Erythropoietin-independent erythrocyte production: signals through gp130 and c-kit dramatically promote erythropoiesis from human CD34+ cells

Clorfl86/RHEX Is a Negative Regulator of SCF/KIT Signaling in Human Skin Mast Cells

Mast cells (MCs) are key effector cells in allergic and inflammatory diseases, and the SCF/KIT axis regulates most aspects of the cells' biology. Using terminally differentiated skin MCs, we recently reported on proteome-wide phosphorylation changes initiated by KIT dimerization. C1orf186/RHEX was revealed as one of the proteins to become heavily phosphorylated. Its function in MCs is undefined and only some information is available for erythroblasts. Using public databases and our own data, we now report that RHEX exhibits highly restricted expression with a clear dominance in MCs. While expression is most pronounced in mature MCs, RHEX is also abundant in immature/transformed MC cell lines (HMC-1, LAD2), suggesting early expression with further increase during differentiation. Using RHEX-selective RNA interference, we reveal that RHEX unexpectedly acts as a negative regulator of SCF-supported skin MC survival. This finding is substantiated by RHEX's interference with KIT signal transduction, whereby ERK1/2 and p38 both were more strongly activated when RHEX was attenuated. Comparing RHEX and capicua (a recently identified repressor) revealed that each protein preferentially suppresses other signaling modules elicited by KIT. Induction of immediate-early genes strictly requires ERK1/2 in SCF-triggered MCs; we now demonstrate that RHEX diminution translates to this downstream event, and thereby enhances NR4A2, JUNB, and EGR1 induction. Collectively, our study reveals RHEX as a repressor of KIT signaling and function in MCs. As an abundant and selective lineage marker, RHEX may have various roles in the lineage, and the provided framework will enable future work on its involvement in other crucial processes.

Uncovering a Cryptic Site of Malaria Pathogenesis: Models to Study Interactions Between Plasmodium and the Bone Marrow

The bone marrow is a critical site of host-pathogen interactions in malaria infection. The discovery of Plasmodium asexual and transmission stages in the bone marrow has renewed interest in the tissue as a niche for cellular development of both host and parasite. Despite its importance, bone marrow in malaria infection remains largely unexplored due to the challenge of modeling the complex hematopoietic environment in vitro. Advancements in modeling human erythropoiesis ex-vivo from primary human hematopoietic stem and progenitor cells provide a foothold to study the host-parasite interactions occurring in this understudied site of malaria pathogenesis. This review focuses on current in vitro methods to recapitulate and assess bone marrow erythropoiesis and their potential applications in the malaria field. We summarize recent studies that leveraged ex-vivo erythropoiesis to shed light on gametocyte development in nucleated erythroid stem cells and begin to characterize host cell responses to Plasmodium infection in the hematopoietic niche. Such models hold potential to elucidate mechanisms of disordered erythropoiesis, an underlying contributor to malaria anemia, as well as understand the biological determinants of parasite sexual conversion. This review compares the advantages and limitations of the ex-vivo erythropoiesis approach with those of in vivo human and animal studies of the hematopoietic niche in malaria infection. We highlight the need for studies that apply single cell analyses to this complex system and incorporate physical and cellular components of the bone marrow that may influence erythropoiesis and parasite development.

Recent Advances in the Role of Arid5a in Immune Diseases and Cancer

AT-rich interactive domain 5a (Arid5a) is a nucleic acid binding protein. In this review, we highlight recent advances in the association of Arid5a with inflammation and human diseases. Arid5a is known as a protein that performs dual functions. In in vitro and in vivo studies, it was found that an inflammation-dependent increase in Arid5a expression mediates both transcriptional and post-transcriptional regulatory effects that are implicated in immune regulation and cellular homeostasis. A series of publications demonstrated that inhibiting Arid5a augmented several processes, such as preventing septic shock, experimental autoimmune encephalomyelitis, acute lung injury, invasion and metastasis, immune evasion, epithelial-to-mesenchymal transition, and the M1-like tumor-associated macrophage (TAM) to M2-like TAM transition. In addition, Arid5a controls adipogenesis and obesity in mice to maintain metabolic homeostasis. Taken together, recent progress indicates that Arid5a exhibits multifaceted, both beneficial and detrimental, roles in health and disease and suggest the relevance of Arid5a as a potential therapeutic target.

The novel long noncoding RNA AU021063, induced by IL-6/Arid5a signaling, exacerbates breast cancer invasion and metastasis by stabilizing Trib3 and activating the Mek/Erk pathway

Interleukin (IL-6) is a pleotropic cytokine with both tumor-promoting and -inhibitory effects on breast cancer growth. However, the mechanisms governing the outcome of IL-6 on cancer progression remain to be clarified. Our study unraveled a novel long noncoding RNA (lncRNA) AU021063 downstream of IL-6 signaling. We found that IL-6 induced the expression of AU021063 predominantly in breast cancer compared to other cancer types. Mechanistically, IL-6 induced AT-rich interactive domain 5a (Arid5a) expression, which promotes the transcription of AU021063. In turn, AU021063 promotes breast cancer metastasis through stabilizing tribbles homolog 3 (Trib3) and activating Mek/Erk signaling pathway. Genetic ablation of either Arid5a, AU021063 or Trib3 abolished breast cancer metastasis in vitro and in vivo. Overall, our study highlights the importance of IL-6-Arid5a-AU021063 axis in regulating breast cancer invasiveness and metastasis, which may provide potential novel therapeutics for breast cancer.

In vitro expansion of fetal liver hematopoietic stem cells

Fetal liver hematopoietic stem and progenitor cells (HSPCs) have been considered appropriate for the management of aplastic anemia owing to their proliferative potential. Bone marrow recovery was possible in some cases; the engraftment potential of these cells, however was unsatisfactory, possibly due to the availability of a smaller number of these cells from a single fetus. The present study explores how we can expand fetal liver hematopoietic stem cells under in vitro conditions. We isolated mononuclear cells from fetal liver and hematopoietic stem cells were identified and analyzed by cell surface marker CD34. CD34⁺ fetal liver HSPCs cells were separated by magnetic cell sorting positive selection method. HSPCs (CD34⁺) were cultured by using 5 cytokines, stem cell factor (SCF), granulocyte macrophages-colony stimulating factor (GM-CSF), interleukin-6 (IL-6), Fms-related tyrosine kinase 3 (FLT-3) and erythropoietin (EPO), in 4 different combinations along with supplements, in serum-free culture media for 21 days. Cell viability continued to be greater than 90% throughout 21 days of culture. The cells expanded best in a combination of media, supplements and 5 cytokines, namely SCF, FLT-3, IL6, EPO and GM-CSF to yield a large number of total (CD34⁺ & CD34^-) cells. Even though the total number of nucleated cells increased in culture significantly, levels of CD34 antigen expression declined steadily over this period.

Recent Advances in Replication and Infection of Human Parvovirus B19

Parvovirus B19 (B19V) is pathogenic to humans and causes bone marrow failure diseases and various other inflammatory disorders. B19V infection exhibits high tropism for human erythroid progenitor cells (EPCs) in the bone marrow and fetal liver. The exclusive restriction of B19V replication to erythroid lineage cells is partly due to the expression of receptor and co-receptor(s) on the cell surface of human EPCs and partly depends on the intracellular factors essential for virus replication. We first summarize the latest developments in the viral entry process and the host cellular factors or pathways critical for B19V replication. We discuss the role of hypoxia, erythropoietin signaling and STAT5 activation in the virus replication. The B19V infection-induced DNA damage response (DDR) and cell cycle arrest at late S-phase are two key events that promote B19V replication. Lately, the virus infection causes G2 arrest, followed by the extensive cell death of EPCs that leads to anemia. We provide the current understanding of how B19V exploits the cellular resources and manipulate pathways for efficient virus replication. B19V encodes a single precursor mRNA (pre-mRNA), which undergoes alternate splicing and alternative polyadenylation to generate at least 12 different species of mRNA transcripts. The post-transcriptional processing of B19V pre-mRNA is tightly regulated through cis-acting elements and trans-acting factors flanking the splice donor or acceptor sites. Overall, in this review, we focus on the recent advances in the molecular virology and pathogenesis of B19V infection.

