Colony formation by primitive haemopoietic progenitors in cocultures of bone marrow cells and stromal cells

Sources of Human Hematopoietic Stem Cells for Transplantation–A Review

Transplantation of hematopoietic stem cells provides a means of replacing a defective hematopoietic system in patients with a wide range of malignant and nonmalignant disorders that affect the blood forming tissue. The same procedure has also allowed dose-escalation of standard chemotherapy and radiotherapy in the treatment of malignant disease of nonhematological origin. Until recently, bone marrow has been the sole source of hematopoietic stem cells, but limitations of conventional bone marrow transplantation have stimulated a search for alternative sources and uses of stem cells. Fetal tissues (especially liver) are a recognized source of transplantable stem cells and offer the great advantage of reduced immunogenicity, potentially removing the problems of tissue type matching. Umbilical cord blood is also a rich source of stem cells and, although it contains alloreactive cells, it is readily available without special ethical constraints. Both fetal tissue and cord blood suffer the disadvantages of limited numbers of stem cells per donation, and there is much interest in the development of technologies for the safe and reliable expansion and/or pooling of stem and progenitor cells. The observation that small numbers of stem cells are found in the peripheral blood of adults has led to the exploitation of the blood as a further source of stem cells. The ability to mobilize these cells from the medullary compartment into the periphery by the use of chemotherapy and/or recombinant hematopoietic growth factors has enabled the collection of sufficient numbers of cells for transplantation purposes. All of these advances are increasing the options and the range of choices available to clinicians and patients in the arena of hematopoietic stem cell transplantation.

Human marrow mesenchymal stem cell culture: serum-free medium allows better expansion than classical alpha-MEM medium

The expansion of mesenchymal stem cells (MSCs) strongly depends on the culture conditions and requires medium supplemented with 10-20% fetal calf serum (FCS) to generate relevant numbers of cells. However, the presence of FCS is a major obstacle for their clinical use. Therefore, we have evaluated the capacity of expansion of MSC in a commercial serum-free medium (UC) supplemented with a serum substitute (ULTROSER) in comparison with a classical medium alpha-MEM containing 15% FBS. Bone marrow-mononuclear cells collected from 12 volunteer healthy donors were expanded in two different culture media. MSCs isolated in the both media were morphologically similar and expressed identical phenotypic markers. After the primoculture (P0) and one passage, we obtained significantly more MSC and CFU-F progenitors in UC medium than in alphaMEM. Their multipotentiality was preserved during culture, as well as their capacity to support haematopoiesis. In conclusion, our observations strongly suggest that UC is an optimal medium for ex vivo expansion of MSC: it allows a better cell expansion, preserves cell multipotentiality, reduces the culture period and contains low concentration of serum substitute. This medium seems suitable for clinical scale expansion of MSC.

Stromal cells from murine embryonic aorta-gonad-mesonephros region, liver and gut mesentery expand human umbilical cord blood-derived CAFC(week6) in extended long-term cultures

The first definitive long-term repopulating hematopoietic stem cells (HSCs) emerge from and undergo rapid expansion in the embryonic aorta-gonad-mesonephros (AGM) region. To investigate the presumptive unique characteristics of the embryonic hematopoietic microenvironment and its surrounding tissues, we have generated stromal clones from subdissected day 10 and day 11 AGMs, embryonic livers (ELs) and gut mesentery. We here examine the ability of 19 of these clones to sustain extended long-term cultures (LTCs) of human CD34(+) umbilical cord blood (UCB) cells in vitro. The presence of in vitro repopulating cells was assessed by sustained production of progenitor cells (extended LTC-CFC) and cobblestone area-forming cells (CAFC). The embryonic stromal clones differed greatly in their support for human HSCs. Out of eight clones tested in the absence of exogenous cytokines, only one (EL-derived) clone was able to provide maintenance of HSCs. Addition of either Tpo or Flt3-L + Tpo improved the long-term support of about 50% of the tested clones. Cultures on four out of 19 clones, ie the EL-derived clone mentioned, two urogenital-ridge (UG)-derived clones and one gastrointestinal (GI)-derived clone, allowed a continuous expansion of primitive CAFC and CFU-GM with over several hundred-fold more CAFC(week6) produced in the 12th week of culture. This expansion was considerably higher than that found with the FBMD-1 cell line, which is appreciated by many investigators for its support of human HSCs, under comparable conditions. This stromal cell panel derived from the embryonic regions may be a powerful tool in dissecting the factors mediating stromal support for maintenance and expansion of HSCs.

Blast colony-forming cell binding from CML bone marrow, or blood, on stromal layers pretreated with G-CSF or SCF

Blast colony-forming cells (CFU-BL) represent a specific subpopulation of special primitive progenitors characterized by colony formation only in close contact with a preformed stromal layer. CFU-BL derived from bone marrow of chronic myeloid leukaemia (CML) patients have been proved to adhere poorly to bone marrow derived stromal layers suggesting that the appearance of progenitors and precursors in the circulation is due to a defective adhesion of these cells to the bone marrow microenvironment. In the present experiments the effect of short-term incubation of preformed normal bone marrow stroma on the adherence of CML derived CFU-BL was studied. For stroma cultures bone marrow cells were cultured in microplates in the presence of hydrocortisone. Cultures were used when stromal layers became confluent and no sign of haemopoiesis could be observed. CFU-BL were studied by panning plastic non-adherent mononuclear (PNAMNC) bone marrow or blood cells. 8.9 +/- 2.4 colonies/103 PNAMNC (six experiments) were formed from normal bone marrow on stromal layers and 4.8 +/- 2.1 colonies/103 PNAMNC (five experiments) from CML bone marrow. Colony formation from normal bone marrow was not increased if stromal layers were incubated with 100 ng/mL granulocyte colony-stimulating factor (G-CSF) or stem cell factor (SCF). Incubation of stroma with G-CSF or SCF, however, increased the colony formation of PNAMNC from CML bone marrow or blood significantly. These findings suggest that local concentration of haemopoietic growth factors at the time of panning may influence the attachment of CML progenitors to the stroma.

