Antibody Discovery Platforms

The Great Debate of Antibody Discovery Platforms

The great debate on the use of in vivo versus in vitro sources and strategies for antibody discovery platforms continues to thrive among antibody research groups. On one side of the debate is the argument for non-animal-derived antibodies due to the technical advancements of current in vitro technologies, and the moral obligation to reduce animal usage. On the other side of the debate is the counterargument for animal-derived antibodies due to their better performance in affinity, specificity, and reduced immunogenicity risk.

Both sides have valid concerns, but the decision of which strategy to implement requires a detailed look at each type of antibody and the technologies used for their discovery and generation. In this article, we will compare in vivo and in vitro antibody discovery platforms with the hope to foster further discussions around these strategies for current and future workflows.

Traditional Antibody Discovery Technologies

The approach to antibody discovery and generation is a key factor to consider in the context of discovery campaigns. Traditional routes (Figure 1) that are still in use today include:

1. Direct isolation from animal plasma
2. Generation of hybridoma cells
3. Screening of primary B cells
4. Expression of recombinant antibody repertoires

Figure 1. Schematic illustration of traditional strategies for antibody discovery and generation. Abbreviations: pAbs, polyclonal antibodies; mAb, monoclonal antibody.

Animal Plasma Isolation

Antibody isolation from animal plasma involves the animal’s immunization with an antigen (ie. full-length protein, peptide, stimulatory DNA) to drive the antibody response and maturation in vivo. By harvesting the animal plasma, removing non-antibody proteins, and antigen affinity purification, this approach yields the generation of an undefined mixture of polyclonal antibodies (pAbs). pAbs are widely known to have strong performance but suffer from batch-to-batch variability, loss of production animals, and difficulty with characterization. All other techniques in this article are centered on generating monoclonal antibodies (mAbs).

Hybridoma Generation

Hybridoma technology is an immortalization technique of short-lived antibody-secreting B cells.  This process also begins by immunizing the animal with an antigen to provoke an immune response in vivo. The antibody-secreting B cells are then harvested typically from the animal spleen – though other organs and compartments have been harvested as well, including the bone marrow, lymph nodes, and peripheral blood mononuclear cells (PBMCs). Upon generation of hybridomas, by way of fusing antibody-secreting B cells with immortal myeloma cells, the hybridomas are cultured and its supernatant screened in vitro (ie. ELISA) for the presence of antigen-specific mAbs. Though hybridomas are accessible and widely used, they are often unstable and commonly express additional, productive heavy or light chains resulting in mAbs that are not monospecific.

B Cell Screening

Though hybridoma generation falls under the umbrella of ‘B cell screening’, there are alternative screening technologies that do not rely on the immortalization process. These alternatives are collectively referred to as ‘B cell screening’ and are distinct from hybridoma technology due to the direct application of primary B cells. B cells can be directly cultured, stained, and sorted by fluorescence-activated cell sorting (FACS), followed by in vitro screening for binding activity (ie. ELISA). Further downstream, the total collective of B cells can be sequenced using next-generation sequencing (NGS), known as B cell repertoire sequencing, or they can be sequenced individually, known as single B cell sequencing (described in the next section). 

Like the hybridoma technology, B cell screening also relies on in vivo sources (ie. animal, human, transgenic animals) for mAb discovery and generation. The success of a discovery campaign depends on the sampling of B cells, the ability to isolate the critical antibody-secreting B cells, and the sustainability of the B cells ex vivo.

Display Technologies

Improvements in current display technologies (phage, yeast, ribosome, bacterial, or mammalian display) have put a spotlight on this in vitro approach to antibody discovery and generation. Relying heavily on the linkage of genotype to phenotype, each given DNA sequence of an antibody fragment can be encoded within a phage or cell to be expressed on its surface. This underlying concept can be exploited to generate antibody repertoire libraries displaying millions of different antibodies, which can be screened iteratively, referred to as “panning”, against a given target antigen. Each sequential round of panning enriches the subsequent gene pool for the phages or cells that encode for the antigen binders.

Arguments could be made for display technologies to be entirely animal-free with the use of naïve antibody repertoires that do not reflect an immune system’s response to an antigen. Alternatively, display technologies can be used in combination with immunization, B cell sequencing, or hybridoma approaches to exploit DNA sequences of mAbs from an immunogenic response. 

Proponents of display technologies argue that it is an effective way to iterate and test many mAb sequences to find the best binders. Detractors argue that since it is an in vitro approach, these synthetically derived sequences are likely to cause developability and immunogenicity challenges later on.