Hematopoietic stem cell emergence in embryonic life: developmental hematology revisited

Electrospun poly (3-hydroxybutyrate-co-3-hydroxyvalerate)/hydroxyapatite scaffold with unrestricted somatic stem cells for bone regeneration

The combination of scaffolds and cells can be useful in tissue reconstruction. In this study, nanofibrous poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV)/nanohydroxyapatite (nano-HAp) scaffolds, filled with unrestricted somatic stem cells (USSCs), were used for healing calvarial bone in rat model. The healing effects of these scaffolds, with and without stem cells, in bone regeneration were investigated by computed tomography (CT) analysis and pathology assays after 28 days of grafting. The results of CT analysis showed that bone regeneration on the scaffolds, and the amounts of regenerated new bone for polymer/nano-HAp scaffold with USSC, was significantly greater than the scaffold without cell and untreated control samples. Therefore, the combination of scaffold especially with USSC could be considered as a useful method for bone regeneration.

Bone formation in calvarial defects by injectable nanoparticular scaffold loaded with stem cells

OBJECTIVE

Calcium phosphates are one of biomaterials that are used for bone regeneration. In this study, calcium phosphate nanoparticles such as hydroxyapatite (HA)/fluorapatite (FA),with chitosan gel filled with unrestricted somatic stem cells (USSCs) were used for healing calvarial bone in rat model.

METHODS

The healing effects of these injectable scaffolds, with and without stem cells, in bone regeneration were investigated by computed tomography (CT) analysis and pathology assays after 28 days of grafting.

RESULTS

The results of CT analysis showed that bone regeneration on the scaffolds, and the amounts of regenerated new bone for USSC scaffold were significantly greater than the scaffold without cell and untreated controls.

CONCLUSION

Therefore, the combination of scaffold especially with USSC could be considered as a useful method for bone regeneration.

Apoptotic bone marrow CD34+ cells in cirrhotic patients

AIM: To access the frequency and level of apoptotic CD34+ cells isolated from the marrow fluid of patients with post-hepatitis cirrhosis.

METHODS: The frequency of bone marrow CD34+ cells and apoptotic bone marrow CD34+ cells in 31 in-patients with post-hepatitis cirrhosis (cirrhosis group), and 15 out-patients without liver or blood disorders (control group) was calculated by flow cytometry. Parameters were collected to evaluate liver functions of patients in cirrhosis group.

RESULTS: The percentage of normal bone marrow CD34+ cells was 6.30% ± 2.48% and 1.87% ± 0.53% (t = 3.906, P < 0.01) while that of apoptotic marrow CD34+ cells was 15.00% ± 15.81% and 5.73% ± 1.57% (t = 2.367, P < 0.05) in cirrhosis and control groups, respectively. The percentage of apoptotic marrow CD34+ cells was 6.25% ± 3.30% and 20.92 ± 18.5% (t = 2.409, P < 0.05) in Child-Pugh A and Child-Pugh B + C cirrhotic patients, respectively. The percentage of late apoptotic marrow CD34+ cells was positively correlated with the total bilirubin and aspartate aminotransferase serum levels in patients with cirrhosis.

CONCLUSION: The status of CD34+ marrow cells in cirrhotic patients may suggest that the ability of hematopoietic progenitor cells to transform into mature blood cells is impaired.

In vitro and in vivo evaluation of osteogenesis of human umbilical cord blood-derived mesenchymal stem cells on partially demineralized bone matrix

The osteogenic differentiation potential of umbilical cord blood-derived mesenchymal stem cells (UCB-MSCs) has been documented previously, and partially demineralized bone matrix (pDBM) represents a promising candidate for bone tissue engineering scaffolds. In this study, pDBM scaffolds derived from porcine cancellous bone were evaluated for their ability to support human UCB-MSCs osteogenic differentiation in vitro and bone-forming capacity in vivo to assess the potential use of UCB-MSCs in bone tissue engineering applications. MSCs were isolated from full-term human UCB and expanded, and their cell surface antigen markers and multilineage capability to differentiate into osteoblasts, chondrocytes, and adipocytes were analyzed. The in vitro proliferation and osteogenic differentiation of UCB-MSCs loaded onto the three-dimensional pDBM scaffolds were determined. Critical-sized full-thickness circular defects (5 mm in diameter) created bilaterally in the parietal bones of athymic rats were treated with one of the following: osteogenically induced UCB-MSC/pDBM composites (Group A, n = 8), noninduced UCB-MSC/pDBM composites (Group B, n = 8), pDBM alone (Group C, n = 8), or left untreated (Group D, n = 8). Microcomputed tomography analysis showed that new bone was formed in Group A at 6 weeks postimplantation, and greater bone volume and density were found after 12 weeks. In other groups, new bone formation was not evident after 6 weeks, and no bone union was found at 12 weeks. Histological examination revealed that the defect was repaired by tissue-engineered bone in Group A at 12 weeks, and fibrous union was observed in Groups B, C, and D. These results demonstrate that pDBM can support osteogenic differentiation of human UCB-MSCs in vitro and in vivo, and UCB-MSCs may serve as an alternative cell source for bone tissue engineering and regeneration.

Relationships between hematopoiesis and hepatogenesis in the midtrimester fetal liver characterized by dynamic transcriptomic and proteomic profiles

In fetal hematopoietic organs, the switch from hematopoiesis is hypothesized to be a critical time point for organogenesis, but it is not yet evidenced. The transient coexistence of hematopoiesis will be useful to understand the development of fetal liver (FL) around this time and its relationship to hematopoiesis. Here, the temporal and the comparative transcriptomic and proteomic profiles were observed during the critical time points corresponding to the initiation (E11.5), peak (E14.5), recession (E15.5), and disappearance (3 ddp) of mouse FL hematopoiesis. We found that E11.5-E14.5 corresponds to a FL hematopoietic expansion phase with distinct molecular features, including the expression of new transcription factors, many of which are novel KRAB (Kruppel-associated box)-containing zinc finger proteins. This time period is also characterized by extensive depression of some liver functions, especially catabolism/utilization, immune and defense, classical complement cascades, and intrinsic blood coagulation. Instead, the other liver functions increased, such as xenobiotic and sterol metabolism, synthesis of carbohydrate and glycan, the alternate and lectin complement cascades and extrinsic blood coagulation, and etc. Strikingly, all of the liver functions were significantly increased at E14.5-E15.5 and thereafter, and the depression of the key pathways attributes to build the hematopoietic microenvironment. These findings signal hematopoiesis emigration is the key to open the door of liver maturation.