Beyond Hemoglobin: Screening for Malaria Host Factors

Severe malaria is caused by the Apicomplexan parasite Plasmodium falciparum, and results in significant global morbidity and mortality, particularly among young children and pregnant women. P. falciparum exclusively infects human erythrocytes during clinical illness, and several natural erythrocyte polymorphisms are protective against severe malaria. Since erythrocytes are enucleated and lack DNA, genetic approaches to understand erythrocyte determinants of malaria infection have historically been limited. This review highlights recent advances in the use of hematopoietic stem cells to facilitate genetic screening for malaria host factors. While challenges still exist, this approach holds promise for gaining new insights into host-pathogen interactions in malaria.

Nucleated Red Blood Cells as a Marker of Acute and Chronic Fetal Hypoxia in a Rat Model

OBJECTIVE

To examine the relationship between duration of fetal hypoxia, nucleated red blood cell (NRBC) count, and fetal growth.

METHODS

Pregnant rats were exposed to a severe hypoxia (9.5%-10% O₂) for varying time intervals (2, 6, 12, 24, 48, and 120 hours; n=4 for each time interval) immediately prior to delivery at term. Normoxic controls were exposed to room air (21% O₂) and matched for all other study variables (n=4 rats for each time interval). Pups were delivered via hysterotomy while maintaining exposure gas concentrations. Blood gas analysis and NRBC counts were performed, and fetal body and liver weights were recorded. Student's t test and simple regression were used for statistical analysis.

RESULTS

As the duration of hypoxia increased, fetal weight, liver weight, blood bicarbonate, and base excess levels decreased significantly; concomitantly, NRBC counts increased. This increase in NRBCs became statistically significant after 24 hours of exposure. After 48 hours of hypoxia there was a 2.5-fold rise in NRBC count, and after 120 hours of hypoxia there was a 4.5-fold rise in NRBC count over control levels. After 12 or more hours of hypoxia, fetal body weights were significantly reduced; 120 hours of hypoxia resulted in a 35% reduction in fetal body weight, a 34% reduction in fetal liver weight, and 356% increase in NRBC count.

CONCLUSION

In a pregnant rat model, chronic maternal hypoxia (≥24 hours) results in a significant increase in fetal NRBC counts as well as reduced fetal body weight and organ growth.

Growth of erythroid cells from thawed unseparated cord blood in vitro without exogenous erythropoietin

INTRODUCTION

Previous erythroid cell cultures have depended on added serum or erythropoietin. In this paper, the growth of erythroid cells from thawed unseparated cord blood units in vitro without serum or exogenous erythropoietin is reported.

METHODS

Thawed volume-reduced cord blood was cultured in conditions designed to support the megakaryocytic lineage, with thrombopoietin and interleukins 3 and 6. Erythroid cells were detected with glycophorin A (GlyA), CD71, and benzidine (flow cytometry and immunocytochemistry).

RESULTS

Nucleated and anucleated GlyA-positive, as well as benzidine-positive cells were observed from day 9. In flow cytometry, at days 0 and 9, 5.9% and 14% of all events were GlyA+, and 14% and 53% were CD71+, respectively. At days 0 and 9, 4.5% and 12% of the events were double-positive for GlyA and CD71, respectively. By day 14, the percentages of GlyA+, CD71+ and double-positive events had started to decrease (9.7%, 35%, and 5.3%, respectively).

CONCLUSIONS

Erythroid cells were generated from thawed unseparated cord blood units without exogenous erythropoietin. Thawed cord blood possesses the potential for erythroid growth in vitro in a culture medium designed for other cell types.

The soluble interleukin-6 receptor is a mediator of hematopoietic and skeletal actions of parathyroid hormone

Both PTH and IL-6 signaling play pivotal roles in hematopoiesis and skeletal biology, but their interdependence is unclear. The purpose of this study was to evaluate the effect of IL-6 and soluble IL-6 receptor (sIL-6R) on hematopoietic and skeletal actions of PTH. In the bone microenvironment, PTH stimulated sIL-6R protein levels in primary osteoblast cultures in vitro and bone marrow in vivo in both IL-6(+/+) and IL-6(-/-) mice. PTH-mediated hematopoietic cell expansion was attenuated in IL-6(-/-) compared with IL-6(+/+) bone marrow, whereas sIL-6R treatment amplified PTH actions in IL-6(-/-) earlier than IL-6(+/+) marrow cultures. Blocking sIL-6R signaling with sgp130 (soluble glycoprotein 130 receptor) inhibited PTH-dependent hematopoietic cell expansion in IL-6(-/-) marrow. In the skeletal system, although intermittent PTH administration to IL-6(+/+) and IL-6(-/-) mice resulted in similar anabolic actions, blocking sIL-6R significantly attenuated PTH anabolic actions. sIL-6R showed no direct effects on osteoblast proliferation or differentiation in vitro; however, it up-regulated myeloid cell expansion and production of the mesenchymal stem cell recruiting agent, TGF-β1 in the bone marrow microenvironment. Collectively, sIL-6R demonstrated orphan function and mediated PTH anabolic actions in bone in association with support of myeloid lineage cells in the hematopoietic system.

Lentiviral-mediated knockdown during ex vivo erythropoiesis of human hematopoietic stem cells

Erythropoiesis is a commonly used model system to study cell differentiation. During erythropoiesis, pluripotent adult human hematopoietic stem cells (HSCs) differentiate into oligopotent progenitors, committed precursors and mature red blood cells. This process is regulated for a large part at the level of gene expression, whereby specific transcription factors activate lineage-specific genes while concomitantly repressing genes that are specific to other cell types. Studies on transcription factors regulating erythropoiesis are often performed using human and murine cell lines that represent, to some extent, erythroid cells at given stages of differentiation. However transformed cell lines can only partially mimic erythroid cells and most importantly they do not allow one to comprehensibly study the dynamic changes that occur as cells progress through many stages towards their final erythroid fate. Therefore, a current challenge remains the development of a protocol to obtain relatively homogenous populations of primary HSCs and erythroid cells at various stages of differentiation in quantities that are sufficient to perform genomics and proteomics experiments. Here we describe an ex vivo cell culture protocol to induce erythroid differentiation from human hematopoietic stem/progenitor cells that have been isolated from either cord blood, bone marrow, or adult peripheral blood mobilized with G-CSF (leukapheresis). This culture system, initially developed by the Douay laboratory, uses cytokines and co-culture on mesenchymal cells to mimic the bone marrow microenvironment. Using this ex vivo differentiation protocol, we observe a strong amplification of erythroid progenitors, an induction of differentiation exclusively towards the erythroid lineage and a complete maturation to the stage of enucleated red blood cells. Thus, this system provides an opportunity to study the molecular mechanism of transcriptional regulation as hematopoietic stem cells progress along the erythroid lineage. Studying erythropoiesis at the transcriptional level also requires the ability to over-express or knockdown specific factors in primary erythroid cells. For this purpose, we use a lentivirus-mediated gene delivery system that allows for the efficient infection of both dividing and non-dividing cells. Here we show that we are able to efficiently knockdown the transcription factor TAL1 in primary human erythroid cells. In addition, GFP expression demonstrates an efficiency of lentiviral infection close to 90%. Thus, our protocol provides a highly useful system for characterization of the regulatory network of transcription factors that control erythropoiesis.

Maternal snoring during pregnancy is associated with enhanced fetal erythropoiesis--a preliminary study

OBJECTIVE AND BACKGROUND

Snoring is common among pregnant women and early reports suggest that it may bear a risk to the fetus. Increased fetal erythropoiesis manifested by elevated circulating nucleated red blood cells (nRBCs) has been found in complicated pregnancies involving fetal hypoxia. Both erythropoietin (EPO) and interleukin-6 (IL-6) mediate elevation of circulating nRBCs. The intermittent hypoxia and systemic inflammation elicited by sleep-disordered breathing (SDB) could affect fetal erythropoiesis during pregnancy. We hypothesized that maternal snoring will result in increased levels of fetal circulating nRBCs via increased concentrations of EPO, IL-6, or both.

METHODS

Women of singleton uncomplicated full-term pregnancies were recruited during labor and completed a designated questionnaire. Umbilical cord blood was collected immediately after birth and analyzed for nRBCs, plasma EPO and plasma IL-6 concentrations. Newborn data were retrieved from medical records.

