In this study, ten subjects known to have long-term microchimerism will undergo either leukapheresis (a blood filtering procedure) or collection of a 500 mL whole blood sample (the amount of a standard blood donation). These samples will then be analyzed to determine whether the microchimeric (donor) cells include hematopoietic stem cells (CD34+) and precursor cells in the red blood cell, white blood cell, and platelet lineages.