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Bispecific & Multispecific Antibody Discovery for Next-Generation Biologics

Supporting Bispecifics and Multispecifics Projects Through Rational Design, Engineering, and Optimization

 

Bispecific antibodies and multispecific antibodies are a rapidly evolving class of engineered biologics designed to engage two or more targets within a single therapeutic entity. By coordinating parallel pathway modulation, physically bridging immune cells to disease-relevant targets, or conditionally activating biological functions within defined microenvironments, these formats expand therapeutic potential beyond the limits of monospecific antibodies.

 

Across therapeutic areas, bispecifics and multispecifics enable diverse biotherapeutic strategies. In oncology, predominant approaches include redirecting T cells or NK cells to tumor cells, blocking dual pathways, and delivering payload to address tumor heterogeneity and resistance. In autoimmune and inflammatory diseases, bispecifics offer the potential to simultaneously modulate multiple inflammatory pathways or activate immune-suppressive signaling to improve efficacy and safety. Beyond these areas, bispecific or multispecific fragment-based constructs are being engineered to cross the blood-brain barrier (BBB) by integrating transport, target engagement, and half-life extension functions into a single molecular architecture.

 

At WuXi Biologics, we advance bispecifics and multispecifics discovery projects with rational design, engineering, and optimization through early developability and functional characterization funnels to generating complex modalities. Whether you are choosing formats or addressing scale-up challenges, you are welcome to discuss it with us or read the following sections for a concise, application-focused guide that drives successful bispecifics and multispecifics development.

 

 

 

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3D visualization of bispecific antibodies in therapeutic antibody discovery.

Bispecifics & Multispecifics Discovery Journey

 

The bispecific and multispecific antibody discovery journey begins with target identification and biology-driven antibody discovery (when parental arms don’t exist). Once the target pair and mechanism of action are defined, projects advance to format design. Key considerations include valency, geometry, immune synapse distance, PK profiles, and production complexity to ensure the selected format aligns with the intended biology and disease indications.

 

Projects then enter pair screening and lead optimization, where binding, specificity, and cellular functional assays are evaluated with in silico analysis, biophysical characterization, poly-specificity/PK assessment, and early stability profiling to iteratively refine leads and reduce downstream risk. Sequences will be changed as needed based on these data. In vivo pharmacology studies may be introduced during or after optimization depending on arm maturity and MOA strategy.

 

This data-driven workflow supports progression into cynomolgus studies and enables confident preclinical candidate selection and validation for bispecific and multispecific antibodies.

 

 

 

Workflow diagram showing bispecifics discovery from target discovery and molecular engineering to expression, functional evaluation, and lead selection.

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How We Support Bispecifics & Multispecifics Discovery

Bispecific and multispecific projects require close coordination across discovery, engineering, production, and functional evaluation, with early identification of developability risks and careful balancing of efficacy and safety. Successful projects depend on rational format selection, optimal pairing and format screening, transition from high-throughput to scalable production, and MOA-aligned functional and translational study design. A one-stop, customized workflow helps generate well-characterized candidates suitable for preclinical development.

 

 

Antibody Design & Engineering
  • Biology-guided antibody design and platform selection with extensive drug development experience
  • Case-specific engineering (e.g., CrossMab and scFv-Fab) to improve developability and efficacy
BsAb Production
  • HTP production of double-tag and tagless bsAbs for optimal pairing screening
  • Chain ratio optimization and LC-MS-guided purification for high titer and purity
Early Developability Assessment
  • Rapid, HTP, low-material workflow to support lead optimization and reduce late-stage CMC risks
  • Fit-for-purpose panels covering in silico, poly-specificity/PK-assessment, biophysical, and stability
In Vitro Assays
  • MOA-driven assay development across cellular, biochemical, immune, and Fc effector functions
  • Evaluation of binding, cytotoxicity, potency, response quality, and durability
In Vivo Pharmacology
  • Science-driven PK/PD/Tox, efficacy, and histology studies in oncology, immunology, and metabolism
  • NHP PK/PD/Tox studies in 6-11 weeks without scheduling delay