RESULTS

One hundred and twenty-two women were recruited. Thirty-nine percent of women reported habitual snoring during pregnancy. Cord blood levels of circulating nRBCs, EPO and IL-6 were significantly elevated in habitual snorers compared with non-snorers (p = 0.03, 0.005 and 0.01; respectively). No differences in maternal characteristics or newborn crude outcomes were found.

CONCLUSIONS

Maternal snoring during pregnancy is associated with enhanced fetal erythropoiesis manifested by increased cord blood levels of nRBCs, EPO and IL-6. This provides preliminary evidence that maternal snoring is associated with subtle alterations in markers of fetal well being.

Role of erythropoietin receptor signaling in parvovirus B19 replication in human erythroid progenitor cells

Parvovirus B19 (B19V) infection is highly restricted to human erythroid progenitor cells. Although previous studies have led to the theory that the basis of this tropism is receptor expression, this has been questioned by more recent observation. In the study reported here, we have investigated the basis of this tropism, and a potential role of erythropoietin (Epo) signaling, in erythroid progenitor cells (EPCs) expanded ex vivo from CD34(+) hematopoietic cells in the absence of Epo (CD36(+)/Epo(-) EPCs). We show, first, that CD36(+)/Epo(-) EPCs do not support B19V replication, in spite of B19V entry, but Epo exposure either prior to infection or after virus entry enabled active B19V replication. Second, when Janus kinase 2 (Jak2) phosphorylation was inhibited using the inhibitor AG490, phosphorylation of the Epo receptor (EpoR) was also inhibited, and B19V replication in ex vivo-expanded erythroid progenitor cells exposed to Epo (CD36(+)/Epo(+) EPCs) was abolished. Third, expression of constitutively active EpoR in CD36(+)/Epo(-) EPCs led to efficient B19V replication. Finally, B19V replication in CD36(+)/Epo(+) EPCs required Epo, and the replication response was dose dependent. Our findings demonstrate that EpoR signaling is absolutely required for B19V replication in ex vivo-expanded erythroid progenitor cells after initial virus entry and at least partly accounts for the remarkable tropism of B19V infection for human erythroid progenitors.

Ex-vivo expansion of CFU-GM and BFU-E in unselected PBMC cultures with Flt3L is enhanced by autologous plasma

BACKGROUND

Previous ex-vivo expansion studies in our laboratory, comparing unselected and CD34(+)-selected PBMC, have shown no advantage for CD34(+) cell selection, in terms of the expansion achieved. Our goal was to develop procedures for consistent generation of large numbers of hematopoietic progenitor and post-progenitor cells from unselected PBMC.

METHODS

Unselected PBMC, collected from cancer patients undergoing apheresis prior to high-dose chemotherapy and autologous stem cell rescue, were expanded ex vivo in static cultures, without a stromal layer, in the presence of Flt3 ligand (Flt3L), a recombinant GM-CSF/IL-3 fusion protein (PIXY321), G-CSF and GM-CSF for 10 days.

RESULTS

The addition of 2% autologous plasma to this cytokine combination enhanced expansion of total cell numbers (3.2 fold versus 1.9 fold; p < 0.01), colony-forming units granulocyte-macrophage (CFU-GM) (22.0 fold versus 8.1 fold, p < 0.01) and burst-forming units erythroid (BFU-E) (17.6 fold versus 7.0 fold, 0.01 < p < 0.02). The optimal seeding density for a given specimen was inversely related to the frequency of CD34(+) cells in the sample. CFU-GM expansion with the Flt3L-containing cytokine cocktail was equivalent to that obtained with IL-3, IL-6, G-CSF and SCF, whether or not the cultures were supplemented with autologous plasma. In plasma-free cultures, BFU-E expansion was significantly higher with IL-3, IL-6, G-CSF and SCF than with Flt3L, PIXY321, G-CSF and GM-CSF. In the presence of autologous plasma, however BFU-E expansion was higher in the Flt3L-containing media. In comparison studies, autologous plasma suppressed BFU-E expansion in SCF-containing cultures. Consistent with our colony assay results, dual-parameter flow cytometric analysis of the expanded cell population revealed that supplementation with autologous plasma yielded a significant increase in the numbers of myeloid progenitors in Flt3L-containing cultures.

DISCUSSION

Unselected PBMC from cancer patients can be effectively expanded ex vivo in Flt3L, PIXY321, G-CSF and GM-CSF, supplemented with autologous plasma, yielding high numbers of myeloid and erythroid progenitors.

Generation of functional erythrocytes from human embryonic stem cell-derived definitive hematopoiesis

A critical issue for clinical utilization of human ES cells (hESCs) is whether they can generate terminally mature progenies with normal function. We recently developed a method for efficient production of hematopoietic progenitors from hESCs by coculture with murine fetal liver-derived stromal cells. Large numbers of hESCs-derived erythroid progenitors generated by the coculture enabled us to analyze the development of erythropoiesis at a clone level and investigate their function. The results showed that the globin expression in the erythroid cells in individual clones changed in a time-dependent manner. In particular, embryonic epsilon-globin-expressing erythroid cells from individual clones decreased, whereas adult-type beta-globin-expressing cells increased to approximately 100% in all clones we examined, indicating that the cells undergo definitive hematopoiesis. Enucleated erythrocytes also appeared among the clonal progeny. A comparison analysis showed that hESC-derived erythroid cells took a similar differentiation pathway to human cord blood CD34(+) progenitor-derived cells when examined for the expression of glycophorin A, CD71 and CD81. Furthermore, these hESC-derived erythroid cells could function as oxygen carriers and had a sufficient glucose-6-phosphate dehydrogenase activity. The present study should provide an experimental model for exploring early development of human erythropoiesis and hemoglobin switching and may help in the discovery of drugs for hereditary diseases in erythrocyte development.

Lhx2 expression promotes self-renewal of a distinct multipotential hematopoietic progenitor cell in embryonic stem cell-derived embryoid bodies

The molecular mechanisms regulating the expansion of the hematopoietic system including hematopoietic stem cells (HSCs) in the fetal liver during embryonic development are largely unknown. The LIM-homeobox gene Lhx2 is a candidate regulator of fetal hematopoiesis since it is expressed in the fetal liver and Lhx2^−/− mice die in utero due to severe anemia. Moreover, expression of Lhx2 in embryonic stem (ES) cell-derived embryoid bodies (EBs) can lead to the generation of HSC-like cell lines. To further define the role of this transcription factor in hematopoietic regulation, we generated ES cell lines that enabled tet-inducible expression of Lhx2. Using this approach we observed that Lhx2 expression synergises with specific signalling pathways, resulting in increased frequency of colony forming cells in developing EB cells. The increase in growth factor-responsive progenitor cells directly correlates to the efficiency in generating HSC-like cell lines, suggesting that Lhx2 expression induce self-renewal of a distinct multipotential hematopoietic progenitor cell in EBs. Signalling via the c-kit tyrosine kinase receptor and the gp130 signal transducer by IL-6 is necessary and sufficient for the Lhx2 induced self-renewal. While inducing self-renewal of multipotential progenitor cells, expression of Lhx2 inhibited proliferation of primitive erythroid precursor cells and interfered with early ES cell commitment, indicating striking lineage specificity of this effect.

Novel method for efficient production of multipotential hematopoietic progenitors from human embryonic stem cells

We propose a novel method for the efficient production of hematopoietic progenitors from human embryonic stem cells (hESC) via coculture with murine fetal liver-derived stromal cells, in which embryonic hematopoiesis dramatically expands at midgestation. We generated various hematopoietic progenitors in coculture, and this hematopoietic activity was concentrated in cobblestone-like cells derived from differentiated hESC. The cobblestone-like cells mostly expressed CD34 and retained an endothelial cell potential. They also contained hematopoietic colony-forming cells, especially erythroid and multilineage colony-forming cells at high frequency. The multipotential hematopoietic progenitors abundant among the cobblestone-like cells produced almost all types of mature blood cells, including adult-type alpha-globin-expressing erythrocytes and tryptase/chymase double-positive mast cells. These progenitors showed neither the immature properties of ESC nor the potential to differentiate into endoderm and ectoderm at a clonal level. The coculture system developed for hESC can provide a novel source of hematopoietic and blood cells for applications in cellular therapy and drug screening.

