# IMGT® Nomenclature of Engineered IGHG Variants Involved in Antibody Effector Properties and Formats

Marie-Paule Lefranc, Gérard Lefranc

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Marie-Paule Lefranc, Gérard Lefranc. IMGT® Nomenclature of Engineered IGHG Variants Involved in Antibody Effector Properties and Formats. Antibodies, 2022, 11 (4), pp.65. 10.3390/antib11040065. [https://doi.org/10.3390/antib11040065](https://doi.org/10.3390/antib11040065)

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Article

# IMGT® Nomenclature of Engineered IGHG Variants Involved in Antibody Effector Properties and Formats

Marie-Paule Lefranc* and Gérard Lefranc*

IMGT®, The International ImMunoGeneTics Information System®, Laboratoire d'ImmunoGénétique Moléculaire (LIGM), Institut de Génétique Humaine (IGH), Centre National de la Recherche Scientifique (CNRS), Université de Montpellier (UM), UMR 9002 CNRS-UM, CEDEX 5, 34396 Montpellier, France

* Correspondence: marie-paule.lefranc@igh.cnrs.fr (M.-P.L.); gerard.lefranc@umontpellier.fr (G.L.)

**Abstract:** The constant region of the immunoglobulin (IG) or antibody heavy gamma chain is frequently engineered to modify the effector properties of the therapeutic monoclonal antibodies. These variants are classified in regards to their effects on effector functions, antibody-dependent cytotoxicity (ADCC), antibody-dependent phagocytosis (ADCP), complement-dependent cytotoxicity (CDC) enhancement or reduction, B cell inhibition by the coengagement of antigen and FcγR on the same cell, on half-life increase, and/or on structure such as prevention of IgG4 half-IG exchange, hexamerisation, knobs-into-holes and the heteropairing H-H of bispecific antibodies, absence of disulfide bridge inter H-L, absence of glycosylation site, and site-specific drug attachment engineered cysteine. The IMGT engineered variant identifier is comprised of the species and gene name (and eventually allele), the letter 'v' followed by a number (assigned chronologically), and for each concerned domain (e.g, CH1, h, CH2 and CH3), the novel AA (single letter abbreviation) and IMGT position according to the IMGT unique numbering for the C-domain and between parentheses, the Eu numbering. IMGT engineered variants are described with detailed amino acid changes, visualized in motifs based on the IMGT numbering bridging genes, sequences, and structures for higher order description.

**Keywords:** IMGT; immunogenetics; immunoinformatics; immunoglobulin (IG); antibody; system biology; bioengineering; allotypes; variants; effector properties

## 1. Introduction

The adaptive immune response, acquired by jawed vertebrates (or *gnathostomata*) more than 450 million years ago and found in all extant jawed vertebrate species from fish to humans, is characterized by a remarkable immune specificity and memory, which are the properties of the B and T cells because of the extreme diversity of their antigen receptors [1]. The antigen receptors of the adaptive immune response [1,2] comprise the immunoglobulins (IG) or antibodies of the B cells and plasmocytes [3,4] and the T cell receptors (TR) of the T cells [5]. The IG recognizes antigens in their native (unprocessed) form, whereas the TR recognizes processed antigens, which are presented as peptides through its highly polymorphic major histocompatibility (MH, in humans HLA for human leucocyte antigens) proteins [6]. Immunoglobulins (IG) or antibodies serve a dual role in immunity. First, they both recognize antigens on the surface of foreign bodies such as bacteria and viruses, and second, they trigger elimination mechanisms such as cell lysis and phagocytosis to rid the body of these invading cells and particles [4]. IMGT®, the international ImMunoGeneTics information system® (https://www.imgt.org) (accessed on 11 October 2022) [1], was created in 1989 by Marie-Paule Lefranc in Montpellier, France, Laboratoire d'ImmunoGénétique Moléculaire (LIGM) des Prof G. and M-P. Lefranc (Université de Montpellier and CNRS) to manage the huge diversity of the IG and TR repertoires. For the first time, immunoglobulin (IG) or antibody and T cell receptor (TR) variable (V),

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**Citation:** Lefranc, M.-P.; Lefranc, G. IMGT® Nomenclature of Engineered IGHG Variants Involved in Antibody Effector Properties and Formats.

*Antibodies* **2022**, *11*, 65. https://doi.org/10.3390/antib11040065

Academic Editor: Aaron T. Wecksler

Received: 17 August 2022

Accepted: 12 October 2022

Published: 18 October 2022

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).
diversity (D), joining (J) and constant (C) genes were officially recognized as ‘genes’ and conventional genes [1,3,5,7–10]. Through its creation, IMGT® marks the advent of a new science, immunoinformatics, which emerged at the interface between immunogenetics and bioinformatics [1]. As an ontology and system, IMGT® bridges genes, sequences and structures of the antigen receptors to better understand their functions. Focusing on the constant region of the IgG, a standardized definition of engineered variants of therapeutic antibodies is provided based on the IMGT concepts.

## 2. An Ontology and a System to Bridge Genes, Sequences and Structures to Functions

IMGT®, the international ImMunoGeneTics information system® (Figure 1) [1,11–21], is an integrated system for the genes, sequences and structures of the IG or antibodies, TR and MH of the adaptive immune responses of the jawed vertebrates, as well as other proteins of the IG superfamily (IgSF) [22] and MH superfamily (MhSF) of vertebrates and invertebrates [23].

<figure><img src="image_5.png" /><figcaption>**Figure 1.** IMGT® is the international ImMunoGenetics information system® (https://www.imgt.org) [11–21]. The IMGT web resources (>25,000 pages, the IMGT Marie-Paule page) are not shown. IMGT/mAb-DB, the interface for therapeutic monoclonal antibodies and fusion proteins for immune applications (FPIA), has been available online since 4 December 2009 and IMGT/HighV-QUEST portal for the next generation sequencing (NGS) high-throughput sequence analysis since 22 November 2010 (with permission from M-P.Lefranc and G. Lefranc, LIGM, Founders of IMGT® from the international ImMunoGeneTics information system® (https://www.imgt.org)).</figcaption></figure>
Immunoinformatics [1] builds and organizes molecular immunogenetics knowledge to be managed and shared in IMGT®. IMGT® comprises seven databases [24–30], 17 tools [31–50] and more than 25,000 pages of web resources (Table 1). IMGT® databases are specialized in sequences (i.e., IMGT/LIGM-DB [24,25]), genes and alleles (IMGT/GENE-DB [26]), two-dimensional (2D) structures (IMGT/2Dstructure-DB) and three-dimensional (3D) structures (IMGT/3Dstructure-DB) [27–29], whereas the IMGT/mAb-DB [30] interface allows the querying of therapeutic monoclonal antibodies (IG, mAb), fusion proteins for immunological applications (FPIA), composite proteins for clinical applications (CPCA) and related proteins (RPI) of therapeutic interest (with links to amino acid sequences in IMGT/2Dstructure-DB, and if available, to 3D structures in IMGT/3D structure-DB. The IMGT® tools include: (1) For nucleotide sequence analysis, IMGT/V-QUEST [31–36] and the integrated IMGT/JunctionAnalysis [37,38] and IMGT/Automat [39,40] tools, and for next generation sequencing, the high-throughput version IMGT/HighV-QUEST [36,41–45] and the downloadable IMGT/StatClonotype [46,47] package (which allows for statistical pairwise analysis of the diversity and expression of the IMGT clonotypes (AA) [43] and repertoire comparisons in adaptive immune responses); (2) for genomic analysis, IMGT/LIGMotif [48] (which allows for the identification and description of new genes in genomic sequences); (3) for amino acid sequence analysis per the domain, IMGT/DomainGap-Align [28,49,50]; and (4) for graphical representations of the domains, the IMGT/Collier-de-Perles tool [51] (e.g., IMGT Colliers de Perles of the variable (V), constant (C) and groove (G) domains). IMGT® Web resources ('the IMGT Marie-Paule page') comprise the IMGT Repertoire (IG and TR, MH and RPI), IMGT Scientific chart, IMGT Education (IMGT Lexique, Aide-mémoire (amino acid physicochemical properties [52], splicing sites) and tutorials, etc.).

<table><caption>**Table 1.** The IMGT databases, tools and web resources ('The IMGT Marie-Paule Page') for sequences, genes and structures.</caption><thead><tr><th></th><th>IMGT Databases</th><th>IMGT Tools</th><th>IMGT Web Resources<br>'The IMGT Marie-Paule Page'</th></tr></thead><tbody><tr><td>Sequences</td><td>IMGT/LIGM-DB [24,25]<br>IMGT/PRIMER-DB<br>IMGT/CLL-DB</td><td>IMGT/V-QUEST [31–36]<br>IMGT/JunctionAnalysis [37,38]<br>IMGT/Automat [39,40]<br>IMGT/HighV-QUEST [36,41–45]<br>IMGT/StatClonotype [46,47]<br>IMGT/PhyloGene<br>IMGT/Allele-Align</td><td>Standardized keywords and labels [53,54]<br>Standardized labels [55–58]<br>IMGT Repertoire (IG and TR, MH, RPI)<br>Alignments of alleles<br>Protein displays<br>Tables of alleles<br>CDR-IMGT lengths<br>Allotypes [59,60]<br>Isotypes, etc.</td></tr><tr><td>Genes</td><td>IMGT/GENE-DB [26]</td><td>IMGT/LIGMotif [48]<br>IMGT/LocusView<br>IMGT/GeneView<br>IMGT/GeneSearch<br>IMGT/CloneSearch<br>IMGT/GeneInfo</td><td>Gene and allele nomenclature<br>[1–5,7–10,61–63]<br>Chromosomal localizations<br>Locus representations<br>Locus description<br>Gene exon/intron splicing sites<br>Gene tables<br>Potential germline repertoires<br>Lists of genes<br>Correspondence between nomenclatures.</td></tr><tr><td>Structures</td><td>IMGT/2Dstructure-DB<br>IMGT/3Dstructure-DB [27–29]<br>IMGT/mAb-DB [30]</td><td>IMGT/DomainGapAlign [28,49,50]<br>IMGT/DomainDisplay<br>IMGT/StructuralQuery<br>IMGT/Collier-de-Perles [51]</td><td>IMGT unique numbering per domain<br>[64–72]<br>2D Colliers de Perles (IG and TR, MH, RPI)<br>[51,73–77]<br>IMGT classes for amino acid physicochemical properties [52]<br>IMGT Colliers de Perles reference profiles [52]<br>3D representations.</td></tr></tbody></table>
The bridging of genes, structures and functions is based on the IMGT-ONTOLOGY axioms and concepts from which were generated the IMGT Scientific chart rules [78–82] (Table 2): CLASSIFICATION for the IMGT standardized gene and allele nomenclature [1–5,7–10,61–63], IDENTIFICATION for IMGT standardized keywords and keyword abbreviations (e.g., clonal type, paratope and epitope, variant, Fc receptor and FcR) [53,54], DESCRIPTION for IMGT standardized labels [55–58] (e.g., complementarity determining region (CDR)-IMGT (CDR1-IMGT to CDR3-IMGT) [57] and framework region (FR-IMGT) (FR1-IMGT to FR4-IMGT) [58]), NUMEROTATION for the IMGT unique numbering [64–72] and the IMGT Colliers de Perles [51,73–77]. IMGT positions per domain are used in Protein displays, Alignments of alleles, CDR-IMGT lengths, Allotypes [59,60] sections of the IMGT Repertoire, and to number amino acids involved in paratope/epitope (antigen receptor V-domains/target interactions [83]) (Table 1) and in effector properties (antigen receptor C-domain/effector binding proteins [6]).

<table><caption>**Table 2.** IMGT-ONTOLOGY axioms, concepts and IMGT Scientific chart rules.</caption><thead><tr><th colspan="2">IMGT-ONTOLOGY Axioms and Concepts</th><th>IMGT Scientific Chart Rules</th></tr></thead><tbody><tr><td>IDENTIFICATION [54]</td><td>Concepts of identification [53]</td><td>Standardized keywords [53,54] (e.g., clonal type, paratope, epitope, variant, Fc receptor, FcR) (1).</td></tr><tr><td>DESCRIPTION [56]</td><td>Concepts of description [55]</td><td>Standardized labels and annotations [55–58] (e.g., CDR-IMGT [57], FR-IMGT [58], antibody description [84])</td></tr><tr><td>CLASSIFICATION [63]</td><td>Concepts of classification [62]</td><td>Reference sequences<br>Standardized IG and TR gene nomenclature (group, subgroup, gene, allele) [1–5,7–10,61–63] (1).</td></tr><tr><td>NUMEROTATION [64]</td><td>Concepts of numerotation [65–72]</td><td>IMGT unique numbering for<br>V- and V-LIKE domains [65–67]<br>C- and C-LIKE domains [68]<br>G- and G-LIKE domains [69]<br>IMGT Colliers de Perles [73–77]</td></tr><tr><td>ORIENTATION</td><td>Concepts of orientation</td><td>Chromosome orientation<br>Locus orientation<br>Gene orientation<br>DNA strand orientation<br>Domain beta-strand orientation</td></tr><tr><td>OBTENTION</td><td>Standardized origin<br>Standardized methodology</td><td></td></tr></tbody></table>

Keyword use versus gene name nomenclature for defining a receptor: in this paper, this concerns the related proteins of immune interest (RPI) such as the Fc receptor's gamma. Owing to the diversity and multiplicity of these receptors, and in the absence of standardized sequence characterization in functional analysis, these receptors are usually identified with keywords, for example for *Homo sapiens*, FcγR, FcγRI, FcγRII, FcγRIII and so on. However, it should be noted that, when there is no ambiguity as to the interactive chain involved, the HGNC gene name should be used (FCGR1A, FCGR2A, FCGR2B, FCRG2C, FCGR3A and FCGR3B). This rule is applied in this paper for the neonatal Fc receptor (FcRn), which is made of the interactive Fc gamma receptor and transporter (FCGR1) chain that is associated with B2M.

IMGT standards have been used since 2006 in the description of the therapeutic antibodies published in the World Health Organization's (WHO) International Nonproprietary Names (INN) programme [84–86]. Since 2003, IMGT® has been widely used in the analysis of therapeutic antibodies for humanization and/or engineering [4, 10, 12, 86–96].