Assay systems for hematopoietic stem and progenitor cells

Progress in our understanding of the hematopoietic system as well as novel cellular and molecular biology techniques are increasingly promoting the ex vivo manipulation and therapeutic use of hematopoietic stem and progenitor cells. For both, development of stem cell therapies and basic hematopoietic research, test systems for hematopoietic stem cells are required to monitor the intrinsic and ex vivo-induced properties of these cells. In vitro assays for primitive hematopoietic cells (colony-forming units-blast, cobblestone area-forming cells, long-term culture-initiating cells [LTC-IC]) have been established which demonstrate the proliferative and differentiation capacities of these populations. The potentials of these assays have been recently enhanced by the extended LTC and the switch LTC modifications. Although some hematopoietic cells characterized in vitro have the multipotential and proliferative properties of pluripotent hematopoietic stem cells (PHSC), their capacity to long-term repopulate hematopoiesis in vivo, a hallmark of PHSC, has not been established. Without this confirmation, populations defined in vitro should not be considered the equivalent of PHSC. In animals, the properties of primitive hematopoietic cells can be systematically analyzed by multiple in vivo assays. Therefore, various strategies have been pursued to develop an animal model for human hematopoiesis. In fetal sheep and immunodeficient mice, the functions of human PHSC are reproduced, and long-term multilineage repopulation capacity and extensive proliferative potential have been demonstrated for xenografted human cells. Thus, both models can be considered stem cell assays and may significantly enhance the study of early hematopoiesis and the development of therapeutic strategies.

Blast colony forming cell-binding capacity of bone marrow stroma from myelodysplastic patients

A specific stroma function can be quantitatively assessed by counting the stroma-adherent blast cell colonies (CFU-BL) that are formed from normal plastic nonadherent mononuclear bone marrow cells (PNAMNC) after a short-term coincubation ("panning") with the preformed stromal layer. In order to obtain information of stroma function in myelodysplasia (MDS), the "CFU-BL-binding capacity" of stroma from normal bone marrow and from patients with MDS were compared. Stromal cell cultures were established from mononuclear bone marrow cells in microplate cultures cultured with or without 10(-6) M hydrocortisone. CFU-BL-binding capacity was studied by counting blast colonies seven days after panning, and the results were expressed as CFU-BL/10(3) PNAMNC. Normal marrow stromal layers bound CFU-BL only if they were cultured with hydrocortisone, while MDS stromal layers also bound CFU-BL in the absence of hydrocortisone. For further studies of the function of MDS stroma, the effect of growth factors (stem cell factor [SCF], G-CSF, interleukin 3 [IL-3] and their combinations) on CFU-BL binding by normal or MDS stroma has also been compared. Twenty-hour incubation of the stromal layers with a standard dose (100 ng/ml) of various hemopoietic growth factors (IL-3 alone or in combination with SCF, G-CSF alone or in combination with SCF) did not have any effect on CFU-BL binding by normal marrow stroma, but increased the CFU-BL binding by stromal layers from MDS bone marrow. These findings suggest that although stromal microenvironment in MDS is capable of supporting hemopoiesis, bone marrow stroma from MDS patients differs in some characteristics from the normal stroma.

VLA-4 and VCAM-1 are the principal adhesion molecules involved in the interaction between blast colony-forming cells and bone marrow stromal cells

The molecular basis and functional significance of interactions between haemopoietic progenitor cells and the stromal microenvironment is still poorly understood. Here we investigated a broad panel of surface adhesion molecules for their involvement. For this purpose, the colony-forming capacity of stroma-adherent Bl-CEC, BFU-E and GM-CFC was studied. Both mononuclear bone marrow cells (BMC) and bone marrow-derived stromal cells (BMSC) express a wide variety of adhesion molecules. However, only antibodies against beta 1-, alpha 4-integrin (both chains of the very late activation antigen-4 (VLA-4)) and vascular cell adhesion molecule (VCAM-1) inhibited colony formation from stroma-adherent Bl-CFC by 50% or more. Antibodies against a panel of other adhesion molecules, including the alpha 5-integrin chain, were without effect. Subsequent pretreatment experiments revealed that VLA-4 on progenitors interacted with stromal VCAM-1. The inhibitory antibodies did not interfere with the clonogenic capacity of but with adhesion of BFU-E and GM-CFC. Whether the inhibitory antibodies act similarly on progenitors which depend on BMSC for growth and/or differentiation, such as BI-CFC, remains to be determined.

