Targeting adhesion molecules may overcome CAM-DR. (A) Blocking monoclonal antibodies against VLA-4 and LFA-1 can overcome CAM-DR. NCI-H929 myeloma cells were treated for 48 hours with 30 μM melphalan in the absence or presence (suspension versus HS-5) of HS-5 stromal cells and PI uptake into CD38⁺ cells was determined by flow cytometry. Blocking monoclonal antibodies directed against VLA-4 (4 μg/mL) and LFA-1 (4 μg/mL) were added as indicated in the figure. (B) LFA-1 inhibitor LFA703 can overcome CAM-DR. NCI-H929 myeloma cells were treated for 48 hours with 20 μM melphalan in the absence or presence (suspension versus HS-5) of HS-5 stromal cells and PI uptake into CD38⁺ cells was determined by flow cytometry. LFA703 (3 μM) was added as indicated in the figure. (C) CAM-DR reversal is not mediated by de-adhesion. NCI-H929 (NCI) myeloma cells were incubated in the presence (+HS-5) or absence (in suspension) of HS-5 stromal cells and 5 μg/mL anti-VLA4 monoclonal antibody or 3 μM LFA703 were added for 48 hours. The number of viable cells in suspension was determined by the WST-1 viability assay. (D) CAM-DR reversal is not mediated by reduced IL-6 secretion. NCI-H929 and HS-5 were coincubated as indicated and 5 μg/mL anti-VLA4 monoclonal antibody or 3 μM LFA703 were added. IL-6 concentration in the supernatant was determined by ELISA. Mean values and standard deviations and P values are shown in the figure. n.s. indicates not significant.