The Fc Review: How do antibody structure and binding dynamics shape ADCC signaling? A recent study in The AAPS Journal explores how multiple antibody design features, including Fab affinity, hinge flexibility, Fc engagement, and antigen density, influence antibody-dependent cellular cytotoxicity (ADCC) signaling. Background: ADCC is a key mechanism of action for many therapeutic antibodies, yet the strength of this response depends on more than Fcγ receptor binding alone. Productive immune activation requires antibodies to bridge target cells and effector cells within the immune synapse, forming receptor crosslinks that trigger downstream signaling. Using a combination of computational modeling and experimental data, this study examines how structural properties of antibodies influence these crosslinking events and ultimately shape ADCC signaling outcomes. The study highlights: ADCC signaling is influenced by multiple antibody properties, including Fab affinity, hinge flexibility, Fc receptor engagement, and antigen expression levels. Antibody structure affects how efficiently Fc receptors and target antigens are crosslinked within the immune synapse. In some cases, moderate Fab affinity supported stronger signaling by favoring productive crosslinking configurations. Antibody valency and hinge flexibility also influenced signaling outcomes by altering the geometry of immune synapse interactions.

The Fc Review: How well do our preclinical models capture human Fc biology? A new Science Immunology study takes a deep look at Fcγ receptor and FcRn expression across humans, non-human primates, and mice, highlighting how species-specific differences shape Fc-mediated immune function. Background: Fc-dependent activity is influenced not only by antibody design, but also by where and how Fcγ receptors are expressed across immune cell types and tissues. While animal models remain central to #antibody development, differences in Fcγ receptor biology across species can complicate interpretation of Fc-driven mechanisms. The study highlights: Species-specific differences in Fcγ receptor expression patterns across immune cell subsets and tissues. Context-dependent regulation of Fcγ receptors by inflammatory cues, with expression shifting across cell types and environments. These differences influence how Fc-mediated functions are engaged and interpreted across experimental systems. Cross-species variation in FcγR and FcRn biology helps explain why Fc-dependent effects observed preclinically may not always translate cleanly to human settings.