Abstract IA07: Enhancing immune effector function via antibody engineering
Authors: Klein Christian 
Published: October 2015

Abstract
Therapeutic antibodies of the IgG1 isotype have been established as important modality for cancer therapy in the clinic. They mediate their anti-tumoral efficacy largely by direct effects such as apoptosis/cell death induction or signaling inhibition, and by recruiting innate immune effector cells such as NK cells, macrophages and monocytes for antibody dependent cellular cytotoxicity and phagocytosis (ADCC, ADCP). Recently, methods to improve the immune effector function of therapeutic antibodies have been developed by enhancing FcgRIII binding including Fc-engineering and engineering the carbohydrate portion of the antibody. We have developed and applied a technology known as “glycoengineering” to improve the immune effector function of therapeutic antibodies. Obinutuzumab (GA101) is a glycoengineered Type II anti CD20 monoclonal antibody of the IgG1 isotype derived by humanization and elbow hinge optimization of the parental B-Ly1 mouse antibody that has recently been approved by the FDA and EMA for first line therapy of chronic lymphocytic leukemia (CLL) patients in combination with chlorambucil.
In nonclinical studies obinutuzumab mediates enhanced direct (caspase independent) cell death induction with a concomitant reduction of complement dependent cytotoxicity compared to rituximab or ofatumumab by virtue of being a Type II CD20 antibody. As a consequence of glycoengineering the Fc region the core fucosylation of obinutuzumab is reduced and it has enhanced affinity for low and high affinity FcγRIIIa receptors resulting in enhanced NK cell mediated antibody dependent cellular cytotoxicity (ADCC). Recently, we demonstrated that glycoengineering not only enhances ADCC, but also results in enhanced antibody dependent cellular phagocytosis (ADCP) as compared to non-glycoengineered antibodies when physiological amounts of immunoglobulins are present. Furthermore, through enhanced affinity for FcγRIIIb that is expressed on neutrophils, obinutuzumab also mediates enhanced activation of neutrophils and neutrophil mediated phagocytosis. Finally, we have shown that in contrast to rituximab or non-glycoengineered obinutuzumab, ADCC mediated by obinutuzumab is largely unaffected by inhibitory KIR/HLA interactions. Thus, the modification of the Fc fragment of obinutuzumab appears as an effective strategy to enhance ADCC and ADCP by NK cells, macrophages/monocytes and neutrophils independent of inhibitory KIR expression. In whole blood assays derived from healthy donors and chronic lymphocytic leukemia (CLL) patients these properties result in superior depletion of normal and malignant B cells in terms of potency and absolute B cell depletion as compared to rituximab.
In order to further enhance the efficacy of ADCC competent therapeutic antibodies we have developed a novel class of tumor-targeted IL2v immunocytokines with the aim to activate and induce the proliferation of innate and adaptive immune effector cells in the tumor. In the FAP-IL2v immunocytokine an IL-2 variant (IL2v) with abolished CD25 binding is fused to the C-terminus of one of the Fc chains of a tumor stroma-targeted FAP antibody. FAP-IL2v lacks binding to CD25, but retains IL-2Rßγ binding so that is no longer preferentially activates Treg cells and reduces sensitivity for Fas-mediated apoptosis as compared to wildtype IL-2-based FAP-IL2wt immunocytokine. In C56BL/6 mice, FAP-IL2v strongly expands and activates NK cells and CD8+ T cells, and skews the CD4:CD8 ratio towards CD8+ T cells. In vitro, FAP-IL2v induces the proliferation and activation of NK cells and enhances the cytotoxic activity of NK cells in combination with ADCC competent antibodies. Similarily, in xenograft (hCD16 transgenic SCID mice) and BALB-neuT (immunocompetent ratHER2 transgenic mice) models, FAP-IL2v strongly enhances the antitumoral efficacy and survival mediated by HER2 antibodies making it a promising combination partner for ADCC-competent antibodies in future clinical investigation.
Citation Format: Christian Klein. Enhancing immune effector function via antibody engineering. [abstract]. In: Proceedings of the AACR Special Conference: Tumor Immunology and Immunotherapy: A New Chapter; December 1-4, 2014; Orlando, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2015;3(10 Suppl):Abstract nr IA07.