Endothelial differentiation of hematopoietic stem and progenitor cells from patients with multiple myeloma

PURPOSE

Vasculogenesis is a physiologic process typical of fetal development in which new blood vessels develop from undifferentiated precursors (or angioblasts). In tumors, near angiogenesis, vasculogenesis contributes to the formation of the microvascular plexus that is important for diffusion. Here, we show that hematopoietic stem and progenitor cells (HSPC) of multiple myeloma (MM) patients are able to differentiate into cells with endothelial phenotype on exposure to angiogenic cytokines.

EXPERIMENTAL DESIGN

Circulating HSPCs were purified with an anti-CD133 antibody from patients with newly diagnosed MM before autologous transplantation and exposed to vascular endothelial growth factor (VEGF), fibroblast growth factor-2 and insulin-like growth factor in a 3-week culture.

RESULTS

HSPCs gradually lost CD133 expression and acquired VEGF receptor-2, factor VIII-related antigen, and vascular endothelial-cadherin expression. The expression pattern overlapped with paired MM endothelial cells (MMEC). During culture, cells adhered to fibronectin, spread, and acquired an endothelial cell shape. Differentiated HSPCs also became capillarogenic in the Matrigel assay with maximal activity at the third week of culture. Bone marrow biopsies revealed HSPCs inside the neovessel wall in patients with MM but not in those with monoclonal gammopathy of undetermined significance.

CONCLUSIONS

In patients with MM, but not in those with monoclonal gammopathy of undetermined significance, HSPCs contribute to the neovessel wall building together with MMECs. Therefore, besides angiogenesis, HSPC-linked vasculogenesis contributes to neovascularization in MM patients. Tentatively, we hypothesize that in HSPC cultures a multipotent cell population expressing low VEGF receptor-2 levels corresponds to the endothelial progenitor cell precursor and seems to be the MMEC precursor.

Ex vivo expansion and transplantation of hematopoietic stem/progenitor cells supported by mesenchymal stem cells from human umbilical cord blood

Human mesenchymal stem cells (MSCs) are multipotential and are detected in bone marrow (BM), adipose tissue, placenta, and umbilical cord blood (UCB). In this study, we examined the ability of UCB-derived MSCs (UCB-MSCs) to support ex vivo expansion of hematopoietic stem/progenitor cells (HSPCs) from UCB and the engraftment of expanded HSPCs in NOD/SCID mice. The result showed that UCB-MSCs supported the proliferation and differentiation of CD34+ cells in vitro. The number of expanded total nucleated cells (TNCs) in MSC-based culture was twofold higher than cultures without MSC (control cultures). UCB-MSCs increased the expansion capabilities of CD34+ cells, long-term culture-initiating cells (LTC-ICs), granulocyte-macrophage colony-forming cells (GM-CFCs), and high proliferative potential colony-forming cells (HPP-CFCs) compared to control cultures. The expanded HSPCs were transplanted into lethally irradiated NOD/SCID mice to assess the effects of expanded cells on hematopoietic recovery. The number of white blood cells (WBCs) in the peripheral blood of mice transplanted with expanded cells from both the MSC-based and control cultures returned to pretreatment levels at day 25 posttransplant and then decreased. The WBC levels returned to pretreatment levels again at days 45-55 posttransplant. The level of human CD45+ cell engraftment in primary recipients transplanted with expanded cells from the MSC-based cultures was significantly higher than recipients transplanted with cells from the control cultures. Serial transplantation demonstrated that the expanded cells could establish long-term engraftment of hematopoietic cells. UCB-MSCs similar to those derived from adult bone marrow may provide novel targets for cellular and gene therapy.

In vitro neuronal and osteogenic differentiation of mesenchymal stem cells from human umbilical cord blood

Mesenchymal stem cells (MSCs) have the capabilities for self-renewal and differentiation into cells with the phenotypes of bone, cartilage, neurons and fat cells. These features of MSCs have attracted the attention of investigators for using MSCs for cell-based therapies to treat several human diseases. Because bone marrow-derived cells, which are a main source of MSCs, are not always acceptable due to a significant drop in their cell number and proliferative/differentiation capacity with age, human umbilical cord blood (UCB) cells are good substitutes for BMCs due to the immaturity of newborn cells. Although the isolation of hematopoietic stem cells from UCB has been well established, the isolation and characterization of MSCs from UCB still need to be established and evaluated. In this study, we isolated and characterized MSCs. UCB-derived mononuclear cells, which gave rise to adherent cells, exhibited either an osteoclast or a mesenchymal-like phenotype. The attached cells with mesenchymal phenotypes displayed fibroblast-like morphologies, and they expressed mesenchym-related antigens (SH2 and vimentin) and periodic acid Schiff activity. Also, UCB-derived MSCs were able to transdifferentiate into bone and 2 types of neuronal cells, in vitro. Therefore, it is suggested that the MSCs from UCB might be a good alternative to bone marrow cells for transplantation or cell therapy.

T-sing progenitors to commit

T-cell development in the thymus is a complex and highly regulated process. During the process of differentiation from multipotent progenitor cells to mature T cells, proliferation, restriction of lineage potential, TCR gene rearrangements and selection events occur, all accompanied by changes in gene expression. A comprehensive understanding of thymocyte differentiation remains to be established. Two related, key issues have received much attention recently: the nature of the thymus seeding cell and the regulation of T-cell lineage commitment. Here we review the perspectives of different researchers working both on murine and human T-cell development and argue that a true T-cell commitment factor might not be required because of the unique properties of the thymus.

Rapid isolation, expansion, and differentiation of osteoprogenitors from full-term umbilical cord blood

There is an urgent clinical requirement for appropriate bone substitutes that can be used for the repair and regeneration of diseased or damaged skeletal tissues. Cell-sourcing limitations in particular have affected progress, largely because of the shortage of accessible tissues capable of yielding sufficient numbers of viable osteoprogenitor cells. Previous work has suggested that umbilical cord blood (UCB) contains circulating progenitor cells (mesenchymal stem cells) capable of osteogenic differentiation, although a comparable number of reports refute this claim. From a screen of more than 20 different culture conditions, we have identified an optimal, simple, and reliable technique to generate, from full-term human UCB, stromal cells with the ability to undergo rapid osteogenic differentiation. By comparing different sorting and culture strategies, we demonstrated that early exposure of mononuclear UCB cells to medium conditioned by osteoblastic cells in the presence of osteogenic supplements and human plasma, markedly increased the frequency of stromal cell growth, the rate of osteogenic differentiation, and their attachment to and spreading on calcium phosphate scaffolds. These findings suggest that full-term UCB may act as an appropriate source of osteoprogenitor cells, which will impact significantly on the development of autologous tissue- engineered bone constructs.

