Alpha-irradiation of Haemopoietic Tissue in Pre- and Postnatal Mice: 2. Effects of Mid-term Contamination with239Puin Utero

The distribution of 239Pu in various tissues of foetal and postnatal offspring of pregnant mice, injected i.v. at 13 days gestation with 30 kBq 239Pu/kg (in some cases with 10 or 100 kBq/kg), together with the numbers of haemopoietic progenitors in the bone marrow, spleen and liver, were measured through to 1 year post-partum. The quality of the haemopoietic microenvironment in these mice was also measured using the renal-capsule implant method. The largest radiation dose received by any haemopoietic organ was that in the liver, amounting to 10-14 mGy, as reported previously. In spite of normal numbers of haemopoietic spleen colony-forming cells (CFC-S) in the liver and seeding, at birth, into the bone marrow where the level of plutonium was minimal, a long-term deficit in their number rapidly developed. The development of the stromal microenvironment, however, was also deficient, suggesting that the dose of alpha-irradiation to the foetal liver was sufficient to cause sublethal damage in those cells destined to become the precursors of the supportive haemopoietic microenvironment in bone marrow and spleen. The results of this study suggest that although the placenta affords significant shielding to the tissues of the developing foetus from maternal contamination, the long-term effects on haemopoiesis are comparable to those in mice contaminated as adults. This further implies that the developing haemopoietic tissues are exquisitely sensitive to 239Pu contamination.

A comparison of potency of and intracellular signaling events provoked by, small molecule and protein-based mpl agonists

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Background: Thrombopoietin (TPO) interacts with its receptor (mpl) to initiate signal transduction and increase platelet production. Other mpl agonists have been developed for clinical use: MDGF (a recombinant protein) and romiplostim (a peptibody) are protein-based mpl agonists; eltrombopag (a small molecule) is a nonpeptide mpl agonist. Methods: Mpl agonists were compared for their ability to induce cellular responses and activate relevant signaling pathways in mpl-expressing cells. Proliferation was assessed by ATP bioluminescence in Baf3/mpl cells treated with mpl agonists for 2 days. Differentiation was assessed by flow cytometric-detection of CD41 and CD61 expression on human CD34+ cells cultured with mpl agonists for 7 days. Activation of signaling pathways was determined by Western blot analysis of proteins from serum-starved Baf3/mpl cells treated with mpl agonists for 20 minutes. Experiments were repeated 3 or more times. Results: The TPO concentration that produced a half-maximal (EC50) proliferative response of Baf3/mpl cells was comparable with that of romiplostim (Table). In contrast, a 30-fold greater concentration of MGDF and a 2,000-fold greater concentration of small molecule were required to produce the same degree of proliferation. In addition, a 1,000,000-fold greater concentration of small molecule compared with romiplostim was required to produce an EC50 for differentiation of CD34+ cells. Mpl agonists activated identical signaling pathways in Baf3/mpl cells: a similar dose-response for phosphorylation of JAK2, Stat3, Stat5, Erk1/2, and AKT was observed at their respective EC10, EC50, and EC100 concentrations. Conclusions: In Baf3/mpl cells, the small molecule was between 1,000- and 1,000,000-fold less potent than protein-based mpl agonists when corrected for molecular mass differences. Small molecule and protein-based mpl agonists were indistinguishable when mpl intracellular signaling was compared at similarly effective concentrations. [Table: see text]

[Table: see text]

Haemopoietic growth factors: their relevance in osteoclast formation and function

The major recent advance in our knowledge of the haemopoietic system has been the purification and characterization of a family of haemopoietic growth factors, and their availability in recombinant form. In the bone marrow the sequences of differentiation and proliferation leading to the production of mature cells that these factors regulate may be determined by the relative availability of the factors in microenvironmental domains. The observation that growth factor-producing cells and haemopoietic progenitor cells are not evenly distributed in the bone marrow leads us to expect that the overall effect of growth factors (and other regulatory molecules) on the production and function of macrophages and osteoclasts may differ when in vivo or in vitro assays are used as end-points and, in the latter case, when whole marrow or purified cell populations are tested. The availability of an in vitro assay in which osteoclast-like cells are generated will allow these concepts to be tested.

The design and development of pegfilgrastim (PEG-rmetHuG-CSF, Neulasta)

Recombinant protein technology produces drugs for human therapy in unprecedented quantity and quality. Research is now focusing on the relationship between pharmacokinetic and pharmacodynamic properties of molecules, with the aim of engineering proteins that possess enhanced therapeutic characteristics in contrast to being used as simple replacements for the natural equivalent. The addition of a polyethylene glycol (PEG) moiety to filgrastim (rmetHu-G-CSF, Neupogen) resulted in the development of pegfilgrastim. Pegfilgrastim is a long-acting form of filgrastim that requires only once-per-cycle administration for the management of chemotherapy-induced neutropenia. The covalent attachment of PEG to the N-terminal amine group of the parent molecule was attained using site-directed reductive alkylation. Pegylation increases the size of filgrastim so that it becomes too large for renal clearance. Consequently, neutrophil-mediated clearance predominates in elimination of the drug. This extends the median serum half-life of pegfilgrastim to 42 hours, compared with between 3.5 and 3.8 hours for Filgrastim, though in fact the half-life is variable, depending on the absolute neutrophil count, which in turn reflects of the ability of pegfilgrastim to sustain production of those same cells. The clearance of the molecule is thus dominated by a self-regulating mechanism. Pegfilgrastim retains the same biological activity as filgrastim, and binds to the same G-CSF receptor, stimulating the proliferation, differentiation and activation of neutrophils. Once-per-chemotherapy cycle administration of pegfilgrastim reduces the duration of severe neutropenia as effectively as daily treatment with filgrastim. In clinical trials, patients receiving pegfilgrastim also had a lower observed incidence of febrile neutropenia than patients receiving filgrastim.

