The fusion protein MEN 11303 (granulocyte-macrophage colony stimulating factor/erythropoietin) acts as a potent inducer of erythropoiesis

OBJECTIVE: A fusion protein made of human granulocyte-macrophage colony-stimulating factor (GM-CSF) and erythropoietin (EPO), referred to as MEN 11303, has been tested for biologic activity using mobilized CD34(+) cells. METHODS AND RESULTS: MEN 11303 and a combination of GM-CSF/EPO produced the same amount of colony-forming unit granulocyte-macrophage (CFU-GM), of burst-forming unit erythroid (BFU-E), and of multipotent CFU-mixed. After 15 days, liquid cultures of CD34(+) cells exposed to MEN 11303 yielded a total cell number larger than that obtained with an equimolar mixture of GM-CSF and EPO, with a clear prevalence of cells exhibiting an erythroid phenotype. A colony-forming cell assay established from CD34(+) cells precultured with MEN 11303 for 7 days yielded a greater amount of BFU-E than GM-CSF/EPO combination. Exposing CD34(+) cells to MEN 11303 for 7 days in liquid culture resulted in higher recoveries of cells expressing a comparatively less differentiated hematopoietic phenotype and of long-term culture initiating cells. A cell-based binding-competition assay using the human EPO-receptor (EPO-R) transfected murine Ba/F3EPOR cell line showed that MEN 11303 bound to EPO-R with a sixfold lower affinity but induced a more sustained receptor phosphorylation. MEN 11303 supported the growth of Ba/F3EPOR cells more efficiently than EPO and remained detectable in the spent culture medium for a longer time. CONCLUSIONS: MEN 11303 and the combination of GM-CSF/EPO are equally potent in recruiting hematopoietic progenitors into cycle, but the fusion protein is superior in promoting the expansion of committed erythroid percursors. Primitive hematopoiesis is less affected by MEN110303 than GM-CSF/EPO combination. Part of these effects may reflect the peculiar interaction of the EPO moiety of MEN 11303 with the EPO-R.     

Porcine brain microvascular endothelial cells support the in vitro expansion of human primitive hematopoietic bone marrow progenitor cells with a high replating potential: requirement for cell-to-cell interactions and colony-stimulating factors

Primary autologous as well as allogeneic and xenogeneic stroma will support human stem cell proliferation and differentiation for several months. In the present study, we investigated the capacity of porcine microvascular endothelial cells (PMVECs) together with combinations of cytokines (granulocyte-macrophage colony-stimulating factor [GM-CSF] + stem factor [SCF], interleukin-3 [IL-3] + SCF + IL-6, and GM-CSF + IL-3 + SCF + IL-6) to support the expansion and development of purified human CD34+ bone marrow cells. In short-term cultures (7 days), the greatest expansion of nonadherent hematopoietic cells and clonogenic progenitors was seen with CD34+ cells in direct contact with PMVEC monolayers (PMVEC contact), followed by PMVEC noncontact and liquid suspension cultures, respectively. Maximal expansion of nonadherent cells (42-fold) and total CD34+ cells (12.6-fold) occurred in PMVEC contact cultures treated with GM-CSF + IL-3 + SCF + IL-6, with similar increases in the number of granulocyte-macrophage colony-forming units (CFU-GM), CFU-mix, erythroid burst-forming units (BFU-E), CFU-blast and CFU-megakaryocyte (CFU-Mk) progenitor cells. Moreover, the number of CD34+ CD38- and CD34+ CD38+ cells increased 148.1-fold and 8.0-fold, respectively. Replating studies show that cells from day 7 dispersed blast cell colonies generated on cytokine-treated PMVEC monolayers have a high replating potential for multilineage progenitor cells. In long- term PMVEC contact cultures, CD34+ cells seeded onto PMVEC monolayers with GM-CSF + IL-3 + SCF + IL-6 showed a total calculated expansion of over 5,000,000-fold of nonadherent cells over 35 days in culture. Maximal clonogenic cell production was observed at day 28, with 6,353- fold for total CFC and comparable increases for CFU-GM, CFU-mix, CFU- blast, BFU-E, and CFU-Mk. The total number of CD34+ cells increased 2,584-fold at day 28. Furthermore, the extended growth kinetics of these cultures indicates that these phenotypically primitive progenitor cells are also functionally expanded on PMVEC monolayers. These results support the hypothesis that direct contact with a PMVEC monolayer supports the initial expansion of hematopoietic progenitor cells with a high replating potential and, possibly, a more primitive phenotype (CD34+, CD34+/CD38-).     

