This study investigates the survival outcomes of patients with certain blood disorders who are likely or unlikely to find a matched unrelated donor (MUD) for a transplant. The conditions include acute myeloid leukemia (AML), acute lymphoblastic leukemia (ALL), myelodysplastic syndromes (MDS), non-Hodgkin lymphoma (NHL), Hodgkin lymphoma (HL), aplastic anemia (AA), and sickle cell disease (SCD). The study aims to understand whether the likelihood of finding a MUD affects overall survival.

Participants will be divided into two study arms based on their likelihood of finding a MUD. The study will compare the overall survival between these two arms. Various conditioning regimens and approaches to prevent graft-versus-host disease (GVHD) will be used, and patients will undergo allogeneic hematopoietic cell transplantation (HCT) if a suitable donor is found.

• Who can participate: Patients of any age with AML, ALL, MDS, NHL, HL, AA, or SCD can participate. They must be suitable candidates for allogeneic transplant and plan to proceed with it within 6 months if a donor is found.
• Study details: Participants will be divided into two arms based on their likelihood of finding a matched unrelated donor. They will undergo different conditioning regimens, which are treatments given to prepare the body for transplant, and graft-versus-host disease prevention approaches, which are methods used to prevent a condition where donor cells attack the recipient's body. A placebo is not involved in this study.