Pegylation: engineering improved pharmaceuticals for enhanced therapy

Conjugating biomolecules with polyethylene glycol (PEG), a process known as pegylation, is now an established method for increasing the circulating half-life of protein and liposomal pharmaceuticals. Polyethylene glycols are nontoxic water-soluble polymers that, owing to their large hydrodynamic volume, create a shield around the pegylated drug, thus protecting it from renal clearance, enzymatic degradation, and recognition by cells of the immune system. Agent-specific pegylation methods have been used in recent years to produce pegylated drugs that have biologic activity that is the same as, or greater than, that of the parent drug. These agents have distinct in vivo pharmacokinetic and pharmacodynamic properties, as exemplified by the self-regulated clearance of pegfilgrastim, the prolonged absorption half-life of pegylated interferon alpha-2a, and the altered tolerability profile of pegylated liposomal doxorubicin. Pegylated agents have dosing schedules that are more convenient and more acceptable to patients, and this can have a beneficial effect on the quality of life of patients with cancer.

Novel erythropoiesis stimulating protein (darbepoetin alfa) alleviates anemia associated with chronic inflammatory disease in a rodent model

OBJECTIVE

We developed a rodent model of noninfectious systemic inflammation to examine the pathogenesis of the associated anemia of chronic disorders (ACD), to evaluate the similarity of this ACD model to human ACD, and to evaluate the potential efficacy of novel erythropoiesis stimulating protein (darbepoetin alfa) as an ACD therapy.

METHODS

Lewis rats were immunized with peptidoglycan-polysaccharide polymers (PG-APS), the chronic inflammation and associated ACD were characterized, and the effects of darbepoetin alfa treatment on complete blood counts (CBC), red blood cell (RBC) indices, and iron metabolism were analyzed weekly.

RESULTS

Acutely inflamed rats had reduced peripheral blood (PB) RBC counts and hemoglobin (Hb) concentrations and increased reticulocyte counts. PB RBC numbers normalized during chronic inflammation, but RBC remained hypochromic and microcytic. Consequently, the rats remained chronically anemic. Anemic rats had fluctuating serum erythropoietin (EPO) concentrations, but mean EPO concentrations never varied significantly from baseline control levels. Histology of anemic rat spleen sections revealed reticuloendothelial siderosis. Total serum iron concentrations were chronically low. Peritoneal exudate cells (PEC) isolated from anemic rats and stimulated with PG-APS in vitro produced more interleukin (IL)-1alpha and interferon (IFN)-gamma, and significantly more tumor necrosis factor (TNF)-alpha and IL-10 than control cultures. Darbepoetin alfa restored Hb concentrations to baseline levels within 2 to 7 weeks, depending on dosage. A refined treatment strategy restored Hb to baseline and maintained those levels with reduced dosing.

CONCLUSION

ACD in this rodent model closely replicates human ACD. Darbepoetin alfa treatment reversed ACD in this model by increasing RBC production and RBC hemoglobinization while reducing siderosis and hypoferremia.

Filgrastim (r-metHuG-CSF) in the 21st century: SD/01

SD/01, a sustained-duration molecule, has been developed by adding a poly [ethylene glycol] molecule to the filgrastim molecule. The pegylation does not change the properties of filgrastim, except that the plasma clearance is decreased and plasma half-life is increased. Increasing the duration of the biological effects of filgrastim may offer certain groups of patients better benefits. Early clinical studies have been encouraging with no serious toxicities noted.

Kinetics of neutrophil production in normal and neutropenic animals during the response to filgrastim (r-metHu G-CSF) or filgrastim SD/01 (PEG-r-metHu G-CSF)

Filgrastim G-CSF has a short, biologically active half-life, and its effective use depends on repeated inoculations. A major aim, therefore, has been to develop a once-per-chemotherapy cycle formulation. To this end, a polyethylene glycolylated form of Filgrastim, known as SD/01, has been developed. In this study, we compared the cellular kinetics of granulocyte production in mice stimulated with SD/01 and granulocyte colony-stimulating factor (G-CSF). Mice were injected with a single dose of SD/01 (1 mg/kg) or G-CSF (125 microg/kg) twice per day for 4 days. Mice rendered leukopenic with a single injection of cyclophosphamide (200 mg/kg) and temozolomide (90 mg/kg) were similarly treated at their 3-day neutrophil nadir. Tritiated thymidine was injected for autoradiographic labeling studies. Bone marrow labeling indices and the release of labeled neutrophils and monocytes into the peripheral blood were assessed. Granulocytopoiesis was stimulated similarly by both SD/01 and G-CSF in both normal and neutropenic animals, with counts rising to >20 x 10(9) polymorphonuclear neutrophils/l in both cases. Bone marrow thymidine labeling indices were increased, indicating a greater proportion of cells in DNA synthesis and an elevated proliferative activity. Compared with the normally slow release of neutrophils into the peripheral blood, labeled neutrophils (and monocytes) were rapidly released, increasing to peak levels at approximately 24 h. The peripheral half-life of neutrophils was not significantly different from normal, and the mitotic amplification factors for increase in granulocytopoiesis, accounted for by 3-3.9 extra cell divisions, were comparable for both factors. We conclude that neutrophil kinetics are stimulated in the same way and to the same extent by both SD/01 and G-CSF.

