Humoral regulation of stem cell proliferation

Review: tissue engineering: reconstitution of human hematopoiesis ex vivo

The reconstruction of functioning human tissues ex vivo is becoming an important part of biotechnology. There are compelling scientific, clinical, and biotechnological reasons for fully or partially reconstituting human tissues such as skin, bone marrow, and liver ex vivo. In particular, bone marrow is a tissue of much importance, and there are significant societal and health benefits derived from a successfully constructed ex vivo hematopoietic system. In this article, we review the current status of this effort. The topics covered include the current understanding of the biology of human hematopoiesis, the motivation for reconstructing it ex vivo, the current state of ex vivo human hematopoietic cultures, the development of important metrics to judge culture performance, and an approach based on in vivo mimetics to accomplish this goal. We discuss some applications of functional ex vivo hematopoietic cultures and the biological and engineering challenges that face research in this area.

Enhancement of hematopoietic reconstitution with recombinant cytokines: effect of rhIL-6 in combination with rhGM-CSF and rhIL-3 on unmodified or T cell-depleted bone marrow

We have investigated the response of unmanipulated and lymphocyte-depleted BM cells (BMC), pretreated with monoclonal rat antihuman lymphocyte (CD52) antibody (Campath-1G) used for prevention of GvHD, to incubation with rhIL-6 alone or in combination with rhGM-CSF, rhIL-3, or both. We investigated optimal conditions needed for incubation of human BMC under conditions that can be upscaled for clinical application prior to autologous (auto-BMT) and allogeneic blood or BM transplantation (allo-BMT). When used as a single agent, rhIL-6 showed no or a minimal effect in enhancing in vitro CFU-GM colony formation of human BMC. A potent additive effect was obtained when rhIL-6 was added to rhGM-CSF, rhIL-3, or a combination of both. Binding of the mAb Campath-1G, which is used for in vivo and in vitro depletion of immunocompetent lymphocytes to BMC, did not reduce the enhancing effect of a combination of rhGM-CSF and rhIL-3 on CFU-GM in the presence or absence of rhIL-6. Our present and previously published observations suggest that enhancement of hematopoiesis by rhIL-6 and other hematopoietic growth factors is T cell independent. Based on the present observations, pilot clinical studies to determine the potential benefit of in vitro activation of BMC prior to BMT with various cytokine combinations, including rhIL-6, seems justified. Our goal is to enhance hematopoietic reconstitution in vivo, focusing on possible enhancement of platelet reconstitution in vivo toward safer auto-BMT and more effective allo-BMT with better engraftment of T cell-depleted allografts while avoiding GvHD.

Randomized Trial of Autologous Filgrastim-Primed Bone Marrow Transplantation Versus Filgrastim-Mobilized Peripheral Blood Stem Cell Transplantation in Lymphoma Patients

Although a large amount of data is available on the effects of filgrastim (granulocyte colony-stimulating factor [G-CSF]) on the mobilization of stem cells in the circulation, data concerning its effects on bone marrow (BM) harvesting is scarce and controversial. We have designed a randomized trial comparing filgrastim-mobilized peripheral blood stem cell (PBSC) transplantation with filgrastim-primed autologous bone marrow transplantation (ABMT). Fifty-five patients affected by non-Hodgkin's (n = 38) or Hodgkin's (n = 17) lymphoma, selected for autologous transplantation over a 12-month period in a single institution, were randomized 2:1 to undergo BM or PB harvest/collection after priming for 3 days with filgrastim, 16 μg/kg body weight daily subcutaneously. BM priming with G-CSF allowed the harvest of a significantly higher number of mononuclear cells (MNC) (0.53 × 108/kg, range, 0.32 to 1.40), as compared with a historical control of unprimed BM harvests (0.43 × 108 MNC/kg, range, 0.15 to 0.72, P = .001). After high-dose ablative therapy, median time to neutrophil recovery above 0.5 × 109/L was 12 days for BM and 11 days for PB (P = .219); median time to platelet recovery above 20 × 109/L was 13 days for BM and 11 days for PB (P = .242). The same number of red blood cells, platelet transfusions, and posttransplant G-CSF doses were required in the two groups of patients. Less patients (50% v 70%) became febrile in the group transplanted with mobilized PB, but days of fever/patient and days on antibiotics were overlapping. The median time spent in the hospital after reinfusion was 16.5 and 15.5 days after primed BM and primed PB, respectively (P = .134). These data suggest that in patients with lymphoma submitted to autologous transplantation, the reinfusion of filgrastim-primed BM or filgrastim-mobilized PB leads to similar results, with an advantage of only 1 day in the neutrophil recovery and 1 day on the time spent in the hospital in favor of primed PB. Either option can be chosen on the basis of the availability of a surgery room or cell separator facilities and considering the patients' characteristics and wishes.

