Multiple sclerosis is a currently incurable inflammatory demyelinating syndrome. Recent reports suggest that bone marrow derived mesenchymal stem cells may have therapeutic potential in experimental models of demyelinating disease, but various alternative mechanisms, ranging from systemic immune effects to local cell replacement, have been proposed. Here we used intraperitoneal delivery of human mesenchymal stem cells to help test (a) whether human cells can indeed suppress disease, and (b) whether CNS infiltration is required for any beneficial effect. We found pronounced amelioration of clinical disease but profoundly little CNS infiltration. Our findings therefore help confirm the therapeutic potential of mesenchymal stem cells, show that this does indeed extend to human cells, and are consistent with a peripheral or systemic immune effect of human MSCs in this model. Keywords Mesenchymal stem cells; Multiple sclerosis; Experimental allergic encephalomyelitisMultiple sclerosis is an acquired inflammatory demyelinating syndrome of unknown cause, and which is currently incurable. In many individuals, progressive disability occurs during the course of the disease, as a consequence of irreversible CNS damage. The ineffectiveness of current therapies has emphasised the importance of novel treatment approaches, and stem cells are widely held as having particular promise.Bone marrow derived mesenchymal stem cells can proliferate substantially, and can differentiate into cells of all three germ cell layers, including neural cells; moreover they are relatively accessible, could be used for autologous therapy, and are capable of entering the CNS (particularly when damaged) from the circulation [6,11]. They are therefore considered good candidates for early clinical stem cell therapeutic studies.Recently, reports have appeared suggesting that bone marrow-derived cells can ameliorate toxic and inflammatory experimental demyelinating disease following intravenous delivery [1,3,5,7,[13][14][15][16]. However, whether this effect is achieved through cell replacement and

Mesenchymal stem cells (MSCs) can abrogate the animal model of multiple sclerosis, experimental autoimmune encephalomyelitis (EAE), but whether this therapeutic effect occurs entirely through systemic immune modulation and whether CNS infiltration occurs after peripheral delivery are uncertain. We studied the clinical and neuropathologic effects of intravenously administered human MSCs (hMSCs) in C57BL/6 mice with EAE. Human MSCs significantly reduced the clinical disease severity, particularly in later disease. Large numbers of hMSCs migrated into gray and white matter at all levels of the spinal cord in both naive mice and mice with EAE. In the latter, hMSCs accumulated over time in demyelinated areas. There were 2 distinct morphological appearances of the hMSCs in the tissue, that is, rounded and less numerous process-bearing forms; very few expressed neural markers. The number of spinal cord white matter lesions and areas of white matter demyelination were reduced after hMSC treatment compared with control treatment. These findings show that central nervous system infiltration occurs after peripheral delivery of hMSCs, that they accumulate where there is myelin damage, and that they are associated with a reduced extent of demyelination. These data support a potential role for hMSCs in autologous cell therapy in multiple sclerosis.