In vitro growth of human fetal CD34+ cells in the presence of various combinations of recombinant cytokines under serum-free culture conditions

Summary. CD34⁺ cells were purified from midtrimester human fetal blood and adult bone marrow samples and seeded in serum-free fibrin-clot cultures in order to evaluate the number and the responsiveness to recombinant cytokines of pluripotent (CFU-GEMM), erythroid (BFU-E), megakaryocyte (BFU-meg and CFU-meg) and granulocyte/macrophage (CFU-GM) haemopoietic progenitor cells.
The number of the different haemopoietic progenitors/1 × 10³ CD34⁺ cells, except CFU-meg, was significantly higher in fetal blood than in adult bone marrow in cultures stimulated by any combination of cytokines including interleukin-3 (IL-3), granulocyte/macrophage colony stimulating factor (GM-CSF) or stem cell factor (SCF) plus erythropoietin (Epo). Nevertheless, whereas adult BFU-E showed a maximal growth in the presence of Epo plus IL-3 or Epo plus SCF, fetal BFU-E showed an optimal growth in the presence of Epo alone, the sensitivity of fetal BFU-E to suboptimal concentrations of Epo being approximately 10–15-fold higher than that of adult BFU-E. Addition of optimal concentrations of IL-3, GM-CSF or SCF, alone or in various combinations, to Epocontaining cultures induced a significant increase in both the number and size of fetal CFU-GEMM, and CFU-GM, and a parallel decrease of fetal BFU-E. Finally, SCF potently syner-gized with IL-3 in increasing the growth of both classes of fetal megakaryocyte progenitors, BFU-meg and CFU-meg.     

Recombinant human stem cell factor enhances the formation of colonies by CD34+ and CD34+lin- cells, and the generation of colony-forming cell progeny from CD34+lin- cells cultured with interleukin-3, granulocyte colony-stimulating factor, or granulocyte-macrophage colony-stimulating factor.

We tested the ability of recombinant human stem cell factor (SCF) to stimulate isolated marrow precursor cells to form colonies in semisolid media and to generate colony-forming cells (CFC) in liquid culture. SCF, in combination with interleukin-3 (IL-3), granulocyte-macrophage colony-stimulating factor (GM-CSF), or granulocyte colony-stimulating factor (G-CSF) caused CD34+ cells to form increased numbers of granulocyte-macrophage colonies (CFU-GM), and to form macroscopic erythroid burst-forming units (BFU-E) in the presence of IL-3, erythropoietin (Epo), and SCF. We tested isolated CD34+lin- cells, a minor subset of CD34+ cells that did not display antigens associated with lymphoid or myeloid lineages, and CD34+lin+ cells, which contain the vast majority of CFC, and found that the enhanced colony growth was most dramatic within the CD34+lin- population. CD34+lin- cells cultured in liquid medium containing SCF combined with IL-3, GM-CSF, or G-CSF gave rise to increased numbers of CFC. Maximal numbers of CFU-GM were generated from CD34+lin- cells after 7 to 21 days of culture, and required the presence of SCF from the initiation of liquid culture. The addition of SCF to IL-3 and/or G-CSF in cultures of single CD34+lin- cells resulted in increased numbers of CFC due to the proliferation of otherwise quiescent precursors and an increase in the numbers of CFC generated from individual precursors. These studies demonstrate the potent synergistic interaction between SCF and other hematopoietic growth factors on a highly immature population of CD34+lin- precursor cells.     

In vitro growth and quantification of early (CD33-/CD38-) myeloid progenitor cells: stem cell factor requirement and effects of previous chemotherapy.

BACKGROUND AND OBJECTIVE: All culture systems exploring the early (pre-CFU) hematopoietic compartment are generally complex, time-consuming and unsuitable for routine application. The aim of our study was to develop a stroma-free culture system to quantify early bone marrow (BM) myeloid progenitor cells. DESIGN AND METHODS: Low density, progenitor cell enriched BM cells underwent a double cytotoxic treatment with CD38 and CD33 monoclonal antibodies + rabbit complement, which depleted 99% of CFU-GM and BFU-E. Then they were cultured, both in agar and in limiting-dilution liquid culture, in the presence of 5637 cell line supernatant (containing GM-CSF, G-CSF and interleukin 1 ), stem cell factor (SCF) and interleukin 3 (IL3). RESULTS: The largest number (median 14.9 on 1x10(5) cells) and size (>50,000 cells) of myelomonocytic cell clones from CD33Eth /CD38Eth progenitors was reached after 3-4 weeks of liquid culture. SCF, but not IL3, was essential for that growth. The frequency of CD33-/ CD38- progenitors grown in liquid culture was approximately three times greater than the LTC-IC frequency in the same cell suspension. An average 93% of CD33-/CD38- progenitors displayed HLA-DR antigens and 43% generated secondary CFU-GM. In the BM of 9/10 patients, previously exposed to chemotherapy, CD33-/CD38- progenitor frequency was quite low (median 0.9 on 1x10(5) cells), in spite of normal cellularity and morphology and sustained disease remission. INTERPRETATION AND CONCLUSIONS: CD33-/CD38- progenitors can be grown and quantified in a stroma-free culture system in a relatively short time. The test can reveal long-lasting, subclinical BM damage induced by chemotherapy and could also be valuable for estimating the amount of early myeloid progenitors for transplantation purposes.     