Randomized Trial of Autologous Filgrastim-Primed Bone Marrow Transplantation Versus Filgrastim-Mobilized Peripheral Blood Stem Cell Transplantation in Lymphoma Patients

Although a large amount of data is available on the effects of filgrastim (granulocyte colony-stimulating factor [G-CSF]) on the mobilization of stem cells in the circulation, data concerning its effects on bone marrow (BM) harvesting is scarce and controversial. We have designed a randomized trial comparing filgrastim-mobilized peripheral blood stem cell (PBSC) transplantation with filgrastim-primed autologous bone marrow transplantation (ABMT). Fifty-five patients affected by non-Hodgkin's (n = 38) or Hodgkin's (n = 17) lymphoma, selected for autologous transplantation over a 12-month period in a single institution, were randomized 2:1 to undergo BM or PB harvest/collection after priming for 3 days with filgrastim, 16 μg/kg body weight daily subcutaneously. BM priming with G-CSF allowed the harvest of a significantly higher number of mononuclear cells (MNC) (0.53 × 108/kg, range, 0.32 to 1.40), as compared with a historical control of unprimed BM harvests (0.43 × 108 MNC/kg, range, 0.15 to 0.72, P = .001). After high-dose ablative therapy, median time to neutrophil recovery above 0.5 × 109/L was 12 days for BM and 11 days for PB (P = .219); median time to platelet recovery above 20 × 109/L was 13 days for BM and 11 days for PB (P = .242). The same number of red blood cells, platelet transfusions, and posttransplant G-CSF doses were required in the two groups of patients. Less patients (50% v 70%) became febrile in the group transplanted with mobilized PB, but days of fever/patient and days on antibiotics were overlapping. The median time spent in the hospital after reinfusion was 16.5 and 15.5 days after primed BM and primed PB, respectively (P = .134). These data suggest that in patients with lymphoma submitted to autologous transplantation, the reinfusion of filgrastim-primed BM or filgrastim-mobilized PB leads to similar results, with an advantage of only 1 day in the neutrophil recovery and 1 day on the time spent in the hospital in favor of primed PB. Either option can be chosen on the basis of the availability of a surgery room or cell separator facilities and considering the patients' characteristics and wishes.

Cytotoxicity of a recombinant diphtheria toxin-granulocyte colony-stimulating factor fusion protein on human leukemic blast cells

Granulocyte colony-stimulating factor (G-CSF) is a potent stimulator of the growth of normal and malignant hematopoietic cells and synergizes with other factors such as interleukin-3 (IL-3) and granulocyte-macrophage colony-stimulating factor (GM-CSF). The action of G-CSF is mediated through a specific membrane receptor, however it is not clear if all of the effects of G-CSF are direct or indirect. As a step towards addressing this problem, a recombinant diphtheria toxin (DT)-related human G-CSF fusion protein has been constructed and purified from E. coli. The 70,000 dalton chimeric protein has immunologic determinants characteristic of both DT and G-CSF. At high concentrations, DAB486-G-CSF is cytotoxic towards G-CSF-dependent OCI/AML1 cells, but not factor independent OCI/AML3 cells; colony formation by G-CSF-responsive leukemic blasts from a patient with acute myeloblastic leukemia (AML) was also inhibited. The G-CSF fusion toxin displayed ADP-ribosyltransferase activity in a cell-free system. Genetic conjugation of G-CSF to an enzymatically inactive DT mutant, CRM197, resulted in a 200-fold reduction in the ability of G-CSF to stimulate normal bone marrow colony formation. These results suggest that fusion of G-CSF to DT sequences interferes with some of the activity but not the specificity of the ligand binding domain of the molecule. Nevertheless, DAB486-G-CSF may be included with the increasing number of other toxin-hormone fusion proteins whose toxicity is directed towards specific receptor-bearing cells, and may represent a novel approach towards the study and treatment of leukemia.

