HIV

     Human Immunodeficiency Virus is a seemingly incurable disease that is almost always terminal. However, a man called Timothy Brown and known as the Berlin Patient may change this. He has been cured of HIV through a process involving bone marrow transplantation between patients. Bone marrow produces lymphocytes, white blood cells that are crucial to the immune system. In Timothy's case, the marrow was of an HIV-immune individual, so Timothy's immune system became immune as well. Aside from slight neurological damage caused by trauma during the treatment, this seems to be a relatively reliable cure (yes, cure).
     Which is, of course, great for the world.