Human IgG1 antibodies suppress angiogenesis in a target-independent manner

Aberrant angiogenesis is implicated in diseases affecting nearly 10% of the world's population. The most widely used anti-angiogenic drug is bevacizumab, a humanized IgG1 monoclonal antibody that targets human VEGFA. Although bevacizumab does not recognize mouse Vegfa, it inhibits angiogenesis in mice. Here we show bevacizumab suppressed angiogenesis in three mouse models not via Vegfa blockade but rather Fc-mediated signaling through Fc gamma RI (CD64) and c-Cbl, impairing macrophage migration. Other approved humanized or human IgG1 antibodies without mouse targets (adalimumab, alemtuzumab, ofatumumab, omalizumab, palivizumab and tocilizumab), mouse IgG2a, and overexpression of human IgG1-Fc or mouse IgG2a-Fc, also inhibited angiogenesis in wild-type and Fc gamma R humanized mice. This anti-angiogenic effect was abolished by Fcgr1 ablation or knockdown, Fc cleavage, IgG-Fc inhibition, disruption of Fc-Fc gamma R interaction, or elimination of FcR gamma-initated signaling. Furthermore, bevacizumab's Fc region potentiated its anti-angiogenic activity in humanized VEGFA mice. Finally, mice deficient in Fc gamma RI exhibited increased developmental and pathological angiogenesis. These findings reveal an unexpected anti-angiogenic function for Fc gamma RI and a potentially concerning off-target effect of hIgG1 therapies.