T cells from patients with polycythemia vera elaborate growth factors which contribute to endogenous erythroid and megakaryocyte colony formation

In the present study, we report that media conditioned by polycythemia vera (PV) CD3+ cells promote BFU-E and CFU-Mk colony formation by both cord blood and PV peripheral blood CD34+ cells in the absence of exogenous cytokines and promoting megakaryocyte proplatelet formation. CD3+ cells constitutively produce elevated levels of IL-11, while stimulation with the addition of phytohemagglutinin (PHA) increased GM-CSF levels in most of the patients with PV. Anti-IL-11-neutralizing antibody partially inhibited the formation of BFU-E and CFU-Mk colonies promoted by PV CD3+ cell-conditioned media. Although IL-11 is not produced by normal T cells, real-time PCR and flow cytometric analysis showed that IL-11 was upregulated in the CD3+ cells of most PV patients as compared to normal CD3+ cells. In addition, a greater percentage of BFU-E colonies formed by PV CD34+ cells in the presence of PV CD3+ cell-conditioned media alone were JAK2V617F-positive as compared with that induced by EPO. We conclude that dysregulated production of soluble growth factor(s), including IL-11 and GM-CSF by PV T cells, contributes to the in vitro formation of erythroid colonies in the absence of exogenous cytokines by PV CD34+ cells and likely plays a role in sustaining hematopoiesis in PV.

Notch ligand Delta-1 differentially modulates the effects of gp130 activation on interleukin-6 receptor alpha-positive and -negative human hematopoietic progenitors

Interleukin (IL)-6 plays pleiotropic roles in human hematopoiesis and immune responses by acting on not only the IL-6 receptor-alpha subunit (IL-6Ralpha)(+) but also IL-6Ralpha(-) hematopoietic progenitors via soluble IL-6R. The Notch ligand Delta-1 has been identified as an important modulator of the differentiation and proliferation of human hematopoietic progenitors. Here, it was investigated whether these actions of IL-6 are influenced by Delta-1. When CD34(+)CD38(-) hematopoietic progenitors were cultured with stem cell factor, flt3 ligand, thrombopoietin and IL-3, Delta-1, in combination with the IL-6R/IL-6 fusion protein FP6, increased the generation of glycophorin A(+) erythroid cells but counteracted the effects of IL-6 and FP6 on the generation of CD14(+) monocytic and CD15(+) granulocytic cells. Although freshly isolated CD34(+)CD38(-) cells expressed no or only low levels of IL-6Ralpha, its expression was increased in myeloid progenitors after culture but remained negative in erythroid progenitors. It was found that Delta-1 acted in synergy with FP6 to enhance the generation of erythroid cells from the IL-6Ralpha(-) erythroid progenitors. In contrast, Delta-1 antagonized the effects of IL-6 and FP6 on the development of monocytic and granulocytic cells, as well as CD14(-)CD1a(+) dendritic cells, from the IL-6Ralpha(+) myeloid progenitors. These results indicate that Delta-1 interacts differentially with gp130 activation in IL-6Ralpha(-) erythroid and IL-6Ralpha(+) myeloid progenitors. The present data suggest a divergent interaction between Delta-1 and gp130 activation in human hematopoiesis.

Stem cell c-KIT and HOXB4 genes: critical roles and mechanisms in self-renewal, proliferation, and differentiation

Hematopoietic stem cells (HSCs) possess a distinct ability to perpetuate through self-renewal and to generate progeny that differentiate into mature cells of myeloid and lymphoid lineages. A better understanding of the molecular mechanisms by which HSCs replicate and differentiate from the perspective of developing new approaches for HSC transplantation is necessary for further advances. The interaction of the receptor tyrosine kinase--c-KIT--with its ligand stem cell factor plays a key role in HSC survival, mitogenesis, proliferation, differentiation, adhesion, homing, migration, and functional activation. Evidence that activating site-directed point mutations in the c-KIT gene contributes to its ligand-independent constitutive activation, which induces enhanced proliferation of HSCs, is accumulating. Similarly, and equally important, self-renewal is a process by which HSCs generate daughter cells via division. Self-renewal is necessary for retaining the HSC pool. Therefore, elucidating the molecular machinery that governs self-renewal is of key importance. The transcription factor, HOXB4 is a key molecule that has been reported to induce the in vitro expansion of HSCs via self-renewal. However, critical downstream effector molecules of HOXB4 remain to be determined. This concisely reviewed information on c-KIT and HOXB4 helps us to update our understanding of their function and mechanism of action in self-renewal, proliferation, and differentiation of HSCs, particularly modulation by c-KIT mutant interactions, and HOXB4 overexpression showing certain therapeutic implications.

The regulatory role of Hyper-IL-6 in the differentiation of myeloid and erythroid progenitors derived from human cord blood

This study was designed to investigate the regulatory role of soluble interleukin-6 receptor (sIL-6R) and interleukin-6 (IL-6) fusion protein (Hyper-IL-6) in the differentiation of human myeloid and erythroid progenitors by a serum-free liquid suspension culture system, using the human cord blood-derived CD34(+)CD38(-) cells as a target. We found that Hyper-IL-6 promoted the generation of CD15(+) granulocytic and CD14(+) monocytic cells and suppressed that of CD14(-)CD1a(+) dendritic cells from CD36(-)CD15(-)CD14(-)CD1a(-)IL-6R(+) myeloid progenitors. Conversely, CD34(+)CD38(-) cell-derived early erythroid progenitors were negative for IL-6R expression. Hyper-IL-6 potentiated the generation of CD36(+)glycophorinA(high) mature erythroid cells from the IL-6R(-) early erythroid progenitors. Our results indicate that Hyper-IL-6 augments the generation of CD15(+) granulocytic, CD14(+) monocytic and CD36(+)glycophorinA(high) cell and suppresses that of CD14(-)CD1a(+) dendritic cells.

The effect of prolonged rupture of membranes on circulating neonatal nucleated red blood cells

OBJECTIVES

To test the hypothesis that absolute nucleated red blood cells (ANRBC) counts are higher at birth in infants who were born after prolonged rupture of membranes (PROM, >24 hours).

STUDY DESIGN

Retrospective study of 31 infants admitted to the neonatal intensive care unit who were born after PROM, and pair matched for gestational age and Apgar scores with 31 no PROM controls. Venous ANRBC counts were obtained within 1 hour of life.

RESULTS

Groups did not differ in birthweight, gestational age, Apgar scores, and platelets counts. The ANRBC counts and hematocrit were significantly higher in infants who were born after PROM than in controls.

CONCLUSIONS

Infants born after PROM have higher ANRBC counts at birth than control infants. We suggest that increased fetal erythropoiesis exists in infants who are delivered after PROM. If correct, our interpretation supports the theory that fetal hypoxia and/or ischemia may result from PROM.

Effects of cytokines on matrix metalloproteinase expression in oral squamous cell carcinoma in vitro

CONCLUSIONS

The intra-tumoral cytokines IL-6, hepatocyte growth factor (HGF) and tumour necrosis factor-a (TNF-a) stimulate oral cancer cells to enhanced secretion of matrix metalloproteinase (MMP)-1 and -9. These results contribute to an understanding of the extracellular events necessary for tumour progression.

OBJECTIVE

MMPs play an important role in enhanced intra-tumoral proteolytic activity, promoting angiogenesis and invasion by acting on extracellular matrix substances. Cytokines secreted by tumour-infiltrating immune cells, fibroblasts and tumour cells can modulate MMP expression and secretion by cancer cells. The objective of this study was to investigate the effects of IL-6, soluble IL-6 receptor (sIL-6R), HGF, TNF-a and IL-8 on MMP-1, -2 and -9 expression by two oral squamous cell carcinoma cell lines (UT-SCC-20A and -24A).

MATERIAL AND METHODS

ELISA was used to analyse secretion of total MMP protein and gelatin zymography was used for activity analysis.

RESULTS

IL-6 had a moderate stimulatory effect on MMP-1 secretion in both cell lines, whereas sIL-6R had no effect. When these cytokines were added together, a dose-dependent, synergistic stimulatory effect was observed. HGF also upregulated MMP-1 secretion, especially in one cell line (UT-SCC-24A), and a synergistic effect was observed when HGF was added to IL-6 in both cell lines. MMP-9 secretion by UT-SCC-24A was increased when stimulated with HGF and IL-6 combined with sIL-6R, whereas no effect was found in the other cell line. TNF-a stimulated MMP-9 secretion in both cell lines, but only stimulated MMP-1 secretion in one (UT-SCC-24A). The zymographic results were consistent with the ELISA results, indicating an upregulation of active enzyme when a stimulatory effect on protein expression was detected.

