Phage Display Library –Single Domain Antibody Library Construction Service

Single-domain antibodies (sdAbs), or nanoantibodies, are part of a class of recombinant antibody fragments, representing the smallest antibody that was proven of great usefulness. With a molecular weight of 12-15 kDa, single-domain antibodies, which consist only of a single heavy-chain variable domain and engineer from single monomeric variable domains of either camelids' heavy-chain antibody (VHH) or cartilaginous fishes' IgNAR (VNAR) without loss of antigen-binding ability. On the other hand, scientists can also develop sdAbs from camelized antibodies, such as camelized human and other species antibodies.

sdAb is similar to conventional VH domains (Ig VH) in that VHHs contain four framework regions (FRs) that form the core structure of the immunoglobulin domain and three complementarity-determining regions (CDR1, CDR2 and CDR3) that are involved in antigen binding. This contrasts with shark single-domain antibodies (IgNAR V) that have a vestigial CDR2 that does not contribute to antigen binding. Compared with traditional antibodies, single-domain antibodies have been shown to remain functional at 90°C and recognize antigenic sites that are normally not recognized by conventional antibodies such as enzyme active sites.

Alpha Lifetech Inc. can offer two kinds of single-domain antibody (sdAb) libraries as below:

Construction of Immunized Single Domain Antibody Library

The scientists at Alpha Lifetech Inc. have extensive experience in constructing and expressing recombinant antibodies based on our proprietary phage display platform. An immunized single-domain antibody library is suitable for the generation of high-affinity and antigen-special VHH or NAR V antibodies, thus avoiding time-consuming in vitro antibody affinity maturation effort. Here, we produce an antigen-special single-domain antibody library for our clients from immunized alpaca, camel, llama or shark, and even humans (PBL cells activated by antigens in vitro). By reverse transcription and polymerase chain reaction, a library of single-domain antibodies containing 10-100 million clones is regularly produced.

Construction of Synthetic Single Domain Antibody Library

Synthetic single-domain antibody libraries often developed from the CDR1 and CDR3 of either naïve VHH or VNAR. This synthetic antibody library is by definition a naïve library and has a high complexity of 3x10¹⁰ VHHs ensuring a very satisfying diversity. It is naïve so it does not require llama or shark immunization. This helps us save a lot of time to get a specific antibody and makes possible antibody selection for non-immunogenic or conserved proteins. 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. In case the selection of high-soluble single-domain antibodies is a concern, we have designed a shuttle phagemid vector system, including several phagemids, which can express the single-domain antibodies in E. coli (yeast) or display them on the surface of phage particles.