Volunteers will have physical examinations and laboratory tests at certain times while they receive the vaccine and for a period afterwards. These procedures will require about 14 clinic visits of about 1 to 2 hours each, and up to 6 hours on vaccination days. Blood will be drawn at all visits. Some of the blood will be used for genetic tests, and some will be stored for future tests of the immune system and the body's response to the study vaccine. The study will last about 12 months from the date of the first injection. After it is completed, clinic staff may contact volunteers once or twice a year for at least 3 years to follow up.