Improving Blood Stem Cell Collection and Transplant Procedures

Background: \- People who have some kinds of cancer can benefit from donated bone marrow stem cells. These stem cells help produce healthy bone marrow and slow or stop the spread of abnormal cells. However, stem cells transplants do not always work. Also, they may have serious side effects that can cause illness or death. The Bone Marrow Stem Cell Transplant Program is studying methods to make stem cell transplant procedures safer and more effective. Objectives: \- To test a new procedure that may improve the success and decrease the side effects of stem cell transplants. Eligibility: * Individuals 10 to 75 years of age who have a life-threatening illness that may require a stem cell transplant. * Healthy siblings who are able to provide stem cells for transplant. Design: * Participants will be screened with a medical history, physical exam, and blood and urine tests. * Donor procedures: * Stem cell donors will start by having apheresis to donate white blood cells. * Donors will receive filgrastim shots for 5 days to help move stem cells into the blood for collection. * Donors will have another round of apheresis to donate the stem cells for transplant. * Recipient procedures: * Before the transplant, recipients will have radiation twice a day for 3 days and chemotherapy for 7 days. * After the radiation and chemotherapy, recipients will receive the stem cells provided by the donor. * After the transplant, recipients will receive the white blood cells provided by the donor. * Recipients will be monitored closely for 4 months to study the success of the transplant. They will have more followup visits at least yearly thereafter. * Recipients will have a research apheresis prior to transplant and at 3 months.