Augmentation of pre-B cell growth by SC1/ECM2 overexpressed on the surface of stromal cells. An N-SC1-HPC4-TF/pEFBOS plasmid or an F-SC1-HPC4-TF/pEFBOS plasmid was stably transfected into NIH3T3 cells. (A) BM cells (2 × 10⁴) or (B) a pre-B cell line, DW34 (1 × 10³), were cocultured in the presence of 1 ng/mL IL-7. Each dot represents means of recovered nonadherent cells from cocultures with each transfected clone. Statistically significant differences from control (cocultures with NIH3T3 transfected with HPC4-TF/pEFBOS plasmid) values are indicated by one (P < .05) or two (P < .01) asterisks. Similar results were observed in four independent experiments.