Thy-1 expression is linked to functional properties of primitive hematopoietic progenitor cells from human umbilical cord blood

We have previously shown that the most primitive human hematopoietic cells are included within a cell subpopulation expressing high levels of CD34 and low or undetectable levels of CD45RA and CD71. In this study, cord blood cells with this phenotype were sorted and further separated based on their expression on the Thy-1 antigen. The proliferation and differentiation of the purified cell fractions in response to a mixture of hematopoietic cytokines was analyzed in serum- and stroma-free liquid cultures. Thy-1+ cells (25% of CD34+ CD45RAlo CD71lo cells) were particularly enriched for high proliferative potential colony-forming cells (HPP-CFC; up to 45% of the clonogenic cells), whereas Thy-1- cells were enriched for multipotential colony- forming cells (CFU-MIX; up to 46% of the clonogenic cells). When both subpopulations were cultured in serum-free liquid cultures supplemented with a cytokine mixture that included steel factor, interleukin-6 (IL- 6), granulocyte-macrophage colony-stimulating factor (GM-CSF)/IL-3 fusion protein, M-CSF, G-CSF, and erythropoietin, Thy-1+ cells showed a much higher numerical expansion of CD34+ cells (30,000-fold) and colony- forming cells (4,700-fold) than was observed in cultures initiated with Thy-1- cells (900-fold increase in CD34+ cell numbers and 241-fold increase in CFC numbers). Cells coexpressing CD34 and Thy-1 were only transiently expanded (up to 29-fold) and were not detected after day 22 of culture. When CD34+ CD45RAlo CD71lo Thy-1+ cells were cultured, either in semi-solid or liquid cultures, in the presence of anti-Thy-1 antibody, a significant reduction in progenitor cell numbers (particularly HPP-CFC) was observed. In contrast, CD34+ CD45RAlo CD71lo Thy-1- cells were not affected by anti-Thy-1. The results of this study indicate that Thy-1 is expressed on primitive cord blood progenitors with the highest in vitro proliferative potential, and further suggest that Thy-1 is involved in hematopoietic cell development, possibly by mediating a negative signal that results in inhibition of primitive cell proliferation.     

Cytokine-induced selective expansion and maturation of erythroid versus myeloid progenitors from purified cord blood precursor cells

To study the role of different cytokine combinations on the proliferation and differentiation of highly purified primitive progenitor cells, a serum-free liquid culture system was used in combination with phenotypic and functional analysis of the cells produced in culture. CD34+ CD45RAlo CD71lo cells, purified from umbilical cord blood by flow cytometry and cell sorting, were selected for this study because of their high content of clonogenic cells (34%), particularly multipotent progenitors (CFU-MIX, 12% of all cells). Four cytokine combinations were tested: (1) mast cell growth factor (MGF; a c-kit ligand) and interleukin-6 (IL-6); (2) MGF, IL-6, IL-3, and erythropoietin (Epo); (3) MGF, IL-6, granulocyte-macrophage colony- stimulating factor (GM-CSF)/IL-3 fusion protein (FP), macrophage colony- stimulating factor (M-CSF), and granulocyte-CSF (G-CSF); and (4) MGF, IL-6, FP, M-CSF, G-CSF, and Epo. Maximum numbers of erythroid progenitors (BFU-E, up to 55-fold increase) and mature erythroid cells were observed in the presence of MGF, IL-6, IL-3, and Epo, whereas maximum levels of myeloid progenitors (CFU-C, up to 70-fold increase) and mature myeloid cells were found in cultures supplemented with MGF, IL-6, FP, M-CSF, and G-CSF. When MGF, IL-6, FP, M-CSF, G-CSF, and Epo were present, maximum levels of both erythroid and myeloid progenitors and their progeny were observed. These results indicate that specific cytokine combinations can act directly on primitive hematopoietic cells resulting in significant expansion of progenitor cell numbers and influencing their overall patterns of proliferation and differentiation. Furthermore, the observations presented in this study suggest that the cytokine combinations used were unable to bias lineage commitment of multipotent progenitors, but rather had a permissive effect on the development of lineage-restricted clonogenic cells.     

The effect of interleukin-12 in ex-vivo expansion of human haemopoietic progenitors

Summary. We evaluated progenitor cell proliferation in cultures supplemented by different cytokine combinations in the presence or absence of IL-12. In cultures of low density cells, cytokine combinations including IL-12 were associated to a greater proliferation (up to 6.7 ± 2.5 CFU-GM fold expansion). However, in cultures of purified CD34⁺ cells the more efficient cytokine combination (147 ± 49 CFU-GM fold expansion) was SCF, IL-3, IL-11 and MlP-la, and the addition of IL-12 did not further enhance expansion of progenitors.
These results indicate that accessory cells, lost in CD34⁺ cell purification, could be in part responsible for IL-12 effect on progenitor cell proliferation. In CD34⁺ cell cultures the addition of IL-12 led to CD19 mRNA generation, suggesting that IL-12 acts on haemopoietic cells with both myeloid and lymphoid potential.     

