A Reliable Indirect Cell-Labelling Protocol for Optical Imaging allows Ex Vivo Visualisation of Mesenchymal Stem Cells after Transplantation

We set out to assess the feasibility of exploiting expression of the mCherry gene, after lentiviral infection, in order visualise bone marrow-derived human mesenchymal stem cells (hMSCs) by optical imaging, and to provide proof of principle of this approach as a method for cell tracking and quantification in pre-clinical models. Commercial hMSCs were infected with a lentiviral vector carrying the mCherry gene under the control of the phosphoglycerate kinase promoter. After extensive in vitro culture, infected hMSCs were analysed for viability, morphology, differentiation capability, and maintenance of fluorescence. Thereafter, mCherry-positive cells were transplanted into unilaterally 6-hydroxy-dopamine lesioned rats (an experimental model of Parkinson's disease). Our analysis showed that hMSCs can be efficiently transduced with the lentiviral vector, retaining their biological features even in the long term. Intrastriatally transplanted mCherry-positive hMSCs can be detected ex vivo by a sensitive cooled CCD camera, both in the whole brain and in serial slices, and relatively quantified. Our protocol was found to be a reliable means of studying the viability of implanted hMSCs. mCherry labelling appears to be readily applicable in the post-transplantation tracking of stem cells and could favour the rapid development of new therapeutic targets for clinical treatments.