Prolonged neutropenia in a novel mouse granulocyte colony-stimulating factor neutralizing auto-immunoglobulin G mouse model

Therapeutic use of recombinant human cytokines in humans can result in the generation of drug-specific antibodies. To predetermine the maximum potential effects of a granulocyte colony-stimulating factor (G-CSF) neutralizing auto-immunoglobulin G (auto-IgG) response during recombinant human G-CSF therapy, we developed a mouse model of mouse G-CSF (mG-CSF) neutralizing auto-IgG response. Mice were immunized and boosted with mG-CSF chemically conjugated to either keyhole limpet hemocyanin or ovalbumin on an alternating schedule. Sera were analyzed for mG-CSF-specific titers and full blood counts were performed on a Technicon H-1E. On day 252, tissues were collected for histology. IgG was protein A affinity purified from pooled mG-CSF autoimmune sera. Mice immunized with mG-CSF conjugates produced mG-CSF-specific auto-IgG responses that lasted for the length of the study. Significant neutropenia (p(max) < 0.004) was concurrent with the rise in mG-CSF-specific IgG titers. However, neutrophil counts remained at approximately 20% of preimmunization levels through day 252. Endogenous mG-CSF neutralizing auto-IgG had no significant effect on hemoglobin, erythrocyte, lymphocyte, eosinophil, basophil, and platelet counts, and had minor, transient, or no effects on monocyte counts. Bone marrow colony assays from mG-CSF autoimmune mice demonstrated no significant effect of G-CSF neutralization on the numbers or proliferative capacity of preneutrophil lineage progenitors. Purified IgG from mG-CSF autoimmune mice neutralized mG-CSF in vitro. High-titer G-CSF neutralizing auto-IgG in adult mice partially inhibited steady-state granulopoiesis and had little or no effect on steady-state levels of other hematopoietic cells.

Efficient mobilization of haematopoietic progenitors after a single injection of pegylated recombinant human granulocyte colony-stimulating factor in mouse strains with distinct marrow-cell pool sizes

We have compared the efficacy of a single injection of SD/01, a newly engineered, pegylated form of recombinant human granulocyte colony stimulating factor (rhG-CSF), with a single injection of glycosylated rhG-CSF (Filgrastim). SD/01 was administered to regular and recombinant inbred strains of mice (AKR, C57L/J, DBA/2, C57BL/6, AKXL) known to have widely distinct marrow-cell pool sizes and proliferation kinetics. A single injection of G-CSF was unable to mobilize granulocyte-macrophage colony-forming units (CFU-GM). In sharp contrast, a single dose of SD/01 resulted in massive mobilization of progenitors and stem cells. Although all mice strains showed qualitatively similar mobilization responses, large interstrain differences remained. C57L and C57BL/6 mice mobilized relatively poorly, whereas AKR and DBA/2 mice showed threefold to tenfold superior responses. In order to explain these different phenotypes, we studied the effects of SD/01 in nine AKXL recombinant inbred strains, derived from well-responding AKR and poorly responding C57L parental strains. The best predictor for SD/01 responsiveness in these strains was marrow cellularity prior to mobilization. Comparison of the AKXL strain distribution pattern for marrow cellularity with loci previously mapped in these strains showed complete concordance with Aat, a serine protease inhibitor mapping to chromosome 12.

PEG-rHuMGDF promotes multilineage hematopoietic recovery in myelosuppressed mice

PEG-rHuMGDF administered to normal mice is a lineage-specific growth factor for megakaryocytes and platelets as judged by morphologic examination of hematologic cells in marrow and peripheral blood smears. The purpose of this study was to document that PEG-rHuMGDF in myelosuppressed mice promotes multilineage hematopoietic recovery. High-dose 5-fluorouracil (5-FU) in mice results in profound myelosuppression and 0-30% survival. Mice receiving a single dose of PEG-rHuMGDF (1000 microg/kg) 1 day after 5-FU (225 mg/kg) demonstrate an increased survival (76% vs 27% in control mice at 14 days). Compared to surviving controls, PEG-rHuMGDF-treated mice not only show the expected higher platelet counts, but also increased marrow colony-forming unit granulocyte-macrophage, increased multilineage marrow cellularity, and increased neutrophil, monocyte, and lymphocyte counts in peripheral blood. PEG-rHuMGDF- and vehicle-treated mice both develop hepatic abscesses after 5-FU treatment, but the abscesses in the PEG-rHuMGDF-treated mice contain more neutrophils, suggesting that myeloid reconstitution contributes to their survival. Furthermore, survival in 5-FU-treated mice is significantly improved by granulocyte colony-stimulating factor and antibiotics, suggesting that infection rather than thrombocytopenia is the predominant cause of death. PEG-rHuMGDF after 5-FU promotes survival accompanied by accelerated lymphohematopoietic repopulation, suggesting that PEG-rHuMGDF, a lineage-specific thrombopoietic factor in normal mice, promotes multilineage hematopoietic recovery in myelosuppressed mice.

A new form of Filgrastim with sustained duration in vivo and enhanced ability to mobilize PBPC in both mice and humans

Granulocyte colony-stimulating factor (G-CSF) has proven effective in the prophylaxis of chemotherapy-induced neutropenia and as a mobilizer of peripheral blood progenitor cells. The longevity of G-CSF action is limited by its removal from the body by two mechanisms. The first is thought to be mediated via receptors (receptor mediated clearance [RMC]) predominantly on neutrophils, the second process is likely the result of renal clearance. With the intention of developing a novel form of Filgrastim (r-met HuG-CSF) with a sustained duration of action in vivo, a new derivative named SD/01 has been made by association of Filgrastim with poly(ethylene glycol). The desired properties of this new agent would include a prolonged duration of action sufficient to cover a complete single course of chemotherapy. SD/01 is shown here to sustain significantly elevated neutrophil counts in hematopoietically normal mice for 5 days. In neutropenic mice effects were noted for at least 9 days, accompanying a significant reduction in the duration of chemotherapy induced neutropenia. Normal human volunteers showed higher than baseline ANC for around 9 to 10 days after a single injection of SD/01. Data from these normal volunteers also indicate that mobilization of CD34+ cells and progenitors may occur in a more timely manner and to around the same absolute numbers as with repeated daily injections of unmodified Filgrastim. These data indicate that SD/01 represents an efficacious novel form of Filgrastim with actions sustained for between one and two weeks from a single injection.

