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 antiangiogenic 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.

Control of embryonic stem cell metastability by L-proline catabolism

The molecular mechanisms controlling mouse embryonic stem cell(ESC)metastability,i.e.their capacity to fluctuate between different states of pluripotency,are not fully resolved.We developed and used a novel automation platform,the Cellmaker,to screen a library of metabolites on two ESC-based phenotypic assays(i.e.proliferation and colony phenotype)and identified two metabolically related amino acids,namely L-proline(L-Pro)and L-ornithine(L-Orn),as key regulators of ESC metastability.Both compounds,but mainly L-Pro,force ESCs toward a novel epiblast stem cell(EpiSC)-like state,in a dose-and time-dependent manner.Unlike EpiSCs,L-Pro-induced cells(PiCs)contribute to chimeric embryos and rely on leukemia inhibitor factor(LIF)to self-renew.Furthermore,PiCs revert to ESCs or differentiate randomly upon removal of either L-Pro or LIF,respectively.Remarkably,PiC generation depends on both L-Pro metabolism(uptake and oxidation)and Fgf5 induction,and is strongly counteracted by antioxidants,mainly L-ascorbic acid(vitamin C,Vc).ESCs↔PiCs phenotypic transition thus represents a previously undefined dynamic equilibrium between pluripotent states,which can be unbalanced either toward an EpiSC-like or an ESC phenotype by L-Pro/L-Orn or Vc treatments,respectively.All together,our data provide evidence that ESC metastability can be regulated at a metabolic level.

Intravenous immune globulin suppresses angiogenesis in mice and humans

Human intravenous immune globulin(IVIg),a purified IgG fraction composed of~60%IgG1 and obtained from the pooled plasma of thousands of donors,is clinically used for a wide range of diseases.The biological actions of IVIg are incompletely understood and have been attributed both to the polyclonal antibodies therein and also to their IgG(IgG)Fc regions.Recently,we demonstrated that multiple therapeutic human IgG1 antibodies suppress angiogenesis in a target-independent manner via FcγRI,a high-affinity receptor for IgG1.Here we show that IVIg possesses similar anti-angiogenic activity and inhibited blood vessel growth in five different mouse models of prevalent human diseases,namely,neovascular age-related macular degeneration,corneal neovascularization,colorectal cancer,fibrosarcoma and peripheral arterial ischemic disease.Angioinhibition was mediated by the Fc region of IVIg,required FcγRI and had similar potency in transgenic mice expressing human FcγRs.Finally,IVIg therapy administered to humans for the treatment of inflammatory or autoimmune diseases reduced kidney and muscle blood vessel densities.These data place IVIg,an agent approved by the US Food and Drug Administration,as a novel angioinhibitory drug in doses that are currently administered in the clinical setting.In addition,they raise the possibility of an unintended effect of IVIg on blood vessels.