The role of interleukin 6 in megakaryocyte formation, megakaryocyte development and platelet production

Megakaryocytopoiesis is the cellular amplification and differentiation of precursors into immature megakaryocytes, and the cytoplasmic maturation of these megakaryocytes, a process terminating in the release of platelets into the circulation. Interleukin 6 (IL-6) stimulates megakaryocytopoiesis in the bone marrow, increasing platelet numbers in the circulation. IL-6 alone is poorly active on the growth of stem cell populations, but acts in synergy with stem cell factor (c-kit ligand) to expand the committed myeloid progenitor compartments but not the megakaryocyte progenitors. IL-6 has a direct action on megakaryocyte progenitors but only in synergy with low doses of interleukin 3 (IL-3), increasing the number of immature megakaryocytes and enhancing the processes of development into mature megakaryocytes. IL-6 is about 10 times more active on megakaryocytes than on megakaryocyte progenitors in cell culture. It is active alone and will stimulate increases in cell size and DNA content. IL-6 does not appear to stimulate the process of platelet release. IL-6 is found in bone marrow, in both macrophage subsets and megakaryocytes, indicating that it may be an important physiological regulator of both paracrinal (microenvironmental) and autocrinal mechanisms controlling megakaryocyte development in bone marrow.

CD45 fraction bone marrow cells as potential delivery vehicles for genetically corrected dystrophin loci

Targeted correction of mutations in muscle can be delivered by direct i.m. injection of corrective DNA to the dystrophic muscle or by autologous injection of cells that have been genetically corrected after isolation from the individual with the dystrophic muscle. The successful application of chimeraplasty and short fragment homologous replacement to correct the exon 23 nonsense mdx transition at the mouse dys locus has opened up the possibility that with further development, targeted gene correction may have some future application for the treatment of muscular dystrophies. In vitro, application of targeted gene correction at the mdx dys locus results in better correction efficiencies than when applied directly to dystrophic muscle. This suggests that at least for the time being, a strategy involving ex vivo correction may be advantageous over a direct approach for delivery of gene correction to dystrophic muscle. This, particularly in view of recent developments indicating that bone-marrow-derived cells are able to systemically remodel dystrophic muscle, whilst penetration of DNA introduced to muscle is limited to individually injected muscles. Application of targeted gene correction to Duchenne dystrophy needs to account for the fact that about 65% of Duchenne muscular dystrophy cases involve large frame-shift deletion of gene sequence at the dys locus. Traditionally, whilst targeted gene correction is able to restore point mutations entirely, it remains to be seen as to whether a strategy for the 'correction' of frame shift deletions may be engineered successfully. This communication discusses the possibility of applying targeted gene correction to dystrophic muscle in Duchenne dystrophy.

Periwound dopaminergic sprouting is dependent on numbers of wound macrophages

Injury to many regions of the central nervous system, including the striatum, results in a periwound or 'abortive' sprouting response. In order to directly evaluate whether macrophages play an important role in stimulating periwound sprouting, osteopetrotic (op/op) mice, which when young are deficient in a variety of macrophage subtypes, were given striatal wounds and the degree of dopaminergic sprouting subsequently assessed. Two weeks postinjury, significantly fewer wound macrophages were present in the striata of op/op mice compared with controls (144 +/- 30.1 in op/op mice vs. 416.6 +/- 82.3 in controls, P < 0.005, analysis performed on a section transecting the middle of the wound). Dopamine transporter immunohistochemistry revealed a marked decrease in the intensity of periwound sprouting in the op/op group of animals. Quantification of this effect using [H3]-mazindol autoradiography confirmed that periwound sprouting was reduced significantly in the op/op mice compared with controls (71.4 +/- 21.7 fmol/mg protein in op/op mice vs. 210.7 +/- 27.1 fmol/mg protein in controls, P < 0.0005). In the two groups of animals the magnitude of the sprouting response in individuals was closely correlated with the number of wound macrophages (R = 0.83, R2 = 0.69). Our findings provide strong support for the crucial involvement of macrophages in inducing dopaminergic sprouting after striatal injury.

Gene targeting of Desrt, a novel ARID class DNA-binding protein, causes growth retardation and abnormal development of reproductive organs

We have cloned and characterized a novel murine DNA-binding protein Desrt, with a motif characteristic of the ARID (A-T rich interaction domain) family of transcription factors. The Desrt gene encodes an 83-kD protein that is shown to bind DNA and is widely expressed in adult tissues. To examine the in vivo function of Desrt, we have generated mice with a targeted mutation in the ARID domain of Desrt. Homozygous mutants have reduced viability, pronounced growth retardation, and a high incidence of abnormalities of the female and male reproductive organs including cryptorchidism. This may thus serve as a model to dissect the mechanisms involved in the development of the reproductive tract including testicular descent. Gene-targeted mice also display a reduction in the thickness of the zona reticularis of the adrenal gland and transient aberrations of the T and B cell compartments of primary lymphoid organs. These data show that this novel DNA-binding protein, Desrt, has a nonredundant function during growth and in the development of the reproductive system.

Defective stem cell factor expression in c-myb null fetal liver stroma

High levels of c-Myb are observed in immature precursor myeloid and lymphoid cells, while downregulation of c-myb accompanies terminal differentiation to a mature phenotype. This has established c-Myb as a crucial transcription factor for hematopoiesis. Further evidence for this is the embryonic death of the c-myb homozygous mutant mouse at ED15 due to defective fetal liver erythropoiesis. Cells from fetal liver of wild-type and c-myb-/- embryos were examined in detail for their hematopoietic potential and the capacity of the stroma to support wild-type hematopoiesis. The c-myb-/- fetal liver was shown to harbor sevenfold fewer spleen focus-forming cells and a similarly lower number of cells with long-term repopulating capacity (high proliferative potential cells). However, shorter term repopulating cells were not substantially reduced. c-myb-/- stromal cells were unable to support the proliferation of wild-type bone marrow lineage-negative cells. This was found to be partly due to a decrease in stem cell factor (SCF) expression while partial rescue of the stromal cell cultures was achieved through the addition of exogenous SCF. DNA binding studies for two sites within the SCF promoter demonstrated an in vitro interaction between the SCF promoter and c-Myb and transient transfection studies demonstrated that c-Myb could substantially transactivate the SCF promoter in HEK293 cells. These data explain why the c-myb-/- embryos are so impaired in their ability to establish hematopoiesis.

c-Myb is critical for murine colon development

The mammalian colon develops from a simple tube of undifferentiated cells into a complex, highly ordered organ, with a continuously self-renewing epithelial layer. We have previously described c-Myb expression in the epithelia of murine and human colon crypts and documented increased expression in colorectal adenocarcinoma cells. To investigate the role of c-Myb in colonic epithelium development, we have used embryos with a disrupted c-myb gene. Prior to the in utero death of these embryos at E15, we excised colon tissue and transplanted it under the kidney capsule of recipient mice to allow further development and cyto-differentiation. Compared to the colons of wildtype and heterozygous littermates, the c-myb homozygous knockout colon is highly irregular with a disordered epithelium and abnormal crypts. In addition, the expression of Bcl-2, a known target of c-Myb, is reduced and apoptosis is increased, indicating a critical requirement for c-Myb in normal colon development.

