<qa>  What is a disorder in the bone marrow that affects the bodys abilityParticipants in this study have a hematologic malignancy a disorder in the bone marrow that affects the bodys ability to create blood that might benefit from receiving an allogeneic stem cell transplant meaning the cells come from a donor from a family member or nearly identical matched donor. The donor may either be a matched sibling, a mismatched family member, or an unrelated person. 