Engineering mesenchymal stem cells to improve their exosome efficacy and yield for cell-free therapy

Abstract

Through traditional medicine, there were diseases and disorders that previously remained untreated or were simply thought to be incurable. Since the discovery of mesenchymal stem cells (MSCs), there has been a flurry of research to develop MSC-based therapy for diseases and disorders. It is now well-known that MSCs do not typically engraft after transplantation and exhibit their therapeutic effect via a paracrine mechanism. In addition to secretory proteins, MSCs also produce extracellular vesicles (EVs), membrane-bound nanovesicles containing proteins, DNA and RNA. The secreted vesicles then interact with target cells and deliver their contents, imparting their ultimate therapeutic effect. Unlike the widely studied cancer cells, the yield of MSC-exosomes is a limiting factor for large-scale production for cell-free therapies. Here we summarise potential approaches to increase the yield of such vesicles while maintaining or enhancing their efficacy by engineering the extracellular environment and intracellular components of MSCs.

Keywords: Mesenchymal stem cells; extracellular vesicles.

Figure 1.

Biogenesis and release of extracellular vesicles, both microvesicles and exosomes (A). The contents of the exosomes are shown as well (B).

Figure 2.

Common methods in isolating the extracellular vesicles. Ultracentrifugation is the method often utilised in experiments (A). Precipitation involves the use of an agent that allow for the pelleting of EVs (B). Ultrafiltration uses a filter to separate the EVs from the other molecules based off pore size in the filter (C). Immunoaffinity uses antibody to capture the EVs based on their surface markers (D). Size exclusion chromatography separate the EVs from the non-EVs molecules with a packed column of certain materials (E).

Figure 3.

The different forms of an extracellular matrix and their interactions with the cells. The tissue culture treated plastic surface is the most common surface for culturing the MSCs (A). The ECM sheet can be in form of decellularised native ECM or an artificial matrix, which can include different oriented fibres (B). A hydrogel can be manufactured from the decellularised ECM or a chemical mixture for culturing seeded or encapsulated MSCs (C). The porous scaffold is the most similar to the native environment of the MSCs, perhaps allowing the most suitable culture environment (D).

Figure 4.

The schematics of spinner flask containing microcarriers containing the cells (A) as well as the hollow-fibre bioreactor and its cross section with cells inside (B).