Mesenchymal Stem Cells Form 3D Clusters Following Intraventricular Transplantation Nicole Jungwirth 1,2 & Laura Salinas Tejedor 2,3 & Wen Jin 1,2 & Viktoria Gudi 2,3 & Thomas Skripuletz 3 & Veronika Maria Stein 4 & Andrea Tipold 2,4 & Andrea Hoffmann 5 & Martin Stangel 2,3 & Wolfgang Baumgärtner 1,2 & Florian Hansmann 1,2 Received: 8 March 2018 /Accepted: 19 April 2018 /Published online: 28 April 2018 # Springer Science+Business Media, LLC, part of Springer Nature 2018 Abstract Mesenchymal stem cells (MSCs) are regarded as an immune privileged cell type with numerous regeneration-promoting effects. The in vivo behavior of MSC and underlying mechanisms leading to their regenerative effects are largely unknown. The aims of this study were to comparatively investigate the in vivo behavior of canine (cMSC), human (hMSC), and murine MSC (mMSC) following intra-cerebroventricular transplantation. At 7 days post transplantation (dpt), clusters of cMSC, hMSC, and mMSC were detected within the ventricular system. At 49 dpt, cMSC-transplanted mice showed clusters mostly consisting of extracel- lular matrix lacking transplanted MSC. Similarly, hMSC-transplanted mice lacked MSC clusters at 49 dpt. Xenogeneic MSC transplantation was associated with a local T lymphocyte-dominated immune reaction at both time points. Interestingly, no associated inflammation was observed following syngeneic mMSC transplantation. In conclusion, transplanted MSC formed intraventricular cell clusters and exhibited a short life span in vivo. Xenogeneically in contrast to syngeneically transplanted MSC triggered a T cell-mediated graft rejection indicating that MSCs are not as immune privileged as previously assumed. However, MSC may mediate their effects by a Bhit and run^ mechanism and future studies will show whether syngeneically or xenogeneically transplanted MSCs exert better therapeutic effects in animals with CNS disease. Keywords Mesenchymal stem cells . Canine mesenchymal stem cells . Human mesenchymal stem cells . Cell clusters . CD44 . Host versus graft reaction Introduction Mesenchymal stem cells (MSCs) can be isolated from a large variety of different tissues including bone marrow and adipose tissue (Barry and Murphy 2004; Singer and Caplan 2011). MSCs are characterized by their adherence to plastic, an ex- pression of a specific marker panel, and their ability to differ- entiate along the mesodermal lineage (Dominici et al. 2006; Edamura et al. 2012; Friedenstein et al. 1966; Hernigou 2015; Singer and Caplan 2011; Woodbury et al. 2000). Within the last years, MSCs were frequently applied as the second- or third-line regenerative approach in a variety of inflammatory, degenerative, and demyelinating diseases. Therapeutic appli- cation of MSC was promoted by various in vitro and in vivo studies demonstrating homing of MSC towards damaged tis- sue sites as well as their immunomodulatory and regenerative properties (Barry and Murphy 2004; Bernardo and Fibbe 2013; Karp and Leng Teo 2009; Le Blanc and Mougiakakos 2012; Uccelli et al. 2008). Furthermore, more than 500 studies are listed in the database at www.ClinicalTrials.gov , testing the therapeutic efficiency of MSC in human medicine. Recently, interest in dogs significantly increased since the dog serves as a large animal model for spontaneously occurring inflammatory and degenerative diseases of the * Wolfgang Baumgärtner wolfgang.baumgaertner@tiho–hannover.de 1 Department of Pathology, University of Veterinary Medicine Hannover, Bünteweg 17, 30559 Hanover, Germany 2 Center for Systems Neuroscience, Hannover, Germany 3 Clinical Neuroimmunology and Neurochemistry, Department of Neurology, Hannover Medical School, Hannover, Germany 4 Department of Small Animal Medicine and Surgery, University of Veterinary Medicine Hannover, Hannover, Germany 5 Department of Orthopaedic Surgery, Hannover Medical School, Hannover, Germany Journal of Molecular Neuroscience (2018) 65:60–73 https://doi.org/10.1007/s12031-018-1070-x