BIOTECHNOLOGY
ANTIBODY ADVICE
When it comes to the production and application of antibody fragments, it pays to be smaller, but more specific, says Shengnan Shao
VHH, VNAR, or sdAb, is a kind of antibody fragment consisting of a single monomeric variable antibody domain and lacking the light chain and CH domain of the heavy chain in conventional Fab region. Both scFv and VHH nanobodies can be linked to the Fc fragment of the desired species and keep their specificity and binding properties.
All these antibody fragments, Fab, scFv, Full IgG Antibody A
ntibodies are modular defence systems that identify and neutralise foreign objects such as bacteria and viruses. Each of them
could recognise a specific antigen unique to its target as they possess the antigen- binding sites. What’s more, antibodies are now recognised as routine molecules in many therapeutic fields, no longer restricted to oncology and inflammation. To a better specificity, the variable regions are more concerned by scientists. Te antigen-binding fragment (Fab)
is a region on an antibody that binds to antigens. It contains one constant and one variable domain of each of the heavy and the light chains. Only the variable regions of the heavy and light chains are fused together to form a single-chain variable fragment (scFv), which is half
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the size of the Fab fragment, yet the original specificity is retained. Another small antibody fragment, single domain antibody, also known as domain antibody,
and VHH, have a smaller size than a whole antibody. It enables their binding to hidden epitopes not accessible to whole antibodies. Te smaller size can help to provide lower scattering, thus less contrast in images. In the context of therapeutic applications, a small molecular weight also means efficient penetration and fast clearance. Some therapeutic use also needs the fragments due to a better penetration into tissue. It also could lead to the expression of the functional antibody and their fusion in bacteria and also allow their display on filamentous phage. In addition, the combination of small antibody molecules together with the efficient microbial production systems
Fragments: Fab, scFv, VHH (from left to right)
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