Potent Fc Receptor Signaling by IgA Leads to Superior Killing of Cancer Cells by Neutrophils Compared to IgG

Abstract

Antibody therapy of cancer is increasingly used in the clinic and has improved patient's life expectancy. Except for immune checkpoint inhibition, the mode of action of many antibodies is to recognize overexpressed or specific tumor antigens and initiate either direct F(ab′) 2 -mediated tumor cell killing, or Fc-mediated effects such as complement-dependent cytotoxicity (CDC) and antibody-dependent cell-mediated cytotoxicity/phagocytosis (ADCC/P) after binding to activating Fc receptors. All antibodies used in the clinic are of the IgG isotype. The IgA isotype can, however, also elicit powerful anti-tumor responses through engagement of the activating Fc receptor for monomeric IgA (FcαRI). In addition to monocytes, macrophages and eosinophils as FcαRI expressing immune cells, neutrophils are especially vigorous in eliminating IgA opsonized tumor cells. However, with IgG as single agent it appears almost impossible to activate neutrophils efficiently, as we have visualized by live cell imaging of tumor cell killing. In this study, we investigated Fc receptor expression, binding and signaling to clarify why triggering of neutrophils by IgA is more efficient than by IgG. FcαRI expression on neutrophils is ~2 times and ~20 times lower than that of Fcγ receptors FcγRIIa and FcγRIIIb, but still, binding of neutrophils to IgA- or IgG-coated surfaces was similar. In addition, our data suggest that IgA-mediated binding of neutrophils is more stable compared to IgG. IgA engagement of neutrophils elicited stronger Fc receptor signaling than IgG as indicated by measuring the p-ERK signaling molecule. We propose that the higher stoichiometry of IgA to the FcαR/FcRγ-chain complex, activating four ITAMs (Immunoreceptor Tyrosine-based Activating Motifs) compared to a single ITAM for FcγRIIa, combined with a possible decoy role of the highly expressed FcγRIIIb, explains why IgA is much better than IgG at triggering tumor cell killing by neutrophils. We anticipate that harnessing the vast population of neutrophils by the use of IgA monoclonal antibodies can be a valuable addition to the growing arsenal of antibody-based therapeutics for cancer treatment.

Novel chimerized IgA CD20 antibodies: Improving neutrophil activation against CD20-positive malignancies

“…inducing mechanism by neutrophils is profoundly more effective when mediated by the IgA isotype, and can be attributed to a strong triggering of CD89 present on neutrophils. 8,21 Strikingly, we did not observe IgG-mediated B cell reduction with whole blood leukocytes as effector cells, although CD20 IgG1 antibodies have shown clear clinical benefit. One possible explanation could be that IgG-mediated trogocytosis of CD20 by the vast numbers of neutrophils in blood does not reflect the tumor microenvironment in patients.…”

“…Therefore, we chose to chimerize them to the human IgA isotype, since this isotype was previously shown to elicit superior killing of tumor cells via PMN. 8,9 Here, we compared the effector mechanisms of five novel antibodies as IgG1, IgA1 and IgA2(m1) in vitro and assessed their efficacy in vivo.…”

IgA: Structure, Function, and Developability

“…Therefore, targeting this receptor leads to additional neutrophil migration to tumour sites [80]. Although FcαRI expression in neutrophils is lower than that of Fcγ receptors naturally expressed in these cells (FcγRIIa and FcγRIIIb), binding of IgA or IgG to neutrophils is similar, which suggests a more stable binding by IgA and a higher efficiency at triggering neutrophils than IgG [178]. For instance, the use of an IgA anti-Ep-CAM mAb was shown to kill colon carcinoma cells, unlike the IgG1 mAb counterpart [179].…”

Efficient N-Glycosylation of the Heavy Chain Tailpiece Promotes the Formation of Plant-Produced Dimeric IgA

“…While recombinant IgGs are currently most widely used as therapeutic antibodies to combat infections or diseases, alternative antibody formats are gaining attention as potential biopharmaceuticals due to their specific structural properties and binding to different immune receptors (Loos et al, 2014;Brandsma et al, 2019;Montero-Morales et al, 2019). Polymeric antibody formats have a higher valency of antigen-binding sites which has several advantages compared to monomeric antibodies.…”