Granulocyte-macrophage Colony-forming Cells Research Articles

Peripheral Blood Progenitor Cells Mobilized by Recombinant Human Granulocyte Colony-Stimulating Factor Plus Recombinant Rat Stem Cell Factor Contain Long-Term Engrafting Cells Capable of Cellular Proliferation for More Than Two Years as Shown by Serial Transplantation in Mice

Mobilized peripheral blood progenitor cells (PBPC) have been shown to provide rapid engraftment in patients given high-dose chemotherapy. PBPC contain cells with long-term engraftment potential as shown in animal models. In this study we have further analyzed mobilized PBPC for their ability to support serial transplantation of irradiated mice. Transplantation of recombinant human granulocyte colony-stimulating factor (rhG-CSF) plus recombinant rat stem cell factor (rrSCF) mobilized PBPC resulted in 98% donor engraftment of primary recipients at 12 to 14 months post-transplantation. Bone marrow (BM) cells from these primary recipients were harvested and transplanted into secondary recipients. At 6 months posttransplantation, all surviving secondary recipients had donor engraftment. Polymerase chain reaction (PCR) analysis showed greater than 90% male cells in spleens, thymuses, and lymph nodes. Myeloid colonies from BM cells of secondary recipients demonstrated granulocyte/macrophage colony-forming cells (GM-CFC) of male origin in all animals. In comparison, transplantation of rhG-CSF mobilized PBPC resulted in decreased male engraftment in secondary recipients. BM cells from secondary recipients, who originally received PBPC mobilized by the combination of rrSCF and rhG-CSF, were further passaged to tertiary female recipients. At 6 months posttransplantation, 90% of animals had male-derived hematopoiesis by whole-blood PCR analysis. These data showed that PBPC mobilized with rhG-CSF plus rrSCF contained cells that are transplantable and able to maintain hematopoiesis for more than 26 months, suggesting that the mobilized long-term reconstituting stem cells (LTRC) have extensive proliferative potential and resemble those that reside in the BM. In addition, the data demonstrated increased mobilization of LTRC with rhG-CSF plus rrSCF compared to rhG-CSF alone.

The effect of interleukin-4 with or without mast cell growth factor on peripheral blood granulocyte-macrophage colony-forming cells in healthy controls and in myeloproliferative disorders

The effect of interleukin-4 with or without mast cell growth factor on peripheral blood granulocyte-macrophage colony-forming cells in healthy controls and in myeloproliferative disorders

Progenitor cells in the blood and marrow of patients with chronic phase chronic myeloid leukaemia respond differently to macrophage inflammatory protein-1α

Macrophage inflammatory protein-1α (MIP-1α) is a negative regulator of normal haemopoietic stem cell proliferation. Insensitivity to MIP-1α of progenitor cells in chronic myeloid leukaemia (CML) could, therefore, explain myeloid expansion in this disease. We compared the effects of MIP-1α on progenitor cells in normal marrow and in the blood and marrow of patients with chronic phase CML. Plastic-adherent precursors of granulocyte-macrophage colony-forming cells (PΔ progenitors) are very primitive progenitor cells and are detected by incubating them for 1 week in liquid culture and assaying the CFU-GM released into the supernatant. Direct CFU-GM assays were also used in this study. Daily addition of 300 ng/ml/day of MIP-1α to PΔ progenitor assays of normal marrow cells suppressed CFU-GM production by 50% and in CML bone marrow PΔ cultures by 20–30%. The response of CML blood PΔ progenitors was heterogeneous. In five of nine cases, CFU-GM production was doubled in the presence of MIP-1α and in four of nine cases, it was reduced. Addition of 100-500 ng MIP-1α to direct assays of CFU-GM stimulated colony formation by normal marrow and CML blood cells to a similar extent.

The effect of interleukin-4 with or without mast cell growth factor on peripheral blood granulocyte-macrophage colony-forming cells in healthy controls and in myeloproliferative disorders.

