Big news from Berlin! Doctors there treated an HIV-positive man for leukemia back in 2007 by transplanting stem cells into his system. Now the doctors are reporting that the transplant seems to have accidentally cured him of HIV. The infection is completely gone from his body and, if his progress holds up, he could be the first person ever cured of HIV. From Pop Sci:

The “Berlin patient,” an American citizen living in Berlin, received a stem cell transplant back in 2007 as a treatment for his leukemia. Before the transplant he received chemotherapy treatment and total body irradiation that eradicated most of his immune cells, and received further immunosuppressive drugs to prevent his body from rejecting the stem cells.

But these were no ordinary stem cells — a mutation found in just one percent of Caucasians in northern and western Europe causes CD4 cells to lack the CCR5 receptor, a receptor necessary for early-stage HIV to infect CD4 immune system cells. People with this mutation are more or less immune to HIV infection.

Those anti-HIV stem cells took root in the Berlin patient and repopulated there. At the same time, the host CD4 cells that hadn’t been destroyed in chemotherapy and radiation completely disappeared. After 38 months, doctors still couldn’t find HIV infection in the Berlin patient — in other words, it seems by all measures that his HIV has been cured.

New Scientist wrote up a pretty in-depth description of the science behind the "cure" back in 2008, noting that since it's unique to this one patient, the stem-cell transfer approach might not work for other people with HIV. But after monitoring the patient for the past two years, the researchers just published a follow-up article arguing that based on the years of extensive tests, “It is reasonable to conclude that cure of HIV infection has been achieved in this patient.”

Quick, buy someone a drink! This could be a pretty big deal.