Developing Bispecific Antibodies

Bispecific antibodies (bsAbs) harness the specificities of two antibodies and combine them to simultaneously recognize different antigens or epitopes. This ‘two-target’ functionality has meant that interest in their use for therapeutic applications has increased considerably. We spoke to GenScript’s Liusong Yin, PhD, Senior Director of Antibody Services and Jie Ma, Product Manager of Antibody Services, to learn more about bispecific antibodies and the associated challenges developing them. They also highlight GenScript’s single-domain Ab fused to monoclonal Ab (SMAB) platform and the benefits of using SMABs.

A: What are bispecific antibodies?

Q: While natural antibodies are monospecific, bispecific antibodies (bsAbs) recognize two different epitopes either on the same or on different antigens.  Because of this, a bsAb has two-target functionality, meaning that it can interfere with two distinct mechanisms simultaneously. BsAbs can also enable the linking of two targets which are normally not in close proximity to one another, such as a cell membrane receptor and its ligand. BsAbs have become increasingly of interest for therapeutic applications. Currently, there are two FDA approved bsAb drugs, catumaxomab and blinatumomab. Both of these drugs use their bi-specificity in order to link activated cytotoxic T cells to cancerous cells in order to induce an immune attack on tumors. Because of their high efficacy, there are currently more than 200 bsAb based therapeutics entering or currently in clinical trials. Of these 200 bsAbs, over 80% induce a synapse between immune cells and cancerous tissue to initiate cancerous cell death. This wide array of bsAbs has been called a bispecific “zoo”, because it is populated by many different species, comprising around 100 different formats, including various engineering of antibody fragments in symmetric or asymmetric manner. Some of the most common formats of bsAbs include bispecific T cell engagers (BiTE) composed of two different single chain variable fragments, bispecific (mAb)2 composed of two linked full length monoclonal antibodies, and bispecific nanobodies composed of two linked camelid variable heavy chains. 

Q: Could you tell us more about GenScript’s single-domain Ab fused to monoclonal Ab (SMAB) platform?

A: There are two major challenges in developing bispecific antibodies: 1) over-engineering of naturally generated antibodies may lead to an antibody therapeutic to produce its own immune response, making the drug ineffective; 2) commercially generating bispecific antibodies can have manufacturing problems due to their non-natural format, such as product instability, low expression level, & complex purification process. In order to avoid these issues, GenScript’s SMAB platform combines camelid single domain antibodies with naturally generated monoclonal antibody backbones to make a bispecific antibody in symmetric format with good biological efficacy and developability. 

Q: How does the SMAB platform integrate into the stages of antibody drug discovery and development?

A: SMAB discovery begins by identifying a camelid single domain antibody (sdAb) which binds effectively with the target antigen. From there, we will construct the 10-20 SMABs with varying formats, composed of a monoclonal antibody backbone and two sdAbs in different places on the mAb backbone.  Once we recombinant express these constructs we will screen them through our “design and profiling” service in order to identify the highest functioning formats. Lastly, we will evaluate and optimize the developability of the highest binding SMAB. However, if a client has their own monoclonal antibody which they would like to use for the SMAB backbone or a good single domain antibody for binding, we can directly start their project from our design of profiling service using the existing mAbs and sdAbs. 

Q: What are the benefits of using SMABs?

A: Thanks to our design concept of “being natural”, the SMAB platform has several advantages over mono-specific therapeutics and other bispecific antibody designs: (1) BsAbs show bio-superiority and a better safety profile over monotherapy or combinatorial therapeutics; (2) the SMAB platform has good developability and therefore can generate high yields and concentration in formulation with desirable stability; (3) the SMAB platform has the same manufacturing process as conventional antibody therapeutics; (4) the sdAb in GenScript’s SMAB platform has the ability to bind to “hidden” epitopes, such as enzymes, ion channels, etc, as well as being highly flexible for construction of multi-valent molecules using a “plug and play” fashion. 

Liusong Yin and Jie Ma were speaking to Laura Elizabeth Mason, Science Writer for Technology Networks.