The effect of interleukin-4 (IL-4) on peripheral blood (PB) granulocyte-macrophage (GM) progenitors was investigated in the presence and absence of other hematopoietic growth factors, especially the mast cell growth factor (MGF), in eight healthy controls and in 26 patients with myeloproliferative disorders (MPDs) using a clonogenic cell culture assay. In the controls IL-4 was effective alone, stimulating myeloid colony growth in 50%, while MGF had no effect as a single factor. When either IL-4 or MGF was added to the combination of IL-3, GM-CSF, G-CSF, and IL-6, a statistically significant increase in the colony number was observed. The most potent colony formation took place when all these GFs were combined. In the combinations, the effect of IL-4 was additive, while MGF worked synergistically. In the MPDs, IL-4 had no effect at all on the GM progenitors in the whole group of MPDs or on the different subgroups.

Radioprotection of Mouse Hemopoiesis by Dipyridamole and Adenosine Monophosphate in Fractionated Treatment

The purpose of the studies reported here was to investigate the ability of the combined administration of dipyridamole and adenosine monophosphate, drugs known to elevate extracellular adenosine, to protect mice undergoing treatment with fractionated irradiation (five doses of 2 or 3 Gy each) given at 24-h intervals. Based on observations of hemopoietic recovery (endogenous hemopoietic spleen colony formation, marrow granulocyte-macrophage colony-forming cells, peripheral blood cells) after the completion of fractionated irradiation and on survival studies, it was demonstrated that the repeated administration of the drugs 60 min before each of the radiation fractions mitigates the hemopoietic injury and enhances the survival of mice irradiated with an additional "top-up" dose. It could be deduced that the single protective actions of the drugs retain their efficacy in repeated treatment and enhance the sparing effect of dose fractionation on hemopoiesis. Interestingly, the toxic side effects of the drugs tend to decrease when they are administered repeatedly, probably due to the development of tolerance to their cardiovascular action. This reduction in toxicity offers benefit with respect to the potential use of these hemopoiesis-protecting drugs in clinical radiotherapy.

Cytokines and progenitor cells of granulocytopoiesis in peripheral blood of patients with bacterial infections.

To investigate the physiological role of granulocyte colony-stimulating factor (G-CSF) and granulocyte-macrophage colony-stimulating factor (GM-CSF) in the adaptation mechanisms of myelopoiesis to enhanced demand, we studied both cytokines and their myeloid target cells in hematologically healthy patients suffering from acute bacterial infections. Endogenous serum levels of G-CSF and GM-CSF, granulocyte-macrophage colony-forming cell (GM-CFC) concentrations, and differential counts were determined for the peripheral blood of 57 patients with clinically apparent bacterial infections (26 males and 31 females aged 16 to 89 years) and 18 healthy controls (8 males and 10 females aged 23 to 84 years). Patients were selected for acute-phase protein and at least two additional clinical signs reflecting a bacterial infection. Patients showed significantly higher numbers of myeloid progenitor cells than controls (median, 68 versus 26 GM-CFC/ml; P < or = 0.01). G-CSF but not GM-CSF levels were found to be elevated (> or = 50 to 863 pg/ml). In the acute stage of infection, progenitor and cytokine levels were not influenced by gender, differences in therapy, or localization of the infection. Progenitor and G-CSF levels were not associated with absolute neutrophil counts or C-reactive protein. However, a negative correlation between number of GM-CFC per milliliter and age (R = -0.47; P < or = 0.001) and an inverse relationship between the incidence of high GM-CFC concentrations and elevated G-CSF levels (phi = -0.34; P < or = 0.01) were found. Combining both parameters into a cytokine-progenitor pattern, we observed a highly significant age-dependent response of myelopoiesis to inflammation (P < or = 0.001). Younger patients had high progenitor counts (> 75 GM-CFC/ml) associated with G-CSF levels below 50 pg/ml, whereas for the older patients, the reverse pattern was predominant. The results indicate that the age-dependent myelopoietic response to acute bacterial infections is characterized by an inverse relationship between progenitor cells and G-CSF. The observed cytokine-progenitor patterns could have implications for therapy with G-CSF and the prognosis of infectious diseases.