 

 

Challenges & Next-Gen Solutions Throughout Discovery Journey

Parental Antibody Discovery for Challenging Targets

Bispecifics and multispecifics discovery begins with selection of the parental arms based on the biology and mechanism, with rational considerations such as target co-expression and spatial proximity, pathway relationship, epitope type (soluble vs. membrane), antigen density, tissue penetration limits, and local physicochemical environment (e.g., pI). Leveraging strong expertise in classical immune-redirecting targets, e.g., anti-CD3 × tumor-associated antigen, and challenging targets lacking existing parental antibodies, e.g., multi-pass membrane proteins or low-affinity targets (Case Study 1), we support high-quality parental antibody discovery aligned with the intended MOA and bispecific format requirements.

 

Case Study 1: TCR Affinity Maturation & TCR-TCE Production with PBMC-Based Functional Characterization

Among challenging modalities, TCR-based T-cell engagers (TCR-TCEs) present a representative example where parental binder discovery requires specialized optimization strategies. Since the TCR arm functions as one binding arm in TCR-TCE formats, achieving sufficient TCR affinity is a central requirement for effective TCR-TCE discovery. However, natural TCRs typically exhibit micromolar affinity due to thymic selection constraints, which may limit their effectiveness against tumors expressing low levels of peptide-HLA complexes. To address these limitations, discovery workflows combine phage display with affinity maturation, structure-guided engineering, and high-throughput (HTP) ranking and production to obtain high-affinity, high-specificity TCRs. The optimized TCRs are then treated as a regular antibody-like arm within the bispecific formats to enable robust production and downstream functional characterization.

Case study illustrating TCR affinity maturation achieving ~10,000-fold improvement, followed by high-throughput CHO production of a TCR-TCE.

 

Key Considerations and Challenges in Bispecifics and Multispecifics Format Design

 

Format design for bispecific and multispecific antibodies follows shared core principles: constructs are engineered to achieve the desired efficacy, safety, pharmacokinetics (PK), and developability profiles. Formats are broadly categorized as IgG-like and non-IgG-like. IgG-like formats retain Fc-mediated stability, half-life, and purification advantages but are larger and may have reduced tissue penetration. Non-IgG-like formats assemble linked binding modules (Fab, scFv, and/or VHH) into compact architectures that improve penetration but some exhibit faster clearance and lower stability (Wu & Demarest, Methods 2019).

 

Schematic showing how arm properties and bsAb format control cytotoxicity and cytokine responses of bispecific T cell engager.

  • Biology and PK: Once target pairs are selected, biological requirements and the desired pharmacokinetic (PK) profile become key factors guiding detailed format design.

     

    • The distance of the epitope from the cell membrane can influence the optimal antibody format. Compact formats, such as diabodies, are often selected when targeting membrane-distal epitopes, whereas IgG-like formats are typically chosen for membrane-proximal epitopes.

    • Arm-specific properties must also be considered together with format geometry. For example, in T-cell engager projects, the epitope position and affinity/avidity of the tumor-targeting arm must be coordinated with the anti-CD3 binding arm and the overall format to ensure proper immune synapse formation while maintaining an acceptable safety profile.
    • From a PK perspective, diabody-based constructs generally exhibit shorter half-life than IgG-like formats, and scFv-based designs are often less stable than nanobody- or Fab-based architectures.

 

  • Production Complexity: Production complexity should be considered, such as Duobody increasing the burden of scale-up via multi-system expression and in vitro assembly. A major cross-format challenge remains chain mispairing, particularly in multi-chain architecture. Technologies such as knobs-into-holes and CrossMab help enforce correct assembly, but non-functional species and impurities can still arise and must be carefully characterized during downstream purification.

