Lymphoma sensitivity to CD20 mAb. (A) CD20 mAb-induced lymphoma phagocytosis by macrophages. Peritoneal macrophages were cocultured for 24 hours with dye-labeled primary lymphoma cells previously incubated with control or CD20 mAb. Representative contour plots of F4/80+ macrophages vs labeled BL3750 cells show mean (± SEM) frequencies of phagocytosed lymphoma cells within the indicated gates (left and middle panels). The graph shows mean results for the indicated representative lymphomas (n = 2 experiments per group). (B-D) CD20 mAb-induced lymphoma clearance in vivo. Mice given 1 × 105 primary lymphoma cells were treated with either CD20 (closed circles) or control (open circles) mAb 1 day later. (B) Kaplan-Meier survival plots of mice given the indicated lymphomas and CD20 or control mAb. Pooled results represent 2 to 3 independent experiments (n = 4-13 total mice per group) with significant cumulative survival differences between groups treated with CD20 vs control mAb indicated. (C) Primary lymphoma sensitivity to CD20 immunotherapy. Significant differences between sample means are indicated. **P ≤ .01. (D) CD20 expression (Figure 1A) and lymphoma sensitivity (B) to CD20 immunotherapy are not correlated.
