Stem-cell research: Stem-cell research studies how stem cells can be extracted and used to treat a variety of medical conditions and diseases. There are two basic types of stem cells: adult stem cells and early, or embryonic, stem cells. Adult stem cells are partially specialized cells that can turn into some body cells and tissues. For example, blood-forming adult stem cells in bone marrow can turn into certain types of blood-related cells. Human adult stem cells are used to treat about 10 medical conditions, primarily blood-related diseases, such as certain types of leukemia. Adult-type stem cells are found in body tissues, such as tissues in the bodies of adults and discarded umbilical cords and placentas. Scientists believe they can be useful but potentially not as versatile as early stem cells.
Early stem cells are “pluripotent,” meaning they are unspecialized cells that have potential to turn into and regenerate any type of cell or tissue in the human body. Scientists believe early stem cells could provide cures for many currently incurable or common diseases and injuries, such as diabetes, Parkinson’s, Alzheimer’s, sickle cell disease, cancer, heart disease and spinal cord injury. There are currently two sources of early stem cells: leftover fertility clinic embryos that would otherwise be discarded and destroyed, and a laboratory process called Somatic Cell Nuclear Transfer, which provides a way to make early stem cells in a lab dish for medical purposes. Use of these cells from embryos is controversial for many in the religious community on the basis that it could amount to human cloning, an unnatural act of “creation” taken from the hand of God, with an array of ethical ramifications; and that embryos could be — or develop into — human beings with rights to life.
Techniques: Embryos used in stem-cell research are at the stage before they would be implanted in a uterus, usually within one to five days after fertilization. Stem cells are isolated from the embryo, which eliminates its potential to develop into a complete human being. In Somatic Cell Nuclear Transfer, the nucleus of an unfertilized egg is removed and replaced with the nucleus of a patient’s body cell that contains a full set of genetic information. The patient’s genetic material incorporates into the egg and causes it to develop into a blastocyst (an early-stage embryo with about 100 undifferentiated cells) which almost identically matches the patient’s DNA. This pre-embryo contains a cluster of stem cells. The inner cell mass of the embryo is extracted, leaving the stem cells, and destroying the embryo. This technique is currently the basis for cloning animals, such as Dolly the sheep. SCNT research in humans requires human eggs. The most common source is eggs extracted from women during in vitro fertilization procedures in excess of clinical need. Presently, no human stem cell lines have been derived from SCNT research.
Some researchers are trying to find alternative methods of obtaining embryonic stem cells that don’t involve the death of an embryo. One uses a process similar to “Pre-implantation Genetic Diagnosis,” a procedure requested by prospective human parents who are aware that they are carriers of an incurable genetically-based disease or disorder and are concerned about passing the problem to their child. Fertility clinics extract a single cell from each embryo produced by the couple and test it for the genetic problem. Embryos found to be free of the disorder are implanted in the woman’s womb; defective embryos are discarded. Scientists used a similar procedure on two-day-old mouse embryos that contained eight cells each. They found that a single cell – called a blastomere – removed from each embryo behaved like embryonic stem cells, while the seven remaining cells continued to develop. Previous research showed that one or even two cells could be removed from an eight-cell embryo without adverse effect. The embryos were implanted in the wombs of mice, and continued to mature into normal baby mice. Researchers ended up with only a single stem cell from each embryo — rather than about 150 stem cells harvested from an entire embryo — but methods exist to produce stem cells from a single cell.
In other research on mouse embryos, researchers used a modified version of Somatic Cell Nuclear Transfer. They blocked the action of a key gene in the nucleus before inserting the nucleus into the egg, so that the resulting “non-embryonic entity” would not be able to develop into a conventional embryo that could be implanted in a uterus and induce a pregnancy. Scientists argue that if this technique were successful with human embryos, “patient-specific” embryonic stem cells could be produced without destroying potential human life.