A third person has reportedly been cured of HIV infection, according to a report released February 15 at the annual meeting of the Conference on Retroviruses and Opportunistic Infection.

The patient in this case is described as "a middle-aged, mixed-race woman." The cure was effected through a "haplo/cord transplant" that included a mixture of stem cells from a relative (the "haplo" part) and stem cells from an infant's umbilical cord.

The infant stem cells contained a naturally occurring, but rare, feature that made them resistant to HIV. They possessed a deletion in the CCR5 gene that made it impossible for the virus to infect cells. That deletion usually occurs in people of northern European or Caucasian descent, which is why the woman's race is significant.

The transplanted stem cells were different from those used in previous cases. Those cases depended on stem cells from adults, and they are harder to match with a recipient.

The patient stopped taking the antiretroviral drugs that kept her HIV in check 14 months ago, and there has been no rebound of the virus.

The level of virus in her blood was "undetectable through this whole period," said Yvonne J. Bryson, an infectious diseases physician at the David Geffen School of Medicine at the University of California at Los Angeles, who presented the case.

"This provides hope for the use of cord blood cells... to achieve HIV remission for individuals requiring transplant for other diseases," Bryson said. "This provides additional proof that HIV reservoirs can be cleared sufficiently to afford remission and cure."

Scientists said the report was exciting because of some unusual factors in the patient's case that may help answer fundamental questions about how these patients are able to clear the reservoir of HIV in their bodies.

In other successful cases of remission, patients had received their transplants but also suffered from graft vs. host disease, when the donor cells attack the recipient's immune system. That did not happen in this case.

"Each of these cases is unique and different, and are there clues that help us focus on the next patient that comes along?" said Carl W. Dieffenbach, director of the Division of AIDS at the National Institute of Allergy and Infectious Diseases, who was not involved in the research.

Sharon Lewin, president-elect of the International AIDS Society, said in an email that the finding was exciting.

"A bone marrow transplant is not a viable large-scale strategy for curing HIV, but it does present a proof of concept that HIV can be cured. It also further strengthens using gene therapy as a viable strategy for an HIV cure," Lewin added.

In 2009, scientists first reported that a white man with leukemia, originally known to the world only as "the Berlin patient," had been cured of HIV with a transplant of stem cells resistant to HIV.

"The Berlin patient," later revealed to be Timothy Ray Brown, eventually died — when his leukemia, but not his HIV, returned. A decade later, the same approach was used in "the London patient," a Hispanic man with Hodgkin's lymphoma.

While these findings open up new avenues for research, scientists caution that stem cell transplants are not likely to be widely used as a treatment for otherwise healthy people living with HIV.