The prolonged hematologic effects of a single injection of PEG-rHuMGDF in normal and thrombocytopenic mice

A single injection of > or =10 microg/kg PEG-rHuMGDF in mice causes a dose-dependent increase in circulating platelets beginning on day 3 and peaking on days 5-6. The mean platelet volume and platelet distribution width at doses > or =100 microg/kg initially increase in a dose-dependent fashion and later decrease. However, the mean platelet volume does not change when platelets are incubated with PEG-rHuMGDF in vitro. The number of marrow megakaryocytes increases in a dose-dependent fashion as early as day 1 and peaks on day 3. Marrow megakaryocyte colony-forming units (CFU-Meg) do not increase on days 1-3 at a dose of 100 microg/kg (a dose that increases platelet numbers two- to threefold and may be clinically relevant), but the relative frequency of high ploidy megakaryocytes and the proportion of large marrow megakaryocytes (29-50 microm in diameter) increases. After a dose of 1,000 microg/kg the percentage of megakaryocytes in mitosis peaks at 24-48 hours and the percentage of megakaryocytes incorporating BrdU is maximal at 48 hours, the relatively delayed peak of BrdU incorporation most likely representing endomitosis. The relative frequency of type II and III megakaryocytes peaks on days 3 and 4, respectively. Pharmacokinetic analysis of PEG-rHuMGDF shows peak serum concentrations at 2-4 hours and a terminal half-life of 11.4+/-2.5 hours. A single injection of PEG-rHuMGDF ameliorates carboplatin-induced megakaryocytopenia and thrombocytopenia in a dose-response dependent fashion. In conclusion, a single injection of PEG-rHuMGDF increases megakaryocyte and platelet production in normal and myelo-suppressed mice.

Flt-3 ligand synergizes with granulocyte colony-stimulating factor to increase neutrophil numbers and to mobilize peripheral blood stem cells with long-term repopulating potential

Flt-3 ligand (FL) shares many features with stem cell factor (SCF), a widely documented cofactor for peripheral blood progenitor cell (PBPC) mobilization. We investigated the mobilization of PBPCs by FL in combination with granulocyte colony-stimulating factor (G-CSF). As a single agent, FL was a relatively modest mobilizer of PBPCs, resulting in 360 granulocyte/macrophage colony-forming cells (GM-CFCs)/mL blood (control, 155 GM-CFCs/mL blood) and no advantage in leukocyte recovery when these PBPCs were transplanted to irradiated recipient mice. G-CSF, on the other hand, mobilized over 20,000 GM-CFCs/mL blood, and the combination of G-CSF + FL resulted in over 100,000 GM-CFCs/mL blood. The combination of G-CSF + FL stimulated increased levels of monocytes and basophils in the peripheral blood. The performance of the mobilized PBPC product in irradiated hosts correlated with progenitor numbers resulting in long-term engraftment in association with accelerated short-term recovery of both leukocytes and platelets. These data demonstrate the potential of FL to synergize with G-CSF to mobilize PBPCs with both short- and long-term engraftment potential. The effect is similar to the synergistic interaction of G-CSF and SCF on PBPC mobilization. The use of FL as opposed to SCF may elicit a different spectrum of toxicities including lymphoid proliferation effects, in contrast to the mast cell degranulation effects of SCF. Clinical studies of FL are needed to evaluate its usefulness in man.

An analysis of the effects of combined treatment with rmGM-CSF and PEG-rHuMGDF in murine bone marrow transplant recipients

We have studied the potential of combination growth factor treatment with GM-CSF and megakaryocyte growth and development factor (MGDF) to stimulate hematopoietic recovery in mice following bone marrow transplantation. More rapid recovery of neutrophils occurred in mice treated with recombinant murine (rm)GM-CSF plus pegylated recombinant human (PEG-rHu)MGDF than carrier treated controls, however this recovery was equivalent to the effect of treatment with rmGM-CSF alone. PEG-rHuMGDF stimulated a more rapid recovery of platelets with no effect on neutrophil recovery. At the two tested doses of rmGM-CSF (72 and 200 microg/kg/day) the platelet recovery was inferior to that in carrier treated mice. Also, the addition of rmGM-CSF to PEG-rHuMGDF had a dose-related negative impact on platelet recovery compared to PEG-rHuMGDF alone. These data suggest that the use of combination therapy in some clinical indications may lead to unexpected results. Furthermore, careful dosage studies may be necessary to identify the full potential of combined growth factors to obtain additive or synergistic effects on multilineage hematopoietic reconstitution in vivo.

Megakaryocyte growth and development factor stimulates enhanced platelet recovery in mice after bone marrow transplantation

Megakaryocyte growth and development factor (MGDF) is a recently characterized ligand for the cell surface receptor mpl. We have evaluated the effects of polyethylene glycollated recombinant human MGDF (PEG-rHuMGDF) on recovery of hematopoietic cells in mice following bone marrow transplantation (BMT) to support lethal irradiation. Mice treated with PEG-rHuMGDF (50 micrograms/kg/d) had accelerated recovery of platelet numbers compared with BMT mice treated with carrier or recombinant human granulocyte colony-stimulating factor (rHuG-CSF, 72 or 200 micrograms/kg/d). In contrast, PEG-rHuMGDF had no effect on white blood cell (WBC) or red blood cell (RBC) recovery. As previously reported, animals treated with rHuG-CSF had an enhanced recovery of WBC but not platelet or RBC levels. Interestingly, BMT receipient mice treated with the combination of PEG-rHuMGDF and rHuG-CSF showed simultaneous enhanced recovery of both leukocytes and platelets. PEGylated rHuMGDF was found to be considerably more potent than non-PEGylated rHuMGDF in this setting. PEG-rHuMGDF is an effective growth factor for enhancing platelet recovery in mice following BMT either alone or in combination with rHuG-CSF. It will be of interest to evaluate in a clinical setting the ratios of PEG-rHuMGDF and rHuG-CSF for simultaneous administration of these factors and accelerated recovery of both leukocytes and platelets.

