In multicellular organisms,<unk> s are undifferentiated or partially differentiated cells that can differentiate into various types of cells and proliferate indefinitely to produce more of the same<unk> . They are the earliest type of cell in a cell lineage. They are found in both embryonic and adult organisms, but they have slightly different properties in each. They are usually distinguished from progenitor cells, which cannot divide indefinitely, and precursor or blast cells, which are usually committed to differentiating into one cell type. In mammals, roughly 50–150 cells make up the inner cell mass during the blastocyst stage of embryonic development, around days 5–14. These have<unk>  capability. In vivo, they eventually differentiate into all of the body's cell types (making them pluripotent). This process starts with the differentiation into the three germ layers – the ectoderm, mesoderm and endoderm – at the gastrulation stage. However, when they are isolated and cultured in vitro, they can be kept in the<unk>  stage and are known as embryonic<unk> s (ESCs). Adult<unk> s are found in a few select locations in the body, known as niches, such as those in the bone marrow or gonads. They exist to replenish rapidly lost cell types and are multipotent or unipotent, meaning they only differentiate into a few cell types or one type of cell. In mammals, they include, among others, hematopoietic<unk> s, which replenish blood and immune cells, basal cells, which maintain the skin epithelium, and mesenchymal<unk> s, which maintain bone, cartilage, muscle and fat cells. Adult<unk> s are a small minority of cells; they are vastly outnumbered by the progenitor cells and terminally differentiated cells that they differentiate into. Research into<unk> s grew out of findings by Canadian biologists Ernest McCulloch, James Till and Andrew J. Becker at the University of Toronto and the Ontario Cancer Institute in the 1960s. , the only established medical therapy using<unk> s is hematopoietic<unk>  transplantation, first performed in 1958 by French oncologist Georges Mathé. Since 1998 however, it has been possible to culture and differentiate human embryonic<unk> s (in<unk>  lines). The process of isolating these cells has been controversial, because it typically results in the destruction of the embryo. Sources for isolating ESCs have been restricted in some European countries and Canada, but others such as the UK and China have promoted the research. Somatic cell nuclear transfer is a cloning method that can be used to create a cloned embryo for the use of its embryonic<unk> s in<unk>  therapy. In 2006, a Japanese team led by Shinya Yamanaka discovered a method to convert mature body cells back into<unk> s. These were termed induced pluripotent<unk> s (iPSCs).
Stem cell
Blood cell
Progenitor cell
Hematopoietic stem cell
Neural stem cell
Lymphoblast
Cancer stem cell
Brain cell