Small and mighty: single-domain antibodies pack a biological punch

What are VHH antibodies?

VHH antibodies, single‑domain antibodies (sdAbs) or nanobodies, are tiny, highly stable antibody fragments. They are gaining attention, because they combine powerful biological activity with unique structural advantages that traditional antibodies don’t have. They’re small, stable, and highly engineerable, which makes them ideal for therapeutics, diagnostics, and even industrial applications. However, whilst they offer strong advantages for biological development, they also introduce complexities for development and manufacturing.

The discovery of the distinctive structure of heavy chain-only antibodies in species belonging to the Camelidae family in 1993 created interest in their variable antigen binding domain (VHH). The first FDA approved VHH therapeutic; Caplacizumab (Cablivi®) opened the door to many more programs. That interest has continued to build with five VHH‑based therapeutics, gaining global regulatory approval by the end of 2025, and more than 49 VHH sequences had advanced into clinical development.

In addition to indicators of growing clinical confidence and investment in next generation biologics, the global VHH nanobody market is growing, with CAGR estimates around 15%. This growth is driven by their promise for use in applications such as oncology, immunology, and diagnostic imaging.

VHH antibodies have been shown to accelerate progress from concept to clinic when supported by the right development infrastructure. This infrastructure is key, as they differ fundamentally from conventional monoclonal antibodies, and so they bring distinct challenges in discovery, humanization, expression, and analytical characterization. However, there are differences in structure that give VHH antibodies their potential.

What’s so different about VHH structure?

VHHs antibodies differ from traditional antibodies in several critical ways:

Small size - VHH antibodies are extremely small (12–15 kDa), allowing them to access hidden epitopes that conventional antibodies can’t. Their compact, hydrophilic structure enables improved tissue penetration, and they can even cross biological barriers such as the blood–brain barrier.

Simple but stable structure - VHHs consist of a single variable domain, making folding straightforward. They exhibit exceptional thermal and chemical stability, enabling use across challenging formulation conditions, including respiratory and digestive environments. This inherent stability also supports robust, efficient manufacturability.

Flexible engineering - The lack of a light chain gives VHHs exceptional design flexibility for multi‑specific formats. Their unique paratope geometry creates an adaptable scaffold, enabling modular use as building blocks for complex therapeutics. VHHs can be readily fused with effector domains, including enzymes, toxins, and Fc regions, to create highly functional, customizable molecules.

Low-cost manufacturing - Unlike conventional monoclonal antibodies that require mammalian expression, VHHs can be produced in simpler systems such as E. coli, yeast, and plants. This flexibility significantly shortens production timelines and can reduce overall process development costs.

What are the challenges for VHH development and manufacturing?

As this is an emerging technology, there are limited established CMC pathways compared to IgG monoclonals. Full-length monoclonal antibodies benefit from decades of GMP experience and well-defined regulations. This lack of clarity can prolong the development time for VHH antibodies.

Discovery challenges can often occur in library generation and diversity, as although library-based sdAb discovery technology is well-developed, some limitations remain, such as sequence diversity loss, difficulties in conducting functional assays, and the considerable time required.

Process development and manufacturing challenges can include issues around platform fit and expressions systems, due to the differences in the host system used. Scaling the process is often challenging as the small size of the VHH antibodies increases their risk of loss during filtration and ultrafiltration. In addition, tailored analytical methods may be required.

Where next for VHH antibodies?

VHH (single‑domain) antibodies already have strong scientific momentum, but commercial success depends on:

• Discovery quality - VHH success begins with producing high‑quality binders that match or surpass full‑length antibodies
• Engineering robustness - well‑engineered VHHs can outperform IgGs on size, tissue penetration, and manufacturability, with careful design
• Manufacturability - VHHs promise lower COGS, but only if manufacturing is optimized
• Regulatory clarity – clear regulatory pathways and comparability frameworks will be essential

VHH antibodies: they’re not just small; they are modular engineering platforms. The only limit is our imagination!