TWO years on, hopes are rising that the first form of gene therapy to be given to newborn babies will be a success. A Californian team of researchers announced last week that three children who received experimental therapy for a rare genetic immunodeficiency disease had made better progress than expected.
鈥淚鈥檝e always tried to stay cautious,鈥� said Donald Kohn of the Childrens Hospital Los Angeles, who reported his team鈥檚 results at the American Pediatric Society in San Diego. 鈥淏ut for the first time I鈥檓 really thinking that this might ultimately cure these kids.鈥�
Severe combined immunodeficiency (SCID) is caused by a gene defect that leaves children without a critical enzyme called ADA. Without the enzyme, T cells are poisoned and the body cannot fight off infections.
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Kohn and his colleagues attempted to correct the defect in three babies born with SCID. They took 鈥渟tem鈥� cells from the children鈥檚 umbilical cord blood, inserted working copies of the ADA gene into them, and reinfused them. Stem cells are long-lived and give rise to many different types of immune cells. The team hoped that, by altering stem cells, they would encourage T cells carrying healthy copies of the gene to develop.
After two years, the gene is still present in the children鈥檚 blood cells, indicating that the altered gene reached its target, says Kohn. At present, the T cells that carry the gene are in a minority and the children are being given a drug to keep them alive at a cost of $250 000 a year each. The researchers have now begun to reduce the amount of the drug given to the children, and have noticed that as they do so, the proportion of engineered T cells rises.
At present, about 1 in 100 of the children鈥檚 T cells carry the ADA gene. If that number rises to 1 in 10 or above, the researchers believe the children may be able to fight off infections on their own, and the drug treatment may no longer be necessary.