Modification of immune response in mice by ciprofloxacin

Some studies have suggested that the addition of ciprofloxacin to in vitro cultures of mitogen-stimulated lymphocytes exerts inhibitory effects on cell cycle progression and immunoglobulin (Ig) secretion. We tested the effects of this drug on some immunity parameters in BALB/c mice. Mice treated intraperitoneally with ciprofloxacin (10 mg/kg of body weight per day) for 3 consecutive days and immunized with sheep erythrocytes 24 h after the last injection showed significant suppression of hemolytic IgG-forming cells, whereas the response of IgM-forming cells remained unchanged. When treatment lasted 7 days the response of antibody-forming cells was not modified. When the 3-day treatment was started at 24 h after immunization with sheep erythrocytes, the response of IgM-forming cells was increased, whereas the response of IgG-forming cells was suppressed. Delayed-type hypersensitivity to sheep erythrocytes was significantly suppressed in animals that received the 3-day treatment with ciprofloxacin and were immunized subcutaneously 24 h after the last injection. In vitro proliferation of lymphocytes from ciprofloxacin-treated mice in response to either lipopolysaccharide or concanavalin A was also suppressed. Leukopenia and an increase in the level of granulocyte-macrophage colony-forming cells in bone marrow were also observed in ciprofloxacin-treated mice. These results, together with those from other reports, suggest that modification of the biological responses by ciprofloxacin is a complex phenomenon that may be influenced by several factors.

Proliferation-differentiation schema of murine haemopoietic lineages: a transient response

. A steady state model of haemopoiesis was derived recently from correlations of lineages (Novak JP & Necas E (1994). Proliferation differentiation pathways of murine haemopoiesis correlation of lineage fluxes. Cell Proliferation, 27, 597). Since the determination of some branching points was based on incomplete knowledge, the proposed schema was not necessarily a unique interpretation of the experimental data. This communication presents a first verification of the model usiing a comparison of calculated characteristics and observed data of post-radiation recovery (following Necas E & Znojil V (1988) Bone marrow response to single small doses of irradiation: Implications for stem cell functional organization. Exp. Hematol. 16, 871). The measured population and S-phase fraction of colony-forming units-spleen provided the entry variables and the time response of the granulocyte-macrophage colony-forming cells and neutrophils was calculated from the parameters of the model and some known kinetic coefficients. Good agreement with experiment is a strong indication that the earlier derived schema of haemopoietic pathways is truly representative of reality.

Administration of the bacterial extract Broncho-Vaxom® enhances radiation recovery and myelopoietic regeneration

In the present study, we show that the bacterial extract Broncho-Vaxom® (BV, 500 μg/mouse; free of endotoxin) has radiation recovery activity when administered i.p. 24 h before sublethal irradiation. In the postirradiation period (5–12 days), pretreatment of mice with BV induced significantly increased bone marrow cellularity and accelerated myelopoietic regeneration (committed progenitor granulocyte-macrophage colony-forming cells; GM-CFC) in the bone marrow compared with saline-treated controls. The earlier hemopoietic recovery in BV-injected mice was not associated with an increase in the number of bone marrow GM-CFC and CFU-S (colony-forming units-spleen) within 24 h after injection. Simultaneously, a significant diminution in bone marrow cellularity occurred. In addition, the percentage of both GM-CFC and CFU-S in the S-phase of the cell cycle was significantly increased 24 h after a single treatment. In our experiments colony stimulating activity (CSA) in the serum of treated mice was not observed within 24 h after injection. Administration of BV 24 h prior to lethal irradiation, resulted in an increase in the number of surviving mice. Combined administration of BV (24 h) and indomethacin (24 h and 3 h) to mice, prior to irradiation, caused an additional radioprotective effect. These results demonstrate that BV stimulates myelopoietic regeneration and suggest a mechanism by which this treatment protects mice from otherwise lethal irradiation.

Cytokine-mediated protein kinase C activation is a signal for lineage determination in bipotential granulocyte macrophage colony-forming cells.

Granulocyte macrophage colony-forming cells (GM-CFC) have the potential to develop into either macrophages and/or neutrophils. With a highly enriched population of these cells we have found that although GM-CFC are equally responsive to macrophage colony stimulating factor (M-CSF) and stem cell factor (SCF) in terms of DNA synthesis, M-CSF stimulated the development of colonies containing macrophages in soft gel assays, while SCF promoted neutrophilic colony formation. When SCF and M-CSF were combined, mainly macrophage development was stimulated both in soft agar colony-forming assays and liquid cultures. An analysis of some potential signaling mechanisms associated with cytokine-mediated developmental decisions in GM-CFC revealed that M-CSF, but not SCF, was able to chronically stimulate phosphatidylcholine breakdown and diacylglycerol production, indicating that protein kinase C (PKC) may be involved in the action of M-CSF. Furthermore, M-CSF, but not SCF, can increase the levels of PKC alpha (PKC alpha) expression and stimulate the translocation of PKC alpha to the nucleus. When the PKC inhibitor, calphostin C, was added to GM-CFC cultured in M-CSF then predominantly neutrophils were produced, conversely PKC activators added with SCF stimulated macrophage development. The data indicate a role for PKC in M-CSF-stimulated macrophage development from GM-CFC.

