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A Cure for HIV?

HIV Cured in Berlin Patient -- What It Means

Why did the HIV cure work in the Berlin patient?

Nobody is really sure.

Three things happened during the Berlin patient's treatment.

First, chemotherapy killed off most of the cells infected with HIV. By itself, this would not be enough to cure HIV.

Second, the donor cells repopulated the patient's immune system. The new cells attacked and killed the patient's remaining white blood cells -- a process Zaia calls a "graft-versus-leukemia" response. This process likely killed off many of the remaining cells carrying HIV.

Third, the donor cells were resistant to HIV infection. As HIV emerged from resting cells, the virus helped kill off the old, susceptible cell. When the new donor cells expanded to take their place, the HIV had no place to go and withered away.

But none of these things fully explains what happened. One puzzle is that the stem cells used to repopulate the patient's immune system were HIV resistant -- but not HIV proof.

The cells lacked the most common doorway, CCR5, that HIV needs to infect cells. But people with long-term HIV infection usually carry HIV capable of using another doorway called CXCR4. And tests showed that the Berlin patient's blood carried HIV like this. Moreover, tests also showed that the donor cells were susceptible to infection via the CXCR4 pathway.

Even so, the Berlin patient mysteriously remains HIV free.

Does the Berlin patient's HIV cure mean other people can be cured of HIV?

Yes, but not right away. There's still no available cure for HIV. But the finding that it's really possible finally to cure AIDS has revitalized research.

"The Berlin case has moved the whole field," Zaia says. "Now major money is being directed from the National Institutes of Health into the area of a cure for HIV."

Several approaches show promise. Clearly it isn't practical -- or desirable -- to submit relatively healthy people with HIV to massive chemotherapy. But what if just a mild chemotherapy were used to create just enough room for HIV-resistant stem cells to gain a foothold?

Zaia's team is exploring the use of taking a patient's own cells and genetically engineering them to fight HIV. The first studies are being done on patients with HIV lymphoma, who already require chemotherapy. Four patients already have been treated with low doses of genetically modified cells -- and the good news is that the modified cells can survive and expand for at least two years.

Other researchers are using different techniques to alter stem cells to fight HIV. Until the Berlin patient, most experts considered all of these treatments unlikely to succeed. Now all eyes are upon them.

"In the future there will be a mild method of making space for these new HIV-resistant stem cells, so that they grow out and repopulate the immune system," Zaia says. "That is the goal. It may take a long time to get to that, but it will happen."

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Reviewed on December 14, 2010

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