Activation of phosphatidylinositol 3-kinase is important for erythropoietin-induced erythropoiesis from CD34(+) hematopoietic progenitor cells

OBJECTIVE: Several transducing molecules, including JAK2, STAT5, MAP kinases, phosphatidylinositol 3-kinase (PI3K), phospholipase C-gamma1, and PKC are activated by interaction between erythropoietin (EPO) and the EPO receptor. The aim of this was to examine the relative involvement of PI3K in the development of glycophorin A (GPA)(+) erythroid cells from normal hematopoietic progenitor cells. MATERIALS AND METHODS: CD34(+) hematopoietic progenitor cells or subpopulations obtained by FACS sorting were cultured in serum-free medium containing EPO with or without inhibitors for PI3K, p38, MEK, or PKC for various time periods before phenotypic analysis or detection of apoptosis by flow cytometry, cell cycle analysis, high-resolution tracking of cell division, Western blot analysis, or Akt kinase assay were performed. RESULTS: The PI3K inhibitor LY294002 completely counteracted the EPO-induced proliferation of CD34(+) progenitor cells and CD34(+)CD71(+)CD45RA(-) erythroid progenitors. LY294002 also highly suppressed the expanded erythropoiesis induced by the combined action of EPO and stem cell factor. The profound inhibitory effect of LY294002 on proliferation was caused by its induction of cell cycle arrest in the G(0)/G(1) phase of the cell cycle. Some cells acquired GPA expression before they went through cell division. This was completely blocked by LY294002, implying an inhibitory effect on maturation. In addition, LY294002 completely blocked the viability-enhancing effect of EPO in CD34(+)CD71(+)CD45RA(-) erythroid progenitors. LY294002 and various inhibitors of PKC completely suppressed the EPO-induced increase in the activity of Akt kinase, a direct downstream target of PI3K. CONCLUSIONS: Our results point to an important role for PI3K in mediating EPO-induced survival, proliferation, and possibly maturation of early erythroid progenitors.     

Disparate regulation of human fetal erythropoiesis by the microenvironments of the liver and bone marrow

The liver and the bone marrow (BM) are the major organs that support hematopoiesis in the human fetus. Although both tissues contain the spectrum of hematopoietic cells, erythropoiesis dominates the liver. Previous studies suggested that a unique responsiveness of fetal burst-forming units erythroid (BFU-E) to erythropoietin (EPO) obviates the need for cytokines with burst-promoting activity (BPA) in fetal erythropoiesis. This potential regulatory mechanism whereby fetal erythropoiesis is enhanced was further investigated. Fluorescence-activated cell sorting was used to isolate liver and BM progenitors based on their levels of CD34 and CD38 expression. The most mature population of CD34+ lineage (Lin-) cells was also the most prevalent of the three subpopulations and contained BFU-E responsive to EPO alone under serum-deprived conditions. Kit ligand (KL) also strongly synergized with EPO in stimulating the growth of these BFU-E. An intermediate subset of CD34++CD38+Lin- cells contained erythroid progenitors responsive to EPO alone, but also displayed synergism between EPO and KL, granulocyte-macrophage colony-stimulating factor (GM-CSF), or interleukin (IL)-3, demonstrating that erythroid progenitors that respond to cytokines with BPA do exist in fetal tissues as in the adult BM. Candidate stem cells (CD34++CD38-Lin- cells) did not respond to EPO. Synergisms among KL, GM-CSF, and IL-3, and to a lesser extent granulocyte colony-stimulating factor (G-CSF) and FLK-2/FLT-3 ligand (FL), supported the growth of primitive multipotent progenitors that became responsive to EPO. These data define the limits of EPO activity in fetal erythropoiesis to cells that express CD38 and demonstrate the potential for various cytokine interactions to be involved in regulating fetal erythropoiesis. Furthermore, a comparison of the responses of liver and BM erythroid progenitors revealed similarity in their responses to cytokines but a difference in the frequency of BFU-E among the three subpopulations examined. A higher frequency of BFU-E among the intermediate and late progenitor subsets in the liver indicates that regulatory factors acting on stem cells and their immediate progeny are partially responsible for the high content of erythropoiesis in the liver. These data implicate a critical role for the microenvironments of the liver and BM in regulating the disparate levels of erythropoiesis in these tissues.     

