Human leukemic cells: in vitro growth of colonies containing the Philadelphia (Ph) chromosome.

Human leukemic cells with a marker (Philadelphia; Ph(1)) chromosome gave rise to granulocytic and mononuclear cell colonies when grown in vitro. All metaphases from a single colony were either Ph(1) positive or Ph(1) negative. No colonies contained a mixed cell population. This suggests that leukemic and normal cells exist simultaneously and that in vitro colonies are clonal in origin.