As trispecifics, cell engagers and other complex formats multiply, drug developers are seeking discovery and engineering partners to help navigate an expanding universe of molecular possibilities.
For every new binding arm added to a molecule construct, the number of potential combinations expands, making molecule selection an increasingly complex exercise. As multispecific formats proliferate, service providers are increasingly working with sponsors to determine which molecule to build in the first place.
Challenges present in determining which format, affinity profile and molecular architecture are most likely to balance efficacy, safety, manufacturability and developability. As a result, the infrastructure of discovery and engineering partners is growing beyond simple antibody generation to support shared strategic decision-making in molecular design.
As BioSpace previously reported, bispecifics established the first generation of multitarget biologics. Bispecifics are immunotherapies designed with two different “arms” that can bind to two separate targets simultaneously. They have made trade news headlines as Chinese biotechs launched an unprecedented wave of bispecific programs between 2020 and 2025.
The next wave of multispecifics include trispecifics, T-cell engagers with co‑stimulation, NK engagers and dual agonists. Their development poses new considerations beyond bispecifics’ inherent complexity.
Varied multispecific options
As the number of possible molecules grows, the greater goal has shifted from candidate discovery to selection.
The benefit of multispecifics is they allow greater possibilities to fight cancer, said Roland Green, CEO, co-founder and chairman of antibody discovery, design and delivery company Invenra. In the case of trispecific antibody-drug conjugates (ADCs), the addition of a third arm can be used to drive better internalization of ADC payloads. In laymen’s terms, this means the tumor can absorb the drug more effectively.
In terms of the trispecific landscape, T cell engagers are quite common, where one arm binds the T cell from the immune system and the others bind to tumor cells. Pharma clients are also very interested in cell engagers, Green said, where one arm binds to an immune cell, one arm to the tumor and a third arm that binds to the first immune cell. The final arm acts as co-stimulant and boosts the potential for the body’s immune cells to attack the tumor.
“You don’t build a more complex molecule just because you can,” Green noted. “You build a molecule to solve a problem that hasn’t been solved.”
Molecule format decision-making
Screening methodologies need to match that complexity with the relevant throughput, said Oren Beske, head of biologics at Twist Bioscience. In February, Twist announced that it had entered into a licensing agreement to become the co-exclusive provider, together with Invenra, of the latter’s’ B-Body® bispecific antibody platform.
Often, the nuances and biological relevance of matching the desired affinities to multiple targets within a single molecule makes this task formidable, Beske said. There can be hundreds of combinations to be considered for bispecifics and potentially thousands for trispecifics.
Usually, a partner hopes a multispecific molecule, when binding to specified targets and in a particular format, will address their chosen disease biology, said Eric Krauland. Krauland is president and chief science officer at Adimab, which offers an antibody discovery and engineering platform.
If the partner does not have a format they want to work with, Adimab will typically guide partners toward IgG-like/full Fab-based multispecifics rather than using scFv-based multispecifics to facilitate manufacturing, he added.
Fab fragments are the first two domains of both an antibody heavy chain (HC) and light chain (LC), with the first domain of each chain containing the regions that confer target specificity. An scFv (single-chain variable fragment) is just those two binding domains, one from each chain, linked together in a single protein by inserting a flexible peptide sequence.
Adimab is seeing more projects featuring unvalidated biology and sponsors that are keen to explore multiple format configurations. T cell engagers have driven significant interest following clinical validation; sponsor goals are now shifting to increase potency and safety. When it comes to T cell engagers, the company offers a panel of CD3 antibodies that have a wide range of affinities.
Controlling heterogeneity
Solutions aim to reduce the amount of heavy chain/heavy chain (HC/HC) and heavy chain/light chain (HC/LC) mispairing and increase usable product for later downstream manufacturing, Krauland said.
Mispairing can cause heterogeneity, but heterogeneity has multiple causes besides mispairing. For the latter, the final product becomes an undesirable blend of multiple molecular species rather than one uniform molecule.
Eleva Biologics’ two moss-specific platform capabilities significantly reduce heterogeneity from the outset, said Björn Cochlovius, CEO and managing director. They allow correct folding and multimeric assembly, handled natively by plant-specific chaperones. This is a space where other approaches often struggle, he said.
“By avoiding product heterogeneity and reducing analytical and QC complexity, the platform can help shortens timelines, lowers cost of goods and delivers cleaner chemistry, manufacturing and controls,” he said.
Concentrated engineering exercise
An important quality to consider at the molecular creation stage is developability, which includes expressability, Krauland said. Developability considers how suitable a molecule is for successful drug development beyond its biological activity. Expressability is how easily and efficiently a cell can produce the molecule.
Aggregation is also a key factor to consider and can be attributed both to the antibody components and to the multispecific format chosen. It’s an important consideration because aggregation can negatively affect the yield at the end of the purification as well as portend downstream issues, such as shelf-life stability and immunogenicity.
Other general properties that can signal developability challenges, are hydrophobicity—a molecule’s tendency to repel water—and polyreactivity, or “stickiness”, a molecule’s tendency to weakly interact with many other substrates.
Hydrophobicity can influence a molecule’s stability, and overall ease of downstream manufacturing. Stickiness can lead to formulation challenges, as well as possible pharmacokinetic/pharmacodynamic issues once the therapeutic is administered into the body.
From promise to proof
The challenge of addressing these molecular properties is one reason why next-generation formats such as trispecifics have been slower to mature than their bispecific predecessors.
Trispecifics are at the stage where bispecifics were five years ago, Green said. Their complexity in terms of design and manufacturing has meant the industry is nascent, so there needs to be some success stories before there is large-scale investment.
“The bigger question to ask on developing increasingly complicated molecules beyond the multispecifics of today (such as cytokine fusions, radiotherapies and ADCs) is whether doing so will benefit patients beyond the current tried and true modalities,” Beske said. “Of course, time and appropriate investments will be required to answer that question.”
