Checkpoint Agonist Antibody Assays

Detect Agonistic Potential of Antibody Therapeutic Candidates Targeting Checkpoint Receptors

Agonist antibodies present a promising approach for therapeutic development due to their ability to modulate immune cell response. Targeting co-stimulatory checkpoint receptors (e.g., OX40) leads to activation of T-cell receptor (TCR) signaling, resulting in an anti-tumor response. Conversely, by targeting inhibitory checkpoint receptor (e.g. PD-1, BTLA) signaling, agonistic antibodies can suppress T-cell activation that prevents exaggerated immune responses observed in autoimmune diseases. Furthermore, when an agonist antibody binds to multiple checkpoint receptors on the cell surface, it can physically cluster them together, amplifying the inhibitory signal and resulting in significant immune suppressive response. Given their ability to regulate immune function, agonist antibodies have emerged as an important class of therapeutics that can target both co-stimulatory receptors for cancer and co-inhibitory receptors for auto-immune diseases.

Current assays for measuring antibody agonism have design limitations, exhibiting low to modest signaling, making them unsuitable for further characterization of candidate drug molecules. These current assays’ inability to replicate necessary physiological conditions may confer an antibody with none or lower agonistic activity than intended. Thus, it is crucial to adopt an appropriate assay design for capturing the agonistic potential of any therapeutic antibody candidate.

Eurofins DiscoverX^® has developed stable cell lines expressing Fcγ receptors (FcγR) that mediate antibody crosslinking and present the antibody molecule more efficiently to the target immune cells without triggering intracellular signaling. Including clustering cells in the assay design represents a novel approach to assess the agonistic potential of antibodies targeting checkpoint receptors and other target classes of receptors.