Comparative analysis of cytokines released by bone marrow stromal cells from normal donors and B-cell chronic lymphocytic leukemic patients

We studied the production of cytokines (G-CSF, GM-CSF, IL-6, LIF and IL-10) by bone marrow stromal cells of five untreated patients with B-CLL, in Rai stage 0, I and II, and of 8 healthy subjects. The production of G-CSF, GM-CSF, LIF and IL-10 did not differ significantly between controls and B-CLL patients. However, the ability of stromal cells to release IL-6 in response to LPS was decreased in all patients: 36 +/- 5 ng/ml versus 123 +/- 47 ng/ml for normal controls (p < 0.004). Moreover, a soluble activity that inhibited hematopoietic colony formation was detected in B-CLL stromal cell conditioned media. Some potential inhibitors were envisaged and the results indicated an increased production of TGF-beta by B-CLL stromal cells compared to normal stromal cells (respectively 53 +/- 10 versus 15 +/- 4 ng/ml, p < 0.03). The reduced capacity of B-CLL stromal cells to produce IL-6 was associated with this excessive release of TGF-beta; indeed, addition of anti-TGF-beta neutralizing antibody to B-CLL stromal cells, before LPS stimulation, totally normalized the production of IL-6. TGF-beta and IL-6 were also measured in serum samples from normal subjects and B-CLL patients. No significant difference was seen in the production of total TGF-beta (bioactive and latent forms) between normal and B-CLL sera but the mean level of bioactive protein in B-CLL sera was increased in comparison with normal sera (1.74 +/- 0.44 versus 0.67 +/- 0.2 ng/ml, p < 0.04).(ABSTRACT TRUNCATED AT 250 WORDS)

Hemopoietic stem cells: analysis of some parameters critical for engraftment

In this review four parameters relevant to the grafting of hemopoietic stem cells (HSC) are analyzed: the nature and amounts of grafted HSC, the sources of HSC and the "in vivo" fate of the grafted cells. One may oppose cells with short-term repopulating ability to cells with long-term reconstitutive capacity. The former comprise progenitors, while the latter consist of primitive stem cells, corresponding to murine pre-colony forming units-spleen (pre-CFU-S) (and to some murine CFU-S) or to human pre-colony forming units (pre-CFU). In the mouse, the number of progenitors involved in short-term reconstitution is large, while that of primitive cells operating months after the transplantation is reduced. These results may be extrapolated to humans, suggesting that it is possible to engraft a limited number of genetically modified HSC. However, the administration of large numbers of reconstituting cells appears to be a cautionary procedure, since it should insure polyclonal hemopoiesis, which is the physiological situation in mammals. Besides marrow, peripheral blood from adult patients treated with chemotherapy and growth factors, and cord blood from newborns, are promising sources of HSC. Successful engraftment depends not only on the quality and quantity of HSC, but also on the integrity of the marrow microenvironment. This microenvironment may be impaired by chemo- and radiotherapy, which provides a theoretical basis for the transplantation of stromal cells along with that of HSC.

The in-vitro detection and quantitation of ovine bone marrow precursors of multipotential colony-forming cells

The in-vitro detection and quantitation of ovine bone-marrow precursors of multipotential colony-forming cells (pre-multi CFC) is described. After 5 and 10 days in liquid culture containing medium conditioned by long term bone marrow stromal cell layers (SCM) along with lymph node-conditioned medium (LNCM) or recombinant ovine interleukin-3 (rov IL-3), increased numbers of multi CFC developed from bone marrow precursors as detected by subsequent soft agar clonogenic assay of mixed phenotype colonies. From a variety of cytokines and conditioned media (CM) tested that included recombinant ovine granulocyte-macrophage colony-stimulating factor (rov GM-CSF) and recombinant human macrophage colony-stimulating factor (rhu M-CSF), the combination of SCM plus LNCM or rov IL-3 supported the maximum numbers of multi-CFC in liquid culture. The development of multi CFC from precursors was demonstrated in bone marrow cells treated with a dose of mafosfamide that inactivated > 98% of clonogenic CFC. Quantitative limit dilution analysis of 10 bone marrow samples revealed an average of one pre-multi CFC per 34147 unfractionated cells (range 1:14230-81433). Pre-multi CFC were enriched 38-fold (average) in the 2.0% of bone marrow cells remaining after depletion of lymphocytes and myeloid/erythroid cells expressing the antigen recognized by monoclonal antibody 175. The quantitative assay also revealed preliminary evidence that the pre-multi CFC may consist of subpopulations differing in their sensitivity to mafosfamide.

Stem cells and the microenvironment in aplastic anaemia

Normal blast colony-forming cells (BI-CFC) bind to stroma cultured in the presence of methylprednisolone (MP+) but not to MP- stroma. In aplastic marrow, the incidence of BI-CFC is variable (0-4 x normal values) and there is no consistent relationship with the CFU-GM (granulocyte-macrophage colony-forming cell) content. Normal stroma require MP to induce BI-CFC binding function and form fat cells whereas MP- stroma grown from 4/9 aplastic patients formed fat cells and bound BI-CFC. The 5/9 aplastic cases that did not form fat cells spontaneously also bound BI-CFC moderately better than normal stroma. This suggests that the haemopoietic microenvironment in aplastic anaemia responds physiologically to bone marrow failure by increasing its haemopoietic support capacity.