Genetic regulation of hematopoietic stem cell exhaustion during development and growth

OBJECTIVE

During aging, hematopoietic stem cell (HSC) exhaustion is more severe in BALB/cByJ (BALB) mice than in C57BL/6J (B6) mice. Our objective is to determine whether HSC exhaustion during development from fetus to adult also is more severe for BALB than for B6 mice.

MATERIALS AND METHODS

Hematopoietic stem cells from fetal liver cells (FLCs) and from young adult bone marrow cells (BMCs) were compared using the competitive repopulation assay to measure long-term repopulating ability (LTRA) and HSC expansion after serial transplantation. LTRAs were measured in repopulating units (RU), as the ability to produce donor-type erythrocytes and lymphocytes in lethally irradiated recipients relative to the congenic fresh marrow competitor. To test expansion, FLCs or BMCs were serially transplanted into lethally irradiated carriers whose marrow cells were compared using fluorescence-activated cell staining (FACS), and subsequently tested for LTRA.

RESULTS

BALB and B6 FLCs, respectively, repopulated 2.6 and 13.5 times as well as BMCs. LTRAs correlated with HSC expansion for BALB, but not B6. Per million donor cells, CD34(-) HSC-enriched fractions (HEFs) and total RU values were 6.8 and 4.6 times higher for FLCs than for BMCs in BALB carriers, while these ratios were only 1.2 and 0.97 higher in B6 carriers.

CONCLUSION

In B6 HSC development, LTRA is dissociated from expansion. Although 1 x 10(6) BMCs have much lower LTRA, they expand HSCs as well as 1 x 10(6) FLCs. HSC expansion is partly exhausted in BALB, but not B6, during development.

Commentary: the role of cell migration in the ontogeny of the lymphoid system

The foundations of experimental hematology were laid by histologists, and while their contributions were enormous, they were limited in their interpretation of very dynamic processes by the static nature of the methodology. The middle of the twentieth century saw the introduction of techniques for hematopoietic cell marking and development of in vitro and in vivo assays for primitive hematopoietic cells, allowing dynamic studies of hematopoiesis. Paralleling this was an understanding of cellular immunology with the discovery of the role of the thymus and the identification of T and B lymphocyte lineages. In the 1960s a series of ontogenetic studies in birds and subsequently in mice revealed that hematopoietic and lymphoid development involved migration streams of primitive cells that colonized developing primary lymphoid organs as well as spleen, marrow, and liver. The yolk sac was proposed as the ultimate origin of these lympho-hematopoietic precursors. Subsequent studies identified a region associated with the dorsal aorta as the primary site of "definitive" stem cells. These opposing views are currently achieving a compromise that recognizes that both sites contribute stem cells involved in seeding the developing tissues. The clear distinction between the local origin of the inducing microenvironment provided by the endoderm or by stroma derived from mesenchymal stem cells of mesodermal origin, and the immigrant origin of the hematopoietic stem cells and progenitors, raises intriguing questions in the current climate of stem cell plasticity, cell fusion, and discovery of stem cells in adult marrow with the capacity to generate hematopoiesis as well as other mesodermal, ectodermal, and endodermal lineages.

Ontogenic emergence of definitive hematopoietic stem cells

Research in the past 10 years has dramatically increased our knowledge of the development of the mammalian hematopoietic system and has provided insight into the embryonic sites of hematopoietic cell generation, the variety of hematopoietic cell types produced, and some of the microenvironmental influences on the rapidly growing blood system. Indeed, within mammalian embryos, it is now widely accepted that the embryo proper produces the first adult repopulating hematopoietic stem cells. This mesodermally derived intraembryonic region, known as the aorta-gonad-mesonephros region or, at a slightly earlier developmental stage, the paraaortic splanchnopleura, produces, respectively, potent hematopoietic stem cells and multipotent progenitor cells before their appearance in the yolk sac. This review focuses on the most recent findings concerning qualitative and quantitative aspects of hematopoietic stem-cell development, the endothelium as a possible direct precursor population of hematopoietic stem cells, and the microenvironment leading to the onset and maintenance of hematopoietic stem cells in the mammalian embryo.

Roles of spleen and liver in development of the murine hematopoietic system

OBJECTIVE

Hematopoietic stem cells (HSCs) and colony-forming progenitor cells (CFCs) are believed to migrate from liver to bone marrow (BM) around the time of birth, where they remain throughout the animal's life. Although in mice the spleen is also a hematopoietic organ, neither the origin nor the contribution of spleen HSCs to hematopoietic homeostasis has been assessed relative to that of BM HSCs. To investigate these issues we quantitated CFC and HSC activity in the spleen, BM, peripheral blood, and liver of the mouse during ontogeny.

METHODS

CFCs were assessed by clonogenic colony formation, and HSCs by long-term reconstituting ability.

RESULTS

CFCs gradually increased in the BM and decreased in the liver with age. Increased prevalence of CFCs in fetal and pup blood occurred at day (d) 12 postcoitus (pc) and during the period of d16 pc to 4d postbirth, corresponding to the times when hematopoietic cells migrate from the yolk sac and/or aorta-gonad-mesonephros (AGM) to the fetal liver and from the neonatal liver to the BM, respectively. In the spleen, CFCs displayed two peaks of activity at 2d and 14d-15d postbirth. Spleen HSCs also fluctuated during this time period. Neonatal splenectomy did not alter CFC or HSC frequencies in the BM, but CFCs increased in the livers of splenectomized mice.

CONCLUSIONS

These data demonstrate that the liver may act as a site of extramedullary hematopoiesis in the neonate, especially in the absence of the spleen, and imply that the spleen, BM, and liver cooperatively contribute to hematopoietic homeostasis.

