Prospective isolation of human myeloerythroid progenitors in fetal liver and embryonic stem cell differentiation cultures
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Human embryonic stem cells (HESCs) can be used to investigate human hematopoiesis for transplantation based therapies. The induction of adult red blood cells (RBCs) from hESCs for the application of therapeutic transfusion has been unachievable. This field requires a developmental model of hematopoiesis. Defining myeloerythroid development from embryonic to adult hematopoietic stages by isolating hematopoietic stem (HSC) and progenitor cells from distinct developmental sources can define a guide for the generation of adult RBCs from hESCs.;We demonstrate that common myeloid progenitors (CMP) and their myeloid downstream progeny, granulocyte/ macrophage (GMP) and megakaryocyte/ erythrocyte (MEP) progenitors, can be isolated from lineage CD34+CD38 + fractions of human fetal liver (FL) and that these populations are characterized by the differential expression of CD123 and CD45RA. We show that the myeloerythroid lineage relationships of the human adult hematopoietic system are mirrored in the first site of definitive hematopoiesis, the fetal liver. We also demonstrate that these markers cannot be used to prospectively isolate embryonic hematopoietic progenitors from hESC differentiation cultures because of differences in expression of CD38 and CD90.;To further characterize human myelo-erythoid fractions, we analyzed globin profiles of prospectively isolated LT-HSCs, ST-HSCs, CMPs and MEPs generated from FL and adult bone marrow (BM). HSCs and progenitor cells isolated from adult BM produces erythroid cells that express adult hemoglobin and those isolated from FL express fetal hemoglobin. We conclude that the globin expression program is specified early during hematopoietic differentiation since prospectively isolated HSCs and progenitor cells grown in the same chemically-defined serum-free conditions gave rise to different globin expression profiles which corresponded to the developmental stage at which they were harvested.;We report that a hESC-derived population of hematopoietic cells is defined by the expression of CD34 and CD31. We verified that CD31+/34 + cells have both endothelial and myelo-erythroid potential and showed that CD31-/34+ cells give rise to functional endothelial myeloid cells but not erythroid cells, while CD31+/34 -+ cells could not. We did not find evidence of cells with CMP properties in hESC differentiation cultures but found that CD31 and CD34 expression could be used to prospectively isolate erythroid and myeloid progenitors.
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