TNT signaling is important for the survival of primary BCP-ALL cells. (A) Flowchart and flow cytometric gating strategy used to study the effect of TNTs on BCP-ALL cell survival. Cocultures of CD19^positive leukemic cells and CD19^negative MSCs were stained with Brilliant Violet 421 anti-human CD19 antibody, FITC Annexin V, and PI. MSCs were excluded (red gate), and the percentage of viable BCP-ALL blasts (AnnexinV^neg/PI^neg/CD19^pos cells) was determined within the MSC-negative fraction. (B) Percentage of viable primary leukemic patient cells (n = 3 TEL-AML1, n = 2 B-Other, n = 2 BCR-ABL1-like) in monoculture (▪) or coculture with patient MSCs (□) after 5-day coculture. (C) The survival benefit for primary leukemic patient cells (n = 3 TEL-AML1, n = 2 B-Other, n = 2 BCR-ABL1-like) in coculture with patient MSCs. (D) The mean survival benefit for primary leukemic patient cells in coculture with patient MSCs (n = 7; 1-tailed t test, paired). Data are means ± SEM; ***P ≤ .001.