Effect of recombinant human stem cell factor on mafosfamide-treated bone marrow clonogenic cells

The availability of early-acting cytokines could allow the establishment of new approaches to chemical marrow purging. It was the aim of the present study to investigate the capability of recombinant human stem cell factor (SCF) in combination with other growth factors to support the in vitro growth of mafosfamide-treated progenitor cells such as mixed colony forming units (CFU-GEMM), erythroid burst forming units (BFU-E) and granulocyte-macrophage CFU (CFU-GM). When marrow cells were incubated (30 min, 37 degrees C) with increasing doses of mafosfamide (30-120 micrograms/ml) a statistically significant (p < or = .05), dose-dependent suppression of colony growth was observed. Addition of SCF (50 ng/ml) to marrow cultures stimulated with the standard mixture of growth factors (interleukin 3 or IL-3, granulocyte-macrophage colony stimulating factor or GM-CSF, and erythropoietin or Epo) significantly increased the mean (+/- SD) concentration of mafosfamide inducing 95% inhibition of CFU-GM (106 +/- 17 versus 130 +/- 29, p < or = .0005), but not granulocyte/erythroid/macrophage/megakaryocyte CFU (CFU-GEMM) (85 +/- 4 versus 90 +/- 1, p < or = .1) and BFU-E (90 +/- 5 versus 92 +/- 5, p < or = .1). SCF induces a dose-dependent, statistically significant enhancement of colony formation by CD34+, mafosfamide-treated cells. As shown by single colony transfer experiments, mafosfamide-resistant clones promoted by SCF have a significantly higher replating capacity as compared with mafosfamide-resistant clones grown without SCF.(ABSTRACT TRUNCATED AT 250 WORDS)

Fractionation of chronic myelogenous leukemia marrow cells by stroma adherence: implications for marrow purging

Chronic myelogenous leukemia (CML) progenitor cells have been shown to be defective in their ability to adhere to marrow stroma. It was the aim of the present study to investigate at the cytogenetic level marrow-derived CML clonogenic cells fractionated on the basis of their ability to adhere to preformed, allogeneic, normal marrow-derived stromal layers. Mononuclear marrow cells from CML patients (n = 15) were incubated with mafosfamide (100 micrograms/ml) or control medium, seeded onto marrow stromal layers and allowed to adhere (3 hrs, 37 degrees C). Following a short-term liquid culture, the different cell fractions were harvested and incorporated in methylcellulose cultures. CFU-GM grown from these cultures were analyzed by single colony karyotyping. On direct cytogenetic analysis, the overall mean (+/- SD) percentage of Ph-negative metaphases was 7 +/- 20%. Following stroma adherence and shortterm suspension culture, the mean (+/- SD) percentages of Ph-negative clones were as follows: 33 +/- 25% for adherent CFU-GM, 59 +/- 40% for adherent, mafosfamide-treated CFU-GM, 12 +/- 16% for non-adherent CFU-GM, and 32 +/- 26% for non-adherent-mafosfamide-treated CFU-GM. If only the patients showing a percentage of Ph-negative clones > or = 20% were included in this analysis, the mean (+/- SD) percentages of Ph-negative clones were 47 +/- 19% for adherent CFU-GM, and 81 +/- 21% for adherent-Mafosfamide-treated CFU-GM. In contrast, the majority of pH-positive CFU-GM were detected within the stroma non-adherent cell fraction.(ABSTRACT TRUNCATED AT 250 WORDS)

Rapid decline of chronic myeloid leukemic cells in long-term culture due to a defect at the leukemic stem cell level

In this report we describe a quantitative in vitro assay for the most primitive type of leukemic precursors yet defined in patients with chronic myeloid leukemia (CML). This assay is based on the recently described "long-term culture-initiating cell" (LTC-IC) assay for primitive normal human hematopoietic cells. Such cells, when cocultured with competent fibroblast feeder layers, give rise after a minimum of 5 weeks to multiple single and multilineage clonogenic progenitors detectable in secondary semisolid assay cultures. Similar cultures initiated by seeding a highly enriched source of leukemic cells from patients onto normal feeders showed the clonogenic cell output after 5 weeks to be linearly related to the input innoculum over a wide range down to limiting numbers of input cells, thus allowing absolute frequencies of leukemic LTC-ICs to be determined using standard limiting dilution analysis techniques. Leukemic LTC-IC concentrations in CML marrow were found to be decreased, on average to less than 10% of the normal LTC-IC concentration in normal marrow, but were greatly increased (up to greater than 10(5) times) in CML blood. Assessment of the number of clonogenic cells produced per leukemic LTC-IC by comparison to normal blood or marrow LTC-IC values showed this function to be unchanged in leukemic LTC-ICs [i.e., 3.1 +/- 0.4 clonogenic cells per CML LTC-IC (mean +/- SEM, n = 6) versus 3.7 +/- 1.2 (n = 3) and 4.3 +/- 0.4 (n = 5), respectively, for normal blood and marrow LTC-ICs]. In contrast, leukemic LTC-IC maintenance in LTC proved to be highly defective by comparison to normal LTC-IC of either blood or marrow origin. Thus, when cells from primary LTC were subcultured into secondary LTC-IC assays, leukemic LTC-IC rapidly declined (greater than 30-fold) within the first 10 days of culture, whereas normal LTC-IC numbers remained unchanged during this period. These findings illustrate how self-maintenance and differentiation events in primitive human hematopoietic cells can be differentially modulated by an oncogenic process and provide a framework for further studies of their manipulation, analysis, and therapeutic exploitation.

