In Multiple Sclerosis (MS), the immune system of a patient turns on his or her nervous system, destroying the myelin sheaths that serve as insulation around nerves, disrupting the transmission of nerve signals. The myelin damage often occurs in a patchy manner, at first. See the Medline Plus page from the National Institutes for Health for more information, including a patient tutorial in English and in Spanish. The Journal of the American Medical Association has a similar patient education page in pdf.
There have been trials using adult stem cell treatments in the form of bone marrow transplants and injection of adult stem cells in different manners for several years. (See ClinicalTrial.gov for some of these – if my search lapses, search “stem cell multiple sclerosis.)
The March issue of Lancet Neurobiology reports (Free access to the abstract) success from research at Northwestern University using the patients’ own bone marrow stem cells, after harvesting those cells, preserving them, and then using chemotherapy to destroy the immune system before replacing the patient’s stem cells. A review of the study is at the Science Daily and at this blog, Science Codex.
Any sort of bone marrow transplant is dangerous due to the lost red blood cells, platelets (to make blood clots), and the white blood cells that function as the immune system. This trial was set up to preserve all but the immune system. While it’s still not a procedure to take lightly, it appears that the researchers at Northwestern have made it safer.