Cathepsin K knockout mice develop osteopetrosis due to a deficit in matrix degradation but not demineralization

Cathepsin K is a cysteine protease expressed predominantly in osteoclasts. Activated cathepsin K cleaves key bone matrix proteins and is believed to play an important role in degrading the organic phase of bone during bone resorption. Mutations in the human cathepsin K gene have been demonstrated to be associated with a rare skeletal dysplasia, pycnodysostosis. The degree of functional activity of the mutated forms of cathepsin K in these individuals has not been elucidated, but is predicted to be low or absent. To study the role of cathepsin K in bone resorption, we have generated mice deficient in the cathepsin K gene. Histologic and radiographic analysis of the mice revealed osteopetrosis of the long bones and vertebrae, and abnormal joint morphology. X-ray microcomputerized tomography images allowed quantitation of the increase in bone volume, trabecular thickness, and trabecular number in both the primary spongiosa and the metaphysis of the proximal tibiae. Not all bones were similarly affected. Chondrocyte differentiation was normal. The mice also had abnormalities in hematopoietic compartments, particularly decreased bone marrow cellularity and splenomegaly. The heterozygous animals appeared normal. Close histologic examination of bone histology revealed fully differentiated osteoclasts apposed to small regions of demineralized bone. This strongly suggests that cathepsin K-deficient osteoclasts are capable of demineralizing the extracellular matrix but are unable to adequately remove the demineralized bone. This is entirely consistent with the proposed function of cathepsin K as a matrix-degrading proteinase in bone resorption.

Fluoro-Gold: An alternative viability stain for multicolor flow cytometric analysis

BACKGROUND

The viability stains propidium iodide (PI) and 7-amino-actinomycin D (7-AAD) are excited at 488 nm, as are the commonly used antibody conjugates fluorescein isothiocyanate (FITC), phycoerythrin (PE), and cyanine 5 dye covalently coupled to R-phycoerythrin (RPE-Cy5). When excited by a single laser, spectral overlap in the emission of PI and 7-AAD with RPE-Cy5 precludes the use of these viability stains for three-color immunophenotyping, particularly when evaluating low levels of marker expression in viable target cells. The ultraviolet excitable dye hydroxystilbamidine methanesulfonate (Fluoro-Gold, or FG) binds to DNA at the A-T-rich regions of the minor groove in permeabilized or dead cells. We assessed the suitability of this dye as a viability stain.

METHODS

The ability of FG to detect nonviable cells in fresh and cryopreserved human apheresed peripheral blood cells was compared with that of PI and 7-AAD. The stability of FG staining and the effects of dye and cell concentration on the discrimination of nonviable cells was determined by measuring changes in the median fluorescence of viable and nonviable cells.

RESULTS

FG labeling at dye concentrations of 2-8 microM is stable for at least 3 h over a wide range of cell concentrations (4 x 10(5) to 4 x 10(7) cells/ml). Costaining studies and linear regression analysis show that cell viability as determined by FG is strongly correlated with estimates using PI (r = 0.9636) and 7-AAD (r = 0.9879).

CONCLUSIONS

FG is a reliable, alternative viability stain that can be used in conjunction with fluorochromes including FITC, PE, and RPE-Cy5 for multicolor analysis using dual-laser instruments.

Lymphohematopoietic stem cell engraftment

Traditional dogma has stated that space needs to be opened by cytoxic myeloablative therapy in order for marrow stem cells to engraft. Recent work in murine transplant models, however, indicates that engraftment is determined by the ratio of donor to host stem cells, i.e., stem cell competition. One hundred centigray whole body irradiation is stem cell toxic and nonmyelotoxic, thus allowing for higher donor chimerism in a murine syngeneic transplant setting. This nontoxic stem cell transplantation can be applied to allogeneic transplant with the addition of a tolerizing step; in this case presensitization with donor spleen cells and administration of CD40 ligand antibody to block costimulation. The stem cells that engraft in the nonmyeloablated are in G0, but are rapidly induced (by 12 hours) to enter the S phase after in vivo engraftment. Exposure of murine marrow to cytokines (IL-3, IL-6, IL-11 and steel factor) expands progenitor clones, induces stem cells into cell cycle, and causes a fluctuating engraftment phenotype tied to phase of cell cycle. These data indicate that the concepts of stem cell competition and fluctuation of stem cell phenotype with cell cycle transit should underlie any new stem cell engraftment strategy.

Ultrastructure of primitive hematopoietic stem cells isolated using probes of functional status

The most primitive hematopoietic stem cells capable of longterm reconstitution of the entire hematopoietic system following transplantation are characterized by their ability to exclude both Rhodamine 123 and Hoechst 33342 dyes (Rh/Ho(dull)), and are an appropriate target population for the determination of stem cell ultrastructure. We have used a fluorescence-activated cell sorter to enrich to near purity these rare, highly quiescent cells. Analysis of the in vitro growth characteristics of Rh/Ho(dull) cells demonstrated an obligatory requirement for multiple growth factors, with 62% of the sorted population having the capacity to form colonies in the presence of CSF-1 + IL-1alpha + IL-3 + SCF. The Rh/Ho(dull) cells were small, with profiles having a mean diameter of 4.6 microm. Ultrastructural examination showed numerous ribosomes and several mitochondria in the thin rim of cytoplasm surrounding the nucleus, with other cytoplasmic organelles revealed in serial sections. The cells were generally homogeneous in appearance apart from the nucleus, which had an irregular shape with a single deep indentation. The heterochromatin around the margin was distinctly more pronounced in about 50% of nuclei. The findings provide a basis for studying the structural changes that occur with progressive differentiation of early hematopoietic cells.

Macrophage lineage cells in inflammation: characterization by colony-stimulating factor-1 (CSF-1) receptor (c-Fms), ER-MP58, and ER-MP20 (Ly-6C) expression

Macrophage populations resident in tissues and at sites of inflammation are heterogeneous and with local proliferation sometimes evident. Using the convenient murine peritoneal cavity as an inflammation model, the appearance of macrophage lineage cells was followed with time in both thioglycollate- and sodium periodate-induced exudates. The cells were characterized by their proliferative response in vitro in response to colony-stimulating factor-1 (CSF-1) (or macrophage colony-stimulating factor [M-CSF]), particularly by their ability to form colonies in agar, in combination with flow cytometry (surface marker expression and forward and side scatter characteristics). We propose that c-Fms (CSF-1 receptor), unlike other markers, is a uniformly expressed and specific marker suitable for the detection of macrophage-lineage cells in tissues, both in the steady state and after the initiation of an inflammatory reaction. It was shown that the bone marrow myeloid precursor markers, ER-MP58 and ER-MP20 (Ly-6C), but not ER-MP12 (PECAM-1), are expressed by a high proportion of macrophage-lineage cells in the inflamed peritoneum. The macrophage colony-forming cells (M-CFCs) in a 16-hour thioglycollate-induced exudate were phenotyped as c-Fms+ERMP12-20+58+, properties consistent with their being more mature than bone marrow M-CFCs. It is proposed that ER-MP58, as well as ER-MP20, may be a useful marker for distinguishing inflammatory macrophage-lineage cells from the majority of those residing normally in tissues.