Growth kinetics and blast-colony forming cell binding capacity of aplastic anaemic stromal cells

The kinetics of bone marrow cell growth and a special function of stromal cells (the capability of binding blast colony forming cells) were studied in patients with aplastic anaemia (AA). All 10 patients studied showed faster growth of bone marrow stromal cells. The time for a confluent stromal layer formation was 24.5 days for AA bone marrow as opposed to 33.0 days for normal bone marrow. This faster growth rate could also be observed if normal bone marrow cells, depleted of plastic non-adherent fraction, were plated, suggesting that at least one of the reasons for altered stromal cell growth kinetics in AA is the changes in the ratio of plastic adherent/non-adherent cells. Functionally, i.e. in supporting the growth of normal bone marrow blast colonies, AA stromal layers did not differ from that of normal stromal layers, independently of the clinical state of the disease (AA or SAA; in one patient before or after ATG treatment; in two patients after successful allogenic bone marrow transplantation). Moreover, in some AA patients this blast colony forming cell binding function of AA stromal layers could also be detected in samples cultured without hydrocortisone (i.e. in the absence of fat cells), suggesting that AA stroma also differs qualitatively from normal stroma without inducing a defective microenvironment for stem cell homing.

Immunochemical localization of extracellular materials in bone marrow of rats

The distribution of type I collagen, fibronectin, laminin, and heparan sulfate was studied in marrow of rats by indirect immunofluorescence. Most of the type I collagen of marrow is associated with large blood vessels and connective tissue trabeculae, but type I collagen was also localized in a delicate meshwork throughout the marrow and in the basement membrane of the sinusoidal endothelium. Fibronectin is partially co-distributed with type I collagen, but is much more widely distributed. Sheets or septa of fibronectin-rich material divide the marrow into small compartments that contain and appear to separate clusters of developing blood cells. These septa may serve as a substrate for anchorage and migration of blood cells. Labeling of laminin was observed in the basement membranes of blood vessels, of fat cells, and of the sinusoidal wall, but only scattered labeling was seen in other extracellular materials. Heparan sulfate proteoglycan was poorly labeled in the extracellular matrix of marrow.

Erythroid lineage-specific activity in conditioned medium derived from cloned human marrow stromal cells (CFU-RF)

Using long-term culture techniques, it has been shown that stromal cells in the marrow microenvironment are essential for the continued production and self-renewal of hematopoietic stem cells. We previously reported the development of a methylcellulose colony assay for a population of marrow stromal progenitors called CFU-RF. In this paper, a method is described for subculturing cells from individual CFU-RF-derived colonies to allow conditioned medium production (StCM). StCM, prepared in this way, was found to possess an erythroid lineage-specific activity that stimulated the formation of macroscopic erythroid colonies in cultures containing erythropoietin (epo). Using dose-response curves, the KG1 colony assay, and antibody neutralization, it was shown that the activity could not be attributed to interleukin 3 (IL3) or granulocyte-macrophage colony-stimulating factor (GM-CSF). However, it was further shown that a monolayer of stromal cells, which had earlier been producing the erythroid activity, could be stimulated by IL1 to produce granulocytic colony-stimulating activity, but only as long as IL1 was present in the culture medium. These findings indicate a mechanism whereby the same stromal population could be modulated to promote growth and differentiation of different hematopoietic lineages.

Effect of (dl)-5-methyltetrahydrofolate on acute non-lymphocytic leukemia cells in primary culture

High doses of (dl)-5-methyltetrahydrofolate (mTHF) cause strong inhibition of growth of leukemic cell lines. We studied the effect of mTHF, at concentrations ranging from 10(-3) M to 10(-4) M, on peripheral leukemic cells obtained from 15 acute non-lymphocytic leukemia (ANLL) patients, by [3H]-thydimidine uptake inhibition. Unlike leukemic cell lines, mTHF exerts a variable effect on ANLL cells in primary culture. While about 33% of cases are strongly inhibited, 55% are only slightly affected, showing a reduction in growth comparable to normal cell populations tested (unstimulated and PHA-stimulated lymphocytes, day 7 and day 14 colony forming units-granulocyte/monocyte (CFU-GM), normal blast colonies). In a minority of cases we observed stimulation of growth. This study reflects the metabolic variability of single-case leukemic cell populations, possibly in relationship to folate transport and accumulation.

The effects of interferon-alpha on the proliferation of CML progenitor cells in vitro are not related to the precise position of the M-BCR breakpoint

We investigated the effects of brief (2 h) and continuous exposure to recombinant interferon-alpha (2a) (rIFN-alpha) on the proliferation of primitive (blast colony-forming cells, Bl-CFC) and committed myeloid progenitor cells (BFU-E and GM-CFC) derived from blood and bone marrow of patients with chronic myeloid leukaemia (CML) and normal subjects. In all three clonogenic assays, rIFN-alpha suppressed colony formation in a dose-dependent manner. No differences were detected in the proliferation of CML or normal Bl-CFC and GM-CFC exposed to rIFN-alpha. Erythroid colony formation by normal, but not by CML BFU-E, was inhibited by relatively low concentrations (100 U/ml) of rIFN-alpha. However, in patients whose blood or marrow contained a mixture of Philadelphia chromosome (Ph)-positive and Ph-negative BFU-E, cytogenetic analysis of individual erythroid colonies showed no differential inhibition by rIFN-alpha. We found no difference in the sensitivity to rIFN-alpha of GM-CFC from patients whose leukaemic cells expressed BCR/ABL mRNA with the b2a2 junction and that of GM-CFC from patients with the b3a2 mRNA. We conclude that (1) rIFN-alpha does not have a significant leukaemia-specific effect on the progenitor cells detected in these assays, and (2) the sensitivity of CML GM-CFC to rIFN-alpha is independent of the type of BCR/ABL message present in the cells. The clinical efficacy of rIFN-alpha could be due to selective toxicity to cells not assayed in this study, to effects on accessory cells or to alterations induced in progenitor cell/stromal cell interactions.

