Virus-Like Particles: The Empty Viral Shells Behind Some of Modern Medicine’s Most Elegant Technologies

June 22, 2026

Virus-Like Particles: The Empty Viral Shells Behind Some of Modern Medicine’s Most Elegant Technologies

Author: Martin Trinker

A virus is one of nature’s most efficient delivery systems: compact, highly organized, and optimized to protect and deliver genetic information into host cells. Its surface architecture often contains repeating molecular patterns that the immune system can detect – even though many viruses have evolved sophisticated ways to hide, disguise or suppress that recognition. That is exactly what makes viruses dangerous – but it is also what makes them scientifically useful. Now imagine keeping the useful architecture while removing the infectious core.

That is the idea behind virus-like particles, or VLPs: nanoscale protein shells that look structurally like viruses but do not contain the viral genetic material needed to replicate. They are, in simple terms, empty viral lookalikes. To the immune system, they can appear convincing enough to trigger a strong response. To a manufacturer, they can be engineered as modular particles. To biotechnology, they offer a bridge between vaccines, targeted delivery, diagnostics and nanomedicine. VLPs are widely described as self-assembling structures made from viral structural proteins that mimic native viruses but are non-infectious. This combination explains why VLPs have become one of the most important nanoparticle formats in modern biotechnology. Their use is already proven in licensed human vaccines, and their future may extend much further: targeted transport, antigen display, cancer immunotherapy, diagnostic tools and programmable protein nanoparticles.

What exactly is a VLP?

A virus-like particle is not a weakened virus. It is not a live vaccine. It is not a viral vector. A VLP is usually made from one or more viral structural proteins that self-assemble into a particle resembling the outer architecture of a virus, but without the infectious genome. That distinction is important. A live-attenuated vaccine uses a weakened version of a pathogen. An inactivated vaccine uses a killed pathogen. A viral vector uses a virus or virus-derived delivery vehicle to carry genetic information. A VLP, by contrast, is mainly a protein-based particle that presents viral geometry without viral replication. Reviews describe VLPs as particles that mimic viral particles formed from self-assembly of structural proteins and emphasize that they lack viral genetic material.

Why does the immune system care so much about this shape? Because it is built to detect repetitive molecular patterns. Many viruses present highly ordered arrays of proteins on their surface. VLPs copy this architecture: they display antigens repeatedly and densely, which can cross-link immune receptors and produce strong immune recognition. In vaccine science, this repetitive display is one of the reasons VLPs can be so immunogenic even without being infectious. VLP reviews consistently highlight their ability to stimulate humoral and cellular immune responses and their use as strong vaccine platforms. A helpful everyday analogy is this: a VLP is like an eggshell without the chick inside. The recognizable outer form is present, but the living, reproducing core is absent. For the immune system, that outer form can already be enough to learn what to recognize. But the analogy goes further: because the shell is empty, it can also be engineered as a tiny container or display platform. Researchers can decorate the outside with selected antigens, epitopes or targeting signals, or explore the inside as a space for cargo such as drugs, nucleic acids, enzymes or imaging molecules. This is why VLPs are interesting not only for vaccines, but also for targeted delivery, diagnostics and nanobiotechnology.

The origin story: from hepatitis B particles to recombinant vaccines

The history of VLPs begins with hepatitis B. In the late 1960s, researchers studying sera from people infected with hepatitis B observed small particles associated with the hepatitis B surface antigen. These particles helped establish the idea that viral structural proteins could form non-infectious particle-like assemblies. Later, recombinant DNA technology made it possible to produce hepatitis B surface antigen in yeast, where it self-assembled into particles that could be used as a vaccine antigen. This was a landmark shift. The recombinant hepatitis B vaccine Recombivax HB was approved in 1986 and is widely recognized as the first recombinant DNA vaccine for human use. That step mattered for two reasons. Scientifically, it showed that a viral surface protein could self-assemble into a safe, highly useful vaccine particle. Industrially, it proved that recombinant production could replace older approaches that relied on human plasma-derived material. It was one of the moments where biotechnology began to move vaccines from “harvested from biological material” toward “engineered and manufactured.”

The next major public milestone came with HPV vaccines. Human papillomavirus vaccines use the HPV L1 major capsid protein, which self-assembles into VLPs. In June 2006, the US FDA approved Gardasil, a quadrivalent HPV vaccine targeting HPV types 6, 11, 16 and 18, for prevention of diseases including cervical cancer associated with those types. This was not just a technical success; it changed the cancer-prevention landscape by using a VLP-based vaccine to prevent infections that can lead to cancer.

