Short answers, pulled from the story.
Ernest McCulloch and James Till at the University of Toronto's Faculty of Medicine and the Ontario Cancer Institute first defined the key properties of stem cells in the early 1960s. Working with graduate student Andrew John Becker and senior scientist Louis Siminovitch, they demonstrated that blood-forming stem cells could both give rise to new cells and renew themselves. Their results were published in Nature in 1963.
The first documented therapeutic use of stem cells was a bone marrow transplant performed by French oncologist Georges Mathé in 1956. Mathé treated five workers from the Vinča Nuclear Institute in Yugoslavia who had been exposed to a criticality accident. All five workers survived.
Induced pluripotent stem cells (iPSCs) are ordinary adult cells that have been reprogrammed to behave like embryonic stem cells. Shinya Yamanaka and his colleagues at Kyoto University first demonstrated this in 2006, converting mouse fibroblast cells into pluripotent cells using four transcription factors: Oct3/4, Sox2, c-Myc, and Klf4.
Deriving embryonic stem cells typically requires destroying the early-stage embryo, which critics argue violates the sanctity of human life. The debate centers on the moral status of the human blastocyst. Several European countries and Canada have restricted sources for isolating these cells, while the United States limits federal funding to approved existing cell lines and bars funds for creating new ones.
Hematopoietic stem cell transplantation is the only widely established stem cell therapy. It has been used for more than 50 years to treat conditions such as leukaemia and lymphoma, most commonly through bone marrow transplantation. Umbilical cord blood is also used as a source of these cells.
Stem cells are classified by how many cell types they can produce. Totipotent cells can build a complete organism including extraembryonic membranes. Pluripotent cells can become any of the more than 200 cell types of the adult body. Multipotent cells are limited to a related family of cell types, oligopotent cells produce only a few types, and unipotent cells generate only one type but retain self-renewal ability.