 

  • Multispecific Extensions (e.g., Trispecifics): Multispecific constructs are often introduced to enhance target selectivity, enable cell bridging or trafficking, or incorporate additional functional modules (e.g., scFv-Fc fusions, tandem scFv or nanobody architectures, or VHH/scFv appendages on a bispecific scaffold). Design begins with target-related considerations, such as the spatial distance between targets and their accessibility on the cell surface, which influence feasible format geometry and domain spacing. Binding arms must then be optimized for affinity, avidity, and domain orientation to enable coordinated simultaneous engagement. However, adding additional binding modules increases structural complexity and may introduce challenges such as higher expression burden, chain mispairing, and reduced stability. These factors can also influence tissue penetration, efficacy, and pharmacokinetic behavior. As a result, multispecific constructs require careful control of assembly and purification to ensure correct molecular composition and product quality.

 

  • Case-Specific Design Considerations: Beyond structural architecture, format design should also consider immunogenicity, scalability, regulatory readiness, IP and licensing constraints, and flexibility for future format iteration. Practical design decisions are therefore case-specific.
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Pair Screening Empowered by High-Throughput Production

Small-scale, high-throughput (HTP) expression enables parallel screening of diverse bispecific constructs. Leads are ranked based on binding affinity, specificity, assembly quality, and functional performance in cell-based assays, allowing rapid down-selection to the most promising pairings for further optimization.

 

At this stage, high-throughput production is important to facilitate rapid screening. BsAbs with zero or one light chain readily support HTP production for functional evaluation. In contrast, four-chain bispecifics present light-chain mispairing challenges, so dedicated pairing and expression strategies are applied to enable tagless HTP production. This is particularly valuable when material is needed for bispecific ADC conjugation and in vitro & in vivo studies (Case Study 2).

 

Case Study 2: High-Throughput Production of Four-Chain Bispecific Antibodies for ADC Conjugation, In Vitro Assays, and In Vivo Studies

Bispecific ADCs present unique compounded design and development complexity because both binding arms and the payload conjugation strategy must function together. Before payload conjugation, the bispecific scaffold is first engineered and validated as a functional bsAb to ensure alignment with the intended MOA and target biology. This requires rapid screening of multiple constructs for conjugation compatibility, dual binding, and internalization. As a result, high-throughput screening, production, and cell-based assay workflows are more demanding than in conventional ADC projects.

 

This case study highlights a high-throughput workflow for producing and screening 26 bispecific antibodies for ADC conjugation and downstream in vitro and in vivo evaluation. High-throughput, tagless bsAb production enabled by codon optimization and customized purification workflows, combined with parallel conjugation, allowed rapid dual binding, internalization, and cytotoxicity evaluation. This one-stop workflow supports rapid pairing selection and functional ranking of bispecific ADC leads prior to scale-up and preclinical characterization.

 

High-throughput bispecific ADC workflow showing rapid bsAb production, parallel conjugation, FACS binding, internalization, and cytotoxicity screening across multiple bispecific antibody pairings.

 

 

Overcoming Chain Mispairing in Bispecific and Multispecific Antibodies with LC-MS-Guided Purification

After optimal pairing and format screening, mispairing risks and overall production complexity should be considered in bispecifics and multispecifics down-selection. Follow-up expression and purification scouting from pilot scale are typically performed to align formats and to generate sufficient material suitable for extended characterization and in vivo studies. During scale-up or gram-level expression, chain ratio optimization is first applied to achieve desired yield and reduce incorrect assembly in the starting materials. Purification workflows then combine affinity capture with multi-step polishing based on pI and hydrophobicity, such as CEX, HIC, and mixed-mode chromatography, to remove aggregates, half antibodies, and mispaired species. Intact MS plays a central role throughout purification by confirming correct bispecific or trispecific assembly and detecting chain loss, mispairing, homodimers, and other byproducts (Case Studies 3 and 4).

 

Case Study 3: High-Purity CrossMab Production Using High-Titer CHO Expression and LC-MS-Guided Purification

Asymmetric constructs are prone to chain mispairing and subunit stoichiometry imbalance, which can generate half antibodies, homodimers, and LC mispairing. To address this, engineered pairing strategies such as CrossMab/domain crossover, knobs-into-holes, charged pairing, and scFv-Fab, are used to facilitate correct assembly. In parallel, LC-MS-guided purification workflows are applied to directly confirm heterodimer formation and detect mispaired species, enabling efficient removal of byproducts and improved overall yield and purity.

