These studies have two primary goals, to compare and contrast the fate of transplanted human cells from two immature cell sources (umbilical cord blood and human embryonic stem cell), and to use in vivo imaging to monitor the fate of the transplanted cells. Major findings during the reporting period include that expanded cord blood cells showed high levels of engraftment when monitored by imaging; no adverse events were detected; imaging was a good predictor of transplant tolerance and that the cells were not rejected; and that transplant of undifferentiated or differentiated human embryonic stem cells did not result in teratoma formation or adverse effects. Umbilical cord blood cells were found to be the most efficient using the paradigms tested.