Megakaryocyte growth and development factor accelerates platelet recovery in peripheral blood progenitor cell transplant recipients

We have investigated the potential of PEGylated recombinant human megakaryocyte growth and development factor (PEG-rHuMGDF), a molecule related to thrombopoietin (mpl ligand or TPO) in minimizing the thrombocytopenia associated with hematopoietic ablation and peripheral blood progenitor cell (PBPC) transplant. Irradiated mice that received PBPC mobilized by PEG-rHuMGDF or granulocyte colony-stimulating factor (G-CSF) had a reduced number of thrombocytopenic days with platelets below 100 x 10(6) per mL of blood. Recipients of unmobilized PBPC had a 9 day thrombocytopenic phase which was shortened to 7 days if they were given granulocyte-macrophage colony-stimulating factor (GM-CSF)-mobilized PBPC. This was further reduced to 2 or 3 days of thrombocytopenia in recipients of G-CSF- or PEG-MGDF-mobilized PBPC. Despite our observation that PEG-rHuMGDF is a relatively modest stimulator of the mobilization of myeloid progenitors to the blood, MGDF-mobilized PBPC do effect accelerated recovery of platelets after transplantation. However, the most effective use of PEG-rHuMGDF is when it is given during the recovery phase after PBPC transplantation to hematopoietically ablated mice. Posttransplant treatment with PEG-rHuMGDF reduces thrombocytopenia to a single day or less, in recipients of most types of PBPC. Mice that were treated during the first 2 weeks after PBPC transplant with PEG-rHuMGDF had 1 thrombocytopenic day compared to 9 days in carrier-treated recipients of unmobilized PBPC and 2 to 3 days in carrier-treated recipients of the optimally mobilized PBPC from G-CSF or G-CSF/PEG-rHuMGDF treated donors. In groups where PEG-rHuMGDF was included in the mobilization protocol and used to treat recipients as well thrombocytopenia was effectively eliminated. These data show that PEG-rHuMGDF is a highly effective agent in eliminating the thrombocytopenia associated with PBPC transplantation.

CD34-deficient mice have reduced eosinophil accumulation after allergen exposure and show a novel crossreactive 90-kD protein

CD34 is expressed on the surface of hematopoietic stem/progenitor cells, stromal cells, and on the surface of high-endothelial venules (HEV). CD34 binds L-selectin, an adhesion molecule important for leukocyte rolling on venules and lymphocyte homing to peripheral lymph nodes (PLN). We generated CD34-deficient mutant animals through the use of homologous recombination. Wild-type and mutant animals showed no differences in lymphocyte binding to PLN HEV, in leukocyte rolling on venules or homing to PLN, in neutrophil extravasation into peritoneum in response to inflammatory stimulus, nor in delayed type hypersensitivity. Anti-L-selectin monoclonal antibody (MEL-14) also inhibited these immune responses similarly in both CD34-deficient and wild-type mice. However, eosinophil accumulation in the lung after inhalation of a model allergen, ovalbumin, is several-fold lower in mutant mice. We found no abnormalities in hematopoiesis in adult mice and interactions between mutant progenitor cells and a stromal cell line in vitro were normal. No differences existed in the recovery of progenitor cells after 5-fluorouracil treatment, nor in the mobilization of progenitor cells after granulocyte colony-stimulating factor treatment compared with wild-type animals. Surprisingly, although CD34 was not expressed in these mice, a portion of its 90-kD band crossreactive with MECA79 remained after Western blot. Thus, we have identified an additional molecule(s) that might be involved in leukocyte trafficking. These results indicate that CD34 plays an important role in eosinophil trafficking into the lung.

Total marrow failure induced by pegylated stem-cell factor administered before 5-fluorouracil

To examine the potential role of stem-cell factor (SCF) in cancer chemotherapy, we have administered it to mice either before or after 5-fluorouracil (5-FU). When polyethylene glycolated (PEG-ylated) SCF was administered to mice before 5-FU, it had a significant sensitizing effect on primitive bone marrow cells. Examination of the hematopoietic status of these mice showed that the damage caused by 5-FU to both bone marrow and spleen hematopoiesis was exaggerated when it was preceded by SCF. SCF given before each of two 5-FU treatments at 7-day intervals resulted in the death of all treated mice. The time of death and hematopoietic status of these animals are compatible with the onset of hypoplastic marrow failure leading to pancytopenia and death. SCF given after 5-FU had little impact either on the initial degree of hematopoietic damage or subsequent recovery. Gut populations were similarly sensitized to 5-FU by prior treatment with SCF, and the damage caused to intestinal populations was greater than that resulting from 5-FU alone. This indicates that the different tissues may be similarly sensitized by SCF. The sensitizing effect of SCF was reversed by concurrent administration of transforming growth factor (TGF)-beta 3, and survival of the majority of the mice was ensured. Examination of hematopoiesis in mice treated concurrently with SCF and TGF-beta 3 showed that the degree of marrow and spleen damage had reverted to that caused by 5-FU alone. In further experiments, 100% survival and normal hematopoiesis could be attained by transplantation of 1 million syngeneic bone marrow cells 24 hours after 5-FU treatment following SCF sensitization. These data indicate that PEG-ylated SCF can sensitize normally resistant hematopoietic and gut stem cells to the effects of 5-FU. This sensitization resulted in effective eradication of hematopoiesis in SCF-pretreated/5-FU-treated animals and their subsequent death from marrow failure. These findings imply that SCF pretreatment may represent a novel method of increasing the effectiveness of conventional chemotherapy, making marrow ablation more effective without drug dose escalation and perhaps sensitizing some tumor cells to the effects of therapy.

