CCR7 expression and migration of CD40L-activated BCP-ALL cells in response to CCL19. BCP-ALL cells were cocultured on HBMS stroma. For CD40 cross-linking, BCP-ALL cells were cocultured with the CD40 ligand–transfected J558 cell line. (A) After 48 hours of culture, BCP-ALL cells (□) and CD40L-activated BCP-ALL (▪) were detached by scraping and were washed and stained with anti-CCR7 mAb. Results are expressed as the percentage of positive cells in the gate of viable cells. (B) Results show net numbers of migrated cells in response to CCL19 (100 ng/mL) and are shown as mean ± SE of 5 microscope fields. Migration was evaluated in a modified Boyden chamber for 90 minutes.