6. Allogeneic peripheral blood stem cell collection. Allogeneic donors will undergo a routine procedure for the mobilization and collection of peripheral blood stem cells. This includes the subcutaneous administration of G-CSF, to be self-administered as an outpatient, beginning three days prior to the start of peripheral blood stem cell harvesting. The peripheral blood stem cells will be collected as an outpatient in the Blood Center on the fourth day of G-CSF administration. A central line may be placed for this purpose on the first day of leukopheresis. Leukopheresis will be continued on a daily basis (up to four consecutive days) until an adequate number of peripheral blood stem cells have been collected. G-CSF will continue to be administered until leukopheresis is completed. The pheresis catheter will be discontinued when stem cell harvesting is completed. Processed cells will be frozen and stored until they are reinfused after the conditioning regimen.