Differential effects in cells exposed to ultra-short, high intensity electric fields: cell survival, DNA damage, and cell cycle analysis

High power, nanosecond pulsed electric field (nsPEF) effects have been focused on bacterial decontamination, but the impact on mammalian cells is now being revealed. During nsPEF applications, electrical pulses of 10, 60 or 300 ns durations were applied to cells using electric field amplitudes as high as 300 kV/cm. Because of the ultra-short pulse durations, the energy transferred to cells is negligible, and only non-thermal effects are observed. We investigated the genotoxicity of nsPEF on adherent and non-adherent cell lines including 10 human lines and one mouse cell line with different origin and growth characteristics. We present data examining the effects of nsPEF exposure on cell survival assessed by clonogenic formation or live cell count; DNA damage determined by the comet assay and chromosome aberrations; and cell cycle parameters by measuring the mitotic indices of exposed cells. Using each of these indicators, we observed differential effects among cell types with non-adherent cells being more sensitive to the genotoxic effects of nsPEF exposures than adherent cells. Non-adherent cultures showed a rapid decrease in cell viability (90%), induction of DNA damage, and a decrease in the number of cells reaching mitosis after one 60 ns pulse with an electric field intensity of 60 kV/cm. These effects were not observed in cells grown as adherent cultures, with the exception of the mouse 3T3 cell line, which showed survival characteristics similar to non-adherent cultures. These data suggest that nsPEF genotoxicity may be cell type specific, and therefore have potential applications in the selective removal of one cell type from another, for example, in diseased states.

Differentiation and maturation of growth factor expanded human hematopoietic progenitors assessed by multidimensional flow cytometry

Non-adherent cord blood and bone marrow mononuclear cells were analyzed by multiparameter flow cytometry before and at day 2, 4, 7, and 11 of culture in recombinant interleukin 3 (IL-3) and granulocyte colony-stimulating factor (G-CSF, cord blood) or stem cell factor (SCF), IL3 and granulocyte-macrophage colony-stimulating factor (GM-CSF, BM) to assess the differentiation and maturational pathway of myeloid cells. Before cell culture cord blood contained progenitor cells (CD34+) in various differentiation stages (CD38(-)----CD38bright), mature lymphocytes, monocytes, and neutrophils, but no immature neutrophils and immature monocytes. During cell culture, all CD34+ cells acquired the CD38 antigen between day 2 and 5 of cell culture, the CD34 antigen was lost between day 5 and 11 of cell culture. Differentiation of cells into the myeloid cell lineage was characterized by the acquisition of both CD33 and CD71. The latter is indicative for the active proliferation of these cells. Maturation of the cells into the neutrophilic pathway was indicated by the acquisition of first the CD15 antigen followed by CD11b and CD16 respectively. Whereas maturation of the cells into the monocytic pathway was indicated by the acquisition of first CD11b followed by CD14 and a dim expression of both CD15 and CD16. In normal bone marrow, cells of various maturational stages are already present before cell culture. During cell culture differentiation of cells into the myeloid lineage and maturation of the cells along the monocyte and neutrophilic lineage followed identical pathways as was observed before cell culture. Differentiation and maturational pathways of cord blood and adult bone marrow were identical. The results confirm the surface-antigen-defined pathways of myeloid cell differentiation described previously for non-cultured normal bone marrow aspirates. The detailed assessment of cell maturation and differentiation of cultured cells by multidimensional flow cytometry permits the determination of the specific effects of various recombinant human growth factors on myeloid cells.

Stimulation of myelopoiesis in a patient with congenital neutropenia: biology and nature of response to recombinant human granulocyte-macrophage colony-stimulating factor

To stimulate granulopoiesis, we gave recombinant human granulocyte-macrophage colony-stimulating factor (GM-CSF; 120 microgram/m2/d) to a patient with congenital neutropenia. The treatment resulted in marked increases in white blood cell counts (maximum, 17,400/microL), consisting mainly of eosinophils (maximum, 13,050/microL) and monocytes (maximum, 1305/microL), rather than neutrophils (maximum, 798/microL). Circulating phagocytes (97% eosinophils) derived after GM-CSF treatment were less effective in chemotaxis, slower but equally effective in phagocytosis, and more effective in H2O2 production compared with normal control neutrophils, but comparable in chemotaxis and H2O2 production to control eosinophils. Before GM-CSF treatment, the bone marrow showed a maturation defect in the neutrophilic series that persisted after treatment despite marked increases in mature cells of other lineages. In vitro agar culture of bone marrow cells before GM-CSF treatment showed a normal number of granulocyte colonies; however, maturation was limited to the metamyelocyte stage. Although the absolute number and cycling rates of myeloid colony forming cells (predominantly eosinophils) increased after treatment, the maturation defect in the neutrophilic series persisted. The finding that GM-CSF induced stimulation of proliferation, which was coupled with maturation in the eosinophilic and monocytic but not the neutrophilic components, suggests that this patient had an intrinsic cellular or humoral defect in neutrophil maturation.

