Antibody-dependent cellular cytotoxicity & phagocytosis (ADCC & ADCP)

ADCC and ADCP are two major modes of action of therapeutic monoclonal Abs (mAbs). These protective functions rely on the mAb dual structure:

– the variable region ensures the specific recognition of an antigen expressed by a microbe or a target cell
– the “crystallizable fragment” Fc in the constant region binds to Fc receptors at the surface of effector cells

Fc-gamma receptors (FcγRs):

Human IgGs bind to activatory (FcγRI, FcγRIIA (CD32A), FcγRIIa (CD16A), and inhibitory (FcγRIIb) receptors. The IgG-FcγR interaction is regulated by the Ab isotype and glycosylation [1, 2].
FcγRs differ in their cellular distribution and are often co-expressed, e.g:

FcgRIIA (CD32A) is expressed myeloid cells including monocytes, macrophages, and dendritic cells (DCs)
FcgRIIIa (CD16A) is expressed on macrophages and Natural Killer (NK) cells.

FcγR-mediated cellular responses:

ADCC and ADCP are initiated when multiple IgG molecules bind simultaneously to FcγRs. The binding of antibody-antigen complexes to activatory and inhibitory FcγRs induces their cross-linking and subsequent signaling through immunoreceptor tyrosine-based activation motifs (ITAMs) and inhibition motifs (ITIMs), respectively. Cytoplasmic signaling includes an increase in intracellular calcium concentration and calcineurin/calmodulin-mediated dephosphorylation of NFAT (nuclear factor of activated T cells), allowing its nuclear translocation and binding to promoter regions of ADCC and ADCP relevant genes [1, 2].

The balance in FcγR signaling controls the immune outcome.

No response: inhibiting signals counterbalance activating signals.
ADCC: an excess of engaged CD16A induces the release of cytotoxic granules which kill the target [1].
ADCP: an excess of engaged CD32A induces the phagocytosis of the microbe or target cell, thus facilitating antigen presentation and stimulating inflammatory cytokine secretion [2].

InvivoGen's ADCC and ADCP reporter assays:

Classical ADCC and ADCP assays to test mAb functionalities are laborious, as they mainly rely on NK cells and peripheral blood monocytes. InvivoGen offers a convenient alternative by using:

Engineered human NFAT-reporter T-cell lines with readily assessable Lucia luciferase reporter activity
Raji-derived target cells with stable antigen expression
Clinically-relevant mAb isotypes with modified effector function potencies.

View our product flyer on Clinically-relevant monoclonal antibodies

References:

1. Quast I. et al. 2017. Regulation of antibody effector functions through IgG fc N-glycosylation. Cell. Mol. Life. Sci. 74(5):837.
2. Tay M.Z. et al., 2019. Antibody-Dependent Cellular Phagocytosis in Antiviral Immune Responses. Front Immunol. 10:332.