Different behaviour of fresh and cultured CD34+ cells during immunomagnetic separation

In-vitro expansion of human cord blood (CB) cells could enhance peripheral blood recovery and ensure long-term engraftment of larger recipients in the clinical transplant setting. Enrichment of CD34+ cells using the MiniMACS column has been evaluated for the preparation of CB CD34+ cells before and after expansion culture. Repurification of CD34+ cells after culture would assist accurate phenotypic and functional analysis. When fresh CB mononuclear cells (MNC) were separated, the MACS positive (CD34+) fraction (90.1% pure) contained a mean (+/- SD, n = 5) of 93.0 +/- 8.0% of the eluted CD34+ cells, 99.6 +/- 0.7% of the CFU-GM and all of the eluted long-term culture-initiating cells (LTC-IC). Cord blood CD34+ cells were then cultured for 14 d with IL-3, IL-6, SCF, G-CSF and GM-CSF, each at 10 ng/ml. The total cell expansion was 2490 +/- 200-fold and the CD34+ cell expansion was 49 +/- 17-fold. The percentage of CD34+ cells present after expansion culture was 1.2 +/- 0.85%. When these cells were repurified on the MiniMACS column, the MACS positive fraction only contained 40.3 +/- 13.4% of the eluted CD34+ cells which was enriched for the mature CD34+ CD38+ subset, 24.4 +/- 8.8% of the eluted CFU-GM and 79.5 +/- 11.0% of the LTC-IC. The remaining cells were eluted in the MACS negative fraction. In conclusion, repurification of cultured CD34+ cells does not yield a representative population and many progenitors are lost in the MACS negative fraction. This can give misleading phenotypic and functional data. Cell losses may be important in the clinical setting if cultured cells were repurified for purging.     

Long-term culture-initiating cell expansion is dependent on frequent medium exchange combined with stromal and other accessory cell effects

Despite considerable effort, the expansion of long-term culture- initiating cells (LTC-ICs) in cultures of purified hematopoietic cells has not yet been achieved. In contrast, LTC-IC expansion has been attained in cultures of bone marrow mononuclear cells (MNC) using frequent medium exchange. The use of frequent medium exchange was, therefore, examined in cultures of CD34-enriched cells. In stromal- free, CD34-enriched cell cultures, medium exchange intervals ranging from 2 days to no feeding for 14 days gave similar results. Six different growth factor combinations, reported by other groups to give optimal expansion of CD34-enriched cells, were tested in comparison with the control combination of IL-3/GM-CSF/Epo/SCF. None of the combinations resulted in improved colony-forming unit-granulocyte macrophage (CFU-GM) expansion or LTC-IC maintenance, although two were equivalent. All stromal-free cultures resulted in loss of LTC-IC to half of input. Because of the limited effect of medium exchange and growth factor variations on CD34-enriched cell cultures, the effect of preformed stroma was next examined. Preformed stroma increased cell (3- fold), CFU-GM (5-fold), and LTC-IC (3-fold) output, but only when the medium was exchanged every other day. Under these conditions, the number of LTC-IC was maintained near input level. The lack of LTC-IC expansion in CD34-enriched cell cultures prompted experiments to examine the effect of cell purification. Parallel cultures were performed at CD34+lin- cell purities of 20%, 40%, 70%, and 95%, with each well containing exactly 4,000 CD34+lin- cells in addition to the CD34- accessory cells required to give the desired percentage. Also, MNC from the same source (approximately 2% CD34+lin-) were cultured at a concentration to give 4,000 CD34+lin- cells per well. As CD34+lin- cell purity was decreased from 95% to 2%, the output of cells, CFU-GM, and LTC-IC increased by threefold to fivefold. The loss of culture performance with purification was likely due to the removal of important accessory cells, because the levels of endogenously produced leukemia inhibitory factor and IL-6 were found to decline significantly with increasing CD34+lin- cell purity. In summary, preformed stroma abrogated the decrease in cell and CFU-GM output from cultured CD34- enriched cells and led to LTC-IC maintenance. In contrast, MNC inocula resulting in a growing stromal layer during the culture led to LTC-IC expansion (3.2-fold).(ABSTRACT TRUNCATED AT 400 WORDS)     

