Rituximab induces cell growth inhibition. (A) Daudi cells (3 × 10⁶) were either untreated (□) or incubated with rituximab (▪), an irrelevant IgG (○), or alemtuzumab (▵), all at 10 μg/mL. At various time points, cell number was estimated by trypan blue exclusion assay. Results are mean of triplicate determinations and are representative of 3 independent experiments. (Ai) Determination of rituximab saturation concentration. Aliquots of Daudi cells were incubated at 4°C for 30 minutes in the presence of various concentrations of rituximab or an irrelevant human IgG (10 μg/mL). Saturating concentration of rituximab (10 μg/mL) was obtained from the fluorescence difference (ΔFL2) between rituximab- and IgG-treated cells as described in “Materials and methods.” (B) Clonogenic assay. Daudi cells were either untreated or treated with rituximab at 0.5, 1, 5, 10, or 50 μg/mL. After 7 days, the number of colonies was determined under an inverted microscope, and the percentage of survival was determined. Results are mean of triplicate determinations ± SD. (C) Cell cycle analysis. Daudi cells were treated with 10 μg/mL rituximab, and cell distribution into the cell cycle was performed as described in “Materials and methods.” Results are representative of 3 independent experiments.