Blood disorders such as leukemia or lymphoma or hemoglobinopathies can benefit from receiving an allogeneic (meaning that the cells are from a donor) stem cell transplant. Stem cells are created in the bone marrow. They grow into different types of blood cells that the body needs, including red blood cells, white blood cells, and platelets. In a transplant, the body's stem cells would be killed and then replaced by stem cells from the donor. Usually, patients are given very high doses of chemotherapy (drugs which kill cancer cells) prior to receiving a stem cell transplant. However, patients that are older, have received several prior treatments, or have other organ diseases are at a high risk of getting life-threatening treatment-related side effects from high doses of chemotherapy. Over the past several years, some doctors have begun to use lower doses of chemotherapy for preparing patients for a stem cell transplant.