Hematopoietic Stem Cells
Hematopoietic stem cells (HSC) are multipotent stem cells that can differentiate into all blood cell types including myeloid (monocytes and macrophages, neutrophils, basophils, eosinophils, erythrocytes, megakaryocytes/platelets, dendritic cells) and lymphoid lineages (T cells, B cells, NK cells). HSCs also have plasticity to transdifferentiate into other cell types such as muscle, endothelial cells, and bone cells. HSC transplantation is the earliest stem cell-based therapy that started in 1950s and has been widely used to treat cancers, as well as many blood and immune system disorders. Currently, human BM, mobilized peripheral blood, and umbilical cord blood (UCB) represent the major sources of transplantable HSCs. However, there are many drawbacks to the current sources of all these cells. The availability of these cells is dramatically limited due to the limited number of tissue-derived HSCs, the limited expansion of the HSCs in vitro, rare histocompatibility or match of human leukocyte antigen (HLA) types between donors and recipients, and the risk of transmission of infectious diseases. Thus, sources with robust, continuous supply of hematopoietic cells are highly desired. hESC and iPS cells provide great promise for this purpose.