What is an Antibody Library?

By Reginald DaveyReviewed by Sophia Coveney

The prevalence of diseases such as cancer and the increased need for immunotherapy is driving the development of technologies that target disease-causing cells and organisms. This has led to the development of what is known as an antibody library. This article will discuss this subject.

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Antibodies and the fight against disease

When a pathogen infects a healthy host, the host’s immune system responds to fight it off and maintain health. The host produces antibodies that recognize the antigens present on the surface of the invading cell. However, the host’s immune system must be able to recognize the antigen in the first place: when infection occurs for the first time, this is not possible as the host has not previously encountered the pathogen.

This is why initial infection by a pathogen can lead to a higher risk of mortality or health complications. The body is not ready for the disease as it cannot recognize the antigen and therefore the pathogen. However, if a person recovers from the initial infection, their body will have the antibodies necessary for fighting off further reinfection.

Antibody libraries: speeding up the drug discovery process

Historically, the main approach to developing vaccines and therapeutics for disease prevention has been to harvest antibodies from people who have survived infection.  Immune cells need to be isolated, and large numbers of antibodies must be screened to find those which bind the tightest to the specific pathogen. However, this can be time-consuming, and sometimes time is of the essence – something the COVID-19 pandemic has been a key reminder of.

Antibody libraries are, as the name suggests, libraries of existing antibodies that can be searched to provide those that could be effective against a pathogen. By taking this approach, the drug discovery process can be significantly sped up.  By harvesting samples from a few hundred people, many times more human antibodies can be stored in an antibody library.

Antibody libraries can be “panned” for matches (much like panning for gold in a stream) which means that researchers do not even have to wait for infected patients to recover and produce antibodies. When Chinese scientists published the genetic sequence of the SARS-CoV-2 virus, a team at the University of Pittsburgh generated the spike protein which was then used as bait for the antibodies within their library. This approach should prepare us better for future pandemics.

Antibody library construction

There are two main strategies that are used to construct antibody libraries. Either random combinations genes can be used, or they can be designed by amplifying the variable gene sequences of one or more individuals. Both human plasma cells and splenocytes from naïve or immunized animals are used to construct antibody libraries. Antibody libraries work better when there is sufficient diversity in them.

There are four types of combinatorial antibody libraries. These are immune, naïve, semi-synthetic, and synthetic libraries. Immune libraries use antibodies from immunized humans or animals, whereas naïve libraries use antibodies harvested from unimmunized subjects (or, alternatively, synthetic or shuffled human V genes.)

In semi-synthetic libraries, diversity is controlled by oligonucleotide synthesis, whereas synthetic libraries are built from the ground up using wholly artificial, randomly integrated codons into complementary determining regions (CDRs.)

A commonly used technology in antibody libraries is phage display, where genetically manipulated bacteriophages with antibodies on their surfaces bind to the immobilized antigen. After washing, any remaining bacteriophages will display antibodies of interest. These can then be inserted into E. Coli bacteria to amplify the antibodies for further research.

The number of combinations stored in antibody libraries can be staggering: some libraries contain 10⁸ combinations. An antibody library can identify which antibodies should provide protection against a pathogen in an extremely short period of time.

Examples of antibody library use in disease research

Antibody libraries have provided researchers with a tool that has solved fundamental issues in disease research. This has seen the use of antibody libraries in several studies in recent years.

Using antibody libraries led to the discovery of the Ab1 antibody for SARS-CoV-2 in February 2020 by a team at the University of Pittsburgh and UPMC. Most companies that took a more traditional approach did not have monoclonal antibodies until the end of March or early April 2020. Antibody libraries were instrumental in the quick development of vaccines to fight COVID-19.

Antibody libraries have also been used in cancer research. A 2010 study published in Molecular Cell Proteomics demonstrated the use of a single-chain antibody library to discover biomarkers for early detection of cancer. Using the library, they screened ovarian serum for novel biomarkers. This research offers an approach to decrease the morbidity in patients afflicted by ovarian and other cancers.

Antibody libraries also offer biological insights into the growing use of intracellular antibodies. These are biological tools that are expressed intracellularly and directed to a target antigen, where they can then interrupt the function of antigens at the post-translational level.

In conclusion

Antibody libraries are increasingly being used by researchers to find new drug targets, antibodies, biomarkers of disease, and so forth. As more antibodies are discovered and more combinations are included within them, the development of new drugs and vaccines will continue to show improvement. This technology is a vital part of biomedical research in the 21^st century.

Further Reading

• All Antibodies Content
• VHH Antibodies (Nanobodies) Advantages and Limitations
• Fluorescent Antibody Techniques
• Antibody Selection using DNA Origami Scaffolds
• Uses of Histone Deacetylase (HDAC) Antibodies in Research