 

This case study illustrates a CrossMab production workflow using high-titer CHO transient expression followed by CEX and HIC polishing to resolve mispaired and homodimer species. Analytics by SEC-HPLC, SDS-PAGE, and Intact MS confirm correct assembly, 100% heterodimer purity, and <0.01 EU/mg endotoxin levels within a four-week timeline, supporting rapid bsAb discovery and downstream studies.

 

CrossMab bispecific antibody production case study showing CEX and HIC purification steps, SDS-PAGE and SEC-HPLC results, and Intact Mass confirmation demonstrating high heterodimer purity.

 

 

Case Study 4: LC-MS-Guided Purification Enables High-Purity Production of a Complex 2+1 Bispecific Antibody at Liter Scale

This case study demonstrates purification of a 2+1 bispecific antibody with significant byproduct heterogeneity from LC mispairing, chain loss, and half-antibody species. Such asymmetric, multi-chain formats are structurally similar to many IgG-like trispecific formats and therefore exhibit comparable assembly and heterogeneity risks. Post-Protein A analysis by SEC-HPLC, SDS-PAGE, and intact LC-MS confirmed a complex impurity profile typical of structurally asymmetric 2+1 bispecific formats. A CEX-HIC polishing workflow was introduced to remove mispaired and truncated variants. Final material from 5 L CHO culture achieved 1.05 g/L titer, 926 mg yield, 99.75% monomer purity, and 97% heterodimer purity within 4 weeks. This workflow illustrates how increasing molecular complexity in bispecific architecture leads to more complex byproduct profiles and necessitates LC-MS-guided purification strategies.

 

A complex 2+1 bispecific antibody showing multiple LC mispairing and half-antibody byproducts after Protein A, followed by CEX-HIC purification and LC-MS-guided polishing to achieve high heterodimer purity at 5 L transient scale.

 

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Often-Overlooked Early Developability and Functional Insights in Lead Optimization

Lead optimization focuses on improving affinity, selectivity, stability, efficacy, safety, and PK performance through MOA-aligned functional testing and early-stage developability assessment. These assays not only support selection of the most promising candidates but also provide data-driven guidance for molecular engineering and optimization.

 

Early developability assessment is performed not only on individual arms, but also on full bispecific molecules. Typical checks include sequence liabilities, PTM risks, early stability, poly-specificity/PK assessment, biophysical, and forced degradation studies to guide lead optimization and reduce late-stage failure (Case Study 5).

 

Functional assays are designed based on MOA and indications, such as cytokine release, pathway modulation, T cell killing, and reporter gene assays. Immune engager projects typically require multiple rounds of TAA/CD3 affinity and ratio tuning, with functional and developability checks performed in each optimization cycle. In vivo studies may be performed during or after lead optimization depending on how well each arm is characterized and the MOA strategy. PK behavior is format-dependent and influenced by purity, solubility, pI, valency, FcRn binding, immunogenicity, and target-mediated drug disposition (TMDD). Fc engineering or adding albumin-binding modules are often needed for half-life extension (Case Study 6). Efficacy model selection needs to match MOA and follow strategic considerations and study design. For example, immune-redirecting bispecifics often require humanized or immune-reconstituted models such as CDX/PBMC or CDX/hCD34 systems. Ultimately, PK/PD, toxicology, and efficacy data support confident preclinical candidate selection for bispecific and multispecific antibodies.