Tissue hyperplasia and enhanced T-cell signalling via ZAP-70 in c-Cbl-deficient mice

The c-Cbl protein is tyrosine phosphorylated and forms complexes with a wide range of signalling partners in response to various growth factors. How c-Cbl interacts with proteins, such as Grb2, phosphatidylinositol 3-kinase, and phosphorylated receptors, is well understood, but its role in these complexes is unclear. Recently, the Caenorhabditis elegans Cbl homolog, Sli-1, was shown to act as a negative regulator of epidermal growth factor receptor signalling. This finding forced a reassessment of the role of Cbl proteins and highlighted the desirability of testing genetically whether c-Cbl acts as a negative regulator of mammalian signalling. Here we investigate the role of c-Cbl in development and homeostasis in mice by targeted disruption of the c-Cbl locus. c-Cbl-deficient mice were viable, fertile, and outwardly normal in appearance. Bone development and remodelling also appeared normal in c-Cbl mutants, despite a previously reported requirement for c-Cbl in osteoclast function. However, consistent with a high level of expression of c-Cbl in the hemopoietic compartment, c-Cbl-deficient mice displayed marked changes in their hemopoietic profiles, including altered T-cell receptor expression, lymphoid hyperplasia, and primary splenic extramedullary hemopoiesis. The mammary fat pads of mutant female mice also showed increased ductal density and branching compared to those of their wild-type littermates, indicating an unanticipated role for c-Cbl in regulating mammary growth. Collectively, the hyperplastic histological changes seen in c-Cbl mutant mice are indicative of a normal role for c-Cbl in negatively regulating signalling events that control cell growth. Consistent with this view, we observed greatly increased intracellular protein tyrosine phosphorylation in thymocytes following CD3epsilon cross-linking. In particular, phosphorylation of ZAP-70 kinase in thymocytes was uncoupled from a requirement for CD4-mediated Lck activation. This study provides the first biochemical characterization of any organism that is deficient in a member of this unique protein family. Our findings demonstrate critical roles for c-Cbl in hemopoiesis and in controlling cellular proliferation and signalling by the Syk/ZAP-70 family of protein kinases.

Peripheral blood CD34+ cell count reliably predicts autograft yield

A reliable measure to predict peripheral blood progenitor cell (PBPC) autograft CD34+ cell content is required to optimize the timing of PBPC collection. We prospectively examined the peripheral blood (PB) CD34+ cell count in 59 consecutive patients with various malignancies and analyzed the correlation between the PB CD34+ cell count and various parameters in the PBPC autograft. Two hundred and thirty-five collections were performed with a median of 4.0 collections per patient (range, 2-10). The median PB CD34+ cell count at the time of collection was 39 x 10(6)/1 (range, 0.0-285.6). The PBPC autograft parameters measured were the CD34+ cell, colony-forming unit granulocyte-macrophage (CFU-GM) and mononuclear cell (MNC) content. There was a strong linear correlation between PB CD34+ cells/l and autograft CD34+ cells/kg (r = 0.8477). The correlation with CFU-GM/kg (r = 0.5512) was weaker. There was no correlation between autograft CD34+ cells/kg and PB WBC (r= 0.0684), PB MNC (r = 0.1518) or PB platelet count (r = 0.2010). At our institution we aim to obtain a minimum of 0.5 x 10(6) CD34+ cells/kg with each day of collection. We demonstrate that such a collection can be reliably obtained if the PB CD34+ cell count exceeds 5.0 x 10(6)/l.

Quiescence, cycling, and turnover in the primitive hematopoietic stem cell compartment

Continuous oral bromodeoxyuridine (BrdU) administration was used for the non-invasive measurement of the in vivo cell cycling characteristics of hematopoietic stem and progenitor cell populations of increasing maturity, isolated on the basis of their relative levels of Rhodamine 123 (Rh) and Hoechst 33342 (Ho) fluorescence. The results showed that whereas primitive hematopoietic stem cells (PHSCs) are hierarchically ordered on the basis of quiescence, the most primitive of these, characterized by their Rh/Ho(dull) phenotype and their capacity for long-term hematopoietic reconstitution, are not dormant, but cycle slowly in normal steady-state bone marrow (BM). Cell cycle analysis showed that 30 +/- 7% of Rh/Ho(dull) PHSCs had cycled and incorporated BrdU following continuous administration over 1 week, whereas 60 +/- 14% and 89 +/- 3% of these cells were BrdU positive at 4 and 12 weeks, respectively. Linear regression analysis of these data showed that Rh/Ho(dull) PHSCs cycle with an average turnover time of 4.3 weeks (30 days), and a t1/2 (time to 50% cycled) of 2.75 weeks (19 days).

Expression of mdr1 and mrp in the normal B-cell homologue of B-cell chronic lymphocytic leukaemia

B-cell chronic lymphocytic leukaemia (CLL) cells commonly express the multidrug resistance phenotype. The aim of this study was to establish whether the normal homologue in B-cell ontogeny of B-CLL also expressed the multidrug resistance (mdr) phenotype. Human tonsillar lymphocytes were sorted to yield two B-cell subsets based on the expression of CD19, CD5 and CD10. The normal homologue was represented by a population of B cells that was CD19 positive, CD10 negative and weakly expressed CD5. Based upon functional analysis and the detection of mdr1 mRNA by semi-quantitative PCR, these cells expressed the mdr phenotype. In contrast, functional multidrug resistance could not be demonstrated in CD19-positive CD10-positive cells with strong expression of CD5, nor could mdr1 mRNA be found in these cells. MRP was variably expressed in both B-cell subsets with no discernable differences in the pattern of expression. We conclude that normal B cells with a phenotype resembling that of B-CLL cells express the multidrug resistance phenotype.

Mutation in Sos1 dominantly enhances a weak allele of the EGFR, demonstrating a requirement for Sos1 in EGFR signaling and development

We have investigated the role of the mammalian Son of sevenless 1 (Sos1) protein in growth factor signaling in vivo by generating mice and cell lines that lacked the Sos1 protein. Homozygous null embryos were smaller than normal, died mid-gestation with cardiovascular and yolk sac defects, and their fibroblasts showed reduced mitogen-activated protein kinase activation in response to epidermal growth factor (EGF). An intercross of mice mutant for Sos1 and the EGF receptor (EGFR) demonstrated that a heterozygous mutation in Sos1 dominantly enhanced the phenotype of a weak allele of the EGFR allele (wa-2). These animals had distinctive eye defects that closely resembled those seen in mice that were null for the EGFR or its ligand, TGF alpha. Our findings provide the first demonstration of a functional requirement for Sos1 in growth factor signaling in vivo. They also show that the genetic test of enhancement of weak receptor allele by heterozygous mutation in one component represents a powerful tool for analyzing the ras pathway in mammals.

A null mutation in the gene encoding a type I interferon receptor component eliminates antiproliferative and antiviral responses to interferons alpha and beta and alters macrophage responses

To examine the in vivo role(s) of type I interferons (IFNs) and to determine the role of a component of the type I IFN receptor (IFNAR1) in mediating responses to these IFNs, we generated mice with a null mutation (-/-) in the IFNAR1 gene. Despite compelling evidence for modulation of cell proliferation and differentiation by type I IFNs, there were no gross signs of abnormal fetal development or morphological changes in adult IFNAR1-/- mice. However, abnormalities of hemopoietic cells were detected in IFNAR1 -/- mice. Elevated levels of myeloid lineage cells were detected in peripheral blood and bone marrow by staining with Mac-1 and Gr-1 antibodies. Furthermore, bone marrow macrophages from IFNAR1 -/- mice showed abnormal responses to colony-stimulating factor 1 and lipopolysaccharide. IFNAR1 -/- mice were highly susceptible to viral infection: viral titers were undetected 24 hr after infection of IFNAR1 +/+ mice but were extremely high in organs of IFNAR1 -/- mice, demonstrating that the type I IFN system is a major acute antiviral defence. In cell lines derived from IFNAR1 -/- mice, there was no signaling in response to IFN-alpha or -beta as measured by induction of 2'-5' oligoadenylate synthetase, antiviral, or antiproliferative responses. Importantly, these studies demonstrate that type I IFNs function in the development and responses of myeloid lineage cells, particularly macrophages, and that the IFNAR1 receptor component is essential for antiproliferative and antiviral responses to IFN-alpha and -beta.

