In 1999, With Marina Cavazzana-Calvo and Salima Hacein-Bey, Fischer achieved the first clinical successes in the world of gene therapies for about ten bubble children,^[8] two of whom unfortunately developed leukaemias after a few months, one of whom had died. The test was stopped urgently in 2002. The trial was restarted in 2004, according to a modified protocol using better retroviral vectors, and was stopped again in 2005 due to new complications.