The AFSSAPS (French Agency for Health Product Safety) has again suspended gene therapy trials for X-linked severe combined immunodeficiency (X-SCID) led by Alain Fischer and Marina Cavazzana-Calvo at the Necker hospital in Paris. Treatment of children with this rare genetic deficiency began in 1999, but the trial was suspended between 2002 and 2004 when two of eleven children treated at that point developed the same form of leukaemia caused by insertion of the retroviral vector used for the gene therapy (see journal club article). One of these children has subsequently died; however, the trials were resumed due to the severity of the disease; without therapy, affected children will die anyway due to overwhelming infections. Now the trials have been halted again because a child treated in 2002 has developed abnormal T-cell lymphoproliferation (an overgrowth of white blood cells), which could be another form of leukaemia. This complication is under investigation.