All camelids (llama and camels) have unique antibodies comprising a homodimer of heavy chain polypeptides. The target antigen of these heavy chain-only antibodies is recognized by virtue of one single variable domain. A straightforward technology was developed to immunize a camelid, to clone the repertoire of antigen-binding fragments, from which the antigen-specific fragments are rapidly identified after phage display selections. The resulting monoclonal, recombinant, antigen-binding single-domain antibody fragments are also referred to as Nanobodies (Nbs) because of their size of 4 nm by 2.5 nm in diameter.
Nanobodies are well produced in microbial systems, very robust and highly soluble, bind their cognate antigen with high affinity and specificity. Very often the Nanobody recognizes an epitope that is difficult to target with human or mouse antibodies. The ‘humanization’ or ‘PetizationTM’ of Nanobodies is/should be straightforward. Probably, the largest advantages of Nanobodies come from their strict monomeric behavior, the ease to tailor them into larger pluripotent constructs and their functionality when expressed intracellularly.
Such beneficial properties of Nanobodies over other antigen-binding fragments from conventional antibodies inspired many researchers to employ Nanobodies as a versatile tool in various innovative applications in biotechnology and medicine as: