WEDNESDAY, Dec. 15 (HealthDay News) -- In a rare case, a man living in Germany who had both leukemia and AIDS no longer has any detectable HIV cells in his blood following a stem cell transplant for his leukemia three years ago.

But experts were quick to caution that the case does not have practical implications for the treatment of AIDS worldwide.

As it turns out, the donor for that transplant carried a rare mutation in a gene that increases immunity against the most common form of HIV. First reported in 2009, this follow-up study, published online in the journal Blood, confirms that the recipient patient is still free of both leukemia and HIV three years after the transplant.

But one expert issued strong words of caution in interpreting the finding.

"Our phones have been ringing off the hook," said Dr. Margaret Fischl, director of the AIDS clinical research unit at the University of Miami Miller School of Medicine. "We are having patients calling us and asking if they can stop their antiretroviral therapy -- and the answer is uncategorically no."

The theory is that if you could wipe out every infected cell you could cure HIV, Fischl said, but this is a unique case.

The patient had intense chemotherapy and radiation, then relapsed and was given a second transplant from the same donor. The donor was unique in that he had a gene that could fight the most common form of HIV. This mutation is seen in about one in every million people, Fischl explained.

"How much did a second transplant contribute to the slow takeover of the donor cells that are resistant to one form of HIV? The extent that that happened is remarkable," she said.

However, this patient also was infected with another form of HIV as well, Fischl said. "What they are hoping is that the chemotherapy and radiation therapy wiped out that form, too. Could that patient still rebound with HIV in the future? Yes," she said.

This treatment also carries with it a 30 percent risk of death, Fischl added.

"That he was young and got through it is quite remarkable," she said. "I would never give this to a healthy patient. I could never justify it. If you use this therapy, 30 percent of your patients could die from the intervention."

Fischl said the study does present new ways to look for an HIV cure, however. "This is leading to looking at gene therapy in a totally different way," she said.

"We tell our patients that this was a very particular situation. What made this work was that he got a very rare donor. It opens doors for us, but we are years away from potentially making gene therapy more broadly available," Fischl said. "It shows us the hurdles we have to get over to get to the cure."

Rowena Johnston, director of research at the Foundation for AIDS Research, also added a note of caution but said that the case "speaks to the promise of research."

"We need to be clear that what was done for this patient was not something that can be done on a wide scale," Johnston said. "It really was a lucky case for this one guy that all the stars aligned and that all of the factors that needed to come together really did."

However, gene therapy might be an avenue to pursue, Johnston said. "We're a long way from that. There's a lot of technology that needs to be perfected, there's a lot of issues that need to be considered in terms of how you would deliver this to patients in a safe way and how the long-term effectiveness of that treatment might pan out," she said.

But the man's example has given gene therapy a "shot in the arm," Johnston said. "It's not just a pipe dream any more, somebody has been cured and we need to work out how we can come up with a cure that will be more readily available to everybody out there who needs it. That's over 30 million people living with HIV."

More information

For more on HIV and AIDS, go to AIDS.gov.