FRENCH gene-therapy pioneers are to resume their treatment of 鈥渂ubble-boy鈥� babies after the suspension of their trial in January 2003, when two of the children developed leukaemia. 鈥淥ur trial reopened last summer, and we are now under way to treat three patients,鈥� says Alain Fischer, head of the team at the Necker Hospital for Sick Children in Paris.
Until the leukaemia cases emerged, the trial had been seen as a rare success for gene therapy. The team successfully treated 10 infants with X-linked severe combined immunodeficiency (SCID-X1), a gene defect which prevents the boys鈥� immune systems from developing properly. To avoid infection, the boys must be kept totally isolated.
Fischer took bone marrow cells from the boys, used a virus to add normal copies of the defective gene and then re-implanted the corrected cells. But in 2 of the 10 boys they treated, the added gene landed near a cancer-related gene, LMO-2, and activated it. One boy is in complete remission. The other died.
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Both boys were treated very early in life, one at 1 month old and one at 3 months old. Fischer thinks the risk of cancer is greater during this period of rapid growth, so in future he will not treat patients until they are 6 months old. The boys will be screened to see whether the virus has inserted the corrected gene near LMO-2, and for early signs of leukaemia, so treatment can be given if needed.
A team at Great Ormond Street Hospital in London has continued to treat boys using a similar procedure, without problems. Details of the first four patients were reported in The Lancet last month (vol 364, p 2181), and the team has begun to treat three more children.
鈥淚n future patients will be screened to make sure the gene has been inserted correctly and for early signs of leukaemia鈥�
The US Food and Drug Administration halted all planned trials in 2003 after the leukaemia cases emerged. Only one trial, at the National Institutes of 91色情片 in Bethesda, Maryland, has been allowed to begin. It involves treating patients as old as 20 as a last resort, after bone marrow transplants have failed. The team will treat their third patient this month.
