Fc-Engineering for Modulated Effector Functions-Improving Antibodies for Cancer Treatment

Abstract

The majority of monoclonal antibody (mAb) therapeutics possess the ability to engage innate immune effectors through interactions mediated by their fragment crystallizable (Fc) domain. By delivering Fc-Fc gamma receptor (FcγR) and Fc-C1q interactions, mAb are able to link exquisite specificity to powerful cellular and complement-mediated effector functions. Fc interactions can also facilitate enhanced target clustering to evoke potent receptor signaling. These observations have driven decades-long research to delineate the properties within the Fc that elicit these various activities, identifying key amino acid residues and elucidating the important role of glycosylation. They have also fostered a growing interest in Fc-engineering whereby this knowledge is exploited to modulate Fc effector function to suit specific mechanisms of action and therapeutic purposes. In this review, we document the insight that has been generated through the study of the Fc domain; revealing the underpinning structure-function relationships and how the Fc has been engineered to produce an increasing number of antibodies that are appearing in the clinic with augmented abilities to treat cancer.

Keywords: Fc gamma receptor; Fc-engineering; antibody immunotherapy; antibody-dependent cellular cytotoxicity (ADCC); antibody-dependent cellular phagocytosis (ADCP); complement.

Figure 1

Fragment crystallizable (Fc) modifications which augment antibody effector function. (A) Timeline of events detailing techniques used to discover variants with enhanced effector cell function and when the Fc variants were first described [40,41,42,43,44,45,46,47,48]. Letters refer to the common notation of the introduced amino acid substitutions as discussed in the main text. (B) Previously identified point mutations within the Fc that impact effector cell function annotated on a hIgG1 Fc crystal structure model (PDB: 3AVE; [49,50]) and detailed in Table 1.

Figure 2

Fc modifications which increase complement-dependent cytotoxicity. (A) Previously identified point mutations within the Fc that modulate complement dependent cytotoxicity are annotated on a human IgG1 Fc crystal structure model (PDB: 3AVE; [49,50]). (B) Fold change in effector function or binding affinity to C1q in complement dependent cytotoxicity (CDC)-enhancing variants compared to wild type (WT) antibodies. Magnitude of effector function or binding affinity of variants were compared to WT antibodies of the same IgG isotype and F(ab) region. Each row depicts an independent experiment and therefore often independent methods, utilizing a different IgG backbone from a particular study as referenced in the last column. NB = no detectable binding, n.d. = no data, − = no change, ↑ <2 fold upregulation, ↑↑ 2–9.99 fold upregulation, ↑↑↑ 10–99.99 fold upregulation, ↓↓ 2–9.99 fold downregulation,.

Figure 3

Fc modifications which enhance binding to FcγRIIB. (A) Previously identified point mutations within the Fc that impact binding to FcγRIIB annotated on a hIgG1 Fc crystal structure model (PDB: 3AVE; [49,50]). (B) Magnitude of binding affinity of variants were compared to WT antibodies of the same IgG isotype and F(ab) region. Each row depicts an independent experiment and therefore often independent methods, utilizing a different IgG backbone from a particular study as referenced in the last column. NB = no detectable binding, n.d. = no data, − = no change, ↑ < 2 fold upregulation, ↑↑ 2–9.99 fold upregulation, ↑↑↑↑ > 100 fold upregulation, ↓↓ 2–9.99 fold downregulation, ↓↓↓ 10–99.99 fold downregulation, FcγRIIA^H FcγRIIA-H131, FcγRIIA^R FcγRIIA-R131, FcγRIIIA^F FcγRIIIA-F158, FcγRIIIA^V FcγRIIIA-V158.

Figure 4

Fc modifications which reduce antibody effector function and/or FcγR binding. (A) Timeline of events detailing major discoveries, techniques used to discover variants that have a silenced Fc region and when the Fc variants were first described in the literature [57,115,124,127,128,129,130,132,133,134,135,136]. Letters refer to the common notation of the introduced amino acid substitutions as discussed in the main text. (B) Previously identified point mutations within the Fc that silence Fc functions annotated on a hIgG1 Fc crystal structure model (PDB: 3AVE; [49,50]) and detailed in Table 3.

Figure 5

Fc modifications that improve half-life. (A) Timeline of events detailing when major discoveries were made regarding Fc:IgG interactions, techniques used to discover variants that have enhanced half-life and when the Fc variants were first described in the literature [40,162,163,164,165,166,167,168,169,170,171,172,177]. Letters refer to the common notation of the introduced amino acid substitutions as discussed in the main text. (B) Previously identified point mutations within the Fc that impact effector cell function annotated on a hIgG1 Fc crystal structure model (PDB: 3AVE; [49,50]) and detailed in the table below. (C) Magnitude of change to half-life or binding affinity for FcRn of variants were compared to WT antibodies of the same IgG isotype and F(ab) region. Each row depicts an independent experiment and therefore often independent methods, utilizing a different IgG backbone from a particular study as referenced in the last column. NB—no detectable binding, n.d.—no data, − no change, ↑ < 2 fold upregulation, ↑↑ 2–9.99 fold upregulation, ↑↑↑ 10–99.99 fold upregulation, ↑↑↑↑ > 100 fold upregulation.