to repair cardiovascular damage and of improved cancer treatment. Moreover, there are many other diseases and afflictions that stand to be positively impacted by stem cell research including: stroke, respiratory disease, diabetes (respectively 3, 4 and 7 on the CDC list of causes of death), neurological disorders, spinal cord injuries, and some birth defects. Potential benefits of stem cell research are numerous and range from development and testing of new drugs to cell-based therapies in which stem cells are used to replace ailing or destroyed tissue or cells. However, there are many technical hurdles between the promise of stem cells and the realization of these uses, which will only be overcome by continued intensive stem cell research.
What are the risks of stem cell therapy?
As with any treatment, there are certain risks to stem cell therapy, including immune rejection of the cells used in treatment. Stem cells have the potential to divide many times and differentiate into many cell types, which is their great promise. Paradoxically, because of these abilities, stem cells also have the potential to form tumors. These potential risks dictate that both doctors and patients proceed with caution, and thus it is critically important that further research is conducted.
What is the difference between reproductive and therapeutic cloning?
Reproductive cloning involves creating an animal that is genetically identical to a donor animal through somatic cell nuclear transfer. In reproductive cloning, the newly created embryo is placed back into the uterine environment where it can implant and develop. Dolly the sheep is perhaps the most well known example. In therapeutic cloning, an embryo is created in a similar way, but the resulting "cloned" cells remain in a dish in the lab; they are not implanted into a female's uterus. [NOTE: ESSC Board statute specifically prohibits support for research that directly or indirectly involves human reproductive cloning.]
What about all the advertisements or news stories of people going abroad for stem cell treatment ("medical tourism")?
While many clinics advertise stem cell cures for many different diseases, clinical trials on the use of stem cells are very limited. Most of the success stories reported in the news and on the internet are anecdotal accounts. The reports on the success of such treatments cannot replace large-scale, rigorously controlled clinical trials to prove both the safety and efficacy of treatments. Additionally, the people running such clinics and profiting from them are the same people declaring them to be safe and successful, presenting potential conflicts of interest. Finally, participation in these treatments may preclude participation in future clinical trials in this country. The International Society for Stem Cell Research (ISSCR) has published a useful guide to clinical uses of stem cells. Please consult your physician before undertaking any therapy or treatment.
Where can I find information on clinical trials using stem cells?
The National Institutes of Health maintains a registry of current clinical trials, including trials that are recruiting new volunteers. The FDA recently approved the first clinical trial in the US using hESC-derived cells. However, this trial uses cells derived from hESCs; hESCs themselves have not yet been approved for use in clinical trials.
Where can I find more information on donating eggs for research?
Human embryonic stem cell research is dependant on the availability of donated eggs. However, before donating eggs, you should speak with a physician so you are aware of the risks involved in the procedure, and the processes for which your eggs may be used. New York State prepared information related to egg donation for infertile couples. In 2007, the National Academy of Sciences published a book on evaluating the risks of egg donation for stem cell research.
How can I donate eggs (oocytes) for stem cell research in New York State?
The NYSTEM program is not directly involved in obtaining eggs (oocytes) for use in stem cell research. The NYSTEM program provides funds to New York State stem cell researchers to conduct all types of stem cell research, including research involving plant, animal and human stem cells. On June 11, 2009 the Empire State Stem Cell Board revised the standards that apply to NYSTEM-funded research to compensate oocyte donors donating specifically for research purposes. The NYSTEM program does not maintain a listing of researchers who are engaged in, or considering, research using oocytes retrieved specifically for research purposes. As a result, we do not have a list of investigators or institutions that are seeking oocyte donations for stem cell research. You may be able to identify a facility that will assist you in donating oocytes for research purposes by contacting the research office of a local university or a health clinic providing in vitro fertilization (IVF) that is associated with a research institution or university. Please note that any institution providing such a service in New York State must be licensed by the New York State Department of Health. Other states may have similar requirements or laws, and the Department of Health in your state may be able to provide state-specific information.