VHH antibodies, also known as nanobodies, are derived from the heavy-chain-only antibodies of camelids. These single-domain antibodies retain full antigen-binding functionality, despite their small size (~15 kDa) and lack of a light chain. Their compact structure, high solubility, and thermal and chemical stability make them favorable candidates for therapeutic and diagnostic applications.
One of the major drivers in VHH antibody engineering is the ability to construct multivalent and bispecific formats. These formats can improve tissue penetration and pharmacokinetics by extending half-life and support the development of novel mechanisms of action, including immune cell redirection, dual checkpoint blockade, and tumor microenvironment modulation.
Interest in bispecific VHH formats continues to grow, as evidenced by multiple ongoing clinical trials for oncology, inflammatory, and infectious disease indications.
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Multivalent VHH constructs consist of multiple VHH domains targeting the same or different epitopes on a single antigen. These formats increase functional avidity, enhancing binding strength and residence time, particularly important when targeting low-affinity or low-abundance antigens. For instance, bivalent VHHs against VEGF and CD38 have demonstrated improved in vivo performance, including increased inhibition of angiogenesis and enhanced complement-dependent cytotoxicity.
Bispecific VHH antibodies are engineered to bind two distinct antigens or epitopes. They enable dual-target engagement within a single molecule, facilitating new therapeutic mechanisms. Notable applications include:
Immune cell engagement (e.g., Vγ9Vδ2 T cells and NK cells)
Checkpoint blockade (e.g., PD-L1 and CTLA-4)
Blood-brain barrier translocation via receptor-mediated transport
Compared to conventional IgG bispecifics, VHH-based bispecifics are structurally simpler, easier to manufacture, and more tunable for specific applications.
Higher tissue penetration due to small molecular size
Reduced steric hindrance, facilitating access to cryptic or concave epitopes
Improved developability and stability through hallmark framework residues and disulfide bond engineering
Increased modularity in combining VHH units with Fc domains, albumin-binding domains, or other payloads
Lower immunogenic potential with humanized VHH frameworks showing >80% identity to human VH3 domains
These properties translate into a highly versatile antibody platform suitable for rapid prototyping, clinical translation, and scalable manufacturing.
Tandem fusions involve genetically linking two or more VHH domains using flexible linkers (e.g., (G₄S)n motifs). Linker orientation and domain order significantly affect binding affinity and functional output. For example, in bispecific constructs targeting CD16 and EGFR, domain positioning at the N-terminus enhanced functional performance in NK cell assays.
Fusion to the Fc region of IgG enhances plasma half-life via FcRn-mediated recycling and enables effector functions (e.g., ADCC, CDC). Examples include INBRX105, a PD-L1/CD137-targeting construct currently in Phase II trials. Fc fusions also simplify purification and analytical workflows.
Linker selection is critical for construct geometry and function. Long, flexible linkers promote interdomain mobility, while rigid linkers enforce spatial constraints. These design variables affect binding cooperativity, target specificity, and protein expression. Studies have also explored trimeric and tetravalent topologies (e.g., ATTACK trimerbodies) to increase target density sensitivity and therapeutic window.
Immuno-oncology: VHH-based bispecifics have shown efficacy in T-cell and NK cell redirection, checkpoint blockade (e.g., PD-L1/CTLA-4), and tumor microenvironment reprogramming. Constructs like LAVA-051 simultaneously engage Vγ9Vδ2 T-cells and CD1d-positive tumor cells.
Infectious disease: Multivalent VHHs have demonstrated potent virus neutralization (e.g., SARS-CoV-2) by targeting multiple conserved epitopes, reducing escape mutation risk.
Neurodegenerative diseases: By targeting transferrin receptors, VHHs enable blood-brain barrier crossing, allowing delivery of therapeutic agents into the CNS.
Diagnostic imaging: Rapid renal clearance of VHHs enables high signal-to-noise imaging with radiolabels such as 68Ga and 99mTc. Bivalent formats provide improved target accumulation in PET/SPECT imaging applications.
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Maintaining affinity and specificity in multi-domain constructs
Risk of aggregation, particularly in constructs with unoptimized linker regions or unstable VHH clones
Linker design complexity, affecting folding, solubility, and in vivo behavior
Expression platform selection, balancing yield, glycosylation needs, and regulatory compliance (E. coli, yeast, CHO)
Immunogenicity concerns, including PEAR (Pre-existing Anti-drug Reactivity) to VHH C-termini
Mitigation strategies include in silico stability screening, framework engineering, and high-throughput screening of candidate clones.
Phage display libraries (naïve, immune, or synthetic) for high-affinity VHH selection
Machine learning for epitope prediction, developability profiling, and optimization of CDR loop geometry
High-throughput screening platforms to assess construct stability, binding kinetics, and functional assays in parallel
Computational modeling (e.g., Rosetta, AlphaFold2) for domain positioning, linker conformation, and construct design
Biointron supports these workflows with its in-house VHH discovery, engineering, and expression platforms, enabling fast turnaround and optimized construct output for research and preclinical programs.
Trispecific and tetravalent formats expanding functional capacity (e.g., IL-17A/F/HSA trispecifics, VEGF/Ang2 bispecifics)
AND-gate logic antibodies for conditional tumor targeting based on dual antigen expression
Humanization frameworks reducing immunogenicity and improving clinical compatibility
Fc-engineered bispecifics for extended half-life and immune effector engagement
Synergistic therapeutic combinations, including VHH-CAR T cells and nanobody-drug conjugates
Clinical-stage molecules such as Ozoralizumab, BI836880, and KN046 exemplify the expanding therapeutic space for modular nanobody formats.
What is a VHH bispecific antibody?
A recombinant construct built from two distinct VHH domains capable of binding different epitopes or antigens within a single molecule.
What are the benefits of using multivalent VHH constructs?
Binding avidity, prolonged target engagement, and inhibition of multiple signaling pathways.
Can VHH antibodies cross the blood-brain barrier?
Yes, some VHHs can cross the blood-brain barrier (BBB) directly or be delivered indirectly, and act either on their own or by delivering an active payload into the brain.
How are tandem VHH fusions designed?
By genetically linking two VHH domains via peptide linkers, with attention to domain orientation and linker flexibility.
What are the key challenges in developing multivalent VHH antibodies?
Stability, expression yield, aggregation, and immunogenicity must be carefully managed through design and screening strategies.
References:
Wang, J., Kang, G., Yuan, H., Cao, X., Huang, H., & De Marco, A. (2022). Research Progress and Applications of Multivalent, Multispecific and Modified Nanobodies for Disease Treatment. Frontiers in Immunology, 12, 838082. https://doi.org/10.3389/fimmu.2021.838082
Mullin, M., McClory, J., Haynes, W., Grace, J., Robertson, N., & van Heeke, G. (2024). Applications and challenges in designing VHH-based bispecific antibodies: leveraging machine learning solutions. mAbs, 16(1). https://doi.org/10.1080/19420862.2024.2341443
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