Establishing the transcriptional programme for blood: the SCL stem cell enhancer is regulated by a multiprotein complex containing Ets and GATA factors

Stem cells are a central feature of metazoan biology. Haematopoietic stem cells (HSCs) represent the best-characterized example of this phenomenon, but the molecular mechanisms responsible for their formation remain obscure. The stem cell leukaemia (SCL) gene encodes a basic helix-loop-helix (bHLH) transcription factor with an essential role in specifying HSCs. Here we have addressed the transcriptional hierarchy responsible for HSC formation by characterizing an SCL 3' enhancer that targets expression to HSCs and endothelium and their bipotential precursors, the haemangioblast. We have identified three critical motifs, which are essential for enhancer function and bind GATA-2, Fli-1 and Elf-1 in vivo. Our results suggest that these transcription factors are key components of an enhanceosome responsible for activating SCL transcription and establishing the transcriptional programme required for HSC formation.

Non-cell autonomous requirement for thebloodlessgene in primitive hematopoiesis of zebrafish

Vertebrate hematopoiesis occurs in two distinct phases, primitive (embryonic) and definitive (adult). Genes that are required specifically for the definitive program, or for both phases of hematopoiesis, have been described. However, a specific regulator of primitive hematopoiesis has yet to be reported. The zebrafish bloodless (bls) mutation causes absence of embryonic erythrocytes in a dominant but incompletely penetrant manner. Primitive macrophages appear to develop normally in bls mutants. Although the thymic epithelium forms normally in bls mutants, lymphoid precursors are absent. Nonetheless, the bloodless mutants can progress through embryogenesis, where red cells begin to accumulate after 5 days post-fertilization (dpf). Lymphocytes also begin to populate the thymic organs by 7.5 dpf. Expression analysis of hematopoietic genes suggests that formation of primitive hematopoietic precursors is deficient in bls mutants and those few blood precursors that are specified fail to differentiate and undergo apoptosis. Overexpression of scl, but not bmp4 or gata1, can lead to partial rescue of embryonic blood cells in bls. Cell transplantation experiments show that cells derived from bls mutant donors can differentiate into blood cells in a wild-type host, but wild-type donor cells fail to form blood in the mutant host. These observations demonstrate that the bls gene product is uniquely required in a non-cell autonomous manner for primitive hematopoiesis, potentially acting via regulation of scl.

Origin of endothelial progenitors in human postnatal bone marrow

This study demonstrates that a CD34(-), vascular endothelial cadherin(-) (VE-cadherin(-)), AC133(+), and fetal liver kinase(+) (Flk1(+)) multipotent adult progenitor cell (MAPC) that copurifies with mesenchymal stem cells from postnatal human bone marrow (BM) is a progenitor for angioblasts. In vitro, MAPCs cultured with VEGF differentiate into CD34(+), VE-cadherin(+), Flk1(+) cells - a phenotype that would be expected for angioblasts. They subsequently differentiate into cells that express endothelial markers, function in vitro as mature endothelial cells, and contribute to neoangiogenesis in vivo during tumor angiogenesis and wound healing. This in vitro model of preangioblast-to-endothelium differentiation should prove very useful in studying commitment to the angioblast and beyond. In vivo, MAPCs can differentiate in response to local cues into endothelial cells that contribute to neoangiogenesis in tumors. Because MAPCs can be expanded in culture without obvious senescence for more than 80 population doublings, they may be an important source of endothelial cells for cellular pro- or anti-angiogenic therapies.

Basic anatomical and physiological data for use in radiological protection: reference values. A report of age- and gender-related differences in the anatomical and physiological characteristics of reference individuals. ICRP Publication 89

This report presents detailed information on age- and gender-related differences in the anatomical and physiological characteristics of reference individuals. These reference values provide needed input to prospective dosimetry calculations for radiation protection purposes for both workers and members of the general public. The purpose of this report is to consolidate and unify in one publication, important new information on reference anatomical and physiological values that has become available since Publication 23 was published by the ICRP in 1975. There are two aspects of this work. The first is to revise and extend the information in Publication 23 as appropriate. The second is to provide additional information on individual variation among grossly normal individuals resulting from differences in age, gender, race, or other factors. This publication collects, unifies, and expands the updated ICRP reference values for the purpose of providing a comprehensive and consistent set of age- and gender-specific reference values for anatomical and physiological features of the human body pertinent to radiation dosimetry. The reference values given in this report are based on: (a) anatomical and physiological information not published before by the ICRP; (b) recent ICRP publications containing reference value information; and (c) information in Publication 23 that is still considered valid and appropriate for radiation protection purposes. Moving from the past emphasis on 'Reference Man', the new report presents a series of reference values for both male and female subjects of six different ages: newborn, 1 year, 5 years, 10 years, 15 years, and adult. In selecting reference values, the Commission has used data on Western Europeans and North Americans because these populations have been well studied with respect to antomy, body composition, and physiology. When appropriate, comparisons are made between the chosen reference values and data from several Asian populations. The first section of the report provides summary tables of all the anatomical and physiological parameters given as reference values in this publication. These results give a comprehensive view of reference values for an individual as influenced by age and gender. The second section describes characteristics of dosimetric importance for the embryo and fetus. Information is provided on the development of the total body and the timing of appearance and development of the various organ systems. Reference values are provided on the mass of the total body and selected organs and tissues, as well as a number of physiological parameters. The third section deals with reference values of important anatomical and physiological characteristics of reference individuals from birth to adulthood. This section begins with details on the growth and composition of the total body in males and females. It then describes and quantifies anatomical and physiological characteristics of various organ systems and changes in these characteristics during growth, maturity, and pregnancy. Reference values are specified for characteristics of dosimetric importance. The final section gives a brief summary of the elemental composition of individuals. Focusing on the elements of dosimetric importance, information is presented on the body content of 13 elements: calcium, carbon, chloride, hydrogen, iodine, iron, magnesium, nitrogen, oxygen, potassium, sodium, sulphur, and phosphorus.

