It turned out that the virus used to deliver the genetherapy was also inserting itself into cancer-causing areas of the genome, and not just where it was needed to cure the kids.
In China, Shenzhen SiBiono GeneTech won approval for a genetherapy drug for head and neck cancer in 2003 but no products have been approved until now in Europe or the United States.
In 2003 the company's treatment for head and neck cancer, which accounts for about 10% of the 2.5m new cancer patients in China every year, gained the first commercial approval of a gene-therapy treatment.
Researchers reported fresh evidence Wednesday that using genetherapy to manipulate the immune system is emerging as a promising new strategy in the fight against cancer.