Mesenchymal Stem Cells Extracellular Vesicles as Therapy

An emerging interest in acellular therapeutics has led researchers to focus on the extracellular vesicles (EVs) released by mesenchymal stem cells (MSCs). Investigating the potential of MSC-EVs switches attention from cell harvest to media collection and processing, with an emphasis on scaling up to meet R&D supply demand. Here's a further look into what MSC-EVs can do.

From Mesenchymal Stems Cells to Extracellular Vesicles

Since their discovery in the 1970s, MSCs have been well-studied and their therapeutic potential thoroughly explored. Clinical trials over several decades show that these pluripotent stem cells are extremely valuable in regenerative medicine. An August 2020 review in Stem Cell Research and Therapy notes their role in tissue regeneration and immunomodulation, with potential therapeutic success in cardiovascular disease, stroke, and osteoarthritis, among other areas. Stem Cell Research and Therapy also notes that there has even been interest in stem cells as treatment for the acute lung injury and acute respiratory distress seen during severe COVID-19 infection.

Initially, MSC success was thought to be through direct migration into affected tissues, where the stem cells would "transplant" themselves to occupy, differentiate, and thus repair damage. However, further studies showed that their action is paracrine. They secrete growth factors and cytokines, among other molecules, and are responsible for their therapeutic benefit.

But bioactive molecules aren't the only thing secreted by mesenchymal stem cells. MSCs also package biomolecules into lipid bilayer-bound packages, or extracellular vesicles (EVs), for secretion. Mesenchymal stem cell derived extracellular vesicles (MSC-EVs) cross biological barriers and avoid many of the issues seen with stem cell therapy, such as adverse immune responses.

In the last decade, MSC-EVs have emerged as potential acellular therapeutics. Dr. Amy Kauffman, a senior development engineer with Corning, notes that some attention is switching from the cell monolayer to what they produce into the medium. This switch brings even greater focus on EV harvesting.

Extracellular Vesicles Pack a Therapeutic Load

EVs are membrane-bound vesicles released from the cell that are between 30 and 1,000 nanometers in diameter. MSC-EVs contain proteins and RNA, with an outer lipid layer covered in transmembrane proteins. A 2020 study in Nature's Scientific Reports notes the methods in which EVs have been isolated from many body fluids, including serum, urine, and bile.

Once researchers understood the importance of EVs in mediating MSC therapeutic effects, they turned attention to using them as treatments. In vivo studies show success in stroke, traumatic brain injury, and wound healing, with the EV treatment giving results similar to those seen with the parent whole-cell therapies.

Furthermore, research suggests that since EV treatment is acellular, it avoids complications seen with traditional stem cell therapies. The lipid bilayer protects from the immune system, so EV therapy avoids issues with immunogenicity and rejection. Since they are acellular and therefore have none of the cellular mechanisms for replication, there is no risk of ectopic tumor formation. This higher safety profile, coupled with the ability to cross biological barriers, make MSC-EVs a therapeutic option worth studying.

Extracellular Vesicle Production and Isolation

Collecting MSC-EVs can take place at the petri dish level, but running comprehensive in vivo and clinical studies takes volume. As an illustration, for in vivo studies, one rodent needs the EVs harvested from around 2 million MSCs in 48 hours. Stem Cell Research notes that a human-sized dose would require around 500 million cells. Scaling up should be considered right from the start at the clinical level, according to Kauffman, especially in terms of simple cell culture basics. For instance, passage number affects cell and thus MSC-EV characteristics.

It pays to start off with high-quality parent cells and characterize them to understand their growth characteristics fully.

"You really need to think about your growth space [when approaching MSC-EVs]," advises Kauffman. "If you start in a small volume, then need to split your cells early, then you lose one passage already. If you do start too small, you're in trouble."

This is where moving into platforms such as the HYPER Technology platform from Corning work well. Efficient multi-layer cell culture vessel technology, combined with unique ultra-thin gas-permeable growing surfaces, increases surface area and cell yield. Compared to vessels with similar footprints, more cells can be grown in a smaller area and the EV yield potential is much greater. Researchers can move on easily from single flask characterization into stacked HYPERFlasks and then, once familiar, can scale up with larger HYPERStack cell culture vessels.

Consistency in processing is key when aiming for high yield and high consistency. Not only does HYPER platform technology help with scaling up, but straightforward and robust platform handling steps also become routine for consistent EV harvests. Once you've established culture conditions, the platform makes it easy to investigate ways to optimize production. With more efficient and consistent production methods, researchers will be able to maximize the full potential of EVs for research and therapeutic application.

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