Stromal cell growth and blast colony-forming cells in AML bone marrow

Bone marrow cells (BMC) from normal donors and from patients with acute myeloid leukaemia (AML) were cultured. Growth kinetics and the efficiency of stromal layers in supporting the adhesion of normal blast-colony forming cells (BL-CFCs) were studied. BMC from treated AML patients formed confluent stromal layers faster than normal BMCs. BL-CFC binding capacity of normal and AML stromal layers did not differ: on normal stromal layers 67.3-147, on AML stromal layers 63-117 colonies per 5 x 10(5) plastic non-adherent BMC were formed. The amount and/or binding capacity of BL-CFCs was found to be normal in two AML patients in complete remission, while a significantly reduced number and/or binding capacity of BL-CFCs was found in AML non-treated patients and in patients within 4 weeks after the last cytostatic course.

Purified primitive human hematopoietic progenitor cells with long-term in vitro repopulating capacity adhere selectively to irradiated bone marrow stroma

We enriched bone marrow cells from 10 normal individuals for primitive hematopoietic progenitors using a two-step technique, and examined resultant primitive progenitors for their in vitro long-term repopulating capacity and their ability to adhere to irradiated stroma. Immunomagnetic depletion of mature myeloid and lymphoid progenitors resulted in a lineage-negative (Lin-) cell population. Subsequent dual-color fluorescence activated sorting of cells with low forward and vertical light scatter properties, expressing CD34 antigen (34+) and either bearing (DR+) or lacking (DR-) the HLA-DR antigen, resulted in the selection of Lin-34+ DR+ and Lin-34+ DR- cell populations. When the Lin-34+ DR+ cell fraction was cultured in a short-term methylcellulose assay, we demonstrated a 61-fold enrichment for colony forming cells (CFC) compared with undepleted bone marrow mononuclear cells. In contrast to the Lin-34+ DR+ cells, direct culture of Lin-34+ DR- cells in short-term methylcellulose generated significantly less CFC (p less than or equal to 0.001). We then compared the capacity of Lin-34+ DR+ and Lin-34+ DR- cells to generate sustained hematopoiesis when plated in long-term bone marrow culture (LTBMC). When LTBMC were initiated with plated Lin-34+ DR+ cells, we recovered high numbers of CFC during the first week, but observed a rapid decline in the number of harvested CFC over the following weeks. No CFC could be recovered after week 7. In contrast, LTBMC initiated with plated Lin-34+ DR- cells yielded significantly greater numbers of CFC than LTBMC initiated with plated Lin-34+ DR+ cells (p less than or equal to 0.001), and this was sustained for at least 12 wk of culture. The Lin-34+ DR+ population was only 6.6-fold enriched for primitive progenitors capable of initiating and sustaining hematopoiesis in LTBMC when compared with undepleted bone marrow mononuclear cells, while the Lin-34+ DR- population was 424-fold enriched for such primitive progenitors (p less than or equal to 0.001). Finally, we examined the capacity of both Lin-34+ DR+ and Lin-34+ DR- populations to adhere to irradiated allogeneic stroma. We used a previously described "panning method" in which cells are plated onto stroma for 2 h, the nonadherent cells removed by extensive washing, and the adherent fraction maintained under conditions favoring LTBMC growth. When stroma was panned with Lin -34+ DR+ cells, 79 +/- 10% of the cells were recovered in the panning effluent. In contrast, when stroma was panned with Lin -34 + DR- cells, significantly fewer (37 +/- 7%) (p less than or equal to 0.001) cells were recovered in the panning effluent. Unlike LTBMC initiated with plated Lin -34 + DR+ cells, virtually no CFC were recovered from LTBMC initiated with panned Lin -34 + DR+ cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Release of basic fibroblast growth factor-heparan sulfate complexes from endothelial cells by plasminogen activator-mediated proteolytic activity

Cultured bovine capillary endothelial (BCE) cells synthesize heparan sulfate proteoglycans (HSPG), which are both secreted into the culture medium and deposited in the cell layer. The nonsoluble HSPGs can be isolated as two predominant species: a larger 800-kD HSPG, which is recovered from preparations of extracellular matrix, and a 250-kD HSPG, which is solubilized by nonionic detergent extraction of the cells. Both HSPG species bind bFGF. 125I-bFGF bound to BCE cell cultures is readily released by either heparinase or plasmin. When released by plasmin, the growth factor is recovered from the incubation medium as a complex with the partly degraded high molecular mass HSPG. Endogenous bFGF activity is released by a proteolytic treatment of cultured BCE cells. The bFGF-binding HSPGs are also released when cultures are incubated with the inactive proenzyme plasminogen. Under such experimental conditions, the release of the extracellular proteoglycans can be enhanced by treating the cells either with bFGF, which increases the plasminogen activating activity expressed by the cells, or decreased by treating the cells with transforming growth factor beta, which decreases the plasminogen activating activity of the cells. Specific immune antibodies raised against bovine urokinase also block the release of HSPG from BCE cell cultures. We propose that this plasminogen activator-mediated proteolysis provides a mechanism for the release of biologically active bFGF-HSPG complexes from the extracellular matrix and that bFGF release can be regulated by the balance between factors affecting the pericellular proteolytic activity.