### 3. Immunoglobulin IgG Receptor, Chains, Domains and Amino Acids

The *Homo sapiens*'s IgG1-kappa (Figure 2) is taken as an example (Table 3) because it is the most represented subclass in therapeutic antibodies.
<figure><img src="image_6.png" /><figcaption>**Figure 2.** Immunoglobulin IgG1. The structure is that of the antibody b12, an IgG1-kappa, and so far is the only complete human IG crystallized (PDB code: 1hzh, from IMGT® https://www.imgt.org, IMGT/3Dstructure-DB). H-GAMMA-1 and L-KAPPA (used for the chains), VH, CH1, CH2, CH3, V-KAPPA and C-KAPPA (for the domains) are written in capital letters as they are IMGT standardized labels (DESCRIPTION) [1]. This first 3D-structure of a complete *Homo sapiens* IG shows the expected Y shape with the two Fragment antigen binding (Fab) arms (one L-KAPPA light chain (V-KAPPA-C-KAPPA) paired to the VH-CH1 of each H-GAMMA-1 heavy chain) and the Fragment crystallisable (Fc), made of the paired hinge-CH2-CH3 of the two H-GAMMA-1 heavy chains. The figure also shows the relative position, in space, of the L-KAPPA relative to the VH-CH1 in each Fab (in the front on the left hand side, and the back right hand side). The sequences of the two H-GAMMA1 chains (colored in purple and dark blue for a better visibility) are identical and the sequences of the two L-KAPPA chains (colored in orange and green for a better visibility) are identical (with permission from M-P. Lefranc and G. Lefranc, LIGM, Founders of IMGT®, the international ImMunoGeneTics information system®, https://www.imgt.org).</figcaption></figure>

<table><caption>**Table 3.** The immunoglobulin IgG1 receptor, chain and domain structure labels and correspondence with sequence labels. IMGT standardized labels are in capital letters. They are shown with the example *Homo sapiens* IgG1-kappa.</caption><thead><tr><th rowspan="2">Receptor</th><th rowspan="2">Chain</th><th colspan="2">IG Structure Labels<br>(IMGT/3Dstructure-DB [27–29])</th><th>Sequence Labels<br>(IMGT/LIGM-DB [24,25])</th></tr><tr><th>Domain Type</th><th>Domain</th><th>Region <sup>1</sup></th></tr></thead><tbody><tr><td rowspan="6">IG-GAMMA-1_KAPPA</td><td rowspan="4">H-GAMMA-1</td><td>V</td><td>VH</td><td>V-D-J-REGION</td></tr><tr><td>C</td><td>CH1</td><td>C-REGION <sup>2</sup></td></tr><tr><td>C</td><td>CH2</td><td></td></tr><tr><td>C</td><td>CH3</td><td></td></tr><tr><td rowspan="2">L-KAPPA</td><td>V</td><td>V-KAPPA</td><td>V-J-REGION</td></tr><tr><td>C</td><td>C-KAPPA</td><td>C-REGION</td></tr></tbody></table>

<footnote n="1">¹ The VH-domain (or V-D-J-REGION) and the VL-domain (V-KAPPA or V-LAMBDA) (or V-J-REGION) are encoded by rearranged V-(D)-J genes, whereas the remainder of the chain is the C-REGION (encoded by a C gene). The C-REGION comprises one C-domain (C-KAPPA or C-LAMBDA) for the L chain, or several C-domains (CH) for the H chain. ² The heavy chain C-REGION also includes the HINGE-REGION, and for membrane IG (mIG), the CONNECTING-REGION (CO), TRANSMEMBRANE-REGION (TM) and CYTOPLASMIC-REGION (CY); for secreted IG (sIG), the C-REGION includes CHS instead of CO, TM and CY.</footnote>
In the IMGT system, the C-domain includes the C-DOMAIN of the IG and of the TR [1] and the C-LIKE-DOMAIN of the IgSF other than IG and TR [22]. The C-domain description of any receptor, any chain and any species is based on the IMGT unique numbering for the C-domain (C-DOMAIN and C-LIKE-DOMAIN) [68]. A C-domain (Figure 3) comprises about 90–100 amino acids and is made up of seven antiparallel beta strands (A, B, C, D, E, F and G), linked by beta turns (AB, DE and EF), a transversal strand (CD) and two loops (BC and FG), and forms a sandwich of two sheets [ABED] [GFC]. A C-domain has a topology and a three-dimensional structure that is similar to that of a V-domain [67], but without the C' and C'' strands and the C'C'' loop, which is replaced by a transversal CD strand [68]. The lengths of the strands and loops (Table 4) are visualized in the IMGT Colliers de Perles on one layer and two layers (Figure 3).

<figure><img src="image_7.png" /><figcaption>**Figure 3.** IG constant (C) domain. (A) 3D structure ribbon representation with the IMGT strand and loop delimitations. (B) IMGT Collier de Perles on two layers with hydrogen bonds. The IMGT Colliers de Perles on two layers show, in the forefront, the GFC strands, and in the back, the ABED strands (located at the interface CH1/CL of the IG), linked by the CD transversal strand. The IMGT</figcaption></figure>
Collier de Perles with hydrogen bonds (green lines online, only shown here for the GFC sheet) is generated by the IMGT/Collier de Perles tool [51] integrated in the IMGT/3Dstructure-DB, from experimental 3D structure data. (C) IMGT Collier de Perles on two layers from IMGT/DomainGapAlign [28,49,50]. (D) IMGT Colliers de Perles on one layer. Amino acids are shown in the one-letter abbreviation. All proline (P) are shown online in yellow. IMGT anchors are represented by squares. Hatched circles are IMGT gaps according to the IMGT unique numbering for the C-domain [68]. Positions with bold (online red) letters indicate the four conserved positions that are common to a V-domain and to a C-domain: 23 (1st-CYS), 41 (CONSERVED-TRP), 89 (hydrophobic), 104 (2nd-CYS), and position 118, which is only conserved in V-DOMAIN. The identifier of the chain to which the CH-domain belongs is 1n0x_H (from the *Homo sapiens* b12 Fab, in IMGT/3Dstructure-DB, https://www.imgt.org) [27–29]. The 3D ribbon representation was obtained using PyMOL and “IMGT numbering comparison” of 1n0x_H (CH1) from IMGT/3Dstructure-DB (https://www.imgt.org) [27–29].

<table><caption>**Table 4.** C-domain strands, turns and loops, IMGT positions and lengths, based on the IMGT unique numbering for C-domain (C-DOMAIN and C-LIKE-DOMAIN) [68]. (With permission from M-P. Lefranc and G. Lefranc, LIGM, Founders of IMGT®, the international ImMunoGeneTics information system®, https://www.imgt.org).</caption><thead><tr><th>C Domain Strands, Turns and Loops <sup>a</sup></th><th>IMGT Position <sup>b</sup></th><th>Lengths <sup>c</sup></th><th>Characteristic IMGT Residue@Position <sup>d</sup></th></tr></thead><tbody><tr><td>A-STRAND</td><td>1–c15</td><td>15 (14 if gap at 10)</td><td></td></tr><tr><td>AB-TURN</td><td>15.1–15.3</td><td>0–3</td><td></td></tr><tr><td>B-STRAND</td><td>16–26</td><td>11</td><td>1st-CYS 23</td></tr><tr><td>BC-LOOP</td><td>27–31<br>34–38</td><td>10 (or less)</td><td></td></tr><tr><td>C-STRAND</td><td>39–45</td><td>7</td><td>CONSERVED-TRP 41</td></tr><tr><td>CD-STRAND</td><td>45.1–45.9</td><td>0–9</td><td></td></tr><tr><td>D-STRAND</td><td>77–84</td><td>8 (or 7 if gap at 82)</td><td></td></tr><tr><td>DE-TURN</td><td>84.1–84.7<br>85.1–85.7</td><td>0–14</td><td></td></tr><tr><td>E-STRAND</td><td>85–96</td><td>12</td><td>hydrophobic 89</td></tr><tr><td>EF-TURN</td><td>96.1–96.2</td><td>0–2</td><td></td></tr><tr><td>F-STRAND</td><td>97–104</td><td>8</td><td>2nd-CYS 104</td></tr><tr><td>FG-LOOP</td><td>105–117</td><td>13 (or less, or more)</td><td></td></tr><tr><td>G-STRAND</td><td>118–128</td><td>11 (or less)</td><td></td></tr></tbody></table>

There are six IMGT anchors in a C-domain (four of them identical to those of a V-domain): Positions 26 and 39 (anchors of the BC loop), 45 and 77 (by extension, anchors of the CD strand as there is no C'-C" loop in a C-domain [68]), and 104 and 118 (anchors of the FG loop). A C-domain has five characteristic amino acids at given positions (positions with bold (online red) letters in the IMGT Colliers de Perles). Four of them are highly conserved and hydrophobic [52] and are common to the V-domain: 23 (1st-CYS), 41 (CONSERVED-TRP), 89 (hydrophobic) and 104 (2nd-CYS). These amino acids contribute to the two major features shared by the V and C-domains: The disulfide bridge (between the two cysteines 23 and 104) and the internal hydrophobic core of the domain (with the side chains of tryptophan W41 and amino acid 89). The fifth position, 118, is diverse and is characterized as being an FG loop anchor. In the IMGT system, the C-domains (C-DOMAIN and C-

<footnote><sup>a</sup> IMGT labels (concepts of description) are written in capital letters (no plural) [55,56]. <sup>b</sup> based on the IMGT unique numbering for C-domain (C-DOMAIN and C-LIKE-DOMAIN) [68]. <sup>c</sup> in number of amino acids (or codons). <sup>d</sup> IMGT Residue@Position is a given residue (usually an amino acid) or a given conserved property amino acid class, at a given position in a domain, based on the IMGT unique numbering [68].</footnote>
LIKE-DOMAIN) are delimited considering the exon delimitation, whenever appropriate, allowing the integration of strands A and G, which do not have structural alignments.

The 20 usual amino acids (AA) have been classified in eleven IMGT physicochemical classes [52] (IMGT® https://www.imgt.org, IMGT Education > Aide-mémoire > Amino acids) (Figure 4).

<figure><img src="image_8.png" /><figcaption>**Figure 4.** IMGT physicochemical classes of the 20 usual amino acids (AA) [52] (with permission from M-P. Lefranc and G. Lefranc, LIGM, Founders of IMGT®, the international ImMunoGeneTics information system®, https://www.imgt.org).</figcaption></figure>

## 4. IGHG, IGKC and IGLC2 Engineered Variants

One hundred and fourteen IGHG engineered variants have been defined by their IMGT gene nomenclature, the IMGT unique numbering for C-domain [68] and IMGT motifs in domain strands and/or loops (Table 4, Figure 3), with corresponding Eu positions [97] (IMGT https://www.imgt.org, IMGT Scientific chart > Correspondence between C numberings > Correspondence between the IMGT unique numbering for C-DOMAIN, the IMGT exon numbering, the EU and Kabat numberings: Human IGHG [97,98] https://www.imgt.org/IMGTScientificChart/Numbering/Hu_IGHGnber.html) (Supplementary Table S1). The IGKC and IGLC2 engineered variants involved in the structure have also been defined similarly by their IMGT gene nomenclature, the IMGT unique numbering for the C-domain [68] and IMGT motifs in the domain strands and/or loops (Table 4), with corresponding Eu positions [97] (IMGT https://www.imgt.org, IMGT Scientific chart > Correspondence between C numberings > Correspondence between the IMGT unique numbering for the C-DOMAIN, the IMGT exon numbering, the EU and Kabat numberings: Human IGKC [97,98].

The correspondence between the IMGT unique numbering and the Eu positions are provided here in a horizontal format for the IGHG1 CH1, hinge, CH2 and CH3-domains (Figure 5), and hinges of IGHG1, IGHG2, IGHG3 and IGHG4 (Figure 6), and by extension to the alignment of IGKC and IGLC2 with IGHG1 CH1 (Figure 7).
<figure><img src="image_9.png" /><figcaption>**Figure 6.** Correspondence between the *Homo sapiens* IGHG1, IGHG2, IGHG3 (4 exons) and IGHG4 IMGT numbering with the IGHG1 Eu positions. The top line indicates the IMGT numbering for the IGHG1, IGHG2 and IGHG4 hinges and for the four exons (H1 to H4) of the IGHG3 hinge. The Eu numbers are read vertically (on three lines top to down) at each position below the amino acid sequence. Dashes indicate the positions that are absent in the Eu numbering. Cysteines (C) and prolines (P) with Eu positions are highlighted in pink and yellow, respectively. (Drawn by Marie-Paule Lefranc and Gérard Lefranc, LIGM, Founders and Authors of IMGT®, the international ImMunoGeneTics information system®, https://www.imgt.org, Copyright 2022).</figcaption></figure>

<figure><img src="image_10.png" /><figcaption>**Figure 7.** Correspondence between the *Homo sapiens* IGKC, IGLC2 and IGHG1 CH1 sequences, based on the IMGT unique numbering [68] and the Eu positions [97]. The first amino acid of each sequence results from the splicing. The IGHG1 CH1 chosen as the CH representative is from Figure 5A. The IMGT unique numbering is shown on the top horizontal line one with additional IMGT positions on line two. Amino acids at these additional positions (by comparison to the V-domain IMGT unique</figcaption></figure>
numbering [67]) are highlighted in bold in the Homsap IGKC, IGLC2 and IGHG1 CH1 sequences. The Eu numbers are read vertically (on three lines top to down) at each position below the amino acid sequences. For example, the first amino acid of IGKC R1.4 corresponds to Eu 108, that of IGLC2 G1.5 to Eu 107, and that of IGHG1 CH1 A1.4 to Eu 118, the last amino acid of IGKC C126 corresponds to Eu 214, that of IGLC2 S215 to 'deduced Eu position 215' and that of IGHG1 CH1 V at position IMGT 121 corresponds to Eu 215. The four conserved amino acids of the C-DOMAIN C23, W41, hydrophobic 89 and C104 are highlighted in colors (C23 and C104 in pink, W41 and hydrophobic 89 (L, V) in blue). The four AA and IMGT positions C23, W41, hydrophobic 89 and C104 correspond, respectively, to Eu 134, 148, 179, 194 for IGKC and IGLC2 and to Eu 144, 158, 186 and 200 in IGHG1 CH1. The amino acids of the C-domain BC-LOOP and FG-LOOP (Table 4) are highlighted in bold and brown color. (Drawn by Marie-Paule Lefranc and Gérard Lefranc, LIGM, Founders and Authors of IMGT®, the international ImMunoGeneTics information system®, https://www.imgt.org, Copyright 2022.)

Standardized characterization has become a necessity, owing to the increasing number of engineered antibodies of effector properties [99,100] and/or various formats. Based on the IMGT Scientific chart rules, we propose a standardized IMGT nomenclature of engineered variants involved in effector properties (ADCC, ADCP and CDC), half-life and structure of therapeutic monoclonal antibodies. The standardized variant characterization comprises (1) the IMGT engineered Fc variant name (e.g. G1v1), (2) the IMGT variant definition (for each amino acid (AA) change: domain, AA in the one-letter abbreviation [52] and its position in the IMGT unique numbering for C domain [68], e.g. CH2 P1.4, (3) the IMGT amino acid changes on the IGHG CH domain with the Eu numbering between parentheses (e.g., CH2 E1.4 > P (233)), (4) the Eu numbering variant (e.g., E233P), (5) the IMGT motif positions according to the IMGT unique numbering [68], followed between parentheses, by the Eu numbering, motif with AA before and after the AA change in bold (e.g., IGHG1 CH2 1.6–3 (231–239) APELLGGPS > APPLGGPS; underlined amino acids in the motif correspond to additional positions in the IMGT unique numbering for the C-domain [68,70–72], e.g., APELLG and APPLLG which correspond to 1.6, 1.5, 1.4, 1.3, 1.2 and 1.1), and (6) information from the literature regarding 'property and function'.

