Occurrence of leukaemia following gene therapy of X-linked SCID

Recombinant viral vectors have allowed gene transfer to be developed as a promising approach to the treatment of genetic diseases. Recently, gene therapy of children with X-linked severe combined immune deficiency resulted in impressive levels of immune reconstitution-a triumph that was later overshadowed by the development of leukaemia in two patients. What were the causes of this cancer, and how can the therapeutic benefits of gene therapy be achieved while minimizing risk to the patient?