PRIOR CONCURRENT THERAPY: Biologic therapy: See Disease Characteristics At least 14 days since prior interferon alfa No other concurrent biologic therapy Chemotherapy: At least 6 weeks since prior busulfan At least 14 days since prior cytarabine At least 7 days since prior hydroxyurea No other concurrent chemotherapy Endocrine therapy: Not specified Radiotherapy: Not specified Surgery: Not specified Other: At least 28 days since prior investigational agents No other concurrent investigational agents