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February 23, 2009


Gene therapy and stem cell research are two of the most exciting and fastest growing sciences in the world today. Their applications are becoming more and more far-reaching with every passing day.

In fact, either or both of two different avenues of research in gene therapy alone could very well prove to have yielded the most important discoveries ever made in the seemingly endless battle against HIV/AIDS.

For decades now, scientists have known that some people who have been repeatedly exposed to the HIV virus through unprotected sex, never developed the disease. They've been baffled and frustrated by this phenomena because they weren't able to figure out why. Until now.

In a February 3rd posting at Wired.com, Aaron Rowe reported:

Most people have a gene called CCR5, which makes them vulnerable to HIV infections. The naturally resistant people have mutant CCR5 genes that inhibit HIV.

Previously, scientists found that by cutting the CCR5 gene out of white blood cells involved in the immune response known as T-cells, they could protect a tube full of human cells from the virus. The gene editing technique relies on proteins called zinc finger nucleases that can delete any gene from a living cell.

In theory, zinc finger nucleases could give that immunity to anyone.

When this story first broke, I decided not to cover it on my blog because I didn't want to, once again, get people's hopes up. I wanted to wait until there was at least a little more concrete proof that this was more than just another interesting theory.

Well, it seems that things really are "closer than they appear in your rearview mirror." In a February 18th story by Andy Coghlan in NewScientist magazine:

The story begins with a man in Germany who last week was reported to be free of HIV following a bone marrow transplant. The donor was known to have two copies of a gene that prevents HIV from invading white blood cells. For the first time, it may be possible to eliminate the virus from the body, as opposed to simply keeping it in check with antiretroviral therapies (ART).

The story went on to say:

Word first surfaced last November that a man had been "cured" of HIV through a bone marrow transplant, but this wasn't confirmed until last week, when the full results were published in The New England Journal of Medicine (vol 360, p 692). "It's now almost exactly two years ago that we treated him, and the virus is nowhere to be seen," says Gero Hütter of the Charité University of Medicine in Berlin, head of the team that treated the man.

Hütter exploited a finding a decade ago that some individuals naturally defy HIV. It turned out that they had inherited two copies of a "delta32" mutation in a gene called CCR5, one from each parent. That mutation means CD4 white blood cells can't make a protein on their surface that HIV uses as a "door handle" to invade the cells, so the virus can't get in.

Then, when a man with HIV developed leukaemia and needed a bone marrow transplant, Hütter reasoned that it might be possible to treat his cancer and also give him an HIV-resistant immune system, since his own would be destroyed by chemotherapy anyway. The hunt was on to find a donor with two delta32 mutations. From 80 potentials, he found one. After the transplant, HIV-resistant cells took over the man's immune system, "curing" him of HIV. "Every new immune cell that grew thereafter in the bone marrow had these deletions, and so was resistant," says Hütter.

Now, although these are very dramatic results, the reality of being able to find people with the CCR5 variant who would also be compatible bone marrow donors with each individual HIV/AIDS patient would be, to say the least, a challenge. That's where gene therapy, a way of mimicking the same result without a donor, comes in.

Sangamo Biosciences of Richmond, California, began the first human trial of a promising gene therapy last week. "The German patient is the definitive proof that if you replace patients' immune cells, it's sufficient to protect the patient," says Philip Gregory of Sangamo.

Sangamo makes artificial versions of natural enzymes called zinc finger nucleases (ZFNs), which zero in on and disrupt any genes you choose - in this case the CCR5 gene, so that it stops making the HIV door-handle protein.

The company plans to take blood samples from 12 patients and extract the CD4 cells. It will then add a harmless virus to the cell carrying genes that code for the ZFNs. The altered CD4 cells produce the ZFNs, which sabotage the CCR5 gene. The ZFNs and the virus are then washed away and the genetically modified cells injected back into the patient.

There are, of course, many other trials and tests that would have to be done but this whole avenue of research could finally be the real light-at-the-end-of-the-tunnel we've all be waiting for and not just another fleeting reflection of our hopes.

The NewScientist article is a somewhat lengthy, in-depth piece that would be worth a few minutes of your time. If you would like to read the full report, go to: NewScientist.com

BTW - the report also talks about the possibility of using stem cells to accomplish the same result.