 

Case Study 5: Eliminating Bispecific Antibody Precipitation Through Structure-Guided Re-Engineering and Developability Assessment

This case study illustrates how early developability assessment can help identify and de-risk common liabilities in bispecific antibody discovery. Initial stability testing revealed severe agitation-induced aggregation, a frequently observed challenge in complex antibody formats. Subsequent in silico mapping and structural analysis identified conformational and surface property liabilities in antibody B. Structure-guided residue substitutions were then introduced to mitigate these risks. The optimized variant showed improved thermal stability (Tm shift from ~63 °C to ~68 °C) while preserving FACS binding and reporter gene activity, resulting in a bispecific antibody with reduced precipitation and improved developability.

 

Structural analysis and engineering improve bispecific antibody thermal stability and maintain binding and function after optimization.

 

 

Case Study 6: Anti-HSA VHH Enabling Half-Life Extension for Bispecific T-Cell Engager in Mouse PK Studies

Many fragment-based and immune-redirecting bispecific formats lack Fc-mediated recycling and therefore show rapid systemic clearance during early functional assessment. Half-life extension strategies typically incorporate Fc engineering or albumin-binding domains, followed by iterative optimization to improve pharmacokinetics while maintaining potency and safety margins, particularly for highly potent immune-engaging constructs.

 

This case study evaluates integration of an anti-HSA VHH molecule into a bispecific T-cell engager to build a trispecific antibody, extending exposure in a mouse model. ELISA measurements showed extended half-life comparable to a benchmark bispecific antibody. The workflow provides a practical framework for designing half-life-extended, immune-engaging antibodies with improved mouse PK performance.

 

Mouse PK study showing anti-HSA VHH-mediated half-life extension in a bispecific T-cell engager, with ELISA-based half-life comparison.

 

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Growing Opportunities in Bispecifics & Multispecifics Development

The clinical and preclinical bispecific landscape is increasingly shaped by mechanism-driven target pairing, format specialization, and data-driven considerations. Programs are moving beyond proof-of-concept immune redirection toward integrated pathway modulation and improved tumor selectivity into a single molecular architecture.

 

High-Impact Target Pairings:

  • EGFR × MET: The approval and continued clinical expansion of amivantamab, an EGFR/MET bispecific antibody, has established dual receptor targeting as a validated strategy in non-small cell lung cancer (NSCLC). This class highlights how coordinated blockade of parallel oncogenic pathways can overcome resistance mechanisms and improve clinical response. Follow-on programs such as emifentamab (EGFR/MET) further illustrate growing investment in receptor co-targeting formats.

 

  • PD-1/PD-L1 × VEGF: A rapidly expanding class of PD-1/PD-L1 × VEGF bispecific antibodies is advancing through global clinical trials, reflecting strong rationale for coupling immune checkpoint inhibition with angiogenesis modulation. Programs such as BNT327, JS207, and SSGJ-707 demonstrate how dual-pathway engagement may enhance tumor immune infiltration while reshaping the tumor microenvironment.

 

  • CD3-Based T Cell Engagers: BiTE-like formats and CD3-based T cell engagers, including clinically established classes such as BCMA/CD3 and CD19/CD3 bispecifics, and CD19/CD3/BCMA trispecifics, continue to expand across hematologic and solid tumor indications. Format engineering increasingly focuses on tuning CD3 affinity, synapse geometry, and half-life extension to optimize potency while managing cytokine release risks.

 

Stay Current on BsAb Market Trends:

 

Quarterly newsletter covers news, trends, and insights in bispecifics and multispecifics field.

 

The growing list of FDA-approved bispecific antibodies and the surge in late-stage clinical programs across diverse disease areas highlight sustained momentum for this modality class. Investment continues to concentrate around validated mechanisms while enabling exploration of novel pairings in inflammation, infectious disease, and multiple indications.

 

For up-to-date insights into clinical trial updates, emerging players, strategic shift, and competitive landscapes, download our quarterly newsletter Bispecifics Market Watch for comprehensive market trends and insights.

 

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Advance your bispecifics and multispecifics projects with our one-stop, modular CRO services. By uniting molecular design and engineering, high-throughput to scalable production with premium quality, advanced analytical characterization, and mechanism-driven functional evaluation, our innovative platforms enable confident progression of diverse candidates from discovery through preclinical development.

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