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 (aka CD32A), FcγRIIa (aka CD16A), and inhibitory (FcγRIIb) receptors. ADCC and ADCP outcomes depend on the preferential affinity of each Ab for one FcgR. The Ab-FcgR interaction is regulated by the Ab isotype and glycosylation [1, 2]. 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].

FcγR-mediated cellular responses:

FcγRs differ in their cellular distribution and are often co-expressed.

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

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.