Identification of mesenchymal stem/progenitor cells in human first-trimester fetal blood, liver, and bone marrow

Human mesenchymal stem/progenitor cells (MSCs) have been identified in adult bone marrow, but little is known about their presence during fetal life. MSCs were isolated and characterized in first-trimester fetal blood, liver, and bone marrow. When 10(6) fetal blood nucleated cells (median gestational age, 10(+2) weeks [10 weeks, 2 days]) were cultured in 10% fetal bovine serum, the mean number (+/- SEM) of adherent fibroblastlike colonies was 8.2 +/- 0.6/10(6) nucleated cells (69.6 +/- 10/microL fetal blood). Frequency declined with advancing gestation. Fetal blood MSCs could be expanded for at least 20 passages with a mean cumulative population doubling of 50.3 +/- 4.5. In their undifferentiated state, fetal blood MSCs were CD29(+), CD44(+), SH2(+), SH3(+), and SH4(+); produced prolyl-4-hydroxylase, alpha-smooth muscle actin, fibronectin, laminin, and vimentin; and were CD45(-), CD34(-), CD14(-), CD68(-), vWF(-), and HLA-DR(-). Fetal blood MSCs cultured in adipogenic, osteogenic, or chondrogenic media differentiated, respectively, into adipocytes, osteocytes, and chondrocytes. Fetal blood MSCs supported the proliferation and differentiation of cord blood CD34(+) cells in long-term culture. MSCs were also detected in first-trimester fetal liver (11.3 +/- 2.0/10(6) nucleated cells) and bone marrow (12.6 +/- 3.6/10(6) nucleated cells). Their morphology, growth kinetics, and immunophenotype were comparable to those of fetal blood-derived MSCs and similarly differentiated along adipogenic, osteogenic, and chondrogenic lineages, even after sorting and expansion of a single mesenchymal cell. MSCs similar to those derived from adult bone marrow, fetal liver, and fetal bone marrow circulate in first-trimester human blood and may provide novel targets for in utero cellular and gene therapy.

Association of stress during delivery with increased numbers of nucleated cells and hematopoietic progenitor cells in umbilical cord blood

OBJECTIVE

Umbilical cord blood can be used as a source of bone marrow repopulating cells for allogeneic stem cell transplantation. Large variations in the frequencies of white blood cells and hematopoietic progenitor cells have been found for umbilical cord blood. These variations may be due in part to specific circumstances during labor and delivery.

STUDY DESIGN

In this study we analyzed the relationship between stress factors occurring during parturition and the frequencies of nucleated cells, leukocyte subsets, CD34(+) cells, and hematopoietic progenitor cells, as determined in semisolid medium cultures of umbilical cord blood.

RESULTS

We observed that a prolonged first stage of labor resulted in increases in the numbers of nucleated cells, granulocytes, CD34(+) cells, and hematopoietic progenitor cells in umbilical cord blood. Evaluation of parameters that indicate stress of the infant during delivery demonstrated higher numbers of nucleated cells, granulocytes, CD34(+) cells, and hematopoietic progenitor cells in umbilical cord blood from children with lower venous pH.

CONCLUSION

Longer duration stress during delivery increased the numbers of nucleated cells, granulocytes, CD34(+) cells, and hematopoietic progenitor cells, possibly by causing mobilization of various cell populations by endogenous cytokines. As long as umbilical cord blood harvesting does not interfere with the delivery, umbilical cord blood collected after stressful deliveries may provide optimal units for hematopoietic stem cell transplantation.

Mesenchymal progenitor cells in human umbilical cord blood

Haemopoiesis is sustained by two main cellular components, the haematopoietic cells (HSCs) and the mesenchymal progenitor cells (MPCs). MPCs are multipotent and are the precursors for marrow stroma, bone, cartilage, muscle and connective tissues. Although the presence of HSCs in umbilical cord blood (UCB) is well known, that of MPCs has been not fully evaluated. In this study, we examined the ability of UCB harvests to generate in culture cells with characteristics of MPCs. Results showed that UCB-derived mononuclear cells, when set in culture, gave rise to adherent cells, which exhibited either an osteoclast- or a mesenchymal-like phenotype. Cells with the osteoclast phenotype were multinucleated, expressed TRAP activity and antigens CD45 and CD51/CD61. In turn, cells with the mesenchymal phenotype displayed a fibroblast-like morphology and expressed several MPC-related antigens (SH2, SH3, SH4, ASMA, MAB 1470, CD13, CD29 and CD49e). Our results suggest that preterm, as compared with term, cord blood is richer in mesenchymal progenitors, similar to haematopoietic progenitors.

Circulating hematopoietic progenitor cells in first trimester fetal blood

The yolk sac and aorto-gonad-mesonephros region are well recognized as the principal sites of hematopoiesis in the developing embryo, and the liver is the principal site of hematopoiesis in the fetus. However, little is known about circulating hematopoietic stem and progenitor cells in early fetal life. We investigated the number and characteristics of circulating progenitors in first trimester blood of 64 human fetuses (median gestational age, 10+4 weeks; range, 7+6-13+6 weeks). CD34+ cells accounted for 5.1 ± 1.0% of CD45+ cells in first trimester blood, which is significantly more than in term cord blood (0.4 ± 0.03%;P = .0015). However, the concentration of CD34+ cells (6.6 ± 2.4 × 104/mL) was similar to that in term cord blood (5.6 ± 3.9 × 104/mL). The total number of progenitors cultured from unsorted mononuclear cells (MNCs) in first trimester blood was 19.2 ± 2.1 × 103/mL, which is similar to that in term cord blood (26.4 ± 5.6 × 103/mL). All lineages were seen: colony-forming unit–GEMM (CFU-GEMM), CFU-GM, BFU-e, BFU-MK, and CFU-MK. Clonogenic assays of CD34+ cells purified from first trimester samples produced mainly two lineages: BFU-e (39.0 ± 9.6 × 103/mL CD34+ cells) and CFU-GEMM (22.6 ± 4.7 × 103/mL CD34+ cells). Short-term liquid culture of first trimester blood MNCs in SCF + IL-3 + Flt-3 (stem cell factor + interleukin-3 + Flt-3) increased, by 7-fold, the numbers of CFU-GEMM and induced a dramatic increase in BFU-e (65.6 ± 12.1–fold). These data show that significant numbers of committed and multipotent progenitors with capacity for expansion circulate in first trimester fetal blood and can be CD34 selected. These cells should be suitable targets for gene transfer and stem cell transplantation and, because fetal hematopoietic progenitors have been demonstrated in the maternal circulation from early gestation, may also be manipulated for noninvasive prenatal diagnosis of major genetic disorders.