Murine M2-10B4 and SL/SL cell lines differentially affect the balance between CD34+ cell expansion and maturation

The ability of bone marrow stroma to modulate hematopoietic progenitor cell expansion is of considerable interest for gene transfer strategies and transplantation of limited stem cell numbers. We compared the capacity of 2 murine stromal cell lines to affect the balance between maturation and proliferation of human CD34+ cells in short-term expansion cultures. In 7-day serum-free cultures, cytokine-induced amplification of granulocyte-macrophage colony-forming cells (CFC-GM), erythroid burst-forming units (BFU-E), and total cells was significantly increased by the presence of genetically engineered Sl/Sl and M2-10B4 stromal cells in a 1:1 ratio (Sl/M2 cells) compared with stroma-free cultures (P < .05). Sl/M2 cultures generated 21-fold more mature CD15+ cells than stroma-free cultures, without further amplifying the number of CD34+ cells. The addition of serum led to a further increase of CFC-GM, total cells, and CD15+ cells, whereas BFU-E were no longer maintained. Pure Sl/Sl stromal layers were likewise superior to stroma-free cultures in expansion of CD34+ cells and total cells when serum was present. However, the differentiation of CD34+ cells was less pronounced in Sl/Sl cultures compared with Sl/M2 layers, as demonstrated by a lower content of CD15+ cells. Neutralization experiments revealed differential contributions of Flt3 ligand and thrombopoietin to the support of total cell and CFC expansion by Sl/M2 and Sl/Sl stromal feeders.     

A comparative study of the cell cycle status and primitive cell adhesion molecule profile of human CD34+ cells cultured in stroma-free versus porcine microvascular endothelial cell cultures

Porcine microvascular endothelial cells (PMVECs) plus cytokines support a rapid proliferation and expansion of human CD34+CD38- cells that are capable of multilineage engraftment within the bone marrow of a secondary host. CD34+CD38- cells contain the self-renewing, long-term culture-initiating cells (LTC-IC) that are ideal targets for retroviral gene transfer experiments. Previous experiments attempting retroviral infection of CD34+CD38- cells have failed partly because these cells do not enter cell cycle in response to cytokine combinations. In this study, we determined the cell cycle status and the cell adhesion molecule profile on purified CD34+ cells and the CD34+CD38- subset before and after ex vivo expansion on PMVECs. Purified human CD34+ cells were cocultured with PMVECs for 7 days in the presence of optimal concentrations of granulocyte/macrophage-colony-stimulating factor (GM-CSF) + interleukin (IL)-3 + IL-6 + stem cell factor (SCF) + Flt-3 ligand. The total CD34+ population and the CD34+CD38- subset increased 8.4- and 67-fold, respectively, with absolute increases in the number of colony-forming unit-granulocyte macrophage (CFU-GM) (28.2-fold), CFU-Mix (8.7 fold), and burst-forming unit-erythroid (BFU-E) (4.0-fold) progenitor cells. After 7 days of coculture with PMVECs, 44% of the CD34+CD38+ subset were found to be in G1, and 51% were in G2/S/M phase of the cell cycle. More remarkably, 53% of the CD34+CD38- subset were in G1, and 17% were in G2/S/M phase after 7 days of PMVEC coculture. In contrast, only 22% of the CD34+CD38- subset remaining after 7 days of stroma-free culture were in G1, and 6% were in G2/S/M phase. Despite the high level of cellular activation and proliferation induced by PMVEC coculture, the surface expression of adhesion molecules CD11a (LFA-1), CD11b, CD15s (sialyl-Lewis x), CD43, and CD44 (HCAM) on the total CD34+ population was maintained, and the surface expression of CD49d (VLA-4), CD54 (ICAM), CD58, and CD62L (L selectin) increased after ex vivo expansion. In contrast, CD34+ cells expanded on stroma-free cultures showed lower and more variable expression of CD62L and CD15s. These findings demonstrate that the primitive CD34+CD38- subset of marrow progenitor cells can be induced to enter cell cycle and can be significantly expanded ex vivo on a hematopoietic supportive microenvironment (PMVECs) while preserving the expression of cell adhesion molecules that may be important in stem cell homing and engraftment.     