These properties and functions have allowed to classify the IMGT engineered variants in 19 types (#1 to #19) corresponding to four categories. The first category 'Effector' refers to the variants that affect the effector properties: ADCC reduction #1 (Table 5), ADCC enhancement #2 (Table 6), ADCP and CDC enhancement #3 (Table 7), CDC enhancement #4 (Table 8), CDC reduction #5 (Table 9), ADCC and CDC reduction #6 (Table 10), B cell inhibition by the coengagement of antigen and FcγR on the same cell #7 (Table 11), knock out CH2 84.4 glycosylation #8 (Table 12), the second category 'Half-life' refers to the variants that affect (most of them increasing) the half-life #9 (Table 13), the third one 'Protein A' refers to the abrogation of binding to protein A #10 (Table 14), the fourth one 'Structure' refers to variants that affect the stability or structure of monospecific, bispecific or multispecific antibodies and include: formation of additional bridge stabilizing CH2 in the absence of N84.4 (297) glycosylation #11 (Table 15), prevention of IgG4 half-IG exchange #12 (Table 16), hexamerisation #13 (Table 17), knobs-into-holes and the enhancement of heteropairing H-H of bispecific antibodies #14 (Table 18), suppression of inter H-L and/or inter H-H disulfide bridges #15 (Table 19), site-specific drug attachment #16 (Table 20), enhancement of hetero pairing H-L of bispecific antibodies #17 (Table 21), control of half-IG exchange of bispecific IgG4 #18 (Table 22), reducing acid-induced aggregation #19 (Table 23).
<table><caption>**Table 5.** IMGT nomenclature, Eu positions and IMGT motif of engineered Fc variants involved in antibody-dependent cellular cytotoxicity (ADCC) reduction (Effector #1).</caption><thead><tr><th>IMGT Engineered<br>Fc Variant Name</th><th>IMGT Engineered<br>Variant Definition</th><th>IMGT Amino Acid<br>Changes on IGHG CH<br>Domain (Eu Numbering<br>between Parentheses)</th><th>Amino Acid Changes<br>With the Eu Positions</th><th>Motif Identifiable in Gene<br>and Domain with Positions<br>According to the IMGT<br>Unique Numbering and<br>with Eu Positions between<br>Parentheses</th><th>1. Property and Function</th><th>2. Property and Function</th></tr></thead><tbody><tr><td>G1v1</td><td>CH2<br>P1.4</td><td>CH2<br>E1.4 > P (233)</td><td>E233P</td><td>IGHG1 CH2<br>1.6-3 (231-239)<br>APELLGGPS ><br>APPLGGPS</td><td>ADCC reduction.<br>Prevents FcγRI binding [101]</td><td></td></tr><tr><td>G1v2</td><td>CH2<br>V1.3</td><td>CH2<br>L1.3 > V (234)</td><td>L234V</td><td>IGHG1 CH2<br>1.6-3 (231-239)<br>APELLGGPS ><br>APEVLGGPS</td><td>ADCC reduction<br>Decreases FcγRI binding [101]</td><td></td></tr><tr><td>G1v3</td><td>CH2<br>A1.2</td><td>CH2<br>L1.2 > A (235)</td><td>L235A</td><td>IGHG1 CH2<br>1.6-3 (231-239)<br>APELLGGPS ><br>APELAGGPS</td><td>ADCC reduction.<br>Prevents FcγRI binding [101]</td><td></td></tr><tr><td>G1v5</td><td>CH2<br>W109</td><td>CH2<br>K109 > W (326)</td><td>K326W</td><td>IGHG1 CH2 FG<br>105-117 (322-332)<br>KVSNKA..LPAPI ><br>KVSNWA..LPAPI</td><td>ADCC reduction [102]</td><td>CDC enhancement.<br>Increases C1q binding [102]</td></tr><tr><td>G1v47</td><td>CH2<br>delG1.1</td><td>CH2<br>G1.1 > del (326)</td><td>G236del</td><td>IGHG1 CH2<br>1.6-3 (231-239)<br>APELLGGPS ><br>APELLGPS</td><td>ADCC reduction.<br>Eliminates binding to FcγRI,<br>FcγRIIA, FcγRIIIA [103]</td><td></td></tr><tr><td>G1v50</td><td>CH2<br>P1.4<br>V1.3<br>A1.2<br>delG1.1</td><td>CH2<br>E1.4 > P (233),<br>L1.3 > V (234),<br>L1.2 > A (235),<br>G1.1 > del (236)</td><td>E233P,<br>L234V,<br>L235A,<br>G236del</td><td>IGHG1 CH2<br>1.6-3 (231-239)<br>APELLGGPS ><br>APPVA-GPS</td><td>ADCC reduction.<br>Decreases FcγgammaR binding<br>(G2-like motif). [Combines<br>G1v1, v2, v3 and v47]</td><td></td></tr></tbody></table>
<table><caption>Table 5. *Cont.*</caption><thead><tr><th>IMGT Engineered<br>Fc Variant Name</th><th>IMGT Engineered<br>Variant Definition</th><th>IMGT Amino Acid<br>Changes on IGHG CH<br>Domain (Eu Numbering<br>between Parentheses)</th><th>Amino Acid Changes<br>With the Eu Positions</th><th>Motif Identifiable in Gene<br>and Domain with Positions<br>According to the IMGT<br>Unique Numbering and<br>with Eu Positions between<br>Parentheses</th><th>1. Property and Function</th><th>2. Property and Function</th></tr></thead><tbody><tr><td>G1v52</td><td>CH2<br>R11, R113</td><td>CH2<br>G1.1 > R (231)<br>L113 > R (328)</td><td>G236R,<br>L328R<br>GRLR</td><td>IGHG1 CH2<br>1.6–3 (231–239)<br>APELLGGPS ><br>APELLRGPS<br>IGHG1 CH2<br>FG 105–117 (322–332)<br>KVSNKA..LPAPI ><br>KVSNKA..RPAPI</td><td>ADCC reduction.<br>Abrogates FcgammaR binding</td><td></td></tr><tr><td>G1v66</td><td>CH2<br>A27</td><td>CH2<br>D27 > A</td><td>D265A</td><td>IGHG1 CH2<br>23–31 (261–269)<br>CVVVVDVSHE ><br>CVVVAVSHE</td><td>ADCC reduction.<br>Reduces FcγR binding.</td><td></td></tr><tr><td>G1v67</td><td>CH2<br>S27</td><td>CH2<br>D27 > S</td><td>D265S</td><td>IGHG1 CH2<br>23–31 (261–269)<br>CVVVVDVSHE ><br>CVVVSVSHE</td><td>ADCC reduction.<br>Reduces FcγR binding.</td><td></td></tr></tbody></table>

Engineered amino acid changes are in bold in the IMGT variants (red before the change, green after the change. The motif is in yellow and shown before and after the AA change(s). Amino acids of the motifs at additional positions in the IMGT unique numbering for C-domain [68] (by comparison to the V-domain IMGT unique numbering [67]) are underlined. Alias variant names found in the literature are written in blue in column 4 'Amino Acid Changes with the Eu Positions'. The background color indicates a reduction (pink color) or an enhancement (green color) of the involved effector 'Property and Function'. For other 'Property and Function', background colors refer to structure (yellow), half-life (pale blue color) or protein A (pale orange).
<table><caption>**Table 6.** IMGT nomenclature, Eu positions and IMGT motif of engineered Fc variants involved in antibody-dependent cellular cytotoxicity (ADCC) enhancement (Effector #2).</caption><thead><tr><th>IMGT Engineered Fc Variant Name</th><th>IMGT Engineered Variant Definition</th><th>IMGT Amino Acid Changes on IGHG CH Domain (Eu Numbering between Parentheses)</th><th>Amino Acid Changes with the Eu Positions</th><th>Motif Identifiable in Gene and Domain with Positions According to the IMGT Unique Numbering and with Eu Positions between Parentheses</th><th>1. Property and Function</th><th>2. Property and Function</th><th>3D</th></tr></thead><tbody><tr><td>G1v6</td><td>CH2<br>A85.4,<br>A118,<br>A119</td><td>CH2<br>S85.4 > A (298),<br>E118 > A (333),<br>K119 > A (334)</td><td>S298A,<br>E333A,<br>K334A</td><td>IGHG1 CH2<br>84.1-85.1 (294-301)<br>EQYNSTYR ><br>EQYNATYR<br>FG 105-117,118,119 (322-334)<br>KVSNKA..LPAPIEK ><br>KVSNKA..LPAPIAA</td><td>ADCC enhancement.<br>Increases FcγRIIIa binding [104]</td><td></td><td></td></tr><tr><td>G1v7</td><td>CH2<br>D3,<br>E117</td><td>CH2<br>S3 > D (239),<br>I117 > E (332)</td><td>S239D,<br>I332E<br>DE</td><td>IGHG1 CH2<br>1.6-3 (231-239)<br>APELLGGPS ><br>APELLGGPD<br>FG 105-117 (322-332)<br>KVSNKA..LPAPI ><br>KVSNKA..LPAPE</td><td>ADCC enhancement.<br>Increases FcγRIIIA binding [105]</td><td></td><td></td></tr><tr><td>G1v8</td><td>CH2<br>D3,<br>L115,<br>E117</td><td>CH2<br>S3 > D (239),<br>A115 > L (330),<br>I117 > E (332)</td><td>S239D,<br>A330L,<br>I332E<br>DLE, 3M</td><td>IGHG1 CH2<br>1.6-3 (231-239)<br>APELLGGPS ><br>APELLGGPD<br>FG 105-117 (322-332)<br>KVSNKA..LPAPI ><br>KVSNKA..LPAPE</td><td>ADCC enhancement.<br>Increases FcγRIIIA binding [105]</td><td>Decreases<br>FcγRIIB binding<br>[105]</td><td>3D [106]</td></tr><tr><td>G1v9</td><td>CH2<br>L7,<br>P83,<br>L85.2,<br>I88.<br>CH3<br>L83</td><td>CH2<br>F7 > L (243),<br>R83 > P (292),<br>Y85.2 > L (300),<br>V88 > I (305)<br>CH3<br>P83 > L (396)</td><td>F243L,<br>R292P,<br>Y300L,<br>V305I,<br>P396I<br>LPLIL</td><td>IGHG1 CH2<br>6-10 (242-246)<br>LFPPK ><br>LLPPK<br>83-88 (292-305)<br>REEQYNSTYRVVSV ><br>PEEQYNSTLRVVSI<br>CH3 83-84.4 (396-401)<br>PVLDSD ><br>IVLDSD</td><td>ADCC enhancement.<br>100% increase. [107]</td><td></td><td></td></tr></tbody></table>
<table><caption>Table 6. *Cont.*</caption><thead><tr><th>IMGT<br>Engineered Fc<br>Variant Name</th><th>IMGT Engineered<br>Variant Definition</th><th>IMGT Amino Acid Changes on<br>IGHG CH Domain (Eu<br>Numbering between Parentheses)</th><th>Amino Acid<br>Changes with the<br>Eu Positions</th><th>Motif Identifiable in Gene and<br>Domain with Positions According to<br>the IMGT Unique Numbering and<br>with Eu Positions between Parentheses</th><th>1. Property and Function</th><th>2. Property and<br>Function</th><th>3D</th></tr></thead><tbody><tr><td>G1v10</td><td>CH2<br>Y1.3,<br>Q1.2,<br>W1.1,<br>M3,<br>D30,<br>E34,<br>A85.4</td><td>CH2<br>L1.3 > Y (234),<br>L1.2 > Q (235),<br>G1.1 > W (236),<br>S3 > M (239),<br>H30 > D (268),<br>D34 > E (270),<br>S85.4 > A (298)</td><td>L234Y,<br>L235Q,<br>G236W,<br>S239M,<br>H268D,<br>D270E,<br>S298A</td><td>IGHG1 CH2<br>1.6-3 (231-239)<br>APELLGGPS ><br>APEYQWGPM<br>27-31,34 (265-270)<br>DVSHED ><br>DVSDEE<br>84.1-85.1<br>(294-301)<br>EQYNSTYR ><br>EQYNATYR</td><td>ADCC enhancement.<br>Increases FcγIIIA binding [108]<br>>2000-fold (F158), >1000-fold<br>(V158) in the association of G1v10<br>and G1v11 [108]</td><td></td><td></td></tr><tr><td>G1v11</td><td>CH2<br>E34,<br>D109,<br>M115,<br>E119</td><td>CH2<br>D34 > E (270),<br>K109 > D (326),<br>A115 > M (330)<br>K119 > E (334)</td><td>D270E,<br>K326D,<br>A330M,<br>K334E</td><td>IGHG1 CH2<br>27-31,34 (265-270)<br>DVSHED ><br>DVSHEE<br>FG 105-117,118,119 (322-334)<br>KVSNKA..LPAPIEK ><br>KVSNDA..LPMPIEE</td><td>ADCC enhancement.<br>Increases FcγIIIA binding [108]<br>>2000-fold (F158), >1000-fold<br>(V158) in the association of G1v10<br>and G1v11 [108]</td><td></td><td></td></tr><tr><td>G2v1</td><td>CH2<br>L1.3,<br>L1.2,<br>G1.1</td><td>CH2<br>V1.2 > LL (234,235)<br>A1.1 > G (236)</td><td>V235LL,<br>A236G</td><td>IGHG2 CH2<br>1.6-3 (231-239)<br>AP.PVAGPS ><br>APPLGGPS</td><td>ADCC enhancement.<br>Confers FcγRI binding (WT does<br>not show any binding capacity)<br>[101]</td><td></td><td></td></tr><tr><td>G4v1</td><td>CH2<br>L1.3</td><td>CH2<br>F1.3 > L (234)</td><td>F234L</td><td>IGHG4 CH2<br>1.6-3 (231-239)<br>APEFLGGPS ><br>APELLGGPS</td><td>ADCC enhancement.<br>Increases FcγRI affinity [101]</td><td></td><td></td></tr><tr><td>Mus musculus<br>G2Bv1</td><td>CH2<br>L1.2</td><td>CH2<br>E1.2 > L (235)</td><td>E235L</td><td>IGHG2B CH2<br>1.6-3 (231-239)<br>APNLEGGPS ><br>APNLLGGPS</td><td>ADCC enhancement.<br>Increases FcγRI affinity [109]</td><td></td><td></td></tr></tbody></table>
<table><caption>**Table 7.** IMGT nomenclature, Eu positions and IMGT motif of engineered Fc variants involved in antibody-dependent cellular cytotoxicity (ADCC) and antibody-dependent cellular phagocytosis (ADCP) enhancement (Effector #3).</caption><thead><tr><th>IMGT Engineered Fc Variant Name</th><th>IMGT Engineered Variant Definition</th><th>IMGT Amino Acid Changes on IGHG CH Domain (Eu Numbering between Parentheses)</th><th>Amino Acid Changes with the Eu Positions</th><th>Motif Identifiable in Gene and Domain with Positions According to the IMGT Unique Numbering and with Eu Positions between Parentheses</th><th>1. Property and Function</th><th>2. Property and Function</th><th>3D</th></tr></thead><tbody><tr><td>G1v12</td><td>CH2<br>A1.1,<br>D3,<br>L115,<br>E117</td><td>CH2<br>G1.1 > A (236),<br>S3 > D (239),<br>A115 > L (330),<br>I117 > E (332)</td><td>G236A,<br>S239D,<br>A330L,<br>I332E<br>GASDALIE</td><td>IGHG1 CH2<br>1.6-3 (231-239)<br>APELLGGPS ><br>APELLAGPD<br>FG 105-117 (322-332)<br>KVSNKA..LPAPI ><br>KVSNKA..LPLPE</td><td>ADCC<br>enhancement.<br>Increases FcγRIIIA<br>binding [110]</td><td>ADCP enhancement.<br>NK cell activation.<br>Increases FcγRIIIA<br>binding [110]</td><td>5d4q,<br>5d6d</td></tr><tr><td>G1v13</td><td>CH2<br>A1.1,<br>D3,<br>E117</td><td>CH2<br>G1.1 > A (236),<br>S3 > D (239),<br>I117 > E (332)</td><td>G236A,<br>S239D,<br>I332E<br>GASDIE, ADE</td><td>IGHG1 CH2<br>1.6-3 (231-239)<br>APELLGGPS ><br>APELLAGPD<br>FG 105-117 (322-332)<br>KVSNKA..LPAPI ><br>KVSNKA..LPAPE</td><td>ADCC<br>enhancement.<br>Increases FcγIIIA<br>binding [111]</td><td>ADCP enhancement.<br>NK cell activation.<br>Increases FcγRIIIA<br>binding (70>fold)<br>Increases FcγRIIIA/FcγRIIB<br>binding ratio (15-fold) [111]</td><td></td></tr><tr><td>G1v45</td><td>CH2<br>A1.1,<br>L115,<br>E117</td><td>CH2<br>G1.1 > A (236),<br>A115 > L (330),<br>I117 > E (332)</td><td>G236A,<br>A330L,<br>I332E<br>GAALIE</td><td>IGHG1 CH2<br>1.6-3 (231-239)<br>APELLGGPS ><br>APELLAGPS<br>FG 105-117 (322-332)<br>KVSNKA..LPAPI ><br>KVSNKA..LPLPE</td><td>ADCC enhancement<br>Increases FcγIIIA<br>binding</td><td>ADCP enhancement<br>NK cell activation</td><td></td></tr></tbody></table>
<table><caption>**Table 8.** IMGT nomenclature, Eu positions and IMGT motif of engineered Fc variants involved in complement-dependent cytotoxicity (CDC) enhancement (Effector #4).</caption><thead><tr><th>IMGT<br>Engineered<br>Variant Name</th><th>IMGT Engineered<br>Variant Definition</th><th>IMGT Amino Acid<br>Changes on IGHG<br>CH Domain (Eu<br>Numbering between<br>Parentheses)</th><th>Amino Acid Changes<br>with the Eu Positions</th><th>Motif Identifiable in Gene and<br>Domain with Positions According<br>to the IMGT Unique Numbering<br>and with Eu Positions between<br>Parentheses</th><th>1. Property and Function</th><th>2. Property and<br>Function</th></tr></thead><tbody><tr><td>G1v5</td><td>CH2<br>W109</td><td>CH2<br>K109 > W (326)</td><td>K326W</td><td>IGHG1 CH2<br>FG 105–117 (322–332)<br>KVSNKA..LPAPI ><br>KVSNWA..LPAPI</td><td>CDC enhancement.<br>Increases C1q binding [102]</td><td>ADCC reduction [102].</td></tr><tr><td>G1v15</td><td>CH2<br>S118</td><td>CH2<br>E118 > S (333)</td><td>E333S</td><td>IGHG1 CH2<br>FG 105–117,118 (322–333)<br>KVSNKA..LPAPIE ><br>KVSNKA..LPAPIS</td><td>CDC enhancement.<br>Increases C1q binding [102]</td><td></td></tr><tr><td>G1v16</td><td>CH2<br>W109,<br>S118</td><td>CH2<br>K109 > W (326),<br>E118 > S (333)</td><td>K326W,<br>E333S</td><td>IGHG1 CH2<br>FG 105–117,118 (322–333)<br>KVSNKA..LPAPIE ><br>KVSNWA..LPAPIS</td><td>CDC enhancement.<br>Increases C1q binding [102]</td><td></td></tr><tr><td>G1v17</td><td>CH2<br>E29,<br>F30,<br>T107</td><td>CH2<br>S29 > E (267),<br>H30 > F (268),<br>S107 > T (324)</td><td>S267E,<br>H268F,<br>S324T<br>EFT</td><td>IGHG1 CH2<br>27–31 (265–269)<br>DVSHE ><br>DVEFE<br>FG 105–117 (322–332)<br>KVSNKA..LPAPI ><br>KVTNKA..LPAPI</td><td>CDC enhancement<br>Increases C1q binding [112]</td><td></td></tr><tr><td>G1v18</td><td>CH3<br>R1,<br>G109,<br>Y120</td><td>CH3<br>E1 > R (345),<br>E109 > G (430),<br>S120 > Y (440)</td><td>E345R,<br>E430G,<br>S440Y</td><td>IGHG1 CH3<br>1.4–2 (341–346)<br>GQPREP ><br>GQPRRP<br>105–110 (426–431)<br>SVMHEA ><br>SVMHGA<br>118–125 (438–445)<br>QKSLSLSP ><br>QKYLSLSP</td><td>CDC enhancement.<br>Increases C1q binding [113].<br>The triple mutant<br>IgG1-005-RGY (IGHG1v18)<br>form IgG1 hexamers [113]</td><td>Favors IgG1<br>hexamerization.</td></tr></tbody></table>
<table><caption>Table 8. *Cont.*</caption><thead><tr><th>IMGT<br>Engineered<br>Variant Name</th><th>IMGT Engineered<br>Variant Definition</th><th>IMGT Amino Acid<br>Changes on IGHG<br>CH Domain (Eu<br>Numbering between<br>Parentheses)</th><th>Amino Acid Changes<br>with the Eu Positions</th><th>Motif Identifiable in Gene and<br>Domain with Positions According<br>to the IMGT Unique Numbering<br>and with Eu Positions between<br>Parentheses</th><th>1. Property and Function</th><th>2. Property and<br>Function</th></tr></thead><tbody><tr><td>G1v35</td><td>CH2<br>E29</td><td>CH2<br>S29 > E (267)</td><td>S267E<br>SE</td><td>IGHG1 CH2<br>27-31 (265-269)<br>DVSHE ><br>DVEHE</td><td>CDC enhancement.<br>Increases C1q binding [112]</td><td>Binds to FCGRT and<br>FcγRIIB,<br>but not to other FcγR in<br>a mouse model [114].</td></tr><tr><td>G1G3v1</td><td>CH2<br>Q38,<br>K40,<br>F85.2</td><td>CH2<br>K38 > Q (274),<br>N40 > K (276),<br>Y85.2 > F (300)</td><td>K274Q,<br>N276K,<br>Y300F<br>chimere<br>G1-G3<br>(1)</td><td>IGHG1 CH2<br>34-41 (270-277)<br>DPEVKFNW ><br>DPEVQFKW<br>84.1-85.1 (294-301)<br>EQYNSTYR ><br>EQYNSTFR</td><td>CDC enhancement.<br>Increases C1q binding [115].</td><td></td></tr><tr><td>G4v2</td><td>CH2<br>P116</td><td>CH2<br>S116 > P (331)</td><td>S331P</td><td>IGHG4 CH2<br>FG 105-117 (322-332)<br>KVSNKG..LPSSI ><br>KVSNKG..LPSPI</td><td>CDC enhancement [116].<br>(G1-, G2-, G3-like).</td><td></td></tr></tbody></table>

