Differentiation commitment and regulator-specific granulocyte-macrophage maturation in a novel pro-B murine leukemic cell line

The cloned pro-B-lymphocyte murine leukemic cell line GB2, was established from a leukemic Max41 x E mu-myc double transgenic mouse. Its Igh alleles a re rearranged and its surface markers are primarily B-lymphoid, but a small proportion of the cells also express surface Gr-l and some cells develop t he morphology of maturing granulocytes. The cell line grows continuously in suspension culture without the addition of growth factors, but expresses m RNA for M-CSF, TPO and Flt-3-ligand. When stimulated in agar cultures by GM -CSF, G-CSF, M-CSF, IL-3, SCF, IL-6, leukemia inhibitory factor (LIF), IL-5 or IFN gamma, GB2 cells generated blast colonies or colonies of maturing g ranulocytes and macrophages. There was a striking similarity in colony type s, relative colony numbers and maturation of colony cells to those formed b y normal bone marrow cells in response to the same stimuli. GB2 blast colon y-forming cells exhibited self-renewal as well as an ability to form granul ocyte-macrophage colony-forming progeny, with evidence that a hierarchical sequence of clonogenic cells is generated in the cell line even after subcl oning. Factor-specific maturation was clearly initiated by the action of th e added growth factors. In contrast, FAGS-sorting experiments showed that c ommitment to various types of colony-forming cell occurs in maintenance sus pension cultures in the apparent absence of potentially relevant growth fac tors.