VLPs then entered another global health story: malaria. RTS,S/AS01 (“MosquirixTM”) and R21/Matrix-M are malaria vaccines based on hepatitis B surface antigen particle concepts that display malaria circumsporozoite protein antigen components. The World Health Organization’s 2024 malaria vaccine position paper includes recommendations for RTS,S/AS01 and R21/Matrix-M for reducing malaria morbidity and mortality in children in areas of moderate and high malaria transmission.

The broad lesson from this history is simple: VLPs are not speculative. They have already delivered licensed vaccines and public-health impact. What is changing now is the ambition: from individual VLP vaccine products toward flexible VLP platforms.

Why VLPs are so attractive as platforms

The word “platform” is sometimes overused in biotechnology, but for VLPs it is appropriate. A VLP is not only a product; it can be a scaffold. Its surface can be engineered. Its internal cavity can be explored for loading strategies. Its geometry can be used to present antigens, ligands or targeting motifs in a controlled arrangement. This is why VLPs appear in so many areas of current research and development. In vaccines, VLPs can present antigens in a repetitive and highly ordered format, often improving immune recognition compared with soluble proteins and there are many VLP-candidates in preclinical and clinical development. In targeted delivery, VLPs are attractive because they are nanoscale containers or carriers whose surfaces can, in principle, be modified to interact with selected cells or tissues. For this purpose, it’s important to insert specific epitopes on the VLP surface to enable targeted transport.

In diagnostics and nanobiotechnology, VLPs can act as defined, repetitive protein nanoparticles. Their uniformity and modularity make them interesting for assay development, display technologies and nanoscale materials. From an industry perspective, the appeal is the same across applications: VLPs offer biological recognition, nanoscale order and engineering flexibility in one format.

If VLPs are so promising, why isn’t everything already VLP-based?

Because the particle is only half the story. The other half is manufacturing. Making a VLP is more complicated than making a single soluble protein. The protein must be expressed, purified and assembled into the correct particle. It must have the right morphology, size distribution, structural integrity and surface presentation. And if the VLP is intended as a delivery vehicle, the challenge becomes even greater: the cargo must be correctly loaded, protected during processing, retained during storage and transport, and remain functionally available at the intended target. An “empty shell” is useful for some vaccine and display applications – but for drug, nucleic-acid, enzyme or imaging-cargo delivery, particle formation and cargo incorporation have to be controlled together. For vaccine or medical applications, host-derived contaminants must also be carefully controlled. All of this has to be achieved at acceptable cost, yield, purity and reproducibility. Different production hosts are used today, and each has a rationale. Yeast has a strong track record, including recombinant hepatitis B or and other VLP vaccines. It is robust, scalable and eukaryotic, but product-specific optimization and post-translational differences can matter.

Insect-cell systems, often using baculovirus vectors, are widely used for complex VLPs and viral-vector-related products. They can support more complex protein expression than bacteria and are often considered scalable alternatives to mammalian cells, but they involve more complex cell culture and process development than simple bacterial fermentation. Recent industry-facing discussions describe insect-cell expression as a scalable alternative to mammalian cells for viral vector and VLP manufacturing, while still emphasizing the manufacturing-process-development challenge. Plants can produce VLPs and offer interesting scalability concepts, but plant-based systems require specialized cultivation, extraction and downstream workflows, and product timelines can depend strongly on the platform.

Mammalian cells can provide human-like post-translational processing and are useful for complex particles or proteins requiring specific folding and modifications. But they are generally associated with higher media and process costs, slower growth and more complex scale-up than microbial systems. E. coli is the contrasting option: fast growth, well-understood genetics, comparatively low-cost cultivation and highly established fermentation infrastructure. The central industrial question, however, is: can we combine the biological promise of VLPs with the speed and cost advantages of E. coli?

Why E. coli is so attractive - and why it is technically difficult

For many recombinant proteins, E. coli is the default workhorse. It grows fast, reaches high cell densities, is genetically tractable, and can be run in inexpensive media compared with many eukaryotic systems. In early-stage development, it also supports rapid design-build-test cycles.