A systematic strategy to optimize ex vivo expansion medium for human hematopoietic stem cells derived from umbilical cord blood mononuclear cells

OBJECTIVE: In this study, a serum-free, stroma-free, and chemically defined medium for hematopoietic stem cell (HSC) expansion was systematically developed and optimized using factorial design and the steepest ascent method. MATERIALS AND METHODS: Mononuclear cells (MNCs) were isolated from umbilical cord blood (UCB). HSCs were stimulated to proliferate ex vivo in the MNC culture system with variable serum substitutes, cytokines, and basal media according to experimental design. The expanded cells were assessed for cellular characteristics by surface antigen analysis, colony-forming cell assay (CFC assay), and long-term culture-initiating cell assay (LTC-IC assay). RESULTS: The optimal compositions of serum substitutes and the cytokine cocktail for HSC expansion in the MNC culture system were BIT (4 g/L BSA, 0.71 microg/mL insulin, and 27.81 microg/mL transferrin), and CC-9 (5.53 ng/mL TPO, 2.03 ng/mL IL-3, 16 ng/mL SCF, 4.43 ng/mL FL, 2.36 ng/mL IL-6, 1.91 ng/mL G-CSF, 1.56 ng/mL GM-CSF, 2.64 ng/mL SCGF, and 0.69 ng/mL IL-11) in the Iscove's modified Dulbecco's medium. After 6-day culture, the absolute fold expansions for white blood cells, CD34+ cells, CD34+CD38- cells, CFC, and LTC-IC were 1.4-, 30.4-, 63.9-, 10.7-, 2.8-fold, respectively. CONCLUSION: Using the statistic methodology to develop HSC medium, our formula had lower cytokine concentrations comparing to other literatures and commercial media, but had superior or comparable expansion ability on HSC growth.     

Myeloid differentiation of purified CD34+ cells after stimulation with recombinant human granulocyte-monocyte colony-stimulating factor (CSF), granulocyte-CSF, monocyte-CSF, and interleukin-3.

CD34+ cells isolated from bone marrow or umbilical cord blood from healthy donors were studied for proliferation and differentiation in liquid cultures in the presence of recombinant human granulocyte-monocyte colony-stimulating factor (GM-CSF), granulocyte CSF (G-CSF), monocyte CSF (M-CSF), and interleukin-3 (IL-3), followed by immunophenotyping for myeloid and myeloid-associated cell surface markers. IL-3, either alone or together with GM-CSF, G-CSF, or M-CSF, induced, on average, 50-fold cell multiplication, GM-CSF five fold to 10-fold, and G-CSF and M-CSF less than fivefold. Cells from cultures stimulated with GM-CSF, G-CSF, or M-CSF alone contained cells with a "broad" myeloid profile, "broader" than observed in cultures with IL-3. However, since IL-3 induced rapid cell multiplication, high numbers of cells expressing early (CD13, CD33) and late myeloid markers (CD14, CD15) were recovered. The presence of other CSFs together with IL-3 did not alter the IL-3-induced effect on the cells. When 5,000 CD34+ cells were cultured with IL-3 alone, the cultures still contained 2,000 to 5,000 CD34+ cells after 14 days of culture, while cells cultured with GM-CSF, G-CSF, or M-CSF contained less than 1,000 CD34+ cells. Furthermore, 1,000 to 3,000 cells were positive for the megakaryocytic lineage marker CD41b after cultures with GM-CSF or IL-3, while cultures with G-CSF or M-CSF did not contain detectable numbers of CD41b+ cells. Finally, erythroid cells could also be generated from purified CD34+ cells. The results show that IL-3 and GM-CSF can induce rapid proliferation of purified CD34+ cells in vitro with differentiation to multiple myeloid lineages, while certain subsets maintain expression of CD34.     

Functional,phenotypic and molecular characterization of cytokine low-responding circulating CD34+ haemopoietic progenitors

Circulating CD34⁺ cell populations characterized by a low rate (up to five) or high rate (more than five) of cell divisions were isolated from 8 d cultures in the presence of stem cell factor (SCF), interleukin-3 (IL-3), granulocyte-macrophage colony stimulating factor (GM-CSF), granulocyte colony stimulating factor (G-CSF), erythropoietin (EPO), Flt3 ligand and Peg-rHu megakaryocyte growth and development factor (Peg-rHuMGDF) using the fluorescent dye 5,6-carboxyfluorescein diacetate succinimidyl ester (CFDA-SE) and flow cytometric cell sorting. Phenotypic characterization of cells which had experienced up to five divisions (CFDA-SE^bright) showed a similar surface antigen expression to starting, freshly isolated CD34⁺ cells. Conversely, cells which experienced more than five divisions (CFDA-SE^dim) showed a differentiating behaviour, down-regulating CD34 antigen and acquiring differentiation markers. CFDA-SE^bright cells were significantly enriched in CD105 (endoglin) positive precursors as compared to both freshly isolated CD34⁺ and CFDA-SE^dim cells. Functional analysis indicated that CFDA-SE^bright had a 3-fold and 10-fold greater cumulative cloning efficiency as compared to freshly isolated CD34⁺ cells and CFDA-SE^dim cells, respectively. CFDA-SE^bright cells retained the vast majority of LTC-IC and showed a LTC-IC frequency 2.8-fold higher than that found in freshly isolated CD34⁺ cells. RT-PCR and Western blot analyses showed significantly higher bcl-2 RNA and protein levels in CFDA-SE^bright cells as compared to freshly isolated CD34⁺ and CFDA-SE^dim cells. This study indicates that cytokine low-responding circulating CD34⁺ cells (CFDA-SE^bright cells) represent a functionally, phenotypically and molecularly distinct multipotent progenitor population with biological properties associated with primitive precursors.     

