Early Human Hemogenic Endothelium Generates Primitive and Definitive Hematopoiesis In Vitro

Abstract

The differentiation of human embryonic stem cells (hESCs) to hematopoietic lineages initiates with the specification of hemogenic endothelium, a transient specialized endothelial precursor of all blood cells. This in vitro system provides an invaluable model to dissect the emergence of hematopoiesis in humans. However, the study of hematopoiesis specification is hampered by a lack of consensus in the timing of hemogenic endothelium analysis and the full hematopoietic potential of this population. Here, our data reveal a sharp decline in the hemogenic potential of endothelium populations isolated over the course of hESC differentiation. Furthermore, by tracking the dynamic expression of CD31 and CD235a at the onset of hematopoiesis, we identified three populations of hematopoietic progenitors, representing primitive and definitive subsets that all emerge from the earliest specified hemogenic endothelium. Our data establish that hemogenic endothelium populations endowed with primitive and definitive hematopoietic potential are specified simultaneously from the mesoderm in differentiating hESCs. Following the in vitro differentiation of human ESCs, Garcia-Alegria et al. demonstrate how the timing of endothelial cell isolation influences hemogenic potential. Early endothelial cells have the highest hemogenic potential, giving rise to two waves of hematopoiesis that are distinguished by CD31/CD235a expression. Multilineage potential is restricted to CD31+ cells and commitment toward primitive erythropoiesis coincides with CD31 loss.