Results of chemoresistance assays. Survivability is defined as the viability of cells exposed to cytotoxic agents, relative to the viability of unexposed cells, expressed as a percentage. Loss of survivability is the absolute decrease in survivability after exposure to α4-blocking agents. (A) Chemotherapy resistance assay results for cells plated on retronectin from patients with data for anti-VLA-4 antibody (N = 7) or sVCAM-1 (N = 3). Compared with the IgG isotype, survivability after exposure to Ara-C (N = 5, ●) or Ara-C plus daunorubicin (N = 2, ○) was an average of 26 plus or minus 7 (SE) percentage points lower for cells preincubated with α4 blocking antibody CD49d (one-sided P = .006 based on paired t test). A 66% decrease in survivability in cells preincubated with CD49d was observed for 1 patient; however this patient, who had more than 100% survivability in the cells preincubated with IgG isotype, was a possible outlier; for the remaining 6 patients, survivability was an average of 19 plus or minus 3 percentage points lower for cells preincubated with CD49d (P < .001). Survivability was an average of 29 plus or minus 4 percentage points lower for cells preincubated with sVCAM-1 (P = .010). (B) Chemotherapy resistance assay results for cells on immobilized VCAM-1 from the 3 patients with sVCAM-1 data in panel A. Compared with the IgG isotype, survivability after exposure to Ara-C on VCAM-1 was an average of 18 plus or minus 5 percentage points lower for cells preincubated with CD49d (P = .031) and an average of 21 plus or minus 5 percentage points lower for cells preincubated with sVCAM-1 (P = .024).
