Stroke is the leading cause of disability in adult. Less than 10% of patients can be treated with thrombolysis. Except rehabilitation, no effective treatment exists to improve functional recovery after the acute phase. Therefore, there is a wide need to develop an effective therapy applicable after several days or weeks following stroke. Using a multiparametric approach (microvascular MRI, analysis of angiogenic genes expression and behavioral study) in rat ischemic stroke model, we defined a transition stage (D3-D7) followed by a subacute phase (D7-D25) during post-stroke remodeling. These two phases represent an interesting target time-window for administration of pro-angiogenic therapies. Since 20 years, cell therapy, notably by human mesenchymal stem/stromal cells (hMSC), emerged as a “regenerative treatment” with threefold increase in clinical trial during the last 10 years. However, still limited data are available regarding the mechanisms by which hMSC benefit, especially at the subacute phase. We progressed in understanding the microvascular plasticity that occurs after an intravenous injection of hMSC in a rat model of transient focal cerebral ischemia. Our preclinical studies were carried out simultaneously with a phase II clinical trial that currently goes on in Grenoble (ISIS: Intravenous Stem Cells After Ischemic Stroke). We reported a sustained functional and cognitive long-term benefit of hMSC IV injected at the subacute stage correlated to an increase of angiogenesis. Ang2, Ang1, SDF-1 and TGFβ1, whose endogenous level tends to be overexpressed by hMSC, would enhance stabilization and survival of newborn vessels, accounting for benefit of these cells. As part of the hMSC development as an advanced therapy medicinal product, we realized an in vivo tumorigenicity assay and showed the absence of tumor development after hMSC injection. We also retrospectively analyzed hMSC produced for the phase II clinical trial. We confirmed the feasibility to produce hMSC, conformed to specifications and in adequate quantity, in the Cell Therapy Unit. In addition, we showed that ex vivo expanded hMSC can present, non clonal, erratic chromosomal abnormalities. Such chromosomal abnormalities appeared to be more related to the maintenance in culture than to the manufacturing process. A “donor” component may also contribute to emergence of such abnormalities.
