Abstract A095: Discovering the immune profiles of a novel antifolate receptor alpha IgE antibody associated with monocyte-mediated antitumor functions

Monoclonal antibodies are an established modality for the clinical management of many cancers. To date, all antibodies approved for cancer treatment are of the IgG class, and many are targeted towards non-solid tumors. We hypothesized that antibodies of the IgE class may be able to recruit and activate immune cells against tissue resident tumors based on very high affinity of IgE for cognate Fcϵ Receptors on potent effector cells such as masT-cells, monocytes and macrophages. A novel IgE-based antibody against folate receptor alpha (FRα) for ovarian carcinoma was developed and demonstrated to engender superior anti-tumor effector functions compared with those triggered by its IgG counterpart in different in vivo models of cancer. We have now translated this concept to a first-in-man clinical trial. We have previously reported that monocytes and macrophages are important IgE effector cells against tumors. However, the underlying mechanisms of how IgE exerts antitumor immunity by engaging these effector cells are insufficiently characterized. Here, we sought to investigate the immune profile signatures triggered by the engagement of tumor antigen-specific IgE with Fc-receptors on the surface of monocytes, a key immune effector cell recruited by IgE antibodies. In order to investigate the above aim, the following methods were utilized: Antibody dependenT-cell-mediated cytotoxicity (ADCC) and phagocytosis (ADCP) were measured by flow cytometry. Cell stimulation studies with cytokines or by cross-linking of IgE monoclonal antibodies on the surface of monocytes were conducted. Expression and secretion of immune mediators were assessed using quantitative-PCR and ELISA. Toxicity of cytokines towards immune and tumor cells were investigated by cell viability (MTS) assays. As a result, tumor antigen-specific IgE-mediated tumor cell cytotoxicity mediated by human monocytes correlated with increased levels of TNFα, MCP-1 and IL-10. Cross-linking of IgE, but not IgG, on the monocyte surface, triggered up-regulation of the proinflammatory mediator TNFα. TNFα stimulation of monocytes and of tumor cells triggered stimulation of MCP-1 by both cells. Neither cross-linking of IgE or IgG antibodies on tumor cells or monocytes, nor stimulation of these cells with TNFα or MCP-1, was sufficient to upregulate IL-10. However, IL-10 expression was induced by monocytic cells when stimulated by TNFα and MCP-1 in combination, and by stimulation with IL-10 in an autocrine manner. None of these stimulation conditions was sufficient to upregulate IL-10 in cancer cell lines of different origins. None of the three cytokines had direct cytotoxic effects towards immune or tumor cells. However, blockade of TNFα receptor on monocytes reduced ADCC and increased levels of the chemoattractant MCP-1 recruited monocytes in chemotaxis assays in vitro and macrophages in tumor lesions in a rat model of cancer treated with anti-tumor IgE. These findings suggest that IgE-dependent monocyte-mediated tumor cell cytotoxicity triggers TNFα, MCP-1 and IL-10, an axis normally associated with IgE-mediated anti-parasite immune functions. This cascade appears to be responsible for a prominent recruitment of monocytes and macrophages towards tumor cells but may not be solely responsible for IgE-mediated antitumor cytotoxic functions. Identifying the immune profiles involved in IgE-mediated monocyte antitumor mechanisms may help identify markers of effector cell activation and support the development of IgE class as a novel immuno-oncology strategy. Citation Format: Mano Nakamura, Heather J. Bax, James F. Spicer, Katie E. Lacy, Sophia Tsoka, Debra H. Josephs, Sophia Karagiannis. Discovering the immune profiles of a novel antifolate receptor alpha IgE antibody associated with monocyte-mediated antitumor functions [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr A095.