Retroviral gene transfer to primitive normal and leukemic hematopoietic cells using clinically applicable procedures

Clinical uses of gene transfer to bone marrow transplants require the establishment of a reproducible method for infecting large numbers of very primitive hematopoietic cells at high efficiency using cell-free retrovirus-containing media. In this study we report the results of experiments with preparations of a high-titer (2-5 x 10(7)/ml) helper-free recombinant neo(r) retrovirus that indicate this goal can now be achieved based on measurements of gene transfer efficiencies to cells referred to as long-term culture initiating cells (LTC-IC) because they give rise to clonogenic cells after greater than or equal to 5 wk in long-term culture (LTC). Intermittent, repeated exposure of normal human marrow mononuclear cells to virus-containing supernatant over a 3-d period of cell maintenance on an IL-3/granulocyte colony-stimulating factor (G-CSF) producing stromal layer resulted in gene transfer efficiencies to LTC-IC of 41%; a level previously obtainable only using co-cultivation infection techniques. Marrow cells enriched greater than or equal to 500-fold for LTC-IC (1-2% pure) by flow cytometry showed gene transfer efficiencies of 27% when infected in a similar fashion over a shorter period (24 h), but in the presence of added soluble IL-3 and G-CSF without stromal feeders, and this increased to 61% when Steel factor was also present during the infection period. By using a less highly enriched population of LTC-IC obtained by a bulk immunoselection technique applicable to large-scale clinical marrow harvests, gene transfer efficiencies to LTC-IC of 40% were achieved and this was increased to 60% by short-term preselection in G418. Southern analysis of DNA from the nonadherent cells produced by these LTC over a 6-wk period provided evidence of clonal evolution of LTC-IC in vitro. Leukemic chronic myelogenous leukemia LTC-IC were also infected at high efficiency using the same supernatant infection strategy with growth factor supplementation. These data demonstrate the feasibility of using cell-free virus preparations for infecting clinical marrow samples suitable for transplantation, as well as for further analysis of human marrow stem cell dynamics in vitro.

Increased production of tumor necrosis factor-alpha by bone marrow leukocytes following benzene treatment of mice

Hematopoiesis is regulated by cytokines released from bone marrow stromal cells and mature leukocytes. Recent studies have identified these cells as targets for benzene-induced hematotoxicity. In the present studies we analyzed the effects of benzene treatment of mice on the production of interleukin-1 (IL-1), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-alpha) by bone marrow leukocytes. Bone marrow cells isolated from control or benzene-treated mice (660 mg/kg, once/day, 3 days) were purified on lymphocyte separation medium. Cells were then cultured in the presence of varying concentrations of lipopolysaccharide (0.1-10 micrograms/ml) for 0.5-48 hr. IL-1, IL-6, and TNF-alpha activity in culture supernatants was then quantified. We found a significant (p less than or equal to 0.02) increase in TNF-alpha production by bone marrow leukocytes from benzene-treated mice when compared to cells from control animals. Furthermore, this increase was dependent on the macrophage-specific growth factor, colony stimulating factor-1. Benzene treatment was also found to induce a small but significant (p less than or equal to 0.02) increase in the production of IL-1 by bone marrow leukocytes. This increase was rapid and transient, occurring in supernatants collected 2 hr after inoculation of bone marrow cells into culture. In contrast, benzene treatment had no effect on the production of IL-6 by bone marrow leukocytes. These results demonstrate that benzene treatment of mice stimulates mature bone marrow leukocytes to produce elevated levels of growth regulatory cytokines.

