Both growth of wild-type TF-1 and stroma-dependent TF-1S clones on stroma but not growth of suspended cells in absence of stroma can be inhibited by the monoclonal human antibody YB5.B8. (•) Parental TF-1 grown in suspension with GM-CSF (control); (○) parental TF-1 cells grown on stroma; (□) stroma-dependent clones TF-1S #MB5, #MB6, and #MB8. Only one line is drawn for the stroma-dependent clones, because the inhibition was almost identical. Means of three (TF-1 in suspension with GM-CSF), three (TF-1 on stroma), and two (TF-1S #5, #6, and #8 each) independent experiments are shown.