What is a single domain antibody ?

Single domain antibodies(sdAb) were first reported in "Nature" in 1993 by Belgian scientist Hamers et al. There is an antibody that naturally lacks the light chain in the peripheral blood of alpaca. The antibody contains only a heavy chain variable region (VHH) and two conventional CH2 and CH3 regions. SdAb is the smallest unit known to bind to the target antigen. VHH crystals are 2.5nm, 4nm long, and have a molecular weight of only 15KD, so they are also called Nanobody or single domain antibody.

Advantages and applications of single domain antibodies

Because single-domain antibodies have a longer CDR3 region (SdAb CDR3 usually consists of 16-24 amino acids, while traditional monoclonal antibodies have only 7-12 amino acids), this long CDR3 structure is conducive to single-chain Antibodies bind to the concealed epitopes of antigen molecules, which is also the main reason for improving the ability of single-chain antibodies to bind to antigens. At the same time, it results in a very stable structure and can withstand high temperatures and harsh extreme environments. Compared with ordinary Y-type antibodies, SdAb have a simple structure, are easy to carry out antibody engineering transformation, and are more suitable for transformation into monovalent, bivalent, bispecific and multivalent antibodies. At the same time, the production and preparation of sdAb are simple and convenient, and can be prepared by traditional E. coli expression system, and can also be produced by yeast or mammalian cells. SdAb are highly similar to the amino acid sequence of the heavy chain of human antibodies, so they are easy to be humanized and have gradually become an emerging force in a new generation of therapeutic biomedicine and clinical diagnostic reagents.

Single domain antibody acquisition

In order to meet the needs of industrial customers, we have developed a sdAb screening platform based on Single B cell cloning and yeast display to meet the needs of different customers .

Technical Route 1: Obtain sdAb based on Single B cell clone

ABexpress ^R is a rapid antibody screening platform independently developed by our company. This program uses flow cytometry to sort B cells that specifically bind to the target protein in PBMC, and sequence the antibody coding region of a single B cell to finally obtain antibody sequence information. This method is suitable for any animal antibody screening, and can cover all targeted antigen-specific B cells at one time. It has the characteristics of good gene diversity and high efficiency; and it can avoid false positives in the process of using phage libraries to screen monoclonal antibodies, Or non-specific binding, can greatly accelerate the speed of sdAb screening.

Technical process:

Technical Route 2: Obtain SdAb Based on Yeast Display

Phage display technology was once another important technical way to obtain sdAb sequences, but some antibodies cannot be correctly fused with phage capsid protein and displayed, and the non-specific binding of phage itself to the target protein will also affect the subsequent screening work. . To avoid such problems, we display sdAb on the surface of yeast. After sorting positive clones by FACS, we can obtain diverse antibody sequences by sequencing. This method can perfectly simulate the structure of all sdAb on the cell membrane surface, correctly reflect the binding of sdAb to antigens, and rarely occur non-specific binding of phage display libraries. When carrying out multiple sdAb screening work, the yeast display library technology has even more cost advantages.

Technical process: