Embryonic stem (ES) cells were first discovered in mice in 1981 by Martin Evans. In 1998, James Thomson identified a method to isolate embryonic stem cells from humans. Human embryonic stem cells (hESCs) are obtained from 3-5 day old embryos that remain unused after an in vitro fertilization procedure.
ES cells are grown in a culture medium where they can divide indefinitely, creating ES cell lines. Under certain conditions, ES cells can differentiate, either spontaneously into a variety of cell types or in a directed fashion to produce desired cell types. Scientists can control which cell types are generated by manipulating the culture conditions—for example, changing the surface of the culture dish or adding specific growth factors to the culture medium—as well as by genetically modifying the cells. Researchers have generated many distinct cell types from ES cells, including blood, nerve, heart, bone, liver, and pancreatic cells through these methods.
Regenerative Medicine
Regenerative medicine concerns the creation of living, functional tissues to replace dead, diseased, or malfunctioning ones. ES cells are used in regenerative medicine because they can differentiate into any cell type. While this field is still in the early stages, several potentially beneficial cell types have been produced from ES cells, and clinical studies have begun to test their safety and effectiveness in patients. Some initial results have been promising. For instance, paralyzed patients regained some movement after receiving ES-derived nervous system cells. Additionally, ES cells can be used to study early events in human development and provide a source of specific cell types that can be used in drug testing and other scientific research.
Risks and Controversies
In hESC therapy, ES cells may cause immune rejection in recipient patients, as the embryonic cells are ‘foreign’ to the patient. Additionally, ES cells also carry the risk of tumor formation when implanted. Further, the use of hESCs is also controversial as it involves using human embryos. The controversy stems from the different views of an embryo held by scientists, religious leaders, and policy-makers.
