Inclusion Criteria

- INCLUSION CRITERIA:

One of the following:

1. Patients who previously received CAT-3888 and did not have unacceptable toxicity

2. Patients who received CAT 8015 in study CAT 8015-1001 and have progression of disease
or relapse. These patients must be considered off-study for CAT-8015 protocol
specified follow-up

Patient must have histopathological evidence of HCL as confirmed by the Laboratory of
Pathology, NCI.

At least one of the following indications for treatment:

1. Neutropenia (absolute neutrophil count (ANC) less than 1000 cells/microL).

2. Anemia (hemoglobin (Hgb) less than 10 g/dL).

3. Thrombocytopenia (platelet (Plt) less than 100,000/microL).

4. Absolute lymphocyte count of greater than 5000 cells/microL

5. Symptomatic splenomegaly.

6. Enlarging lymph nodes greater than 2cm.

Patient 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 less than 2
years, or if the patient had unacceptable toxicity to purine analog.

Patient must have Eastern Cooperative Oncology Group (ECOG) performance status of 0-2,
unless due to potentially reversible active uncontrolled infection.

Patient must be greater than or equal to 18 years old.

Patient can understand and give informed consent.

Patient must have adequate liver and renal function, as defined by the following criteria:

1. Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) less than or
equal to 2.5-times the upper limits of normal.

2. Albumin greater than or equal to 3.0 g/dL.

3. Total bilirubin less than or equal to 2.2 mg/dL.

4. Creatinine less than or equal to 1.4 mg/dL or creatinine clearance greater than or
equal to 50 mL/min.

Patient must agree to using adequate contraception (hormonal or barrier method of birth
control; abstinence) prior to study entry and for the duration of the study.

EXCLUSION CRITERIA:

Patients who are pregnant or nursing. A negative pregnancy test (urine or serum) must be
documented within one week prior to starting BL22 in women of child-bearing potential.

Patient has developed antibody titer that neutralizes greater than 75% of the activity of
1 microg/mL of BL22 using a bioassay.

Patients who had systemic cytotoxic chemotherapy, immunotherapy, recombinant anti-CD22
immunotoxin (ie, CAT-8015, BL22, or LMB-2) or systemic steroid (with the exception of
stable doses of Prednisone less than or equal to 20 mg/day) treatment within 4 weeks of
enrollment. Patients receiving a limited number of doses (less than 5) of steroid for
non-treatment reasons (eg, allergy prophylaxis connected with medical testing) may not
receive any steroid within one week of enrollment and may not have had any evidence of
disease response to steroid. Subjects who are receiving steroids for other conditions
(e.g., autoimmune disorders) are eligible, as long as there is no increase in the dose or
change in steroid type within 1 week of treatment. Subjects who are using a chronic
steroid must wait for 4 weeks before starting the trial.

Patient had monoclonal antibody therapy (with the exception of BL22 or CAT-8015 or LMB-2)
within 4 weeks of enrollment.

Patient is receiving any other investigational agent.

Uncontrolled intercurrent illness including, but not limited to, symptomatic congestive
heart failure, unstable angina pectoris, cardiac arrhythmia, or psychiatric illness/social
situations that would limit compliance with study requirements.

Patients who discontinued from CAT-8015 or BL22 studies due to toxicity or dose-limiting
toxicity.

Dose limiting toxicity to CAT-8015