Stroke is the leading cause of acquired adult disability. Improving brain plasticity after stroke represents an important therapeutic strategy. Cell therapy favours functional recovery after cerebral ischemia in rodent models. The pioneer clinical studies did not reproduce this benefit for patients due to a limited number of studied patients. In our preclinical studies, we observed a good tolerance and a functional benefit of the intracerebral (at the acute phase) and intravenous (IV) (at the subacute phase) administration of clinical-grade human mesenchymal stem cells (hMSC). The hMSC survival (during several weeks) and their differentiation into neurons or astrocytes are very limited and can not explain alone the functional benefit. Among different mechanisms of action of hMSC (neurotrophic and/or proangiogenic effects, immunomodulation...), we showed by MRI an early microvascular effect. We also showed that hMSC can be labeled for MRI and microscopy by iron microparticles without altering cell properties. This cell labeling is useful to detect and follow hMSC grafted into the brain but is insufficient to follow the IV injected hMSC. To assess the biodistribution of IV injected hMSC, we conducted a nuclear imaging study. This experiment showed that the hMSC are attracted to cerebral ischemic lesion in the first hours following their injection. In parallel, we developed a phase 2 clinical trial. We do not know yet the best route of administration, the best dose and the optimal delay of the graft. The cell therapy optimization needs the development of translational projects with experimental studies linked to clinical trials. Thus cell therapy could become an efficient treatment for stroke.
