Surprise HIV cure after stem cell transplant: a new piece of the puzzle

A seventh person appears to have been cured of HIV following a blood stem cell transplant.

Six previous patients have been cured of HIV under similar circumstances. However, in all but one case, the donor had a specific rare genotype meaning they had natural resistance to HIV infection. In the case reported in Nature a 60-year-old, HIV-positive man was diagnosed with acute myeloid leukaemia, a cancer of the white blood cells. He required a blood stem cell transplant (previously known as a bone marrow transplant) which cured his leukaemia and unexpectedly his HIV.

'It's amazing that ten years ago his chances of dying of cancer were extremely high and now he's overcome this deadly diagnosis, a persistent viral infection, and he's not taking any medications – he's healthy,' said lead author Professor Christian Gaebler from the Berlin Institute of Health in Germany.

HIV infects white blood cells by attaching to specific receptors on the cell surface. Once inside, the virus can evade the immune system by hiding within the very cells which are supposed to be fighting it, which is why it is so difficult to eradicate. The standard management treatment for HIV is antiretroviral therapy, which cannot cure HIV, but stops the virus from multiplying. This can stop people transmitting the virus and prevents them from developing AIDS.

The patient stopped taking his antiretroviral therapy three years after the transplant. His HIV remained at undetectable plasma levels and has remained so for six years so far.

Of the six other people who have been cured of HIV, all had blood stem cell transplants to treat blood cancers. In five of those cases, donors were selected who were homozygous for a genetic variant in the CCR5 gene, which affects a protein in one of the receptors HIV uses to invade cells. People with this rare genotype have a natural resistance to HIV infection.

However, this patient received cells from a heterozygous donor, meaning the new cells had receptors susceptible to HIV. It was reported last year that one previous patient has also achieved remission from HIV after a stem cell transplant from a donor who did not carry the gene variant at all. However, other people who have had stem cell transplants have not been cured of HIV and need to continue to take antiretroviral therapy.

Blood stem cell transplants carry the risk of life-threatening graft-versus-host disease. As such, this approach is not used to treat HIV, and these cases only occur when a patient has another condition, such as cancer, that justifies the risk.

For Professor Gaebler and his team, the cases show that there is more to the puzzle than CCR5. 'Seeing that a cure is possible without this resistance gives us more options for curing HIV,' he said.