Administration of Allogenic Red Blood Cells Loaded L-asparaginase in Cases of Relapse of Acute Lymphoblastic Leukaemia

Primary objective : * To explore the relation between 3 doses of GRASPA and duration of asparagine depletion (\< 2µmol/l) Secondary objective : * Pharmacokinetic / Pharmacodynamic parameters * toxicity * Study duration : 2 years * Study treatment : Red blood cells loaded with L asparaginase versus native L asparaginase * Associated treatments : COPRALL chemotherapy * Randomization : centralised randomisation on scratching list