VHH Antibodies

The science behind VHH antibody structure and function.

What are VHH antibodies?

VHHs are the smallest known, naturally occurring, antigen binding antibody fragment. In practice, this means they are a lot like full-length antibodies but smaller, simpler, and more robust.

Originally isolated from camelid species in the 1990s, these proteins represent the antigen binding region (VH domain) of a Heavy chain-only antibody.

Schematic showing the difference between a full length IgG antibody and a VHH

VHH antibodies are often called by other names, but as proteins they all have identical origins and structure. VHHs are also known interchangeably as:

  • nanobodies (trademarked as Nanobodies® by Ablynx in 2003)
  • heavy-chain single domains
  • single domain antibodies, or sdAbs
  • heavy chain only variable domains

These early drugs were discovered using llama immunisations, but at Isogenica we mine the largest, most diverse synthetic VHH libraries on the market for pre-humanised leads using well-characterised, pre-defined frameworks.

The difference between VH and VHH antibodies

All antibodies have variable (V) regions, which is where the antigen binding function comes from. The part of the antibody that directly comes into contact with the antigen is known as the “paratope”.

In traditional Y-shaped antibodies, including human antibodies, the paratope is usually made up of two halves – one from the heavy (H) chain and one from the light (L) chain. A VH antibody is the half of this variable region paratope that comes from the heavy chain.

As the name suggests, heavy chain only antibodies lack a light chain. This means that all their antigen-binding activity is concentrated into just one place – the VHH domain.

The other important difference between VH and VHH antibodies is in their biochemistry. Because VH domains need to pair with a VL variable light chain domain to build their paratope, they have a “sticky” hydrophobic patch. The role of this hydrophobic surface is to stick to a similar surface on the VL domain, keeping the paratope stable.

However, when you try to express just one of these domains by itself, they can be prone to aggregation or mispairing. This can cause manufacturing or safety issues during drug development, and needs to be screened for carefully.

VHH Features

Isogenica VHH Applications Graphic

At around 10% of the size of a traditional monoclonal antibody, VHHs display the same highly sensitive and specific binding. Because all this binding is concentrated into a single protein unit, they are very simple proteins – easy to make rapidly from microbial or mammalian systems.

Unlike full-length antibodies, they do not naturally form pairs and prefer to exist in a monomeric, soluble form – ideal for therapeutics manufacture.

They are also not associated with complex immune modulatory functions which some full IgG therapies suffer from.

The big reason that Isogenica sees VHHs as special is their versatility. Because of their simplicity, they can easily link to other biomolecules, including other VHHs, for numerous applications.

With a decade of synthetic VHH discovery experience, Isogenica is building on this expertise to develop internal drug assets for oncology. To explore the many different therapeutic and diagnostic uses for VHHs, including Isogenica’s multi-specifics pipeline, check out our applications pages, and for answers to FAQs on VHHs.


VHH in the clinic

VHH single domains are one of the most accepted next generation antibody therapeutic formats.

Cablivi (caplacizumab) was the first FDA-approved single domain antibody therapeutic in 2019.

So far, VHH are being developed as:

  • Monomers 
  • Bi-specifics
  • Half-life extended
  • CAR formats
Cartoon of the different structures of the first 4 approved VHH drugs.
DrugSponsorDomain PropertiesTargetIndicationStatus
CaplacizumabSanofi (Ablynx)​VHHvWFaTTPApproved
LCAR-B38MLegend/JanssenBi-paratopic VHH CAR-TBCMAMultiple MyelomaApproved
OzoralizumabTaisho (Ablynx)VHHTNFRAApproved


Jiangsu Simcere Parmaceutical



Cancer immunotherapy


GefurulimabAlexionVHHC5MyastheniaPhase III
M1095Moonlake ImmunVHH Bi-specificIL-17A
PsoriasisPhase IIb
BI836880Boehringer Ingelheim (Ablynx)VHH Bi-specificVEGF, Ang2NSCLCPhase II
HPN328HarpoonVHH-scFc Tri-specificDLL3SCLCPhase II

Extending half-lives of VHH antibodies

Because VHHs are small, they can be cleared quickly from the bloodstream. This can be a useful feature for some applications, but often a longer plasma half-life is desirable.

Our VHH-based ISOXTEND® technology protects VHH biotherapeutics from kidney clearance by ‘piggybacking’ onto the serum albumin endocytic recycling pathway, significantly extending therapeutic half-life.


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