Growth factors and the molecular control of haematopoiesis.

In the absence of appropriate growth factors, for example interleukin-3 or GM-CSF, cultured bone marrow stem cells die by a process known as apoptosis or programmed cell death. Apoptosis may occur in vivo when concentrations of specific growth factors are limiting and may be a means of regulating cell numbers. Growth factors are also essential for proliferation of bone marrow stem cells but differentiation can occur, provided there is a survival stimulus in the absence of growth factors. Combinations of growth factors may be synergistic in stimulating the survival and proliferation of multipotent stem cells. Although neither stem cell factor, nor GM-CSF alone can significantly induce the proliferation of stem cells, the combination induces the proliferation of these cells. Committed progenitor cells such as granulocyte-macrophage colony-forming cells, however, are stimulated to proliferate by GM-CSF alone, while stem cell factor in combination with GM-CSF results in only a slight additive effect. To date, most research has concentrated on the growth stimulatory factors. GM-CSF has an important role in the reversal of chemotherapy-induced myelosuppression in cancer patients and in other bone marrow disorders. A number of growth inhibitory molecules have now been identified, such as macrophage inhibitory protein-1 alpha. In the future, it is possible that improvements in cure rates may be achieved in cancer patients by combining the growth inhibitory factors with the stimulatory factors. Inhibitory factors may be given before chemotherapy to prevent toxicity and stimulatory factors may be given afterwards to treat neutropenic patients.

Circulating haematopoietic progenitors during treatment of renal anaemia with recombinant human erythropoietin

The effect of recombinant human erythropoietin (rhEPO) and interleukin 3 (IL3) on circulating haematopoietic progenitors consisting mainly of immature burst-forming-units-erythrocytes (BFU-E), was investigated in ten paediatric patients treated by regular haemodialysis. During a 30-week study rhEPO treatment resulted in a rise of median haemoglobin levels from 6.7 g/dl to > 10 g/dl in all patients. Before initiating rhEPO treatment the number of circulating BFU-E in chronic renal failure patients responded to grading doses of rhEPO in vitro similar to that in control children; however, the dose-response curves were not predictive for the in vivo response to rhEPO. After an initial rise in five patients BFU-E numbers declined by week 30 of rhEPO treatment. BFU-E numbers decreased to 35% of pretreatment values. The number of granulocyte-macrophage colony forming cells (GM-CFC) also decreased during rhEPO treatment. Addition of IL3 to the culture medium containing saturating concentrations of granulocyte-macrophage colony stimulating factor did not stimulate BFU-E numbers of patients before rhEPO treatment or those of controls. However, 2 weeks after start of rhEPO treatment IL3 increased the growth of patient's BFU-E in vitro to 220% of pretreatment levels, followed by a gradual decrease of stimulation until the end of observation. These findings indicate that: (1) long-term recruitment of circulating haematopoietic progenitors during rhEPO treatment is low in children with renal anaemia; (2) rhEPO sensitivity of circulating BFU-E is not predictive for the in vivo response; (3) rhEPO treatment results in enhanced sensitivity of BFU-E to IL3.

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.

Induction of granulocyte-macrophage colony-stimulating factor (GM-CSF) and granulocyte colony-stimulating factor (G-CSF) expression in bone marrow and fractionated marrow cell populations by interleukin 3 (IL-3): IL-3-mediated positive feedback mechanisms of granulopoiesis.