But VLP production in E. coli has a common obstacle: capsid or particle-forming proteins can aggregate into inclusion bodies. Inclusion bodies are dense intracellular protein aggregates. They can be useful because they sometimes contain large amounts of target protein and can simplify initial capture. But they also create a downstream problem: the protein must be solubilized, purified and refolded into a functional, assembly-competent form.

This is not a minor detail, since retrieving active, correctly folded protein from E. coli inclusion-bodies is a major manufacturing challenge requiring optimization of both upstream and downstream processing. Also, protein refolding often suffers from precipitation and low recovery yields, and refolding still commonly requires trial-and-error experimentation.

For VLPs, the challenge is even more demanding than “recover a folded protein.” The protein must refold and assemble into particles with structural integrity. That means the process has to manage several linked steps: expression, inclusion-body processing, denaturing purification, contaminant removal, refolding and assembly.

Why manufacturing know-how matters

In biotechnology, production headlines often focus on expression: can the host cell make enough protein? For VLPs, that is only the first question. A high expression level is not enough if most of the product is lost during refolding. A promising particle design is not enough if the preparation contains host-cell contaminants. And a clever surface-display concept is not enough if the assembly workflow depends on slow, multi-stage dialysis that is difficult to scale. This is because VLPs are not ordinary soluble proteins. They belong to the broader class of bionanoparticles – together with viruses, exosomes, extracellular vesicles and other nanoscale biological assemblies. In these products, quality is not defined only by the amino-acid sequence. It also depends on particle structure, size distribution, composition, biological activity, surface properties, purity and, in delivery applications, correct cargo loading.

That makes process development unusually demanding. In cell-culture-based production of therapeutic viruses or VLP, host cells may also release other bionanoparticles such as exosomes, apoptotic bodies, unknown vesicles or adventitious viral particles. Some of these impurities can be physically very similar to the target product, especially for enveloped bionanoparticles, while having completely different biological effects. Separating, identifying and controlling such particles is therefore one of the central challenges in the field.

For E. coli-based VLP production, the challenge looks different but follows the same logic: the process must be understood as an integrated chain. Capsid proteins may be produced at high levels but aggregate into inclusion bodies. These must be solubilized, purified under denaturing conditions, freed from E. coli-derived contaminants, refolded into assembly-competent form and finally assembled into structurally intact particles. Every step influences the next. Losing control at one point can mean losing yield, purity, particle integrity or functionality.

That is why a successful VLP platform has to answer several questions at once: Can we express enough material? Can we remove host-derived impurities efficiently? Can we refold the protein with minimal loss? Can we assemble intact particles in a simplified and scalable way? Can we prove particle quality with suitable analytics? And, if the particle is meant for delivery, can we also control functionalization and cargo incorporation?

acib’s wider bionanoparticle toolbox: complementary expertise beyond E. coli

The E. coli platform presented in this blog focuses on microbial VLP production: expression, inclusion-body handling, denaturing purification, refolding and assembly. Separately, acib has established a broader bionanoparticle process-development environment for cell-culture and virus-related applications, including mammalian and insect-cell processes.

This complementary toolbox is relevant for partners working with more complex bionanoparticles such as viruses, enveloped VLPs, extracellular vesicles or other cell-culture-derived particles. It includes scalable benchtop and lab-scale bioreactor systems for cell culture and virus applications, single-use options, ATF-based cell-retention/process-intensification, preparative chromatography with online light-scattering detection, pilot-scale continuous ultracentrifugation, A4F/HPLC coupled to UV-MALS-DLS-RI detection, nanoparticle tracking analysis and microflow cytometry.

In other words, acib combines two complementary strengths: a dedicated E. coli workflow for suitable customizable VLP scaffolds, and a wider mammalian/insect-cell bionanoparticle toolbox for complex particle products and advanced purification/analytics. This distinction matters because the right production platform depends on the particle’s biology, required modifications, quality attributes and scale-up needs.

acib’s approach: a modular E. coli workflow for customizable VLPs

In regard to the modular E. coli-based production platform for virus-like particles, the goal is to address the main microbial manufacturing bottlenecks – expression, purification and assembly – so that targeted, customizable VLPs become more accessible for biotechnology and nanomedicine applications. The workflow is designed around the reality that many capsid proteins will not be conveniently soluble. Instead of treating inclusion-body formation only as a failure, the platform focuses on recovering value from inclusion-body-derived material: efficient removal of E. coli contaminants under denaturing conditions, followed by refolding into particles with high structural integrity through a simplified assembly step.