Granulocyte-macrophage colony-stimulating factor is not responsible for the correction of hematopoietic deficiencies in the maturing op/op mouse

Osteopetrotic (op/op) mice are characterized by an autosomal recessive inactivating mutation resulting in the absence of biologically active colony-stimulating factor-1 (CSF-1). Consequently, young op/op mice have a severe deficiency of macrophages and osteoclasts resulting in excessive bone formation, occlusion of the marrow cavity, and reduced marrow hematopoietic activity. Recently, we showed that the osteopetrosis and hematopoietic deficiencies evident in young op/op mice are not permanent but are progressively corrected with age. There are increases in osteoclast activity; bone resorption; femoral marrow space; and marrow hematopoietic activity, cellularity, and macrophage content. In the present study we show that CSF-1-/- granulocyte-macrophage colony-stimulating factor (GM-CSF)(-/-)-deficient mice also undergo the same pattern of hematopoietic correction as the op/op mouse. Also, like the op/op mouse, the peritoneal cellularity and macrophage content of CSF-1/GM-CSF-deficient mice remains severely reduced. Our data show that the "knockout" of GM-CSF does not change the op/op phenotype, and that GM-CSF is not essential for the correction of the hematopoietic deficiencies in the op/op mouse. Importantly, the data also show that neither GM-CSF nor CSF-1 is an absolute requirement for the commitment of primitive hematopoietic stem cells to the macrophage lineage or for the differentiation of at least some classes of macrophages. This finding suggests that an alternate regulatory factor can be involved in macrophage and osteoclast commitment, differentiation, and function in vivo.

Developmental hematopoiesis from prenatal to young-adult life in the mouse model

Five measurements of hematopoietic function were made in the mouse from midfetal life to young adulthood. These included two in vivo (day-8 colony-forming unit-spleen [CFU-S8] and day-12 CFU-S [CFU-S12]) and two in vitro clonal measurements of hematopoietic stem and progenitor cells (high proliferative potential colony-forming cell [HPP-CFC] and CFC of low proliferative potential [LPP-CFC]) as well as an in vitro clonal measurement of colony-forming unit-fibroblast (CFU-F). The appearance, increase, subsequent decrease, and later emergence and increase of each of these parameters in the fetal-liver, newborn, growing-infant, and young-adult bone marrow were correlated and found to be in parallel. Exceptions to this included the earlier appearance in the fetal liver of CFU-F and the relatively differentiated hematopoietic LPP-CFC. The pattern of emergence of these progenitor cell subpopulations in the fetal liver may be related, in part to the timing of the hematopoietic microenvironment development and the relative frequencies of progenitor cell types in the circulation. This developmental study in the mouse model describes additional correlations between in vivo and in vitro colony-forming stem cells and fibroblastic stromal colony-forming cells, and it suggests the dependence of hematopoietic stem cells upon the stromal microenvironment for the necessary conditions for hematopoietic stem cell lodgment, growth, and maturation.

Modified thrombopoietic response to 5-FU in mice following transplantation of Lin-Sca-1+ bone marrow cells

An experimental murine model of bone marrow transplantation (BMT) has been used to study the mechanisms of platelet production following transplantation. A defined primitive population of hematopoietic bone marrow cells (1000 Lin-Sca-1+) was isolated and transplanted into lethally irradiated (13 Gy) syngeneic recipient mice. Platelet counts, but neither red nor white blood cell (WBC) counts, were low 30 days after transplantation. By 90 days, platelet levels had normalized in transplanted mice, but this occurred from a reduced megakaryocyte progenitor (CFU-Mk) pool, implying that altered bone marrow control was involved in platelet production. To assess the capacity of the bone marrow of these compensated mice to sustain platelet production, the rate and degree of recovery were examined following administration of 150 mg/kg of 5-fluorouracil (5-FU) 90 days after transplantation. Transplanted mice showed a delay, both in platelet recovery and rebound thrombocytosis, after 5-FU administration when compared to normal littermates treated with 5-FU. The regeneration and expansion of bone marrow CFU-Mk and mature megakaryocytes was retarded in the transplanted mice and explained the altered platelet kinetics. The onset of increased platelet and mature megakaryocyte size, however, was not different between the two groups, indicating that the transplanted mice responded normally to the mechanisms controlling megakaryocyte development and platelet formation. The data suggest that following BMT a limitation in the proliferative capacity of primitive hematopoietic cells results in a smaller pool of megakaryocyte precursors. Compensatory adjustment within the megakaryocyte lineage, nevertheless, results in normalization of megakaryocyte and platelet number. The ability of transplanted mice to sustain platelet production when challenged with increased platelet demand is not limited by megakaryocytic maturation but by a restriction in proliferation or differentiation from the stem cell pool.

Haematopoietic radioprotection by Cremophor EL: a polyethoxylated castor oil

The polyethoxylated castor oil, Cremophor EL (Cremophor) is approved for human use as a vehicle for oral and intravenous administration of water-insoluble compounds. Cremophor has also previously been shown to reverse the multidrug resistance phenotype at clinically acceptable doses. This study demonstrates that doses of Cremophor in the range of 25-50 microliters/kg intravenously (i.v.) administered 1 day prior to near-lethal irradiation protected the regenerative capacity of the marrow, resulting in haematopoietic radioprotection and long-term survival of near-lethally-irradiated mice. In normal mice, Cremophor administration (1) markedly reduced the level of serum haematopoietic inhibitory activity 4-8 h following injection; (2) resulted in a transient decrease in femoral bone marrow cellularity and upregulated B220 (B cells), and 7/4 (neutrophils and activated macrophages), but not Thy-1 (T-cells) surface antigen expression in bone marrow cells within 24 h of injection; and (3) transiently elevated the incidence of both primitive and committed haematopoietic progenitor cells detected in clonal agar culture within 48 h of injection. Bone marrow progenitor cell content, and peripheral blood white cell, platelet and reticulocyte counts were unaffected. This suggests that the haematopoietic radioprotection and recovery observed in irradiated mice pretreated with Cremophor may be the result of accessory cell activation and/or modulation of accessory factors regulating haematopoietic progenitor cells. Our data suggest a potential clinical use of Cremophor as an adjunct to, or as a substitute for, cytokines to minimize myelosuppression following cytotoxic therapy.

