Mesenchymal Stem Cells for Ischemic Stroke: Progress and Possibilities

Stroke is the most common neurological cause of morbidity and mortality in industrialized countries, afflicting 15 million people every year. The numbers are expected to increase, mostly due to aging populations. One in five stroke patients dies, and one in three are left with permanent disabilities. Although some acute phase therapies such as intravenous recombinant tissue plasminogen activator (rt-PA) andendovascular treatment have been shown to improve ischemic stroke outcome, these therapies are available only for a small proportion of patients. The use of stem cells to replace brain cells lost during stroke is a long-term goal, and one which is difficult to achieve given that transplanted cells must integrate and restore neural pathways to regain function of damaged parts of the brain. Over the past decade the use of mesenchymal stromal cells (MSCs) as therapy has emerged as a particularly attractive option. MSCs are a class of multipotent, self-renewing cells that give rise to differentiated progeny when implanted into appropriate tissues. Herein, we present a review of the application of MSCs in ischemic stroke, including the source of MSCs, the route and timing of their delivery into the brain and the endpoints measured. Experimental data of transplantation of MSCs in animal stroke models suggest an improved functional recovery. The transplantation of MSCs influences a wide range of events by modulating the inflammatory environment, stimulating endogenous neurogenesis and angiogenesis and reducing the formation of glial scar, although the precise, underlying mechanism of this phenomenon remains unknown. The results from early clinical trials highlight the need to optimize variables such as cell selection and route of administration in order to translate these results into safe and successful clinical applications.