Stem cells have the remarkable potential to develop into many different cell types in the body during early life and growth. In addition in many tissues they work as a sort of internal repair system, dividing essentially without limit to replenish other cells as long as the person or animal is still alive. When a stem cell divides, each cell has the potential either to remain a stem cell or become another type of cell, a redblood cell or a brain cell.
Stem cells are distinguished from other cell types by two important characteristics. First they are unspecialized cells capable of renewing themselves through cell division, sometimes after long periods of inactivity. Second, under certain physiologic or experimental conditions, they can be induced to proliferate into other mature cells.
Adult stem cells are found in bone marrow, blood, the cornea, adipose tissue (fat), intestine, liver, muscle, nervous system, and the brain, pancreas and skin. Hematopoietic stem cells are blood-forming stem cells, which largely reside in bone marrow. They are responsible for replenishing all blood cell types on a continual basis. Mesenchymal stem cells, also found in bone marrow and fat tissue, can go on to form cells including muscle, fat, skin, and cartilage. Currently stem cells of both types are being tested to treat many conditions including: Alzheimer’s, blood disorders, blood loss, baldness, blindness, cystic fibrosis, deafness, diabetes, heart disease, kidney failure, liver damage, lupus, motor neuron disease, multiple sclerosis, osteoporosis, Parkinson’s disease, spinal cord injuries, cancer and stroke. Perhaps the most important potential application of human stem cells is the generation of cells and tissues that could be used for cell-based therapies.