<footnote>(1) The chimeric chain is the IGHG1*01 CH1-hinge—IGHG3*01 CH2-CH3. Amino acids Q38, K40 (CH2) and F85.2 (CH3) are from IGHG3*01. The changes are shown in comparison to the IGHG1*01 amino acids at the same positions as K38, N40 (CH2) and Y85.2 (CH3).</footnote>
<table><caption>**Table 9.** IMGT nomenclature, Eu positions and IMGT motif of engineered Fc variants involved in complement-dependent cytotoxicity (CDC) reduction (Effector #5).</caption><thead><tr><th>IMGT Engineered<br>Variant Name</th><th>IMGT Engineered<br>Variant Definition</th><th>IMGT Amino Acid Changes on<br>IGHG CH Domain (Eu<br>Numbering between Parentheses)</th><th>Amino Acid Changes<br>with the Eu Positions</th><th>Motif Identifiable in Gene and<br>Domain with Positions According to<br>the IMGT Unique Numbering and<br>with Eu Positions between Parentheses</th><th>Property and Function</th></tr></thead><tbody><tr><td>G1v8</td><td>CH2<br>D3,<br>L115,<br>E117</td><td>CH2<br>S3 > D (239),<br>A115 > L (330),<br>I117 > E (332)</td><td>S239D,<br>A330L,<br>I332E<br>DLE</td><td>IGHG1 CH2<br>1.6–3 (231–239)<br>APELLGGPS ><br>APELLGGPD<br>FG 105–117 (322–332)<br>KVSNKA..LPAPI ><br>KVSNKA..LPLPE</td><td>CDC reduction.<br>Ablates CDC [105]</td></tr><tr><td>G1v19</td><td>CH2<br>A34</td><td>CH2<br>D34 > A (270)</td><td>D270A</td><td>IGHG1 CH2<br>34–41 (270–277)<br>DPEVKFNW ><br>APEVKFNW</td><td>CDC reduction. Reduces<br>C1q binding [117]</td></tr><tr><td>G1v20</td><td>CH2<br>A105</td><td>CH2<br>K105 > A (322)</td><td>K322A</td><td>IGHG1 CH2<br>FG 105–117 (322–332)<br>KVSNKA..LPAPI ><br>AVSNKA..LPAPI</td><td>CDC reduction.<br>Reduces C1q binding [117,118]</td></tr><tr><td>Mus musculus G2Bv2</td><td>CH2<br>A101</td><td>CH2<br>E101 > A (318)</td><td>E318A<br>(2)</td><td>IGHG2B CH2<br>100–110<br>KEFKCKVNNKD ><br>KAFKCKVNNKD</td><td>CDC reduction.<br>Reduces C1q binding [119]</td></tr><tr><td>Mus musculus G2Bv3</td><td>CH2<br>A103</td><td>CH2<br>K103 > A (320)</td><td>K320A<br>(2)</td><td>IGHG2B CH2<br>100–110<br>KEFKCKVNNKD ><br>KEFACKVNNKD</td><td>CDC reduction.<br>Reduces C1q binding [119]</td></tr><tr><td>Mus musculus G2Bv4</td><td>CH2<br>A105</td><td>CH2<br>K105 > A (322)</td><td>K322A<br>(2)</td><td>IGHG2B CH2<br>100–110<br>KEFKCKVNNKD ><br>KEFKCAVNNKD</td><td>CDC reduction.<br>Reduces C1q binding [119]</td></tr></tbody></table>

