Macrophage depletion overcomes human hematopoietic cell engraftment failure in zebrafish embryo.

Zebrafish is widely adopted as a grafting model for studying human development and diseases. Current zebrafish xenotransplantations are performed using embryo recipients, as the adaptive immune system, responsible for host versus graft rejection, only reaches maturity at juvenile stage. However, transplanted primary human hematopoietic stem/progenitor cells (HSC) rapidly disappear even in zebrafish embryos, suggesting that another barrier to transplantation exists before the onset of adaptive immunity.

CD32 captures committed haemogenic endothelial cells during human embryonic development.

During embryonic development, blood cells emerge from specialized endothelial cells, named haemogenic endothelial cells (HECs). As HECs are rare and only transiently found in early developing embryos, it remains difficult to distinguish them from endothelial cells. Here we performed transcriptomic analysis of 28- to 32-day human embryos and observed that the expression of Fc receptor CD32 (FCGR2B) is highly enriched in the endothelial cell population that contains HECs.

Blood Vessel Resident Human Stem Cells in Health and Disease.

The vascular wall is comprised of distinct layers controlling angiogenesis, blood flow, vessel anchorage within organs, and cell and molecule transit between blood and tissues. Moreover, some blood vessels are home to essential stem-like cells, a classic example being the existence in the embryo of hemogenic endothelial cells at the origin of definitive hematopoiesis. In recent years, microvascular pericytes and adventitial perivascular cells were observed to include multi-lineage progenitor cells involved not only in organ turnover and regeneration but also in pathologic remodeling, including fibrosis and atherosclerosis.

Isolation of Mouse Megakaryocyte Progenitors.

Bone marrow megakaryocytes are large polyploid cells that ensure the production of blood platelets. They arise from hematopoietic stem cells through megakaryopoiesis. The final stages of this process are complex and classically involve the bipotent Megakaryocyte-Erythrocyte Progenitors (MEP) and the unipotent Megakaryocyte Progenitors (MKp).

CDX2 expression in the hematopoietic lineage promotes leukemogenesis via TGFβ inhibition.

The intestine-specific caudal-related homeobox gene-2 (CDX2) homeobox gene, while being a tumor suppressor in the gut, is ectopically expressed in a large proportion of acute leukemia and is associated with poor prognosis. Here, we report that turning on human CDX2 expression in the hematopoietic lineage of mice induces acute monoblastic leukemia, characterized by the decrease in erythroid and lymphoid cells at the benefit of immature monocytic and granulocytic cells. One of the highly stimulated genes in leukemic bone marrow cells was BMP and activin membrane-bound inhibitor (Bambi), an inhibitor of transforming growth factor-β (TGF-β) signaling.

CDX2 regulates ACE expression in blood development and leukemia cells.

Expression of caudal-related homeobox gene 2 (CDX2) and angiotensin-converting enzyme (ACE) correlates during hematopoietic emergence. This emergence occurs in human and mouse embryos and in human acute myeloid leukemia; CDX2 homeoprotein also binds to the ACE promoter.

Temporal multiomic modeling reveals a B-cell receptor proliferative program in chronic lymphocytic leukemia.

B-cell receptor (BCR) signaling is crucial for the pathophysiology of most mature B-cell lymphomas/leukemias and has emerged as a therapeutic target whose effectiveness remains limited by the occurrence of mutations. Therefore, deciphering the cellular program activated downstream this pathway has become of paramount importance for the development of innovative therapies. Using an original ex vivo model of BCR-induced proliferation of chronic lymphocytic leukemia cells, we generated 108 temporal transcriptional and proteomic profiles from 1 h up to 4 days after BCR activation.

Renin-angiotensin system is involved in embryonic emergence of hematopoietic stem/progenitor cells.

Angiotensin-converting enzyme (ACE), a key element of the renin-angiotensin system (RAS), has recently been identified as a new marker of both adult and embryonic human hematopoietic stem/progenitor cells (HSPCs). However, whether a full renin-angiotensin pathway is locally present during the hematopoietic emergence is still an open question. In the present study, we show that this enzyme is expressed by hematopoietic progenitors in the developing mouse embryo.