Fetal "nonreassuring status" is associated with elevation of nucleated red blood cell counts and interleukin-6

OBJECTIVE

Previous studies have established the association between fetal hypoxia and elevated nucleated red blood cells (NRBCs). Animal studies have demonstrated that a rise in plasma erythropoietin (EPO) is not detectable until 4 to 6 hours after the initiation of hypoxia. In contrast, interleukin-6 (IL-6) has the capacity to directly induce erythroid maturation. Therefore, we set forth to evaluate the role of EPO and IL-6 as potential mediators of elevated fetal NRBCs in response to acute hypoxia.

STUDY DESIGN

Low-risk pregnancies with a normal fetal heart rate at admission to labor and delivery were eligible for participation. Deliveries for "nonreassuring fetal status" comprised the study group. All other deliveries served as controls. Umbilical cord blood was prospectively collected for blood gas analysis, NRBC counts, EPO, and IL-6.

RESULTS

One hundred women participated in the study. Nonparametric univariate analysis demonstrated a significant association between elevated NRBC counts and Apgar scores, arterial cord blood pH, base excess, EPO, and IL-6 levels (all P values <.01). Stepwise regression analysis identified only pH, IL-6, and EPO as independent variables associated with elevated NRBC counts at birth (all P values <.0001 with R2 of 0.27, 0.42, and 0.46, respectively). A significant increase in NRBC counts was noted in study patients. IL-6 was significantly increased in study patients, whereas there was no difference in EPO between groups.

CONCLUSION

The fact that NRBC counts were elevated in fetuses who were delivered for "nonreassuring fetal status" with EPO being normal and IL-6 being elevated implies that IL-6 may have a unique, short-term role in elevating fetal NRBC counts.

Ex vivo generation of fully mature human red blood cells from hematopoietic stem cells

We describe here the large-scale ex vivo production of mature human red blood cells (RBCs) from hematopoietic stem cells of diverse origins. By mimicking the marrow microenvironment through the application of cytokines and coculture on stromal cells, we coupled substantial amplification of CD34(+) stem cells (up to 1.95 x 10(6)-fold) with 100% terminal differentiation into fully mature, functional RBCs. These cells survived in nonobese diabetic/severe combined immunodeficient mice, as do native RBCs. Our system for producing 'cultured RBCs' lends itself to a fundamental analysis of erythropoiesis and provides a simple in vitro model for studying important human viral or parasitic infections that target erythroid cells. Further development of large-scale production of cultured RBCs will have implications for gene therapy, blood transfusion and tropical medicine.

Complete remission of hyperprolactinemia and erythrocytosis after hysterectomy for a uterine fibroid in a woman with a previous diagnosis of prolactin-secreting pituitary microadenoma

A 44-year-old woman who had been suffering for 10 years from amenorrhea and hyperprolactinemia resistant to high doses of bromocriptine was hospitalized with erythrocytosis, normal serum erythropoietin (sEpo) levels, and hypertension. Erythrocytosis secondary to uterine myoma and a prolactin-secreting pituitary microadenoma were initially diagnosed. The hyperprolactinemia was bromocriptine resistant, despite gradual increase of the dosage to 30 mg/day. Both hyperprolactinemia and erythrocytosis unexpectedly regressed completely after the patient underwent hysterectomy for a uterine fibroid 9 months after the erythrocytosis was first disclosed. Given the well-known effects of prolactin on hematopoietic cells, we hypothesize that--in this very unusual case--the two main, apparently unrelated abnormalities (erythrocytosis with normal sEpo levels and hyperprolactinemia) may have been the clinical consequence of the functional redundancy and pleiotropy of the "pituitary" hormone prolactin, inappropriately secreted by a uterine fibroid for more than 10 years.

Are elevated fetal nucleated red blood cell counts an indirect reflection of enhanced erythropoietin activity?

OBJECTIVE

Animal and human studies demonstrated elevated erythropoietin (EPO) levels in response to intrauterine hypoxic events. Other studies documented an association between fetal hypoxia and elevated nucleated red blood cell (NRBC) counts and have speculated that it is the elevation of EPO that results in an increase in NRBC counts. Thus, the purpose of our study was to determine the correlation between EPO levels and NRBC counts in the human fetus.

STUDY DESIGN

Data were collected prospectively between April and July of 2003. Term singleton pregnancies were eligible to participate in the study. Umbilical cord blood was collected immediately after birth for determination of fetal EPO levels and NRBC counts.

RESULTS

Forty pregnancies formed the study population. The mean gestational age at delivery was 39.5 +/- 1.2 weeks (+/-SD) and the mean birth weight was 3500 +/- 372 g. The median EPO (mU/mL) was 34 (range 13-427). The median NRBC/100 white blood cells was 10 (range 0-150). A simple regression analysis indicated that NRBC counts are significantly and positively correlated with EPO (P=.0004, R(2)=0.287).

CONCLUSION

Our results suggest a significant association between EPO and NRBC counts in term singleton fetuses. These results support the hypothesis that fetal NRBC and EPO are interrelated. However, the relatively low R(2) indicates that there are other (yet to be determined) hypoxia-derived mediators that result in an elevation of fetal NRBC counts.

VEGF-A165 augments erythropoietic development from human embryonic stem cells

Combinations of hematopoietic cytokines and the ventral mesoderm inducer BMP-4 have recently been shown to augment hematopoietic cell fate of human embryonic stem cells (hESCs) during embryoid body (EB) development. However, factors capable of regulating lineage commitment of hESC-derived hematopoiesis have yet to be reported. Here we show that vascular endothelial growth factor (VEGF-A165) selectively promotes erythropoietic development from hESCs. Effects of VEGF-A165 were dependent on the presence of hematopoietic cytokines and BMP-4, and could be augmented by addition of erythropoietin (EPO). Treatment of human EBs with VEGF-A165 increased the frequency of cells coexpressing CD34 and the VEGF-A165 receptor KDR, as well as cells expressing erythroid markers. Although fetal/adult globins were unaffected, VEGF-A165 induced the expression of embryonic zeta (zeta) and epsilon (epsilon) globins, and was accompanied by expression of the hematopoietic transcription factor SCL/Tal-1. In addition to promoting erythropoietic differentiation from hESCs, the presence of VEGF-A165 enhanced the in vitro self-renewal potential of primitive hematopoietic cells capable of erythroid progenitor capacity. Our study demonstrates a role for VEGF-A165 during erythropoiesis of differentiating hESCs, thereby providing the first evidence for a factor capable of regulating hematopoietic lineage development of hESCs.

Placenta growth factor activates monocytes and correlates with sickle cell disease severity

Sickle cell disease (SCD) results in chronic hypoxia and secondarily increased erythropoietin concentrations. Leukocytosis and activated monocytes are also observed in SCD in absence of infection or vaso-occlusion (steady state), the reasons for which are unknown. We found that erythroid cells produced placenta growth factor (PlGF), an angiogenic growth factor belonging to the vascular endothelial growth factor (VEGF) family, and its expression was induced in bone marrow CD34+ progenitor cells in the presence of erythropoietin. Furthermore, the steady state circulating PlGF levels in subjects with severe SCD (at least 3 vaso-occlusive crises [VOCs] per year) were 18.5 +/- 1.2 pg/mL (n = 9) compared with 15.5 +/- 1.2 pg/mL (n = 13) in those with mild SCD (fewer than 3 VOCs per year) and 11.3 +/- 0.7 pg/mL (n = 9) in healthy controls (P <.05), suggesting a correlation between PlGF levels and SCD severity. In addition, PlGF significantly increased mRNA levels of the proinflammatory cytochemokines interleukin-1beta, interleukin-8, monocyte chemoattractant protein-1, and VEGF in peripheral blood mononuclear cells (MNCs) of healthy subjects (n = 4; P <.05). Expression of these same cytochemokines was significantly increased in MNCs from subjects with SCD at steady state (n = 14), compared with healthy controls. Of the leukocyte subfractions, PlGF stimulated monocyte chemotaxis (P <.05, n = 3). Taken together, these data show for the first time that erythroid cells intrinsically release a factor that can directly activate monocytes to increase inflammation. The baseline inflammation seen in SCD has always been attributed to sequelae secondary to the sickling phenomenon. We show that PlGF contributes to the inflammation observed in SCD and increases the incidence of vaso-occlusive events.