The effects on hematopoiesis of recombinant stem cell factor (ligand for c-kit) administered in vivo to mice either alone or in combination with granulocyte colony-stimulating factor

Stem cell factor (SCF) is the ligand for the receptor encoded by the c-kit proto-oncogene. Mutations of either c-kit or the SCF gene are responsible for the defects of W and SI mutant mice, which both suffer a macrocytic anemia, the former associated with defective stem cells and the latter with a defective hematopoietic microenvironment. PEGylated recombinant rat SCF was administered to normal or splenectomized mice for up to 21 days. SCF was found to be a modest stimulator of peripheral blood neutrophil numbers in both groups of animals. The peak in neutrophil numbers was higher and occurred earlier in splenectomized mice. Bone marrow and spleen cellularity changed little during treatment but the content of interleukin-3-responsive progenitor cells and spleen colony-forming cells (CFU-S) reached very high levels, particularly in the spleen. Using recombinant human granulocyte colony-stimulating factor (rhG-CSF), we have shown that SCF induces a greater than additive increase in both blood neutrophils and blood-borne CFU-S. This synergy was seen throughout the dose range and may indicate a clinical role for SCF either alone or in augmenting the activity of G-CSF upon blood neutrophils and transplantable stem cells.

Myeloid cell kinetics in mice treated with recombinant interleukin-3, granulocyte colony-stimulating factor (CSF), or granulocyte-macrophage CSF in vivo

Myeloid cell kinetics in mice treated with pure hematopoietic growth factors have been investigated using tritiated thymidine labeling and autoradiography. Mice were injected subcutaneously with 125 micrograms/kg granulocyte colony-stimulating factor (G-CSF) (in some cases 5 micrograms/kg), or 10 micrograms/kg of granulocyte-macrophage CSF (GM-CSF), or interleukin-3 (IL-3) every 12 hours for 84 hours. 3HTdR labeling was performed in vivo after 3 days of treatment. G-CSF increased the peripheral neutrophil count 14-fold and increased the proportion and proliferation rate of neutrophilic cells in the marrow, suppressing erythropoiesis at the same time. Newly produced mature cells were released into the circulation within 24 hours of labeling, compared with a normal appearance time of about 96 hours. By contrast, GM-CSF and IL-3 had little effect on either marrow cell kinetics or on the rate of release of mature cells, although GM-CSF did stimulate a 50% increase in peripheral neutrophils. Monocyte production was also increased about eightfold by G-CSF and 1.5-fold by GM-CSF, but their peak release was only slightly accelerated. While the peripheral half-lives of the neutrophilic granulocytes were normal, those of the monocytes were dramatically reduced, perhaps due to sequestration in the tissues for functional purposes. The stimulated monocyte production in the case of G-CSF required an additional five cell cycles, a level that might have repercussions on the progenitor compartments.

Long-term effects of plutonium-239 and radium-224 on the distribution and performance of pluripotent haemopoietic progenitor cells and their regulatory microenvironment

Experiments are described which investigate the long-term damage to haemopoietic progenitor cells (CFU-S) and their microenvironment in mouse marrow resulting from the administration of leukaemogenic amounts of plutonium-239 and radium-224. 239Pu (35 Bq g-1 body weight) and 224Ra (555 Bg g-1 body weight) were injected into 10-12-week-old mice, and numbers, proliferative activity and self-renewal capacity of CFU-S were measured at different locations in femoral marrow at intervals over the following 2 years. Parallel measurements were also made of the quality of the haemopoietic microenvironment by ectopic transplantation of bone marrow cells. There was some recovery from the initial effects of 239Pu on CFU-S numbers after 3-6 months, although the recovery was not maintained in all marrow fractions. Following 224Ra administration there was an initial transient increase in CFU-S numbers in the fraction of marrow furthest from bone surfaces but a considerable depression in numbers in other regions of marrow; there was no recovery between 3 and 6 months and subsequent recovery was not complete in all regions of marrow. The differential responses of CFU-S and the haemopoietic microenvironment following 224Ra or 239Pu administration seemed in some ways related to the metabolism of the radionuclides. There was a profound reduction in the ability of marrow to generate ossicles when transplanted under the kidney capsule as a result of the administration of either 224Ra or 239Pu, with only transient recoveries from the effects of 239Pu at 4 days and at 3 months after injection.

Growth inhibitory effects of transforming growth factor-beta 1 in vivo

Transforming growth factor-beta (TGF-beta) can reversibly inhibit the in vitro proliferation of murine and human haemopoietic progenitors and some of their more developmentally restricted progeny. Using an assay for measuring day 8 and day 11 CFU-S, TGF-beta caused a gradual decline in the number of CFU-S undergoing DNA synthesis so that after 5 days of daily treatment only quiescent cells were found. Release of this growth inhibition was seen within 24 hours post-treatment with recovery of all progenitors to normal levels. Similar inhibitory effects of TGF-beta were seen on the cells of the intestinal epithelium, indicating that TGF-beta is a general stem cell growth inhibitor. These results suggest that TGF-beta can be used as a cytostatic agent to protect normal stem cells in patients being treated with cell cycle-specific cytotoxic agents.

Transplantation potential of peripheral blood stem cells induced by granulocyte colony-stimulating factor

The major effect of granulocyte colony-stimulating factor (G-CSF) is to induce neutrophilia in previously untreated animals or after chemotherapy or marrow transplantation in humans, primates and rodents. In addition, it has been reported that migration of committed progenitor cells to the blood occurs during G-CSF therapy. In this article, by using sex mismatched transplants and a molecular probe for Y-chromosome specific DNA sequences, we show that among the peripheral blood cells during G-CSF therapy are substantial numbers of primitive stem cells capable of (1) reconstituting the hematopoietic system in the long term, and (2) making a contribution to the lymphoid populations of the thymus, in radiation ablated recipients. These data suggest that blood from patients treated with G-CSF may provide a convenient source of the most primitive stem cells for autologous or allogeneic bone marrow transplantation.

