Two men with HIV are now free of the virus after a bone marrow transplant to treat lymphoma. But how that happened is a mystery for now.
NY Daily News — Last July Henrich first reported that the two men had undetectable levels of HIV in their blood after their stem-cell treatment, but at that time they were still taking medicines to suppress HIV. Using stem-cell therapy is not seen as a viable option for widespread use, since it is extremely expensive, but the latest cases could open new avenues for fighting the disease, which infects about 34 million people worldwide.
The latest cases resemble that of Timothy Ray Brown, known as “the Berlin patient”, who became the first person to be cured of HIV after receiving a bone marrow transplant for leukaemia in 2007. There are, however, important differences. While Brown’s doctor used stem cells from a donor with a rare genetic mutation, known as CCR5 delta 32, which renders people virtually resistant to HIV, the two Boston patients received cells without this mutation.
Many viruses including HIV gain entry to the cell using a special portal on the cell’s surface in a process called Receptor Mediated Endocytosis. Individuals with one copy of the CCR5 mutation have fewer functional receptors thus making them highly resistance to those kinds of viruses, people with two copies are virtually immune. Ergo, it’s understandable why a marrow transplant from an individual carrying that mutation might confer some resistance on the recipient. But why it happened in these two latest cases, where that marker was absent, is not clear.
As a non expert I’ll go ahead and guess at one possibility though. Prior to a marrow transplant most patients take a big dose of poison that kills off their native bone marrow (We can actually completely cure marrow malignancies like leukemia in many cases, the problem is that cure kills the patient, we need bone marrow to survive). HIV often hides in that material, so if that refuge was destroyed and the virus was under control elsewhere in the system via existing drugs, it could explain these results.