Transferrin receptor expression of AML blasts is related to their proliferative potential

Expression of the transferrin receptor (TfR) was studied on peripheral blood blast cells from 11 patients with acute myeloid leukaemia (AML). Using a monoclonal anti-TfR antibody (OKT9) and a polyclonal antibody against surface membrane-bound transferrin, a proportion of blasts from all the patients was found to express receptors for transferrin. Further analysis of OKT9 expression using a fluorescent activated cell sorter (FACS) showed that the TfR was heterogeneously distributed in the blast cell population. In five out of six samples studied, stimulation of DNA synthesis following short-term culture induced a several-fold increase in TfR display as analysed by flow cytometry using OKT9 or FITC-conjugated transferrin. Blasts from seven patients stained with OKT9 were separated on the FACS into positive and negative or weakly positive fractions. Culture of the TfR negative population in a blast cell colony assay produced no colonies in either of two patients. In a further five patients the colony forming cells were predominantly associated with the TfR strongly positive fraction (52 +/- 25 colonies/10(4) cells) rather than the TfR weakly positive fraction (12 +/- 11 colonies/10(4) cells). Analysis of colony size showed that clones derived from the weakly positive fraction were smaller than clones from the TfR strongly positive fraction. These results suggest that TfR display by AML blasts is related to their proliferative capacity and is expressed by the leukaemic stem cell fraction.

A monoclonal antibody to a human mast cell/myeloid leukaemia-specific antigen binds to normal haemopoietic progenitor cells and inhibits colony formation in vitro

An antigen identified by murine monoclonal antibody YB5.B8 has previously been detected only on acute non-lymphoblastic leukaemia (ANLL) cells and tissue mast cells. We now report that the YB5.B8 antigen is present on a minor population (up to 3%) of normal bone marrow mononuclear cells which overlaps the set of progenitor cells capable of forming haemopoietic colonies in vitro. The results indicate that the antigen is a normal haemopoietic progenitor cell marker which is selectively retained on mast cells during maturation, and that leukaemias which express the antigen are not necessarily committed to the mast cell lineage. Furthermore, the antibody was capable of partially inhibiting the formation of haemopoietic colonies in vitro, indicating an important functional role for the antigen. This is consistent with the observation, reported in the accompanying paper, that expression of the YB5.B8 antigen is strongly correlated with poor response to therapy in patients with ANLL.

Expression of HPCA-1 and HLA-DR antigens on growth factor- and stroma-dependent colony forming cells

The expression of HLA-DR and HPCA-1 antigens (recognized by the L243 and BI.3C5 antibodies respectively) on adult human bone marrow cells was examined by fluorescence activated cell sorting and colony assays. Nearly all the (day 14) lineage restricted and multipotential colony forming cells analysed in methylcellulose cultures in the presence of added growth factors express HLA-DR and HPCA-1 determinants. Two colour cell sorting reveals that the lineage restricted HLA-DR positive progenitors express variable levels of BI.3C5 positivity whereas most of the multipotential progenitors, the multi-CFC or CFU-GEMM, are highly BI.3C5 positive. The isolated HLA-DR and BI.3C5 positive populations also contain haemopoietic precursors which adhere to and form colonies on pre-formed stromal layers. Thus, haemopoietic progenitors assayed in both types of culture system can be analysed and enriched by simultaneous two-colour sorting using anti-HLA-DR and BI.3C5 monoclonal antibodies. Similarities in the antigenic phenotype of such cells, however, precludes the use of these reagents for segregating growth factor-dependent from stroma-dependent progenitors.

CFU-F circulating in cord blood

CFU-F (colony forming units-fibroblast) were studied from cord blood and, as controls, from normal bone marrow of older children and adults. Numbers of CFU-F in cord blood buffy coat cells are lower by a factor of 10 in comparison to bone marrow CFU-F. Cytomorphology and staining with monoclonal antibody identify the progeny cells of CFU-F as fibroblasts. Cord blood CFU-F derived fibroblasts have properties supporting hematopoiesis: They produce CSF (colony stimulating factor) to which fresh cord blood CFU-GM (colony forming units-granulocytic, monocytic) react by colony formation in a dose-response manner. In addition, fibroblast colonies discharge clonogenic round cells into the medium forming CFU-GM and CFU-F colonies in secondary methyl cellulose cultures. We conclude that fetal blood contains clonogenic stromal cells (CFU-F) that give rise to fibroblasts with properties of hematopoietic support.

Compartmentalization of a haematopoietic growth factor (GM-CSF) by glycosaminoglycans in the bone marrow microenvironment

Haematopoietic progenitor cells proliferate and mature in semisolid media when stimulated by exogenous haematopoietic cell growth factors (HCGFs) such as granulocyte-macrophage colony-stimulating factor (GM-CSF). They also proliferate in association with marrow-derived stromal cells although biologically active amounts of HCGFs cannot be detected in stromal culture supernatants. It is possible that HCGFs are synthesized in small amounts by stromal cells but remain bound to the stromal cells and/or their extracellular matrix (ECM). This interpretation accords with haematopoietic progenitor cell proliferation in close association with stromal layers in long-term cultures. Glycosaminoglycans (GAGs) are found in the ECM produced by stromal cells. They are prime candidates for selectively retaining HCGFs in the stromal layer; they influence embryonic morphogenesis and cyto-differentiation and they may regulate haematopoiesis. We now report that granulocyte-macrophage colony-stimulating activity can be eluted from cultured stromal layers and that exogenous GM-CSF binds to GAGs from bone marrow stromal ECM. Selective compartmentalization of HCGFs in this manner may be an important function of the marrow microenvironment and may be involved in haematopoietic cell regulation.

