TNTs are important players in signaling from BCP-ALL cells to MSCs. (A) Model of crosstalk between leukemic cells and MSCs in the hematopoietic niche. (B) Graphs showing quantification of dye transfer from DiI-stained NALM6 cells toward unstained hTERT-MSCs. Blue and gray histograms represent staining intensity at the start of each experiment. Red histogram represents signaling efficiency via TNTs (normal coculture; left panel) and via ECVs (3.0-μm transwell; right panel). (C) Bar graphs of experiment shown in panel B after 6 hours (left panel) and 24 hours (right panel) of coculture (n = 4; 2-tailed t test, unpaired). (D) Graphs showing quantification of dye transfer from BCP-ALL cell line NALM6, stained with either DiI or calcein, toward primary MSCs after 24 hours of coculture. Blue and gray histograms represent staining intensity at the start of each experiment. Red histogram shows signaling efficiency via TNTs (left panel) and via gap junctions (right panel). (E) Bar graphs of experiment shown in panel D after 8 hours (n = 6; left panel) and 24 hours (n = 4; right panel) of coculture (2-tailed t test, unpaired). (F) Bar graphs representing dye transfer from DiI-stained REH cells toward unstained primary MSCs with and without integrin blocking. Integrin signaling was blocked by addition of RGDS peptide, and compared with addition of the integrin nonbinding peptide GRADSP (n = 5; 1-tailed t test, paired). Data are means ± SEM; *P ≤ .05, **P ≤ .01, ***P ≤ .001.