WECHE: a novel hematopoietic regulatory factor

Previously, we described AGM-derived endothelial cell lines that either inhibited or permitted the development of erythroid or B cells. We utilized a differential gene expression method to isolate a chemokine, termed WECHE, from one of these cell lines. WECHE inhibited the formation of erythroid cells but had no effect on either myeloid or B cell formation. WECHE repressed BFU-E development from either mouse fetal liver or bone marrow progenitor cells but had no effect on colony formation induced by IL-3 or IL-7. WECHE reduced HPP-CFC production from fetal liver-derived stem cells. WECHE hindered the growth of yolk sac-derived endothelial cells. WECHE was also chemotactic for bone marrow cells. Thus, WECHE is a novel chemokine that regulates hematopoietic differentiation.

Functional and Molecular Analysis of Hematopoietic Progenitors Derived From the Aorta-Gonad-Mesonephros Region of the Mouse Embryo

Herein, we show that CD34, c-kit double-positive (CD34+c-kit+) cells from the aorta-gonad-mesonephros (AGM) region of the developing mouse are multipotent in vitro and can undergo both B-lymphoid and multimyeloid differentiation. Molecular analysis of individual CD34+c-kit+ cells by single-cell reverse transcriptase–polymerase chain reaction (RT-PCR) shows coactivation of erythroid (β-globin) and myeloid (myeloperoxidase [MPO]) but not lymphoid-affiliated (CD3, Thy-1, and λ5) genes. Additionally, most cells coexpress the stem cell–associated transcriptional regulators AML-1, PU.1, GATA-2 and Lmo2, as well as the granulocyte colony-stimulating factor receptor (G-CSF-R). These results show that the CD34+c-kit+ population from the AGM represents a highly enriched source of multipotent hematopoietic cells, and suggest that limited coactivation of distinct lineage-affiliated genes is an early event in the generation of hematopoietic stem and progenitor cells during ontogeny.

Functional and Molecular Analysis of Hematopoietic Progenitors Derived From the Aorta-Gonad-Mesonephros Region of the Mouse Embryo

Herein, we show that CD34, c-kit double-positive (CD34+c-kit+) cells from the aorta-gonad-mesonephros (AGM) region of the developing mouse are multipotent in vitro and can undergo both B-lymphoid and multimyeloid differentiation. Molecular analysis of individual CD34+c-kit+ cells by single-cell reverse transcriptase–polymerase chain reaction (RT-PCR) shows coactivation of erythroid (β-globin) and myeloid (myeloperoxidase [MPO]) but not lymphoid-affiliated (CD3, Thy-1, and λ5) genes. Additionally, most cells coexpress the stem cell–associated transcriptional regulators AML-1, PU.1, GATA-2 and Lmo2, as well as the granulocyte colony-stimulating factor receptor (G-CSF-R). These results show that the CD34+c-kit+ population from the AGM represents a highly enriched source of multipotent hematopoietic cells, and suggest that limited coactivation of distinct lineage-affiliated genes is an early event in the generation of hematopoietic stem and progenitor cells during ontogeny.

Umbilical cord blood from preterm human fetuses is rich in committed and primitive hematopoietic progenitors with high proliferative and self-renewal capacity

Human umbilical cord blood (CB) has been recognized as a source of hematopoietic stem cells for transplantation. While hematopoietic properties of neonatal CB from full-term pregnancies have been well characterized, little is known about CB from early gestational ages. We analyzed the content and the growth properties of primitive and committed hematopoietic progenitors in preterm CB from second trimester (week 16-28; n = 17) and early third trimester (week 29-34; n = 17) in comparison with term CB (n = 18). The frequency of CD34+ and CD34+CD38- cells was significantly higher in preterm than in term CB (mean, 2.51% and 0.56% vs 0.88% and 0.13%;p < 0.002). The number of colony forming units (CFU) in preterm CB was about twofold higher (230 +/- 6 vs 133 +/- 14/ 10(5) mononuclear cells; p < 0.05) and correlated with the content of CD34+ progenitors (r = 0.73). Long-term culture initiating cells (LTC-IC) were enriched about 2.5-fold (6.7 +/- 2.9 vs 2.6 +/- 1.2/10(5) cells; p < 0.05). Progenitors from preterm CB could be expanded in stroma-free liquid cultures supplemented with hematopoietic growth factors as efficiently as progenitors from term neonates. In short-term cultures containing erythropoietin (Epo), interleukin (IL)-1, IL-3, and IL-6, or granulocyte- (G-) and granulocyte-macrophage colony-stimulating factor (GM-CSF) together with stem cell factor (SCF) or Flt3 ligand (FL), expansion of CFUs was six- to eightfold at week 1. In long-term cultures containing thrombopoietin (TPO) and FL, an approximately 1000-fold expansion of multilineage progenitors was observed at week 10. In summary, we show that preterm CB compared with term CB is richer in hematopoietic progenitors, and that precursors from preterm CB can be extensively expanded ex vivo. This may have implications for the development of transplantation and gene transfer strategies targeting circulating fetal stem cells.

Fetal cord blood as an alternative source of hematopoietic progenitor cells: immunophenotype, maternal cell contamination, and ex vivo expansion

The present study was performed to investigate the character of hematopoietic progenitor cells in fetal cord blood (CB). Thirty blood samples from fetuses at a median of 24 weeks of gestation (range 19-29) and 30 neonatal CB samples were analyzed for their immunophenotype by three-color flow cytometry and examined for the presence of female cells by fluorescence in situ hybridization (FISH). We tested the effects of different cytokine combinations (rhIL-1beta, rhIL-3, rhIL-6, rh erythropoietin [rhEPO], rhGM-CSF plus rhSCF, and rhSCF plus rhflt3-ligand) on the differentiation of 100 CD34+-enriched neonatal CB cells for up to 21 days. Ex vivo expansion of 32 unselected fetal blood samples cells was performed in the presence of rhSCF and rhflt3-ligand. The percentage of CD34+ cells in fetal blood was significantly higher compared with neonatal CB (1.24%+/-0.82% versus 0.33%+/-0.18%, p = 0.0001) and inversely correlated with the age of gestation. The contamination of fetal and neonatal CB with maternal cells was low (1.72%+/-0.89%, range 1.0%-4.0%). By using rhflt3-ligand we were able to expand committed progenitor cells while maintaining cells with stem cell function. The use of expanded fetal immature progenitors might have implications for in utero transplantation and autologous gene therapy.

