Stem cells were genetically engineered to kill cells infected with HIV. This is a big discovery but still a long way from finding a cure for the virus. Viruses constantly change. This presents a difficult task trying to eradicate them for good.
Moreover, the risk of tampering with genetics is always present as with the issue with the banana which is about to go to extinct due to the disruption of natural selection.
Source:
http://www.huffingtonpost.com/2012/04/16/stem-cell-aids-hiv-study-ucla_n_1428660.html