Classes of primitive murine megakaryocytic progenitor cells

We describe high proliferative potential colony-forming cells-megakaryocyte (HPP-CFU-Mk) from mouse bone marrow preparations using known cytokine combinations. These primitive precursors, which generate at least 80 megakaryocytes per colony, were detected from bone marrow populations enriched for primitive cells, either following treatment with 5-fluorouracil (5-FU) or after enrichment from normal bone marrow using immunological procedures. HPP-CFU-Mk were most reproducibly grown in the presence of interleukin-1 (IL-1) plus IL-3 plus IL-6, and mostly grew as a single large aggregate, rarely forming multiple foci. Cell separation studies showed that the HPP-CFU-Mk have membrane properties that characterized these cells as being intermediate between high proliferative myeloid primitive progenitors (high proliferative colony-forming cells [HPP-CFC]) and committed megakaryocyte progenitors (CFU-Mk). The data show that HPP-CFU-Mk can be designated as primitive cells on the basis of their being spared in vivo after 5-FU treatment, their proliferative potential to produce megakaryocytes, and their cofractionation with a proportion of primitive myeloid progenitor cells.

The development and establishment of hemopoiesis in fetal and newborn osteopetrotic (op/op) mice

Previous studies of young CSF-1-less osteopetrotic (op/op) mice demonstrate a severe deficiency of both macrophages and osteoclasts, resulting in excessive bone formation, occlusion of the marrow cavity, and reduced hemopoietic activity. The accompanying splenomegaly and prolonged splenic hemopoiesis observed in these mice suggests that osteopetrosis may perturb the normal progression of fetal hemopoietic development and obstruct the seeding of hemopoietic precursors into the bone marrow. This study demonstrates that the absence of CSF-1 does not affect the progression of hemopoietic development in fetal op/op mice until after colonization of the bone marrow. Significant deficiencies in marrow cellularity and progenitor cell content in the long bones of op/op mice were not evident prior to Day 2 postnatal, suggesting that the altered hemopoietic state of young op/op mice is not a consequence of abnormal fetal hemopoietic development, but is primarily due to the lack of functional osteoclasts in op/op fetuses and hence, impaired remodeling of the marrow cavity after birth.

The relationship between different high proliferative potential colony-forming cells in mouse bone marrow

Previous work has shown that part of the hierarchical structure of the hematopoietic system can be described by HPP-CFC-1 (primitive high proliferative potential colony-forming cells responding to colony-stimulating factor-1 [CSF-1] + interleukin-3 [IL-3] + IL-1), HPP-CFC-2 (more mature HPP-CFC responding to CSF-1 + IL-3), and mature HPP-CFC responding to the single factors, CSF-1, granulocyte-macrophage colony-stimulating factor (GM-CSF), or IL-3. In this study, we have attempted to relate the murine HPP-CFC, stimulated by various combinations of growth factors (GFs)--CSF-1, GM-CSF, IL-3, IL-6, IL-1, stem cell factor (SCF), and transforming growth factor-beta (TGF-beta)--and by CSF-1, GM-CSF, and IL-3 on their own, to these known progenitors. Studies involving regeneration of the bone marrow after 5-fluorouracil (5-FU) treatment, generation of progenitors in liquid cultures in response to different GF combinations, and the HPP-CFC content of lineage-negative rhodamine-sorted bone marrow (BM) fractions have indicated that: 1. the combinations CSF-1 + IL-3 + IL-1 + SCF and CSF-1 + IL-3 + IL-1 + IL-6, and possibly CSF-1 + GM-CSF + IL-3 + IL-1, stimulate pre-HPP-CFC-1; 2. the combinations CSF-1 + IL-1 + GM-CSF, CSF-1 + IL-1 + IL-6, CSF-1 + IL-1 + SCF, CSF-1 + IL-3 + SCF, CSF-1 + IL-6 + SCF, and IL-3 + SCF, appear to overlap with the CSF-1 + IL-3 + IL-1 combination to stimulate the more mature cells of the HPP-CFC-1 compartment; 3. the combinations CSF-1 + GM-CSF, CSF-1 + IL-1, CSF-1 + IL-6, and CSF-1 + SCF may stimulate the more mature cells of the HPP-CFC-2 population, while the single factors CSF-1, GM-CSF, and IL-3, as suggested in other reports, may stimulate HPP-CFC that are more mature than the HPP-CFC-2; 4. the combinations IL-3 + IL-6 and SCF + IL-6 appear to stimulate HPP-CFC that overlap with the HPP-CFC-1 population, while those responding to the combination GM-CSF + TGF-beta overlap with the HPP-CFC-2 population within the hematopoietic hierarchy; and 5. CSF-1 and GM-CSF appear to be interchangeable in the combinations studied.

Anchorage-independent culture of bovine granulosa cells: the effects of basic fibroblast growth factor and dibutyryl cAMP on cell division and differentiation

During ovarian folliculogenesis granulosa cells divide while in contact with stromal cells and other granulosa cells. Following ovulation, however, they cease dividing and differentiate into large luteal cells. When cultured in monolayer, granulosa cells spontaneously differentiate into luteal cells, thus confounding the study of the follicular functions of granulosa cells in vitro, such as cell division. We have found that bovine granulosa cells were able to divide in an anchorage-independent culture system consisting of soft agar and an overlay of methylcellulose. The cells grew in colonies and retained the ultrastructural features of follicular granulosa cells. They also secreted an extracellular matrix with features of basal lamina. The granulosa cells responded to basic fibroblast growth factor (bFGF) in a dose- and time-dependent manner, with a three- to five-fold increase (at 50 ng bFGF/ml for 14 days) in the level of DNA per dish. This mitogenic effect was inhibited by dibutyryl cAMP (dbcAMP) (1 mM). In the presence of dbcAMP the cells hypertrophied considerably, did not secrete extracellular matrix, and developed the ultrastructural features of luteal cells. They also secreted threefold more progesterone. This system offers the ability to study the follicular functions of granulosa cells in culture.

Age-related changes in extramedullary hematopoiesis in the spleen of normal and perturbed osteopetrotic (op/op) mice

Occlusion of the marrow cavity by excessive bone formation in young osteopetrotic (op/op) mice results in a significant reduction in the space available for hematopoiesis. At this time, splenomegaly is evident, and the spleen is a site of significant extramedullary hematopoiesis. In vitro clonal assays of spleen cell suspensions in young op/op mice demonstrated a 22-fold elevation in the content of high proliferative potential colony-forming cells (HPP-CFC) (4 weeks of age) and a 14-fold elevation in the content of committed progenitors responsive to colony-stimulating factor-1 (CSF-1) (6 weeks of age). Flow-cytometric analysis also demonstrated a shift in the myeloid:lymphoid cell ratio in the spleens of young op/op mice, with a 35% reduction in the number of B220+ cells, and a two-fold increase in myeloid cells expressing the hematopoietic cell surface lineage antigens Mac-1 and Gr-1. However, the hematopoietic deficiencies of op/op mice are not permanent. An age-related progressive remodeling of the bone marrow cavity results in the correction of bone marrow parameters by 22 weeks of age. This correction in marrow hematopoietic activity is accompanied by a resolution of the splenomegaly, a progressive decrease in splenic hematopoietic activity at both the primitive and committed progenitor cell levels, and a correction of the lymphoid:myeloid cell ratio. Negative immunomagnetic selection of splenic hematopoietic progenitor cells from op/op and control littermate mice, followed by analysis of their expansion in liquid culture, demonstrated that primitive hematopoietic progenitor cells of high proliferative potential continued to reside in the spleen of old op/op mice. The response of these mice to a 5-fluorouracil (5-FU) cytotoxic challenge suggested that this pool of primitive progenitor cells acted as a hematopoietic reserve capable of rapidly responding to hematopoietic perturbation.

