Functional Attributes of Antibodies, Effector Cells, and Target Cells Affecting NK Cell–Mediated Antibody-Dependent Cellular Cytotoxicity

Abstract

Ab-dependent cellular cytotoxicity (ADCC) is one of the most important effector mechanisms of tumor-targeting Abs in current immunotherapies. In ADCC and other Ab-dependent activation of myeloid effector cells, close cell-cell contact (between effector and target cell) and formation of immunological synapses are required. However, we still lack basic knowledge on the principal factors influencing ADCC potential by therapeutic Abs. In this study we investigated the combined roles of five factors affecting human NK cell-mediated ADCC, namely: 1) Ag density, 2) target cell membrane composition, 3) IgG FcgR polymorphism, 4) FcgR-blocking cytophilic Abs, and 5) Ab fucosylation. We demonstrate that the magnitude of NK cell-mediated ADCC responses is predominantly influenced by Ag density and Ab fucosylation. Afucosylation consistently induced efficient ADCC, even at very low Ag density, where fucosylated target Abs did not elicit ADCC. On the side of the effector cell, the FcgRIIIa-Val/Phe158 polymorphism influenced ADCC potency, with NK cells expressing the Val158 variant showing more potent ADCC. In addition, we identified the sialic acid content of the target cell membrane as an important inhibitory factor for ADCC. Furthermore, we found that the presence and glycosylation status of aspecific endogenous Abs bound to NK cell FcgRIIIa (cytophilic Abs) determine the blocking effect on ADCC. These five parameters affect the potency of Abs in vitro and should be further tested as predictors of in vivo capacity.

Considerations of Antibody Geometric Constraints on NK Cell Antibody Dependent Cellular Cytotoxicity

“…By far the most important contributor to antibody ADCC activity studied so far is antibody subclass and glycosylation. While the basis of subclass remains somewhat of a mystery, we do have substantial evidence as to the importance of Fc glycosylation (43,47,49,105,107,108). Specifically, if the glycan at Asn 297 is fucosylated, then the binding to FcγRIIIa is impaired (43,(47)(48)(49)109).…”

“…Such examples include, but are not limited to, HIV, influenza, ebolaviruses, marburgviruses, SARS, MERS, Hepatitis, Chikungunya virus, Zika virus, Dengue virus and Noroviruses, among many others. Antibodies are capable of binding to nearly any epitope presented on enveloped viral antigens ( Figure 4 ), however their capacity to induce ADCC varies widely ( 103 – 105 ). The reason for such variance is unknown but may be related to where an epitope is located and the way in which an antibody binds, as well as genetic variation in FcγRs ( 106 ).…”

Immune Complex Vaccine Strategies to Combat HIV-1 and Other Infectious Diseases

“…The low-affinity FcγRIIB, on the other hand, is expressed on B cells as a negative regulator of antibody production. FcγRIIIA on NK cells and some macrophages serves as the key receptor for inducing ADCC [6,7]. In contrast, the type II FcRs, which include C-type lectins DC-SIGN and CD23 (FceRII) [8], bind the Fc domain of IgG in a close conformation at the CH2-CH3 interface in a 2:1 stoichiometry.…”

Generation of FX−/− and Gmds−/−CHOZN host cell lines for the production of afucosylated therapeutic antibodies

“…For some marketed oncology mAbs such as Trastuzumab, Rituximab, and Ipilimumab, the primary mechanism of actions could be attributed to antibody‐dependent cellular cytotoxicity (ADCC), a process that therapeutic marketed therapeutic antibodies (mAbs) bind to specific targeted cells and recruit effector cells, which induce the apoptosis of targeted cells 1‐4 . The ADCC effect is highly dependent on the ability of therapeutic mAbs to recruit effector cells such as Natural Killer (NK) cells 5,6 . The recruitment of effector cells by mAbs is determined mainly by glycan‐glycan interaction between N‐glycosylations on the Fc domain of mAbs and FcγRIIIa (CD16a) on effector cells 7 .…”