A US patient is believed to be the third person in the world, and first woman, to be cured of HIV.
The patient was being treated for leukaemia when she received a stem cell transplant from someone with natural resistance to the Aids-causing virus.
The woman has now been free of the virus for 14 months.
But experts say the transplant method used, involving umbilical cord blood, is too risky to be suitable for most people with HIV.
The patient’s case was presented at a medical conference in Denver on Tuesday and is the first time that this method is known to have been used as a functional cure for HIV.
The patient received a transplant of umbilical cord blood as part of her cancer treatment and has since not needed to take the antiretroviral therapy required to treat HIV.
The case was part of a larger US study of people living with HIV who had received the same type of blood transplant to treat cancer and serious diseases.
The transplanted cells that were selected have a specific genetic mutation which means they can’t be infected by the HIV virus.
Scientists believe the immune system of recipients can develop resistance to HIV as a result.
The potential of stem cell transplants was demonstrated in 2007 when Timothy Ray Brown was the first person to be “cured” of HIV.
He had a transplant from a donor who was naturally resistant to HIV.
Since then the feat has been repeated only twice with Adam Castillejo and now the New York patient.
All three had cancer and needed a stem cell transplant to save their lives.
The woman’s treatment involved umbilical cord blood, unlike the two previous known cases where patients had received adult stem cells as part of bone marrow transplants.
Umbilical cord blood is more widely available than the adult stem cells previously used and it does not require as close a match between donor and recipient.