Regulated expression of MUC1 epithelial antigen in erythropoiesis

MUC1 is a large surface glycoprotein expressed by epithelial cells, which is overexpressed and aberrantly glycosylated in carcinomas. MUC1 is involved in epithelial cell interactions and appears to function as a signal-transducing molecule. The finding that MUC1 can also be expressed in the haematopoietic lineages prompted us to further investigate the possible function(s) of this molecule in haematopoietic cells. In bone marrow differentiating cells, MUC1 was strongly and selectively expressed during erythropoiesis; it was also weakly expressed during megakaryocytopoiesis and granulomonocytopoiesis; however, no correlation between MUC1 and differentiation marker expression was observed in these lineages. In vitro CD34+ cells, induced towards erythroid differentiation, acquired MUC1 transiently, while expressing increasing levels of the lineage marker glycophorin A. MUC1 was absent in the circulating erythrocytes. During erythropoiesis, MUC1 expression was transcriptionally regulated and the molecule underwent phosphorylation. To investigate the possible role of MUC1 during erythropoiesis, we studied the ability of MUC1 to act as ligand for cell-cell interaction. The sialylated MUC1 glycoforms selectively expressed on erythroid cells were able to bind the macrophage-restricted molecule sialoadhesin. These results suggest that MUC1 can function as a cross-talk molecule between the erythroblasts and the surrounding cells during erythropoiesis.

Reconstitution of human haematopoiesis in non-obese diabetic/severe combined immunodeficient mice by clonal cells expanded from single CD34+CD38- cells expressing Flk2/Flt3

In the present study, we examined the expression of Flk2/Flt3, a tyrosine kinase receptor, on human cord blood CD34+ haematopoietic progenitor/stem cells. In flow cytometric analysis, Flk2/Flt3 was expressed on 80% of CD34+ cells and their immature subpopulations, CD34+CD33- and CD34+CD38- cells. Methycellulose clonal culture of sorted CD34+Flk2/Flt3+ and CD34+Flk2/Flt3- cells showed that most of myelocytic progenitors expressed Flk2/Flt3, but erythroid and haematopoietic multipotential progenitors were shared by both fractions. When 1 x 10(4) lineage marker-negative (Lin-)CD34+Flk2/Flt3- cells were transplanted into non-obese diabetic/severe combined immunodeficient (NOD/SCID) mice, none of the recipients possessed human CD45+ cells in bone marrow 11-12 weeks after the transplantation. In contrast, all recipients transplanted with 1 x 10(4) Lin-CD34+Flk2/Flt3+ cells showed successful engraftment. Furthermore, clonal cells expanded from single Lin-CD34+CD38-Flk2/Flt3+ cells in the culture with Flk2/Flt3 ligand, stem cell factor, thrombopoietin, and a complex of interleukin 6/soluble interleukin 6 receptor were individually transplanted into NOD/SCID mice. At 20 to 21 weeks after the transplantation, three out of 10 clones harvested at d 7 of culture, and three out of six clones at d 14 could reconstitute human haematopoiesis in recipient marrow. These results demonstrated that Flk2/Flt3 was expressed on a wide variety of human haematopoietic cells including long-term-repopulating haematopoietic stem cells.

Maxadilan, the vasodilator/immunomodulator from Lutzomyia longipalpis sand fly saliva, stimulates haematopoiesis in mice

Protozoal parasites of the genus Leishmania are transmitted to their vertebrate host within the saliva of the sand fly during a blood meal. The saliva of the sand fly Lutzomyia longipalpis contains maxadilan, a potent vasodilator and immunomodulator. Maxadilan has been shown to enhance the virulence of L. major in all strains of laboratory mice when injected along with the organism. Increased haematopoiesis has been associated with enhanced susceptibility to Leishmania organisms. Here, we show that maxadilan alone stimulates bone marrow haematopoiesis through its ability to stimulate interleukin-6 production by bone marrow stromal cells. Moreover, these effects of maxadilan are mediated through the interaction of maxadilan with the pituitary adenylate cyclase activating polypeptide receptor. These data suggest that increasing haematopoiesis may be yet another way that maxadilan enhances susceptibility of mice to Leishmania infection.

gp130-linked signal transduction promotes the differentiation and maturation of dendritic cells

In order to explore the role of gp130-linked signal transduction in the differentiation and maturation of dendritic cells (DC), the mAb, B-S12, an agonist of gp130, was used for the activation of gp130 on DC. The effects of cytokines and of anti-gp130 mAb on the proliferation of DC, and their expression of IL-12 and CD80 (B7-1) by DC were evaluated. DC differentiating from peripheral blood mononuclear cells did not express the IL-6 receptor alpha chain, but expressed gp130. Anti-gp130 mAb promoted the proliferation of DC, induced by IL-4 and granulocyte macrophage colony stimulating factor (GM-CSF), by up-regulating the GM-CSF receptor on DC. DC induced by gp130 mAb and cytokines expressed DC-derived CC chemokine, as measured by RT-PCR. Induced DC also stimulated strong proliferation of autologous T cells in mixed lymphocyte reaction since an up-regulated expression of IL-12 and CD80 (B7-1) was observed in DC activated by anti-gp130 mAb. Thus, gp130 signal transduction is important for the differentiation and maturation of DC.

Ex vivo expansion of human hematopoietic stem cells

There has been great interest in the ex vivo expansion of human long-term repopulating hematopoietic stem cells (LTR-HSCs) for a variety of clinical applications such as umbilical cord blood transplantation. The glucoprotein130 signal, activated by a complex of interleukin 6 (IL-6) and soluble IL-6 receptor (IL-6/sIL-6R), acts dramatically in synergy with the c-Kit or Flk2/Flt3 signal to expand immature human HSCs. We demonstrate a significant ex vivo expansion of human LTR-HSCs capable of repopulating in newly discovered nonobese diabetes/Shi-severe combined immunodeficient (NOD/Shi-SCID) mice. The proportion of human CD45+ cells in recipient marrow was 10 times higher in animals receiving the cultured cells with stem cell factor, Flk2/Flt3 ligand, thrombopoietin, and IL-6/sIL-6R than in those receiving comparable numbers of fresh cord blood CD34+ cells. The expansion rate provided by this combination was estimated to be 4.2-fold by a limiting dilution method. Addition of IL-3 to the culture with the cytokine combination abrogated the repopulating ability of the expanded cells. The culture method with the IL-6/sIL-6R complex and other cytokines may pave the way for ex vivo expansion of human transplantable HSCs suitable for clinical applications.

Inhibitory effect of interleukin 3 on early development of human B-lymphopoiesis

Interleukin 3 (IL-3) is known as a stimulator of proliferation and differentiation of non-lymphoid cells, but information about the activity of IL-3 in lymphopoiesis is limited. In the present study, we examined the effect of IL-3 on human B-lymphopoiesis using the co-culture system on a murine stromal cell line, MS-5, with stem cell factor (SCF) and granulocyte colony-stimulating factor (G-CSF). Although a large number of CD45+CD19+ B cells were generated in the co-culture of cord blood CD34+ cells, the addition of IL-3 to the co-culture suppressed the B-cell generation in a dose-dependent manner. In the co-culture, CD34+IL-3 receptor alpha-chain (IL-3Ralpha)+ cells, but not IL-3Ralpha- cells, produced B cells, and IL-3 suppressed the B-cell generation from CD34+IL-3Ralpha+ cells, suggesting that IL-3 exerts an inhibitory effect through the binding to IL-3Ralpha on CD34+ cells. Because the delayed addition of IL-3 and the short-term exposure to IL-3 showed that IL-3 acted as an inhibitor at an early stage of B-cell development from CD34+ cells, before the generation of CD19+ B cells, the effect of IL-3 on the early development of B cells from immature CD34+CD38- cells was examined. Individual colonies, produced from clone-sorted CD34+CD38- cells by SCF, thrombopoietin and a complex of IL-6/soluble IL-6R with or without IL-3, were divided into two fractions and analysed for B-cell potential using co-culture on MS-5 with SCF and G-CSF, and haematopoietic potential using methylcellulose clonal culture. Although some colonies cultured without IL-3 showed both B-cell and haematopoietic potential, all the colonies cultured with IL-3 showed only haematopoietic potential. These results indicate that IL-3 has an inhibitory effect on the B-cell generation from human lymphohaematopoietic progenitor cells.

