Peculiarities of Gene Transfer into Mesenchymal Stem Cells

Nestin-GFP transgene labels immunoprivileged bone marrow mesenchymal stem cells in the model of ectopic foci formation

Immune privileges are demonstrated for different types of quiescent stem cells of adult mammalian organisms. Mesenchymal stem cells (MSCs) are believed to have immune privileges; however, an accurate experimental confirmation hasn’t been presented. Here, we provide direct experimental evidence that MSCs of C57Black/6J murine bone marrow (BM) are immune privileged in vivo and retain their functionality after prolonged exposure to the uncompromised immune system. The BM of Nes-Gfp transgenic mice was implanted as a tissue fragment under the kidney capsule in isogenic C57Black/6J immunocompetent recipients. Nestin-Gfp strain provides a fluorescent immunogenic marker for a small fraction of BM cells, including GFP+CD45– MSCs. Despite the exposure of xenogenically marked MSCs to the fully-functional immune system, primary ectopic foci of hematopoiesis formed. Six weeks after implantation, multicolor fluorescence cytometry revealed both GFP+CD45– and GFP+CD45+ cells within the foci. GFP+CD45– cells proportion was 2.0 × 10–5 ×÷9 and it didn’t differ significantly from syngenic Nes-GFP transplantation control. According to current knowledge, the immune system of the recipients should eliminate GFP+ cells, including GFP+ MSCs. These results show that MSCs evade immunity. Primary foci were retransplanted into secondary Nes-GFP recipients. The secondary foci formed, in which CD45–GFP+ cells proportion was 6.7 × 10–5 ×÷2.2, and it didn’t differ from intact Nes-GFP BM. The results demonstrate that MSCs preserve self-renewal and retain their functionality after prolonged immune exposure. The success of this study relied on the implantation of BM fragments without prior dissociation of cells and the fact that the vast majority of implanted cells were immunologically equivalent to the recipients.

Protein Expression Profile on Differentiation of Bone Marrow Mesenchymal Stem Cells into Retinal Ganglion-Like Cells

To explore possible approaches to differentiating rat bone marrow mesenchymal stem cells (BMSCs) into retinal ganglion-like cells and to demonstrate the dynamic changes in protein expression profiles of BMSCs throughout the differentiation. BMSCs were isolated from adult rats and cultured in medium conditioned by neonatal rat retinal cells to induce BMSC differentiation into retinal ganglion-like cells. Immunostaining for neurofilament, nestin, Map2, and Thy1.1 was used to follow the differentiation process. Two types of protein arrays were employed to profile the BMSCs, the differentiated retinal ganglion-like cells, and the primary retinal ganglion cells (RGCs) using the Biomarker Wizard System. After 7 days of culture in conditioned medium, cells showing a neural-cell-like modality appeared. The differentiated retinal ganglion-like cells showed that network-like connections were positive for nestin, neurofilament, Map2, and Thy1.1. In total, 16 marker proteins were highly expressed in both retinal ganglion-like cells and RGCs and no obvious expression was observed in BMSCs. Among them, nine proteins were expressed more highly in RGCs than in retinal ganglion-like cells. BMSCs can be induced to differentiate into retinal ganglion-like cells by neonatal rat retinal cells, and the induced cells show protein profiles resembling those of isolated RGCs.

Investigation of the Mesenchymal Stem Cell Compartment by Means of a Lentiviral Barcode Library

The hematopoietic bone marrow microenvironment is formed by proliferation and differentiation of mesenchymal stem cells (MSCs). The MSC compartment has been less studied than the hematopoietic stem cell compartment. To characterize the structure of the MSC compartment, it is necessary to trace the fate of distinct mesenchymal cells. To do so, mesenchymal progenitors need to be marked at the single-cell level. A method for individual marking of normal and cancer stem cells based on genetic "barcodes" has been developed for the last 10 years. Such approach has not yet been applied to MSCs. The aim of this study was to evaluate the possibility of using such barcoding strategy to mark MSCs and their descendants, colony-forming units of fibroblasts (CFU-Fs). Adherent cell layers (ACLs) of murine long-term bone marrow cultures (LTBMCs) were transduced with a lentiviral library with barcodes consisting of 32 + 3 degenerate nucleotides. Infected ACLs were suspended, and CFU-F derived clones were obtained. DNA was isolated from each individual colony, and barcodes were analyzed in marked CFU-F-derived colonies by means of conventional polymerase chain reaction and Sanger sequencing. Barcodes were identified in 154 marked colonies. All barcodes appeared to be unique: there were no two distinct colonies bearing the same barcode. It was shown that ACLs included CFU-Fs with different proliferative potential. MSCs are located higher in the hierarchy of mesenchymal progenitors than CFU-Fs, so the presented data indicate that MSCs proliferate rarely in LTBMCs. A method of stable individual marking and comparing the markers in mesenchymal progenitor cells has been developed in this work. We show for the first time that a barcoded library of lentiviruses is an effective tool for studying stromal progenitor cells.