A third person has been cured of HIV, scientists report

A woman became the third person to be cured of HIV after she received a stem-cell transplant.

The two people cured of HIV, Timothy Brown and Adam Castillejo, both received bone marrow transplants from donors who carried a genetic abnormality that blocks HIV infections. Adult hematopoietic stem cells, which are stem cells that develop into all types of blood cells, are a key component of the immune system.

The New York Times reported that only 20,000 bone marrow donors have been identified with this genetic variation. The bone marrow transplant procedure takes a heavy toll on the body, both during and after the procedure. In Brown and Castillejo, the immune cells from the donors launched an attack against the cells in the patients' bodies, which resulted in their cure.

The woman cured of HIV had a different experience than the other two men.

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The patient left the hospital 17 days after her procedure without any signs of disease. The International AIDS Society's president-elect, Sharon Lewin, told the Times that she did not participate in the work.

Acute myeloid leukemia is a cancer that affects blood-forming cells in the bone marrow, and the woman was HIV-positive as well. She received the cord blood as a treatment for her cancer and as a donor for her HIV, as her doctors identified a donor with the HIV-blocking genetic mutation. The blood is collected at the time of a baby's birth and then donated by the parents.

The advantage of cord blood over bone marrow is that donors don't need to be closely matched with their transplant recipient. Doctors check the donor's and recipient's human leukocyte antigen (HLA) tissue type, which refers to whether the individuals carry specific proteins, called HLAs, in the tissues of their bodies. A bone marrow donor and a recipient need to be closely matched to avoid a catastrophic immune reaction.

The baby and cord blood recipient don't have to match as closely as the bone marrow donor and recipient because the baby's immune system is still immature. The immature cells of the baby adapt to the recipient's body more quickly than adult cells. In the woman's case, her donor was partially matched, and she also received stem cells from a close relative to help bolster her immune system after the transplant procedure, the Times reported.

The transplant from the relative is like a bridge that got her through to the point of the cord blood being able to take over.

The woman had a procedure in August of last year. She stopped taking the standard treatment for HIV 37 months after her transplant. Since that time, there has been no trace of the virus in her blood, the Times reported.

The woman is part of a larger study that will follow 25 people with HIV. The trial organizers will monitor these individuals to see if their HIV status changes following the transplant procedure. In general, cord blood is more widely available than bone marrow. Some scientists think the procedure may be more accessible than bone marrow transplants.

There are about 50 patients a year in the US who could benefit from this procedure, according to Dr. Koen van Besien, director of the stem cell transplant program. According to the Times, 38 million people are living with HIV.

Van Besien said that the ability to use partially matched umbilical cord blood grafts greatly increases the likelihood of finding suitable donors for such patients.

It was originally published on Live Science.