Cell Type-Associated Differences in Migration, Survival, and Immunogenicity following Grafting in CNS Tissue

Abstract

Cell transplantation has been suggested to display several neuroprotective and/or neuroregenerative effects in animal models of central nervous system (CNS) trauma. However, while most studies report on clinical observations, currently little is known regarding the actual fate of the cell populations grafted and whether or how the brain's innate immune system, mainly directed by activated microglia and astrocytes, interacts with autologous cellular implants. In this study, we grafted well-characterized neural stem cell, mouse embryonic fibroblast, dendritic cell, bone marrow mononuclear cell, and splenocyte populations, all isolated or cultured from C57BL/6-eGFP transgenic mice, below the capsula externa (CE) of healthy C57BL/6 mice and below the inflamed/demyelinated CE of cuprizone-treated C57BL/6 mice. Two weeks postgrafting, an extensive quantitative multicolor histological analysis was performed in order (i) to quantify cell graft localization, migration, survival, and toxicity and (ii) to characterize endogenous CNS immune responses against the different cell grafts. Obtained results indicate dependence on the cell type grafted: (i) a different degree of cell graft migration, survival, and toxicity and (ii) a different organization of the endogenous immune response. Based on these observations, we warrant that further research should be undertaken to understand-and eventually controlcell graft-induced tissue damage and activation of the brain's innate immune system. The latter will be inevitable before cell grafting in the CNS can be performed safely and successfully in clinical settings.

Expression of Vascular Endothelial Growth Factor-C (VEGF-C) and Its Receptor (VEGFR-3) in the Glial Reaction Elicited by Human Mesenchymal Stem Cell Engraftment in the Normal Rat Brain

“…Previous studies have proposed that reactive astrocytes form scar-like barriers surrounding the grafted MSCs, which sequesters them from immune effector cells, or that astrocytes infiltrating the graft may provide cellular and structural support for graft survival (Coyne et al 2006;De Vocht et al 2013a;De Vocht et al 2013b;Praet et al 2012). Our data demonstrated the induction of VEGFR-3 protein, but not its ligand, in reactive astrocytes at the graft site.…”

“…Thus, only a limited number of stem cells can be stably engrafted into the brain (Bergwerf et al 2011;De Vocht et al 2013a;De Vocht et al 2013b;Praet et al 2012;Reekmans et al 2012;Tambuyzer et al 2009). These data suggest the interaction between cellular grafts and the microenvironment of the host brain, especially the glia, is important for graft survival.…”

Distinct In Vitro Properties of Embryonic and Extraembryonic Fibroblast-Like Cells are Reflected in their in Vivo Behavior following Grafting in the Adult Mouse Brain

“…For cell expansion and to establish a growth curve, cell culture medium was replaced every 3 days, and cells were split 1:2 and counted every 4 days. mEFs were cultured from eGFP + and eGFP − embryos following crossing of female wild-type C57BL/6 mice with male transgenic C57BL/6-eGFP mice, according to previously described procedures (21). For cell expansion, mEF medium [Dulbecco's modified Eagle's medium (DMEM) with 4.5 g/L glucose and L-glutamine (Gibco) supplemented with 10% FCS, 100 U/ml penicillin, and 100 mg/ml streptomycin] was replaced every 2-3 days, and cells were split 1:3 every 4-5 days.…”

“…In our preceding studies regarding mMSC and mEF grafting in the CNS of immune-competent mice, we noted that mMSC and mEF grafts became highly infiltrated by microglia (at week 2 postgrafting, up to 50-80% of cells within the graft site are microglia) and surrounded by microglia and astrocytes (4,5,10,21). From the representative Iba1/eGFP, S100b/eGFP, and GFAP/eGFP images provided in Figure 2A, it is clear that mFMSC grafts, too, become highly infiltrated by microglia and surrounded by both microglia and astrocytes.…”

“…However, while extensive in vitro experiments have shed light on potential working mechanisms for the improved clinical outcome following fibroblastic cell grafting in several disease models, including those of the central nervous system (CNS), currently little is known about the actual in vivo behavior of these cellular grafts (1,7). In our preceding studies, we contributed to a better understanding of the cellular events following syngeneic reporter gene-modified murine bone marrowderived mesenchymal stromal cell (mBMMSC) and murine embryonic fibroblast (mEF) grafting in the healthy and injured CNS of immune-competent mice (4,5,10,21). In the course of these studies, it was noted that both mMSC and mEF grafting in the CNS, independent of a preceding injury, results in the activation of strong microglial and astroglial cell responses.…”