Continuous activation of primitive hematopoietic cells in long-term human marrow cultures containing irradiated tumor cells

Human hematopoietic cells can be maintained in vitro for many weeks in the absence of exogenously provided hematopoietic growth factors if an adequate stromal cell containing adherent layer is present. We have now extended the use of this type of long-term culture (LTC) system to create a model of perturbed hematopoiesis in which human tumor cells that constitutively produce a variety of factors are co-cultured together with normal human marrow cells. In the present study, we used the human bladder carcinoma cell line (5637) because these cells were known to produce not only a variety of factors active directly on hematopoietic cells but also factors that can stimulate hematopoietic growth factor production by human marrow stromal cells. Analysis of mRNA extracted from the adherent layer and measurement of growth factor bioactivity in the medium of established LTC of human marrow containing irradiated 5637 cells, showed increased levels of interleukin-1 and -6, as well as granulocyte and granulocyte-macrophage colony-stimulating factor production by comparison to control cultures. As in normal cultures, high proliferative potential clonogenic hematopoietic cells were found almost exclusively in the adherent layer of these co-cultures, but these primitive cells were maintained in a state of continuous turnover, in contrast to control cultures where the same cell types showed the expected oscillation between a quiescent and a proliferating state following each weekly change of the medium. A similar perturbation of primitive progenitor cycling was achieved by adding medium conditioned by 5637 cells twice a week to otherwise normal LTC. The presence of irradiated 5637 cells in the LTC or the addition of 5637 conditioned medium also resulted in modest (2- to 3-fold) but sustained increases in the total hematopoietic progenitor population, as well as in the final output of terminally differentiated granulocytes and macrophages. These findings indicate that primitive hematopoietic cells in LTC can be kept in a state of continuous activation for many weeks by appropriate endogenous or exogenous hematopoietic growth factor provision and that this does not necessarily lead either to their rapid exhaustion or to a large amplification in output of mature progeny.

Development of multipotential haemopoietic stem cells to neutrophils is associated with increased expression of receptors for granulocyte macrophage colony-stimulating factor: altered biological responses to GM-CSF during development

Interleukin-3 (IL-3) dependent multipotent haemopoietic stem cells FDCP-Mix A4 (A4) were induced to differentiate and develop into mature neutrophils in response to Granulocyte Macrophage Colony Stimulating Factor (GM-CSF) plus granulocyte CSF (G-CSF). This resulted in an increase in cell number over seven days of culture, following which the cells lost the ability to undergo further proliferation. The effect of GM-CSF on these cells has been assessed at various stages of development. Clonogenic cells, able to respond to GM-CSF, were generated only at days 3, 4 post-induction. From day 5 onwards, mature post-mitotic neutrophils are produced and clonogenic cells are lost. Loss of proliferative potential, in response to GM-CSF, was confirmed using [3H]-thymidine incorporation. Receptors for GM-CSF, were also measured during development using [125I]-GM-CSF binding assays. Although the dissociation constant for GM-CSF binding sites did not vary considerably, the number of such sites increased dramatically from about 20 (day 0, when the cells have a primitive morphology) to about 1000 by day 6 (when the cells are predominantly mature neutrophils). GM-CSF-stimulated Na+/H+ antiport activation was also determined. Although few GM-CSF receptors are expressed at day 0, there is a significant response (63% of maximal) to GM-CSF in terms of intracellular alkalinisation: this response increased markedly until, by day 4 (700 GM-CSF binding sites/cell), there is a maximal activation of the antiport by GM-CSF. By day 7 (greater than 900 GM-CSF binding sites/cell), however, there is significant reduction in activation of the Na+/H+ antiport by GM-CSF. Nonetheless, increased viability of these mature cells is still seen in response to GM-CSF. These results suggest that not only does expression of GM-CSF receptors alter during development of multipotential cells to mature neutrophils, but that these receptors are coupled to different intracellular effector mechanisms as the cells progressively mature.