Constitutive HOXA5 expression inhibits erythropoiesis and increases myelopoiesis from human hematopoietic progenitors.

The role of the homeobox gene HOXA5 in normal human hematopoiesis was studied by constitutively expressing the HOXA5 cDNA in CD34(+) and CD34(+)CD38(-) cells from bone marrow and cord blood. By using retroviral vectors that contained both HOXA5 and a cell surface marker gene, pure populations of progenitors that expressed the transgene were obtained for analysis of differentiation patterns. Based on both immunophenotypic and morphological analysis of cultures from transduced CD34(+) cells, HOXA5 expression caused a significant shift toward myeloid differentiation and away from erythroid differentiation in comparison to CD34(+) cells transduced with Control vectors (P =.001, n = 15 for immunophenotypic analysis; and P <.0001, n = 19 for morphological analysis). Transduction of more primitive progenitors (CD34(+)CD38(-) cells) resulted in a significantly greater effect on differentiation than did transduction of the largely committed CD34(+) population (P =.006 for difference between HOXA5 effect on CD34(+) v CD34(+)CD38(-) cells). Erythroid progenitors (burst-forming unit-erythroid [BFU-E]) were significantly decreased in frequency among progenitors transduced with the HOXA5 vector (P =.016, n = 7), with no reduction in total CFU numbers. Clonal analysis of single cells transduced with HOXA5 or control vectors (cultured in erythroid culture conditions) showed that HOXA5 expression prevented erythroid differentiation and produced clones with a preponderance of undifferentiated blasts. These studies show that constitutive expression of HOXA5 inhibits human erythropoiesis and promotes myelopoiesis. The reciprocal inhibition of erythropoiesis and promotion of myelopoiesis in the absence of any demonstrable effect on proliferation suggests that HOXA5 diverts differentiation at a mulitpotent progenitor stage away from the erythroid toward the myeloid pathway.     

Anemia of chronic disease in rheumatoid arthritis is associated with increased apoptosis of bone marrow erythroid cells: improvement following anti-tumor necrosis factor-alpha antibody therapy

Circumstantial evidence has implicated tumor necrosis factor alpha (TNF-alpha) in the pathogenesis of anemia of chronic disease (ACD) in rheumatoid arthritis (RA). We investigated the role of TNF-alpha in erythropoiesis of patients with active RA (n = 40) and the effect of anti-TNF-alpha antibody administration (cA2). Patients with RA had lower numbers of CD34+/CD71+ and CD36-/glycophorin A+ (glycoA+) bone marrow (BM) cells and increased proportions of apoptotic cells within the CD34+/CD71+ and CD36+/glycoA+ cell compartments, compared to healthy controls (n = 24). Erythroid burst-forming units (BFU-Es) obtained by BM mononuclear or purified CD34+ cells were significantly lower in RA patients compared to controls. These abnormalities were more pronounced among patients with ACD. Increased TNF-alpha levels in patient long-term BM culture supernatants inversely correlated with BFU-Es and hemoglobin levels and positively with the percentage of apoptotic CD34+/CD71+ and CD36+/glycoA+ cells. Following cA2 therapy, a normalization was documented in the number of CD34+/CD71+ and CD36-/glycoA+ cells, the number of BFU-Es, and the proportion of apoptotic CD34+/CD71+ and CD36+/glycoA+ cells, which was associated with a significant increase in hemoglobin levels compared to baseline. Recovery from anemia was more prominent in patients with ACD. The exogenous addition of an anti-TNF-alpha antibody in the cultures increased BFU-E number in patients prior to cA2 treatment but not after treatment, further substantiating the inhibitory role of TNF-alpha on patients' erythropoiesis. We conclude that TNF-alpha-mediated apoptotic depletion of BM erythroid cells may account for ACD in RA and that cA2 administration may ameliorate ACD in these patients by down-regulating the apoptotic mechanisms involved in erythropoiesis.     

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.     

