Inclusion Criteria:

          -  Patients with relapsed (second or subsequent bone marrow relapse or bone marrow
             relapse after allo-SCT) or refractory (not achieving an initial complete response (CR)
             after 2 cycles of standard chemotherapy) CD19-positive B-acute lymphoblastic leukaemia

          -  Morphologically confirmed with leukemic blasts in the bone marrow or a quantifiable
             MRD load of 1x10-4 (by multiparameter flow cytometry and/or quantitative polymerase
             chain reaction)

          -  Eligible and fit for allogeneic hematopoietic stem cells transplantation with suitable
             donor available

          -  Estimated life expectancy ≥ 12 weeks

          -  Lansky (age < 16 years at the time of assent/consent) or Karnofsky (age ≥ 16 years at
             the time of assent/consent) performance status ≥ 50 Eastern Cooperative Oncology Group
             ECOG performance status < 2

        Exclusion Criteria:

          -  Patients/parents unwilling to undergo a follow-up for 15 years

          -  Foreseeable poor compliance to the study procedures

          -  CD19-negative B-cell leukaemia

          -  Evidence of disease progression after cytoreduction

          -  Uncontrollable CNS leukaemia or neurological symptoms defined as CNS grade 3 (per
             National Comprehensive Cancer National guidelines). Patients developing grade 3 CNS
             disease at any time after enrolment will be excluded.

          -  Absence of suitable HLA matched or mismatched donor

          -  Weight < 6 kgs

          -  Presence of donor-specific anti-HLA antibodies directed against PBLTT52CAR19

          -  GvHD requiring systemic therapy

          -  Systemic steroid therapy prednisolone >0.5mg/kg/day

          -  Known hypersensitivity to any of the test materials or related compounds

          -  Active bacterial, fungal, or viral infection not controlled by a standard of care
             anti-microbial or anti-viral treatment. Uncontrolled bacteraemia/ fungaemia is defined
             as the ongoing detection of bacteria/fungus on blood cultures despite antibiotic or
             anti-fungal therapy.

          -  Uncontrolled viraemia is defined as rising viral loads on two consecutive occasions
             despite antiviral therapy.

          -  Risk of pregnancy or non-compliance with contraception (if applicable). Girls of
             childbearing potential must have been tested negative in a pregnancy test within 14
             days prior to inclusion.

          -  Lactating female participants unwilling to stop breastfeeding

          -  Intrathecal methotrexate within 4 weeks or intrathecal chemotherapy (e.g Ara-C) within
             2 weeks of lymphodepletion

          -  Less than 2 half-lives from prior therapy with immune checkpoint pathway modifiers to
             lymphodepletion

          -  Prior CAR19 therapy known to be associated with ≥Grade 3 cytokine release syndrome
             (CRS) or ≥Grade 3 drug-related CNS toxicity