Natural Nanoparticles with Pharmaceutical Potential
Every cell in the human body releases extracellular vesicles (EVs). These membrane-bound particles, ranging from roughly 30 nanometres to several micrometres in size, carry proteins, lipids, nucleic acids, and metabolites between cells. They are natural intercellular communication vehicles, evolved to transfer biological cargo across biological barriers.
The pharmaceutical interest in EVs is obvious. A delivery system that is intrinsically biocompatible, that crosses biological barriers efficiently, that can be loaded with therapeutic cargo, and that does not trigger the immune activation associated with synthetic nanoparticles sounds like exactly what drug delivery scientists have been trying to engineer for decades.
The development challenges are equally obvious. You cannot manufacture EVs the way you manufacture LNPs. They are produced by living cells, isolated from complex biological matrices, and extraordinarily heterogeneous. Controlling their composition, their cargo loading efficiency, and their biological activity from batch to batch is a hard problem that has not yet been fully solved.
EV Subclasses and Their Relevance to Drug Delivery
| EV Subclass | Size Range | Biogenesis | Therapeutic Interest |
| Exosomes | 30-150 nm | Formed within multivesicular endosomes; released when MVE fuses with cell membrane | Natural intercellular communication; potential for loading with nucleic acids or small molecules; low immunogenicity |
| Microvesicles | 100-1000 nm | Direct budding from plasma membrane | Larger cargo capacity; surface proteins reflect parent cell; less well characterised than exosomes |
| Apoptotic bodies | 500-5000 nm | Released by cells undergoing programmed cell death | Less clinical interest for drug delivery; relevant to clearance and inflammation biology |
| Engineered EVs (synthetic biology) | Variable | Cells engineered to overexpress targeting or therapeutic proteins on EV surface | Most therapeutically relevant near term; allows systematic engineering of surface and cargo |
The Manufacturing Problem
Natural EVs are produced in tiny quantities. A litre of cell culture medium yields micrograms of EVs after isolation. Scaling that to the quantities needed for clinical trials requires either enormous bioreactor volumes or manufacturing platforms that produce engineered EVs at higher yields than natural cell secretion.
Isolation adds further complexity. The standard methods, ultracentrifugation, size exclusion chromatography, and tangential flow filtration, each have different selectivity for different EV populations. There is no universal isolation method, and different methods produce products with different purity, yield, and biological activity. This makes batch-to-batch comparability extremely challenging when the isolation process is not tightly controlled.
The Characterisation Gap
Characterising EVs to the standard required for a regulatory filing is harder than characterising LNPs. Particle size by DLS gives an ensemble average that poorly represents a heterogeneous population. Single-particle tracking methods like NTA are more informative but harder to standardise. Protein cargo is highly variable depending on the source cell and culture conditions. The ISEV Society’s minimal information for studies of extracellular vesicles (MISEV) guidelines provide a framework for EV characterisation in research, but translating those standards to a GMP context remains an open challenge for the field.
Where the Clinical Evidence Stands
Several EV-based products have reached clinical trials. MSC-derived exosomes have been investigated for graft-versus-host disease and COVID-19 acute respiratory distress syndrome. Tumour-derived EVs have been explored as cancer vaccines. Plant-derived EVs are being investigated as oral drug delivery vehicles.
Results have been mixed. The field has not yet produced the definitive clinical proof-of-concept that would drive widespread investment, and the manufacturing and characterisation challenges mean that many programmes have struggled to produce consistent clinical-grade material. But the pace of basic science, engineered EVs with defined surface proteins, cell-free EV production systems, improved isolation methods, is accelerating.
How Ardena Is Positioned for EV Programme Support
Ardena’s nanomedicine team at Oss monitors the EV therapeutics field closely and is developing the analytical and formulation capabilities needed to support early-stage EV programmes as the field matures. The physicochemical characterisation infrastructure at Oss, including DLS, NTA, and TEM, is applicable to EV characterisation, and the team can advise on the analytical strategy and formulation challenges facing EV development programmes at the current stage of the technology.