<footnote>(2) *Mus musculus* IGHG2B CH2 E101, K103 and K105 form a common core in the interactions of IgG and C1q [119].</footnote>
<table><caption>**Table 10.** IMGT nomenclature, Eu positions and IMGT motif of engineered Fc variants involved in antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC) reduction (Effector #6).</caption><thead><tr><th>IMGT Engineered Fc<br>Variant Name</th><th>IMGT Engineered<br>Variant Definition</th><th>IMGT Amino Acid<br>Changes on IGHG CH<br>Domain (Eu Numbering<br>between Parentheses)</th><th>Amino Acid<br>Changes with the Eu<br>Positions</th><th>Motif Identifiable in Gene<br>and Domain with Positions<br>According to the IMGT<br>Unique Numbering and<br>with Eu Positions between<br>Parentheses</th><th>1. Property and<br>Function</th><th>2. Property and Function</th><th>3. 3D and<br>Property and<br>Function</th></tr></thead><tbody><tr><td>G1v4</td><td>CH2<br>A114</td><td>CH2<br>P114 > A (329)</td><td>P329A)</td><td>IGHG1 CH2<br>FG 105–117 (322–332)<br>KVSNKA..LPAPI ><br>KVSNKA..LAAPI</td><td>ADCC reduction.<br>Reduces FcγR binding<br>[117]</td><td>CDC reduction.<br>Reduces C1q binding [117]</td><td></td></tr><tr><td>G1v14</td><td>CH2<br>A1.3,<br>A1.2</td><td>CH2<br>L1.3 > A (234),<br>L1.2 > A (235)</td><td>L234A,<br>L235A<br>LALA</td><td>IGHG1 CH2<br>1.6–3 (231–239)<br>APELLGGPS ><br>APEAAGGPS</td><td>ADCC reduction.<br>Reduces FcγR binding<br>[118,120]</td><td>CDC reduction.<br>Reduces C1q binding<br>[118,120]</td><td></td></tr><tr><td>G1v14-1</td><td>CH2<br>A1.3,<br>A1.2,<br>A1</td><td>CH2<br>L1.3 > A (234),<br>L1.2 > A (235),<br>G1 > A (237)</td><td>L234A,<br>L235A,<br>G237A</td><td>IGHG1 CH2<br>1.6–3 (231–239)<br>APELLGGPS ><br>APEAAGAPS</td><td>ADCC reduction.<br>Reduces FcγR binding.</td><td>CDC reduction.<br>Reduces C1q binding.</td><td></td></tr><tr><td>G1v14-4</td><td>CH2<br>A1.3,<br>A1.2,<br>A114</td><td>CH2<br>L1.3 > A (234),<br>L1.2 > A (235),<br>P114 > A (329)</td><td>L234A,<br>L235A,<br>P329A</td><td>IGHG1 CH2<br>1.6–3 (231–239)<br>APELLGGPS ><br>APEAAGGPS<br>FG 105–117 (322–332)<br>KVSNKA..LPAPI ><br>KVSNKA..LAAPI</td><td>ADCC reduction.<br>Reduces FcγR binding.</td><td>CDC reduction.<br>Reduces C1q binding.</td><td></td></tr><tr><td>G1v14-48</td><td>CH2<br>A1.3,<br>A1.2,<br>R113</td><td>CH2<br>L1.3 > A (234),<br>L1.2 > A (235),<br>L113 > R (328)</td><td>L234A,<br>L235A,<br>L328R</td><td>IGHG1 CH2<br>1.6–3 (231–239)<br>APELLGGPS ><br>APEAAGGPS<br>FG 105–117 (322–332)<br>KVSNKA..LPAPI ><br>KVSNKA..RPAPI</td><td>ADCC reduction.<br>Reduces FcγR binding.</td><td>CDC reduction.<br>Reduces C1q binding.</td><td></td></tr><tr><td>G1v14-49</td><td>CH2<br>A1.3,<br>A1.2,<br>G114</td><td>CH2<br>L1.3 > A (234),<br>L1.2 > A (235),<br>P114 > G (329)</td><td>L234A,<br>L235A,<br>P329G<br>LALAPG</td><td>IGHG1 CH2<br>1.6–3 (231–239)<br>APELLGGPS ><br>APEAAGGPS<br>FG 105–117 (322–332)<br>KVSNKA..LPAPI ><br>KVSNKA..LGAPI</td><td>ADCC reduction.<br>Reduces FcγR binding<br>[121]</td><td>CDC reduction.<br>Reduces C1q binding [121]</td><td></td></tr></tbody></table>
<table><caption>Table 10. *Cont.*</caption><thead><tr><th>IMGT Engineered Fc<br>Variant Name</th><th>IMGT Engineered<br>Variant Definition</th><th>IMGT Amino Acid<br>Changes on IGHG CH<br>Domain (Eu Numbering<br>between Parentheses)</th><th>Amino Acid<br>Changes with the Eu<br>Positions</th><th>Motif Identifiable in Gene<br>and Domain with Positions<br>According to the IMGT<br>Unique Numbering and<br>with Eu Positions between<br>Parentheses</th><th>1. Property and<br>Function</th><th>2. Property and Function</th><th>3. 3D and<br>Property and<br>Function</th></tr></thead><tbody><tr><td>G1v14-67</td><td>CH2<br>A1.3,<br>A1.2,<br>S27</td><td>CH2<br>L1.3 > A (234),<br>L1.2 > A (235),<br>D27 > S (265)</td><td>L234A,<br>L235A,<br>D265S</td><td>IGHG1 CH2<br>1.6-3 (231-239)<br>APELLGGPS ><br>APEAAGGPS<br>23-31 (261-269)<br>CVVVDVSHE ><br>CVVVVSHE</td><td>ADCC reduction.<br>Reduces FcγR binding<br>[121].</td><td>CDC reduction.<br>Reduces C1q binding [121].</td><td>Combines<br>Homsap G1v14<br>and G1v67 (G1<br>CH2 S27).</td></tr><tr><td>G1v23</td><td>CH2<br>E1.2</td><td>CH2<br>L1.2 > E (235)</td><td>L235E</td><td>IGHG1 CH2<br>1.6-3 (231-239)<br>APELLGGPS ><br>APELEGGPS</td><td>ADCC reduction.<br>Reduces FcγR binding<br>[122]</td><td>CDC reduction.<br>Reduces C1q binding [122]</td><td></td></tr><tr><td>G1v38</td><td>CH2<br>S108,<br>F113</td><td>CH2<br>N108 > S (325),<br>L113 > F (328)</td><td>N325S,<br>L328F</td><td>IGHG1 CH2<br>FG 105-117 (322-332)<br>KVSNKA..LPAPI ><br>KVSSKA..FPAPI</td><td>ADCC reduction.<br>Abrogates FcγRIII<br>binding, increases<br>FcγRII binding, retains<br>FcγRI high affinity<br>binding [123]</td><td>CDC reduction.<br>Abrogates C1q binding.</td><td></td></tr><tr><td>G1v39</td><td>CH2<br>F1.3,<br>E1.2,<br>S116</td><td>CH2<br>L1.3 > F (234),<br>L1.2 > E (235),<br>P116 > S (331)</td><td>L234F,<br>L235E,<br>P331S<br>FES, TM</td><td>IGHG1 CH2<br>1.6-3 (231-239)<br>APELLGGPS ><br>APEFEGGPS<br>FG 105-117 (322-332)<br>KVSNKA..LPAPI ><br>KVSNKA..LPASI</td><td>ADCC reduction<br>Reduces FcγR effector<br>properties [124] (2)</td><td>CDC reduction.<br>Reduces C1q binding [122]</td><td>3D<br>3c2s</td></tr><tr><td>G1v40</td><td>CH2<br>A1.3,<br>A1.2,<br>S116</td><td>CH2<br>L1.3 > A (234),<br>L1.2 > A (235),<br>P116 > S (331)</td><td>L234A,<br>L235A,<br>P331S</td><td>IGHG1 CH2<br>1.6-3 (231-239)<br>APELLGGPS ><br>APEAAGGPS<br>FG 105-117 (322-332)<br>KVSNKA..LPAPI ><br>KVSNKA..LPASI</td><td>ADCC reduction.<br>Reduces FcγR binding.</td><td>CDC reduction.<br>Reduces C1q binding.</td><td></td></tr></tbody></table>
<table><caption>Table 10. *Cont.*</caption><thead><tr><th>IMGT Engineered Fc<br>Variant Name</th><th>IMGT Engineered<br>Variant Definition</th><th>IMGT Amino Acid<br>Changes on IGHG CH<br>Domain (Eu Numbering<br>between Parentheses)</th><th>Amino Acid<br>Changes with the Eu<br>Positions</th><th>Motif Identifiable in Gene<br>and Domain with Positions<br>According to the IMGT<br>Unique Numbering and<br>with Eu Positions between<br>Parentheses</th><th>1. Property and<br>Function</th><th>2. Property and Function</th><th>3. 3D and<br>Property and<br>Function</th></tr></thead><tbody><tr><td>G1v41</td><td>CH2<br>F1.3,<br>E1.2</td><td>CH2<br>L1.3 > F (234),<br>L1.2 > E (235)</td><td>L234F,<br>L235E<br>FE</td><td>IGHG1 CH2<br>1.6-3 (231-239)<br>APELLGGPS ><br>APEFEGGPS</td><td>ADCC reduction.<br>Reduces FcγR binding<br>[124]</td><td>CDC reduction.<br>Reduces C1q binding</td><td></td></tr><tr><td>G1v43</td><td>CH2<br>A1.3,<br>E1.2,<br>A1</td><td>CH2<br>L1.3 > A (234),<br>L1.2 > E (235),<br>G1 > A (237)</td><td>L234A,<br>L235E,<br>G237A</td><td>IGHG1 CH2<br>1.6-3 (231-239)<br>APELLGGPS ><br>APEAEGAPS</td><td>ADCC reduction.<br>Reduces FcγR binding</td><td>CDC reduction.<br>Reduces C1q binding</td><td></td></tr><tr><td>G1v48</td><td>CH2<br>R113</td><td>CH2<br>L113 > R (328)</td><td>L328R</td><td>IGHG1 CH2<br>FG 105-117 (322-332)<br>KVSNKA..LPAPI ><br>KVSNKA..RPAPI</td><td>ADCC reduction.<br>Reduces FcγR binding</td><td>CDC reduction.<br>Reduces C1q binding</td><td></td></tr><tr><td>G1v49</td><td>CH2<br>G114</td><td>CH2<br>P114 > G (329)</td><td>P329G</td><td>IGHG1 CH2<br>FG 105-117 (322-332)<br>KVSNKA..LPAPI ><br>KVSNKA..LGAPI</td><td>ADCC reduction.<br>Reduces FcγR binding<br>[121]</td><td>CDC reduction.<br>Reduces C1q binding</td><td></td></tr><tr><td>G1v51</td><td>CH2<br>K29</td><td>CH2<br>S29 > K (267)</td><td>S267K</td><td>IGHG1 CH2<br>27-31 (265-269)<br>DVSHE ><br>DVKHE</td><td>ADCC reduction.<br>Reduces FcγR binding</td><td>CDC reduction.<br>Reduces C1q binding</td><td></td></tr><tr><td>G1v53</td><td>CH2<br>F1.3,<br>Q1.2,<br>Q105</td><td>CH2<br>L1.3 > F (234)<br>L1.2 > Q (235)<br>K105 > Q (322)</td><td>L234F,<br>L235Q,<br>K322Q,<br>FQQ</td><td>IGHG1 CH2<br>1.6-3 (231-239)<br>APELLGGPS ><br>APEFQGGPS<br>FG 105-117 (322-332)<br>KVSNKA..LPAPI ><br>QVSNKA..LPAPI</td><td>ADCC reduction.<br>Reduces FcγR binding</td><td>CDC reduction.<br>Reduces C1q binding</td><td></td></tr></tbody></table>
<table><caption>Table 10. *Cont.*</caption><thead><tr><th>IMGT Engineered Fc<br>Variant Name</th><th>IMGT Engineered<br>Variant Definition</th><th>IMGT Amino Acid<br>Changes on IGHG CH<br>Domain (Eu Numbering<br>between Parentheses)</th><th>Amino Acid<br>Changes with the Eu<br>Positions</th><th>Motif Identifiable in Gene<br>and Domain with Positions<br>According to the IMGT<br>Unique Numbering and<br>with Eu Positions between<br>Parentheses</th><th>1. Property and<br>Function</th><th>2. Property and Function</th><th>3. 3D and<br>Property and<br>Function</th></tr></thead><tbody><tr><td>G1v53, G1v21</td><td>CH2<br>F1.3,<br>Q1.2,<br>Q105<br>Y15.1,<br>T16,<br>E18</td><td>CH2<br>L1.3 > F (234),<br>L1.2 > Q (235),<br>K105 > Q (322)<br>M15.1 > Y (252),<br>S16 > T (254),<br>T18 > E (256)</td><td>L234F,<br>L235Q,<br>K322Q,<br>M252Y,<br>S254T,<br>T256E<br>FQQ-YTE</td><td>IGHG1 CH2<br>1.6-3 (231-239)<br>APELGGGPS ><br>APEFQGGPS<br>15-18 (251-256)<br>LMI.SRT ><br>LYITRE<br>FG 105-117 (322-332)<br>KVSNKA..LPAPI ><br>QVSNKA..LPAPI</td><td>ADCC reduction.<br>Reduces FcγR binding<br>[125] (G1v53)</td><td>CDC reduction.<br>Reduces C1q binding [125]<br>(G1v53)</td><td>Extends<br>half-life [125]<br>(G1v21).</td></tr><tr><td>G1v59</td><td>CH2<br>S1.3<br>T1.2<br>R1.1</td><td>CH2<br>L1.3 > S (234)<br>L1.2 > T (235)<br>G1.1 > R (236)</td><td>L234S<br>L235T<br>G236R</td><td>IGHG1 CH2<br>1.6-3 (231-239)<br>APELGGGPS ><br>APESTRGPS</td><td>ADCC undetectable.<br>Abrogates FcγR binding<br>[126]</td><td>CDC undetectable.<br>Abrogates C1q binding [126]</td><td></td></tr><tr><td>G1v60</td><td>CH2<br>S115,<br>S116</td><td>CH2<br>A115 > S (330)<br>P116 > S (331)</td><td>A330S<br>P331S</td><td>FG 105-117 (322-332)<br>KVSNKA..LPAPI ><br>QVSNKA..LPSSI</td><td>ADCC reduction.<br>Reduces FcγR binding.</td><td>CDC reduction.<br>Reduces C1q binding.</td><td></td></tr><tr><td>G1v63</td><td>CH2<br>S2</td><td>CH2<br>P2 > S</td><td>P238S</td><td>IGHG1 CH2<br>1.6-3 (231-239)<br>APELGGGPS ><br>APELLGGSS</td><td>ADCC reduction.<br>Reduces FcγR binding.</td><td>CDC reduction.<br>Reduces C1q binding.</td><td></td></tr><tr><td>G1v65</td><td>CH2<br>delE1.4,<br>delL1.3,<br>delL1.2</td><td>CH2<br>E1.4 > del,<br>L1.3 > del,<br>L1.2 > del</td><td>E233del,<br>L234del,<br>L235del</td><td>IGHG1 CH2<br>1.6-3 (231-239)<br>APELLGGGPS ><br>AP---GGPS</td><td>ADCC reduction.<br>Reduces FcγR binding.</td><td>CDC reduction.<br>Reduces C1q binding.</td><td></td></tr><tr><td>G1v70</td><td>h<br>S5,<br>S11,<br>S14,<br>CH2<br>S2</td><td>h<br>C5 > S (220),<br>C11 > S (226)<br>C14 > S (226)<br>CH2<br>P2 > S</td><td>C220S<br>C226S<br>C229S<br>P238S</td><td>IGHG1 h<br>1-15 (216-230)<br>EPKSCDKTHTCPPCP ><br>EPKSSDKTHTSPPSP<br>IGHG1 CH2<br>1.6-3 (231-239)<br>APELLGGGPS ><br>APELLGGSS</td><td>ADCC reduction.<br>Reduces FcγR binding.</td><td>CDC reduction.<br>Reduces C1q binding.</td><td>Combines G1v63<br>with G1v37 (no<br>H-L), G1v61 (no<br>H-H h11) and<br>G1v62 (no H-H<br>h14).</td></tr></tbody></table>
<table><caption>Table 10. *Cont.*</caption><thead><tr><th>IMGT Engineered Fc<br>Variant Name</th><th>IMGT Engineered<br>Variant Definition</th><th>IMGT Amino Acid<br>Changes on IGHG CH<br>Domain (Eu Numbering<br>between Parentheses)</th><th>Amino Acid<br>Changes with the Eu<br>Positions</th><th>Motif Identifiable in Gene<br>and Domain with Positions<br>According to the IMGT<br>Unique Numbering and<br>with Eu Positions between<br>Parentheses</th><th>1. Property and<br>Function</th><th>2. Property and Function</th><th>3. 3D and<br>Property and<br>Function</th></tr></thead><tbody><tr><td>G2v2</td><td>CH2<br>Q30,<br>L92,<br>S115,<br>S116</td><td>CH2<br>H30 > Q (268),<br>V92 > L (309),<br>A115 > S (330),<br>P116 > S (331)</td><td>H268Q,<br>V309L,<br>A330S,<br>P331S<br>IgG2m4</td><td>IGHG2 CH2<br>27-38 (265-274)<br>DVSHEDPEVQ ><br>DVSQEDPEVQ<br>89-96 (306-313)<br>LTVVHQDW ><br>LTVLHQDW<br>FG 105-117 (322-332)<br>KVSNKG..LPAPI ><br>KVSNKA..LPSSI</td><td>ADCC reduction.<br>Reduces FcγR binding<br>[127]</td><td>CDC reduction.<br>Reduces C1q binding [127]</td><td></td></tr><tr><td>G2v3</td><td>CH2<br>A1.2,<br>A1,<br>S2,<br>A30,<br>L92,<br>S115,<br>S116</td><td>CH2<br>V1.2 > A (235),<br>G1 > A (237),<br>P2 > S (238),<br>H30 > A (268),<br>V92 > L (309),<br>A115 > S (330),<br>P116 > S (331)</td><td>V235A,<br>G237A,<br>P238S,<br>H268A,<br>V309L,<br>A330S,<br>P331S<br>G2sigma</td><td>IGHG2 CH2<br>1.6-3 (231-239)<br>AP.PVAGPS ><br>AP.PAAASS<br>27-38 (265-274)<br>DVSHEDPEVQ ><br>DVSAGEDPEVQ<br>89-96 (306-313)<br>LTVVHQDW ><br>LTVLHQDW<br>FG 105-117 (322-332)<br>KVSNKG..LPAPI ><br>KVSNKA..LPSSI</td><td>ADCC reduction.<br>Reduces FcγR binding<br>[124]. Undetectable<br>ADCC andV1 ADCP<br>[124]</td><td>CDC reduction.<br>Reduces C1q binding [124].<br>Undetectable CDC [124]</td><td></td></tr><tr><td>G2G4v1<br>(1)</td><td>CH2<br>E1.4 > del<br>P1.3,<br>V1.2,<br>A1.1</td><td>CH2<br>E1.4 > del (233),<br>F1.3 > P (234),<br>L1.2 > V (235),<br>G1.1 > A (236)</td><td>E233del,<br>F234P,<br>L235V,<br>G236A</td><td>IGHG4 CH2<br>1.6-3 (231-239)<br>APEFLGGPS ><br>AP.PVAGPS</td><td>ADCC reduction.<br>Reduces FcγR binding<br>[128]</td><td>CDC reduction.<br>Reduces C1q binding [128]</td><td></td></tr><tr><td>G4v3</td><td>CH2<br>E1.2</td><td>CH2<br>L1.2 > E (235)</td><td>L235E<br>LE</td><td>IGHG4 CH2<br>1.6-3 (231-239)<br>APEFLGGPS ><br>APEFEGGPS</td><td>ADCC reduction.<br>Reduces FcγR binding<br>[122]</td><td>CDC reduction.<br>Reduces C1q binding<br>[122]</td><td></td></tr></tbody></table>
<table><caption>Table 10. *Cont.*</caption><thead><tr><th>IMGT Engineered Fc<br>Variant Name</th><th>IMGT Engineered<br>Variant Definition</th><th>IMGT Amino Acid<br>Changes on IGHG CH<br>Domain (Eu Numbering<br>between Parentheses)</th><th>Amino Acid<br>Changes with the Eu<br>Positions</th><th>Motif Identifiable in Gene<br>and Domain with Positions<br>According to the IMGT<br>Unique Numbering and<br>with Eu Positions between<br>Parentheses</th><th>1. Property and<br>Function</th><th>2. Property and Function</th><th>3. 3D and<br>Property and<br>Function</th></tr></thead><tbody><tr><td>G4v3<br>G4v5</td><td>h<br>P10,<br>CH2<br>E1.2</td><td>h<br>S10 > P (228)<br>CH2<br>L1.2 > E (235)</td><td>S228P,<br>L235E<br>SPLE</td><td>IGHG4 h<br>1-12 (216-230)<br>ESKYGPPCPSCP ><br>ESKYGPPCPPCP<br>CH2<br>1.6-3 (231-239)<br>APEFLGGPS ><br>APEFEGGPS</td><td>ADCC reduction.<br>Reduces FcγR binding<br>[122] (G4v3)</td><td>CDC reduction.<br>Reduces C1q binding [122]<br>(G4v3)</td><td>Prevents IgG4<br>half-IG exchange<br>[129] (G4v5)</td></tr><tr><td>G4v3-49</td><td>CH2<br>E1.2<br>G114</td><td>CH2<br>L1.2 > E (235)<br>P114 > G (329)</td><td>L235E<br>P329G<br>LEPG</td><td>IGHG4 CH2<br>1.6-3 (231-239)<br>APEFLGGPS ><br>APEFEGGPS<br>FG 105-117 (322-332)<br>KVSNKA..LPAPI ><br>KVSNKA..LGAPI</td><td>ADCC reduction.<br>Reduces FcγR binding<br>[121]</td><td>CDC reduction.<br>Reduces C1q binding [121]</td><td></td></tr><tr><td>G4v3-49<br>G4v5</td><td>h<br>P10,<br>CH2<br>E1.2<br>G114</td><td>h<br>S10 > P (228)<br>CH2<br>L1.2 > E (235)<br>P114 > G (329)</td><td>S228P,<br>L235E<br>P329G<br>SPLEPG</td><td>IGHG4 h<br>1-12 (216-230)<br>ESKYGPPCPSCP<br>ESKYGPPCPPCP<br>CH2<br>1.6-3 (231-239)<br>APEFLGGPS ><br>APEFEGGPS<br>FG 105-117 (322-332)<br>KVSNKA..LPAPI ><br>KVSNKA..LGAPI</td><td>ADCC reduction.<br>Reduces FcγR binding<br>[121] (G4v3-49)</td><td>CDC reduction.<br>Reduces C1q binding [121]<br>(G4v3-49)</td><td>Prevents IgG4<br>half-IG exchange<br>[129] (G4v5).</td></tr><tr><td>G4v4</td><td>CH2<br>A1.3,<br>A1.2</td><td>CH2<br>F1.3 > A (234),<br>L1.2 > A (235)</td><td>F234A<br>L235A<br>FALA</td><td>IGHG4 CH2<br>1.6-3 (231-239)<br>APEFLGGPS ><br>APEAAGGPS</td><td>ADCC reduction.<br>Reduces FcγR binding<br>[120].</td><td>CDC reduction.<br>Reduces C1q binding [120].</td><td></td></tr></tbody></table>
<table><caption>Table 10. *Cont.*</caption><thead><tr><th>IMGT Engineered Fc<br>Variant Name</th><th>IMGT Engineered<br>Variant Definition</th><th>IMGT Amino Acid<br>Changes on IGHG CH<br>Domain (Eu Numbering<br>between Parentheses)</th><th>Amino Acid<br>Changes with the Eu<br>Positions</th><th>Motif Identifiable in Gene<br>and Domain with Positions<br>According to the IMGT<br>Unique Numbering and<br>with Eu Positions between<br>Parentheses</th><th>1. Property and<br>Function</th><th>2. Property and Function</th><th>3. 3D and<br>Property and<br>Function</th></tr></thead><tbody><tr><td>G4v4<br>G4v5</td><td>h<br>P10,<br>CH2<br>A1.3,<br>A1.2</td><td>h<br>S10 > P (228)<br>CH2<br>F1.3 > A (234)<br>L1.2 > A (235)</td><td>S228P,<br>F234A,<br>L235A<br>IgG4ProAlaAla</td><td>IGHG4 h<br>1–12 (216–230)<br>ESKYGPCPSCP ><br>ESKYGPCPPCP<br>CH2<br>1.6–3 (231–239)<br>APEFLGGPS ><br>APEAAGGPS</td><td>ADCC reduction.<br>Reduces FcγR binding<br>[124] (G4v4)</td><td>CDC reduction.<br>Reduces C1q binding [120]<br>(G4v4)</td><td>Prevents IgG4<br>half-IG exchange<br>[129] (G4v5).</td></tr><tr><td>G4v7</td><td>CH2<br>delE1.4,<br>P1.3,<br>V1.2,<br>A1.1</td><td>CH2<br>E1.4 > del (233)<br>F1.3 > P (234),<br>L1.2 > V (235),<br>G1.1 > A (236),</td><td>E233del,<br>F234P,<br>L235V,<br>G236A</td><td>IGHG4 CH2<br>1.6–3 (231–239)<br>APEFLGGPS ><br>AP-PVAGPS<br>(G2-like)</td><td>ADCC reduction.<br>Reduces FcγR binding</td><td>CDC reduction.<br>Reduces C1q binding</td><td></td></tr><tr><td>G4v49</td><td>CH2<br>G114</td><td>CH2<br>P114 > G (329)</td><td>P329G</td><td>IGHG4 CH2<br>FG 105–117 (322–332)<br>KVSNKA..LPAPI ><br>KVSNKA..LGAPI</td><td>ADCC reduction.<br>Reduces FcγR binding<br>[121]</td><td>CDC reduction.<br>Reduces C1q binding [121]</td><td></td></tr><tr><td>Canis lupus<br>familiaris<br>G2v1</td><td>CH2<br>A1.3,<br>A1.2,<br>A1</td><td>CH2<br>M1.3 > A (234),<br>L1.2 > A (235),<br>G1 > A (237).</td><td>M234A,<br>L235A,<br>G237A</td><td>IGHG2 CH2<br>1.6–3 (231–239)<br>APEMLGGPS ><br>APEAAGAPS</td><td>ADCC reduction.<br>Reduces FcγR binding</td><td>CDC reduction.<br>Reduces C1q binding</td><td></td></tr><tr><td>Canis lupus<br>familiaris<br>G2v2</td><td>CH2<br>A1.3,<br>A1.2,<br>G114</td><td>CH2<br>M1.3 > A (234),<br>L1.2 > A (235)<br>P114 > G (329)</td><td>M234A,<br>L235A,<br>P329G</td><td>IGHG2 CH2<br>1.6–3 (231–239)<br>APEMLGGPS ><br>APEAAGGPS<br>IGHG1 CH2<br>FG 105–117 (322–332)<br>KVNNKA..LPSPI ><br>KVNNKA..LGSPI</td><td>ADCC reduction.<br>Reduces FcγR binding</td><td>CDC reduction.<br>Reduces C1q binding</td><td></td></tr></tbody></table>

