Here to show you how recombinant antibody expression works.
Mouse-human Chimeric Antibody
The gene of human antibody constant regions is combined with the gene of variable regions from mouse monoclonal antibodies. The combination forms a mouse-human chimeric antibody, and the human region accounted for 60-70%.
Humanized Antibody
As the chimeric antibodies retain a large proportion of murine regions, it is still a risk in clinical practice. In order to further reduce the murine region, the CDR grafting technology was invited, which only retains the CDR region of murine mAb. The obtained antibodies are called humanized antibodies, and the process is named humanization. In humanized antibodies, human regions can be as high as 80-90%.
Human Antibody
Although humanized antibodies have significantly reduced the risk of “HAMA” response, they are not perfect as they still retain murine region. In recent years, scientists have obtained the full human antibodies by a new technology, called phage display technology. Phage display antibody library utilizes phage to fuse a gene fragment encoding a variable region of an antibody with a gene encoding a phage surface protein, which can ‘display’ the variable regions of antibody on the surface of phages. When a phage library is constructed by using human antibody variable region genes, the human antibody can be obtained from screening the library. After screening, using in vitro protein expression technology can achieve the full human antibodies which comprises human antibody heavy and light chains.
Small Molecule Antibody
Generally, the antibody we are talking about is a full-length antibody, including the light chains and the heavy chains, and with a full-length antibody molecule between 150 and 196 KDa. Such a large molecular weight often encounters problems, such as poor tissue permeability and easy degradation in practical use. In order to solve these problems, scientists have developed antibody fragments with small molecular weight and strong binding affinity, such as single-chain antibodies (scFv) and antigen binding fragments (Fab).
Single-chain Variable Fragment (scFv)
scFv is only composed of a heavy chain variable region and a light chain variable region, and has a molecular weight of only 1/6 of the full length antibody which gives it the good tissue permeability. As scFv retains antigen-binding sites, it still has good binding specificity, result in being widely applied in clinical treatment. In addition, the poly peptide linker of the single-chain antibody can be designed as other sites such as metal chelation sites, linked drug sites, etc., makes it being a powerful tool in clinical applications.
Antigen Binding Fragments (Fab)
Fab retains the antigen binding region with 1/3 molecular weight compared to the full length of the antibody, and has good tissue permeability and low immunogenicity.
Multivalent Antibodies
Multivalent antibodies are antibodies that can bind multiple antigens and are a novel antibody prepared by combining genetic engineering techniques and chemical coupling techniques. At present, more attention is paid to "bispecific antibodies", which can combine two different antigens and have significant advantages in tumor immunotherapy. For example, a bispecific monoclonal antibody that binds to tumor cell surface antigens and killer T cell surface antigens can promote the close proximity of the two cells to each other, which facilitates the killing of tumor cells by killer T cells and promotes therapeutic effects.
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