Hematopoiesis

Abstract

Higher organisms have the capacity to produce blood cells throughout their life span to meet the normal physiological requirements of blood cell turnover as well as respond to needs for increased demand in response to injury or infection. An average sized human adult produces approximately one trillion blood cells every day. This lifelong process of continuous formation and turnover of blood cells is termed hematopoiesis. The long-term repopulating hematopoietic stem cell is the key cell producing both new stem cells, a process termed self-renewal, and all mature blood cells, a process termed differentiation. Self-renewal and proliferation of blood stem cells are regulated in both stochastic and instructive fashion orchestrated by growth factors, accessory cytokines, and cellular interactions within the hematopoietic niche. This article will provide a brief overview of the key findings that have contributed to the understanding of the capacity for lifelong blood cell production, including identification and characterization of stem cells and the lineage-restricted progenitor cells they produce, intrinsic and extrinsic regulation of stem cell function, methods used to evaluate stem cell function, and current and future therapeutic uses of hematopoietic stem cells.