Inclusion Criteria

          1. Pre-B ALL, low and high grade NHL who underwent an alloHSCT using posttransplant CY
             GVHD prophylaxis (Pt-Cy alone or combination with MMF/tacrolimus or sirolimus) as
             follows:

             A. Pre-B ALL patients in CR1 with high-risk features such as adverse cytogenetics
             including t(9;22) or Ph-like ALL, t(4;11) or other MLL (KMT2A) rearrangements,
             t(v;14q23)/IgH, complex karyotype (≥5 chromosomal abnormalities), hypodiploidy (<44
             chromosomes), low hypodiploidy (30-39 chromosomes)/near triploidy (60-68 chromosomes),
             intrachromosomal amplification of chromosome 21 (iAMP21), high WBC count at
             presentation (≥30,000), lack of achievement of complete remission after standard
             induction chemotherapy (but achieved CR1 following salvage or consolidation), or
             persistence of detectable disease after induction and consolidation (intensification)
             or pre-transplant as documented on any of routine clinical tests (morphology, flow
             cytometry, cytogenetics or molecular studies) OR all Pre-B ALL patients in second and
             higher CR B. Low and high grade NHL following a nonmyeloablative (reduced-intensity
             conditioning) transplant irrespective of pre-transplant disease status

          2. Patients should be at least 60 but not more than 180 days from transplant with
             documented count recovery (ANC >1 x109/L, and non-transfused platelets >30x109/L) and
             no evidence of disease progression

          3. ECOG performance status 0-2

          4. Ability to give informed consent

          5. In agreement to use an effective barrier method of birth control (hormonal or barrier
             method of birth control; abstinence) to avoid pregnancy during the study and for a
             minimum of 30 days after study treatment, for all male and female patients who are
             fertile

          6. Age ≥18 years

          7. Patients may have received any number of prior regimens to achieve remission. Patients
             previously treated with blinatumomab will be eligible as long as they did not
             experience unacceptable toxicities with prior blinatumomab administration. If patient
             was refractory (no response) to blinatumomab in the past, patient will be eligible if
             there was no evidence of CD19 loss on leukemia cells.

        Exclusion Criteria

          1. Lack of engraftment (less than 85% donor DNA in bone marrow or peripheral blood after
             allogeneic HSCT).

          2. Active or untreated disease in central nervous system or testes

          3. Patient has received chemotherapy or radiotherapy (with the exception of intrathecal
             chemotherapy) within 2 weeks of starting blinatumomab. Patient could receive
             intrathecal prophylactic chemotherapy within a week prior to starting blinatumomab.

          4. Patients with active uncontrolled infection or uncontrolled intercurrent illness
             including, but not limited to symptomatic congestive heart failure, unstable angina
             pectoris, cardiac arrhythmia, or psychiatric illness/social situations that would
             limit compliance with study requirements.

          5. Patients with prior history of severe (grade 3 or 4) acute GVHD or active severe
             chronic GVHD even if resolved will not be eligible. Patients with history of active
             acute GVHD (grade 2) and active moderate chronic GVHD who required steroids for the
             treatment of GVHD will need to be off steroids for at least 4 weeks prior to treatment
             start. (Topical steroids or physiologic adrenal replacement steroid doses are
             allowed).

          6. Patients requiring calcineurin inhibitors (i.e. tacrolimus or sirolimus) or other
             systemic immunosuppressants (cyclosporine (CNI); methotrexate or similar) for GVHD
             prophylaxis or treatment within 4 weeks prior to treatment start.

          7. Inadequate end organ function defined as AST, ALT, and alkaline phosphatase > 3X ULN,
             bilirubin >=1.5X ULN, or creatinine >=2 mg/dL

          8. Patients with Ph-positive ALL who are eligible for post-transplant TKI maintenance
             based on a demonstrated sensitivity to TKIs pre-transplant (patients with known
             intolerance or resistance to TKI will be eligible)

          9. Evidence of progressive disease post-transplant

         10. Women who are pregnant or lactating

         11. Known hypersensitivity to blinatumomab

         12. Patients with a concurrent active malignancy for which they are receiving treatment

         13. Concurrent use of any other investigational drugs

         14. Patient who have a history or presence of clinically relevant CNS pathology such as
             epilepsy, seizure, paresis, aphasia, stroke, severe brain injuries, dementia,
             Parkinson's disease, cerebellar disease, psychosis, or other significant CNS
             abnormalities. A history of treated CNS leukemia or lymphoma will be allowed if recent
             imaging and CSF studies confirm the absence of active CNS disease at the time of study
             entry

         15. Weight <45 kg

         16. Patients receiving other post-transplant maintenance therapies

         17. Infection with human immunodeficiency virus (HIV) or chronic infection with hepatitis
             B virus or hepatitis C virus (HCV)