PI3K/Akt-dependent Epo-induced signalling and target genes in human early erythroid progenitor cells

Erythropoietin (Epo) is the major regulator of differentiation, proliferation and survival of erythroid progenitors, but the Epo-induced changes in gene expression that lead to these effects are not fully understood. The aim of this study was to examine how Epo, via activation of phosphatidylinositol 3-kinase (PI3K)/Akt, exerts its role in the development of erythroid progenitors from CD34+ cells, and to identify early Epo target genes in human erythroid progenitors. In CD34+ progenitor cells, Epo alone was able to induce cell cycle progression as demonstrated by upregulation of cyclin D3, E and A leading to hyperphosphorylation of the retinoblastoma protein (RB). These effects were completely counteracted by the PI3K inhibitor LY294002. Furthermore, enforced expression of an activated form of Akt kinase highly augmented Epo-induced erythropoiesis. Fluorescent-activated cell sorting (FACS)-sorted CD34+CD71+CD45RA-GPA- erythroid progenitors stimulated with Epo in the presence or absence of LY294002 were subjected to gene expression profiling. Several novel target genes of Epo were identified, and the majority were regulated in a PI3K-dependent manner, including KIT (CD117) and CDH1 (E-cadherin). FACS analysis of Epo-stimulated erythroid progenitors showed that the increased mRNA expression of KIT and CDH1 was accompanied by an induction of the corresponding proteins CD117 and E-cadherin.     

Basic fibroblast growth factor-stimulated ex vivo expansion of haematopoietic progenitor cells from human placental and umbilical cord blood

We investigated whether basic fibroblast growth factor (bFGF) is effective in inducing ex vivo expansion of CD34+ haematopoietic progenitor cells derived from human placental and umbilical cord blood. bFGF significantly promoted the clonal growth of various haematopoietic progenitor cells, including granulocyte-macrophage colony-forming units (CFU-GM), mixed colony-forming units (CFU-Mix) and megakaryocyte colony-forming units (CFU-Meg) under semisolid culture conditions, with an optimal bFGF concentration of 30 ng/ml. CD34+ cells were then cultured in serum-free liquid medium containing various combinations of early-acting cytokines, including thrombopoietin (TPO), stem cell factor (SCF), interleukin 3 (IL-3) and flt3-ligand (FL), with or without bFGF, for 6 and 12 d. Without bFGF, TPO + IL-3, TPO + SCF + FL and TPO +SCF + IL-3 + FL dramatically increased the total numbers of erythroid progenitors, CFU-GM and CFU-Mix by d 12 of culture respectively. However, the addition of bFGF did not promote further proliferation of these progenitors, except for the erythroid progenitors, by d 6 when stimulated with all four cytokines. In contrast, total CFU-Meg numbers were approximately doubled when these cultures were supplemented with bFGF, producing 100- to 120-fold increases compared with the baseline control cultures. These results suggest that bFGF is effective in supporting the generation of megakaryocytic progenitor cells during ex vivo expansion.     

Modulation of erythropoiesis and myelopoiesis by exogenous erythropoietin in human long-term marrow cultures

In spite of their ability to support myelopoiesis for several months, human long-term marrow cultures (LTMC) are unable to sustain the production of mature erythroid cells for greater than 4 weeks. Because this preference correlates with the presence of myeloid growth factors and possible absence of erythroid factors in LTMC, we studied the effects of the erythroid growth and differentiation factor erythropoietin (Epo) on both erythropoiesis and myelopoiesis in human LTMC. Either natural or recombinant Epo was added weekly to LTMC for 10 weeks, and total cell number, numbers of hemopoietic progenitors (mixed lineage colony-forming units, CFU-MIX; erythroid burst-forming units, BFU-E; erythroid CFU, CFU-E; granulocyte-macrophage CFU (CFU-GM); granulocyte CFU, CFU-G; and macrophage CFU, CFU-M), erythroblasts (early and late), granulocytes, and macrophages were quantitated separately in the adherent and nonadherent layers of the cultures. In the absence of Epo, mature erythroid cells disappeared within the first 3-4 weeks, whereas in cultures supplemented with Epo, erythropoiesis was supported for up to 8 weeks. Results indicate that erythroid maturation is blocked at the BFU-E stage and that exogenous Epo may act on a mature subpopulation of BFU-E located in the nonadherent fraction of the cultures, promoting its maturation into CFU-E, which in turn develop into erythroblasts. However, despite Epo supplementation, erythropoiesis was not restored to in vivo proportions, suggesting that additional factors or conditions necessary for erythropoiesis are lacking in LTMC. Interestingly, we found that exogenous Epo reduced the numbers of presumably more mature (nonadherent) myeloid CFU (CFU-C), granulocytes, and macrophages compared to controls and did not alter the levels of any of the most primitive hemopoietic progenitors measured (CFU-MIX, adherent BFU-E, and adherent CFU-C). Thus the data show that exogenous Epo modulates hemopoiesis in human LTMC, enhancing erythropoiesis and suppressing myelopoiesis, but that its effects appear limited to modulating levels of the nonadherent (more mature) progenitors, leaving the numbers of the adherent (immature) progenitor cells unchanged.     

