What are embryonic stem cells?
Embryonic stem cells make up the inner cell mass of the blastocyst, a body of cells that forms in the first few days immediately following fertilization. Blastocysts are about the size of a grain of sand and typically consist of about 150 cells. What's so special about these cells?
Most cells can only produce limited copies of the same kind. Embryonic stem cells, by contrast, can develop into many different cell types in the body, and have a limitless ability to divide and replenish. As a result, embryonic stem cells are an ideal research material. Scientists hope they can manipulate these cells to one day produce therapies targeting specific diseases, and even regrow damaged or destroyed tissues for any part of the body. Have doctors cured anyone using human embryonic stem cells?
The jury is still out. Some researchers, mostly in developing countries, have claimed success. But no one has yet published successful results in a peer-reviewed medical journal -- a step required for scientific acceptance and confirmation. Why are some people opposed to embryonic stem-cell research?
Extracting embryonic stem cells from the blastocyst destroys the embryo. Some religious and other groups believe human life begins at conception, and therefore are ethically opposed to embryonic stem-cell research. Is it currently illegal to conduct embryonic stem-cell research in the United States?
No. Existing regulations only restrict the funding activities of the National Institutes of Health, or NIH, the organization that allocates federal funds for medical research. Under the current rules, the NIH can't fund embryonic stem-cell research except with stem-cell lines approved by the president. But scientists can use private funding to perform embryonic stem-cell research. What happens Tuesday?
The Senate will vote on three stem-cell bills, all of which are expected to pass. Two of those bills are in line with the Bush administration's embryonic stem-cell policy. The third is expected to force a showdown and face an almost-certain veto.
The Stem Cell Research Enhancement Act (SB471) is the Senate version of HR810, a bill approved by the House of Representatives last year that would allow researchers to use surplus embryos produced at fertility clinics that would otherwise be discarded. The bill was amended to bar federal funding for research that results in the destruction of embryos; but it would supersede a 2001 executive order from Bush that restricts NIH funding of embryonic stem-cell research to embryonic stem-cell lines that were already created by that date. Are embryos the only source of stem cells?
No. Stem cells can be found in many mature tissues, including bone marrow, blood, the brain, hair follicles, fat, the pancreas and umbilical cords. These stem cells are called "adult" stem cells. Researchers have also derived stem cells from fetal tissue taken from embryos older than eight weeks, usually following abortion or spontaneous miscarriage. Does anyone object to using adult stem cells?
No. Objections to date have been focused on harvesting embryonic stem cells. So why don't scientists just use adult stem cells instead?
Doctors have been using adult stem cells, such as the blood-forming type in bone marrow (called hematopoietic stem cells), to perform bone-marrow transplants for more than 40 years. Similar techniques have since been developed for treating leukemia, lymphoma and several inherited blood disorders. But scientists believe adult stem cells are not as flexible as embryonic stem cells, and hold far less promise for extreme therapies, such as rebuilding nerves severed in a spinal cord injury. Are there any other options?
Maybe. Scientists and ethicists have been working on alternatives for obtaining stem cells as powerful as those that come from embryos without actually creating or destroying an embryo. Scientists presented several proposals to the President's Council on Bioethics in May 2005. One of the bills up for vote this week asks the NIH to focus on making these alternative methods viable.