Inclusion Criteria:

- Confirmed diagnosis of B-Cell Leukemia (CLL, PLL, or SLL)

- Measurable Disease

- Disease characteristics: Patients with chronic lymphocytic leukemia (CLL) or Small
Lymphocytic Leukemia (SLL) are eligible if they have failed 2 or more prior courses
of standard chemo and/or biologic therapy (e.g. Rituxan)_ and prolymphocytic leukemia
(PLL) will be eligible if they have failed at least one prior standard
chemotherapeutic regimen. Medical indications for treatment include progressive
disease-related symptoms, progressive cytopenias due to marrow involvement,
progressive or painful splenomegaly or adenopathy, rapidly increasing lymphocytosis,
autoimmune hemolytic anemia or thrombocytopenia and increased frequency of
infections.

- ECOG performance status of 0-2

- Patients with other cancers who meet eligibility criteria and have had less than 5
yrs. of disease-free survival will be considered on a case-by-case basis

- Life expectancy of greater than 6 mos., as assessed by the principal investigator

- Must be able to understand and sign the informed consent

- Must be at least 18 years old

- Female and Male patients agree to use an approved method of contraception during the
study

Exclusion Criteria:

- History of allogeneic bone marrow transplant.

- Documented and ongoing central nervous system involvement with their malignant
disease (history of CNS involvement is not an exclusion criterion.)

- Pregnant or breast-feeding females

- Patients who plasma contains either a significant level of antibody to CAT-8015 as
measured by ELISA, or antibody that neutralizes the binding of CAT-8015 to CD22 as
measured by a competition ELISA.

- HIV positive serology (due to increased risk of severe infection and unknown
interaction of CAT-8015 with antiretroviral drugs)

- Hepatitis B surface antigen positive

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

- Hepatic function:Serum transaminases (either ALT or AST) or direct bilirubin greater
than or equal to Grade 2, unless bilirubin is due to Gilbert's disease

- Renal function: Serum creatinine clearance is less than or equal to 60 mL/min as
estimated by Cockcroft-Gault formula

Hematologic function:

- The ANC less than 1000/cmm, or platelet count less than 50,000/cmm, if these
cytopenias are not judged by the investigator to be due to underlying disease (i.e.,
potentially reversible with anti-neoplastic therapy).

- A patient will not be excluded because of pancytopenia greater than or equal to Grade
3, or erythropoietin dependence, if it is due to disease, based on the results of
bone marrow studies.

- Baseline coagulopathy greater than or equal to grade 3 unless due to anticoagulant
therapy

Pulmonary function:

- Patients with less than 50% of predicted forced expiratory volume (FEV-1) or less
than 50% of predicted diffusing capacity for carbon monoxide (DLCO) corrected for
hemoglobin concentration and alveolar volume. Note: Patients with no prior history
of pulmonary illness are not required to have PFTs. FEV1 will be assessed after
bronchodilator therapy.

Recent prior therapy:

- Cytotoxic chemotherapy, corticosteroids (except stable doses of prednisone), whole
body electron beam radiation therapy, hormonal, biologic or other standard or any
investigational therapy of the malignancy for 3 three wks. prior to entry into the
trial.

- Less than or equal to 1 mos. prior monoclonal antibody therapy (i.e. rituximab)

- Patients who are receiving or have received radiation therapy less than 3 weeks prior
to study entry will not be excluded providing the volume of the bone marrow treated
is less than 10% and also the patient has measureable disease outside the radiation
port.

- Any history of prior pseudomonas - exotoxin immunotoxin administrator