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Objectives: Neuroinflammation plays a critical role in the pathophysiology of mesial temporal lobe epilepsy. We aimed to evaluate whether intracerebral transplantation of interleukin 13-producing mesenchymal stem cells (IL-13 MSCs) induces an M2 microglia/macrophage activation phenotype in the hippocampus with an epileptogenic insult, thereby providing a neuroprotective environment with reduced epileptogenesis., Methods: Genetically engineered syngeneic IL-13 MSCs or vehicle was injected within the hippocampus 1 week before the intrahippocampal kainic acid-induced status epilepticus (SE) in C57BL/6J mice. Neuroinflammation was evaluated at disease onset as well as during the chronic epilepsy period (9 weeks). In addition, continuous video-electroencephalography (EEG) (vEEG) monitoring was obtained during the chronic epilepsy period (between 6 and 9 weeks after SE)., Results: Evaluation of vEEG recordings suggested that IL-13 MSC grafts did not affect the severity and duration of SE or the seizure burden during the chronic epilepsy period, when compared to the vehicle treated SE mice. An M2-activation phenotype was induced in microglia/macrophages that infiltrated the -13 MSC graft site, as evidenced by the arginase1 expression at the graft site at both the 2-week and 9-week time-points. However, M2-activated immune cells were rarely observed outside the graft site and, accordingly, the neuroinflammatory response or cell loss related to SE induction was not altered by IL-13 MSC grafting. Moreover, an increase in the proportion of F4/80 + cells was observed in the IL-13 MSC group compared to the controls., Significance: Our data suggest that MSC-based IL-13 delivery to induce M2 glial activation does not provide any neuroprotective or disease-modifying effects in a mouse model of epilepsy. Moreover, use of cell grafting to deliver bioactive compounds for modulating neuroinflammation may have confounding effects in disease pathology of epilepsy due to the additional immune response generated by the grafted cells., (Wiley Periodicals, Inc. © 2017 International League Against Epilepsy.)

The therapeutic effects of mesenchymal stem cell (MSC) transplantation following spinal cord injury (SCI) to date have been limited. Therefore, we aimed to enhance the immunomodulatory properties of MSCs via continuous secretion of the anti-inflammatory cytokine interleukin-13 (IL-13). By using MSCs as carriers of IL-13 (MSC/IL-13), we investigated their therapeutic potential, compared with non-engineered MSCs, in a mouse model of SCI. We show that transplanted MSC/IL-13 significantly improve functional recovery following SCI, and also decrease lesion size and demyelinated area by more than 40%. Further histological analyses in CX 3 CR1 EGFP/+ CCR2 RFP/+ transgenic mice indicated that MSC/IL-13 significantly decrease the number of resident microglia and increase the number of alternatively activated macrophages. In addition, the number of macrophage-axon contacts in MSC/IL-13-treated mice was decreased by 50%, suggesting a reduction in axonal dieback. Our data provide evidence that transplantation of MSC/IL-13 leads to improved functional and histopathological recovery in a mouse model of SCI., (Copyright © 2016 The Authors. Published by Elsevier Inc. All rights reserved.)

Background: Promoting the neuroprotective and repair-inducing effector functions of microglia and macrophages, by means of M2 polarisation or alternative activation, is expected to become a new therapeutic approach for central nervous system (CNS) disorders in which detrimental pro-inflammatory microglia and/or macrophages display a major contribution to the neuropathology. In this study, we present a novel in vivo approach using intracerebral grafting of mesenchymal stem cells (MSC) genetically engineered to secrete interleukin 13 (IL13-MSC)., Methods: In the first experimental setup, control MSC and IL13-MSC were grafted in the CNS of eGFP + bone marrow chimaeric C57BL/6 mice to histologically evaluate IL13-mediated expression of several markers associated with alternative activation, including arginase1 and Ym1, on MSC graft-recognising microglia and MSC graft-infiltrating macrophages. In the second experimental setup, IL13-MSC were grafted on the right side (or on both the right and left sides) of the splenium of the corpus callosum in wild-type C57BL/6 mice and in C57BL/6 CX 3 CR1 eGFP/+ CCR2 RFP/+ transgenic mice. Next, CNS inflammation and demyelination was induced by means of a cuprizone-supplemented diet. The influence of IL13-MSC grafting on neuropathological alterations was monitored by non-invasive T 2 -weighted magnetic resonance imaging (MRI) and quantitative histological analyses, as compared to cuprizone-treated mice with control MSC grafts and/or cuprizone-treated mice without MSC injection., Results: In the first part of this study, we demonstrate that MSC graft-associated microglia and MSC graft-infiltrating macrophages are forced into alternative activation upon grafting of IL13-MSC, but not upon grafting of control MSC. In the second part of this study, we demonstrate that grafting of IL13-MSC, in addition to the recruitment of M2 polarised macrophages, limits cuprizone-induced microgliosis, oligodendrocyte death and demyelination. Furthermore, we here demonstrate that injection of IL13-MSC at both sides of the splenium leads to a superior protective effect as compared to a single injection at one side of the splenium., Conclusions: Controlled and localised production of IL13 by means of intracerebral MSC grafting has the potential to modulate cell graft- and pathology-associated microglial/macrophage responses, and to interfere with oligodendrocyte death and demyelinating events in the cuprizone mouse model.

