Treatment Block 2: Patients receive TIT on days 1 and 22. Patients then receive cyclophosphamide, etoposide, G-CSF, methotrexate IV, leucovorin calcium, and imatinib mesylate as in arm I. After each block is completed, disease is assessed. The next block is started on day 36 if blood counts have recovered and marrow during block 1 is at least M2/M3. Patients are removed from protocol therapy if disease progresses, unacceptable toxicity occurs, marrow is M2/M3 at day 15 of the second administered block of treatment, or cerebrospinal fluid blasts persist after 6 weekly doses of TIT.