Bispecifics

Introduction

Bispecifics (BsAbs) are a class of engineered antibody and antibody-like proteins that can simultaneously bind to two different types of antigen or two different epitopes on the same antigen. The principle behind BsAbs is the targeting of two molecules through a single platform to take into account the multifactorial side of diseases and simultaneously affect multiple pathways to increase efficacy. But building a safe and effective BsAbs is challenging. The antibody needs to be able to activate immune cells but not so much that it causes side effects such as cytokine release syndrome. Now BsAbs have become increasingly of interest for diagnostic and therapeutic applications.

Structural Types and Production

Although there are many different bispecific constructs, the 2 major classes are those with an Fc region (IgG-like) and those without (non-IgG-like). Non-IgG-like BsAbs only have therapeutic effects through antigen-binding because of the lack of Fc fragments. BsAbs without an Fc region only have therapeutic effects through antigen binding. They are small and easy to produce and have low immunogenicity. The main drawback is a short half-life, requiring frequent or continuous dosing. The Fc portion provides stability in the circulation, allowing for intermittent rather than continuous dosing, and can also promote antibody-dependent cellular cytotoxicity and complement activation.

• IgG-like formats roughly include “knob into hole” IgG, crossMab, ortho-Fab IgG, two in one IgG, IgG-scFv and scFv2-Fc.
• Non-IgG-like formats include tandem scFvs, diabody format, single-chain diabodies, tandem diabodies (TandAbs), and sdAb.

Fig.1 Molecular formats of BsAbs. (Yu, 2017)

BsAbs with defined specificities are artificial molecules, per se not found in nature. They must, therefore, be generated by biochemical, molecular or genetic means. BsAbs can be generated by ligation of heavy and light chains corresponding to desired targets, single domain antibodies, single-scFvs, or other modified recombinant modalities with additional binding domains present on either N- or C-terminal of monoclonal antibodies.

Mechanisms of Action of BsAbs

• Forced protein association allows them to perform their proximity-requiring function.
• Interference with dual signaling pathways by selective binding of a (pathogenic) cell subset expressing both epitopes.
• Recruitment and activation of immune cells.

Fig.2 Examples of the unique mechanisms of action of BsAbs. (Szijj, 2021)

Advantages & Disadvantages

The benefits of BsAbs over monoclonal therapeutics are huge, due to their higher binding avidity to targets, which can interact with more than one surface antigen; boost cytotoxic effects. There is a lower rate of resistance to them due to the matched targeting of two different antigens. However, BsAbs also have disadvantages such as potential antigenic cytokine release syndrome, low production yields and product instability. In addition, small BsAbs can be rapidly cleared; larger ones may aggregate; potential immunogenicity.

BsAbs are power tools adopted by immunology. Scientists at Creative Biolabs have experience in producing a variety of BsAbs formats. Based on the antibody development and engineering platform, we've expanded our capabilities to provide different antibody services including monoclonal antibody, antibody fragment, Fc engineering, BsAbs, and more. Please feel free to contact us for further information.

References

1. Yu, S.; et al. Recent advances of bispecific antibodies in solid tumors. Journal of hematology & oncology, 2017, 10(1): 1-16.
2. Szijj, P.; Chudasama, V. The renaissance of chemically generated bispecific antibodies. Nature Reviews Chemistry, 2021, 5(2): 78-92.

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