Temporal thrombocytopenia after engraftment with defined stem cells with long-term marrow reconstituting activity

Delayed platelet recovery and altered marrow megakaryocytopoiesis was observed in highly irradiated mice following transplantation with 1000 lineage-negative, stem cell antigen-positive (Lin-Sca-1+) cells. Thirty days after transplantation, the mice were thrombocytopenic. Normal platelet levels were reestablished by 90 days after transplantation. Platelet levels were established from the bone marrow with altered megakaryocytopoiesis, however. Megakaryocyte progenitor numbers were found at reduced levels in the reconstituted marrow at all time points assessed. Bone marrow function was also different in that marrow reserve was also diminished. While the transplantation regime did give long-term reconstitution of blood cells, the quality of the marrow reserve was significantly impaired as revealed by response to further hematopoietic challenge. The data indicate that mice transplanted with a population of highly defined stem cells have perturbed marrow function, one characteristic being an altered process of megakaryocytopoiesis.

Identification and cloning of a protein kinase-encoding mouse gene, Plk, related to the polo gene of Drosophila

We have determined the nucleotide sequence of a cDNA encoding a protein kinase that is closely related to the enzyme encoded by the Drosophila melanogaster mutant polo and that we have designated Plk (polo-like kinase). Plk is also related to the products of the Saccharomyces cerevisiae cell cycle gene MSD2 (CDC5) and the recently described early growth response gene Snk. Together, Plk, polo, Snk, and MSD2 define a subfamily of serine/threonine protein kinases. Plk is expressed at high levels in a number of fetal and newborn mouse tissues but is not expressed in the corresponding adult organs. With the exception of adult hemopoietic tissues, the only adult tissues in which we could detect Plk expression were ovaries and testes. Taken together, the patterns of Plk expression suggest an association with proliferating cells. Since polo is required for mitosis in Drosophila it is possible that Plk is involved in some aspect of cell cycle regulation in mammalian cells.

Accelerated establishment of murine long-term bone marrow cultures by addition of stem cell factor

The effect of stem cell factor (SCF) on the establishment of hematopoietic activity in murine long-term bone marrow cultures (LTBMC) was investigated by addition of SCF to (a) normal LTBMC from the onset of culture and (b) pre-established irradiated bone marrow stroma inoculated with lineage negative (Lin-) primitive hematopoietic progenitor cells enriched on the basis of low rhodamine-123 uptake (Rh-dull). Hematopoietic activity was established more rapidly in LTBMC grown in the presence of SCF (70 ng/mL), and the typical decline in cellularity and progenitor cell content during the first weeks of culture was not observed. SCF also promoted the rapid expansion of progenitor cells derived from Lin-, Rh-dull primitive hematopoietic cells inoculated onto irradiated preestablished bone marrow stroma. The data demonstrate that exogenous SCF augments hematopoietic activity in LTBMC, and that the levels of endogenous SCF elaborated in LTBMC may be suboptimal for expansion of hematopoietic cells.

Expansion of hemopoietic activity in long-term culture of human bone marrow by c-kit ligand (stem cell factor)

The response of hemopoietic activity in long term culture of human bone marrow (LTMC) to exogenous c-kit ligand has been investigated. Addition of c-kit ligand as recombinant Stem Cell Factor after the adherent stromal cell layer had become confluent failed to increase the content of hemopoietic cells in the culture system. Production of hemopoietic progenitors and differentiated progeny was on the other hand amplified by addition of c-kit ligand at regular intervals from the initiation of the culture, and resulted in net formation of these cells in the culture system. The characteristics of the response were consistent with consequences of increased survival of hemopoietic progenitors during a vulnerable initial phase in which the availability of endogenous c-kit ligand was limited by the initially low number of stromal cells. The increase in differentiated progeny was essentially due to increased formation of neutrophil series, and the lack of increased basophil production under these circumstances presumably reflected the nature of the contributory effects of endogenously generated growth regulatory molecules which acted in a synergistic manner with added c-kit ligand.

Delayed hematopoietic development in osteopetrotic (op/op) mice

Changes in structure, cellularity, hematopoietic progenitor cell and macrophage content, and osteoclast activity were investigated in the hematopoietic organs of the colony-stimulating factor 1(CSF-1)-less osteopetrotic (op/op) mouse. The data indicated that op/op mice undergo an age-related hematopoietic recovery and resolution of osteopetrosis, suggesting that the hematopoietic system has the capacity to use alternative mechanisms to compensate for the absence of an important multifunctional growth factor, CSF-1. In young animals, op/op femurs were heavily infiltrated with bone, and marrow cellularity was significantly reduced. After 6 wk of age, there was an increase in the marrow space available for hematopoiesis. The femoral cavity of op/op mice progressively enlarged, and by 22 wk of age its appearance and marrow cellularity was comparable to that of controls. The percentage of op/op mononuclear phagocytes, defined by F4/80 antigen expression, progressively increased to normal levels by 35 wk of age. There was no difference in the incidence of both primitive and mononuclear phagocyte-committed, CSF-1-responsive progenitor cells in op/op marrow, but their femoral content was significantly reduced in young mice. During the period of reduced hematopoiesis in the marrow of young op/op mice, splenic hematopoietic activity was elevated. This mutant mouse represents a system for the study of the CSF-1-independent regulatory mechanisms involved in hematopoietic regulation.

Recombinant rat stem cell factor stimulates the amplification and differentiation of fractionated mouse stem cell populations

The role of recombinant rat stem cell factor (rrSCF) was studied on defined primitive bone marrow cell populations. In agar culture of 500 lineage-negative/Sca-1-positive (Lin-/Sca-1+) cells, rrSCF alone stimulates small colonies of predominantly granulocytic cells. The combinations of rrSCF plus interleukin-3 (IL-3), granulocyte-macrophage colony-stimulating factor (GM-CSF), or macrophage CSF (CSF-1) stimulated primitive progenitor cells defined as high proliferative potential colony-forming cells (HPP-CFC). Synergistic increases in total colony numbers were obtained with rrSCF plus GM-CSF, granulocyte CSF (G-CSF), CSF-1, or IL-6, but not IL-1 or IL-3. Lin-/Sca-1+ cells were incubated in liquid culture at 3,000 cells/mL for 6 days in the presence of rrSCF alone or in combination with other growth factors. The total number of cells was increased twofold in the presence of rrSCF, with the progeny primarily myeloid in nature. The greatest increase in cell number was obtained with rrSCF plus IL-3, where the cell number increased 40-fold. These factors also stimulated an increase in HPP-CFC (10-fold) and GM-CFC (500-fold). To determine if these interactions were direct, single Lin-/Sca-1+ cells were sorted into microtiter wells and the cell proliferation scored 6 days later. RrSCF synergized with IL-3, IL-6, and G-CSF to stimulate the proliferation of single cells. The cells in positive wells were subcultured into colony-forming assays and up to 400 CFC per well were obtained after 14 days incubation of the secondary cultures. These data demonstrate that rrSCF acts in combination with various growth factors to directly stimulate the amplification potential of hematopoietic primitive precursors, resulting in differentiation of these precursors.

