As discussed, stem cells are used to treat degenerative diseases. One form of a degenerative disease that can occur in the brain as well as throughout the body is an autoimmune disease. Autoimmune diseases cause the body to "attack" its own cells and therefore destroys those cells as well as whatever functional purpose those cells have or contribute to. One form of an autoimmune disease that affects the central nervous system is multiple sclerosis. In this disease the body attacks the glial cells that form myelin coats around the axons on neurons. This causes the nervous system to essentially "short circuit" and pass information very slowly. Stem cells therapy has been used to try to cure some of the damage caused by the body in MS. Hematopoietic stem cell transplantation has been used to try and cure MS patients by essentially "reprogramming" their immune system. The main risk encountered with this form of treatment is the possibility of rejection of the stem cells. If the hematopoietic stem cells can be harvested from the individual, risk of rejection is much lower. But, there can be the risk of those cells being programmed to induce MS. However, if the tissue is donated from another individual there is high risk of rejection leading to possibly fatal toxicity in the recipient's body. Considering that there are fairly good treatments for MS, the use of stem cells in this case may have a higher cost than the benefits they produce. However, as research continues perhaps stem cells will truly become a viable treatment for MS as well as other autoimmune diseases.