<footnote>(1) The monoclonal antibody is eculizumab. The heavy chain is the chimeric IGHG2*01 CH1-hinge—IGHG4*01 CH2-CH3. The CH2 and CH3 are from IGHG4*01, except for the CH2 positions 1.6-1.1 (AP.PVA) with del 1.4 and amino acids P1.3, V1.2 and A1.1 being from IGHG2*01. The changes are shown in comparison to the IGHG4*01 amino acids at the same positions as E1.4, F1.3, L1.2 and G1.1.</footnote>
<table><caption>**Table 11.** IMGT nomenclature, Eu positions and IMGT motif of engineered Fc variants involved in the B cell inhibition by the coengagement of antigen and FcγR on the same cell (Effector #7].</caption><thead><tr><th>IMGT Engineered Fc Variant Name</th><th>IMGT Engineered Variant Definition</th><th>IMGT Amino Acid Changes on IGHG CH Domain (Eu Numbering between Parentheses)</th><th>Amino Acid Changes with the Eu Positions</th><th>Motif Identifiable in Gene and Domain with Positions According to the IMGT Unique Numbering and with Eu Positions between Parentheses</th><th>Property and Function</th></tr></thead><tbody><tr><td>G1v25</td><td>CH2<br>E29,<br>F113</td><td>CH2<br>S29 > E (267),<br>L113 > F (328)</td><td>S267E,<br>L328F</td><td>IGHG1 CH2<br>27–31 (265–269)<br>DVSHE ><br>DVEHE<br>FG 105–117 (322–332)<br>KVSNKA..LPAPI ><br>KVSNKA..FPAPI</td><td>Increases FcγRIIB binding (400-fold) [130]<br>Inhibits by downstream ITIM signaling in B cells [131]</td></tr></tbody></table>

<table><caption>**Table 12.** IMGT nomenclature, Eu positions and IMGT motif of engineered Fc variants involved in the knock out CH2 84.4 glycosylation (Effector #8).</caption><thead><tr><th>IMGT Engineered Variant Name</th><th>IMGT Engineered Variant Definition</th><th>IMGT Amino Acid Changes on IGHG CH Domain (Eu Numbering between Parentheses)</th><th>Amino Acid Changes with the Eu Positions</th><th>Motif Identifiable in Gene and Domain with Positions According to the IMGT Unique Numbering and with Eu Positions between Parentheses</th><th>Property and Function</th></tr></thead><tbody><tr><td>G1v29</td><td>CH2<br>A84.4</td><td>CH2<br>N84.4 > A (297)</td><td>N297A</td><td>IGHG1 CH2<br>83–86<br>REEQYNSTYRVV ><br>REEQYASTYRVV</td><td>ADCC reduction. Reduces FcγR binding [132]</td></tr><tr><td>G1v30</td><td>CH2<br>G84.4</td><td>CH2<br>N84.4 > G (297)</td><td>N297G</td><td>IGHG1 CH2<br>83–86<br>REEQYNSTYRVV ><br>REEQYGSTYRVV</td><td>ADCC reduction. Reduces FcγR binding [132]</td></tr><tr><td>G1v36</td><td>CH2<br>Q84.4</td><td>CH2<br>N84.4 > Q (297)</td><td>N297Q</td><td>IGHG1 CH2<br>83–86<br>REEQYNSTYRVV ><br>REEQYQSTYRVV</td><td>ADCC reduction. Reduces FcγR binding</td></tr><tr><td>G4v36</td><td>CH2<br>Q84.4</td><td>CH2<br>N84.4 > Q (297)</td><td>N297Q</td><td>IGHG4 CH2<br>83–86<br>REEQFNSTYRVV ><br>REEQFQSTYRVV</td><td>ADCC reduction. Reduces FcγR binding</td></tr><tr><td>Canis lupus familiaris<br>G2v29</td><td>CH2<br>A84.4</td><td>CH2<br>N84.4 > A (297)</td><td>N297A</td><td>IGHG1 CH2<br>83–86<br>REEQFNGTYRVV ><br>REEQFAGTYRVV</td><td>ADCC reduction. Reduces FcγR binding</td></tr></tbody></table>
<table><caption>**Table 13.** IMGT nomenclature, Eu positions and IMGT motif of engineered Fc variants involved in half-life increase (Half-life #9).</caption><thead><tr><th>IMGT Engineered<br>Variant Name</th><th>IMGT Engineered<br>Variant Definition</th><th>IMGT Amino Acid Changes on<br>IGHG CH Domain (Eu<br>Numbering between Parentheses)</th><th>Amino Acid Changes<br>with the Eu Positions</th><th>Motif Identifiable in Gene and<br>Domain with Positions According to<br>the IMGT Unique Numbering and<br>with Eu Positions between Parentheses</th><th>Property and Function</th></tr></thead><tbody><tr><td>G1v21</td><td>CH2<br>Y15.1,<br>T16,<br>E18</td><td>CH2<br>M15.1 > Y (252),<br>S16 > T (254),<br>T18 > E (256)</td><td>M252Y,<br>S254T,<br>T256E<br>YTE</td><td>IGHG1 CH2 13–18 (249–256)<br>DTLMISRT ><br>DTLYITRE</td><td>Half-life increase<br>Enhances FCGRT binding at<br>pH 6.0 [133,134] (1)</td></tr><tr><td>G1v22</td><td>CH2<br>Y15.1,<br>T16,<br>E18,<br>CH3<br>K113,<br>F114,<br>H116</td><td>CH2<br>M15.1 > Y (252)<br>S16 > T (254)<br>T18 > E (256)<br>CH3<br>H113 > K (433)<br>N114 > F (434)<br>Y116 > H (436)</td><td>M252Y<br>S254T<br>T256E<br>H433K<br>N434F<br>Y436H</td><td>IGHG1 CH2 13–18 (249–256)<br>DTLMISRT ><br>DTLYITRE<br>CH3<br>FG 105–117 (426–437)<br>SVMHEA.LHNYT ><br>SVMHEA.LKFHHT</td><td>Half-life increase<br>Enhances FCGRT binding at<br>pH 6.0 [134]</td></tr><tr><td>G1v24</td><td>CH3<br>L107,<br>S114</td><td>CH3<br>M107 > L (428),<br>N114 > S (434)</td><td>M428L,<br>N434S</td><td>GHG1 CH3-<br>FG 105–117 (426–437)<br>SVMHEA.LHNYT ><br>SVLHEA.LHSHYT</td><td>Half-life increase<br>Enhances FCGRT binding at<br>pH 6.0 (11-fold increase in<br>affinity) [135] (2)</td></tr><tr><td>G1v42</td><td>CH2<br>Q14,<br>CH3<br>L107</td><td>CH2<br>T14 > Q (250)<br>CH3<br>M107 > L (428)</td><td>T250Q<br>M428L</td><td>IGHG1 CH2<br>13–18 (249–256)<br>DTLMISRT ><br>DQLMISRT<br>CH3-<br>FG 105–117 (426–437)<br>SVMHEA.LHNYT ><br>SVLHEA.LHNYT</td><td>Half-life increase<br>Enhances FCGRT binding at<br>pH 6.0 [134]</td></tr><tr><td>G1v46</td><td>CH3<br>K113,<br>F114</td><td>CH3<br>H113 > K (433),<br>N114 > F (434)</td><td>H433K,<br>N434F</td><td>IGHG1 CH3-<br>FG 105–117 (426–437)<br>SVMHEA.LHNYT ><br>SVMHEA.LKFHYT</td><td>Half-life increase<br>Enhances FCGRT<br>binding at pH 6.0.</td></tr></tbody></table>
<table><caption>Table 13. *Cont.*</caption><thead><tr><th>IMGT Engineered<br>Variant Name</th><th>IMGT Engineered<br>Variant Definition</th><th>IMGT Amino Acid Changes on<br>IGHG CH Domain (Eu<br>Numbering between Parentheses)</th><th>Amino Acid Changes<br>with the Eu Positions</th><th>Motif Identifiable in Gene and<br>Domain with Positions According to<br>the IMGT Unique Numbering and<br>with Eu Positions between Parentheses</th><th>Property and Function</th></tr></thead><tbody><tr><td>G2v4</td><td>CH2<br>Q14</td><td>CH2<br>T14 > Q (250)</td><td>T250Q</td><td>IGHG2 CH2<br>13–18 (249–256)<br>DTLMISRT ><br>DQLMISRT</td><td>Half-life increase<br>Enhances FCGRT binding at<br>pH 6.0 [136]</td></tr><tr><td>G2v5</td><td>CH3<br>L107</td><td>CH3<br>M107 > L (428)</td><td>M428L</td><td>IGHG2 CH3<br>FG 105–117 (426–437)<br>SVMHEA.LHNYT ><br>SVLHEA.LHNYT</td><td>Half-life increase<br>Enhances FCGRT binding at<br>pH 6.0 [136]</td></tr><tr><td>G2v6</td><td>CH2<br>Q14,<br>CH3<br>L107</td><td>CH2<br>T14 > Q (250)<br>CH3<br>M107 > L (428)</td><td>T250Q<br>M428L</td><td>IGHG2 CH2<br>13–18 (249–256)<br>DTLMISRT ><br>DQLMISRT<br>CH3<br>FG 105–117 (426–437)<br>SVMHEA.LHNYT ><br>SVLHEA.LHNYT</td><td>Half-life increase<br>Enhances FCGRT binding at<br>pH 6.0 [136]</td></tr><tr><td>G2v8-1</td><td>CH2<br>A93</td><td>CH2<br>H93 > A (310)</td><td>H310A</td><td>IGHG2 CH2<br>89–96 (306–313)<br>LTVVHQDW ><br>LTVVAQDW</td><td>Abrogates FCGRT binding<br>at pH 6.0<br>(G2v8 any amino acid<br>replacement of H93 except<br>cystein) [137]. Number 1 of<br>G2v8-1 is for A</td></tr><tr><td>G3v1</td><td>CH3<br>H115</td><td>CH3<br>R115 > H (435)</td><td>R435H</td><td>IGHG3 CH3<br>FG 105–117 (426–437)<br>SVMHEA.LHNRFT ><br>SVMHEA.LHNHFT</td><td>Half-life increase<br>Extends half-life [138]</td></tr><tr><td>G4v21</td><td>CH2<br>Y15.1,<br>T16,<br>E18</td><td>CH2<br>M15.1 > Y (252),<br>S16 > T (254),<br>T18 > E (256)</td><td>M252Y,<br>S254T,<br>T256E<br>YTE</td><td>IGHG4 CH2<br>13–18 (249–256)<br>DTLMISRT ><br>DTLYITRE</td><td>Half-life increase<br>Enhances FCGRT binding at<br>pH 6.0 [134]</td></tr></tbody></table>
<table><caption>Table 13. *Cont.*</caption><thead><tr><th>IMGT Engineered<br>Variant Name</th><th>IMGT Engineered<br>Variant Definition</th><th>IMGT Amino Acid Changes on<br>IGHG CH Domain (Eu<br>Numbering between Parentheses)</th><th>Amino Acid Changes<br>with the Eu Positions</th><th>Motif Identifiable in Gene and<br>Domain with Positions According to<br>the IMGT Unique Numbering and<br>with Eu Positions between Parentheses</th><th>Property and Function</th></tr></thead><tbody><tr><td>G4v22</td><td>CH2<br>T16,<br>P91,<br>CH3<br>A114</td><td>CH2<br>S16 > T (254),<br>V91 > P (308)<br>CH3<br>N114 > A (434)</td><td>S254T,<br>V308P<br>N434A</td><td>IGHG4 CH2<br>13–18 (249–256)<br>DTLMISRT ><br>DTLYITRE<br>CH3<br>FG 105–117 (426–437)<br>SVMHEA.LHNHYT ><br>SVMHEA.LHAHYT</td><td>Half-life increase<br>Enhances FCGRT binding at<br>pH 6.0 [139]</td></tr><tr><td>G4v24</td><td>CH3<br>L107<br>S114</td><td>CH3<br>M107 > L (428)<br>N114 > S (434)</td><td>M428L,<br>N434A</td><td>CH3<br>FG 105–117 (426–437)<br>SVMHEA.LHNHYT ><br>SVLHEA.LHSHYT</td><td>Half-life increase<br>Enhances FCGRT binding at<br>pH 6.0</td></tr></tbody></table>