Delineation of T-progenitor cell activity within the CD34+ compartment of adult bone marrow

T-cell production is largely dependent on the presence of a thymus gland where CD34+ precursors mature into T lymphocytes. Prethymic stages of T-cell development are less defined. Therefore, this study aims to delineate T-progenitor cell potential within the CD34+ Lineage-- (Lin-) cell compartment of adult bone marrow (ABM). Fractionation of CD34+ Lin- ABM cells with CD45RA, Thy-1, CD38, and HLA-DR failed to absolutely segregate T-cell reconstituting ability, indicating broad distribution of T-progenitor cell potential. Titration experiments showed that low numbers of CD34+ Lin- CD45RA+ (RA+) cells had greater thymus repopulating ability than CD34+ Lin- CD45RA- cells (RA-). The great majority (> 95%) of RA+ cells expressed CD38, HLA-DR and 70% to 90% of RA+ cells lacked Thy-1 surface expression. RA+ cells contained colony-forming unit granulocyte-macrophage (CFU-GM) progenitor cells but were depleted of erythroid potential, did not provide hematopoietic reconstitution of human bone fragments implanted into SCID mice, and did not efficiently maintain CD34+ cells with secondary clonogenic potential in bone marrow cultures. Thus, RA+ cells are oligopotent (nonprimitive) CD34+ progenitors with T-cell reconstituting ability. In contrast, these same assays indicated that CD34+ Lin- CD45RA- cells (RA- cells) comprised hematopoietic stem cells (HSC) with primitive multilineage (T, B, myeloid, and erythroid) hematopoietic potential. It was confirmed that HSC-containing populations, such as CD34+ Lin- CD45RA- Thy-1+ cells had thymus repopulating ability. Culture of RA- cells on murine bone marrow stromal cells in the presence of interleukin (IL)-3, IL-6, and leukemia inhibitory factor (LIF) generated CD34+ CD45RA+ progeny engrafting in a secondary severe combined immunodeficiency (SCID)-hu thymus assay. Altogether, our results underscore the fact that T-cell reconstituting potential can be dissociated from HSC activity. Furthermore, we speculate that HSC might develop into the T lineage indirectly, via differentiation into an intermediate oligopotent CD34+ CD45RA+ stage. Finally, T-progenitor cells can be cultured in vitro.     

Enrichment of CD34 (My10)-positive myeloid and erythroid progenitors from human marrow and their growth in cultures supplemented with recombinant human granulocyte-macrophage colony-stimulating factor

Myeloid and erythroid progenitor cells were enriched from human marrow by selecting CD34-positive (CD34 + ve) cells, labeled with the My10 (HPCA-1) antibody, using a fluorescence-activated cell sorter. Seventy-one percent of CD34 + ve cells were blasts and most of these were too primitive to be identified by standard morphological criteria. On average, 9.5% of CD34 + ve cells formed clones after 14 days of culture in semisolid medium supplemented with erythropoietin and medium conditioned by 5637 bladder carcinoma cells. Over 2.5% of CD34 + ve cells were day-14 myeloid colony-forming cells and 2.4% were erythroid colony (burst)-forming progenitors. The remaining progenitors formed myeloid and erythroid clusters. A subpopulation of day-14 myeloid colony-forming cells failed to respond to recombinant human granulocyte-macrophage colony-stimulating factor (rhuGM-CSF) after accessory cells were removed during enrichment, so it appears that this factor can induce myeloid growth indirectly as well as directly. Recombinant human GM-CSF also supported erythroid colony-formation in cultures of CD34 + ve cells, which suggests that this hemopoietin may act directly on erythroid progenitors.     

Preclinical ex vivo expansion of G-CSF-mobilized peripheral blood stem cells: effects of serum-free media, cytokine combinations and chemotherapy