Origin of the hematopoietic system in the human embryo.

The continuous generation of blood cells throughout life relies on the existence of hematopoietic stem cells (HSC) generated during embryogenesis. Given the importance of HSC transplantation in cell-based therapeutic approaches, considerable efforts have been made toward understanding the developmental origins of embryonic HSC. Adult-type HSC are first generated in the aorta-gonad-mesonephros (AGM) region between days 27 and 40 of human embryonic development, but an elusive blood-forming potential is present earlier in the underlying splanchnopleura.

Primitive macrophages control HSPC mobilization and definitive haematopoiesis.

In vertebrates, haematopoietic stem/progenitor cells (HSPCs) first emerge in the aorta-gonad-mesonephros (AGM) before colonizing transitory and subsequently definitive haematopoietic organs allowing haematopoiesis throughout adult life. Here we identify an unexpected primitive macrophage population accumulated in the dorsal mesenteric mesoderm surrounding the dorsal aorta of the human embryo and study its function in the transparent zebrafish embryo. Our study reveals dynamic interactions occurring between the HSPCs and primitive macrophages in the AGM.

Intra-aortic clusters undergo endothelial to hematopoietic phenotypic transition during early embryogenesis.

Intra-aortic clusters (IACs) attach to floor of large arteries and are considered to have recently acquired hematopoietic stem cell (HSC)-potential in vertebrate early mid-gestation embryos. The formation and function of IACs is poorly understood. To address this issue, IACs were characterized by immunohistochemistry and flow cytometry in mouse embryos.

Angiotensin-converting enzyme (CD143) specifies emerging lympho-hematopoietic progenitors in the human embryo.

Adult-type lympho-myeloid hematopoietic progenitors are first generated in the aorta-gonad-mesonephros region between days 27 and 40 of human embryonic development, but an elusive blood forming potential is present earlier in the underlying splanchnopleura. In the present study, we show that angiotensin-converting enzyme (ACE, also known as CD143), a recently identified cell-surface marker of adult human hematopoietic stem cells, is already expressed in all presumptive and developing blood-forming tissues of the human embryo and fetus: para-aortic splanchnopleura, yolk sac, aorta-gonad-mesonephros, liver, and bone marrow (BM). Fetal liver and BM-derived CD34(+)ACE(+) cells, but not CD34(+)ACE(-) cells, are endowed with long-term culture-initiating cell potential and sustain multilineage hematopoietic cell engraftment when transplanted into NOD/SCID mice.

Embryonic origin of human hematopoiesis.

Hematopoietic stem cells (HSC) are at the origin of the adult hematopoietic system. They give rise to all blood cells through a complex series of proliferation and differentiation events that occur throughout the lifespan of the individual. Because of their potential clinical importance in transplantation, recent research has focused on the developmental origins of embryonic HSC.

CDX2 in congenital gut gastric-type heteroplasia and intestinal-type Meckel diverticula.

The mechanisms that determine organ identity along the digestive tract in humans are poorly understood. Here we describe the rare case of a young patient who presented with congenital gastric-type heteroplasia in the midjejunum. The lesions, located along the antimesenteric midline of the gut, were made of histologically and functionally normal gastric epithelium without inflammation or in situ/invasive carcinoma.

PA6-induced human embryonic stem cell-derived neurospheres: a new source of human peripheral sensory neurons and neural crest cells.

Human embryonic stem cells (hESC) have been directed to differentiate into CNS cells with clinical importance. However, for study of development and regeneration of the human PNS, and peripheral neuropathies, it would be useful to have a source of human PNS derivatives. We have demonstrated that peripheral sensory neuron-like cells (PSN) can also be derived from hESC via neural crest-like (NC) intermediates, and from neural progenitors induced from hESC using noggin.

Angiotensin-converting enzyme (CD143) marks hematopoietic stem cells in human embryonic, fetal, and adult hematopoietic tissues.

Previous studies revealed that mAb BB9 reacts with a subset of CD34(+) human BM cells with hematopoietic stem cell (HSC) characteristics. Here we map BB9 expression throughout hematopoietic development and show that the earliest definitive HSCs that arise at the ventral wall of the aorta and surrounding endothelial cells are BB9(+). Thereafter, BB9 is expressed by primitive hematopoietic cells in fetal liver and in umbilical cord blood (UCB).

