Participants will be given a continuous infusion of glucose at a dose of up to 60 grams (about 2 ounces) per day for up to 5 days. The glucose will be delivered through a catheter (thin plastic tube) placed in an arm vein. Blood samples will be collected as often as daily in the first week following the infusion and then from twice a week to once a month for up to 4 years. Alternatively, patients may undergo leukapheresis a procedure for collecting quantities of lymphocytes up to 10 times during the first month after the infusion, and possibly later as well, but no more often than once every 2 weeks. For this procedure, whole blood is collected through a needle in an arm vein. The blood circulates through a machine that separates it into its components. The white cells are removed and the rest of the blood is returned to the body either through the same needle or through a second needle in the other arm. Participants may be asked to receive up to four glucose infusions. There will be at least a 2-week interval between infusions. Participants who have more than three leukapheresis procedures within 3 weeks will have at least 6 weeks between infusions.