OBJECTIVES: Ex vivo expansion of granulocyte-colony stimulating factor (G-CSF)-mobilized peripheral blood stem cells (PBSC) is a promising approach for overcoming the developmental delay of bone marrow (BM) reconstitution after transplantation. This project investigated the effects of culture duration, serum-free media, cytokine combinations, and chemotherapy on the outcomes of expansion. METHODS: Enriched CD34+ cells were cultured for 8 or 10 d in serum-free media (QBSF-60 or X-Vivo 10) and four combinations of cytokines consisting of recombinant human pegylated-megakaryocyte growth and development factor, stem cell factor, flt-3 ligand, G-CSF, interleukin (IL)-6, platelet-derived growth factor (PDGF), and IL-1beta. RESULTS: Eight days of culture in QBSF-60 significantly supported efficient expansions of CD34+ cells, CD34+ CD38- cells, colony-forming units (CFU) of myeloid, erythroid, megakaryocytic, and mixed lineages to 3.76-, 14.4-, 28.3-, 24.0-, 38.1-, and 15.7-fold, respectively. Whilst PDGF or IL-6 enhanced the expansion of early, myeloid, and erythroid progenitors, IL-1beta specifically promoted the megakaryocytic lineage. Engraftment of human CD45+ cells were detectable in all non-obese diabetic/severe-combined immunodeficient mice transplanted with expanded PBSC from donor samples, being 5.80 +/- 3.34% of mouse BM cells. The expansion and engraftment capacity of CD34+ cells from subjects postchemotherapy were significantly compromised across the panel of progenitor cells. CONCLUSION: Our results provided an optimized protocol for PBSC expansion, applicable to ameliorating neutropenia and thrombocytopenia in post-BM transplant patients by the prompt provision of progenitor cells. For postchemotherapy patients, expansion products might provide committed progenitors for improving short-term engraftment, but not self-renewable stem cells.     

Purification, amplification and characterization of a population of human erythroid progenitors

In humans, studies of the erythroid cell lineage are hampered by difficulties in obtaining sufficient numbers of erythroid progenitors. In fact, these progenitors in bone marrow or peripheral blood are scarce and no specific antibodies are available. We describe a new method which allows proliferation in liquid culture of large numbers of pure normal human erythroid progenitors. CD34+ cells were cultured for 7 d in serum-free conditions with the cytokine mixture interleukin (IL)-3/IL-6/stem cell factor (SCF). This resulted in cell expansion and the appearance of a high proportion of CD36+ cells which were purified on day 7. Methylcellulose clones from these cells were composed of 96.6% late BFU-E and 3.4% CFU-GM. These CD36+ cells could be recultured with the same cytokine mixture plus or minus erythropoietin (Epo) for a further 2-7 d. In both conditions further amplification of CD36+ cells was observed, but Epo induced a more dramatic cell expansion. Glycophorin-positive mature cells appeared only in the presence of Epo, and terminal red cell differentiation was observed after 7 d of secondary culture. Cells obtained from adult CD34+ progenitors mostly contained adult haemoglobin, whereas cord blood-derived cells contained equal proportions of adult and fetal haemoglobin. Activation of STAT5 and tyrosine phosphorylation of the Epo receptor and JAK2 were observed after Epo stimulation of these cells. This new method represents a straightforward alternative to the procedures previously described for the purification of normal erythroid progenitors and is useful in the study of erythropoietic regulation.     

Flow cytometric and functional characterization of AC133+ cells from human umbilical cord blood

AC133+ cells may represent an alternative source of transplantable haemopoietic progenitor cells to CD34+ cells. Here, we have addressed the characterization of umbilical cord blood (UCB) AC133+ cells and compared their immunophenotypic and functional features with those of UCB CD34+ cells. UCB AC133+ and CD34+ cell fractions were purified by magnetic cell sorting, analysed by flow cytometry, tested for their content in blast cell colony-forming units (CFU-Bl), erythroid and granulocyte-macrophage colony-forming units before and after expansion in the presence of various haemopoietic growth factor combinations. Median AC133+ cell yield was 62.3%, and median AC133+ population purity was 97.9%. AC133+ cells were found to contain significantly more CFU-Bl than CD34+ cells; furthermore, the replating efficiency, i.e. the number of CFU-Bl capable of generating secondary colonies, was higher in the former than in the latter cells. Both AC133+ and CD34+ cells displayed an increased ability to give rise to committed progenitors after 7-day expansion in liquid cultures. These data suggest that the AC133+ cell subset is a heterogeneous pool of immature and more differentiated cells that can be maintained and expanded in well-defined culture conditions. In comparison with CD34+ cells, UCB AC133+ cells appear to contain a higher number of early haemopoietic progenitors.     

CD64/Fc gamma RI is a granulo-monocytic lineage marker on CD34+ hematopoietic progenitor cells

