This study will compare the immune system response to booster vaccines for tetanus/diphtheria and hepatitis B in healthy volunteers with that of patients who have had a blood transplant. (A blood transplant is an infusion of donated stem cells-i.e., cells that mature into white blood cells, red blood cells and platelets). The study will also look at how age of the blood cell donor and recipient, the type of blood transplant, the amount of certain types of white cells in donor blood, and other variables may influence the vaccine response among the transplant patients.