Murine c-myc retroviruses alter the growth requirements of myeloid cell lines

Recombinant retroviruses encoding a murine c-myc gene were utilised to explore the consequences of constitutive c-myc expression for interleukin 3-dependent murine myeloid cell lines. The c-myc virus-infected cells exhibited a diminished requirement for growth factor and serum when grown in soft agar, but no factor-independent cells could be isolated and the cells were not tumorigenic. Thus deregulated expression of a c-myc gene at physiological levels apparently renders myeloid cells more responsive to growth factors but cannot abrogate this requirement or render the cells malignant.

Autostimulatory mechanisms in myeloid leukemogenesis

WEHI-274 is a monocytic leukemia that arose in a BALB/c mouse infected with Abelson murine leukemia virus. A series of subclones were derived from early passages of this tumor. Three subsets of these leukemogenic subclones were identified. Two subsets demonstrated autostimulatory patterns of growth. This was due to the ectopic production of the T-cell lymphokine the panspecific hemopoietin IL-3 in one case and of the T-cell lymphokine granulocyte-macrophage colony-stimulating factor (GM-CSF) in the other. The third type of subclone did not secrete any autostimulatory growth factor. In the subclone producing IL-3, one copy of IL-3 gene was rearranged and abnormal IL-3 RNA transcripts were present in the nucleus. Subclones producing GM-CSF also contained abnormal GM-CSF RNA transcripts, although no rearrangement of the GM-CSF gene was detected. All three sets of subclones shared a common rearrangement of one c-myb oncogene, suggesting that they share a common ancestor. These results suggest that initiation or progression of leukemogenic behavior in this abnormal clone occurred in three different ways, two of which involved autostimulation by the ectopic activation of T-cell lymphokine genes.

In vitro studies on lymphocyte differentiation. II. Generation of terminal deoxynucleotidyl transferase-positive cells in long-term cultures of mouse bone marrow

The enzyme TdT is the earliest known marker of lymphocytic differentiation in rodents. Cells containing this enzyme were demonstrated in suspension cultures of mouse bone marrow cells that had been maintained in vitro for periods of 7 to 45 days. The cells were detected by immunofluorescence using purified antibodies to homogeneous TdT. Between 0.04 and 2.0% of cultured bone marrow cells from a variety of mouse strains were positive. More than 40% of the TdT-positive cells incorporated 3H-thymidine during a 20-min pulse. Surface Ig and Thy-1 antigens were not detected on the TdT-positive cells. The prevalence of TdT-positive cells was decreased 10-fold in cultures that had been treated with 10(-6) M hydrocortisone 24 hr before harvesting. The results indicate that lymphoid progenitor cells can be generated in vitro.

In vitro studies on lymphocyte differentiation. I. Long term in vitro culture of cells giving rise to functional lymphocytes in irradiated mice

In vitro cultures of mouse bone marrow cells, maintained for periods up to 7 wk, were shown to contain cells able to repopulate irradiated hosts with T and B lymphocytes. The lymphocytes were fully functional and there did not appear to be any gross restriction of their receptor repertoire. The cultured cells reconstituted irradiated semiallogenic hosts without evidence of graft-versus-host disease, suggesting that culture of donor marrow might be a useful preliminary to transplantation when tissue matching is incomplete.

Immunologic functions and in vitro activation of cultured macrophage tumor lines

Five murine monocyte of macrophage tumor lines adapted to culture were characterized for differentiated properties. They ingested zymosan and latex beads, bore receptors for immunoglobulin and complement, synthesized lysozyme (most of which was secreted), and produced granulocyte colony-stimulating activity, either spontaneously or inducibly. Some of the lines also mediated phagocytosis and exocytosis of red blood cells (RBC) and lysis of tumor targets, dependent on the presence of specific antitarget sera. All the lines were growth inhibited by zymosan and Mycobacterium bovis BCG, but not by latex beads. Other macrophage-activating agents, dextran sulfate and lipopolysaccharide (LPS), as well as tuberculin purified protein derivative (PPD), inhibited most of the lines. Except for Fc and C receptors, most of the above properties were not found with other types of hematopoietic tumors in culture. In attempts to activate the macrophage lines in vitro to the "angry" state, we found that preincubation with concentrations of LPS and PPD cytostatic to the cells stimulated antibody-dependent RBC lysis, but not antibody-independent or tumor cytolysis. A classification of monocyte-related tumors and normal cells is proposed based on functional activities and differential sensitivity to immunostimulating agents.