The aim of this study was to identify markers specific for granulo- monocytic commitment of progenitor cells. Large panels of antibodies were screened for selective staining of subsets of CD34+ cells from fetal and adult bone marrow. Flow cytometric analysis showed that CD64/fc gamma RI was undetectable on noncommitted progenitor cells (CD34++, CD38-/lo, HLA-DR+) and expressed on a subset of lineage- committed progenitors (CD34+, CD38+) with higher mean orthogonal light scatter than the remaining CD34+ cells. The CD34+, CD64+ cells were CD19- and the majority were CD45RA+, CD71lo, suggesting that CD64 recognized granulomonocytic progenitor cells. Specificity of CD64 for the granulo-monocytic lineage was shown by demonstrating that colonies arising from CD34+, CD64+ cells consisted of 98% +/- 2% colony-forming unit-granulocyte-macrophage (CFU-GM) in semisolid medium containing stem cell factor (SCF), interleukin-3 (IL-3), IL-6, granulocyte- macrophage colony-stimulating factor (GM-CSF), and erythropoietin (EPO). In contrast, 63% +/- 15% of the colonies from the CD34+, CD64- cells were burst-forming unit-erythroid/colony-forming unit-erythroid (BFU-E/CFU-E). Furthermore, four-color immunofluourescence and cell sorting was used to analyze the progeny of cells cultured in liquid medium containing identical cytokines as used in the semisolid medium. This analysis showed that CD34+, CD64+ cells gave rise to 83% +/- 10% granulo-monocytic cells whereas progeny of the CD34+, CD64- cells contained 81% +/- 11% erythroid cells. Neutrophils as well as basophils and monocytes/macrophages were present in the cultures from CD34+, CD64+ cells, showing that this population contains progenitors of most types of granulo-monocytic cells. Two widely used myeloid markers, CD13 and CD33, were not myeloid-specific, because both were clearly positive on noncommitted progenitor cells. Of 40 antigens tested, CD15 was the only other marker fulfilling the criteria of a myeloid-specific marker. However, at concentrations of CD15 that did not induce aggregation, CD15+ cells constituted less than 50% of the CD34+, CD64+ cells. Furthermore, the CD34+, CD15- cells showed more than 50% higher CD34 mean fluorescence intensity than the CD64+, CD15+ cells, indicating that CD64 appears earlier than CD15 during differentiation. Thus, among a large number of antigens screened, CD64 was the most useful for the identification and purification of granulo-monocytic progenitor cells.     

In vitro proliferation and differentiation of erythroid progenitors from patients with myelodysplastic syndromes: evidence for Fas-dependent apoptosis

Erythropoiesis results from the proliferation and differentiation of pluripotent stem cells into immature erythroid progenitors (ie, erythroid burst-forming units (BFU-Es), whose growth, survival, and terminal differentiation depends on erythropoietin (Epo). Ineffective erythropoiesis is a common feature of myelodysplastic syndromes (MDS). We used a 2-step liquid-culture procedure to study erythropoiesis in MDS. CD34(+) cells from the marrow of patients with MDS were cultured for 10 days in serum-containing medium with Epo, stem cell factor, insulin-like growth factor 1, and steroid hormones until they reached the proerythroblast stage. The cells were then placed in medium containing Epo and insulin for terminal erythroid differentiation. Numbers of both MDS and normal control cells increased 10(3) fold by day 15. However, in semisolid culture, cells from patients with refractory anemia (RA) with ringed sideroblasts and RA or RA with excess of blasts produced significantly fewer BFU-Es than cells from controls. Fluorescence in situ hybridization analysis of interphase nuclei from patients with chromosomal defects indicated that abnormal clones were expanded in vitro. Epo-signaling pathways (STAT5, Akt, and ERK 1/2) were normally activated in MDS erythroid progenitors. In contrast, apoptosis was significantly increased in MDS cells once they differentiated, whereas it remained low in normal cells. Fas was overexpressed on freshly isolated MDS CD34(+) cells and on MDS erythroid cells throughout the culture. Apoptosis coincided with overproduction of Fas ligand during the differentiation stage and was inhibited by Fas-Fc chimeric protein. Thus, MDS CD34(+)-derived erythroid progenitors proliferated normally in our 2-step liquid culture with Epo but underwent abnormal Fas-dependent apoptosis during differentiation that could be responsible for the impaired erythropoiesis.     

Cytogenetically aberrant cells in the stem cell compartment (CD34+lin-) in acute myeloid leukemia