Human granulocyte-macrophage colony-stimulating factor (GM-CSF) stimulates immature marrow precursors but no CFU-GM, CFU-G, or CFU-M

Human granulocyte-macrophage colony-stimulating factor (GM-CSF) has been described as a multilineage growth factor that induces in vitro colony formation from erythroid burst-forming units (BFU-E), eosinophil colony-forming units (CFU-Eo), and multipotential CFU (CFU-GEMM) as well as from granulocyte-macrophage CFU (CFU-GM), granulocyte CFU (CFU-G), and macrophage CFU (CFU-M). In this paper we provide evidence indicating that GM-CSF, when tested for its stimulating capacities expressed upon highly enriched hematopoietic progenitor cells (CD34+/monocyte-depleted), is unable to induce colonies from CFU-GM, CFU-G, or CFU-M. Only BFU-E, CFU-Eo, and CFU-GEMM were stimulated, and thus GM-CSF induces a similarly restricted spectrum of progenitor cells as does recombinant human interleukin 3 (IL-3). We then compared the relative stimulating potencies of GM-CSF and IL-3 by measuring colony numbers of CFU-GEMM, BFU-E, and CFU-Eo generated from CD34+ progenitor cells. IL-3 and GM-CSF as single factors were equally active in stimulating CFU-GEMM, but the combination of both factors produced additive stimulative effects upon CFU-GEMM. IL-3 was a more potent stimulus of BFU-E, and GM-CSF was the more active stimulating factor for CFU-Eo. We conclude that GM-CSF and IL-3, although stimulating the outgrowth of identical types of progenitor cells, particularly differ as regards their comparative quantitative efficiency of stimulation.     

A comparative study of the phenotype and proliferative capacity of peripheral blood (PB) CD34+ cells mobilized by four different protocols and those of steady-phase PB and bone marrow CD34+ cells

Peripheral blood (PB) CD34+ cells from four commonly used mobilization protocols were studied to compare their phenotype and proliferative capacity with steady-state PB or bone marrow (BM) CD34+ cells. Mobilized PB CD34+ cells were collected during hematopoietic recovery after myelosuppressive chemotherapy with or without granulocyte- macrophage colony-stimulating factor (GM-CSF) or granulocyte colony- stimulating factor (G-CSF) or during G-CSF administration alone. The expression of activation and lineage-associated markers and c-kit gene product were studied by flow cytometry. Proliferative capacity was measured by generation of nascent myeloid progenitor cells (granulocyte- macrophage colony-stimulating factor; CFU-GM) and nucleated cells in a stroma-free liquid culture stimulated by a combination of six hematopoietic growth factors (interleukin-1 (IL-1), IL-3, IL-6, GM-CSF, G-CSF, and stem cell factor). G-CSF-mobilized CD34+ cells have the highest percentage of CD38- cells (P < .0081), but otherwise, CD34+ cells from different mobilization protocols were similar to one another in their phenotype and proliferative capacity. The spectrum of primitive and mature myeloid progenitors in mobilized PB CD34+ cells was similar to their steady-state counterparts, but the percentages of CD34+ cells expressing CD10 or CD19 were lower (P < .0028). Although steady-state PB and chemotherapy-mobilized CD34+ cells generated fewer CFU-GM at day 21 than G-CSF-mobilized and steady-state BM CD34+ cells (P < .0449), the generation of nucleated cells and CFU-GM were otherwise comparable. The presence of increased or comparable numbers of hematopoietic progenitors within PB collections with equivalent proliferative capacity to BM CD34+ cells is not unexpected given the rapid and complete hematopoietic reconstitution observed with mobilized PB. However, all four types of mobilized PB CD34+ cells are different from steady-state BM CD34+ cells in that they express less c-kit (P < .0002) and CD71 (P < .04) and retain less rhodamine 123 (P < .0001). These observations are novel and suggest that different mobilization protocols may act via similar pathways involving the down-regulation of c-kit and may be independent of cell-cycle status.     