Flt-1, vascular endothelial growth factor receptor 1, is a novel cell surface marker for the lineage of monocyte-macrophages in humans

Flt-1, also known as vascular endothelial growth factor receptor 1 (VEGFR-1), is a high-affinity tyrosine kinase receptor for VEGF and is expressed almost exclusively on vascular endothelial cells. As an exception, Flt-1 transcript was recently found to be expressed in human peripheral blood monocytes. However, the protein of the Flt-1 receptor on the cell surface of monocytes is yet to be identified, and whether the Flt-1 protein is expressed during the differentiation of monocyte-macrophage lineage cells has not been examined. Using monoclonal antibodies against 2 different antigenic epitopes on the Flt-1 extracellular domain, this study found that the major population of the monocyte-marker CD97+ cells in human peripheral blood express Flt-1 as a cell surface molecule. VEGFR-2 (KDR/Flk-1) was not expressed at detectable levels in these cells. An Flt-1 neutralizing monoclonal antibody significantly suppressed VEGF-induced migration of the monocytes, suggesting an important role for Flt-1 in the biologic function of monocytes. Furthermore, CD34+ cells in human cord blood, originally negative for the Flt-1 expression, differentiated into Flt-1+ cells in association with the appearance of monocyte-macrophage markers after a 2-week culture in the presence of hematopoietic cytokines. In addition, the Flt-1+ CD11b+ cell fraction from CD34+ cells was found to efficiently differentiate into multinuclear osteoclasts in the presence of macrophage colony-stimulating factor and osteoclast differentiation factor. These results strongly suggest that Flt-1 is a novel cell surface marker as well as a biologically functional molecule for monocyte-macrophage lineages in humans.

CD34 expression on long-term repopulating hematopoietic stem cells changes during developmental stages

The CD34 antigen serves as an important marker for primitive hematopoietic cells in therapeutic transplantation of hematopoietic stem cells (HSC) and gene therapy, but it has remained an open question as to whether or not most HSC express CD34. Using a competitive long-term reconstitution assay, the results of this study confirm developmental changes in CD34 expression on murine HSC. In fetuses and neonates, CD34 was expressed on Lin(-)c-Kit(+) long-term repopulating HSC of bone marrow (BM), liver, and spleen. However, CD34 expression on HSC decreased with aging, and in mice older than 10 weeks, HSC were most enriched in the Lin(-)c-Kit(+)CD34(-) marrow cell fraction. A second transplantation was performed from primary recipients who were transplanted with neonatal Lin(-)c-Kit(+) CD34(high) HSC marrow. Although donor-type HSC resided in CD34-expressing cell fraction in BM cells of the first recipients 4 weeks after the first transplantation, the stem cell activity had shifted to Lin(-)c-Kit(+)CD34(-) cells after 16 weeks, indicating that adult Lin(-)c-Kit(+)CD34(-) HSC are the progeny of neonatal CD34-expresssing HSC. Assays for colony-forming cells showed that hematopoietic progenitor cells, unlike HSC, continue to express CD34 throughout murine development. The present findings are important because the clinical application of HSC can be extended, in particular as related to CD34-enriched HSC and umbilical cord blood HSC.

An IL-6/IL-6 soluble receptor (IL-6R) hybrid protein (H-IL-6) induces EPO-independent erythroid differentiation in human CD34(+) cells

H-IL-6 is a hybrid protein constructed to contain IL-6 and its soluble receptor linked by a flexible peptide chain. Here we show that H-IL-6 strongly enhances proliferation of human CD34(+)cells in serum-free liquid culture, and that the majority of the cells generated belong to the erythroid lineage, being positive for the marker Glycophorin A. Conversely, H-IL-6 does not increase the number of myeloid, CD13-positive cells. Comparable effects are observed on progenitors from cord blood and adult peripheral blood. Therefore, H-IL-6 triggers an erythroid-inducing signal in haematopoietic progenitor cells, independently from erythropoietin (EPO).

Hematopoietic repopulating ability of cord blood CD34(+) cells in NOD/Shi-scid mice

Although umbilical cord blood (CB) is increasingly being used as an alternative to bone marrow (BM) as a source of transplantable hematopoietic stem cells (HSC), information on the hematopoietic repopulating ability of CB HSC is still limited. We recently established a xenotransplantation system in NOD/Shi-scid mice to evaluate human stem cell activity. In the present study, we transplanted 5 to 10 x 10(4) CB CD34(+) cells into six NOD/Shi-scid mice treated with anti-asialo GM1 antiserum to investigate the hematopoietic repopulating ability of CB. The BM of all recipients contained human CD45(+) cells 10 to 12 weeks after the transplantation (43.8 +/- 17.7%). Clonal culture of the recipient BM cells revealed the formation of various types of human hematopoietic colonies, including myelocytic, erythroid, megakaryocytic, and multilineage colonies, indicating that CB HSC can differentiate into hematopoietic progenitors of various lineages. However, the extent of the differentiation and maturation differed with each lineage. CD13(+)/CD14(+)/CD33(+) myelocytic cells were mainly repopulated in BM and peripheral blood (PB). While CD41(+) megakaryocytic cells and platelets were present, few glycophorin A(+)CD71(+) or hemoglobin alpha-containing erythroid cells were detected. CD19(+) B cells were the most abundantly repopulated in NOD/Shi-scid mice, but their maturational stage differed among the hematopoietic organs. Most of the BM CD19(+) cells were immature B cells expressing CD10 but not surface immunoglobulin (Ig) M, whereas more mature CD19(+)CD10(-) surface IgM(+) B cells were predominantly present in spleen and PB. CD3(+) T cells were not detected even in the recipient thymus. The transplantation to the NOD/Shi-scid mouse may provide a useful tool for evaluating the repopulating ability of transplantable human HSC.

Mechanisms mediating the inhibitory effect of all-trans retinoic acid on primitive hematopoietic stem cells in human long-term bone marrow culture

All-trans retinoic acid (RA) has generally been found to stimulate late committed (colony-forming unit- granulocyte, macrophage [CFU-GM]) and inhibit early (CFU-Blast) normal human myeloid progenitor cells. The present study provides the first evidence that the pharmacological concentration of 1 microM RA, exerts an inhibitory effect on the proliferation of functional human primitive hemopoietic stem cells (cobblestone area-forming cell [CFAC]) in long-term bone marrow cultures. Treatment of four-week confluent bone marrow culture with 1 microM RA for five days significantly reduced week 4 CAFC from 88 +/- 10 in control cultures to only 52 +/- 12 per 10(5) cells, p < 0.01. Quantitative enzyme-linked immunosorbent assay measurement of interleukin 6 (IL-6) and IL-11 produced from the four-week bone marrow stroma culture revealed only a slight and moderate increase of IL-6 and IL-11 production after treatment with RA. On the other hand, treatment with RA profoundly increased the soluble receptor gp130 released from the four-week bone marrow stroma by 7.5-fold from only 145 +/- 2.1 pg per ml in control cultures to 1,069.9 +/- 3.8 pg per ml in RA-treated cultures. A similar marked increase in the soluble adhesion molecules ICAM-1, and to a lesser extent VCAM-1, released from the four-week bone marrow stroma was observed after RA treatment. IL-6 has been implicated in the inhibitory effect of RA in several human hemopoietic and nonhemopoietic cells. The common transducing signal chain gp130, for all receptors of the IL-6 cytokine family, is expressed in most primitive human hemopoietic CD34(+) cells and its signaling was shown to synergize with other hemopoietic cytokines to expand primitive human hemopoietic stem cells. Recently, soluble gp130 was shown to be a natural potent antagonist of the human IL-6 cytokine family by binding the ligand and thereby reducing its bioavailability. The profound and rapid 7.5-fold increase in the natural antagonist of human IL-6 cytokine family after RA treatment could abrogate the gp130 signaling required for proliferation and/or expansion of human primitive hemopoietic stem cells and lead to the observed inhibitory effect of RA on CAFC. Both adhesion molecules VCAM-1 and ICAM-1 mediate human hemopoietic stem cell adhesion to marrow stroma. The present significant increase in the soluble form of these adhesion molecules after RA treatment could exert a significant antagonist effect on their function and hence may impair CAFC adhesion to marrow stroma. In conclusion, the RA inhibitory effect on the proliferation of primitive human hemopoietic stem cells could be mediated through: A) an impaired hemopoietic stem cell adhesion due to the significant increase in soluble adhesion molecules released from the marrow stroma after RA treatment, and B) a significantly reduced gp130 signaling that is necessary for stem cell proliferation due to the natural antagonistic effect of the profoundly increased level of soluble gp130 released from the marrow stroma after treatment with RA.

