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With HIV Cure as the Goal, Gene Therapy Research Expands

March 20, 2015

What if someone could have HIV in his or her body, but the virus was incapable of causing harm? That's the tantalizing promise of a "functional cure" for HIV. The U.S. Food and Drug Administration (FDA) has approved another functional cure trial that will evaluate if a form of gene therapy in people with HIV can prevent damage and viral progression by replicating a mutation present in a small percentage of humans that makes them naturally resistant to HIV.

The therapy -- which attempts to cause a specific mutation in white blood cells -- has been found to have few side effects and the mutated cells seem to last in the body for at least four years. The procedure, however, has only been tested on 12 individuals, so that's not enough to be able to judge if it works.

For this technique, physicians edit a gene in blood-producing stem cells taken from HIV-infected patients to create a mutation in a protein known as CCR5 that is located on the surface of these cells. This mutation occurs naturally in a small percentage of the world's population and prevents HIV from attaching to the body's blood cells.

The hope is that by replicating this mutation in stem cells and then injecting those cells back into a person's body, the patient would have similar protection. HIV would remain in his or her body but could not enter the T cells, which means it could not replicate or compromise the person's immune system. This is called a functional cure because it does not eliminate the virus from the body, but it prevents it from causing harm.

To some extent, antiretroviral therapy can be considered a functional cure in many people, because it ensures that CD4 cell counts remain high, viral loads remain low and the immune system keeps functioning. But antiretroviral therapy drug cocktails have to be taken every day in order to keep working (signs of HIV will come back as soon as most people discontinue the medication) and some people don't respond as well as others to these medications.

In 2007, scientists announced that they had "cured" a man whom they called "the Berlin patient." The patient, now known to be Timothy Brown, was suffering from leukemia in 2006 and needed a stem cell transplant to survive. To test a theory, his doctors decided to use stem cells from a donor known to have the CCR5 gene mutation. Brown used the same donor when he needed a second stem cell transplant in 2008. He is now free of both leukemia and HIV. (Though some testing in 2012 suggested his body might have showed signs of the virus again, recent stories on Brown continue to describe him as HIV-free.)

Now, scientists are continuing research on patients undergoing stem cell transplants to try to replicate this functional cure. Unfortunately, researchers have not been able to repeat the success of Brown's case. They have tried six times, all with HIV-positive individuals who were also suffering from cancer, but all six of the patients either died from complications of the transplant or from the cancer itself. Five of them died too soon for researchers to see whether the treatment had any impact on HIV. The other had a strain of the virus that is not deterred by the CCR5 mutation and the virus did return.

Doctors in Boston also tried to use stem cell transplants to knock out HIV along with cancer in two men, though the donors in these cases did not have the CCR5 mutation. Despite initial signs of success, the virus returned to detectable levels in one of the men just one month after announcing this functional cure. A few months later the virus was also detectable in the other man.

Stem cell transplants are only considered appropriate for those currently fighting cancer, because they require a massive amount of chemotherapy, which could be life-threatening itself. But if Brown's results could be instead achieved through gene therapy, that would be a major breakthrough.

Now that they have FDA approval, the clinical trials will be conducted at the City of Hope medical center in California and supported by the California Institute for Regenerative Medicine (CIRM), a state-funded agency. Researchers from Sangamo BioSciences, Inc., (which developed the technology) and Keck School of Medicine at the University of Southern California will run the study and plan to include HIV-positive individuals who have not responded well to antiretroviral therapy.

Martha Kempner is a freelance writer, consultant and sexual health expert.

Follow Martha on Twitter: @marthakempner.

Copyright © 2015 Remedy Health Media, LLC. All rights reserved.

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