The agonistic action of several immunomodulatory monoclonal antibodies (mAb) requires both target antigen binding and clustering of this mAb:target complex by the Fcs interacting with Fcγ receptors (FcγR), in particular… Click to show full abstract
The agonistic action of several immunomodulatory monoclonal antibodies (mAb) requires both target antigen binding and clustering of this mAb:target complex by the Fcs interacting with Fcγ receptors (FcγR), in particular FcγRIIb, on neighbouring bystander cells. Fc mutations were made in the IgG4-based TGN1412 anti-CD28 mAb to define the role of FcγR interactions in its "super-agonist" activity. The dual mutation, IgG4-ED269,270 AA, ablated interaction with all human FcγR and agonistic action was consequentially lost, confirming the FcγR-dependence on the action of TGN1412. The IgG4 lower hinge region (F234 L235 G236 G237 ) was modified by L235 E mutation (F234 E235 G236 G237 ), a mutation commonly used to ablate FcγR binding, including in approved therapeutic mAbs. However, rather than ablating all FcγR binding, IgG4-L235 E conferred specific binding to FcγRIIb, the inhibitory Fc receptor. Furthermore, in combination with the core hinge-stabilising mutation (IgG4-S228 P, L235 E), this mutation increased affinity for FcγRIIb compared to wild type IgG4. In addition to having FcγRIIb specificity, these engineered TGN1412 antibodies also retained their super-agonistic ability, demonstrating that CD28 and FcγRIIb-specific binding are together sufficient for agonistic function. The FcγRIIb-specific nature of IgG4-L235 E has utility for mAb-mediated immune agonism therapies that are dependent on FcγRIIb interaction and of anti-inflammatory mAbs in allergy and autoimmunity that harness FcγRIIb inhibitory signalling.
               
Click one of the above tabs to view related content.