A comparison of hematopoiesis in normal and splenectomized mice treated with granulocyte colony-stimulating factor

Recombinant human granulocyte colony-stimulating factor (rhG-CSF) induces leukocytosis in vivo in both intact and splenectomized mice. Full dose response data showed a plateau in this effect at doses over 500 micrograms rhG-CSF/kg body weight/d in intact mice. The effect is magnified in splenectomized mice, where leukocyte numbers reach 100 x 10(6) mL after 4 days' treatment at 250 micrograms/kg/d. Further hematopoietic precursor populations are also affected in both marrow and the spleen; in general, marrow parameters were depressed, while splenic populations were enlarged. In splenectomized mice, both blood-borne stem cells were enhanced, and foci of extramedullary hematopoiesis were enlarged in addition to the effects seen in intact mice. In the marrow of splenectomized and intact mice treated with a high dose of G-CSF, erythroid suppression in the marrow was confirmed with radioactive iron. Our studies confirm and extend previous work on the mode of action of G-CSF, and indicate that side effects of high dose G-CSF therapy might include erythroid suppression in the bone marrow.

Hemopoietic effects of short-term in vivo treatment of mice with various doses of rhG-CSF

Recombinant human granulocyte colony-stimulating factor (rhG-CSF) was injected s.c., twice daily, into normal adult male BDF1 mice for a period of 4-5 days in doses ranging from 10 to 2500 micrograms/kg/day. The number of peripheral blood cells and their morphology was examined daily from the beginning of the experiment for 6 days. On the 5th day of treatment parameters such as spleen weight and cellularity, bone marrow morphology and cellularity, content of granulocyte-macrophage colony-forming cells (GM-CFC) or multipotential stem cells (CFU-S) in spleen and marrow, and also histology of lung and liver were examined. We observed a dose-dependent increase in the number of blood neutrophils, and an increase in weight, cellularity, and numbers of GM-CFC and CFU-S in the spleen. In the bone marrow, cellularity decreased to 40% of normal. Numbers of GM-CFC and CFU-S in marrow were also decreased, and examination of marrow morphology revealed an inhibition of erythropoiesis.

Effects of long-term in vivo treatment of mice with purified murine recombinant GM-CSF

Normal adult BDF1 mice were injected s.c. with 1 or 10 micrograms/kg/day of recombinant murine granulocyte-macrophage colony-stimulating factor (rmGM-CSF; specific activity 3.9 x 10(7) U/mg) for periods up to 11 weeks. After 1, 3, 7, 9, or 11 weeks, groups of three mice were killed and various hematological parameters were evaluated. Such treatment induced a sustained increase in the number and phagocytic activity of peritoneal macrophages, increased weight and cellularity of the spleen, and increased numbers of lineage-restricted precursor cells and multipotent stem cells in the spleen. No significant differences in blood cell numbers or differential counts were observed during the experiment. Femoral granulocyte-macrophage colony-forming cells (GM-CFCs), mixed-lineage colony-forming cells (Mix-CFCs), and 7- and 12-day spleen colony-forming units (CFU-S) were increased in the first week of treatment, but returned to normal (or subnormal levels) later. Examination of histological preparations of liver, lung, skin, ileum, thymus, Peyer's patches, kidney, skin, and brain revealed no differences from control preparations. Mast cell numbers were not increased in any of these tissues. Despite continuing treatment, most hematological parameters normalized upon prolonged rmGM-CSF treatment. The reasons for this are unclear but are not apparently due to the presence of inhibitory factors in the blood of treated mice. The results indicate little evidence of side effects during prolonged therapy with doses of rGM-CSF commonly used in clinical situations.

On the late seeding of CFU-S to the spleen: 8- vs 12-day CFU-S

Marrow from 5-fluorouracil- or cyclophosphamide-treated mice, injected into lethally irradiated recipients, gives an increasing number of spleen colonies between days 7 and 14. It has been suggested that the later-forming colonies result from the more primitive spleen colony-forming units (CFU-S), which first seed into the marrow, only later to be recirculated and form colonies in the spleen. Strontium 89 (89Sr), a bone-seeking radionuclide, was injected into recipient mice to block such putative recirculation. A dose of 89Sr, which killed at least 99.8% of CFU-S in, or entering, the bone cavities, was incapable of preventing the increase in spleen colony numbers. Similarly, the splenic environment, modified by the presence of spleen colonies and able to provide a better bed for trapping CFU-S from the peripheral circulation, yielded the same number of further CFU-S, whether or not the animal had received 89Sr. Thus, it was concluded that the 12-day CFU-S does not seed initially into the marrow spaces. Direct observation of the quality of CFU-S initially seeding into the bone marrow and spleen showed, by retransplantation into secondary irradiated mice, that a similar spectrum of CFU-S types had seeded both organs.

Residual haemopoietic damage in the mouse after fractionated gamma-irradiation, down to 0.1 Gy per fraction

Residual damage in haemopoietic progenitor cell populations, spleen and granulocyte-macrophage colony-forming cells (CFU-S and GM-CFC) was detected in mice after 15 daily fractions where the dose per fraction was as low as 0.1 Gy. The injury was dose-dependent and after higher total fractionated doses of 7.5-10 Gy the CFU-S population recovered to about 50% of control between 2 and 12 months after irradiation. Residual damage was also detected in the stroma, in the form of reduced numbers of fibroblastoid colony-forming cells and of CFU-S in ossicles under the kidney capsule. The response to a second course of 15 fractions, given 3 weeks after the end of the first course, was similar and additive to the response to the first course in the short term. However, in the long term, recovery levels were similar after either one or two courses.

