Gene therapy has been successfully used to treat a four-year-old boy with no immune system, a team of British scientists has revealed.
Mustaf now attends nursery
The boy, named only as Mustaf, had the rare life-threatening immune disorder known as ada-SCID.
Doctors at Great Ormond Street Hospital used a harmless virus to deliver stem cells containing a corrective gene.
It is the first successful treatment of ada-SCID in the UK. Five children have been treated in Milan, Italy.
Children with ada-SCID have no working immune system. They are susceptible to even the most minor infection.
The condition is one of a number of Severe Combined Immunodeficiency conditions. Children with SCID conditions used to be known as "bubble babies" because they had to live within a protective plastic bubble.
Seven children and one adult with XCID, a related condition which only affects boys, have also been successfully treated using gene therapy at Great Ormond Street.
The conditions differ in that different genes are faulty.
Ada-SCID is more difficult to treat. It results from the lack of an enzyme which helps cells get rid of toxic by-products. Without it, poisons build up and kill immune system cells.
A bone marrow transplant from a good donor can provide a cure in 90% of cases, but only 30% of families have such a donor and the risks are much higher if attempted with a poorer match.
In gene therapy, blood stem cells are removed from the bone marrow, and an artificially created version of the correct, working gene is then inserted into those cells, using a harmless virus.
When these modified cells are infused into the child, they proliferate and come to dominate.
Since stem cells create all the other cells in the blood and immune system, the corrected cells create a new working immune system.
Mustaf was born in September 2000. He was diagnosed with ada-SCID when he was a month old.
In Nov 2003 doctors stopped the enzyme treatment he was receiving after his condition deteriorated.
He was given the gene therapy a month later after a mild dose of chemotherapy to prime his bone marrow for the treatment.
Five weeks after his treatment, Mustaf was allowed to go home.
Professor Adrian Thrasher, who led the treatment, said: "He has made steady progress and his immune function is already better than it was with enzyme replacement therapy.
"He continues to receive prophylactic antibiotics and antibodies, but if his immune system continues to develop we will be able to withdraw these. Doctors are pleased with his progress."
Mustaf, who is from London, is now in pre-school education, and doctors say he can live a life largely free of restrictions.
Dr Peter Fraser, a gene therapy researcher at the Babraham Institute in Cambridge, said: "This whole procedure is in its very early stages, and every success, especially now it has proved effective in a different disease, is a real triumph, not just for the patient, but for scientists involved in gene therapy.
"There are many other genetic diseases for which gene therapy could be really useful.
"There are always concerns about treatments at such an early stage in their development, but it's looking good for this little boy because he doesn't seem to have had any problems."