Mouse and human embryonic stem cell models of hematopoiesis: past, present, and future.

Human embryonic stem (ES) cells provide a unique model and an important resource to analyze early hematopoietic development. Other systems to study mammalian hematopoiesis include mouse ES cells, dissection of timed mouse embryos, or use of human postnatal hematopoietic tissue typically isolated from bone marrow or umbilical cord blood. All these models have particular strengths and weaknesses. The extensive studies on murine hematopoiesis provide a basis for work on the human developmental system. Since there are likely some important species differences, use of human ES cells now provides an optimal means to evaluate basic cellular and molecular mechanisms that regulate the beginning stages of human blood development, prior to derivation of hematopoietic stem cells (HSCs). Eventually, research on human ES cells may provide an alternative source of HSCs and other blood products for hematopoietic cell transplantation or other cellular therapies.