HISTORY OF EXOSOMES

Early investigations using electron microscopy revealed membrane-bound particles released by cells and present in biological fluids. These observations contributed to a growing understanding of extracellular material and membrane-associated cellular processes.

During this period, extracellular particles were often interpreted in relation to cellular turnover, membrane shedding or the removal of cellular components. Their biological significance was not yet fully understood.

Advances in electron microscopy and membrane biology subsequently provided the technical and conceptual foundations for investigating how vesicular structures originate, develop and are released from cells.

These early observations established an important starting point for later extracellular vesicle research.

Research into the maturation of reticulocytes, immature red blood cells, provided a major contribution to the understanding of extracellular vesicle release.

In 1983, Pan and Johnstone investigated the fate of transferrin receptors during reticulocyte maturation. Their findings demonstrated the selective externalisation of receptor-associated membrane components through released vesicles. [1]

Subsequent research further characterised the composition and release of these vesicles.

In 1987, Johnstone and colleagues published a study describing vesicles released during reticulocyte maturation and explicitly referring to them as exosomes. The investigation associated vesicle release with the removal of selected membrane activities during cellular maturation. [2]

These studies became foundational references in the development of modern exosome research.

As extracellular vesicle research expanded, investigators began examining whether released vesicles could participate in biological interactions beyond the removal of cellular material.

In 1996, Raposo and colleagues reported that B lymphocytes release vesicles capable of presenting antigens, contributing to the understanding of extracellular vesicles in immune-related processes. [3]

A further important development emerged in 2007, when Valadi and colleagues demonstrated that exosomes from the cell systems studied contained messenger RNA and microRNA and could transfer RNA between cells. [4]

These findings supported the growing investigation of extracellular vesicles as participants in intercellular communication.

Research increasingly examined the molecular constituents of extracellular vesicles, including proteins, lipids and nucleic acids, as well as the biological circumstances in which vesicle-associated material may influence recipient cells.

The interpretation of these functions remains dependent on vesicle origin, experimental conditions and the evidence available for individual EV populations.

During the early twenty-first century, extracellular vesicle research expanded across multiple areas of biomedical science.

Investigations increasingly addressed EV biology in immunology, oncology, neuroscience, cardiovascular research and tissue-related biological processes.

Research also advanced the methods used to separate and characterise extracellular vesicles, including differential ultracentrifugation, size-exclusion chromatography, immunoaffinity-based approaches, electron microscopy and particle-analysis techniques.

These methods contributed to the development of increasingly detailed experimental approaches, while also revealing challenges associated with sample purity, particle heterogeneity and reproducibility.

2013 — Nobel Recognition of Vesicular Transport Mechanisms

The 2013 Nobel Prize in Physiology or Medicine was awarded to James E. Rothman, Randy W. Schekman and Thomas C. Südhof for discoveries concerning the machinery regulating vesicle traffic, a major transport system within cells. [5]

Their work advanced the understanding of how cellular cargo is organised, transported and delivered through regulated vesicular processes, including mechanisms involved in membrane fusion.

Although the Nobel Prize was not awarded specifically for the discovery of exosomes, the recognised research represents a major achievement in the broader scientific understanding of vesicular transport.

These discoveries form an important part of the cellular biology context in which extracellular vesicle formation, release and transport are investigated.

As the field expanded, the scientific community recognised the need for greater consistency in extracellular vesicle terminology, experimental methods and reporting practices.

In 2014, the International Society for Extracellular Vesicles (ISEV) published a position statement addressing minimum experimental requirements for defining extracellular vesicles and investigating their functions. [6]

The MISEV2018 guidelines subsequently provided expanded recommendations concerning EV collection, separation, characterisation and functional studies. [7]

The MISEV2023 guidelines, published in 2024, further developed these recommendations in response to continuing advances in EV research. [8]

Understanding EV Classification

Extracellular vesicles comprise heterogeneous populations of particles released by cells.

Historically, the term exosome has commonly been associated with vesicles of endosomal origin, while other EV categories have been described according to their proposed formation pathways.

Small EVs are frequently discussed in relation to approximate size ranges and molecular markers such as CD9, CD63 and CD81. However, particle size and individual markers alone do not establish a definitive biogenesis-based identity.

Contemporary research guidelines therefore emphasise careful terminology, appropriate characterisation and transparent reporting of experimental evidence.

This evolution reflects the development of extracellular vesicle science toward more reproducible and internationally comparable research practices.

Contemporary extracellular vesicle research continues to explore vesicle biogenesis, molecular composition, cellular release, uptake and interactions with recipient cells.

The field also investigates the potential relevance of extracellular vesicles in biomarker discovery, disease-related biological mechanisms and experimental therapeutic approaches.

Alongside these developments, researchers continue to address important scientific challenges, including:

• Reliable separation of extracellular vesicles from non-vesicular extracellular particles
• Reproducible characterisation of heterogeneous EV populations
• Identification of molecular cargo and its biological relevance
• Demonstration of vesicle-associated functions under controlled experimental conditions
• Development of appropriate experimental and reporting standards
• Evaluation of research findings for potential translational applications

The history of exosome science illustrates a progressive development from descriptive observations to increasingly detailed molecular investigations.

Its foundations lie in cell biology, membrane trafficking and the scientific study of extracellular communication.

Continued research, methodological refinement and international scientific collaboration remain central to advancing the field.