Antibodies are immunoglobulins produced by B lymphocytes and play an important role in humoral immunity. Nowadays, through genetic engineering technology, an antibody library containing a large number of different antibody sequences can be constructed. After that, antibodies with specific binding ability can be screened from the antibody library through high-throughput screening technology. Recombinant antibodies are generally divided into chimeric antibodies, humanized antibodies, fully humanized antibodies, small molecule antibodies, bispecific antibodies, and antibody fusion proteins. Among them, small molecule antibodies include Fab antibodies, scFv single-chain antibodies, single-domain antibodies, etc.

Classification and characteristics of recombinant antibodies:

The characteristic of chimeric antibodies is that the variable region of mouse monoclonal antibodies and the constant region of human antibodies are combined to form a hybrid antibody molecule. Chimeric antibodies retain the high specificity and affinity of mouse monoclonal antibodies, and the immunogenicity of heterologous antibodies in the human body is greatly reduced. Chimeric antibodies are prepared by connecting the variable region of mouse monoclonal antibodies with the constant region of human antibodies at the genetic level and expressing them in suitable host cells. Based on the high specificity and affinity of chimeric antibodies, they can target antigens on the surface of cancer cells, thereby identifying and killing cancer cells. In cancer treatment, chimeric antibodies are often used as targeted therapy drugs, such as chimeric antibody drugs for HER2-positive breast cancer. Chimeric antibodies can also be used to treat autoimmune diseases. By regulating the function of the immune system, chimeric antibodies can reduce or eliminate the damage to the body caused by autoimmune reactions, thereby alleviating disease symptoms. In the treatment of infectious diseases, chimeric antibodies can neutralize pathogens and prevent them from further infecting body cells.

Antibodies can be modified by transplanting antigen binding sites (CDRs) and preparing humanized antibodies, further improving the safety and therapeutic effects of antibodies. CDR transplantation is based on chimeric antibodies, replacing mouse framework regions with human framework regions (FRs), retaining only CDRs in mouse variable regions to maintain their antigen binding ability and reduce immunogenicity. Fully humanized antibodies are prepared by phage display technology, transgenic mouse technology, ribosome display technology, and RNA-peptide technology.

Single-chain antibodies (scFv) connect VL and VH through short flexible peptides. scFv is the smallest binding unit with antibody activity. Because it lacks the Fc domain, its size is very small, about 25 kDa. scFv is widely used in the study of antigen epitopes, and it also has a broad market in the development of targeted cancer treatment drugs and autoimmune disease drugs. In addition, based on the characteristics of scFv without Fc fragments, its immunogenicity is low and the risk of causing immune response in the human body is relatively small. scFv can also be used for efficient recombinant antibody expression in a variety of expression systems, including prokaryotic expression systems and eukaryotic expression systems, such as Escherichia coli, yeast, insect cells, mammalian cells, etc.

Fig. 1 Comparison of the structures of traditional antibodies and single-chain antibodies

Single-domain antibodies contain only one heavy chain variable region and conventional CH2 and CH3 regions. Although they do not have a VL domain, they can still bind to antigens and are single-domain antibodies with high stability. Nanobodies and traditional antibodies are both composed of 4 relatively conservative framework regions (FRs) and 3 complementary determining regions (CDRs), but compared with traditional antibodies, the CDR3 of nanobodies has a loop structure region, which is longer than the general variable region and has better binding performance. Compared with full-length antibodies, single-domain antibodies are easier to penetrate into tumor tissues and can be used in targeted cancer therapeutics. At the same time, single-domain antibodies also play an important role in detection reagents and in vitro diagnostics. It is reported that single-domain antibodies against Aspergillus flavus can be screened through phage display technology, which can then be applied to the field of food safety to detect the content of aflatoxin in agricultural products.

Bispecific antibodies, also known as bispecific monoclonal antibodies, are antibodies artificially synthesized using genetic engineering technology. They usually belong to the IgG subclass and contain an antigen-binding fragment targeting the CD3 subunit. Bispecific antibodies have two specific antigen-binding sites and can simultaneously bind to and recognize two different antigens, or two different epitopes of an antigen. Compared with monoclonal antibodies, bispecific antibodies have one more specific antigen-binding site, so they have stronger specificity and targeting, can more accurately target tumor cells and reduce off-target toxicity. Bispecific antibodies can simultaneously exert multiple biological functions, such as recruiting immune cells, blocking signal transduction pathways, and directly killing tumor cells.

TekBiotech has a complete recombinant antibody expression and production platform, rich experience in recombinant antibody expression, and can provide customers with full-length and scFv, Fab, VHH nanoantibodies, bispecific antibodies, Fc fusion antibodies, and chimeric antibody preparation services for various species including human, mouse, rabbit, sheep, dog, camel, and cattle. Customers only need to provide antibody sequence information, hybridoma cells or cDNA. The company's technical support can be designed according to customer needs, combined with the company's independently designed high-expression vectors for the lactation system and large-scale recombinant antibody fermentation platform, to provide customers with high-quality one-stop recombinant antibody production services including sequence analysis, linker design, fusion tag design, high-expression vector design and construction, expression scheme design optimization, recombinant expression condition optimization, antibody purification, etc.