Healthy volunteers 18 years or older with sickle cell trait who have no history of sickle cell disease and no known medical problems may be eligible for this study. Participants will have a medical history and physical examination, including blood tests and urinalysis. They will receive injections of G-CSF under the skin once a day for 5 days. On the fifth day, stem cells will be collected through leukapheresis. In this procedure, whole blood is drawn from an arm vein, similar to donating whole blood. The blood then circulates through a cell separator machine, the stem cells are removed, and the rest of the blood is transfused back to the donor through a vein in the other arm.