Human IgG1 antibodies suppress angiogenesis in a target-independent manner

Abstract

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 FcγRI (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 FcγR humanized mice. This anti-angiogenic effect was abolished by Fcgr1 ablation or knockdown, Fc cleavage, IgG-Fc inhibition, disruption of Fc-FcγR interaction, or elimination of FcRγ-initated signaling. Furthermore, bevacizumab’s Fc region potentiated its anti-angiogenic activity in humanized VEGFA mice. Finally, mice deficient in FcγRI exhibited increased developmental and pathological angiogenesis. These findings reveal an unexpected anti-angiogenic function for FcγRI and a potentially concerning off-target effect of hIgG1 therapies.

Intravenous immune globulin suppresses angiogenesis in mice and humans

“…We first studied the transgenic FcγR humanized mouse, which expresses the entire human FcγR family, under the control of their human regulatory elements, on a genetic background lacking all mouse FcγRs. 28 Consistent with our observation, 5 as well as those of others, 29 that human IgG1 binds human FcγRI in vivo , and with the notion that IVIg mediates angioinhibition via FcγRI, IVIg reduced choroidal and corneal angiogenesis in FcγR humanized mice as efficiently as in wild-type mice (Figures 4a and b). Further, concomitant administration of IVIg with a small interfering RNA targeting FCGRIA (the gene encoding human FcγRI) abrogated this angioinhibitory effect in FcγR humanized mice (Figure 4c).…”

“…We recently showed that multiple human IgG1 antibodies and their Fc fragments suppressed angiogenesis via the activating FcγRI, and this anti-angiogenic effect was abolished in mice deficient in this receptor. 5 Consistent with those findings, IVIg did not suppress angiogenesis in Fcgr1 −/− mice, which do not express FcγRI (Figures 2d and e), or in Fcer1g −/− mice, which do not express the γ-chain of Fc receptors, therefore lacking signaling for all activating FcγRs (Figure 2g). In contrast, IVIg did suppress angiogenesis in Fcgr2b −/− mice, which do not express the inhibitory FcγRII (Supplementary Figure 3).…”

“…2 To test which region of IVIg was responsible for its angioinhibitory effect, we treated mice with papain-derived Fc (IVIg-Fc) or Fab (IVIg-Fab) fragments of IVIg (Supplementary Figure 2). Consistent with the idea that IgG-mediated angioinhibition is not because of the specific antigen–antibody targeting of angiogenic molecules, 5 systemic administration of IVIg-Fc inhibited choroidal and tumor angiogenesis in wild-type mice, whereas administration of IVIg-Fab by the same route did not do so (Figures 2a and b). As we had observed previously with full-length IVIg-Fc also inhibited xenograft tumor growth, whereas IVIg-Fab had no effect (Figure 2c).…”

“…The biological actions of IVIg have been attributed both to the polyclonal specificities of the antibodies therein 2 and to immunomodulatory or anti-inflammatory effects driven by their IgG Fc regions. 3,4 In a companion paper, we demonstrate that therapeutic human IgG1 antibodies can suppress angiogenesis in a target-independent manner via FcγRI, 5 a high-affinity receptor for IgG1. 6–8 Therefore, we tested whether IVIg, which is composed of ~ 60% IgG1, also possessed similar anti-angiogenic properties.…”

HDL activation of endothelial sphingosine-1-phosphate receptor-1 (S1P1) promotes regeneration and suppresses fibrosis in the liver

“…Considering that liver is the major metabolic organ that synthesizes HDL, it is likely that HDL produced by expanding hepatocytes stimulates regeneration via activation of S1P 1 on sinusoidal vessels (63,64). This finding might advance our understanding of hepatocyte-LSEC signaling crosstalk (24,25,65) that promotes regeneration and prevents fibrosis, and targeting of maladapted vascular system might spur regeneration and prevent fibrosis (31,(66)(67)(68)(69).…”