AllergoOncology - IgG4 antibody drives macrophages to a regulatory phenotype and negatively influences the ADCP: implications for tumour-mediated immune tolerance

Supported by FWF-project SFB F4606-B28 to EJJ, and by the Messerli Foundation. IgG4 is associated with the intra-tumoral M2 microenvironment and expressed in tumor tissues correlated with poor clinical outcome, but their mechanisms are not explored yet. Recently, we demonstrated that IgG4 drive macrophage derived from healthy donors to a tolerogenic phenotype.(1) Moreover, new anti-tumor therapies use monoclonal anti-tumor antibodies that target malignant cells and eradicate them via antibody-dependent cell-mediated cytotoxicity (ADCC) and antibody-dependent cell-mediated phagocytosis (ADCP) with no particular focus on the IgG subclass used. We hypothesized that both exogenous anti-tumor and endogenous IgG4 antibodies may interfere with both the ADCC and ADCP ability of monocyte/macrophage effector cells and induce a tolerogenic phenotype. We analyzed plasma levels of total IgE, IgG1 and IgG4 from healthy controls and non-metastatic or metastatic colon cancer patients and investigated if cultured monocyte derived macrophages from different donors would respond differently in presence of IgG1 or IgG4 in terms of surface marker expression and cytokine response. Moreover, we investigated in vitro the anti-EGFR IgG1 or IgG4 mediated ADCC and ADCP against EGFR high to low expressing tumor cell lines A431, HT-29 and CaCo-2 by flow cytometry. The monocyte cell line U937 or monocyte-derived macrophages (MDMs) were used as effector cells. A significantly higher IgG4/IgE plasma level ratio was observed in metastatic tumor patients compared to the other groups. This was associated with a lower surface marker expression of CD206, CD163 and CD86 and higher cytokine production of CCL1, IL10 and IL6 in IgG4-stimulated M2a macrophages in all groups, compared to IgG1 or no IgG stimulation. Moreover, higher ADCP of anti-EGFR IgG1 vs. anti-EGFR IgG4 was observed on A431 > HT-29 > CaCo-2 tumor cell lines with U937 and MDM effector cells. Our results indicate that the outcome of monoclonal anti-tumor antibody treatments may critically depend on the IgG1 versus IgG4 subclass used, with IgG4 being detrimental: 1.) intra-tumoral IgG4 may repolarize tumor-associated M2a macrophages to an immunoregulatory M2b-like phenotype; 2.) IgG4 may hinder ADCP mediated macrophage response. Both pro-tumorigenic effects of IgG4 may be decisive for a poor prognostic outcome.