Plerixafor and Sargramostim (GM-CSF) for Mobilization of Allogeneic Sibling Donors

The main purpose of this study is to gather information about the combination the drugs plerixafor with sargramostim in donors of blood-forming cells (stem cells). Stem cells can be taken from the bone marrow of the pelvic bones or from the blood following treatment with drugs called growth factors; sargramostim is such a drug. Once stem cells leave the bone marrow and circulate in the blood, they are called peripheral blood stem cells (PBSCs). These cells can be collected through a routine procedure called apheresis, which involves placing two IVs into the arm which are connected to an apheresis machine; the machine then takes blood from the body, removes the stem cells, and returns the blood to the body. Normally, a growth factor called filgrastim is given to donors in order to collect the stem cells used for transplantation. However, when stem cells collected using filgrastim are transplanted in patients, a possible unpredictable complication is graft versus host disease. It's thought that using a different growth factor such as sargramostim might reduce the occurrences of graft versus host disease in patients. However, sargramostim alone does not provide as many stem cells for transplantation as other growth factors. Plerixafor is another drug that can increase the number of PBSCs in a donor, but like with sargramostim, plerixafor alone does not always provide enough stem cells. This is why sargramostim and plerixafor are being combined in this study: the investigators believe that the two drugs together will provide enough stem cells for transplantation and may also reduce the risk of graft versus host disease.