The in vitro autocrine secretion of CSFs alone does not account for the longterm growth of murine myeloid leukemic cells in suspension cultures.

To investigate the mechanisms supporting the in vitro longterm growth of murine leukemic myeloblastic cells, factor-dependent and autonomous myeloblastic cells have been examined for their CSF responsiveness, CSF secretion, and autostimulation of growth. Purified CSF-1, GM-CSF, and IL-3 stimulated cloning and proliferation of both autonomous (ACL) and factor-dependent cell lines (FDCL), and were unable to induce differentiation of these cells. Sensitivities to CSFs were similar for ACL, FDCL and normal bone marrow cells. Most of the cell lines secreted CSFs, stimulating colony formation from normal bone marrow cells in bilayer agar cultures. The number of induced granulo-macrophagic colonies was similar in the presence of either ACL or FDCL. The ability to stimulate their own proliferation was similar for both ACL and FDCL in a longterm suspension culture assay as well as in a shortterm cloning assay. These results strongly suggest that the autocrine secretion of CSF-related activities are not sufficient to fully account for the in vitro longterm proliferation of virus-transformed myelomonocytic cells.