Inclusion Criteria:

- Subjects with CD22-positive ALL with either refractory disease (i.e. disease
progression or no response while receiving their most recent prior anti-cancer
therapy), or relapsed disease (i.e. response to their most recent prior anti-cancer
therapy with subsequent relapse). Subjects enrolled in the Phase 2 portion of the
study must be due to receive salvage 2 or later therapy.

- Subjects with Philadelphia chromosome-positive (Ph+) ALL must have failed standard
treatment with at least one tyrosine kinase inhibitor.

- Adequate renal and hepatic function, and negative pregnancy test for women of
childbearing potential.

Exclusion Criteria:

- Subjects with isolated extramedullary relapse or active central nervous system (CNS)
leukemia.

- Prior allogeneic hematopoietic stem cell transplant (HSCT) or other anti-CD22
immunotherapy within 4 months, or active graft versus host disease (GvHD) at study
entry.

- Evidence or history of veno-occlusive disease (VOD) or sinusoidal obstruction
syndrome (SOS).