MESENCHYMAL STEM CELLS AND EXTRACELLULAR VESICLES
Mesenchymal Stem Cells (MSCs: cell therapy) and their derived Extracellular Vesicles (MSC-EVs: cell-free therapy) offer a promising regenerative therapy for a wide range of diseases given their pro-angiogenic, anti-inflammatory, immunomodulatory, anti-fibrotic and bioenergetic properties. Our research focuses on characterizing the phenotype of these therapies, at the genomic, proteomic, and lipidomic levels, as well as enhancing their regenerative phenotype using genetic modification and novel priming technologies.
MSCs (Cell therapy)
Mesenchymal stem cells (MSCs) are multipotent adult progenitor cells, which are capable of differentiating into various mesenchymal tissues, most prominently bone, cartilage and adipose. They were first isolated in 1974 from the bone marrow by Friedenstein and colleagues. Since then, MSCs have been isolated from a variety of other tissues, including adipose tissue, bone marrow and umbilical cord.
The International Society for Cellular Therapy (ISCT) has laid down several defining criteria for the identification of MSCs: 1) they must be plastic-adherent in standard culture conditions; 2) express the surface markers CD105, CD90 and CD73; 3) not express other lineage markers CD45 (pan-leukocyte), CD34 (hematopoietic and endothelial), CD14/CD11b (monocytic), CD79a/CD19 (B cell), or HLA class II; and 4) show the classical tri-lineage differentiation into osteoblasts, adipocytes and chondroblasts. Of note, MSCs are not a pure population of stem cells but exist as a heterogeneous, non-clonal mix of multipotent stem cells, committed progenitors and differentiated cells. This fact prompted a change in nomenclature from “mesenchymal stem cell” to “mesenchymal stromal cell”, though the terms are used
used interchangeably.
When tissues are damaged, MSCs are naturally released into the circulation, migrate to the site of injury, and secrete molecules to create a microenvironment that promotes regeneration. Thus, the idea behind their therapeutic potential is that allogenically-transplanted MSCs can home to damaged tissue and act as a “drug store” to aid in recovery, or serve as an effector for tissue regeneration. Upon reaching the target tissue, MSCs secrete a variety of factors with powerful immune-modulating, angiogenic and anti-apoptotic effects.
Extracellular Vesicles (Cell-Free Therapy)
MSCs secret soluble factors, such as chemokines, cytokines, and growth factors, as well as insoluble factors including EVs that are responsible for their therapeutic effect. MSC derived EVs (MSC-EVs) consist of exosomes (30-120nm vesicles released from the endosomal compartment as it fuses with the cell membrane), microvesicles (100nm-1µm vesicles formed by outward budding and fission with the cell membrane) and apoptotic bodies (50nm - 5µm vesicles formed during plasma membrane blebbing when a cell undergoes programmed cell death).
MSC-EVs carry complex cargo including bioactive lipids, proteins, nucleic acids (i.e. mRNA and microRNA); the latter can mediate horizontal transfer of genetic information and confer stem cell like alterations in the phenotype of recipient cells with activation of self-regenerative programs. MSC-EVs offer an attractive “cell free” therapeutic option given that they (i) are smaller, (ii) are less complex, (iii) are easier to produce and store, (iv) are less immunogenic (due to their lower membrane-bound proteins), (v) avoid some of the regulatory issues which MSCs face and (vi) have no risk of tumor formation.
Our lab has been working to determine the molecular phenotype of MSCs and then using detailed bioinformatic analysis to match the correct MSC to the correct disease indication. In addition, we are developing workflows to optimize the isolation, characterization and purification of MSC-EVs from both 2D and 3D cultures as well a genetically modifying MSCs to over-express proteins of interest. We also test these regenerative therapies (both the patent cells and cell-free components) in both cell culture and small animal disease models with a view to optimizing their therapeutic effect by locally delivering them into affected organs as well as priming the tissue microenvironment with novel technologies like pulsed focused ultrasound.