Recombinant antibodies (rAbs) are antibody fragments expressed by using recombinant antibody coding genes. They offer many advantages in medicine and research.
Recombinant antibodies are produced in vitro, in cell lines. Unlike traditional monoclonal antibodies (mAbs), which rely heavily on laboratory animals. Moreover, recombinant monoclonal antibodies have a very well-defined molecular composition, while traditional mAbs are more prone to quality and reproducibility issues.
In general, antibodies (rAbs as well as mAbs) are Y-shaped proteins that are part of the humoral adaptive immune system in vertebrates. They are highly specific binders to pathogens, toxins and malevolent cells, i.e. their respective antigens. This specificity is mediated through the tips of their two prongs (“paratopes”, or antigen-binding sites). This binding marks the antigen as a target and starts a cascade of immunologic processes, ultimately neutralizing the antigen.
Recombinant antibodies are used in medicine as well as in life science. They are therapeutic treatments for many diseases, including cancer or autoimmune disorders.
This overview will illuminate the basics of rAbs without going too deep into the underlying science.
Recombinant antibodies are used in numerous applications in medicine and life sciences, such as:
Despite their profound impact on medicine and life sciences, traditional monoclonal antibodies (mAbs) have several serious disadvantages. Antibodies generated through the use of recombinant technology overcome those issues of traditional mAbs.
Traditional antibody production suffers from longer development and production time scales, whereas recombinant antibody technology is faster and more reliable.
Recombinant Abs are technologically more advanced than monoclonal antibodies, which were developed from polyclonal antibodies. Polyclonal antibodies are produced naturally by B cells that are part of the immune system. When these cells encounter a pathogen, they start to produce antibodies that bind to it, starting the cascade of immune response. Each single B cell produces specific antibodies against an antigen.
Consequently, during an in vivo infection several B cells are activated and produce antibodies. These are polyclonal antibodies and they show a range of affinities and specificities, thus limiting their usefulness in biotechnology.
Fusion of such a B cell with a multiple myeloma cell leads to a so-called hybridoma cell. It is immortal and produces one type of antibody, the monoclonal antibody. This discovery was a major breakthrough and led to antibody production on large scales. Later on, this process proved time consuming, suffered from reproducibility issued and relied heavily on laboratory animals.
Recombinant antibody technology takes the development even further, as it enables scientists to engineer antibodies on the genetic level and to produce them quickly and in high quality in vitro.
Recombinant antibodies are produced in expression systems developed from cell lines. The antibody genes are inserted in a host cell like a CHO cell in the transfection process.
The cells grow in a cell culture medium and in specific intervals the antibodies are harvested from this cell culture medium.
Development of recombinant antibodies involves antibody engineering on the genetic level. This became feasible when phage display technology and single B cell cultures were developed.
Subsequently, molecular biology techniques such as PCR can be utilized to enhance antibody performance. The antibody candidates are exposed to the antigens and selected for specificity and affinity in several increasingly stringent selection rounds. The optimized genetic constructs are then introduced into host cells.
The scope of recombinant antibody applications is tremendous. The recent pandemic outbreak of SARS-CoV-2 virus had a big impact on everybody’s life. The strategies to fight the pandemic rely heavily on recombinant antibodies.
One example is the development of therapeutic antibodies that neutralize virus particles in infected patients. Recombinant antibodies that bind to surface proteins of SARS-CoV-2 are used in lateral flow test kits (“antigen tests”) to detect acute infections.
A recent publication of Canadian scientists in the Journal of Molecular Biology1 highlights the possibility to design highly sensitive and specific reporter assays against SARS-CoV-2 virus particles using recombinant antibodies.
They created a reporter system consisting of two halves of a luminescence enzyme. Each half is attached to an antibody. The antibodies were developed to have affinity to regions of viral surface proteins using recombinant and phage display technologies.
In the presence of the viral surface proteins, the antibodies bind to them, thus enabling the attached enzyme halves to reconstitute to a functional enzyme. The reporter system then emits light. This publication illuminates how rAbs can be rapidly developed into tools for important applications.1
Natural antibodies not only bind their respective antigen, they highlight it to the immune system as harmful and mark it for neutralization. This effect is named antibody dependent cellular cytotoxicity (ADCC) and is of high significance in the development of therapeutic antibodies in oncology.
The underlying signalling process involves the recognition of a chain of carbohydrates on the antibodies. Research has shown that the nature of the carbohydrates influences the severity of the ADCC and that afucosylated antibodies (i. e. lacking fucose in the carbohydrate chain) have a particularly positive effect on ADCC.
Therefore, the ability to effect afucosylation of recombinant antibodies adds a whole new dimension to the scope of antibody technology. In addition to being able to develop highly specific antibodies to virtually any antigen through recombinant antibody technology, afucosylation allows the fine tuning of the strength of the immune system’s response to the antigen.
This fact opens the door to developing more potent and more tolerable therapeutic antibodies.