Functions of MSC- and HSC-Derived Extracellular Vesicles

Two stem cell populations dominate the extracellular vesicle literature, and they are frequently discussed as if interchangeable. They are not. Mesenchymal stromal cells and haematopoietic stem cells release vesicles with different cargo, different targets and different consequences.

What MSC-derived vesicles do

The therapeutic reputation of mesenchymal stromal cells rests increasingly on what they secrete rather than what they become. Their vesicles carry a cargo of microRNA, messenger RNA and protein that is immunomodulatory, pro-angiogenic and anti-apoptotic in character.

In vitro, MSC-derived vesicles polarise macrophages toward a reparative phenotype, suppress T-cell proliferation and promote endothelial tube formation. In vivo, they concentrate preferentially in injured tissue and reproduce a meaningful share of the effect attributed to the parent cell — which is the observation that reoriented an entire field.

What HSC-derived vesicles do

Haematopoietic stem and progenitor cell vesicles operate in a different register. Their cargo influences the marrow niche, progenitor commitment and lineage decisions, functioning as part of the signalling architecture that maintains haematopoiesis. Where MSC vesicles read as reparative and immunomodulatory, HSC vesicles read as instructive within their own compartment.

Why cell-free preparations gained ground

The practical case is unglamorous and decisive. Vesicles cannot proliferate, cannot differentiate into an unwanted lineage and cannot form a teratoma. They tolerate storage conditions that living cells do not. They present a smaller surface for immunological recognition. And because they can be counted, sized and profiled by surface marker, they can be standardised in a way that a living-cell population resists.

The trade is real: vesicles do not persist, do not adapt to their environment and do not respond dynamically to changing conditions. They deliver a defined payload once. For some applications that is a limitation; for others it is precisely the point.

The characterisation floor

None of the above is meaningful without measurement. The MISEV framework sets the expectation: report particle concentration and size distribution, demonstrate the presence of transmembrane and cytosolic markers such as CD9, CD63 and CD81, and document the isolation method. A preparation described only as 'exosomes' with no accompanying analytics has not been characterised.