That’s the question abuzz in the medical community as doctors around the globe discuss a bone marrow transplant, performed in Berlin, that is said to have cured the patient of AIDS. Twenty months after the transplant, some critics suggest the outcome is merely a fluke but even they do not deny the possibilities suggested by the case.

The 42-year-old American patient was being treated at Berlin’s Charite hospital and medical school for both AIDS, which he’d had for more than 10 years, and leukemia unrelated to the AIDS when his hematologist, Dr. Gero Huetter, recalled a specific gene mutation, Delta 32, which makes it impossible for HIV, the AIDS-causing virus, to attach to and infest cells. This AIDS-fighting action only happens when the mutation is inherited from both parents. Huetter wanted to try transplanting it.

To do so, however, called for finding a bone marrow donor who had inherited the Delta 32 mutation from both parents, as about one in every 1,000 Americans and Europeans do. Eighty potential donors were identified and the 61st individual of this pool proved to be the best match for the patient.

In preparation for surgery, the patient underwent drug and radiation treatments that killed all the cells of his own bone marrow and disabled his immune system. This preparatory procedure is fatal 20% to 30% of the time.

The patient also stopped taking the powerful anti-AIDS drugs he’d been taking on the chance they might affect the final outcome of the transplant. By destroying his diseased bone marrow and replacing it with bone marrow that rejects the AIDS virus, the patient’s medical team hoped the new marrow would prove unaffected by the virus.

Huetter says he’s waited every day for 20 months for a bad medical report from the patient but, thus far, the virus has remained at bay.

Two million people die from AIDS every year. There are more than 33 million people infected with the virus. While the German transplant breakthrough may not offer direct hope of cure to these millions, it does strengthen the push for development of more effective gene therapies for fighting AIDS.