HCA, an Immunoglobulin-Like Adhesion Molecule Present on the Earliest Human Hematopoietic Precursor Cells, Is Also Expressed by Stromal Cells in Blood-Forming Tissues

We have previously shown that the HCA/ALCAM (CD166) glycoprotein, a member of the immunoglobulin family that mediates both homophilic and heterophilic cell-cell adhesion, via the CD6 ligand, is expressed at the surface of all of the most primitive CD38−/lo, Thy-1+, rho123lo, CD34+hematopoietic cells in human fetal liver and fetal and adult bone marrow. In the present report we show that HCA is also expressed by subsets of stromal cells in the primary hematopoietic sites that sequentially develop in the human embryo and fetus, ie, the paraaortic mesoderm, liver, thymus, and bone marrow. Adult bone marrow stromal cells established in vitro, including those derived from Stro-1+ progenitors and cells from immortalized cell lines, express HCA. In contrast, no HCA expression could be detected in peripheral lymphoid tissues, fetal spleen, and lymph nodes. HCA membrane molecules purified from marrow stromal cells interact with intact marrow stromal cells, CD34+ CD38−hematopoietic precursors, and CD3+ CD6+peripheral blood lymphocytes. Finally, low but significant levels of CD6 are here for the first time detected at the surface of CD34+ rho123med/lo progenitors in the bone marrow and in mobilized blood from healthy individuals. Altogether, these results indicate that the HCA/ALCAM surface molecule is involved in homophilic or heterophilic (with CD6) adhesive interactions between early hematopoietic progenitors and associated stromal cells in primary blood-forming organs.

HCA, an Immunoglobulin-Like Adhesion Molecule Present on the Earliest Human Hematopoietic Precursor Cells, Is Also Expressed by Stromal Cells in Blood-Forming Tissues

We have previously shown that the HCA/ALCAM (CD166) glycoprotein, a member of the immunoglobulin family that mediates both homophilic and heterophilic cell-cell adhesion, via the CD6 ligand, is expressed at the surface of all of the most primitive CD38−/lo, Thy-1+, rho123lo, CD34+hematopoietic cells in human fetal liver and fetal and adult bone marrow. In the present report we show that HCA is also expressed by subsets of stromal cells in the primary hematopoietic sites that sequentially develop in the human embryo and fetus, ie, the paraaortic mesoderm, liver, thymus, and bone marrow. Adult bone marrow stromal cells established in vitro, including those derived from Stro-1+ progenitors and cells from immortalized cell lines, express HCA. In contrast, no HCA expression could be detected in peripheral lymphoid tissues, fetal spleen, and lymph nodes. HCA membrane molecules purified from marrow stromal cells interact with intact marrow stromal cells, CD34+ CD38−hematopoietic precursors, and CD3+ CD6+peripheral blood lymphocytes. Finally, low but significant levels of CD6 are here for the first time detected at the surface of CD34+ rho123med/lo progenitors in the bone marrow and in mobilized blood from healthy individuals. Altogether, these results indicate that the HCA/ALCAM surface molecule is involved in homophilic or heterophilic (with CD6) adhesive interactions between early hematopoietic progenitors and associated stromal cells in primary blood-forming organs.

Molecular Identity of Hematopoietic Precursor Cells Emerging in the Human Embryo

It is now accepted from studies in animal models that hematopoietic stem cells emerge in the para-aortic mesoderm-derived aorta-gonad-mesonephros region of the vertebrate embryo. We have previously identified the equivalent primitive hematogenous territory in the 4- to 6-week human embryo, under the form of CD34+CD45+Lin− high proliferative potential hematopoietic cells clustered on the ventral endothelium of the aorta. To characterize molecules involved in initial stem cell emergence, we first investigated the expression in that territory of known early hematopoietic regulators. We herein show that aorta-associated CD34+ cells coexpress the tal-1/SCL, c-myb, GATA-2, GATA-3, c-kit, and flk-1/KDR genes, as do embryonic and fetal hematopoietic progenitors later present in the liver and bone marrow. Next, CD34+CD45+ aorta-associated cells were sorted by flow cytometry from a 5-week embryo and a cDNA library was constructed therefrom. Differential screening of that library with total cDNA probes obtained from CD34+embryonic liver cells allowed the isolation of a kinase-related sequence previously identified in KG-1 cells. In addition to emerging blood stem cells, KG-1 kinase is also strikingly expressed in all developing endothelial cells in the yolk sac and embryo, which suggests its involvement in the genesis of both hematopoietic and vascular cell lineages in humans.

Molecular Identity of Hematopoietic Precursor Cells Emerging in the Human Embryo

It is now accepted from studies in animal models that hematopoietic stem cells emerge in the para-aortic mesoderm-derived aorta-gonad-mesonephros region of the vertebrate embryo. We have previously identified the equivalent primitive hematogenous territory in the 4- to 6-week human embryo, under the form of CD34+CD45+Lin− high proliferative potential hematopoietic cells clustered on the ventral endothelium of the aorta. To characterize molecules involved in initial stem cell emergence, we first investigated the expression in that territory of known early hematopoietic regulators. We herein show that aorta-associated CD34+ cells coexpress the tal-1/SCL, c-myb, GATA-2, GATA-3, c-kit, and flk-1/KDR genes, as do embryonic and fetal hematopoietic progenitors later present in the liver and bone marrow. Next, CD34+CD45+ aorta-associated cells were sorted by flow cytometry from a 5-week embryo and a cDNA library was constructed therefrom. Differential screening of that library with total cDNA probes obtained from CD34+embryonic liver cells allowed the isolation of a kinase-related sequence previously identified in KG-1 cells. In addition to emerging blood stem cells, KG-1 kinase is also strikingly expressed in all developing endothelial cells in the yolk sac and embryo, which suggests its involvement in the genesis of both hematopoietic and vascular cell lineages in humans.

