Fig. 2.

IgG subclass influences the efficacy of anti-SIRPα antagonist antibodies in vitro and in vivo. a In vitro phagocytosis experiment with human MDMs cultured in the presence of human AB serum and DLD-1 cells in the presence of cetuximab at a constant concentration and titrated anti-SIRPα antibodies with different IgG subclass. Percent of macrophages that engulfed tumor cells is indicated on the y-axis. On the y-axis, closed circle indicates background phagocytosis observed with media only and closed square indicates cells treated with cetuximab only. b Relative dendritic cell numbers in human PBMCs after 48-h incubation with hAB21-IgG variants. Each bar indicates relative DC number as compared to media only. Statistics were performed using One-Way ANOVA, Dunnett’s multiple comparisons. c, d Raji B-cell lymphoma cells were implanted subcutaneously on the right flanks of NOD-SCID mice. Mice with established tumors (average of 154 mm³) were randomized, n = 10/group, and treated intraperitoneally with vehicle, rituximab, AB21 mIgG1_N297A (inactive) (c), AB21 mIgG2a (active) (d), or AB21 inactive or active + rituximab. Mice were treated five doses every 3 days. Statistics were performed using Two-Way ANOVA, Tukey’s multiple comparisons test. *p < 0.05, **p < 0.01, ***p < 0.001 and ****p < 0.0001