cornea and retina of the eye, the dental pulp of the tooth, liver, skin, gastrointestinal tract, and pancreas. Unlike embryonic stem cells, at this point in time, there are no isolated adult stem cells that are capable of forming all cells of the body. Adult stem cells have been used in transplantation on numerous occasions in the past few decades, especially recently (Saitou 401).
             Stem cells may hold the key to replacing cells lost in many devastating diseases. There is little doubt that this potential benefit underpins the vast interest about stem cell research. Already many forms of adult stem cells are being used in the treatment of cancerous diseases in hematopoietic (blood) cells such as leukemia and lymphoma and in childhood brain tumors and neuroblastoma, an uncommon cancer that occurs most often in children. The bone marrow of a matching donor, generally a direct sibling, is usually the source of hematopoietic stem cells for transplantation. Recently, however, scientists have been able to make transplants using the hematopoietic stem cells from umbilical cord blood. These transplantations have frequently proven to be more efficient and easier to undergo because they take less time and are easier to match a donor, but just like in the bone marrow transplants there are many risks with the procedure (Stem Cells).
             The primary goal for both bone marrow transplants and umbilical cord blood transplants are to obtain a source of stem cells that is the best possible match for a particular patient's tissue type. The tissue type of a cell is determined by the set of genes that make proteins called human leukocyte antigens (HLAs), which can be found on the surface of all somatic cells. The immune system recognizes each cell as part of the body or not by means of these HLA proteins. If the immune system reads that the proteins are not foreign, then it will leave the cell alone. However, the immune system quickly kills al...