BL22 Immunotoxin in Treating Patients Previously Treated With Cladribine for Hairy Cell Leukemia

RATIONALE: The BL22 immunotoxin can locate tumor cells and kill them without harming normal cells. This may be an effective treatment for hairy cell leukemia that has not responded to treatment with cladribine. PURPOSE: This phase II trial is studying BL22 immunotoxin to see how well it works in treating patients previously treated with cladribine for hairy cell leukemia.

OBJECTIVES: Primary * Determine the response rate in patients with cladribine-resistant hairy cell leukemia treated with BL22 immunotoxin. Secondary * Determine the response duration in patients treated with this drug. * Determine the safety of this drug in these patients. * Determine the pharmacokinetics of this drug in these patients. * Correlate BL22 blood levels and toxicity of this drug with the development of neutralizing antibodies in these patients. OUTLINE: Patients receive BL22 immunotoxin IV over 30 minutes on days 1, 3, and 5 followed by rest. Patients are then evaluated at 8 weeks. Patients achieving complete hematologic remission are followed. All other patients continue to receive BL22 immunotoxin as above on days 1, 3, and 5. Treatment repeats every 4 weeks for up to a total of 16 courses in the absence of disease progression or unacceptable toxicity. Patients achieving CR without minimal residual disease (MRD) receive 2 courses beyond CR. Patients achieving CR with MRD receive 4 courses beyond CR. Patients are followed every 4 months for 1 year, every 6 months for 1 year, and then annually thereafter. PROJECTED ACCRUAL: A total of 36 patients will be accrued for this study within 3 years.