Study in Pediatrics With Relapsed or Refractory Pediatric Acute Lymphoblastic Leukemia (pALL) or Lymphoblastic Lymphoma

The primary objective of this study is to evaluate the efficacy of moxetumomab pasudotox in pediatric participants with relapsed or refractory B-cell acute lymphoblastic leukemia (ALL) or B-cell lymphoblastic lymphoma.

This is a global, multicenter, open-label, single-arm Phase 2 study to evaluate the efficacy and safety of moxetumomab pasudotox monotherapy in pediatric participants with relapsed or refractory B-cell ALL or B-cell lymphoblastic lymphoma. Participants will be enrolled at sites in North America, Europe, and Australia. This is an approximate 35 month study.

Eligibility Criteria:
Inclusion Criteria -

1. Between the ages of greater or equal to (≥) 6 months and less than (\<) 18 years of age
2. Must have histologically proven B-cell acute lymphoblastic leukemia (ALL) or B-cell lymphoblastic lymphoma with marrow involvement
3. All participants (both ALL and participants with lymphoblastic lymphoma) must have M2 or M3 bone marrow classification
4. Disease status: a) Participants must have relapsed or refractory disease b) In the event of relapse after prior allogeneic hematopoietic stem cell transplant (HSCT), participants 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, c) Must have resolution of the acute toxic effects to less than or equal to (≤) Grade 2 from prior chemotherapy before entry, in the opinion of the investigator
5. Participants with the following central nervous system (CNS) 1 or 2 status are eligible only in the absence of neurologic symptoms
6. Female participants of childbearing potential and post-pubertal male participants 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. Participants with mixed-lineage leukemia (MLL) gene rearrangement
4. Inadequate Hepatic function
5. Inadequate Renal function
6. Radiologically-detected CNS lymphoma
7. Participants 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. QT interval corrected using Fridericia's formula (QTcF) greater than or equal to a Grade 2, confirmed by 2 additional seperate electrocardiographs (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 gram per deciliter (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. Participants with prior history of thrombotic microangiopathy or hemolytic uremic syndrome (HUS)
20. T-cell ALL or T-cell lymphoblastic lymphoma
21. Participants currently receiving high-dose estrogen therapy defined as \>0.625 milligram per day (mg/day) of an estrogen compound or within 2 weeks prior to starting study drug.