Embryonic stem cells are unique in their ability to renew themselves indefinitely by producing identical cells. In addition, under certain physiologic or experimental conditions, they can be induced to give rise to many different types of cells, each with specialized functions. In 1998, Thomson and colleagues discovered how to isolate such pluripotent embryonic stem cells from human embryos in culture.The embryos used in these experiments were created originally for use in in vitro fertilization (IVF). They existed only in the culture dish and each contained about 20–100 cells. When they were no longer needed for IVF, they were donated for research with the informed consent of the donors. Cells isolated from these embryos, when grown in culture, become pluripotent embryonic stem cells that reproduce indefinitely and are capable of forming many of the specialized cell types of the body. These cells have the potential for use in the treatment of life-threatening lung diseases, such as emphysema, interstitial lung diseases, asthma, lung cancer, and ARDS, as well as Parkinson's and Alzheimer's diseases, spinal cord injury, stroke, burns, heart disease, diabetes, osteoarthritis, and rheumatoid arthritis, through their ability to generate replacement tissue for damaged cells or organs.