Peripheral blood stem cell autografting

Transplantation of haemopoietic stem cells provides a means whereby patients with malignant disease may be treated with increased doses of chemotherapy or chemoradiotherapy. Until recently, the bone marrow has been the sole source of these cells. However, haemopoietic progenitors can also be demonstrated in the blood and it has been known for more than twenty years that peripheral blood mononuclear cells are capable of repopulating the marrow in animals. This phenomenon has recently been reproduced in man. The use of peripheral blood rather than bone marrow for autologous stem cell rescue may have advantages in terms of ready access, availability in patients with compromised pelvic bone marrows, a lower risk of tumour contamination and more rapid granulocyte and immune recovery. However, clinical experience with peripheral blood stem cell autografting is still very small. This review discusses the characteristics of circulating stem cells, the methods by which they can be collected and stored and the information which has come from recent studies of their transplantation in man.

Characterisation of stroma-dependent blast colony-forming cells in human marrow

Human bone marrow contains a population of haemopoietic progenitor cells that can be distinguished by their ability to adhere to preformed stromal layers (cultured in the presence of methylprednisolone [MP+] and form blast cell colonies. The stromal layers function in the colony assay after they have been heavily irradiated but not after they have been passaged. The binding of the progenitor cells to the stromal cells is complete after 2 hours of coincubation, and stromal layers of 9.6 cm2 can provide adhesion sites for at least 2,000 blast colony-forming cells. The blast colony-forming cells were shown by micromanipulation to self-renew as well as to give rise to multipotential and lineage-committed colony-forming progenitor cells.

Autologous transplantation with circulating hemopoietic stem cells

Circulating stem cells exist in sufficient numbers in mouse, dog, and man to allow collection and transplantation after ablative treatment. Preclinical studies in the mouse have shown a low concentration, with a transplantation potential ratio of bone marrow to blood of 1:100. The ratio of circulating stem cells to bone marrow stem cells is more favorable in the dog (1:10-20). Recent pilot studies carried out in different centers with 10 patients have shown that this approach is feasible in man, too. It appears that 5 X 10(8) mononuclear cells/kg of body weight collected by seven or eight leukapheresis procedures of about 4 hrs each is sufficient for fast hemopoietic recovery after marrow ablative treatment. Potential advantages of the use of blood stem cells over bone marrow stem cells are the decreased likelihood of contamination with malignant cells, the avoidance of general anesthesia, and the infusion of immunocompetent cells, which might hasten immunorecovery in the autologous setting.

Primitive progenitor cells in the blood of patients with chronic granulocytic leukemia

We measured the number of blast colony-forming cells (Bl-CFC) in the blood of 11 patients with untreated chronic granulocytic leukemia (CGL). The culture system used detects three types of Bl-CFC (Types I, II and III) in normal marrow, of which Bl-CFC (I) are the most primitive and might represent the putative hemopoietic stem cell. The mean numbers of Bl-CFC (I) in CGL blood, normal bone marrow and normal blood were 134 +/- 29 (+/- SEM), 127 +/- 21 and 1.5 +/- 0 respectively per 1 X 10(6) mononuclear cells. These findings are consistent with the concept that CGL is due to a primary increase in stem cell numbers with secondary increases in committed progenitor and leukocyte numbers.

Fibronectin-plasma membrane interaction in the adhesion of hemopoietic cells

Many hemopoietic cell lines were examined for their ability to adhere to culture dishes coated with extracellular matrix proteins. Adhesion assay was performed with murine and human leukemic cell lines representative of different stages of differentiation along both erythroid and myeloid lineages. All the hemopoietic cell lines tested adhered to fibronectin but not to laminin, types I, III, and IV collagen, serum-spreading factor, and cartilage proteoglycans. In addition to immortalized cell lines, immature erythroid and myeloid mouse bone marrow cells adhered to fibronectin. To define the fibronectin region involved in hemopoietic cell adhesion, proteolytic fragments, monoclonal antibodies, and synthetic peptides were used. Among different fibronectin fragments tested, only a 110-kD polypeptide, corresponding to the fibroblast attachment domain, was active in promoting adhesion. Moreover, a monoclonal antibody to the cell binding site located within this domain prevented hemopoietic cell adhesion. Finally, the tetrapeptide Arg-Gly-Asp-Ser, which corresponds to the fibronectin sequence recognized by fibroblastic cells, specifically and competitively inhibited attachment of hemopoietic cells to this molecule. The cell surface molecule involved in the interaction of mouse hemopoietic cells with fibronectin was identified as a 145,000-D membrane glycoprotein by adhesion-blocking antibodies. This glycoprotein was found to be antigenically and functionally related to the GP135 membrane glycoprotein involved in the adhesion of fibroblasts to fibronectin (Giancotti, F. G., P. M. Comoglio, and G. Tarone, 1986, Exp. Cell Res., 163:47-62). On the basis of these data, we conclude that interaction of hemopoietic cells with fibronectin involves a specific fibronectin sequence and a 145,000-D cell surface glycoprotein. We speculate that this property might be relevant for the interaction of hemopoietic cells with the bone marrow stroma, which represents the natural site of hemopoiesis.