Retreatment Protocol for BL22 Immunotherapy in Relapsed or Refractory Hairy Cell Leukemia

BL22 is a type of protein that scientists have created to interact with certain cancer cells. Experiments have shown that BL22 can bind with cancer cells that have a particular kind of protein (called CD22 ) on their surface, and can kill those cells. CD22 is present on certain types of hairy cell leukemia (HCL) cancer cells, and researchers have been working on treatments that will use BL22 and other related proteins to interact with and kill these kinds of cancer cells. The primary purpose of this study will be to provide access to and treatment with BL22 for patients who have HCL in order to determine their response to the treatment. In addition, the study will assess potential side effects of BL22 and examine why some patients respond better than others to treatment with BL22 and related therapies. This study will include about 21 to 25 adults who have been diagnosed with forms of HCL that have not responded well to standard treatments such as surgery, chemotherapy, or radiation therapy. These adults also will have received anti-CD22 therapies before, potentially including treatments with BL22, and have not developed immunity or resistance to these treatments. Prior to the study, patients will undergo a 1- to 2-week screening period to assess their eligibility for treatment. Eligible patients will participate in the study for up to 16 cycles of treatment, with each cycle lasting approximately 4 weeks. For each cycle, patients will receive 1 prescribed dose of BL22 every other day for a total of 3 doses per cycle, and will be assessed after every cycle to evaluate the success of the treatment. During the evaluation visits, patients will be required to have a brief physical examination, give blood and urine samples for testing, and undergo other tests as need to check heart and kidney function and assess the state of the leukemia. Patients who agree will give additional blood, urine, or bone marrow samples for future research purposes.

Background: BL22, also called CAT-3888 or RFB4(dsFv)-PE38, is a recombinant immunotoxin containing an Fv fragment of an anti-CD22 monoclonal antibody and truncated Pseudomonas exotoxin (PE). In Phase 1 and 2 trials in patients with chemoresistant hairy cell leukemia (HCL), BL22 showed 47-61% complete remission (CR) rates and 12% of HCL patients had a completely reversible hemolytic uremic syndrome (HUS). A mutant of BL22, termed CAT-8015 or HA22, differs by 3 amino acids and has higher binding affinity to CD22 compared to BL22 (15-fold greater). CAT-8015 is currently undergoing Phase 1 testing in HCL and other diseases. HCL patients who have previously received recombinant anti-CD22 immunotoxin (BL22, CAT-8015, or LMB-2) may benefit from additional BL22 administration. Objectives: The primary objective is to provide access to BL22 for HCL patients who have previously received BL22, CAT-8015, or LMB-2, or are ineligible for CAT-8015, but may benefit from BL22. The primary outcome will be response to treatment. Secondary objectives: * Determine immunogenicity and safety profiles of BL22 in patients with prior immunotoxin, using aspirin/enoxaparin to prevent HUS. * To correlate response to ex vivo sensitivity of HCL cells, obtained from blood with or without apheresis, to BL22 and to other recombinant anti-CD22 immunotoxins such as CAT-8015, and to tumor markers. * To correlate neutralizing antibodies with number of cycles of BL22, type and number of prior systemic therapies, and time since prior purine analog. * To correlate CR by bone marrow biopsy with improvement in bone marrow as assessed by magnetic resonance imaging (MRI) of the spine. Eligibility: Patient must have received prior recombinant anti-CD22 immunotoxin (i.e. BL22, CAT-8015, or LMB-2 treatment) or be ineligible for CAT-8015. HCL with cytopenia, high malignant count or symptomatic splenomegaly. Patients must have had at least 2 prior systemic therapies. There must have been at least 2 prior courses of purine analog, or 1 if the response to this course lasted \< 2 years, or if the patient had unacceptable toxicity to purine analog. Design: This is a single institution, expanded access protocol accruing 21-25 patients. Patients will be administered BL22 at 30 microg/kg every other day for 3 doses (QOD times 3) per 4-week cycle (at least 26 days) for a maximum of 16 cycles. Patients in CR may receive up to 2 more cycles if without minimal residual disease (MRD), or 4 more cycles if in CR with MRD, but no more than 16 cycles total. No retreatment if high levels of neutralizing antibodies or progressive disease. Patients who have been off treatment and relapse after greater than 2 months of a CR or partial response may be retreated if eligibility criteria are still met. If any HUS, accrual to the study will be suspended for discussion with FDA.