Scientists have injected a blood-clotting gene into an Australian doctor with severe haemophilia, giving him temporary respite from bleeding episodes.

The treatment ultimately failed due to an immune system response, but experts hope that by suppressing that response for a few months, they may come up with a long-term cure.

Sydney-based doctor Chris Troedson, 35, was one of seven patients in an international trial testing gene therapy as a treatment for the bleeding disease which affects about 1,800 Australian men.

He received a cloned version of what's known as the Christmas disease gene, which expresses the blood-clotting agent Factor IX, deficient in some haemophiliacs because of a genetic defect inherited from their mother.

The gene, which was encased in a harmless virus, known as adeno-associated virus (AAV), was injected via a catheter through his groin into the blood vessel which supplies the liver.

The virus casing allowed the gene, cloned from an anonymous person's DNA, to infiltrate Dr Troedson's liver cells, telling them to make Factor IX.

Haematologist John Rasko, of Sydney's Prince Alfred Hospital, said that in Dr Troedson's case, the treatment worked well temporarily, giving him a welcome break from bleeding episodes and regular Factor IX injections.

"At the highest dose, which is what Chris got, we saw significant production of this essential clotting factor for up to 10 weeks following the gene therapy," said Professor Rasko, who's based at Sydney University's Centenary Institute.

Although his levels of Factor IX eventually returned to what they were before the therapy, Dr Troedson said that since he received the treatment in October 2002, his bleeding episodes had diminished in number and he did not require as many Factor IX injections.

"I don't know if that can necessarily be explained by the gene therapy," he said in an interview.

Prof Rasko said researchers believed the reason the gene therapy eventually failed was because Dr Troedson's immune system attacked the AAV virus attached to the liver cells, which were producing the blood clotting factor.

"We didn't think that he needed any immune suppression drugs at the time, nor did we give him any, but in retrospect in the end we were hampered by the body's own immune system which removed the very gene-modified cells that we were so excited about," he explained.

The scientists hope that eventually, if they suppress the immune system for several months, the patient's body will not attack the virus transporting the gene, allowing it to become established in the liver.

"The gene will be there hopefully permanently to create a cure for this serious disease," Prof Rasko said.

"We're looking forward to the possibility that temporarily suppressing the immune system will lead to some kind of long-term cure."

Further trials of the therapy are planned but these may be a year or two away as the scientists look for another funding source after American pharmaceutical company Avigen pulled out of the research.

Prof Rasko said that if the trials proved successful, the treatment would eventually prove cost effective.

He said the annual cost of treating people with haemophilia in Australia was between $50,000 and $500,000 per person, depending on the severity of the disorder.

Mr Troedson has a type of haemophilia known as Christmas disease, named after Stephen Christmas, the first patient described with the condition.

Results of the study involving Dr Troedson were published in the latest edition of the prestigious journal, Nature Medicine.

He recorded the best results out of the seven patients, suggesting the higher dose he received was most beneficial.

The treatment was performed during a local anaesthetic and Dr Troedson said he experienced no serious side effects.

"When the therapy began to stop working, I got what was described as a mild hepatitis but I didn't feel sick at all," he said.

"It showed up in the blood test but if I hadn't had that, I wouldn't have known."

The research was a collaboration between scientists in Australia, the United States and South America.

Gene therapy has so far produced no successful applications for human disease.

Advances have been limited by severe side effects, failure to deliver sufficient genes, and lack of gene function in the patient's body.