Interleukin 3 directly stimulates both megakaryocyte progenitor cells and immature megakaryocytes

A subset of stem cell antigen (sca-1)-positive mouse megakaryocyte progenitors was identified that correlates with other primitive precursors in bone marrow. The responsive bone marrow cells were obtained by depleting the marrow of cells bearing defined lineage markers (neutrophils, macrophages, and lymphoid cells) and enriched for primitive myeloid progenitor cells with high proliferative potential, selecting for cells expressing sca-1. The sca-1-positive megakaryocyte progenitors formed colonies in the presence of interleukin 3 (IL-3) alone. Immature megakaryocytes depleted of mature megakaryocytes and of cells expressing myeloid and lymphoid lineage markers were also responsive to IL-3. These data indicate that in the presence of high doses of IL-3, accessory cells are not obligatory for growth factor stimulation of megakaryocytopoiesis in vitro.

Transforming growth factor β inhibits the action of stem cell factor on mouse and human hematopoietic progenitors

In agar culture of post 5-fluorouracil mouse bone marrow cells (FUBM), recombinant rat stem cell factor (rrSCF) synergizes with granulocyte colony-stimulating factor (G-CSF), interleukin-3 (IL-3) or interleukin-6 (IL-6) to stimulate primitive progenitor cells (HPP-CFCs). The addition of recombinant human transforming growth factor beta (rhTGF-beta) to cultures of FUBM containing rrSCF plus rhG-CSF, rrSCF plus recombinant murine (rm)IL-3, or rrSCF plus rhIL-6 resulted in 100% inhibition of colony formation. Highly enriched populations of primitive bone marrow cells were obtained by isolating lineage negative (Lin-), Sca-1-positive (Sca-1+) cells from normal mouse bone marrow. RhTGF-beta inhibited 90% of colony formation stimulated by rrSCF plus rmIL-3 in agar culture of the Sca-1+ cells. RhTGF-beta also inhibited colony formation in agar culture of post FU human bone marrow cells. The synergistic increase in colony formation obtained with recombinant human SCF (rhSCF) plus rhGM-CSF and rhSCF plus rhIL-3 was inhibited by rhTGF-beta (approx. 60% and 87% inhibition, respectively). RhTGF-beta also totally inhibited the erythroid colony formation stimulated by rhSCF plus recombinant human erythropoietin (rhEpo). These data demonstrate that TGF-beta inhibits SCF-stimulated colony formation of mouse and human BM. This inhibition on progenitor cells appears to be a direct action of TGF-beta and is consistent with the target cells of SCF being more primitive progenitors than the CFCs stimulated by the CSFs alone.

Antagonism of the inhibitory effects of transforming growth factor-beta on colony formation of mouse bone marrow cells in vitro by increasing concentrations of growth factors

Low concentrations of TGF-beta inhibited the clonal proliferation of three different preparations of mouse bone marrow progenitor cells in vitro. Normal marrow cells responsive to CSF-1; two-day post-fluorouracil cells responsive to CSF-1 plus IL-3 and IL-1 alpha; and regenerating seven-day post-fluorouracil cells responsive to CSF-1 plus IL-3, IL-1 alpha and IL-6 were all severely inhibited by TGF-beta 1; and the inhibitory effects were antagonized by increasing the concentrations of the relevant growth factors.

The resolution, enrichment, and organization of normal bone marrow high proliferative potential colony-forming cell subsets on the basis of rhodamine-123 fluorescence

Cell sorting on the basis of rhodamine-123 (Rh123) fluorescence has been used in conjunction with negative immunomagnetic selection to analyze the high proliferative potential colony-forming cell (HPP-CFC) compartment of normal murine bone marrow and to resolve and enrich HPP-CFC subpopulations responsive to different combinations of the hemopoietic growth factors interleukin 1 alpha (IL-1 alpha), interleukin-3 (IL-3), and colony-stimulating factor 1 (CSF-1). HPP-CFC with a specific requirement for IL-1 alpha plus IL-3 plus CSF-1 in order to proliferate were resolved and enriched on the basis of their low Rh123 retention (Rh-dull), whereas HPP-CFC that grew in the presence of IL-3 plus CSF-1, IL-3 alone, or CSF-1 alone were Rh-bright. Further addition of IL-1 alpha to IL-3 plus CSF-1 stimulated few additional HPP-CFC in the Rh-bright fraction. Our data confirm the value of Rh123 as a probe for the dissection and analysis of the primitive hemopoietic stem cell (PHSC) compartment. These data also show that the Rh123 staining characteristics of IL-1 alpha plus IL-3 plus CSF-1-responsive HPP-CFC are consistent with the hypothesis that these HPP-CFC are closely related to PHSC with long-term reconstituting capacity in vivo and that they are among the most primitive progenitors yet detected in clonal agar culture.

An improved negative immunomagnetic selection strategy for the purification of primitive hemopoietic cells from normal bone marrow

An improved negative immunomagnetic selection strategy has been devised for the enrichment of primitive hemopoietic cells using the high proliferative potential colony-forming cell (HPP-CFC) assay as an index of stem cell purification. Immunomagnetic selection was carried out using goat anti-rat conjugated M-450 Dynabeads and a cocktail of rat monoclonal antibodies directed against lineage antigens expressed on B-lymphocytes (B220), neutrophils and activated macrophages (7/4), differentiating erythroid cells (YW 25.12.7), and T-lymphocyte subsets (Lyt-2 and L3T4). This negative selection strategy results in the highly reproducible enrichment of HPP-CFC with negligible loss of HPP-CFC at the immunomagnetic selection step. A 30-fold enrichment of HPP-CFC stimulated by interleukin 3 (IL-3) plus colony-stimulating factor (CSF-1), or interleukin 1 alpha (IL-1 alpha) plus IL-3 plus CSF-1, is obtained with simultaneous resolution of HPP-CFC from progenitor cells of low proliferative potential responsive to CSF-1 alone (LPP-CFC). Flow cytometric analysis of these lineage-negative cells reveals that they almost exclusively exhibit the light-scattering characteristics of blast cells and the morphology of a candidate hemopoietic stem cell. Positive fluorescence-activated cell sorting of immunomagnetically pre-enriched normal bone marrow cells using wheat germ agglutinin yields cell preparations with a cloning efficiency of up to 45% and a HPP-CFC content of 20%.

Reversal of the multidrug resistance phenotype with cremophor EL, a common vehicle for water-insoluble vitamins and drugs

A polyethoxylated castor oil, Cremophor EL, which is used as a vehicle for p.o. and i.v. administration of water-insoluble compounds in humans, can reverse the multidrug resistance (MDR) phenotype at doses which are likely to be readily achievable clinically. Using flow cytofluorometric analysis of daunorubicin (DNR) uptake as a measure of the expression of the MDR phenotype, Cremophor EL (1:10(3] in the growth medium increased intracellular DNR in an MDR cell line, R100 cells, to levels similar to that observed in the drug-sensitive parental cells, CCRF-CEM. A similar Cremophor EL-induced increase in DNR uptake was also observed in an unrelated MDR cell line derived from K562 cells. Cremophor EL (less than or equal to 3:10(4] did not inhibit the growth of CCRF-CEM cells or its vinblastine-resistant derivative, R100 cells, but would significantly increase the sensitivity of R100 cells to both vinblastine and DNR. Also Cremophor EL did not increase the sensitivity of normal bone marrow progenitor cells cultured in vitro to high concentrations of vinblastine. Cremophor EL may prove to be a relatively pharmacologically inactive addition to chemotherapeutic protocols which may be able to reverse the MDR phenotype in tumors and also help to prevent the selection of MDR cell variants from within a tumor cell population during chemotherapy.

