Disruption of VCAM-1 binding abrogates stromal cell protection of JM-1 cells during chemotherapy.

JM-1 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 that of JM-1 cells on control stromal cells and to that of stromal cells treated with an isotype-matched control antibody. In addition, JM-1 cells in medium, in the presence and absence of drug, were included. After 48 to 72 hours of culture, JM-1 cells were collected and evaluated in triplicate by trypan blue exclusion. Data shown are mean ± SEM and are representative of 3 independent experiments.