Responses of xenografts to dexamethasone in vitro. Xenograft cells were retrieved from cryostorage, and sensitivity to dexamethasone was assessed by MTT assay following a 48-hour drug exposure. The viable cell number at each drug concentration was calculated relative to untreated controls. Xenografts were stratified into good (solid lines, open symbols) or poor (dashed lines, closed symbols) clinical outcome subgroups, as defined in “Sensitivity of childhood ALL xenograft cells to dexamethasone in vitro.” Each data point represents the mean ± SEM of 3 independent experiments.