Erythroid progenitors differentiate and mature in response to endogenous erythropoietin

We reported previously that stimulation of glycoprotein 130 (gp130) by a combination of human IL-6 and soluble IL-6 receptor (sIL-6R) could support proliferation, differentiation, and terminal maturation of erythroid cells in the absence of erythropoietin (EPO) from human CD34(+) cells in culture with stem cell factor (SCF). This observation suggested that differentiation of hematopoietic stem/progenitor cells to erythroid cells progressed according to an intrinsic program and that EPO receptor (EPOR) could be replaced by other cytokine receptors. In other words, EPOR appeared to be dispensable for erythropoiesis. Here we examined the role of EPOR in erythropoiesis stimulated by SCF, sIL-6R, and IL-6. Surprisingly, reduction of EPOR expression using antisense oligodeoxynucleotides suppressed erythropoiesis stimulated not only by SCF and EPO, but also by SCF, sIL-6R, and IL-6. EPO mRNA was detected in erythroid cells but not myeloid cells cultured in the presence of SCF, sIL-6R, and IL-6. Furthermore, high concentrations of anti-EPO-neutralizing antibody abrogated erythropoiesis in cultures without exogenous EPO. Based on these results, we suggest that erythroid progenitors themselves secrete EPO and that they have the potential to differentiate and mature in response to this endogenous EPO.

Stem cell factor and erythropoietin inhibit apoptosis of human erythroid progenitor cells through different signalling pathways

Erythropoietin (EPO) and stem cell factor (SCF) are two important factors in human erythropoiesis. We have recently demonstrated that SCF and EPO synergistically activate mitogen-activated protein (MAP) kinase, thereby promoting growth of human erythroid colony-forming cells (ECFCs). In the present study, we have examined the intracellular mechanisms by which SCF and EPO maintain survival of these cells. In the absence of SCF and EPO, human ECFCs underwent rapid apoptosis. The process was significantly inhibited by addition of a single factor and was totally prevented in the presence of both factors. Treatment of ECFCs with wortmannin, a specific inhibitor of phosphoinositide 3-kinase (PI3K), inhibited the antiapoptotic effect of SCF but had no effect on that of EPO, indicating that SCF but not EPO inhibits apoptosis through the PI3K pathway. In contrast, treatment of ECFCs with PD98059, a specific inhibitor of MAP kinase/ERK kinase (MEK), inhibited cell growth but had no effect on the antiapoptotic activity of either SCF or EPO, suggesting that SCF and EPO prevent apoptosis of human ECFCs independent of the extracellular signal-regulated kinase (ERK) pathway. Interestingly, both EPO and SCF induced activation of PI3K. However, through PI3K, SCF caused activation of protein kinase B (PKB), an anti-apoptosis signal, whereas EPO led to activation of ERKs. Furthermore, the SCF- and EPO-maintained expression of antiapoptotic protein Bcl-XL was correlated with the activation of ERKs and was inhibited by PD98059, suggesting that Bcl-XL may not have a major role in preventing apoptosis of human ECFCs. Phosphorylated BAD was not affected by SCF, EPO or wortmannin. Taken together with our previous results, the present study indicates that SCF and EPO support survival and growth of human ECFCs through different signalling pathways and that they transduce distinctly different signals through activation of PI3K.

Exclusive expression of G-CSF receptor on myeloid progenitors in bone marrow CD34+ cells

Although granulocyte colony-stimulating factor (G-CSF) has been reported to act on cells of neutrophilic lineage, the administration of G-CSF to induce the mobilization of various haematopoietic progenitors into the circulation. We analysed the expression of receptors for G-CSF (G-CSFR) on human bone marrow and G-CSF-mobilized peripheral blood CD34+ cells, and examined the proliferation and differentiation capabilities of sorted CD34+G-CSFR+ and CD34+G-CSFR- cells using methylcellulose clonal culture. Flow cytometric analysis showed that G-CSFR was expressed on 14.9 +/- 4.9% of bone marrow CD34+ cells, most of which were included in CD34+CD33+ and CD34+CD38+ cell fractions. In clonal cultures, CD34+G-CSFR+ cells produced only myeloid colonies, whereas CD34+G-CSFR- cells produced erythroid bursts, megakaryocyte and multilineage colonies. When incubated with the cytokine cocktail for 5 d, CD34+G-CSFR- cells generated CD34+G-CSFR+ myeloid progenitors. In G-CSF-mobilized peripheral blood, CD34+ cells contained 10.8 +/- 5.8% of G-CSFR+ cells, most of which were also myeloid progenitors, although CD34+G-CSFR- cells contained a substantial number of myeloid progenitors. These results indicated that the expression of G-CSFR on CD34+ cells is restricted to myeloid progenitors, suggesting that the specific activity of G-CSF on myelopoiesis depends on the exclusive expression of its receptor on myeloid progenitors, and that the mobilization of various haematopoietic progenitors is not a direct effect of G-CSF in humans.

Expansion of human NOD/SCID-repopulating cells by stem cell factor, Flk2/Flt3 ligand, thrombopoietin, IL-6, and soluble IL-6 receptor

Here, we demonstrate a significant ex vivo expansion of human hematopoietic stem cells capable of repopulating in NOD/SCID mice. Using a combination of stem cell factor (SCF), Flk2/Flt3 ligand (FL), thrombopoietin (TPO), and a complex of IL-6 and soluble IL-6 receptor (IL-6/sIL-6R), we cultured cord blood CD34(+) cells for 7 days and transplanted these cells into NOD/SCID mice. Bone marrow engraftment was judged successful when recipient animals contained measurable numbers of human CD45(+) cells 10-12 weeks after transplantation. When cells were cultured with SCF+FL+TPO+IL-6/sIL-6R, 13 of 16 recipients were successfully engrafted, and CD45(+) cells represented 11.5% of bone marrow cells in engrafted recipients. Cells cultured with a subset of these factors were less efficiently engrafted, both as measured by frequency of successful transplantations and prevalence of CD45(+) cells. In animals receiving cells cultured with all 4 factors, human CD45(+) cells represented various lineages, including a large number of CD34(+) cells. The proportion of CD45(+) cells in recipient marrow was 10 times higher in animals receiving these cultured cells than in those receiving comparable numbers of fresh CD34(+) cells, and the expansion rate was estimated at 4.2-fold by a limiting dilution method. Addition of IL-3 to the cytokine combination abrogated the repopulating ability of the expanded cells. The present study may provide a novel culture method for the expansion of human transplantable hematopoietic stem cells suitable for clinical applications.

Enhancing effects of co-transduction of both human erythropoietin receptor and c-kit cDNAs into hematopoietic stem/progenitor cells from cord blood on proliferation and differentiation of erythroid progenitors

Steel factor (SLF) and erythropoietin (Epo) play critical roles in erythropoiesis. To evaluate interactive effects of Epo and SLF receptors (R) in erythropoiesis, CD34+ and CD34 cord blood cells were transduced with human EpoR and c-kit cDNAs by retroviral mediated gene transfer. Erythroid (BFU-E) colonies derived from CD34+ or CD34 cells transduced with either the EpoR or c-kit gene were significantly increased in the presence of interleukin (IL)-3, granulocyte-macrophage colony-stimulating factor (GM-CSF), Epo, and different concentrations of SLF compared with that from mock transduced cells. This number was further enhanced by co-transduction of both genes. Enhancement was more apparent in the absence of SLF. Cell numbers in individual erythroid colonies were also significantly increased in cells transduced with both genes compared with cells transduced with a single gene. Short-term liquid culture showed that ex vivo expansion for five days and numbers of CD34+CD71+ cells in expanded cells from single CD34 cells co-transduced with both EpoR and c-kit genes were increased compared with those of EpoR or c-kit-transduced cells. These results demonstrate that co-transduction of both c-kit and EpoR enhances the proliferative capacity of erythroid progenitors under cytokine stimulation above that of single-gene transduced cells.