Phase II Study of Post-Transplant Low-Dose Inotuzumab Ozogamicin to Prevent Relapse of Acute Lymphoblastic Leukemia

Inclusion Criteria:

* Diagnosis of CD22-positive Acute Lymphoblastic Leukemia
* Patients who underwent an allogeneic hematopoietic stem cell transplantation(HSCT) from any donor source or auto-HSCT for acute lymphocytic leukemia
* Patients who are after T+60 after transplantation
* Patients who have/are either:

  * High risk B-ALL: (1) high white blood cell(WBC) count when newly diagnosed, (2) Poor risk group according to NCCN guideline 2021 of Acute Lymphoblastic
  * Leukemia
  * Relapsed or refractory to at least 1 line of treatment
  * Minimal residual disease(MRD) positive before HSCT, including flow cytometry and cytogenetic test
* Patients who have \> 99% donor chimerism after allogeneic transplantation.
* Eastern Cooperative Oncology Group(ECOG) Performance status ≤ 2
* Participants must have ANC \> 1,000/µL for 3 days and platelet transfusion independence as defined as a platelet count \> 50,000/µL for 7 days.
* ≥ 18 years old, including male and female
* Participants must have the ability to understand and the willingness to sign a written informed consent document.

Exclusion Criteria:

* Patients with evidence of disease progression prior to enrollment
* Persistent prior treatment toxicities Grade 2 and above according to NCI CTCAE Version 4.03 (with the exception for alopecia, neuropathy, etc.)
* Patients with inadequate organ function and can't tolerate the study treatment determined by investigator as defined by:

  * Severe renal deficiency, with creatinine clearance \< 50ml/min
  * Severe hepatic deficiency
  * Bilirubin, aspartate aminotransferase(AST), and/or ALT(ALT) \> 2X institutional upper limit of normal
  * Severe cardiac or pulmonary deficiency
* Graft-versus-host disease(GVHD) grade III or IV (for patients with a prior allogeneic transplant).
* Active acute or chronic GVHD of the liver (for patients with a prior allogeneic transplant)
* History of veno-occlusive disease(VOD)
* Second active malignancy, other than non-melanoma skin cancer or carcinoma in situ (e.g. cervix, bladder, breast)
* Patients with uncontrolled inter-current illness including, but not limited to ongoing or active infection, symptomatic congestive heart failure, unstable angina pectoris, cardiac arrhythmia, or psychiatric illness/social situations that would limit compliance with study requirements.
* Serologic status reflecting active hepatitis B or C infection. Patients that are positive for hepatitis B core antibody, hepatitis B surface antigen (HBsAg), or hepatitis C antibody must have a negative polymerase chain reaction (PCR) prior to enrollment. (PCR positive patients will be excluded.)
* Any condition that would, in the investigator's judgment, interfere with full participation in the study, including administration of study drug and attending required study visits; pose a significant risk to the participant; or interfere with interpretation of study data.
* Known allergies, hypersensitivity, or intolerance to any of the study medications, excipients, or similar compounds