Hematopoietic Stem Cell Maintenance and Differentiation Are Supported by Embryonic Aorta-Gonad-Mesonephros Region–Derived Endothelium

Hematopoietic stem cells are capable of extensive self-renewal and expansion, particularly during embryonic growth. Although the molecular mechanisms involved with stem cell maintenance remain mysterious, it is now clear that an intraembryonic location, the aorta-gonad-mesonephros (AGM) region, is a site of residence and, potentially, amplification of the definitive hematopoietic stem cells that eventually seed the fetal liver and adult bone marrow. Because several studies suggested that morphologically defined hematopoietic stem/progenitor cells in the AGM region appeared to be attached in clusters to the ventrally located endothelium of the dorsal aorta, we derived cell lines from this intraembryonic site using an anti-CD34 antibody to select endothelial cells. Analysis of two different AGM-derived CD34+ cell lines revealed that one, DAS 104-8, efficiently induced fetal-liver hematopoietic stem cells to differentiate down erythroid, myeloid, and B-lymphoid pathways, but it did not mediate self-renewal of these pluripotent cells. In contrast, a second cell line, DAS 104-4, was relatively inefficient at the induction of hematopoietic differentiation. Instead, this line provoked the expansion of early hematopoietic progenitor cells of the lin−CD34+Sca-1+c-Kit+phenotype and was proficient at maintaining fetal liver–derived hematopoietic stem cells able to competitively repopulate the bone marrow of lethally irradiated mice. These data bolster the hypothesis that the endothelium of the AGM region acts to mediate the support and differentiation of hematopoietic stem cells in vivo.

© 1998 by The American Society of Hematology.

Hematopoietic Stem Cell Maintenance and Differentiation Are Supported by Embryonic Aorta-Gonad-Mesonephros Region–Derived Endothelium

Hematopoietic stem cells are capable of extensive self-renewal and expansion, particularly during embryonic growth. Although the molecular mechanisms involved with stem cell maintenance remain mysterious, it is now clear that an intraembryonic location, the aorta-gonad-mesonephros (AGM) region, is a site of residence and, potentially, amplification of the definitive hematopoietic stem cells that eventually seed the fetal liver and adult bone marrow. Because several studies suggested that morphologically defined hematopoietic stem/progenitor cells in the AGM region appeared to be attached in clusters to the ventrally located endothelium of the dorsal aorta, we derived cell lines from this intraembryonic site using an anti-CD34 antibody to select endothelial cells. Analysis of two different AGM-derived CD34+ cell lines revealed that one, DAS 104-8, efficiently induced fetal-liver hematopoietic stem cells to differentiate down erythroid, myeloid, and B-lymphoid pathways, but it did not mediate self-renewal of these pluripotent cells. In contrast, a second cell line, DAS 104-4, was relatively inefficient at the induction of hematopoietic differentiation. Instead, this line provoked the expansion of early hematopoietic progenitor cells of the lin−CD34+Sca-1+c-Kit+phenotype and was proficient at maintaining fetal liver–derived hematopoietic stem cells able to competitively repopulate the bone marrow of lethally irradiated mice. These data bolster the hypothesis that the endothelium of the AGM region acts to mediate the support and differentiation of hematopoietic stem cells in vivo.

© 1998 by The American Society of Hematology.

Stem cell transplantation into the fetal recipient: challenges and prospects

The interest in therapeutic intervention for those inherited disorders that can be diagnosed early in pregnancy has recently intensified. In-utero transplantation of haematopoietic stem cells (IUT-HSC), a therapy which could be proffered before pathological manifestations of a disorder become apparent, offers considerable potential benefit. However, as reports of IUT-HSC procedures become more prolific, it is necessary to consider the optimum modus operandi for each group of disorders targeted for therapy in order to develop effective procedures that make a real difference to the outcome. This review outlines the current status and prospects of IUT-HSC. It also offers a view of some of the challenges for IUT-HSC to overcome to find wider clinical applications.

High expression of uncoupling protein 2 in foetal liver

To assess the putative role of mitochondrial uncoupling protein 2 (UCP2) during perinatal development, its expression was analysed in mice and rats. Expression was detected in a large range of foetal tissues. A unique developmental pattern of UCP2 expression was found in liver, where the level of UCP2 mRNA was about 30-fold higher in foetuses than in adults (mice data), and started to decline immediately after birth. Neither UCP1 nor UCP3 mRNA was expressed in foetal liver. As in adult liver, immunohistochemical analysis suggested exclusive localisation of UCP2 in the monocyte/macrophage cells. Our results indicate a role of UCP2 in haematopoietic system development.

Characterization of definitive lymphohematopoietic stem cells in the day 9 murine yolk sac

The site of origin of lymphohematopoietic stem cells (HSC) that initiate definitive blood cell production in the murine fetal liver is controversial. Contrary to reports that the preliver yolk sac does not contain definitive HSC, we observed that CD34+ day 9 yolk sac cells repopulated multiple blood cell lineages in newborn hosts for at least 1 year. Furthermore, 100 CD34+c-Kit+ day 9 yolk sac or para-aortic splanchnopleura (P-Sp) cells, known to give rise to embryonic HSC, similarly repopulated hematopoiesis in recipient hosts. Surprisingly, 37-fold more CD34+c-Kit+ cells reside in the day 9 yolk sac than in the P-Sp. In sum, definitive HSC are coexistent, but not equal in number, in the murine yolk sac and P-Sp prior to fetal liver colonization.

In vivo repopulating hematopoietic stem cells are present in the murine yolk sac at day 9.0 postcoitus

The murine yolk sac, being the first site of embryonic blood cell production, has long been theorized to contain the migrating hematopoietic stem cells (HSC) that seed the liver and initiate hematopoiesis on day 10.0 postcoitus (pc). However, it remains controversial whether yolk sac cells isolated before day 11.0 pc possess any long-term repopulating HSC activity upon transplantation into adult recipient mice. We hypothesized that failure to demonstrate engraftment of day <11.0 yolk sac cells in adult hosts may result from an inability of yolk sac cells to home to the active adult hematopoietic sites (spleen and bone marrow). In the present studies, we transplanted yolk sac cells into conditioned newborn mice in whom the liver, as well as the spleen and bone marrow, concomitantly function as a site of blood cell formation. We report that yolk sac cells isolated from day 9.0 pc embryos provide long-term multilineage reconstitution for at least 11 months in primary conditioned newborn mice and for at least 6 months in secondary recipients. Donor yolk sac HSC progeny repopulated mature peripheral blood, thymus, spleen, and bone marrow lymphoid, myeloid, and erythroid compartments. Thus, day 9.0 pc yolk sac HSC can contribute to definitive multilineage hematopoiesis in transplanted recipients. Determination of HSC activity in the day 9.0 pc murine yolk sac suggests that yolk sac HSC are available to seed the liver on day 10.0 pc when definitive hematopoiesis is initiated.