Leukemia may be viewed as a clonal expansion of blast cells; however, the role of primitive cells and/or stem cells in disease etiology and progression is unclear. We investigated stem cell involvement in leukemia using fluorescence in situ hybridization (FISH), immunofluorescence labeling of hematopoietic subpopulations, and flow cytometric analysis/sorting to discriminate and quantify cytogenetically aberrant stem cells in 12 acute myeloid leukemia (AML) and three myelodysplastic (MDS) specimens. Flow cytometric analysis and sorting were used to discriminate and collect a primitive subpopulation enriched in stem cells expressing CD34+ and lacking CD33 and CD38 (CD34+lin-). A subpopulation containing progenitors and differentiating myeloid cells expressed CD34, CD33, and CD38 (CD34+lin+). Nine specimens contained less than 10% CD34+ cells and, thus, were considered to be CD34- leukemias. Mature lymphoid, myeloid, and erythroid subpopulations were sorted on the basis of antigen-linked immunofluorescence. Cytogenetically aberrant cells in sorted subpopulations were identified using FISH with enumerator probes selected on the basis of diagnosis karyotype. Cytogenetically aberrant CD34+lin- cells were present at frequencies between 9% and 99% in all specimens. CD34+lin- cytogenetically aberrant cells comprised between 0.05% and 11.9% of the marrow/blood specimens. Cytogenetically aberrant CD34+lin+ cells constituted 0.01% tp 56% of the marrow/blood population. These data demonstrate that aberrant cells are present in primitive CD34+ stem cell compartments, even in CD34- leukemias. Stem cell involvement was confirmed further by sorting lymphoid and erythroid subpopulations from eight specimens in which the predominant leukemic population lacked lymphoid/erythroid differentiation markers. In these specimens, as well as in multiple lineages, suggests involvement of a cell(s) with multilineage capabilities. The ability of aberrant CD34+lin- stem cells to contribute to clonal and compartment expansion within immunofluorescently defined subpopulations was evaluated to explore the functional phenotype of aberrant CD34+lin- cells. Analysis of compartment size and aberrant cell frequency suggests that frequency of cytogenetically aberrant stem cells is uncoupled from compartment size. These data suggest that cytogenetically aberrant cells in the primitive compartment show varying abilities to expand primitive compartments. Cytogenetically aberrant CD34+lin- cells precede the blast subpopulation in hierarchical maturation and may in some cases by considered preleukemic, requiring maturation or additional mutations before transformation (eg, compartmental expansion) occurs.     

CD34+/CD33- cells reselected from macrophage inflammatory protein 1 alpha+interleukin-3--supplemented "stroma-noncontact" cultures are highly enriched for long-term bone marrow culture initiating cells

Human hematopoietic stem cells are thought to express the CD34 stem cell antigen, low numbers of HLA-DR and Thy1 antigens, but no lineage commitment antigens, CD38, or CD45RA antigens. However, fluorescence- activated cell sorted CD34+ subpopulations contain not more than 1% to 5% primitive progenitors capable of initiating and sustaining growth in long-term bone marrow culture initiating cells (LTBMC-ICs). We have recently shown that culture of fresh human marrow CD34+/HLA-DR- cells separated from a stromal layer by a microporous membrane ("stroma- noncontact" culture) results in the maintenance of 40% of LTBMC-ICs. We hypothesized that reselection of CD34+ subpopulations still present after several weeks in stroma-noncontact cultures may result in the selection of cells more highly enriched for human LTBMC-ICs. Fresh marrow CD34+/HLA-DR- cells were cultured for 2 to 3 weeks in stroma- noncontact cultures. Cultured progeny was then sorted on the basis of CD34, HLA-DR, or CD33 antigen expression, and sorted cells evaluated for the presence of LTBMC-ICs by limiting dilution analysis. We show that (1) LTBMC-ICs are four times more frequent in cultured CD34+/HLA- DR- cells (4.6% +/- 1.7%) than in cultured CD34+/HLA-DR- cells (1.3% +/- 0.4%). This suggests that HLA-DR antigen expression may depend on the activation status of primitive cells rather than their lineage commitment. We then sorted cultured cells on the basis of the myeloid commitment antigen, CD33. (2) These studies show that cultured CD34+/CD33- cells contain 4% to 8% LTBMC-ICs, whereas cultured CD34+/CD33+bright cells contain only 0.1% +/- 0.03% LTBMC-ICs. Because LTBMC-ICs are maintained significantly better in stroma-noncontact cultures supplemented with macrophage inflammatory protein 1 alpha (MIP- 1 alpha) and interleukin-3 (IL-3) (Verfaillie et al, J Exp Med 179:643, 1994), we evaluated the frequency of LTBMC-ICs in CD34+/CD33- cells present in such cultures. (3) CD34+/CD33- cells present in MIP-1 alpha + IL-3-supplemented cultures contain up to 30% LTBMC-ICs. The increased frequency of LTBMC-ICs in cultured CD34+ subpopulations may be the result of terminal differentiation of less primitive progenitors, loss of cells that fail to respond to the culture conditions or recruitment of quiescent LTBMC-ICs. The capability to select progenitor populations containing up to 30% LTBMC-ICs should prove useful in studies examining the growth requirements, self-renewal, and multilineage differentiation capacity of human hematopoietic stem cells at the single-cell level.