 The study involves blood draws and bone marrow aspirates. Participants may be asked to donate 23 to about 9 tablespoons of blood. The volume of blood needed will depend on the experiment being done as different numbers of cells are necessary to run different experiments. Study participants may return for additional blood draws will not donate blood more than twice a week, and will not have more than 16 tablespoons of blood drawn in a one-month period. Participants donating bone marrow will have about 3 12 tablespoons of bone marrow obtained, which will be drawn with a large needle from the bone located in the back of the hip. Bone marrow participants may be asked to donate up to 7 tablespoons of blood as well, in order to correlate the blood with the bone marrow sample and the populations of cells residing in each. Participants donating bone marrow may donate more than once, but must wait a minimum of 8 weeks between donations. 