The effect of low dose rate on recovery of hemopoietic and stromal progenitor cells in gamma-irradiated mouse bone marrow

Long-term recovery of mouse hemopoietic stem cells (CFU-S and CFU-S per colony), granulocyte-macrophage precursor cells (GM-CFC), and stromal colony-forming units (CFU-F) after doses up to 12.5 Gy was almost complete by 1 year when the dose rate was reduced to 0.0005 Gy/min compared to incomplete recovery after doses up to only 6.5 Gy given at greater than 0.7 Gy/min. This sparing effect of dose rate on long-term hemopoietic recovery is in contrast to the generally reported lack of dependence on dose rate for acute survival of hemopoietic progenitors after doses up to 5 Gy. The present results are compatible with the hypothesis that good recovery of the stroma should be reflected in the long-term recovery of hemopoiesis.

The radiation sensitivity of the haemopoietic microenvironment--effect of dose rate on ectopic ossicle formation

The haemopoietic microenvironment (HM) consists of a complex mixture of cellular types and extra-cellular matrix. It is essential for prolonged haemopoiesis in both the normal situation and after bone marrow transplantation. The competence of the HM can be assessed by ectopic grafting of femoral marrow. A complete haemopoietic organ develops at the site of implantation. Stem cells (CFU-S) which inhabit the ossicle formed after ectopic implantation can be measured, to assess the function of the engrafted HM to support haemopoiesis. Using this functional endpoint we have examined the radiation sensitivity of the HM at both high and low dose rates, and conclude that high doses of gamma-irradiation delivered at 4 Gy/min or 0.016 Gy/min have widely different effects on the HM, the former proving much more damaging than the latter.

Standardization of procedures for ectopic marrow grafting. II. Influence on recipients of radiation dose and field size

The ectopic implantation of mouse marrow to the kidney capsule offers considerable scope as an assay of the hemopoietic microenvironment. Our previous work has shown that whole-body irradiation of the graft recipient prior to implantation results in superior ossicle formation in the kidney of the host. Here we report that a range of irradiation doses over a 4-Gy threshold are equivalent with respect to conditioning the graft recipient. We also show that two distinct and separable influences affect graft growth in the irradiated recipient, namely, a local effect brought about in the irradiated kidney (and restricted to it) and secondly, a systemic effect resulting from irradiation of sites other than the kidney, which nevertheless affects ossicle growth in the shielded renal capsule.

Marrow repopulation in mice treated with busulphan or isopropyl methane sulphonate and bone marrow

By using karyotypic analysis of female mice treated with busulphan or isopropyl methane sulphonate (IMS), and injected with male bone marrow the donor contribution to both total marrow cellularity and spleen colony forming cells (CFU-S) was assessed for up to 6 months after transplant. In the mice treated with busulphan the marrow cells yielded metaphases of which between 40% and 83% were of donor type. Between 60% and 97% of metaphases in spleen colonies formed in irradiated mice were of donor type during the 24-week study period. In contrast, mice prepared for the transplant with IMS showed no cells of donor type at any time after transplant, neither did they possess CFU-S of donor type. We were therefore led to conclude that the donor cells made no contribution to longterm engraftment in mice prepared with IMS, whilst in those prepared with busulphan they were the predominantly active haemopoietic cells. These results are consistent with a model of haemopoiesis in which the most primitive cells reside in a 'niche' where they are resistant to the effects of IMS but susceptible to the action of busulphan. Busulphan may vacate some niches to allow engraftment by transplanted marrow, whilst IMS yields no unoccupied niches for grafted cells to occupy, and cannot therefore lead to a stable chimaerism.

A cellular analysis of long-term haematopoietic damage in mice after repeated treatment with cyclophosphamide

Following repeated treatment of mice with cyclophosphamide (5 X 200 mg/kg) it was found that slight, but significant, residual marrow damage persisted for at least half the lifespan of the animals. This long-term damage occurred despite preferential sparing of those multi-potential haematopoietic cells (CFU-S) that had a high self-renewal capacity after each step of the multistep regimen and despite a smaller CFU-S kill after each successive dose. The damage was characterized by low mean numbers of CFU-S and stromal colony-forming cells (CFU-F) which were around 70% of control values. Examination of individual animals revealed that the majority had slightly subnormal numbers of CFU-S and CFU-F, with only a few suffering a more severe injury, including 8% of mice with clinical hypoplasia or myelodysplasia.

Development of spleen CFU-S colonies from day 8 to day 11: relationship to self-renewal capacity

To investigate the persistence of spleen colonies from day 8 to day 11 of their development, we injected low numbers of marrow cells in order to obtain single colonies on the spleens of irradiated mice. Colonies were isolated on either half of the spleen on the eighth day. The position of day-11 colonies, determined relative to the ligature, indicated where novel colonies appear between those times. The results showed no evidence of the persistence of colonies from day 8 to day 11. The self-reproduction capacity of CFU-S that survive various cytotoxic drugs depends on the specific subpopulations that are affected by the drug. Using cyclophosphamide, busulphan, or BCNU, the self-renewal capacity of surviving CFU-S was manipulated. The results show that after cytotoxic treatments, a high day-11-day-8 ratio is not necessarily a reflection of a high self-renewal capacity of the CFU-S population that forms the day-11 colonies.

Long-term bone marrow damage in experimental systems and in patients after radiation or chemotherapy

Long-term bone marrow damage, characterised by stem, progenitor and stromal cell abnormalities is a frequent occurrence after cytotoxic treatments. The relative contributions of each of these components are difficult to analyse, especially in the case of patients who have received combined chemotherapy. The damage may be latent, and not manifested in low numbers of mature functional cells in the blood, but may become apparent as an hypoplastic syndrome at later times. Little tendency of recovery to normal parameters is seen in experimental animals and in patients.