Preventing Stem Cell Transplant Complications With a Blood Separator Machine

Background: \- Researchers are working to make stem cell transplant procedures safer and more effective. One complication of transplants is graft-versus-host disease (GVHD). This complication happens when certain white blood cells from the donor attack the recipient's own body. Researchers want to test a blood separator machine that may help remove more of the donor's white blood cells before transplant. They will study donors and recipients during stem cell transplant to see how well this process can prevent GVHD and other complications. Objectives: \- To see if a new blood separator machine can improve outcomes of stem cell transplants. Eligibility: * Individuals between 10 and 75 years of age who are having a stem cell transplant for leukemia or other blood-related cancers. * Donors for the stem cell transplant. Design: * Recipients and donors will be screened with a physical exam and medical history. * Donors will have two blood collection procedures. The first will collect only white blood cells, and return the rest of the blood. After the first collection, participants will have filgrastim injections to help their stem cells enter their blood. Then, they will have a second blood collection for the stem cells. * Recipients will have radiation and chemotherapy to prepare for the stem cell transplant. They will then have the stem cell transplant with the donor cells that have been treated with the blood separator machine. * Recipients will be monitored closely after the procedure. They may receive some of their donor's white blood cells if needed to fight serious infections. * Recipients will have the regular standard of care after their transplant. Blood samples will be taken and any side effects will be monitored and treated.