More US gene therapy trials were suspended last week, after news that a second patient receiving treatment for a rare immune disease at the Necker Hospital in Paris is showing symptoms of leukaemia. The US Food and Drug Administration (FDA) had already halted three trials in October, after hearing that a patient receiving experimental treatment for X-linked severe combined immune deficiency (X-SCID) in Paris had developed signs of the blood cancer.
It has now suspended a further 27 trials, although it stresses that studies have revealed no other cases of leukaemia in gene therapy patients apart from the two boys in the French trial. The UK's Gene Therapy Advisory Committee (GTAC) says it will not halt the X-SCID trial taking place at Great Ormond Street Hospital in London, but that no new patients will be treated until the evidence from the French trial has been examined.
Children affected by SCID have a faulty gene that means they have no working immune system, so their bodies cannot fight infections. Unless they can be given a matched bone marrow transplant, children with SCID face a lifetime living in a sterile bubble. A team of French scientists, lead by Dr Alain Fischer, has treated eleven X-SCID patients by using a virus to deliver a working gene to the immune cells in the bone marrow. Of these eleven, nine have made a remarkable recovery, but two of these have developed symptoms of leukaemia. Investigations in the first patient revealed that the virus used to transfer therapeutic genes into the patient has inserted itself into a gene previously linked with leukaemia. It is thought that this serious side effect could have been caused by a feature of the virus used in the French trial, and may not necessarily apply to similar gene therapy procedures.
Philip Noguchi of the FDA praised Fischer last week for promptly reporting the second case of leukaemia at the end of last year. He also said: 'We continue to see gene therapy as a promising therapy for all those who have not benefited from current technologies'. The FDA's Biological Response Modifiers Advisory Committee is due to discuss the implications of the latest findings on 28 February.