Abstract
In 1993, Hamers-Casterman and colleagues discovered a novel type of IgG antibodies.1 Camelid serum contains functional heavy-chain homodimeric antibodies without light chains. The variable domain of these single chain antibodies are named as VHHs (nanobodies). The binding ability of VHH to antigens was found to be similar or even better than classical IgG.2 Single-domain antibody was also identified in special cartilaginous fish by Greenberg and colleagues.3 It was also found that they are suitable for expression as multivalent formats like bispecific, enzyme, or toxin-VHH fusions to increase avidity without using current linkers like those that existed between VL and VH domains, which often result in aggregation and decrease affinity because of mispairing of VL and VH domains.4 Lacking of the mispairing problems allows designing more flexible linkers and successfully achieving functional trivalent-bispecific VHHs.5,6 Sequencing and crystallographic analysis of camel VHH has showed homology to the human VHH. The above facts prepare some advantages for biotechnological applications of VHH, such as facile genetic manipulation, increased functional size of libraries, high physicochemical stability, ease of production of multivalent forms, high stability, recognition of hidden antigenic sites, well expression, rapid tissue penetration, and fast blood clearance.7 Soluble VHHs have been produced in Escherichia coli (E. coli), filamentous fungi, Saccharomyces cerevisiae, and Pichia pastoris. 8–11 VHH single-domains can be used whenever high stability is required, such as use in shampoo for preventing dandruff.12 They were used in immunoaffinity purification as capturing reagents and in biosensor technology.13,14 VHH is also reported to be a good candidate for oral immunotherapy because of its resistance against high pH, and its ability to bind to the target in the presence of high concentrations of many other agents.15 This type of functional VHH antibody …
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