Stimulation of myelopoiesis in patients with aplastic anemia by recombinant human granulocyte-macrophage colony-stimulating factor

Aplastic anemia is a syndrome in which pancytopenia occurs in the presence of hypocellularity of the bone marrow. To assess the biologic activities of recombinant human granulocyte-macrophage colony-stimulating factor (GM-CSF) in aplastic anemia, we gave GM-CSF (60 to 500 micrograms per square meter of body-surface area) to 10 patients with moderate or severe disease, by continuous intravenous infusion daily for two weeks, and repeated the treatment after a two-week rest period. The treatment increased the white-cell count (1.6- to 10-fold) in all patients, primarily because of an increase in the numbers of neutrophils (1.5 to 20-fold), eosinophils (12- to greater than 70-fold), and monocytes (2- to 32-fold). Rates of hydrogen peroxide production in purified granulocyte fractions increased during GM-CSF treatment. Increases in bone marrow cellularity, myeloid precursor cells, and myeloid:erythroid cell ratios accompanied the white-cell response. Despite the in vivo response of the white-cells, the concentration of colony-forming cells remained the same. Measurable concentrations of interleukin-2 (2 to 15 units per milliliter) were found in the serum of 8 patients, and high levels of erythropoietin (81 to 1200 IU per liter) were found in 10 patients. The predominant side effects were constitutional symptoms. These results indicate that recombinant human GM-CSF is effective in stimulating myelopoiesis in patients with severe aplastic anemia and may benefit some patients in whom the disorder is refractory to standard forms of therapy.

Stimulation of hematopoiesis in patients with bone marrow failure and in patients with malignancy by recombinant human granulocyte-macrophage colony-stimulating factor

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a multipotential hematopoietin. To assess the toxicity and biological activity of recombinant human GM-CSF (rhGM-CSF) in vivo, 25 patients with malignancy or bone marrow failure were treated with rhGM-CSF (specific activity approximately 5 x 10(7) U/mg) as part of a phase 1 trial. The treatment was administered by continuous intravenous (IV) infusion daily for 2 weeks at fixed dose levels and repeated after a 2-week rest period. Over the entire dose range tested (15 to 500 micrograms/m2/d), rhGM-CSF treatment was associated with dramatic increases (two- to 70-fold) in total leukocyte counts, which consisted predominantly of neutrophils, bands, eosinophils, and monocytes. Furthermore, six of the 14 patients with one or more cytopenias that received at least two cycles of treatment had multilineage responses characterized by twofold or greater increases in platelet count to a level above 100,000, twofold or greater increases in corrected reticulocyte count, and a reduced requirement for red cell transfusions. Three of these patients became independent of both red cell and platelet transfusions for 17 to 37 weeks of follow-up. Treatment was associated also with an increase in bone marrow cellularity and frequency of cycling progenitor cells. The treatment was well tolerated; side effects included constitutional symptoms and bone pain. These results demonstrated that rhGM-CSF has a significant impact on hematopoiesis in patients with advanced malignancy and also in patients with bone marrow failure.

Two new monoclonal antibodies to human monocytes and granulocytes: isolation of membrane antigens and lack of effects of antibodies on leukocyte functions in vitro

Mice were immunized with purified human monocytes or granulocytes obtained by leukapheresis and isolated on dextran gradients or by countercurrent centrifugation-elutriation. A monoclonal antibody, Mo95, was generated in response to monocytes and was found to react strongly with monocytes, large granular lymphocytes (LGL), granulocytes, eosinophils, and some myelomonocytic leukemia cells, but not with normal T or B lymphocytes, platelets, red cells, or leukemic cell lines. Mo95 is an IgG1 antibody, which precipitated a 95 kD molecular weight antigen. Addition of the Mo95 antibody to monocytes in the absence of complement did not inhibit lysozyme secretion nor did it affect superoxide production, C3b-rosetting, nitrotetrazolium blue reduction, phagocytosis, or chemotactic responses. A second antibody, PMN70, was found to react exclusively with granulocytes and not with monocytes, lymphocytes, LGL, platelets, red cells, or any of the myelomonocytic, T-cell-derived or B-cell-derived leukemic cell lines tested. The PMN70 antibody immunoprecipitated a 70 kD molecular weight antigen found only on mature granulocytes. Mo95 and PMN70 appear to be distinct from five other tested monoclonal antibodies reactive to monocytes and/or granulocytes on the basis of the fluorescent cell sorter and immunoprecipitation studies performed.

Monoclonal antibody to human eosinophils recognizing 95 kD surface membrane antigen

Mice were immunized with purified eosinophils obtained from patients with the idiopathic hypereosinophilic syndrome. A hybridoma initially producing an IgM antibody which switched to an IgG1 antibody was selected for cloning and further testing. This IgG1 antibody reacted with human eosinophils, granulocytes, monocytes and large granular lymphocytes, but did not react with T lymphocytes, B lymphocytes, platelets, erythrocytes, or a panel of human leukemia cells and cell lines. Bone marrow analysis revealed staining of myeloid precursor cells but not erythroid precursors or plasma cells. This IgG1 antibody had no effect on aggregation of granulocytes, lysozyme release, superoxide production, chemotaxis, or killing activity; however, there was some stimulation of beta-glucuronidase secretion. While the antibody did not augment the killing of Staphylococcus aureus by granulocytes, the antibody itself was bactericidal. By immunoprecipitation of granulocytes, eosinophils and monocytes, a molecule with a molecular weight of 95 kD was identified.