This study is testing a new way to perform a special type of transplant called hematopoietic cell transplantation (HCT). This transplant helps patients with blood-related illnesses, like leukemia, by using healthy blood-making cells from a donor. In this study, the donors are not perfectly matched to the patient, which is called HLA-mismatched unrelated donors (MMUD). After the transplant, patients will receive medicines like cyclophosphamide to reduce risks of complications. The study is focused on both adults and children.

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• The study involves multiple visits over a period of time to monitor the patient's progress.
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• Patients will receive specific medications to help prevent transplant side effects.
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• There are specific criteria for who can participate, including age and type of illness.
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Eligible adults are between 18 and 66 years old, while children can be as young as 1 year old. Donors must be unrelated and aged between 18 and 35 years. This study is important for patients who have blood cancers and do not have a well-matched donor. Participants need to meet certain health conditions and should not have other serious infections or health problems.