BioWorld International Correspondent

LONDON - Gene therapy trials in the treatment of X-linked severe combined immunodeficiency disease (X-SCID) are being allowed to continue in the UK, despite the suspension of a similar trial in France, after one patient developed leukemia.

The UK government body, the Gene Therapy Advisory Committee (GTAC), said it would be wrong to stop the trial, as children for whom there are no compatible bone marrow donors could die without the treatment. In the past year, four patients have had therapy in two trials currently running at Great Ormond Street Hospital in London, and all are said to be doing well.

The chairman of GTAC, Norman Nevin, was alerted to the French case on Sept. 16, prompting an immediate review of all UK gene therapy trials. Only the two trials at Great Ormond Street were identified as being closely related to the French trial.

"In balancing the potential risks and benefits to these children, and in weighing alternative treatment options, we have decided that, at this time, it would be unjustifiable to withdraw GTAC's approval of the two Great Ormond Street studies," Nevin said.

X-SCID is extremely rare, with only three or four babies born with the condition each year in the UK. Without treatment, babies with X-SCID rarely survive beyond their first birthday. The first boy to be treated in the UK trial, Rhys Evans, has just celebrated his second birthday.

In allowing the trial to continue, GTAC was also influenced by the fact that it represents a significant milestone in the development of gene therapy treatments. "This might one day help many children and adults with incurable diseases," Nevin said. "As with all innovative treatments, there will always be potential for side effects."

When the trial received the go-ahead initially, GTAC recognized that the X-SCID gene therapy may possibly cause cancer. "[GTAC] is satisfied that all parents of children treated were informed of this risk and received appropriate counseling prior to treatment," Nevin said.

Although allowing the trial to continue, GTAC is increasing its scrutiny, and will in the future review each case individually before allowing the entry of any new patient to the studies. In addition, families with children eligible to enter the trial must be informed about the child in the French study.

The X-SCID treatment, pioneered at the Necker-Enfants Malades Hospital in Paris, involves removing bone marrow cells from the patient and using a viral vector to deliver a copy of the missing gene, before re-introducing the marrow cells to the patient.