Question: What are stem cells?
Answer: Most cells in the body are committed to fulfilling specific functions, such as beating heart cells or insulin-secreting pancreas cells. Stem cells are not committed yet -- they are capable of becoming any number of cell types, depending on the biochemical signals they receive from their environment. Stem cells can also replicate indefinitely; other cells usually divide a limited number of times.
For The Record
Los Angeles Times Wednesday August 02, 2006 Home Edition Main News Part A Page 2 National Desk 1 inches; 53 words Type of Material: Correction
Stem cells: A Questions & Answers article in Sunday's Section A stated that some lines of human embryonic stem cells cannot be transplanted into humans because they were grown in the presence of mouse cells. Although some scientists and physicians think this, others are convinced the stem cells are safe for human therapies.
Q: What are embryonic stem cells?
A: Embryonic stem cells are from days-old embryos. They are pluripotent, meaning they can give rise to any type of cell in the body. Researchers harvest the cells from excess embryos donated from in vitro fertilization clinics with the informed consent of the donors. When an embryo has developed for four or five days, it is a ball of cells. Cells from the center of this ball are taken out, destroying the embryo, and are grown in a petri dish into millions of cells -- a "cell line" scientists can study in the laboratory. Some people consider embryo destruction immoral.
Q: What are adult stem cells?
A: Adult stem cells are in some organs and tissues, functioning as resources for renewal. They are less versatile than embryonic stem cells, because they are committed to certain broad pathways instead of being able to become any type of cell. Adult hematopoietic stem cells found in the bone marrow, for example, can become white blood cells or red blood cells, but not heart cells or brain cells. Because nothing is destroyed to obtain adult stem cells, research on these cells is not controversial.
Q: Why are people so interested in stem cells?
A: The special features of stem cells make them key in understanding both normal biological development and development gone awry, such as birth defects or cancer.
Stem cells also have potential medical applications. In cases where a patient's cells have been damaged, such as with Parkinson's disease, diabetes or spinal cord injury, transplantation of stem cells might regenerate lost tissue -- a strategy already used in bone marrow transplants. There is no proof that other types of stem cell transplants would work, but several animal studies have been promising. There is debate over which type of stem cell is better suited to medical applications: Embryonic stem cells could be used to replace many more types of cells, but adult stem cells harvested from a patient could be used to provide a perfect tissue match.
Q: Do stem cells have something to do with cloning?
A: Stem cells and cloning are not the same thing, but they are often discussed together. This is because scientists have used a type of cloning called somatic cell nuclear transfer to create stem cells in animals.
SCNT is the technology that produced Dolly the cloned sheep. In this process, the DNA of an adult cell is put into an egg, which is then allowed to develop into the hollow ball from which stem cells are harvested.
Some scientists think that human SCNT -- also known as "therapeutic cloning" -- could be an alternative to using excess embryos from IVF clinics, although critics say the method still would involve embryo destruction. In addition to making normal embryonic stem cells, scientists could use SCNT to make stem cell lines from diseased cells to study the diseases. Creating stem cells with SCNT would also open the possibility of making personalized embryonic stem cells to treat patients.
Q: What is the law regarding stem cell research?
A: There are no laws against stem cell research, but there are restrictions on the use of federal funding for embryonic stem cell research.
President Bush mandated that no federal money could be used to study embryonic stem cell lines created after Aug. 9, 2001.
Congress recently passed a bill that would have lifted this restriction. The president vetoed the bill, and the bill died because the House of Representatives did not have the two-thirds majority needed to override the veto.
Q: Why is the restriction on federal funding a big deal?
A: Universities depend on federal funding for about 60% of their research budgets. Without this money, scientists must rely on private and state funds to advance their stem cell research.
Many scientists think the number of embryonic stem cell lines eligible for federal funding is too small. When the president announced his stem cell policy in 2001, 78 lines were thought to be available. The number is about 20 now because the rest are unavailable or not research-quality.
Additionally, the remaining cell lines were grown in the presence of mouse cells to help nourish them and get them to stick to the petri dish. This makes them unsuitable for transplanting into humans. Scientists want to make new stem cell lines now that they know how to grow them without mouse cells.
Q: What's the California situation on stem cells?
A: In November 2004, 59% of California voters approved Proposition 71, paving the way for the state to provide $3 billion over 10 years to stem cell research. Connecticut, Illinois, Maryland and New Jersey have also approved state funds to fill in the gap left by the lack of federal funding.
Several groups have challenged the constitutionality of Proposition 71 and are appealing an April state Superior Court decision that upheld the proposition.
The legal wrangling has prevented the use of any Proposition 71 money for research. To get the California Institute for Regenerative Medicine off the ground, the state is selling bonds to philanthropists, and the governor lent $150 million from the general fund.