Stem cells can be described as shape-shifters: They are young, undeveloped cells that have not yet been assigned an adult role. They are a biological blank slate that can be turned into almost any kind of tissue. For this reason, stem cells hold enormous medical potential—to create insulin-producing cells for people with diabetes or new brain cells for those with Parkinson’s disease, for example. But because harvesting stem cells often involves the destruction of human embryos, research involving them has met with controversy.

In the early 1960s, the Canadian scientists James Till (1931–) and Ernest McCulloch (1926–) began experimenting with bone marrow cells injected into mice that had been weakened by radiation, much as humans would be after treatment for a cancer such as leukemia. They observed that tiny lumps grew on the spleens of the mice, and Till and McCulloch speculated that these “spleen colonies” arose from marrow cells they called colony-forming, or multipotent, cells. In 1961 and again in 1963, the pair published its results.

There are two main types of stem cells: Embryonic stem cells are not yet “differentiated” and are generally able to develop into more types of cells. Adult stem cells, which are found in the bone marrow, the brain, and other areas of the body, are less flexible and therefore not as highly valued by researchers. Stem cells can also come from the umbilical cord of a baby or the amniotic fluid of a pregnant woman.

The first stem cells grown in a lab were those of mice. In 1998, researchers at Johns Hopkins University in Baltimore and the University of Wisconsin in Madison successfully extracted and cultured the first human stem cells. One experiment used donated eggs and sperm to create blastocysts (3-to 5-day-old embryos consisting of about 100 cells); the other used cells from aborted fetuses.

Embryonic stem cell research has been opposed by people who believe that blastocysts are human life and are against abortion. This has created controversy and has led to a search for other sources of stem cells, including attempts to induce mature cells to revert to stem cells in the laboratory.

ADDITIONAL FACTS

  1. Congress restricted the study of stem cells in 1996, rules that were reinforced by President George W. Bush (1946–) in 2001 and limited federally funded researchers to using only existing stem cell lines. Some of those restrictions were lifted by President Barack Obama (1961–) in 2009.
  2. In 2008, researchers at the University of California, San Francisco, created the first human embryonic stem cells developed without the destruction of a human embryo.
  3. In 2009, University of Wisconsin–Madison researchers announced that they had changed skin cells back into stem cells, which they then turned into heart muscle cells.