(1) Ten-fold increase at pH 6.0 [134] and four-fold increases half-life in a cynomolgus pK study [140]. The T18>E amino acid change provides two novel salt bridges between the Fc and BM2 of FCGRT IMGT/3Dstructure-DB: 4n0f, 4n0u [137]. A change of IGHG1 CH2 His H93 (310) into any other amino acid (excluding Cys) leads to an undetectable binding to FCGRT (FcRn) at pH 6.0 [137]. (2) An increased reduction in tumor burden in human FCGRT (FcRn) transgenic tumor-bearing mice treated with an anti-EGFR or an anti-VEGF antibody [135]. From the 3D structure, it is postulated that N114>S (434) allows for additional hydrogen bonds with FCGRT (FcRn) [137] IMGT/3Dstructure-DB: 4n0f, 4n0u.

<table><caption>Table 14. IMGT nomenclature, Eu positions and IMGT motif of engineered Fc variants involved in the abrogation of binding to Protein A (Protein A #10).</caption><thead><tr><th>IMGT Engineered<br>Variant Name</th><th>IMGT Engineered<br>Variant Definition</th><th>IMGT Amino acid changes on<br>IGHG CH domain (Eu numbering<br>between parentheses)</th><th>Amino acid changes with<br>the Eu positions</th><th>Motif identifiable in gene and domain<br>with positions according to the IMGT<br>unique numbering and with Eu<br>positions between parentheses</th><th>Property and function</th></tr></thead><tbody><tr><td>G4v8</td><td>CH3<br>R115,<br>F116,<br>P125</td><td>CH3<br>H115 > R (435),<br>Y116 > F (436),<br>L125 > P (445)</td><td>H435R,<br>Y436F,<br>L445P</td><td>IGHG4 CH3-<br>FG 105–117 (426–437)<br>SVMHEA.LHNHYT ><br>SVMHEA.LHNRFT<br>118–125 (438–445)<br>QKSLSLSL ><br>QKSLSLSPL</td><td>Abrogates binding to<br>Protein A</td></tr></tbody></table>
<table><caption>**Table 15.** IMGT nomenclature, Eu positions and IMGT motif of engineered Fc variants involved in the formation of additional bridge stabilizing CH2 in the absence of N84.4 (297) glycosylation (Structure #11).</caption><thead><tr><th>IMGT Engineered<br>Variant Name</th><th>IMGT Engineered<br>Variant Definition</th><th>IMGT Amino Acid Changes on<br>IGHG CH Domain (Eu Numbering<br>between Parentheses)</th><th>Amino Acid Changes<br>with the Eu Positions</th><th>Motif Identifiable in Gene and Domain<br>with Positions According to the IMGT<br>Unique Numbering and with Eu<br>Positions between Parentheses</th><th>Property and Function</th></tr></thead><tbody><tr><td>G1v54</td><td>CH2<br>C83,<br>C85</td><td>CH2<br>R83 > C (292),<br>V85 > C (302)</td><td>R292C,<br>V302C</td><td>IGHG1 CH2 83–86<br>REEQYNSTYRVV ><br>CEEQYASTYRCV (v29)<br>CEEQYGSTYRCV (v30)<br>CEEQYQSTYRCV (v36)</td><td>Stabilizes CH2 in the absence<br>of N84.4 (297) glycosylation</td></tr><tr><td>G1v54-29</td><td>CH2<br>C83,<br>A84.4,<br>C85</td><td>CH2<br>R83 > C (292),<br>N84.4 > A (297)<br>V85 > C (302)</td><td>R292C,<br>N297A<br>V302C</td><td>IGHG1 CH2 83–86<br>REEQYNSTYRVV ><br>CEEQYASTYRCV</td><td>Stabilizes CH2 in the absence<br>of N84.4 (297) glycosylation</td></tr><tr><td>G1v54-30</td><td>CH2<br>C83,<br>G84.4,<br>C85</td><td>CH2<br>R83 > C (292),<br>N84.4 > G (297)<br>V85 > C (302)</td><td>R292C,<br>N297G<br>V302C</td><td>IGHG1 CH2 83–86<br>REEQYNSTYRVV ><br>CEEQYGSTYRCV</td><td>Stabilizes CH2 in the absence<br>of N84.4 (297) glycosylation</td></tr><tr><td>G1v54-36</td><td>CH2<br>C83,<br>Q84.4,<br>C85</td><td>CH2<br>R83 > C (292),<br>N84.4 > Q (297)<br>V85 > C (302)</td><td>R292C,<br>N297Q<br>V302C</td><td>IGHG1 CH2 83–86<br>REEQYNSTYRVV ><br>CEEQYQSTYRCV</td><td>Stabilizes CH2 in the absence<br>of N84.4 (297) glycosylation</td></tr></tbody></table>
<table><caption>**Table 16.** IMGT nomenclature, Eu positions and IMGT motif of engineered Fc variants involved in the prevention of IgG4 half-IG exchange (Structure #12).</caption><thead><tr><th>IMGT Engineered Variant Name</th><th>IMGT Engineered Variant Definition</th><th>IMGT Amino Acid Changes on IGHG CH Domain (Eu Numbering between Parentheses)</th><th>Amino Acid Changes with the Eu Positions</th><th>Motif Identifiable in Gene and Domain with Positions According to the IMGT Unique Numbering and with Eu Positions between Parentheses</th><th>Property and Function</th></tr></thead><tbody><tr><td>G4v5</td><td>h<br>P10</td><td>h<br>S10 > P (228)</td><td>S228P</td><td>IGHG4 h<br>1–12 (216–230)<br>ESKYGPPCPSCP ><br>ESKYGPPCPP CP<br>(G1-like)</td><td>Prevents in vivo and in vitro IgG4 half-IG exchange [129]</td></tr><tr><td>G4v6</td><td>CH3<br>K88</td><td>CH3<br>R88 > K</td><td>R409K</td><td>IGHG1 CH3<br>85.4–89 (404–410)<br>GSFFLYSRL ><br>GSFFLYSKL</td><td>Reduces IgG4 half-IG exchange [141]</td></tr></tbody></table>

<table><caption>**Table 17.** IMGT nomenclature, Eu positions and IMGT motif of engineered Fc variants involved in hexamerisation (Structure #13).</caption><thead><tr><th>IMGT Engineered Variant Name</th><th>IMGT Engineered Variant Definition</th><th>IMGT Amino Acid Changes on IGHG CH Domain (Eu Numbering between Parentheses)</th><th>Amino Acid Changes with the Eu Positions</th><th>Motif Identifiable in Gene and Domain with Positions According to the IMGT Unique Numbering and with Eu Positions between Parentheses</th><th>Property and Function</th></tr></thead><tbody><tr><td>G1v34</td><td>CH3<br>G109</td><td>CH3<br>E109 > G (430)</td><td>E430G</td><td>IGHG1 CH3-<br>FG 105–117 (426–437)<br>SVMHEA.LHNHYT ><br>SVMHGA.LHNHYT</td><td>Favors IgG1 hexamerisation by increased intermolecular Fc-Fc interactions after antigen binding on the cell surface</td></tr></tbody></table>
<table><caption>**Table 18.** IMGT nomenclature, Eu positions and IMGT motif of engineered Fc variants involved in knobs-into-holes and the enhancement of heteropairing H-H of bispecific antibodies (Structure #14).</caption><thead><tr><th>IMGT Engineered Variant Name</th><th>IMGT Engineered Variant Definition</th><th>IMGT Amino Acid Changes on IGHG CH Domain (Eu Numbering between Parentheses)</th><th>Amino Acid Changes with the Eu Positions</th><th>Motif Identifiable in Gene and Domain with Positions According to the IMGT Unique Numbering and with Eu Positions between Parentheses</th><th>Property and Function</th></tr></thead><tbody><tr><td>G1v26</td><td>CH3<br>Y22</td><td>CH3<br>T22 > Y (366)</td><td>T366Y</td><td>IGHG1 CH3<br>20-26 (364-370)<br>SLTCLVK ><br>SLYCLVK</td><td>Knob of knobs-into-holes G1v26<br>knob/G1v31 hole interactions<br>between the CH3 of the two<br>different gamma1 chains [142]</td></tr><tr><td>G1v31</td><td>CH3<br>T86</td><td>CH3<br>Y86 > T (407)</td><td>Y407T</td><td>IGHG1 CH3<br>85.4-89 (404-410)<br>GSFFLYSKL ><br>GSFFLTSKL</td><td>Hole of knobs-into-holes G1v26<br>knob/G1v31 hole interactions<br>between the CH3 of the two<br>different gamma1 chains [142]<br>(G1v26 knob/G1v31 hole)</td></tr><tr><td>G1v32</td><td>CH3<br>W22</td><td>CH3<br>T22 > W (366)</td><td>T366W</td><td>IGHG1 CH3<br>20-26 (364-370)<br>SLTCLVK ><br>SLWCLVK</td><td>Knob of knobs-into-holes G1v32<br>knob/G1v33 hole interactions<br>between the CH3 of the two<br>different gamma1 chains</td></tr><tr><td>G1v33</td><td>CH3<br>S22,<br>A24,<br>V86</td><td>CH3<br>T22 > S (366),<br>L24 > A (368),<br>Y86 > V (407)</td><td>T366S,<br>L368A,<br>Y407V</td><td>IGHG1 CH3<br>20-26 (364-370)<br>SLTCLVK ><br>SLSCAVK<br>85.4-89 (404-410)<br>GSFFLYSKL ><br>GSFFLVSKL</td><td>Hole of knobs-into-holes G1v32<br>knob/G1v33 hole interactions<br>between the CH3 of the two<br>different gamma1 chains</td></tr><tr><td>G1v68</td><td>CH3<br>V6,<br>L22,<br>L79,<br>W81</td><td>CH3<br>T6 > V (350)<br>T22 > L (366)<br>K79 > L (392)<br>T81 > W (394)</td><td>T350V<br>T366L<br>K392L<br>T394W</td><td>IGHG1 CH3<br>3-9 (347-353)<br>QVYTLPP ><br>QVYVLPP<br>20-26 (364-370)<br>SLTCLVK ><br>SLLCLVK<br>77-83 (390-396)<br>NYKTTPP ><br>NYLTWPP</td><td>Enhances, with G1v69, the<br>heteropairing H-H of bispecific<br>antibodies</td></tr></tbody></table>
<table><caption>Table 18. *Cont.*</caption><thead><tr><th>IMGT Engineered<br>Variant Name</th><th>IMGT Engineered<br>Variant Definition</th><th>IMGT Amino Acid Changes on<br>IGHG CH Domain (Eu Numbering<br>between Parentheses)</th><th>Amino Acid Changes<br>with the Eu Positions</th><th>Motif Identifiable in Gene and<br>Domain with Positions According to<br>the IMGT Unique Numbering and<br>with Eu Positions between Parentheses</th><th>Property and Function</th></tr></thead><tbody><tr><td>G1v69</td><td>CH3<br>V6,<br>Y7,<br>A85.1,<br>V86</td><td>CH3<br>T6 > V (350)<br>L7 > Y (351)<br>F85.1 > A (405)<br>Y86 > V (407)</td><td>T350V<br>L351Y<br>F405A<br>Y407V</td><td>IGHG1 CH3<br>3-9 (347-353)<br>QVYTLPP ><br>QVYVYPP<br>IGHG1 CH3<br>85.4-89 (404-410)<br>GSFFLYSKL ><br>GSFALVSKL</td><td>Enhances, with G1v68, the<br>heteropairing H-H of bispecific<br>antibodies</td></tr></tbody></table>

