This week saw a potentially promising, if puzzling, development in treatment for HIV/AIDS as a bone marrow transplant given to a 42 year-old man in Berlin appears to have eradicated every trace of the man's infection. Why and how this happened, and what it implies for the treatment of HIV/AIDS, has been a hotly contested subject since.
The patient in question is an American who lives in Berlin. His bone marrow transplant, conducted at the Charité Hospital in Berlin 20 months ago, was intended to treat his myeloid leukemia, which was in an acute phase. Last week, his doctors reported a twist: that they could find no trace of HIV infection in any of the usual hiding places for the virus: the blood, bone marrow, lymph nodes, intestines or brain. "As of today," the clinic reports, "more than 20 months after the successful transplant, no HIV can be detected in the patient." How did this happen? It may be in the marrow the man was given in the transplant.
A small proportion—roughly 3 percent—of the European population has a genetic mutation that renders them immune to HIV by blocking the receptors that allow the virus to invade their cells. The marrow given to the Berlin patient was intentionally taken from a donor who had two copies of this mutation (one from each parent), in the hope that the mutation would take hold in the recipient. The result seems to be a double cure: not only does the man no longer have discernible leukemia, but there is no trace of HIV anywhere in his body, despite the fact that he ceased any treatment for the virus at the point of the transplant.
The stakes from the bone marrow transplant are high. Though current medications can keep HIV infections suppressed, even to the point where the virus in undetectable in the blood, they do not cure the infection. The virus hides in the body in so-called "reservoirs", from which it can return when treatment ceases. And, eventually, HIV is still fatal. Researchers are in a constant search, therefore, for a treatment that will not only suppress but actually eradicate the presence of HIV in an infected person. The Berlin bone marrow transplant is exciting in its potential promise for the future of gene therapy in the treatment of HIV, where how to use the genetic mutation giving some people a natural immunity has been a pressing question.
Caution is key, however. It is unlikely that bone marrow transplants offer an avenue for anyone who does not have both HIV and leukemia or a similar illness. Bone marrow transplants, in addition to being very expensive, are highly dangerous, especially for people with HIV, because, before the donor marrow can be implanted, all of the recipient's own bone marrow must be killed. This leaves a high risk of infection, which can be fatal. Roughly one-third of patients do not survive a bone marrow transplant. And, the doctors who performed the Berlin transplant warn, it's not yet clear that the patient's HIV is permanently gone—only that it cannot currently be detected. "The virus is tricky," said Dr Gero Hütter, a hematologist on the transplant; "it can always return."