Phase I Study of BL22, A Recombinant Immunotoxin for Chronic Lymphocytic Leukemia and CD22+ Lymphomas

OBJECTIVES:

• Determine the maximum tolerated dose of recombinant BL22 immunotoxin in patients with CD22-positive refractory B-cell chronic lymphocytic leukemia, prolymphocytic leukemia, or indolent non-Hodgkin's lymphoma.
• Determine the safety and efficacy of this drug in these patients.
• Determine the pharmacokinetics of this drug in these patients.
• Determine the immunogenicity of this drug in these patients.
• Determine the effect of this drug on various components of the circulating cellular immune system in these patients.

OUTLINE: This is a nonrandomized, dose-escalation study. Patients are stratified according to disease type (chronic lymphocytic leukemia vs non-Hodgkin's lymphoma).

Patients receive recombinant BL22 immunotoxin IV over 30 minutes on days 1, 3, and 5. Treatment repeats ≥ every 27 days for up to 6 courses in the absence of neutralizing antibodies to BL22 or PE38, disease progression, or unacceptable toxicity. Patients achieving a complete response (CR) receive 2 additional courses beyond CR. Patients who relapse from a CR lasting ≥ 6 months may receive additional courses.

Cohorts of 3-6 patients per stratum receive escalating doses of recombinant BL22 immunotoxin until the maximum tolerated dose (MTD) is determined. The MTD is defined as the dose preceding that at which 2 of 3 or 2 of 6 patients experience dose-limiting toxicity.