Protocol IB: CPM on days 36 and 64; cytarabine (ARA-C) on days 38-41, 45-48, 52-55 and 59-62; 6-mercaptopurine (6-MP) on days 36 to 63 (28 days); MTX IT on day 45 and 59 Protocol IB-ASP+: additional PEG-L-ASP on days 40, 47, 54, and 61 (4 doses) are given to the patients eligible for randomization RHR and randomized into the experimental arm.