The efficacy of monoclonal antibodies attributes to both the antigen-binding fragment (Fab) and crystallizable fragment (Fc). In addition, engineered Fc-derived antibody domains have also shown potential for Fc-based therapeutics in recent years. Fc facilitates engagement with immune effector functions (i.e., cellular immunity through interaction with Fc receptors (FcR) and the complement system through binding to C1q). The Fc also prolongs half-life in circulation through its interaction with the neonatal FcR (FcRn).
Fig.1 Main Fc regions for IgG improvement. (Fonseca, 2018)
Fc engineering is one attractive application to maximize the value or overcome the drawbacks of monoclonal antibodies for therapeutic use. Fc-engineering technologies were predominantly tested in the background of whole antibody molecules, but can also be applied to Fc-containing antibody derivatives such as scFv-Fc fusion protein. Engineering efforts including modification of Fc glycosylation and the introduction of point mutations that collectively shape the affinity of Fc binding to a wide array of canonical and non-canonical Fc-receptors or complements provide a means to drive targeted immune clearing activities.
Fig.2 Fc Engineering to Dial up Function. (Liu, 2020)
A number of mutations within the Fc domain have been identified that enhance binding of FcRs and through this significantly enhance cellular cytotoxicity. Many particular efforts have focussed on increasing the affinity of the Fc domain for the low-affinity receptor FcγIIIa. Investigators have utilized multiple approaches to engineer monoclonal antibodies including glycoengineering and mutating amino acids within the Fc region.
Fig.3 Strategies for improving antibody Fc-mediated effector functions. (Saunders, 2019)
Fc can bind to the C1q to initiate the assembly of membrane attack complex formed by complement cascade proteins to destroy target cells, which is termed complement-dependent cytotoxicity (CDC). There are numerous ways to enhance complement-based effector function through Fc engineering. A series of mutants can enhance C1q binding and concomitant CDC activity. For example, researchers generated a cross IgG subclass variant combining the CH1 and hinge regions of IgG1 with the CH2 and CH3 regions of IgG3, which resulted in up to 50-fold enhanced CDC activity relative to IgG1.
Some cases may be desirable to reduce or eliminate effector function for example to prevent target cell death, off-target cytotoxicity or unwanted cytokine secretion. Fc engineering approaches have been used to mutate or glycosylate the key interaction sites of the Fc domain binding with FcRs and C1q to reduce or abolish their binding.
Association of FcRn molecules to the Fc region of IgG in acidified endosomes and subsequent dissociation of the interaction in neutral pH serum enables IgG molecules to be recycled for prolonged serum persistence after internalization by endothelial cells. Engineering the strictly pH-dependent IgG-FcRn interaction is known to extend IgG half-life. Many researchers have generated various Fc variants exhibiting significantly improved circulating half-lives of therapeutic IgG antibodies.
With years of research experience in the field of recombinant antibody construction and expression, Creative Biolabs provides you the complete and best Fc engineering solution needed to develop the new project. You have the option to start or stop the project from any stage of the antibody generation service. Please feel free to contact us for further information.