Emergence of human angiohematopoietic cells in normal development and from cultured embryonic stem cells.

Human hematopoiesis proceeds transiently in the extraembryonic yolk sac and embryonic, then fetal liver before being stabilized in the bone marrow during the third month of gestation. In addition to this classic developmental sequence, we have previously shown that the aorta-gonad-mesonephros (AGM) embryonic territory produces stem cells for definitive hematopoiesis from 27 to 40 days of human development, through an intermediate blood-forming endothelium stage. These studies have relied on the use of traditional markers of human hematopoietic and endothelial cells.

Tracing the first waves of lymphopoiesis in mice.

RAG1/GFP knock-in mice were used to precisely chart the emergence and expansion of cells that give rise to the immune system. Lymphopoietic cells detectable in stromal co-cultures arose as early as E8.5, i.

Blood-forming endothelium in human ontogeny: lessons from in utero development and embryonic stem cell culture.

During the early weeks of human gestation, hematopoietic cells first emerge within the extraembryonic yolk sac (primitive hematopoiesis) and secondarily within the truncal arteries of the embryo. This second wave includes the stem cells giving rise to adult-type lymphohematopoiesis. In both yolk sac blood islands and embryonic aorta, hematopoietic cells arise in the immediate vicinity of vascular endothelial cells.

The changing cellular environments of hematopoiesis in human development in utero.

The hematopoietic system is indispensable from the earliest stages of development and adapts to the rapidly changing anatomy of the embryo and fetus; this takes place in such different anatomic locations as the yolk sac blood island, hepatic parenchyme, aorta-gonads-mesonephros paravascular mesenchyme, and bone marrow primary logette. We herein summarize our investigation of these serial blood-forming events in the human embryo and fetus. The access to early stages of human development, availability of a large panoply of molecular markers for human blood cell lineages, and recent development of robust assays for the earliest human hematopoietic stem cells have allowed us to gain relatively clear insight into the developmental sequence that underlies the ontogeny of human blood cells.

The vascular wall as a source of stem cells.

We have characterized the emerging hematopoietic system in the human embryo and fetus. Two embryonic organs, the yolk sac and aorta, support the primary emergence of hematopoietic stem cells (HSCs), but only the latter contributes lymphomyeloid stem cells for definitive, adult-type hematopoiesis. A common feature of intra- and extraembryonic hematopoiesis is that in both locations hematopoietic cells emerge in close vicinity to vascular endothelial cells.

Human bronchial fibroblasts exhibit a mesenchymal stem cell phenotype and multilineage differentiating potentialities.

Mesenchymal stem cells (MSCs) are multipotent cells able to differentiate along different pathways including chondrogenic, osteogenic and adipogenic lineages. MSCs with a fibroblast-like morphology have been identified in human fetal lung. However, their frequency and characterization in human adult lung have not been yet evaluated.

Embryonic development of the human hematopoietic system.

Human hematopoiesis is initiated in the yolk sac during the third week of development. At the same time the capacity to produce blood cells also arises in the embryo, within the splanchnopleura, but this potential is not expressed before day 27, when clustered hematopoietic stem cells emerge from the ventral wall of the aorta and vitelline artery. Budding of hematopoietic cells from vessel walls reflects the re-differentiation of local endothelial cells, which are likely derived from angio-hematopoietic mesodermal ancestors emigrated from the splanchnopleura.

Notch/Delta4 interaction in human embryonic liver CD34+ CD38- cells: positive influence on BFU-E production and LTC-IC potential maintenance.

We investigated whether Notch signaling pathways have a role in human developmental hematopoiesis. In situ histochemistry analysis revealed that Notch1, 2, and 4 and Notch ligand (Delta1-4, and Jagged1) proteins were not expressed in the yolk sac blood islands, the para-aortic splanchnopleure, the hematopoietic aortic clusters, and at the early stages of embryonic liver hematopoiesis. Notch1-2, and Delta4 were eventually detected in the embryonic liver, from 34 until 38 days postconception.