Antibody dependent cellular cytotoxicity (ADCC) is a key mechanism by which therapeutic antibodies mediate their anti-tumor effects. Absence of fucose on the heavy chain of the antibody increases the affinity between the antibody and FcγRIIIa, which results in increased in vitro and in vivo ADCC compared to the fucosylated form. However, the cellular and molecular mechanisms responsible for increased ADCC are unknown. Through a series of biochemical and cellular studies, we find that human NK cells stimulated with afucosylated antibody exhibit enhanced activation of proximal FcγRIIIa signaling and downstream pathways, as well as enhanced cytoskeletal rearrangement and degranulation, relative to stimulation with fucosylated antibody. Furthermore, analysis of the interaction between human NK cells and targets using a high-throughput microscope-based antibody-dependent cytotoxicity assay show that afucosylated antibodies increase the number of NK cells capable of killing multiple targets and the rate with which targets are killed. Together, we conclude that the increase in affinity between afucosylated antibodies and FcγRIIIa enhances activation of signaling molecules promoting cytoskeletal rearrangement and degranulation, which, in turn, potentiates the cytotoxic characteristics of NK cells to increase efficiency of ADCC.
- Received July 1, 2014.
- Revision received October 17, 2014.
- Accepted November 4, 2014.
- Copyright © 2014, American Association for Cancer Research.