Fc-Engineered Therapeutic Antibodies: Recent Advances and Future Directions

Abstract

Monoclonal therapeutic antibodies have revolutionized the treatment of cancer and other diseases. Fc engineering aims to enhance the effector functions or half-life of therapeutic antibodies by modifying their Fc regions. Recent advances in the Fc engineering of modern therapeutic antibodies can be considered the next generation of antibody therapy. Various strategies are employed, including altering glycosylation patterns via glycoengineering and introducing mutations to the Fc region, thereby enhancing Fc receptor or complement interactions. Further, Fc engineering strategies enable the generation of bispecific IgG-based heterodimeric antibodies. As Fc engineering techniques continue to evolve, an expanding portfolio of Fc-engineered antibodies is advancing through clinical development, with several already approved for medical use. Despite the plethora of Fc-based mutations that have been analyzed in in vitro and in vivo models, we focus here in this review on the relevant Fc engineering strategies of approved therapeutic antibodies to finetune effector functions, to modify half-life and to stabilize asymmetric bispecific IgGs.

Keywords: Fc engineering; bispecific antibodies; cancer therapy; half-life-extended antibodies; protein engineering; tailored antibodies.

Figure 1

IgG is a Y-shaped protein made up of four polypeptide chains: two identical heavy chains and two identical light chains. The heavy chains are about 50 kDa in size, while the light chains are about 25 kDa. The chains are linked together by disulfide bonds, which form between cysteine residues on the respective chains. The antigen-binding site is located at the tips of the Y-shaped structure, where the variable domains of the light and heavy chains form the antigen-binding variable fragment. The Fc region or Fc fragment is located at the base of the Y-shaped structure and is usually N-glycosylated at N297. The Fc region is responsible for the effector functions of IgG, e.g., complement activation (CDC), antibody-dependent cellular phagocytosis (ADCP) and antibody-dependent cellular cytotoxicity (ADCC). Created with BioRender.com.

Figure 2

Illustration of the relevant effector functions of approved therapeutic antibodies. (A) IVIg or hyperimmune sera are produced from B cells of healthy donors or convalescent patients. (B) Neutralization is probably the best-known activity of therapeutic antibodies and is responsible for highly specific binding to the antigen with high affinity. (C) ADCP, where antibodies bind to target cells or molecular structures and make them more susceptible to phagocytosis, is mostly used for tumor targeting. This effector function is mediated by several FcγRs. (D) ADCC is mediated by FcγRIIIA: therapeutic IgGs bind to target cells and recruit natural killer (NK) cells to kill the target cells. Also, this effector function is highly relevant for cancer therapy. (E) CDC, where antibodies bind to target cells, activate the complement via C1q and finally lyse target cells via the MAC, is of relevance to cancer therapy. (F) FcγRIIB is the only known inhibitory FcR and inhibits innate and adaptive immunity via several pathways. Targeting the feedback inhibition of B cells is not only relevant for the therapy of allergies but also for improved tumor targeting. (G). The FcRn-mediated recycling of proteins that contain an Fc region is responsible for the long plasma half-lives of IgGs. See the main text for details. Created with BioRender.com.

Figure 3

”Knob-into-holes” and CrossMab design of heterodimeric bispecific antibodies. “Knobs” (located on heavy chain 1) and “holes” (found on heavy chain 2) are created using bulky and small amino acids, respectively, in the CH3 region. This design strategy enhances the likelihood of a heterodimeric assembly. The CrossMab technology is employed to fix a light chain to its respective heavy chain. This involves rotating the entire Fab structure, resulting in a “heavy chain” composed of CH3-CH2-CL-VL and a “light chain” consisting of CH1-CL. Since CH1-CL cannot assemble with CH1-VH on the other heavy chain, the “light chain” is affixed to the rotated heavy chain (CrossMab^ab). Similarly, this can also be achieved by exchanging/rotating only one domain of the light chain, either the CL (CrossMab^CH1-CL) or the VL (CrossMab^VL-VH). Created with BioRender.com.