Open-label, multicenter, non-randomized, 3+3 dose escalation study, starting with 1.2 mg/kg brentuximab vedotin i.v. on day 1 of a 21-day cycle in combination with fixed-dose MAD (Methotrexate, L-asparaginase and Dexamethasone) chemotherapy. The first cycle will be evaluated for the determination of the recommended phase II dose.