Stem cells are undifferentiated cells that can be induced to develop into specialized tissue types. They can be derived from a number of cellular sources: adult, fetal, and placental tissues; umbilical cord blood; and embryos. Additionally, cellular reprogramming of body cells can create “induced pluripotent stem cells” that seem to have the full powers of embryonic stem cells. Researchers are investigating how to isolate stem cells from these different sources, culture them, and control their differentiation, in the hope of using them to investigate a variety of biological processes, develop new drugs, and treat a range of diseases.
Human embryonic stem cell research has been politically controversial in the U.S. and some other countries. Some object to any research that destroys human embryos, while others accept investigations that use embryos created but not used for in vitro fertilization (IVF) treatment. In response to restrictions on federal funding, some U.S. states, notably California, have invested large sums in this research.
Exaggerated promises and hopes about stem cell-based procedures have led to a proliferation of unlicensed clinics in the U.S. and elsewhere selling purported stem cell treatments that have not been tested by independent scientists or approved by regulatory authorities. Though some customers report improvements, others have been blinded or experienced unusual cancerous growths.