Leukapheresis is a laboratory procedure for separating white blood cells from a sample of blood for the purposes of treatment. It can be performed to: * Reduce a patient's white blood cell count by separating out the cells and returning the red blood cells and plasma to the patient, for example, to treat leukemia * Store the white blood cells to be re-injected into the patient at a later date, for example, after chemotherapy * To extract white blood cells for research purposes