Interleukin 3 (IL-3) induces proliferation and differentiation of mast cell progenitors in vitro, whereas it induces granulocytosis in vivo. In this paper, a positive feedback mechanism of granulopoiesis was studied in order to elucidate the granulocytosis induced by IL-3 in mouse. IL-3 induced expression of granulocyte-macrophage colony-stimulating factor (GM-CSF) and granulocyte colony-stimulating factor (G-CSF) in total bone marrow cells and a marrow adherent cell population. In fractionated marrow cell populations, a different expression pattern of induction of IL-3 stimulation was observed; GM-CSF was expressed in macrophages and fraction 1 (P < 1.061) and 2(1.061 < P 1.074) of bone marrow cells fractionated by equilibrium density centrifugation, G-CSF was expressed in macrophages and fraction 2 and 3 (1.074 < P < 1.097), and interleukin 6 (IL-6) in macrophages and fraction 1 to 3. These results indicate a hierarchical regulation of cytokine production and the existence of a positive feedback mechanism in granulopoiesis. IL-6, induced by IL-3, stimulates stem cells into cycle and induces stem cells to respond to IL-3. The stem cells differentiate to granulocyte-macrophage colony-forming cells by the combined effect of IL-3 and IL-6. IL-3 also induces GM- and G-CSF expression which in turn makes granulocyte-macrophage colony-forming cells differentiate to granulocytes. These factors organize a cytokine network in granulopoiesis.

Peripheral Blood Progenitor Cell Transplantation in Lymphoma and Leukemia Using a Single Apheresis

AbstractMyeloablative treatment and peripheral blood progenitor cell (PBPC) transplantation are increasingly used for lymphomas and leukemias. We have sought to optimize conditions for priming, collection, and engraftment of the leukapheresis product. Fifty-four consecutive adult patients were eligible, 31 with high-grade non-Hodgkin’s lymphoma of poor prognosis, 12 with Hodgkin’s disease in chemosensitive relapse, and 11 with poor prognosis acute lymphoblastic leukemia. Filgrastim was administered after routine chemotherapy with VAPEC-B or HiCCOM to mobilize PBPC. A rapidly increasing white blood cell count was used to predict the time of peak PBPC release and plan leukapheresis. Forty-five patients underwent leukapheresis. A median of 14 L of blood was processed at a single apheresis. A median of 2.4 × 108/kg mononuclear cells (MNCs), 1.04 × 106/kg granulocyte-macrophage colony-forming cells (GM-CFCs), and 10.6 × 106/kgCD34+ cells were obtained. Slightly fewer MNCs were obtained from the heavily pretreated Hodgkin’s disease group. There were no other significant differences in the size or composition of the leukapheresis harvest in the three patient groups. Forty patients underwent high-dose therapy and PBPC transplantation. Filgrastim was administered by daily subcutaneous injection until the absolute neutrophil count was ≥1 × 109/L for 2 consecutive days. Rapid and sustained hematopoietic engraftment occurred in all patients. The median time to achieve a neutrophil count ≥0.5 × 109/L was 9 days (range, 8 to 16 days); to achieve a platelet count ≥20 × 109/L was 10 days (range, 6 to 88 days); and to achieve a platelet count ≥50 × 109/L was 15.5 days (range, 10 to 100 days). Neutrophil recovery was faster than that of a historical control group treated with autologous bone marrow transplantation and filgrastim, but platelet recovery times were halved in the PBPC group. There was no secondary engraftment failure. Requirements for blood and platelet transfusions, antibiotic use, and parenteral nutrition were similar in the three patient groups. The median number of days in the hospital was 13 (range, 10 to 55) in the PBPC patients, compared with 19 (range, 14 to 51) in the historical controls. Leukapheresis yields (MNC, GM-CFC, and CD34+ cell numbers) were not useful for predicting the times to engraftment. We have shown that sufficient PBPC for transplantation can be obtained at a single leukapheresis after mobilization with routine chemotherapy and filgrastim in patients with non-Hodgkin’s lymphoma, Hodgkin’s disease, and acute lymphoblastic leukemia, even those heavily pretreated. Rapid and sustained hematopoietic reconstitution was seen in all patients. If confirmed with chemotherapy regimens used in other groups, this simple and safe approach makes PBPC transplantation practicable for a wider range of patients.

