Alain Fischer's work has been focused for years on immunodeficiency acquired from birth (such as bubble babies) and curative approaches using gene therapies. With Marina Cavazzana-Calvo and Salima Hacein-Bey, he obtained in 1999, the first clinical successes in the world of gene therapies for about ten bubble children, two of whom unfortunately developed leukaemias after a few months, one of whom had died. The test was stopped urgently in 2002. Research will show that these leukaemias are due to random insertion into a proto-oncogene of the drug gene. The trial is restarted in 2004, according to a modified protocol using better retroviral vectors, and will be stopped again in 2005 due to new complications. However, of the 16 children treated to date, 15 are satisfactorily cured of their acute immune deficiency.