Progenitor cells in murine bone marrow stimulated by growth factors produced by the AF1-19T rat cell line

The AF1-19T rat cell line has been found to produce an activity that acts synergistically with colony-stimulating factor 1 (CSF-1) to stimulate primitive high proliferative potential colony-forming cells (HPP-CFC) in mouse bone marrow (BM) that appear to be the same as those stimulated by the combination of 5637-cell-conditioned medium (CM) plus CSF-1 or recombinant human (rh) interleukin 1 (IL-1) plus recombinant murine (rm) interleukin 3 (IL-3) plus CSF-1. AF1-19T also produced granulocyte-macrophage colony-stimulating factor (GM-CSF), which could be separated from this synergistic activity by gel filtration followed by hydroxylapatite chromatography. Results obtained from the mouse thymocyte costimulation assay for IL-1, the hybridoma growth factor assay for interleukin 6 (IL-6), the ability to stimulate HPP-CFC, and the ability to block this stimulation with an antibody to murine IL-1 alpha suggest that the synergistic activity in AF1-19T-CM is probably a mixture of IL-1 activity and IL-6 or an IL-6-like activity. Other workers have described a progenitor cell population in mouse BM (CFU-A) that forms large colonies in response to AF1-19T-CM plus CSF-1 or GM-CSF plus CSF-1. Experiments involving the kinetics of recovery after 5-fluorouracil treatment and generation of progenitors suggest that the GM-CSF-plus-CSF-1-responsive progenitors, and hence CFU-A, are a more mature cell type than the more primitive HPP-CFC, responsive to 5637-cell-CM plus CSF-1 or rhIL-1 plus rmIL-3 plus CSF-1.

Colony-forming cells with high proliferative potential (HPP-CFC)

Colony-forming cells with a high proliferative potential (HPP-CFC) have been defined by their ability to form large colonies in vitro (diameters greater than 0.5 mm and containing approximately 50,000 cells) in bone marrow cell cultures. The HPP-CFC have been characterized by: 1) a relative resistance to treatment in vivo with the cytotoxic drug 5-fluorouracil, 2) a high correlation with cells capable of repopulating the bone marrow of lethally irradiated mice, 3) their multipotential ability to generate cells of the macrophage, granulocyte, megakaryocyte and erythroid lineages, and 4) their multifactor responsiveness. The HPP-CFC have been described in both mouse and human bone marrow. These properties suggest that the HPP-CFC represent an important cell type in hematopoiesis and provide a model system, particularly in the human, for studying the properties of primitive progenitor cells in vitro.

High proliferative potential colony forming cells

High proliferative potential colony forming cells (HPP-CFC) in mouse bone marrow (BM) were defined functionally by their ability to form large colonies, greater than 0.5 mm diameter, and containing an average of 5 × 10(4) cells, in low-cell-density nutrient agar cultures after 10-14 d of incubation (1).

Changes in cell surface antigen expression during murine bone marrow cell regeneration in vivo and proliferation in vitro

Modulations in surface antigen expression during marrow regeneration in vivo, and proliferation in vitro in response to haemopoietic growth factors, were studied using a panel of monoclonal antibodies recognizing antigenic determinants expressed by primitive multipotential progenitor cells (Thy-1, Qa-m7), or lineage antigens restricted to committed progenitors and differentiated cells of the neutrophil/macrophage (7/4) and B lymphocyte (B220) lineages. These two categories of antigen exhibited differing responses to marrow perturbation and proliferation. Following administration of a cytotoxic dose of 5-fluorouracil, or lethal irradiation and transplantation of normal donor marrow, the levels of Thy-1 and Qa-m7 antigen expression rapidly increase, reaching a peak at the onset of regeneration: the nadir of marrow cellularity. Expression of these antigens returns to normal as regeneration proceeds and marrow is reconstituted. 7/4 and B220 antigen expression reflect the presence or absence of maturing cells bearing these markers: antigen expression declining following perturbation, and re-emerging during the course of regeneration. In vitro, when marrow cells taken from mice 8 days following treatment with 5-FU are grown in liquid culture in the presence of colony-stimulating factor-1 plus bladder cell carcinoma cell line 5637 conditioned medium, marrow cells are stimulated to proliferate and differentiate along the neutrophil/macrophage lineage. 7/4 antigen expression increases throughout the culture period, and B220 antigen is undetectable after the fifth day of culture. Thy-1 antigen expression also rises and remains elevated, and Qa-m7 antigen expression remains stable.

Interleukin 1 plus interleukin 3 plus colony-stimulating factor 1 are essential for clonal proliferation of primitive myeloid bone marrow cells

The clonal growth in nutrient agar at low cell densities of high-proliferative potential colony-forming cells (HPP-CFC) of bone marrow obtained from mice treated 2 days earlier with 5-fluorouracil (FU) (FU2dBM) has been shown to require a combination of three growth factors, interleukin 1 (IL-1), interleukin 3 (IL-3), and macrophage colony-stimulating factor (CSF-1). These HPP-CFC have been enriched 140-fold from FU2dBM by fluorescence-activated cell sorting of 7/4-, B220-, and L3T4-negative cells. The mean of the plating efficiencies of these enriched populations was 4.4% and no growth was observed when the factors were used singly. Similarly, enrichments of 16-fold were obtained from FU2dBM using immunomagnetic Dynabeads with anti-7/4 plus anti-B220 (meaning plating efficiency 0.5%). The further additions of human granulocyte CSF or mouse granulocyte-macrophage CSF or both to IL-1 plus IL-3 plus CSF-1 did not increase HPP-CFC colony formation, but both augmented the small colony formation with IL-1 plus IL-3, IL-3 plus CSF-1, or IL-1 plus CSF-1.

The concentration and resolution of primitive hemopoietic cells from normal mouse bone marrow by negative selection using monoclonal antibodies and Dynabead monodisperse magnetic microspheres

High proliferative potential colony-forming cells (HPP-CFC) detected in clonal agar culture in the presence of the combined stimulus of colony-stimulating factor 1 (CSF-1) + interleukin 3 (IL-3) + interleukin 1 alpha (IL-1 alpha) are closely related to developmentally early progenitor cells capable of reconstituting the hemopoietic system of lethally irradiated mice following transplantation. Flow cytometric analysis and sorting of normal, unperturbed bone marrow has shown that HPP-CFC are B220- and 7/4-, whereas the committed progenitors of the macrophage lineage responsive to CSF-1 alone (CSFCSF-1) are B220- and 7/4+. Negative immunomagnetic selection using an anti-7/4, anti-B220 antibody cocktail and second-antibody-coupled Dynabead microspheres to replace flow cytometry results in the highly reproducible and specific enrichment of HPP-CFC, and simultaneous resolution of HPP-CFC from CFCCSF-1. The tenfold enrichment of HPP-CFC compared with unfractionated bone marrow cell suspensions was comparable to that obtained by fluorescence-activated cell sorting. Enrichment was achieved with negligible loss of HPP-CFC at the immunomagnetic bead selection step, and 65% of HPP-CFC were recovered. The method is rapid, highly reproducible, and efficient, and has wide application to the separation of rare hemopoietic cells from normal bone marrow.