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

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

Effects of CD34+ cell selection and perfusion on ex vivo expansion of peripheral blood mononuclear cells

Ex vivo expansion of peripheral blood mononuclear cells (MNCs), cultured both directly and after selection for CD34+ cells, was compared in static and continuously perfused cultures containing interleukin (IL)-3, IL-6, granulocyte colony-stimulating factor (G- CSF), and stem cell factor (SCF). Cultures inoculated with either MNCs or CD34+ cells produced cells that were remarkably similar after 10 days of culture, as evidence by cell morphology, expression of CD34, CD33, CD15, and CD11b, and the fractions of cells giving rise to colony- forming units granulocyte-monocyte (CFU-GM) and long-term culture- initiating cells (LTC-IC). Static and perfusion cultures gave similar average total cells and CFU-GM expansions for both MNC and CD34+ cell cultures. However, those samples that performed poorly in static culture performed at near-normal levels in perfusion. In addition, perfusion supported higher LTC-IC numbers for both MNC and CD34+ cell cultures. While total cell expansion was about ten times greater in CD34+ cell cultures (approximately 100-fold), CFU-GM expansion (approximately 20-fold) was similar for both MNC and CD34+ cell cultures. The similar distribution of cell types produced in MNC and CD34+ cell cultures allows direct comparison of total and colony- forming cell production. After 15 days in perfusion, MNC cultures produced 1.5-, 2.6-, and 2.1-fold more total cells, CFU-GM, and LTC-IC, respectively, than the same sample selected and cultured as CD34+ cells. Even if the CD34+ selection process was 100% efficient, CFU-GM production would be 1.5-fold greater for MNCs than for CD34+ cells.     

Opposing effects of PI3 kinase pathway activation on human myeloid and erythroid progenitor cell proliferation and differentiation in vitro

OBJECTIVE: To investigate 1) the effects of lineage-specific cytokines (G-CSF and EPO) combined with ligands for different classes of cytokine receptors (common beta chain, gp130, and tyrosine kinase) on proliferation by human myeloid and erythroid progenitor cells; and 2) the signal transduction pathways associated with combinatorial cytokine actions. PATIENTS AND METHODS: CFU-GM and BFU-E were cloned in vitro. Secondary colony formation by replated CFU-GM and subcolony formation by BFU-E provided measures of progenitor cell proliferation. Studies were performed in the presence of cytokine combinations with and without signal transduction inhibitors. RESULTS: Proliferation by CFU-GM and BFU-E was enhanced synergistically when common beta chain receptor cytokines (IL-3 or GM-CSF) were combined with G-CSF or EPO, but not with gp130 receptor cytokines (LIF or IL-6) or tyrosine kinase receptor cytokines (SCF, HGF, Flt-3 ligand, or PDGF). Delayed addition studies with G-CSF+IL-3 and EPO+IL-3 demonstrated that synergy required the presence of both cytokines from the initiation of the culture. The Jak2-specific inhibitor, AG490, abrogated the effect of combining IL-3 with EPO but had no effect on the enhanced CFU-GM proliferation stimulated by IL-3+G-CSF. The PI3 kinase inhibitors LY294002 and wortmannin substituted for G-CSF in combination with IL-3 since proliferation in the presence of LY294002/wortmannin+IL-3 was enhanced to the same extent as in the presence of G-CSF+IL-3. In contrast, LY294002 and wortmannin inhibited proliferation in the presence of EPO and in the presence of EPO+IL-3. CONCLUSION: 1) IL-3 may activate different signal transduction pathways when combined with G-CSF and when combined with EPO; 2) different signal transducing intermediates regulate erythroid and myeloid progenitor cell proliferation; and 3) inhibition of the PI3 kinase pathway suppresses myeloid progenitor cell differentiation and thereby increases proliferation.     

Increased numbers of long-term culture-initiating cells in the apheresis product of patients randomized to receive increasing doses of stem cell factor administered in combination with chemotherapy and a standard dose of granulocyte colony-stimulating factor

Long-term culture-initiating cells (LTC-IC) are arguably the most primitive human hematopoietic cells detectable by in vitro functional assays. We have investigated the mobilization of these cells into the blood of patients with ovarian carcinoma randomized to receive granulocyte colony-stimulating factor (G-CSF; 5 micrograms/kg) plus different doses of stem cell factor (SCF; c-kit ligand) after chemotherapy or G-CSF alone after chemotherapy. We have shown a significant SCF dose response for the mobilization of LTC-IC, with a 5.8-fold increase in LTC-IC mobilization in those patients receiving chemotherapy, G-CSF, and 20 micrograms/kg of SCF, the highest dose used, compared with the patients receiving chemotherapy and G-CSF alone. We have shown a threefold increase in CD34+ cells and up to a 64- fold increase in CD34+/33- cells was seen in patients treated with chemotherapy, G-CSF, and 20 micrograms/kg of SCF compared with those patients treated with chemotherapy and G-CSF alone. However, significant numbers of CD34+/38- cells were only found in the patients receiving 20 micrograms/kg of SCF as part of their mobilization regimen. Patients receiving chemotherapy plus G-CSF and SCF have enhanced mobilization of primitive cells and of the more committed progenitor cells compared with those patients receiving chemotherapy followed by G-CSF alone.     

