What’s the News: After a bone marrow transplant cured a Berlin man of HIV in 2008, scientists have been working to see whether similar, though less drastic, measures could be a treatment for the disease. And judging from the results of a recent clinical trial that used gene therapy to accomplish the goal, there’s potential.
What’s the Context:
- In the original case, an HIV-positive patient was diagnosed with leukemia, and after having chemotherapy to knock down his cancer, he received multiple transplants of blood stem cells from a donor, which took up permanent residency in his body.
- Those stem cells had a rare mutation that deactivated the CCR5 receptor, which the HIV virus uses to enter the blood cells it destroys. The end result was that the patient became the first person in the world to be cured of HIV—with that receptor out of commission, the virus couldn’t grow, and he longer has any detectible levels of HIV.
How the Heck:
- The current trial, run by Sangamo BioSciences, takes samples of patients’ blood cells and sics an enzyme on them that snips the CCR5 gene, disabling it. The cells are then reintroduced to the patient. (We covered an earlier trial from this group on 80beats here.)
- The goal was to see if receiving these altered cells would let patients go off their anti-retroviral drugs. The results, reported at a recent conference in Chicago, were mixed—the cells didn’t always survive long in the fifteen people enrolled. But two patients saw their HIV levels drop 10-fold, and one patient who stopped his anti-retrovirals first saw a spike in virus levels but then had them decline to undetectable levels.
- Further examination of that patient’s cells showed that he had twice as many cells in which both copies of the CCR5 gene had been altered than the other patients. (If you need a quick refresher, we have two copies of each gene, one from each parent.) As long one copy of the intact gene is present in a cell, the virus can still get in, which might be one of the reasons the treatment did not succeed in most of the people.
- Additionally, only about a quarter of the reintroduced cells had the disabled gene at all, something that the company will need to work on improving.
The Future Holds: Though this trial shows promise, there are still a lot of kinks to be worked out before the goal of getting people off retrovirals can be met, let alone the goal of finding a cure. The scientists will need to figure out why the cells didn’t survive in many patients’ bodies, as well investigating ways to boost the number of cells with both genes disabled.