OBJECTIVES: Primary * Determine the complete and partial response rate in patients with fludarabine-refractory B-cell chronic lymphocytic leukemia treated with denileukin diftitox. Secondary * Determine the toxicity profile of this drug in these patients. * Determine the response rate in patients (regardless of CD25 receptor density) treated with this drug. * Determine the progression-free survival and overall survival of patients treated with this drug. OUTLINE: This is a multicenter study. Patients receive denileukin diftitox IV over 1 hour on days 1-5. Treatment repeats every 21 days for up to 8 courses in the absence of disease progression or unacceptable toxicity. Patients achieving a complete response after 8 courses proceed to follow-up. Patients achieving a partial response or stable disease after 8 courses may continue treatment at the discretion of the investigator. Patients are followed every 3 months for 1 year and then annually until relapse. PROJECTED ACCRUAL: A total of 12-44 patients will be accrued for this study within 1 year.
DISEASE CHARACTERISTICS: * Diagnosis of B-cell chronic lymphocytic leukemia (CLL) meeting the following criteria at any time during the course of disease (e.g., at initial diagnosis or relapse): * Absolute lymphocytosis \> 5,000/mm\^3 * Lymphocytes must appear mature with \< 55% prolymphocytes * More than 30% of all nucleated cells are lymphoid on bone marrow aspirate smear * Lymphoid infiltrates compatible with bone marrow involvement by CLL on core bone marrow biopsy * Predominant B-cell monoclonal population of cells share the B-cell marker (CD19) with the CD5 antigen in the absence of other pan-T-cell markers by lymphocyte immunophenotyping * High-risk disease OR intermediate-risk disease * Patients in the intermediate-risk group must have evidence of active disease as demonstrated by at least 1 of the following criteria: * Massive or progressive splenomegaly and/or adenopathy * Weight loss \> 10% within the past 6 months * Common toxicity grade 2-4 fatigue * Fevers \> 100.5°F OR night sweats for more than 2 weeks without evidence of infection * Progressive lymphocytosis with an increase of \> 50% over a 2-month period or an anticipated doubling time of \< 6 months * Failed at least 1 prior fludarabine regimen, as defined by 1 of the following criteria: * Refractory or intolerant to fludarabine * Relapsed within 6 months after completion of fludarabine * No CNS leukemia * No mantle cell lymphoma in leukemic phase PATIENT CHARACTERISTICS: Age * 18 and over Performance status * Zubrod 0-2 Life expectancy * More than 2 months Hematopoietic * Absolute neutrophil count ≥ 1,000/mm\^3 * Platelet count ≥ 50,000/mm\^3 * Hemoglobin ≥ 8 g/dL (transfusion allowed) Hepatic * Albumin ≥ 3 g/dL * AST and ALT ≤ 2.5 times upper limit of normal (ULN) * Bilirubin ≤ 1.5 times ULN * No hepatitis B or C infection Renal * Creatinine ≤ 1.5 mg/dL OR * Creatinine clearance ≥ 40 mL/min Cardiovascular * LVEF ≥ 40% Other * No uncontrolled infection * No other concurrent serious illness * No HIV infection * Not pregnant or nursing * Negative pregnancy test * Fertile patients must use two effective methods of contraception (one must be non-hormonal) during and for at least 1 month after study participation PRIOR CONCURRENT THERAPY: Biologic therapy * Prior denileukin diftitox allowed Chemotherapy * See Disease Characteristics Endocrine therapy * No concurrent corticosteroids as anti-emetics Radiotherapy * No concurrent radiotherapy Surgery * Not specified Other * At least 28 days since prior anticancer therapy and recovered * No other concurrent antineoplastic drugs