Inclusion Criteria:

          -  Age 18 years or older Age 18 years or older

          -  ECOG performance status of 0 or 1

          -  Relapsed or refractory B cell ALL

          -  Patients with Ph+ ALL are eligible if intolerant to TKI, failed two lines of any TKI,
             or failed one line of second-generation TKI, or if TKI is contraindicated

          -  Documented CD19 positivity within 1 month of screening

          -  Phase Ib: Primary Cohort IA: Presence of ≥5% blasts in BM at screening

          -  Phase Ib: Exploratory Cohort IB: MRD-positive defined as ≥ 1E-4 and <5% blasts in the
             BM at screening

          -  Phase II: Primary Cohort IIA: Presence of ≥5% blasts in BM at screening

          -  Phase II: Exploratory Cohort IIB: MRD-positive defined as ≥1E-4 and <5% blasts in the
             BM at screening

          -  Adequate renal, hepatic, pulmonary, and cardiac function

        Exclusion Criteria:

          -  Phase Ib (Cohort IA and Cohort IB) and Phase II Cohort IIA only ALL with isolated EM
             disease

          -  Diagnosis of Burkitt's leukaemia/lymphoma or CML lymphoid in blast crisis

          -  History or presence of clinically relevant CNS pathology

          -  Presence of CNS-3 disease or CNS-2 disease with neurological changes

          -  Presence of active or uncontrolled fungal, bacterial, viral, or other infection
             requiring systemic antimicrobials for management

          -  Active or latent Hepatitis B virus or active Hepatitis C virus

          -  Human Immunodeficiency Virus (HIV), HTLV-1, HTLV-2, syphilis positive test

          -  Prior CD19 targeted therapy other than blinatumomab. Patients who have experienced
             Grade 3 or higher neurotoxicity following blinatumomab.