An anonymous reader writes "For decades, one of cancer's most powerful weapons has been to corrupt the human immune system. Finally, researchers in Philadelphia have developed a way to turn that weapon against certain cancers, and potentially open the door to a whole new generation of therapies for all manner of cancers. From the article: 'It is hard to believe, but last spring Emma, then 6, was near death from leukemia. She had relapsed twice after chemotherapy, and doctors had run out of options. Desperate to save her, her parents sought an experimental treatment at the Children’s Hospital of Philadelphia, one that had never before been tried in a child, or in anyone with the type of leukemia Emma had. The experiment, in April, used a disabled form of the virus that causes AIDS to reprogram Emma’s immune system genetically to kill cancer cells.'"