What's crazy is they used the HIV virus to do it:
"In the Penn experiment, the researchers removed certain types of white blood cells that the body uses to fight disease from the patients. Using a modified, harmless version of HIV, the virus that causes AIDS, they inserted a series of genes into the white blood cells. These were designed to make to cells target and kill the cancer cells. After growing a large batch of the genetically engineered white blood cells, the doctors injected them back into the patients."
So the most feared plague of the modern age may well hold the key to curing one of humanity's oldest diseases. Quite cool. Of course there's a lot more research to be done before victory can be declared. Working in 3 patients doesn't mean it will work large scale.