Although implantation of cellular material in the central nervous system (CNS) is a key direction in CNS regenerative medicine, this approach is currently limited by the occurrence of strong endogenous immune cell responses. In a model of mesenchymal stem cell (MSC) grafting in the CNS of immune-competent mice, we previously described that MSC grafts become highly surrounded and invaded by Iba1(+) myeloid cells (microglia and/or macrophages). Here, following grafting of blue fluorescent protein (BFP)-expressing MSC in the CNS of CX3CR1(+/-) and CX3CR1(-/-) mice, our results indicate: (1) that the observed inflammatory response is independent of the fractalkine signalling axis, and (2) that a significant spatial distribution of Iba1(+) inflammatory cells occurs, in which Iba1(+) CX3CR1(+) myeloid cells mainly surround the MSC graft and Iba1(+) CX3CR1(-) myeloid cells mainly invade the graft at 10 days post transplantation. Although Iba1(+) CX3CR1(+) myeloid cells are considered to be of resident microglial origin, Iba1(+) CX3CR1(-) myeloid cells are most likely of peripheral monocyte/macrophage origin. In order to confirm the latter, we performed MSC-BFP grafting experiments in the CNS of eGFP(+) bone marrow chimeric C57BL/6 mice. Analysis of MSC-BFP grafts in the CNS of these mice confirmed our observation that peripheral monocytes/macrophages invade the MSC graft and that resident microglia surround the MSC graft site. Furthermore, analysis of major histocompatibility complex class II (MHCII) expression revealed that mainly macrophages, but not microglia, express this M1 pro-inflammatory marker in the context of MSC grafting in the CNS. These results again highlight the complexity of cell implantation immunology in the CNS.

Over the past decade a lot of research has been performed towards the therapeutic use of mesenchymal stem cells (MSCs) in neurodegenerative and neuroinflammatory diseases. MSCs have shown to be beneficial in different preclinical studies of central nervous system (CNS) disorders due to their immunomodulatory properties and their capacity to secrete various growth factors. Nevertheless, most of the transplanted cells die within the first hours after transplantation and induce a neuroinflammatory response. In order to increase the efficacy of MSC transplantation, it is thus imperative to completely characterise the mechanisms mediating neuroinflammation and cell death following MSC transplantation into the CNS. Consequently, different components of these cell death- and neuroinflammation-inducing pathways can be targeted in an attempt to improve the therapeutic potential of MSCs for CNS disorders.

Although cell transplantation is increasingly suggested to be beneficial for the treatment of various neurodegenerative diseases, the therapeutic application of such intervention is currently hindered by the limited knowledge regarding central nervous system (CNS) transplantation immunology. In this study, we aimed to investigate the early post transplantation innate immune events following grafting of autologous mesenchymal stromal cells (MSC) in the CNS of immune competent mice. First, the survival of grafted Luciferase/eGFP-expressing MSC (MSC-Luc/eGFP) was demonstrated to be stable from on day 3 post implantation using in vivo bioluminescence imaging (BLI), which was further confirmed by quantitative histological analysis of MSC-Luc/eGFP graft survival. Additional histological analyses at week 1 and week 2 post grafting revealed the appearance of (i) graft-surrounding/-invading Iba1+ microglia and (ii) graft-surrounding GFAP+ astrocytes, as compared to day 0 post grafting. While the density of graft-surrounding astrocytes and microglia did not change between week 1 and week 2 post grafting, the density of graft-invading microglia significantly decreased between week 1 and week 2 post implantation. However, despite the observed decrease in microglial density within the graft site, additional phenotypic analysis of graft-invading microglia, based on CD11b- and MHCII-expression, revealed >50% of graft-invading microglia at week 2 post implantation to display an activated status. Although microglial expression of CD11b and MHCII is already suggestive for a pro-inflammatory M1-oriented phenotype, the latter was further confirmed by: (i) the expression of NOS2 by microglia within the graft site, and (ii) the absence of arginase 1-expression, an enzyme known to suppress NO activity in M2-oriented microglia, on graft-surrounding and -invading microglia. In summary, we here provide a detailed phenotypic analysis of post transplantation innate immune events in the CNS of mice, and warrant that such intervention is associated with an M1-oriented microglia response and severe astrogliosis., (Copyright © 2012 Elsevier GmbH. All rights reserved.)

Stem cell transplantation in the central nervous system (CNS) is currently under intensive investigation as a novel therapeutic approach for a variety of brain disorders and/or injuries. However, one of the main hurdles at the moment is the lack of standardized procedures to evaluate cell graft survival and behavior following transplantation into CNS tissue, thereby leading to the publication of confusing and/or conflicting research results. In this chapter, we therefore provide validated in vivo bioluminescence and postmortem histological procedures to quantitatively determine: (a) the survival of grafted stem cells, and (b) the microglial and astroglial cell responses following cell grafting.