Inclusion Criteria -

1. Between the ages of 6 months and < 18 years of age

2. Must have histologically proven B-cell ALL or B-cell lymphoblastic lymphoma with
marrow involvement.

3. All subjects (both ALL and subjects with lymphoblastic lymphoma) must have M2 or M3
bone marrow classification.

4. Disease status:

1. Subjects must have relapsed or refractory disease

2. In the event of relapse after prior allogeneic HSCT, subjects must be at least 3
months post-transplant and have no evidence of active graft-vs-host disease, and
must have been off immunosuppression for at least 4 weeks.

3. Must have resolution of the acute toxic effects to Grade 2 from prior
chemotherapy before entry, in the opinion of the investigator

5. Subjects with the following central nervous system (CNS 1 or 2) status are eligible
only in the absence of neurologic symptoms

6. Female subjects of childbearing potential and post-pubertal male subjects must use an
approved method of contraception for the study

Exclusion Criteria

1. Concurrent enrollment in another clinical study for cancer treatment, unless the
subject is in the follow-up period from a previous study.

2. Isolated testicular or CNS ALL

3. Subjects with mixed-lineage leukemia (MLL) gene rearrangement

4. Inadequate Hepatic function

5. Inadequate Renal function

6. Radiologically-detected CNS lymphoma

7. Subjects with clear laboratory or clinical evidence of disseminated intravascular
coagulation (DIC

8. Hyperleukocytosis or rapidly progressive disease that would compromise ability to
complete study therapy

9. QTcF interval greater than or equal to a Grade 2, confirmed by 2 additional
seperate ECG's within 28 days prior to starting study drug. The initial screening
ECG need not be repeated for confirmation if the QTcF interval is <481 milliseconds.

10. Pregnant or breast-feeding females

11. Prior treatment with CAT-3888 (BL22), moxetumomab pasudotox, or any
pseudomonas-exotoxin-containing compound

12. Prior treatment with any anticancer biologic therapy within 2 weeks prior to starting
study drug, including but not limited to therapeutic monoclonal antibodies or
antibody-drug conjugates

13. Systemic chemotherapy 2 weeks (6 weeks for nitrosoureas) and radiation therapy 3
weeks prior to starting study drug

14. Clinically significant ophthalmologic findings (evidence of retinal damage or injury)
during the screening

15. Presence of a second invasive malignancy.

16. Uncontrolled pulmonary infection, presence of pulmonary edema

17. Serum albumin < 2 g/dL. Albumin infusions for correction of hypoalbuminemia are
allowed, but cannot have administered within 7 days prior to start of study drug.

18. Radioimmunotherapy within 2 years prior to study start of study drug.

19. Subject with prior history of thrombotic microangiopathy or HUS.

20. T-cell ALL or T-cell lymphoblastic lymphoma

21. Subjects currently receiving high-dose estrogen therapy defined as >0.625mg/day of an
estrogen compound or within 2 weeks prior to starting study drug.

Minimum Eligible Age: 6 Months

Maximum Eligible Age: 18 Years

Eligible Gender: Both