Absolute Antibody is developing engineered antibodies for the research and diagnostics markets. A major advantage of using sequenced and engineered recombinant antibodies is the ability to create chimeric antibodies (Figure 1). A chimeric antibody (cAb) is an antibody made by fusing the antigen binding region (variable domains of the heavy and light chains, VH and VL ) from one species like a mouse, with the constant domain (effector region) from another species such as a rabbit. The chimeric antibodies retain the original antibody’s antigen specificity and affinity and are valuable tools for in vivo and in vitro research.
Chimeric antibodies for in vivo research
- Biotherapeutic research – Many therapeutic monoclonal antibodies were originally generated in mice and chimerized to reduce immunogenicity in humans, before humanization was widely adopted. Examples of chimeric antibodies in the clinic include infliximab, rituximab and abciximab (see our Research Grade Biosimilars range). Chimeric antibodies containing human constant domains and mouse variable domains are substantially cheaper than fully humanized antibodies. This makes them useful at the early stages of biotherapeutics research.
- In vivo research – ‘Species switched’ chimeric antibodies allow the use of an antibody in animal models with reduced anti-species immune responses. Quite often antibodies may be generated in one species, for example rat, and the disease animal model being used maybe another, for example mouse – here a chimeric antibody with mouse constant regions (partially “murinized”) will result in reduced immunogenicity. Note that by subtype switching or using our Fc Silent™ mutations you can also modulate effector functions (ADCC or CDC).
Example Product – OX86; the original monoclonal antibody [OX86] (which has been extensively used in vivo) is rat antibody targeting mouse CD134 (Ab00110-6.1). Using our proprietary recombinant antibody platform, we have generated a mouse anti-mouse version (Ab00110-2.0).
Chimeric antibodies for Assay Development and Diagnostics
Use as calibrators or controls in Immunoassays
Serological immunoassays designed to detect a specific antibody in patient samples rely on serum calibrators (standards) and/or positive controls. Calibrators can be used in an immunoassay to generate standard curves to quantify the test antibody concentration in the patient serum, or as positive controls to assess the performance of the assay and reagents. For a serological assay, calibrators are derived from seropositive serum or plasma and are heterogeneous by nature, so suffer from significant drawbacks:
- Lot to lot variability with respect to antibody class IgG, IgM composition, specificity and affinity
- Difficulty in sourcing large amounts with high titre
- Limitations with respect to characterisation
Recombinant chimeric antibodies are a viable and more reliable alternative to serum based calibrators. Advantages in immunoassays include:
- Minimal lot to lot variation with respect to antibody class, composition, titre, specificity and affinity
- Chimeric antibodies can be generated in unlimited quantities and are homogeneous in specificity and affinity
- Fully characterised because of their recombinant production
Interference from heterophilic antibodies
Heterophilic antibodies are found in human patient serum and plasma. They are poly-reactive antibodies recognising IgG from different animal species. These antibodies are non-specific, have no defined antigen and can bind to the Fc region of the assay antibody causing a false positive test signal. Heterophilic antibodies found in patient serum react with mouse (HAMA) and rat IgG. Since conventional specific and high affinity monoclonal antibodies can only be obtained from the mouse and rat, heterophilic antibodies can be a limitation in diagnostic tests. Chimeric monoclonal antibodies (in particular human chimeric antibodies) are a solution to this problem.
Chimeric antibodies for in vitro R&D
- Chimeric antibodies allow the antibody to be tailored to a specific application – they are not limited to the original antibody species.
- Chimeric antibodies allow the researcher the flexibility to adapt the monoclonal antibody of their choice to any platform or binding module/surface.
- Flow cytometry and IHC : Chimeric antibodies can circumvent potential non-specific binding issues associated with binding of secondary antibodies to the test cell or tissue.
Example product – We have generated a family of anti-myc tag antibodies for use as controls or affinity capture antibodies (eg. ChIP assays; immunoprecipitation). The original anti-c-myc monoclonal antibody [9E10] is a mouse monoclonal IgG1 (Ab00100-1.1). Using our proprietary recombinant platform, we have made this antibody available as a rat IgG1 (Ab00100-6.1), rat IgG2b (Ab00100-8.1), rabbit IgG (Ab00100-23.0) and human IgG1 (Ab00100-10.0).
Current Catalog of Chimeric Antibodies
We offer a range of recombinant chimeric antibodies and fusion proteins for in vivo and in vitro applications. Our antibody engineering platform allows us to quickly generate chimeric versions of any monoclonal antibody in our catalog. We also offer a range of species specific and genetically engineered Fc domains (e.g. Fc Silent™) and species and isotype switching.
Got a specific antibody in mind? Contact us and we’ll be glad to assist you.