Peripheral blood progenitor cell transplantation in lymphoma and leukemia using a single apheresis

Myeloablative treatment and peripheral blood progenitor cell (PBPC) transplantation are increasingly used for lymphomas and leukemias. We have sought to optimize conditions for priming, collection, and engraftment of the leukapheresis product. Fifty-four consecutive adult patients were eligible, 31 with high-grade non-Hodgkin's lymphoma of poor prognosis, 12 with Hodgkin's disease in chemosensitive relapse, and 11 with poor prognosis acute lymphoblastic leukemia. Filgrastim was administered after routine chemotherapy with VAPEC-B or HiCCOM to mobilize PBPC. A rapidly increasing white blood cell count was used to predict the time of peak PBPC release and plan leukapheresis. Forty- five patients underwent leukapheresis. A median of 14 L of blood was processed at a single apheresis. A median of 2.4 x 10(8)/kg mononuclear cells (MNCs), 1.04 x 10(6)/kg granulocyte-macrophage colony-forming cells (GM-CFCs), and 10.6 x 10(6)/kg CD34+ cells were obtained. Slightly fewer MNCs were obtained from the heavily pretreated Hodgkin's disease group. There were no other significant differences in the size or composition of the leukapheresis harvest in the three patient groups. Forty patients underwent high-dose therapy and PBPC transplantation. Filgrastim was administered by daily subcutaneous injection until the absolute neutrophil count was &gt; or = 1 x 10(9)/L for 2 consecutive days. Rapid and sustained hematopoietic engraftment occurred in all patients. The median time to achieve a neutrophil count &gt; or = 0.5 x 10(9)/L was 9 days (range, 8 to 16 days); to achieve a platelet count &gt; or = 20 x 10(9)/L was 10 days (range, 6 to 88 days); and to achieve a platelet count &gt; or = 50 x 10(9)/L was 15.5 days (range, 10 to 100 days). Neutrophil recovery was faster than that of a historical control group treated with autologous bone marrow transplantation and filgrastim, but platelet recovery times were halved in the PBPC group. There was no secondary engraftment failure. Requirements for blood and platelet transfusions, antibiotic use, and parenteral nutrition were similar in the three patient groups. The median number of days in the hospital was 13 (range, 10 to 55) in the PBPC patients, compared with 19 (range, 14 to 51) in the historical controls. Leukapheresis yields (MNC, GM-CFC, and CD34+ cell numbers) were not useful for predicting the times to engraftment. We have shown that sufficient PBPC for transplantation can be obtained at a single leukapheresis after mobilization with routine chemotherapy and filgrastim in patients with non-Hodgkin's lymphoma, Hodgkin's disease, and acute lymphoblastic leukemia, even those heavily pretreated.(ABSTRACT TRUNCATED AT 400 WORDS)

Human primitive hematopoietic progenitor cells are more enriched in KITlow cells than in KIThigh cells

To clarify the phenotypes of various classes of human hematopoietic progenitor cells, we used a multicolor staining protocol in conjunction with CD34 and a newly developed mouse antihuman c-kit proto-oncogene product (KIT) monoclonal antibody (MoAb). We characterized three cell fractions in CD34+ cells that express KITlow and KIThigh cells in addition to KIT- cells. A clonogenic assay showed that most granulocyte- macrophage colony-forming cells (GM-CFC) were present in CD34+KIThigh populations, whereas erythroid burst-forming cells (BFU-E) were detected mainly in the CD34+KITlow population. CD34(+)-KIT- fraction contained a small number of BFU-E. Morphologic analysis showed that blast-like cells were more enriched in the CD34+KITlow fraction. KITlow cells contained CD34+CD38- cells that were considered to be very primitive progenitor cells, as determined by a replating assay. To clarify the biologic differences between both fractions, we examined the more primitive progenitor cell functions by assessing long-term culture-initiating cells (LTC-IC) on the stromal cells. At week 2, more CFC recovered from the culture in the fraction initiated with a CD34+KIThigh population. However, more LTC-IC were present during weeks 5 to 9 in the CD34+KITlow population. These results indicate that primitive progenitors are more enriched in the KITlow population and that the KIThigh population contains many GM-committed progenitor cells. We also showed that anti-KIT MoAb inhibited the ability of CD34+ cells to generate CFC on the stromal layer in the LTC system. This suppressive effect was more evident in the generation of BFU-E by CD34+KITlow cells. Moreover, we confirmed that CD34+KIThigh cells emerged from CD34+KITlow cells during coculture with allogeneic stromal cells or from liquid culture in the presence of stem cell factor (SCF), interleukin-6, and erythropoietin. These results emphasize the pivotal role of the KIT and SCF interaction in hematopoiesis and indicate that KITlow cells are more primitive than KIThigh cells.