A key point is that acib’s approach circumvents the need for multi-stage dialysis in the assembly workflow. That matters because multi-stage dialysis can be slow, labor-intensive and difficult to scale. The acib concept aims to simplify the transition from solubilized protein to structurally intact particles.

The platform is also not limited to making “empty shells.” acib has demonstrated insertion of specific epitopes on the VLP surface to enable targeted transport, with strong potential for extension to additional targeting modalities.

In plain language: acib is building a practical and scalable route from E. coli expression to customized, structurally intact VLPs – with the downstream bottlenecks treated as the core engineering problem.

Why surface customization matters

The surface of a VLP is where much of its value lives. In vaccines, surface display determines how antigens are presented to the immune system. In targeted delivery, surface motifs can influence where particles go. In nanobiotechnology, surface chemistry determines how particles interact with sensors, cells, matrices or other biomolecules. This is why “customizable VLPs” are more than a marketing phrase. A platform becomes truly useful when it can be adapted: different epitopes, different targeting motifs, different scaffolds, different analytical requirements. acib offers tailored insertion of epitopes on the VLP surface to enable targeted transport. That is a crucial step toward partner-specific applications, because it means the platform is not only about lower-cost production, but also about functional engineering.

Why this matters now

Three forces are converging. First, VLPs have clinical credibility. Hepatitis B, HPV and malaria vaccine examples show that VLP-based concepts can become real products and public-health tools. Second, the application space is expanding. VLPs are no longer only “vaccine shells.” They are being explored as antigen-display systems, carriers, targeted delivery tools and protein nanoparticles for nanobiotechnology. Third, manufacturing pressure is increasing. If VLPs are to move into more indications, more personalized or targeted formats, and more cost-sensitive markets, production platforms must become faster, more flexible and more affordable. Reviews on VLP production repeatedly emphasize that each host system has advantages and disadvantages, and that production platform choice remains a central challenge for VLP development.

This is where E. coli has strategic appeal. It might not be the right host for every VLP, especially when complex eukaryotic modifications are essential. But when the particle design is compatible with bacterial production, E. coli can offer speed, cost efficiency and process familiarity that are highly attractive for industrial development.

Who should be interested?

This technology is relevant for companies and organizations working on VLP-based vaccines, antigen-display systems, targeted delivery vehicles, diagnostic particles or nanobiotechnology tools. It is especially relevant if the current bottleneck is not the scientific idea, but the manufacturing route: poor soluble expression, inclusion-body formation, product loss during refolding, difficult contaminant removal, slow dialysis-based workflows, or uncertainty around particle assembly. For a company with a promising VLP concept, the core question is often brutally practical: can we make enough of it, at the right quality, at a cost and process complexity that makes development worthwhile? acib’s platform is designed to help answer that question.

Current status: acib is looking for industrial partners

acib has established a flexible laboratory workflow for E. coli-based VLP production and assembly, including optimized expression and purification, efficient removal of E. coli contaminants under denaturing conditions, refolding into structurally intact particles via a simplified assembly step, and surface epitope insertion for targeted transport.

The E. coli workflow is complemented by acib’s separate bionanoparticle process-development environment for mammalian and insect-cell-based systems. This broader toolbox includes cell-culture bioreactors, process-intensification tools, preparative chromatography with online light-scattering detection, pilot-scale continuous ultracentrifugation, A4F/HPLC coupled to UV-MALS-DLS-RI detection, nanoparticle tracking analysis and microflow cytometry. It is especially relevant for partner projects involving more complex cell-culture-derived bionanoparticles, while the E. coli platform remains the best route for suitable microbial VLP scaffolds.

The next step is partner-specific translation: adapting the platform to selected VLP scaffolds, target epitopes, quality requirements and application needs. acib is seeking industrial partners interested in co-developing tailored VLP production workflows for vaccine development, targeted delivery, diagnostics and nanobiotechnology. The aim is straightforward: make VLPs easier to customize, easier to manufacture and more realistic to scale. VLPs are too promising to be held back by manufacturing bottlenecks. If you are developing a VLP-based vaccine, delivery system, diagnostic particle or nanobiotechnology tool, acib is ready to explore a tailored path from promising particle concept to a manufacturable, quality-controlled workflow.

Picture by acib