Fibronectin does not protect VLA-4⁺VLA-5⁺ RS4 cells from Ara-C or VP-16–induced cell death.

(A) RS4 cells were incubated in 24-well plates for 72 hours in the presence of 0.1 μg/mL Ara-C, 5 μmol/L VP-16, or medium alone (control). Culture plates used were coated with fibronectin (black bars) or uncoated (gray bars). RS-4 cells were collected by vigorous pipetting and were evaluated in triplicate by trypan blue exclusion. (B) RS-4 cells were incubated on confluent stromal cells treated with mouse antihuman VCAM-1 antibody during Ara-C and VP-16 treatment. Before the addition of leukemic cells and chemotherapeutic drugs, stromal cell layers were pretreated with 5 μg anti–VCAM-1; 2.5 μg/mL fresh antibody was added at 24-hour intervals, as described in “Materials and methods.” Viability of leukemic cells cultured on anti–VCAM-1–treated stromal cells was compared to RS-4 cells on control stromal cells. Data shown are mean ± SEM and are representative of 2 independent experiments.