Trends in using mesenchymal stromal/stem cells (MSCs) in treating corneal diseases

Since their inception in the 1960s-70s, mesenchymal stem/stromal cells (MSCs) have gained interest because of their differentiation potential, anti-inflammatory effects, and immune-modulating properties. Both cell-based and cell-free MSC treatments show healing capacity in injured tissues. Cell-based treatment comprises MSCs and all secreted products, whereas cell-free treatments include only the secreted products. MSCs are therapeutically administered to many damaged organs owing to their efficacy. Specifically, the eye is a unique organ system to study the effects of MSCs, as treatment is easily applied and measured owing to its external location. The eye holds an immune-privileged status, wherein inflammation and immune responses are innately down-regulated. As excessive inflammation in the cornea often leads to fibrosis and irreversible corneal hazing, many studies have investigated the anti-inflammatory and immune-modulating capacities of MSCs. Decades of research suggest that MSCs modulate the immune response by secreting cytokines, growth factors, and extracellular matrix proteins that inhibit the infiltration of inflammatory cells following injury and promote a healing phenotype via M2 macrophage polarization. MSCs have also shown trans-differentiation potential into cornea-specific cell types during the wound healing process, such as corneal epithelial, stromal, or endothelial cells. This review discusses recent investigations of MSC treatment in the cornea, focusing on therapeutic efficacy, mechanisms, and future directions.