Stem cell therapies have been expected to bring substantial benefit to patients suffering a wide range of diseases and injuries. It was expected that the benefits of bone marrow transplants for patients needing reconstruction of their hematopoietic and immune systems would apply to stem cell transplants of other cell types, and optimism has been high for the utilization of pluripotent stem cell types (embryonic stem cells [ESCs] and induced pluripotent stem cells [iPSCs]) for a variety of applications.