BERLIN — An American man who suffered from AIDS appears to have been cured of the disease 20 months after receiving a targeted bone marrow transplant normally used to fight leukemia, his doctors said Wednesday.

While researchers — and the doctors themselves — caution the case might be no more than a fluke, others say it could inspire a greater interest in gene therapy to fight the disease that claims 2 million lives each year. The virus has infected 33 million people worldwide.

Dr. Gero Huetter said his 42-year-old patient, an American living in Berlin who was not identified, had been infected with the AIDS virus for more than a decade. But 20 months after undergoing a transplant of genetically selected bone marrow, he no longer shows signs of carrying the virus.

It has not come. Researchers at Berlin's Charite hospital and medical school say tests on his bone marrow, blood and other organ tissues have all been clean.

However, Dr. Andrew Badley, director of the HIV and immunology research lab at the Mayo Clinic in Rochester, Minn., said those tests have probably not been extensive enough.

This isn't the first time marrow transplants have been attempted for treating AIDS or HIV infection. In 1999, an article in the journal Medical Hypotheses reviewed the results of 32 attempts reported between 1982 and 1996. In two cases, HIV was apparently eradicated, the review reported.

Huetter's patient was under treatment at Charite for both AIDS and leukemia, which developed unrelated to HIV.

As Huetter — who is a hematologist, not an HIV specialist — prepared to treat the patient's leukemia with a bone marrow transplant, he recalled some people carry a genetic mutation that seems to make them resistant to HIV infection. If the mutation, called Delta 32, is inherited from both parents, it prevents HIV from attaching itself to cells by blocking CCR5, a receptor that acts as a kind of gateway.