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HTRF Human C1q Binding Kit HTRF®

The Human C1q binding kit is designed to monitor the binding of the IgG Fc region to the human C1q protein.

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The Human C1q binding kit is designed to monitor the binding of the IgG Fc region to the human C1q protein.

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Overview

Complement-Dependent Cytotoxicity (CDC) is an important effector function of antibodies. Activation of the classical complement pathway is initiated by the binding of the complement protein C1q to the Fc region of immunoglobulins bound to a cell surface target antigen. This interaction triggers the sequential enzymatic activation of circulating complement proteins, and finally leads to the formation of the Membrane Attack Complex (MAC) that mediates target cell lysis. 

The capacity of C1q binding and resultant CDC activity can influence the safety and efficacy of therapeutic monoclonal antibodies, and therefore requires characterization during the development process. Engineering the Fc region of IgG antibodies (e.g. by mutations or glycoengineering) is currently an active area of investigation to enhance or reduce the ability of biologics to recruit complement.

The human C1q binding kit measures the binding of the Fc region of aggregated IgG antibodies to human C1q in solution.

Benefits

  • FAST ANTIBODY SELECTION
  • CDC PREDICTION
  • LOW SAMPLE CONSUMPTION

Binding profiles of human IgG isotype controls

Purified human IgG1, IgG2 and IgG4 isotype control antibodies were serially diluted with Diluent #12 and tested in the Human C1q binding assay. The signal intensity obtained for each dose-response binding curve shows that human IgG1 binds efficiently to C1q, and human IgG2 interacts weakly with the complement component, whereas human IgG4 does not bind to the protein. These results are in accordance with the literature (Almagro et al., 2018, Progress and Challenges in the Design and Clinical Development of Antibodies for Cancer Therapy. Front. Immunol. 8:1751).

Validation of human C1q binding assay with human IgG isotype controls

Binding profiles of Rituximab variants

The therapeutic anti-CD20 antibody Rituximab (chimeric IgG1) was tested in the Human C1q binding assay in parallel with the following Rituximab variants: non-fucosylated Rituximab (InvivoGen, #hcd20-mab13), non-glycosylated Rituximab (InvivoGen, #hcd20-mab12), Rituximab IgG2 isotype (InvivoGen, #hcd20-mab2), and Rituximab IgG4 isotype (InvivoGen, #hcd20-mab4). As expected, the absence of the fucose residue on the Fc domain of the non-fucosylated antibody (supposed to modulate ADCC activity only) did not induce any detectable change in C1q binding compared to Rituximab. Conversely, the capacity of interaction of the non-glycosylated variant was altered, demonstrating that antibody Fc glycosylation is essential for Fc-mediated effector mechanisms. Finally, isotype switching from IgG1 to IgG2 or IgG4 induced a considerable decrease or an elimination of the capacity of the antibody to bind to C1q. 

Validation of human C1q binding assay with Rituximab variants

Binding profiles of therapeutic type I & type II anti-CD20 antibodies

The therapeutic anti-CD20 antibodies Rituximab (type I, chimeric IgG1) and Obinutuzumab (type II, humanized IgG1, also known as 'GA101') were tested in the Human C1q binding assay. The lower signal obtained with the type II anti-CD20 Obinutuzumab demonstrates its reduced capacity to bind to C1q compared to the type I anti-CD20 Rituximab. These results are consistent with literature (Herter et al., 2013, Preclinical Activity of the Type II CD20 Antibody GA101 (Obinutuzumab) Compared with Rituximab and Ofatumumab In Vitro and in Xenograft Models, Mol Cancer Ther; 12(10); 2031–42).

Validation of human C1q binding assay with therapeutic type I & type II anti-CD20 antibodies

Binding profiles of Cetuximab variants

The therapeutic anti-EGFR antibody Cetuximab (chimeric IgG1) was tested in the Human C1q binding assay in parallel with the following Cetuximab variants: non-glycosylated Cetuximab (InvivoGen, #hegfr-mab12) and Cetuximab IgG2 isotype (InvivoGen, #hegfr-mab2). As expected, the binding capacity of the non-glycosylated variant was altered, demonstrating that antibody Fc glycosylation is essential for Fc-mediated effector mechanisms. Isotype switching from IgG1 to IgG2 also induces a considerable decrease in the capacity of the antibody to interact with C1q.

Validation of human C1q binding assay with Cetuximab variants

Binding profiles of Ipilimumab and IgG2 isotype variant

The therapeutic anti-CTLA-4 antibody Ipilimumab (fully human IgG1) was tested in the Human C1q binding assay in parallel with its IgG2 isotype variant (InvivoGen, #hctla4-mab2). The signal decrease observed between the biologic and its variant demonstrates that the isotype switching from IgG1 to IgG2 leads to a considerable loss of capacity of the antibody to bind to C1q.

Validation of human C1q binding assay with Ipilimumab and IgG2 isotype variant

Binding profiles of therapeutic anti-PD-L1 & anti-PD-1 antibodies

The therapeutic antibodies Atezolizumab (anti-PD-L1, humanized IgG1) and Spartalizumab (anti-PD-1, humanized IgG4) were tested in the Human C1q binding assay. As expected, the anti-PD-L1 IgG1 antibody Atezolizumab showed strong binding to C1q, whereas the anti-PD-1 IgG4 antibody Spartalizumab did not have the capacity to interact with C1q. 

Validation of human C1q binding assay with therapeutic anti-PD-L1 & anti-PD-1 antibodies

Binding profiles of therapeutic anti-TNF-α antibodies

The therapeutic anti-TNF-α antibodies Infliximab (chimeric IgG1) and Adalimumab (fully human IgG1) were tested in the Human C1q binding assay. The binding dose-response curves showed similar profiles and signal intensity, demonstrating that both anti-TNF-α antibodies have the same capacity to interact with C1q.

Validation of human C1q binding assay with therapeutic anti-TNF-α antibodies

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