Researchers on Tuesday announced that the first woman and third ever person has been cured of HIV after she received a stem cell transplant method that uses umbilical cord blood—an approach that doesn't require as closely matched material as a bone marrow transplant.

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Previous cases of long-term remission

Currently, there are just two other documented cases in which HIV-positive patients have entered long-term remission.

In 2007, Timothy Brown underwent two bone-marrow transplants to treat leukemia after chemotherapy failed to stop the cancer, a process that despite severe complications—including a period during which Brown developed "graft-versus-host" disease—appeared to eliminate both his cancer and his HIV, even after Brown stopped using antiretrovial drugs. Scientists hypothesize Brown's HIV may have been resolved because the bone marrow transplants came from donors with a mutated version of a protein called CCR5, which is resistant to HIV.

In 2019, researchers reported that another HIV-positive patient named Adam Castillejo appeared to be cured after he received a bone marrow transplant from a donor with a mutated version of the CCR5 protein to treat a type of blood cancer called Hodgkin's Lymphoma. The researchers said highly sensitive tests found no traces of the patient's HIV infection nearly three years after the bone marrow transplant, and more than 18 months after the patient stopped using antiretroviral drugs.

Ravindra Gupta, a virologist at University College London who co-led the team of doctors treating the patient, said Castillejo was "functionally cured" and "in remission," but at the time cautioned that it was "too early to say he's cured."

A third HIV-positive patient appears to be cured

Researchers on Tuesday announced that a leukemia patient, who was also HIV-positive, appeared to have been cured of the disease.

To treat her cancer, the woman received umbilical cord blood with the mutation that prevents HIV from entering cells. In addition, she was given partially matched blood stem cells from a first-degree relative since cord blood cells can take about six weeks to engraft, the Times reports.

The half-matched "haplo" cells from her relative bolstered her immune system until the cord blood cells took over, making the transplant much less dangerous, according to Marshall Glesby, an infectious diseases expert at Weill Cornell Medicine of New York who was part of the research team. "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," Glesby said.

More than 14 months after discontinuing antiretroviral therapy, the woman's blood tests did not show any signs of HIV. Researchers also said that she does not seem to have any detectable antibodies to the virus.

Notably, this is believed to be the first documented case of an HIV-positive woman who has been medically cured. Further, researchers highlighted that the sex and racial background of the patient marks a significant step forward in developing a cure for HIV, particularly because HIV is believed to progress differently in women.

In addition, the bone marrow transplants used to treat Brown and Castillejo are invasive, risky, and require close donor matches that are of a similar race and ethnicity. But unlike bone marrow, cord blood does not need to be matched as closely.

Although experts said it is unclear exactly why stem cells from cord blood seem to work so well, Koen Van Besien, director of the transplant service at Weill Cornell, said one possibility is that they are more capable of adapting to a new environment. "These are newborns, they are more adaptable," he said.

In addition, cord blood may contain elements other than stem cells that help make the transplant more successful, the Times reports.

"Umbilical stem cells are attractive," said Steven Deeks, an AIDS expert at the University of California-San Francisco who treated Brown. "There's something magical about these cells and something magical perhaps about the cord blood in general that provides an extra benefit."

And while Deeks said he did not believe this new approach will become commonplace, he added, "These are stories of providing inspiration to the field and perhaps the road map." (Breslin, The Hill, 2/15; Mandavilli, New York Times, 2/15; Chen, Axios, 2/15)