Human Primitive Hematopoietic Progenitor Cells Are More Enriched in KITlow Cells Than in KIThigh Cells

To clarify the phenotypes of various classes of human hematopoietic progenitor cells, we used a multicolor staining protocol in conjunction with CD34 and a newly developed mouse antihuman c-kit proto-oncogene product (KIT) monoclonal antibody (MoAb). We characterized three cell fractions in CD34+ cells that express KITlow and KIThigh cells in addition to KIT- cells. A clonogenic assay showed that most granulocyte-macrophage colony-forming cells (GM-CFC) were present in CD34+KIThigh populations, whereas erythroid burst-forming cells (BFU-E) were detected mainly in the CD34+KITlow population. CD34(+)-KIT- fraction contained a small number of BFU-E. Morphologic analysis showed that blast-like cells were more enriched in the CD34+KITlow fraction. KITlow cells contained CD34+CD38- cells that were considered to be very primitive progenitor cells, as determined by a replating assay. To clarify the biologic differences between both fractions, we examined the more primitive progenitor cell functions by assessing long-term culture-initiating cells (LTC-IC) on the stromal cells. At week 2, more CFC recovered from the culture in the fraction initiated with a CD34+KIThigh population. However, more LTC-IC were present during weeks 5 to 9 in the CD34+KITlow population. These results indicate that primitive progenitors are more enriched in the KITlow population and that the KIThigh population contains many GM-committed progenitor cells. We also showed that anti-KIT MoAb inhibited the ability of CD34+ cells to generate CFC on the stromal layer in the LTC system. This suppressive effect was more evident in the generation of BFU-E by CD34+KITlow cells. Moreover, we confirmed that CD34+KIThigh cells emerged from CD34+KITlow cells during coculture with allogeneic stromal cells or from liquid culture in the presence of stem cell factor (SCF), interleukin-6, and erythropoietin. These results emphasize the pivotal role of the KIT and SCF interaction in hematopoiesis and indicate that KITlow cells are more primitive than KIThigh cells.

Elevation of Extracellular Adenosine Induces Radioprotective Effects in Mice

The radioprotective effectiveness of the elevation of extracellular adenosine induced in mice by the combined administration of dipyridamole, a drug inhibiting the cellular uptake of adenosine, and adenosine monophosphate, a soluble adenosine pro-drug, was evaluated. Based on survival studies, endogenous hemopoietic spleen colony formation, and the postirradiation behavior of bone marrow granulocyte-macrophage colony-forming cells (GM-CFC), it was demonstrated that the combined administration of dipyridamole and AMP protects mice when given either 15 or 60 min before irradiation. It could be deduced that the radioprotective action is induced by at least two independent mechanisms: (1) protection by hypoxia as a result of the effect of the treatment on the cardiovascular system, and (2) and enhanced regeneration of the hemopoietic stem cells due to either enhanced postirradiation repair or an increased proliferation of the hemopoietic stem cells. Both of these protective mechanisms, which are able to increase the regeneration of hemopoiesis, seemed to be effective in enhancing the survival of mice given single radiation exposures, with a dose reduction factor for the LD50/30 of 1.11. The protective efficiency of the mechanisms enhancing the postirradiation recovery of hemopoiesis was also evident in experiments evaluating the survival of mice subjected to fractionated irradiation and a repeated administration of the protective agents.

Activated Natural Killer Cells Suppress Myelopoiesis in Mice with Severe Combined Immunodeficiency

The in vivo effect of natural killer (NK) cell activation on autologous myelopoiesis was studied in an environment deficient of functional T and B cells. Administration of 3,6-bis[2-(Dimethylamino)-ethoxy]-9H-xanthen-9-one dihydrochloride) Tilorone) or recombinant interleukin-2 (rIL-2) to mice with severe combined immunodeficiency (C.B.-17 scid/scid) resulted in an increase in YAC-1 lysis by their splenocytes as well as bone marrow cells. Recombinant IL-2 furthermore led to a fivefold increase in the cellularity of the spleen. When assayed against human NK/lymphokine-activated killer (LAK) target, K562 cell line, the IL-2-activated mouse cells exhibited no cytotoxicity across the species barrier. Both agents induced a profound suppression of myelopoietic progenitor cells as measured in a 7-day granulocyte-macrophage colony forming cell (GM-CFC) assay. We conclude that the presence of neither functional T nor B cells is necessary for NK cells to mediate inhibition of myelopoiesis in the autologous host.