An HIV patient in London remains free of the virus 18 months after he stopped taking antiretroviral drugs. This is the second case of long-term remission since Timothy Ray Brown, also known as “The Berlin Patient” (because his case originated in Berlin), who has effectively been cured of HIV for a decade. Successive treatments to try and replicate Brown’s success have failed, until now.
The new patient, described in , received a bone marrow transplant in 2016 as a treatment for Hodgkin’s lymphoma, a cancer of the lymphatic system. The procedure replaced his white blood cells with those from a donor with a gene mutation that prevents the HIV virus from invading T-cells—specifically CD4-positive T-cells—which destroy infection and keep the immune system healthy.
The gene mutation plus the tissue match that makes such a transplant possible is unfortunately “an improbable event,” , lead author of the study and virologist at the University of Cambridge, Imperial College London, and University College London. A donor needs to have two “deleted or mutated copies” of a receptor called CCR5, one of a set of genes that HIV cleaves to and uses to attack cells. A deletion in the CCR5 gene breaks down the receptors, thereby disabling the vehicle that carries the virus. Only about of people of European descent have two copies of this mutation and would make suitable donors.
What’s more, not all HIV viruses use CCR5 receptors to raid cells. Other co-receptors can serve the same purpose, though they are less common. And even in cases where the infection of T-cells is interrupted, there’s still the problem of cells that have already been infected.
On the upside, this patient’s treatment was more targeted than Timothy Ray Brown’s and did not involve whole-body radiation. The chemotherapy was less invasive as well, suggesting that, to be successful, treatments and their side-effects may not need to be as intensive for future HIV patients.
That said, the risks of stem-cell transplants are altogether too great to make them a matter of course for people living with HIV who don’t have cancer. In that case, the treatment would be more dangerous than the condition, and a patient would be better served by a daily antiretroviral medication, like .
While this latest success may not impact all HIV carriers now, it has altered the research landscape to the extent that more money and energy will likely be dedicated to transplantation and gene therapies targeting CCR5. Some researchers are already busy at work to carry the desired mutation. It’s given the scientific community hope that “The Berlin Patient” may have been, not a singular deviation from the norm, but a first step on the path to a cure for a disease that affects nearly 37 million people around the world.