<table><caption>Table 19. IMGT nomenclature, Eu positions and IMGT motif of engineered Fc variants involved in the suppression of inter H-L and/or inter H-H disulfide bridges (Structure #15).</caption><thead><tr><th>IMGT Variant Name</th><th>IMGT Variant<br>Description</th><th>IMGT Amino Acid Changes on<br>IGHG CH Domain with Eu<br>Numbering between Parentheses</th><th>Eu Numbering Variant</th><th>Motif Identifiable in Gene and<br>Domain with Positions According to<br>the IMGT Unique Numbering</th><th>Property and Function</th></tr></thead><tbody><tr><td>G1v37</td><td>h<br>S5</td><td>h<br>C5 > S (220)</td><td>C220S</td><td>IGHG1 h 1-15<br>(216-230)<br>EPKSCDKTHTCPPCP ><br>EPKSSDKTHTCPPCP</td><td>No disulfide bridge inter H-L</td></tr><tr><td>G1v61</td><td>h<br>S11</td><td>h<br>C11 > S (226)</td><td>C226S</td><td>IGHG1 h<br>1-15 (216-230)<br>EPKSCDKTHTCPPCP ><br>EPKSCDKTHTCPPCP</td><td>No disulfide bridge inter H-H h 11</td></tr><tr><td>G1v62</td><td>h<br>S14</td><td>h<br>C14 > S (229)</td><td>C229S</td><td>IGHG1 h<br>1-15 (216-230)<br>EPKSCDKTHTCPPCP ><br>EPKSCDKTHTCPPCP</td><td>No disulfide bridge inter H-H h 14</td></tr></tbody></table>
<table><caption>**Table 20.** IMGT nomenclature, Eu positions and IMGT motif of engineered Fc variants involved in site-specific drug attachment (Structure #16).</caption><thead><tr><th>IMGT Variant Name</th><th>IMGT Variant Description</th><th>IMGT Amino Acid Changes on IGHG CH Domain with Eu Numbering between Parentheses</th><th>Eu Numbering Variant</th><th>Motif Identifiable in Gene and Domain with Positions According to the IMGT Unique Numbering</th><th>Property and Function</th></tr></thead><tbody><tr><td>G1v27</td><td>CH2<br>C3</td><td>CH2<br>S3 > C (329)</td><td>S239C</td><td>IGHG1 CH2<br>1.6-4 (231-240)<br>APELLGGPSV ><br>APELLGGPCV</td><td>Site-specific drug attachment engineered cysteine</td></tr><tr><td>G1v28</td><td>CH2<br>C(3^4)</td><td>CH2<br>(3^4)C(239^240)</td><td>C(239^240)</td><td>IGHG1 CH2<br>1.6-4 (231-240)<br>APELLGGPSV ><br>APELLGGPSCV</td><td>Site-specific drug attachment engineered cysteine</td></tr><tr><td>G1v44</td><td>CH3<br>C122</td><td>CH3<br>S122 > C (442)</td><td>S442C</td><td>IGHG1 CH3<br>118-125 (438-445)<br>QKSLSLSP ><br>QKSCLSP</td><td>Site-specific drug attachment engineered cysteine</td></tr><tr><td>G1v55</td><td>CH3<br>C123</td><td>CH3<br>L123 > C (443)</td><td>L443C</td><td>IGHG1 CH3<br>118-125 (438-445)<br>QKSLSLSP ><br>QKSLSCHSP</td><td>Site-specific drug attachment engineered cysteine</td></tr><tr><td>G1v56</td><td>CH2<br>F85.2<br>CH3<br>F85.2</td><td>CH2<br>Y85.2 > F (pAMF)<br>CH3<br>F85.2 > F (pAMF)</td><td>Y300F<br>F404F</td><td>IGHG1 CH2<br>84.1-85.1 (294-301)<br>EQYNSTYR ><br>EQYNSTFR<br>CH3<br>84.1-85.1 (398-405)<br>LDSDGSFF<br>LDSDGSFF</td><td>Modified phenylalanine for conjugation (produced in Escherichia coli, non glycosylated)</td></tr><tr><td>G1v64</td><td>CH2<br>C36</td><td>CH2<br>E36 > C</td><td>E272C</td><td>IGHG1 CH2<br>34-41 (270-277)<br>DPEVKFNW ><br>DPCVKFNW</td><td>Conjugation site-specific engineered cysteine</td></tr></tbody></table>
<table><caption>**Table 21.** IMGT nomenclature, Eu positions and IMGT motif of engineered Fc variants involved in the enhancement of hetero pairing H-L of bispecific antibodies (Structure #17).</caption><thead><tr><th>IMGT Variant Name</th><th>IMGT Variant Description</th><th>IMGT Amino Acid Changes on IGHG CH Domain with Eu Numbering between Parentheses</th><th>Eu Numbering Variant</th><th>Motif Identifiable in Gene and Domain with Positions According to the IMGT Unique Numbering</th><th>Property and Function</th></tr></thead><tbody><tr><td>G1v57</td><td>CH1<br>E26,<br>E119</td><td>CH1<br>K26 > E (147),<br>K119 > E (213)</td><td>K147E,<br>K213E</td><td>IGHG1 CH1<br>23-26 (144-147)<br>CLVK ><br>CLVE<br>118-121 (212-215)<br>DKKV ><br>DEKV</td><td>Enhances, with KCv57, the hetero pairing H-L of bispecific antibodies</td></tr><tr><td>KCv57</td><td>IGKC<br>R12,<br>K13</td><td>IGKC<br>E12 > R,<br>Q13 > K</td><td>E123R,<br>Q124K</td><td>IGKC<br>10-15 (121-126)<br>SDEQLK ><br>SDRKLK</td><td>Enhances, with G1v57, the hetero pairing H-L of bispecific antibodies</td></tr><tr><td>G1v58</td><td>CH1<br>C5,<br>h<br>V5</td><td>CH1<br>F5 > C (126),<br>h<br>C5 > V (220)</td><td>F126C,<br>C220V</td><td>IGHG1 CH1<br>1.4-15 (118-136)<br>ASTKGPSVFPLAPSSKSTS ><br>ASTKGPSVCPLAPSSKSTS<br>IGHG1 h<br>1-15 (216-230)<br>EPKSCDKTHTCPPCP ><br>EPKSVDKTHTCPPCP</td><td>Alternative interchain cysteine mutations to enhance, with LC2v58, heteropairing of bispecific antibodies</td></tr><tr><td>LC2v58</td><td>LC2<br>C10,<br>V126</td><td>IGLC<br>S10 > C (121),<br>C126 > V (214)</td><td>S121C,<br>C214V</td><td>IGLC2<br>1.5-15 (107A-126)<br>GQPKAAPSVTLFPPSSEELQ ><br>GQPKAAPSVTLFPPCSEELQ<br>IGLC2<br>118-127 (206-215)<br>EKTVAPTECS ><br>EKTVAPTEVS</td><td>Alternative interchain cysteine mutations to enhance, with G1v58, heteropairing of bispecific antibodies</td></tr></tbody></table>
<table><caption>**Table 22.** IMGT nomenclature, Eu positions and IMGT motif of engineered Fc variants involved in the control of half-IG exchange of bispecific IgG4 (Structure #18).</caption><thead><tr><th>IMGT Variant Name</th><th>IMGT Variant Description</th><th>IMGT Amino Acid Changes on IGHG CH Domain with Eu Numbering between Parentheses</th><th>Eu Numbering Variant</th><th>Motif Identifiable in Gene and Domain with Positions According to the IMGT Unique Numbering</th><th>Property and Function</th></tr></thead><tbody><tr><td>G4v10</td><td>CH3<br>L85.1,<br>K88</td><td>CH3<br>F85.1 > L (405),<br>R88 > K (409)</td><td>F405L,<br>R409K</td><td>IGHG1 CH3<br>85.4–92 (402–413)<br>GSFFLYSRLTVD ><br>GSFLLYSKLTVD</td><td>Control of half-IG exchange of bispecific IgG4</td></tr></tbody></table>

<table><caption>**Table 23.** IMGT nomenclature, Eu positions and IMGT motif of engineered Fc variants involved in reducing acid-induced aggregation (Structure #19).</caption><thead><tr><th>IMGT Engineered Fc<br>Variant Name</th><th>IMGT Engineered<br>Variant definition</th><th>IMGT Amino Acid<br>Changes on IGHG CH<br>Domain (Eu Numbering<br>between Parentheses)</th><th>Amino Acid Changes<br>with the Eu Positions</th><th>Motif Identifiable in Gene<br>and Domain with<br>Positions According to the<br>IMGT Unique Numbering<br>and with Eu Positions<br>between Parentheses</th><th>1. Property and<br>Function</th><th>2. Property and<br>Function</th><th>3. Property and<br>Function</th></tr></thead><tbody><tr><td>G2v7</td><td>CH2<br>Y85.2,<br>L92,<br>A339</td><td>CH2<br>F85.2 > Y (300)<br>V92 > L (309)<br>T339 > A (339)</td><td>F300Y<br>V309L<br>T339A</td><td>IGHG2 CH2<br>85.4–92 (300–309)<br>STFRVVSVLTVV ><br>STYRVVSVLTVL<br>118–125 (333–340)<br>EKTISKTK ><br>EKTISKAK</td><td>Reduces acid-induced<br>aggregation [143]</td><td>Low ADCC Low FcγR<br>binding [143]</td><td>Low CDC<br>Low C1q binding [143]</td></tr></tbody></table>
In the tables, the different columns correspond to the items of the standardized variant characterization detailed above. Engineered amino acid changes are in bold in the IMGT variants (red before the change, green after the change. The motif is in yellow and shown before and after the AA change(s).

The variants involved in antibody-dependent cellular cytotoxicity (ADCC) reduction. include nine *Homo sapiens* IGHG1 variants, which comprise: G1v1 [1], G1v2 [1], G1v3 [1], G1v5 [6], G1v47 [37], G1v50 (the variant G1v50 is a variant combining the G1v1, G1v2, G1v3 and G1v47 amino acid changes), G1v52 ‘GRLR’, G1v66 and G1v67 (Table 5).

The variants involved in antibody-dependent cellular cytotoxicity (ADCC) enhance-
ment include nine variants, of which six *Homo sapiens* IGHG1 variants: G1v6 [3], G1v7
'DE' [4], G1v8 'DLE' '3M' [4] [25], G1v9 [14], G1v10 [15] and G1v11 [15]; one *Homo sapiens*
IGHG2 variant: G2v1 [1]; one *Homo sapiens* IGHG4 variant: G4v1 [1]; and one *Mus musculus*
IGHG2B variant: Musmus G2Bv1 [5] (Table 6).

The variants involved in antibody-dependent cellular cytotoxicity (ADCC) and antibody-
dependent cellular phagocytosis (ADCP) enhancement include three *Homo sapiens* IGHG1
variants: G1v12 ‘GASDALIE’ [26], G1v13 ‘GASDIE’ ‘ADE’ [16] and G1v45 ‘GAALIE’
(Table 7).

The variants involved in complement-dependent cytotoxicity (CDC) enhancement include 8 variants, of which seven *Homo sapiens* IGHG1 variants: G1v5 [6], G1v15 [6], G1v16 [6], G1v17 ‘EFT’ [18], G1v18 [19], G1v35 ‘SE’ [18,27] and the chimeric G1G3v1 [17], and one IGHG4 variant: G4v2 [8] (Table 8).

The variants involved in complement-dependent cytotoxicity (CDC) reduction include six variants, of which three *Homo sapiens* IGHG1 variants: G1v8 ‘DLE’ [4], G1v19 [2] and G1v20 [2,39]; and three *Mus musculus* IGHG2B variants: Musmus G2Bv2 [7], Musmus G2Bv3 [7] and Musmus G2Bv4 [7] (Table 9).

The variants involved in antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC) reduction include 32 variants and four variant associations, of which 22 *Homo sapiens* IGHG1 variants: G1v4 [2], G1v14 ‘LALA’ [21,39], G1v14-1, G1v14-4, G1v14-48, G1v14-49 ‘LALAPG’ [40], G1v14-67, G1v23 [20], G1v38 [35], G1v39 ‘FES’ ‘TM’ [20,24], G1v40, G1v41 [20,24], G1v43, G1v48, G1v49 [40], G1v51, G1v53 ‘FQQ’, G1v59 [41], G1v60, G1v63, G1v65, G1v70 and one association G1v53-G1v21 ‘FQQ-YTE’ [38]; three *Homo sapiens* IGHG2 variants: G2v2 ‘IgG2m4’ [23], G2v3 ‘G2sigma’ [24] and the chimeric G2G4v1 [22]; five *Homo sapiens* IGHG4 variants: G4v3 ‘LE’ [20], G4v3-49 ‘LEPG’ [40], G4v4 ‘FALA’ [21], G4v7, G4v49 [40] and three associations G4v3-G4v5 ‘SPLE’ [12,20], G4v3-49-G4v5 ‘SPLEPG’ [40] [12] and G4v4-G4v5 ‘IgG4ProAlaAla’ [12,24] and two *Canis lupus familiaris* IGHG2 variants: CanlupfamG2v1 and CanlupfamG2v2 (Table 10).

The variants involved in B cell inhibition by coengagement of antigen and FcγR on
the same cell include one *Homo sapiens* IGHG1 variant: G1v25 [33,34] (Table 11).

The variants involved in knock out CH2 84.4 glycosylation include five variants, of which three *Homo sapiens* IGHG1 variants: G1v29 [42], G1v30 [42], G1v36; one *Homo sapiens* IGHG4 variant: G4v36; and one *Canis lupus familiaris* IGHG2 variant: Canlupfam G2v29 (Table 12).

The variants involved in half-life increase or decrease include 13 variants, 12 of them increase half-life, of which five *Homo sapiens* IGHG1 variants: G1v21 ‘YTE’ [9,29–32], G1v22 [30], G1v24 [32], G1v42 [30] and G1v46; 3 *Homo sapiens* IGHG2 variants: G2v4 [10], G2v5 [10] and G2v6 [10]; one *Homo sapiens* IGHG3 variant: G3v1 [11]; three *Homo sapiens* IGHG4 variants: G4v21 ‘YTE’ [30], G4v22 [36] and G4v24. One variant G2v8-1 abrogates binding to FCGRT (FcRn) (Table 13).

The variants involved in abrogation of binding to Protein A include one *Homo sapiens*
IGHG4 variant: G4v8 (Table 14).

The variants involved in formation of additional bridge stabilizing CH2 in the absence of N84.4 (Eu 297) glycosylation include four *Homo sapiens* IGHG1 variants: G1v54, G1v54-29, G1v54-30 and G1v54-36 (Table 15).
The variants involved in prevention of IgG4 half-IG exchange include two *Homo sapiens* IGHG4 variants: G4v5 [12] and G4v6 [13] (Table 16).

The variants involved in hexamerisation include one *Homo sapiens* IGHG1 variant: G1v34 (Table 17).

The variants involved in knobs-into-holes and enhancement of heteropairing H-H of bispecific antibodies include six *Homo sapiens* IGHG1 variants: G1v26 knob [28] and G1v31 hole [28], G1v32 knob and G1v33 hole, G1v68 and G1v69 (Table 18).

The variants involved in suppression of inter H-L and/or inter H-H disulfide bridges includes three *Homo sapiens* IGHG1 variants: G1v37, G1v61 and G1v62 (Table 19).

The variants involved in site-specific drug attachment include six *Homo sapiens* IGHG1 variants: G1v27, G1v28, G1v44, G1v55, G1v56 and G1v64 (Table 20).

The variants involved in enhancement of hetero pairing H-L include two *Homo sapiens* IGHG1 variants: G1v57 used in association with *Homo sapiens* IGKC variant: KCv57, and G1v58, used in association with *Homo sapiens* IGLC2 variant: LC2v58 (Table 21).

The variants involved in control of half-IG exchange of bispecific IgG4 antibodies include one *Homo sapiens* IGHG4 variant: G4v10 (Table 22).

The variants involved in reducing acid-induced aggregation include one *Homo sapiens* IGHG2 variant: G2v7 (Table 23).

Two variants have been assigned to two properties belonging to different types and are therefore found in two tables, G1v5 (Tables 5 and 8) and G1v8 (Tables 6 and 9).

Supplementary Table S2 provides the variants of Tables 5–23 in an alphanumeric order of the IMGT engineered variants involved in the effector properties (ADCC, ADCP and CDC), half-life and structure of the therapeutic monoclonal antibodies.

**5. Conclusions**

The therapeutic monoclonal antibody engineering field is the most promising in the medical field. A standardized analysis of IG genomic and expressed sequences, structures and interactions is crucial for a better molecular understanding and comparison of the mAb specificity, affinity, half-life, Fc effector properties and potential immunogenicity. IMGT has provided the concepts for the IG loci description of newly sequenced genomes [2], antibody structure/function characterization [4], antibody engineering (single chain Fragment variable (scFv), phage displays, combinatorial libraries) and antibody humanization (chimeric, humanized and human antibodies). IMGT® standardization allows the repertoire analysis and antibody humanization studies to move to novel, high-throughput methodologies with the same high-quality criteria. The CDR-IMGT lengths are now required for mAb INN applications and are included in the WHO-INN definitions (84–86). The characterization of the IGHG engineered variants for effector properties, half-life increase, and new structures of bi- and multi-specific antibodies brings a new level of standardized information in the comparative analysis of therapeutic antibodies.

**Supplementary Materials:** The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/antib11040065/s1, Table S1: Correspondence between the IMGT unique numbering for C-DOMAIN, the IMGT exon numbering, the EU and Kabat numberings: Human IGHG [97,98] https://www.imgt.org/IMGTScientificChart/Numbering/Hu_IGHGnber.html; Table S2: IMGT nomenclature (alphanumeric order) of engineered variants involved in effector properties (ADCC, ADCP, CDC), half-life and structure of therapeutic monoclonal antibodies.

**Author Contributions:** Conceptualization, methodology, validation, investigation, data curation, writing, review and editing, visualization, ontology, M.-P.L. and G.L. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Data Availability Statement:** Data is contained within the article or Supplementary material.

**Acknowledgments:** We thank Souphatta Sasorith, Mélissa Cambon and Karima Cherouali for their contribution in the early phase of this work.
**Conflicts of Interest:** The authors declare no conflict of interest.

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