Stem Cells Fast Facts

(CNN)Here is some background information about stem cells.

Scientists believe that stem cell research can be used to treat medical conditions including Parkinson's disease, spinal cord injury, stroke, burns, heart disease, diabetes, osteoarthritis and rheumatoid arthritis.

About Stem Cells

    Sources: National Institutes of Health, Mayo Clinic
      Stem cell research focuses on embryonic stem cells and adult stem cells.
      Stem cells have two characteristics that differentiate them from other types of cells:
      - They are unspecialized cells that can replicate themselves through cell division over long periods of time.
        - Stem cells can be manipulated, under certain conditions, to become mature cells with special functions, such as the beating cells of the heart muscle or insulin-producing cells of the pancreas.
        There are four classes of stem cells: totipotent, multipotent, pluripotent and unipotent.
        - Totipotent stem cells that develop into cells that make up all the cells in an embryo and fetus. (Ex: The zygote/fertilized egg and the cells at the very early stages following fertilization are considered totipotent.)
        - Multipotent stem cells can give rise to multiple types of cells, but all within a particular tissue, organ or physiological system. (Ex: blood-forming stem cells/bone marrow cells, most often referred to as adult stem cells)
        - Pluripotent stem cells (ex: embryonic stem cells) can give rise to any type of cell in the body. These cells are like blank slates, and they have the potential to turn into any type of cell.
        - Unipotent stem cells can self-renew as well as give rise to a single mature cell type. (Ex: sperm producing cells)
        Embryonic stem cells are harvested from four to six-day-old embryos. These embryos are either leftover embryos in fertility clinics or embryos created specifically for harvesting stem cells by therapeutic cloning. Only South Korean scientists claim to have successfully created human embryos via therapeutic cloning and have harvested stem cells from them.
        Adult stem cells are already designated for a certain organ or tissue. Some adult stem cells can be coaxed into or be reprogrammed into turning into a different type of specialized cell within the tissue type - for example, a heart stem cell can give rise to a functional heart muscle cell, but it is still unclear whether they can give rise to all different cell types of the body.
        The primary role of adult stem cells is to maintain and repair the tissue in which they are found.

        Uses of Stem Cell Research

        Regenerative medicine uses cell-based therapies to treat disease.
        Scientists who research stem cells are trying to identify how undifferentiated stem cells become differentiated as serious medical conditions, such as cancer and birth defects, are due to abnormal cell division and differentiation.
        Scientists believe stem cells can be used to generate cells and tissues that could be used for cell-based therapies as the need for donated organs and tissues outweighs the supply.
        Stem cells, directed to differentiate into specific cell types, offer the possibility of a renewable source of replacement cells and tissues to treat diseases, including Parkinson's and Alzheimer's diseases, spinal cord injury, stroke, burns, heart disease, diabetes, osteoarthritis and rheumatoid arthritis.

        Policy Debate

        Cloning human embryos for stem cells is very controversial.
        The goal of therapeutic cloning research is not to make babies, but to make embryonic stem cells, which can be harvested and used for cell-based therapies.
        Using fertilized eggs left over at fertility clinics is also controversial because removing the stem cells destroys them.
        Questions of ethics arise because embryos are destroyed as the cells are extracted, such as: When does human life begin? What is the moral status of the human embryo?

        Timeline

        1998 - President Bill Clinton requests a National Bioethics Advisory Commission to study the question of stem cell research.
        1999 - The National Bioethics Advisory Commission recommends that the government allow federal funds to be used to support research on human embryonic stem cells.
        2000 - During his campaign, George W. Bush says he opposes any research that involves the destruction of embryos.
        2000 - The National Institutes of Health (NIH) issues guidelines for the use of embryonic stem cells in research, specifying that scientists receiving federal funds can use only extra embryos that would otherwise be discarded. President Clinton approves federal funding for stem cell research but Congress does not fund it.
        August 9, 2001 - President Bush announces he will allow federal funding for about 60 existing stem cell lines created before this date.
        January 18, 2002 - A panel of experts at the National Academy of Sciences (NAS) recommends a complete ban on human reproductive cloning, but supports so-called therapeutic cloning for medical purposes.
        February 27, 2002 - For the second time in two years, the House passes a ban on all cloning of human embryos.
        July 11, 2002 - The President's Council on Bioethics recommends a four-year ban on cloning for medical research to allow time for debate.
        February 2005 - South Korean scientist Hwang Woo Suk publishes a st