Finding a stem cell donor with a double copy of the HIV-resistant gene mutation was "an improbable event", said lead researcher Ravindra Gupta of University College London. The transplanted stem cells can also produce immune cells that go on to attack their new host, a problem called graft vs. host disease.
While some commentators are calling this a "cure" for HIV, the scientists who performed the experiment say it's too soon to say that.
"This is the second reported case of prolonged remission off antiretroviral therapy post bone-marrow transplantation from a CCR5-negative donor", International AIDS Society President Anton Pozniak said in the statement.
In some of the past transplant failures, the donor did not have a mutated CCR5, but the conditioning regimen seemed to have significantly reduced the "reservoirs" of cells in the recipient that have latent HIV infections, invisible to the immune system.
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Doctors found a donor with a gene mutation that confers natural resistance to HIV. His drug regiment was much less harsh than the only other known patient who was cured of HIV. Attempts to treat the cancer with a variety of chemotherapies failed, at which point his doctors started considering stem cell transplants, but they were unable to obtain enough stem cells from the patient himself.
Dr. Gero Hütter, who treated the Berlin patient and is now medical director at Cellex Collection Center in Dresden, Germany, said in an email that the treatment used for the London patient is "comparable" to the one he pioneered. Scientific research into the complex virus has led to the development of drug combinations that can keep it at bay in most patients.
But the reason this case is so significant is that it could help experts who are looking for new ways to tackle HIV and achieve a cure. While the virus was under control, he was diagnosed with Hodgkin's lymphoma. Beforehand, each had been treated with toxic chemicals in a "conditioning" regimen meant to kill off their existing cancerous bone marrow cells.
Dr Anthony Fauci, head of the HIV/AIDS division at the National Institutes of Health, told the Daily Mail, we shouldn't expect this type of treatment to become the stock standard for people wanting a cure. The new patient had none of this HIV variant, which probably contributed to the success of this treatment.
Gupta prefers to say the man is instead in long-term remission, in part because the team hasn't looked at tissues other than the patient's blood. For now, experts believe that any remaining HIV in the London patient isn't able to replicate at the pace it needs to change into a different form.