Hamburg - Physicians in Germany who say they have "functionally cured" a patient with HIV/AIDS are warning that their accidental breakthrough is effective for only about 1 per cent of patients who suffer from AIDS.

Headlines in November heralded an "AIDS cure" after Dr Gero Huetter and Dr Eckhard Thiel, blood-cancer specialists at Charite Hospital in Berlin, reported that they had seemingly cured a 42-year- old US patient of HIV/AIDS by giving him a bone-marrow transplant whilst treating him for cancer.

Their breakthrough was made possible by studies in the late 1990s revealing that some people were resistant to HIV/AIDS, according to a report in New Scientist magazine on the Berlin haematologists' discovery.

In these people, the virus cannot enter and destroy the white blood cells that it infects and destroys in most other people. They owed their resistance to a mutation in the gene which makes the molecular "door handle" by which HIV/AIDS gains access to cells.

Called CCR5, the protein door handle was misshapen in the immune individuals, locking HIV/AIDS out of their white blood cells, the New Scientist report noted.

Since the discovery, it has been established that about 1 per cent of Europeans have the same mutation, making them resistant to HIV/AIDS. To be resistant, they had to inherit the same mutation from both parents.

Huetter and Thiel made use of this when treating their patient for leukaemia, which he had developed in addition to HIV/AIDS. To treat the leukaemia, the two doctors did the usual thing and sought a bone-marrow donor to replenish the patient's blood supply following chemotherapy to kill the existing, cancerous blood cells.

But the Berlin doctors' new approach was to get a donor who had the double HIV-resistant CCR5 mutation. This meant that the patient's replenished blood system would effectively be resistant to HIV/AIDS, locking out the virus for good.

This is what appears to have happened, according to the New Scientist analysis, and Huetter declared his patient "functionally cured."

Attempts to use bone-marrow transplants in HIV/AIDS treatment have been made since the 1980s. In one case, a patient with both HIV/AIDS and lymphoma died of the cancer two months later, but was found to harbour no HIV/AIDS. It was not known if something in the transplant had protected him.

And in a famous 1995 case, Jeff Getty, a prominent San Francisco advocate for HIV/AIDS patients, received bone marrow from a baboon, which is resistant to the human virus. The New York Times reported that he survived for 11 years, but died of HIV/AIDS and cancer. The Times said the transplant had not protected him but anti-retroviral triple therapy had been invented in time to help.

Hotter and Thiel have been quick to say that it is far too early to speak of a widespread general cure for HIV/AIDS.

They stress that their breakthrough is a sound proof of principle, demonstrating that there is hope for treatments that literally lock HIV/AIDS out in the cold.

But they warn that an all-out cure for the millions of HIV/AIDS patients worldwide is still a long way off.