A third person has been cured of HIV

A woman became the third person ever to be cured of HIV, the virus that causes AIDS, after she received a stem-cell transplant that used cells from umbilical cord blood.

The two other people cured of HIV, both received bone marrow transplants from donors who carried a genetic mutation that blocks HIV infection. These transplants contained adult hematopoietic stem cells, which are stem cells that develop into all types of blood cells, including white blood cells, a key component of the immune system.

This genetic mutation is rare and has been identified in only about 20,000 bone marrow donors to date.

The bone marrow transplant procedure itself takes a heavy toll on the body, both during the highly invasive procedure and for some time afterward. In both cured people, immune cells from the donors' bone marrow launched an attack against cells in the patients' bodies; this condition is known as "graft versus host disease." Following this initial reaction, though, both men were cured of HIV.