Leveraging the cell line development capabilities, GenScript has developed single-clone derived CHO-K1 cell lines expressing different classes of Fc gamma receptors (FcγRs) and neonatal Fc receptor (FcRn). The Fc receptor cell line portfolio now includes ten cell lines that express one human FcRn, and six human FcγRs containing polymorphic variants of FcγRIIIa, FcγRIIa and FcγRIIb.
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- Determination of binding affinity of antibodies or Fc fusion proteins.
- Determination of half-life of antibodies or Fc fusion proteins.
- Determination of mechanism of action of antibodies or Fc fusion proteins in vitro.
GenScript offers FcγRs and FcRn overexpression cell lines with binding capabilities spanning all IgG subclasses. These cell lines are designed for cell-based binding assays to evaluate Fc-FcγR and Fc-FcRn binding affinity.
Following binding with the Fc region of antibodies that are attached to pathogens or infected cells, FcγRs can mediate effector functions including antibody-dependent cellular phagocytosis (ADCP) or antibody-dependent cell-mediated cytotoxicity (ADCC). During Fc engineering in antibody based drug development, increasing or decreasing Fc-FcγR binding affinity could potentially strengthen or weaken effector functions. FcRn involves in recycling of IgG type antibodies in serum, which increases the stability and half-life of antibodies. Hence, antibody Fc engineering for enhanced Fc-FcRn binding affinity could prolong the circulation half-life of antibody.
Figure 1: Fc receptor expressing cells based binding assay with flow cytometer.
Cell-based binding assay with flow cytometer is one of the accessible methods to evaluate binding affinity.
Single-nucleotide polymorphism contributes to polymorphic FcγRs that can effect an individual’s immune response to antibody based drugs or immune therapies. Same antibody based drugs may have different efficiencies in patients with polymorphic FcγRs. GenScript offers polymorphic FcγRs overexpression cell lines for performing polymorphism studies.
Table 1: Immunoglobulin subclass binding and functions of Human FcRγ and FcRn receptors.
|name||Alias||Polymorphism||IgG subclass binding||Function|
|FcγRIIIa||CD16A||V158||Higher affinity to all human IgGs than F158||Activation /Inhibition|
|F158||Lower affinity to all human IgGs than V158||Activation /Inhibition|
|R131||lower affinity to IgG1 and IgG2 than H131, IgG3, IgG4||Activation /Inhibition|
|FcRn||FcRn||-||IgG1,IgG2,IgG3,IgG4||Recycling, transport, uptake|
The structure of Fc receptors effects their antibody binding affinity and their functions upon antibody binding. All of the FcγRs and FcRn overexpression cell lines provided by GenScript express the receptors mimicking the way they are present in their natural forms.
The FcγRI, FcγRIIa, FcγRIIc and FcγRIIIa are primarily activating receptors, as they express immunoreceptor tyrosine activating motifs (ITAMs) on their α or associated γ chains. On the other hand, the inhibitory receptor FcγRIIb expresses an immunoreceptor tyrosine inhibitory motif (ITIM). The FcγRIIIb receptor is a GPI-anchored protein which expresses neither ITAM nor ITIM motifs, but instead conducts signal transduction through associations with other Fc receptors. The FcRn receptor is structurally a heterodimer consisting of an α chain and a β2-microglobulin (β2m), both of which are important for the receptor’s expression on the cell surface, as well as for optimal IgG binding activity.
Figure 2: Schematic representation of human FcγRs and FcRn on cell surface
Symbols: α (alpha chain), γ (gamma chain), ITAM (immunoreceptor tyrosine activating motifs), ITIM (immunoreceptor tyrosine inhibitory motif), β2m (β2-microglobulin)
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- Kara S, Amon L, Lühr JJ, Nimmerjahn F, Dudziak D, Lux A. Impact of Plasma Membrane Domains on IgG Fc Receptor Function. Front Immunol. 2020;11. doi:10.3389/fimmu.2020.01320