Conventional blood or bone marrow stem cell transplant involves destroying the patient's diseased marrow with radiation or chemotherapy. Healthy marrow from a donor is then infused into the patient where it migrates to the bone marrow space to begin generating new blood cells. The best type of donor is a sibling or unrelated donor with an identical immune system (HLA "match"). However, most patients do not have a matched sibling available and/or are unable to identify an acceptable unrelated donor through the registries in a timely manner. In addition, the aggressive treatment required to prepare the body for these types of transplants can be too toxic for these highly pretreated patients. Therefore doctors are investigating haploidentical transplant using stem cells from HLA partially matched family member donors.