Blockade of the CD47-SIRPα axis improves myeloid effector cell recruitment by CD20 antibodies of the IgA2 isotype. Macrophage-mediated ADCP by CD20 antibodies of the IgA2 isotype was determined by fluorescence microscopy (A), whereas ADCC by PMNs was investigated in 3-hour [⁵¹Cr] release assays (B). An IgG2σ version of the CD47 antibody 5F9 (10 µg/mL) was used to block CD47-SIRPα interactions. The CD20 antibodies RTX, OFA, and OBI were used at 10 µg/mL; E:T ratios were 80:1 in ADCC assays and 1:2 in ADCP assays. (C) Increasing concentrations of IgA2 variants of RTX, OFA, and OBI (left panel) or increasing E:T ratios (right panel) were compared in 3-hour [⁵¹Cr] release ADCC assays using PMNs as effector cells. Target cells were Mino cells (mantle cell lymphoma) and Raji cells (Burkitt lymphoma) (left and right panels, respectively) in (A) and (B) and SU-DHL-4 cells (DLBCL) in (C). CD20 antibodies are depicted as colored circles. Results are mean ± SEM from ≥3 experiments with effector cells from different donors. *Significant difference vs control (ctrl.) antibody. ^XSignificant difference in the absence and presence of CD47 blockade. ^§Significant difference between OBI-IgA2 and RTX-IgA2 or OFA-IgA2. Significant differences (P < .05) were calculated using ANOVA. conc., concentration; mAb, monoclonal antibody; n.s., not significant.