Myeloid differentiation and maturation of SCF+IL-3+IL-11 expanded AC133+/CD34+ cells selected from high-risk breast cancer patients

The AC133 antigen is selectively expressed on subset of CD 34+ cells isolated from leukapheresis products from high risk breast cancer patients receiving chemotherapy plus G-CSF. MiniMACS AC133+ isolated cells contained a mean of 85% (80-90) AC133+ cells. Enriched AC133+ cells coexpressed 80% CD34+, 6.6% CD33+ and 2% CD15+. Separated AC133+ cells contained 600 GFU-GM/10(4) cells and 70 BFU-E/10(4) cells. Flow-cytometric analysis indicated that AC133+ cells were isolated from cells population with low granularity (SS), while CD33+ a CD15+ cells had a high granularity. After a seven-day ex vivo expansion in the presence of SCF + IL-3 + IL11, the expansion of cells increased 19.4 times. The mean percentage of blasts decreased from 100% at the start of culture to 81% on day 3 and 30% on day 7. Promyelocytes were slow to appear with 10% present on day 3, but thereafter increased to 33% on day 7. The appearance of myelocytes and metamyelocytes lagged 3 days behind promyelocytes and continued to increase during culture to become the predominant (30%) cell type on day 7. Very few neutrophils (2%) were observed in any of the cultures on day 7. Monocytes or macrophages were not detected on day 7. By day 7 megakaryocytes were present at low levels (10%). The mean value of CFU-GM in the culture after day 7 of ex vivo expansion in the presence of SCF+IL-3+IL-11 had increased 45-fold, BFU-E 5-fold. After 7 days of expansion with IL-3+SCF+IL-11 cells expressed a mean of 12% CD34+, 8% AC133+, 59% CD33+ and 30% CD15+. The aim of this experiment was to determine whether ex vivo culture of peripheral blood AC133+ cells could generate sufficient numbers of progenitors to potentially abrogate cytopenia after transplantation and passive purging of tumor cells.     

Comparison of megakaryopoiesis in vitro of paired peripheral blood progenitor cells and bone marrow harvested during remission in patients with acute myeloid leukaemia

We have studied paired peripheral blood progenitor cells (PBPC) and bone marrow (BM) samples from 12 acute myeloid leukaemia (AML) patients following intensive chemotherapy, and assessed direct granulocyte-macrophage colony-forming units (CFU-GM), erythroid burst-forming units (BFU-E), megakaryocyte CFU (CFU-Mk) numbers and the production of CD61+ (platelet glycoprotein IIIa) cells in suspension culture in response to various haemopoietic growth factor combinations. We found that CFU-GM and BFU-E numbers per 105 mononuclear cells were similar in both AML PBPC and BM harvests; CFU-Mk numbers, however, were significantly higher in PBPC than BM. In addition, the higher total white cell count of the PBPC harvests meant that PBPC have much higher numbers of total progenitors per collection. CD61+ cell numbers in suspension cultures of AML PBPC and BM were lower than those of harvested normal marrow. However, response to pegylated recombinant human megakaryocyte growth and development factor (PEGrHuMGDF) both alone and in combination with other growth factors was qualitatively similar to that of normal BM. As with normal BM, response to PEGrHuMGDF alone did not increase further with addition of granulocyte colony-stimulating factor (G-CSF), granulocyte-macrophage CSF (GM-CSF), interleukin 6 (IL-6) or erythropoietin (EPO) in the AML PBPC and BM. Further responses over PEGrHuMGDF alone were seen when added with stem cell factor (SCF) or with a combination of SCF + IL-3 + EPO in both AML PBPC and BM cultures; however, the magnitude of the response was greater in the PBPC cultures. Response to PEGrHuMGDF + IL-3 was seen in the PBPC cultures but not in the AML BM. These data suggest that, in AML patients, there are proportionally more megakaryocyte progenitor cells in the mobilized PBPC than in the BM harvests, which would explain the more rapid platelet recovery following PBPC autografts.