antibody domain Single domain antibodies represent the smallest antibody that was proven of diagnostic and therapeutic usefulness. They are antibody fragments that engineered from single monomeric variable domains of either camelids’ heavy-chain antibody (V H H) or cartilaginous fishes’ IgNAR (V NAR ). On the other hand, it is also possible to develop single domain antibodies from camelized human antibodies. In particular, single domain antibodies combine the benefits of conventional antibodies with important features of small molecule drugs. They are able to bind to hidden epitopes that are not accessible to whole antibodies. In addition, in comparison with small molecule drugs that target enzyme active sites and receptor clefts, single domain antibodies have the potential of greater affinity and selectivity, thus promising lower side effect and better efficacy. Furthermore, because of their small size (they are only 1/10 the size of a whole antibody), single domain antibodies can penetrate tissues faster than other antibodies and even break through the blood-brain barrier (BBB), which turns them into excellent candidates for central nervous system disease therapies. Single domain antibodies have higher stability during the changes of temperature and chemical environments and great potential for gastrointestinal stability and oral availability. Also, thanks to its simple nature of a single-chain peptide, single domain antibodies have exceptional drug format flexibility and allow efficient drug discovery and development.

In terms of the advanced phage display technology, Creative Biolabs has unparalleled capabilities for the construction of V H H or V NAR based single domain antibody libraries through immunized camel, llama, alpaca or shark. In comparison with naïve libraries, immune libraries usually produce antibodies of greater affinity, thus avoiding time-consuming in vitroantibody affinity maturation effort. Antibodies from naïve libraries frequently require affinity maturation before they are useful due to affinity issues. Furthermore, in comparison with naïve libraries, which usually require a size of 1-10 billion independent clones to be useful, an immune library can be much smaller. Our experience showed that immune libraries with a size of 1-10 million variants could be sufficient to produce excellent antibodies. Our scientists have extensive experience in cloning the single domain antibody repertoire from immunized plasma cells into our phage display vectors. By reverse transcription and polymerase chain reaction, a library of single domain antibodies containing million clones is regularly produced.

Creative Biolabs also has sufficient expertise in constructing synthetic naïve single domain antibody libraries. By nature, single domain antibodies developed from either V H H or V NAR are more stable and soluble, although their immunogenicity can be higher than single domain antibodies engineered from human antibodies. If the immunogenicity of the single domain antibodies is not a concern, a synthetic V H H or V NAR single domain antibody library can be made by randomizing the CDR1 and CDR3 using trimer codon technology. In case the immunogenicity of single domain antibodies is a concern, our services allow the construction of camelized human single domain antibody libraries which are based on the monomerization of human antibody heavy chain framework. The binding region of normal human IgG consists of two domains (VH and VL) which tend to dimerize or aggregate because of their lipophilicity; the monomerization will be accomplished by replacing lipophilic with hydrophilic amino acids at a few proprietary positions. Such synthetic libraries represent a good source of single domain antibodies against self, non-immunogenic, and toxic antigens since the libraries are usually sufficiently vast and diverse.