Stem cells are unlike any other cells in the body. While most cells can replicate only cells exactly like themselves, stem cells can differentiate into different types of cells, depending on the body's need. Three types of stem cells exist; some are more versatile than others. Much research is being done to increase the potential for use of adult stem cells, the least versatile type of stem cell.
Totipotent Stem Cells
Totipotent cells can turn into any cell in the body, but they don't reproduce themselves indefinitely. The only true totipotent cells are found in a newly fertilized egg. For about 4 days, the totipotent cells multiply, producing only a few cells, and then they change into pluripotent cells which, while versatile, aren't nearly as versatile as the totipotent cells, Brown University Division of Biology and Medicine states. Only totipotent cells can be used to create an entire new individual, including the supporting tissues such as the placenta.
Pluripotent Stem Cells
Pluripotent cells are also found only in embryonic and fetal tissue. Th three types of pluripotent cells include: embryonic cells, taken from the inner layer of cells of a 5-day-old blastocyst; embryonic germ cells, taken from the cells that will create the gonads in an embryo; cells removed from gonad tumors in fetuses. Pluripotent cells can be induced to make any type of differentiated cell in the body, given the right conditions. Pluripotent cells can't create a new individual because they can't form the placenta or other tissues necessary to support embryo growth. Stem cells removed from amniotic fluid during diagnostic amniocentesis have also been found to be pluripotent, according to the Mayo Clinic. Stem cell lines can grow indefinitely in the laboratory under the right conditions.
Multipotent Stem Cells
Multipotent stem cells can differentiate but only within a narrow range. Blood stem cells, for example, can differentiate into different types of blood cells but not into muscle. Adult stem cells are mutipotent. Multipotent stem cells can be difficult to isolate from other cells and are limited to producing only certain lines, or type, of cells. Research laboratories have induced some multipotent cells to "reprogrammed" and become pluripotent; these are called induced pluripotent stem cells, or iPSCs, the National Institutes of Health reports. Reprogramming a person's own adult cells to turn into different type of cells bypasses the problem of rejection of foreign tissue, which includes tissue made from stem cells not from oneself.
