This study investigates the use of non-total body irradiation (non-TBI) conditioning for patients with B-cell Acute Lymphoblastic Leukemia (B-ALL) who are at low risk of relapse. B-ALL is a type of cancer that affects the blood and bone marrow. The study focuses on patients who do not have minimal residual disease (MRD) as detected by next-generation sequencing (NGS) before they receive a hematopoietic cell transplant (HCT).

Participants will be divided into two study arms. Those who are NGS-MRD negative before HCT will receive a non-TBI conditioning regimen. This means they will undergo a treatment that prepares their body for the transplant without using total body irradiation. Those who are NGS-MRD positive will be treated according to the standard care of their treatment center and will be observed as part of the study.

• Who can participate: Patients with B-ALL in their first or second remission who are NGS-MRD negative and have not had a prior allogeneic stem cell transplant may participate. They must also have adequate organ function and no history of CNS relapse in their second remission.
• Study details: Participants in the treatment arm will receive non-TBI conditioning before their hematopoietic cell transplant. This conditioning prepares the body for the transplant without using total body irradiation. In the observational arm, patients will be treated according to the standard care of their treatment center. A placebo is not applicable in this study.