Clinical potential of intravenous neural stem cell delivery for treatment of neuroinflammatory disease in mice?

Stem Cell Interventions in Neurology: From Bench to Bedside

Stem cell therapies are progressively redefining the treatment landscape for a spectrum of neurological and age-related disorders. This review discusses the molecular and functional attributes of stem cells, emphasizing the roles of neural stem cells and mesenchymal stem cells in the context of neurological diseases such as stroke, multiple sclerosis, amyotrophic lateral sclerosis, traumatic brain injury, Parkinson's disease, and Alzheimer's disease. The review also explores the potential of stem cells in addressing the aging process. The paper analyzes stem cells' intrinsic properties of self-renewal, differentiation, and paracrine effects, alongside the importance of laboratory-modified stem cells like induced pluripotent stem cells and transgenic stem cells. Insights into disease-specific stem cell treatments are offered, reviewing both successes and challenges in the field. This includes the translational difficulties from rodent studies to human trials. The review concludes by acknowledging the uncharted territories that warrant further investigation, emphasizing the potential roles of stem cell-derived exosomes and indole-related molecules, and aiming at providing a basic understanding of stem cell therapies.

The Effect of Leukocyte- and Platelet-Rich Fibrin on Central and Peripheral Nervous System Neurons-Implications for Biomaterial Applicability

Leukocyte- and Platelet-Rich Fibrin (L-PRF) is a second-generation platelet concentrate that is prepared directly from the patient's own blood. It is widely used in the field of regenerative medicine, and to better understand its clinical applicability we aimed to further explore the biological properties and effects of L-PRF on cells from the central and peripheral nervous system. To this end, L-PRF was prepared from healthy human donors, and confocal, transmission, and scanning electron microscopy as well as secretome analysis were performed on these clots. In addition, functional assays were completed to determine the effect of L-PRF on neural stem cells (NSCs), primary cortical neurons (pCNs), and peripheral dorsal root ganglion (DRG) neurons. We observed that L-PRF consists of a dense but porous fibrin network, containing leukocytes and aggregates of activated platelets that are distributed throughout the clot. Antibody array and ELISA confirmed that it is a reservoir for a plethora of growth factors. Key molecules that are known to have an effect on neuronal cell functions such as brain-derived neurotrophic factor (BDNF), nerve growth factor (NGF), vascular endothelial growth factor (VEGF), and platelet-derived growth factor (PDGF) were slowly released over time from the clots. Next, we found that the L-PRF secretome had no significant effect on the proliferative and metabolic activity of NSCs, but it did act as a chemoattractant and improved the migration of these CNS-derived stem cells. More importantly, L-PRF growth factors had a detrimental effect on the survival of pCNs, and consequently, also interfered with their neurite outgrowth. In contrast, we found a positive effect on peripheral DRG neurons, and L-PRF growth factors improved their survival and significantly stimulated the outgrowth and branching of their neurites. Taken together, our study demonstrates the positive effects of the L-PRF secretome on peripheral neurons and supports its use in regenerative medicine but care should be taken when using it for CNS applications.

Neural Stem Cell-Based Therapies and Glioblastoma Management: Current Evidence and Clinical Challenges

Gliomas, which account for nearly a quarter of all primary CNS tumors, present significant contemporary therapeutic challenges, particularly the highest-grade variant (glioblastoma multiforme), which has an especially poor prognosis. These difficulties are due to the tumor's aggressiveness and the adverse effects of radio/chemotherapy on the brain. Stem cell therapy is an exciting area of research being explored for several medical issues. Neural stem cells, normally present in the subventricular zone and the hippocampus, preferentially migrate to tumor masses. Thus, they have two main advantages: They can minimize the side effects associated with systemic radio/chemotherapy while simultaneously maximizing drug delivery to the tumor site. Another feature of stem cell therapy is the variety of treatment approaches it allows. Stem cells can be genetically engineered into expressing a wide variety of immunomodulatory substances that can inhibit tumor growth. They can also be used as delivery vehicles for oncolytic viral vectors, which can then be used to combat the tumorous mass. An alternative approach would be to combine stem cells with prodrugs, which can subsequently convert them into the active form upon migration to the tumor mass. As with any therapeutic modality still in its infancy, much of the research regarding their use is primarily based upon knowledge gained from animal studies, and a number of ongoing clinical trials are currently investigating their effectiveness in humans. The aim of this review is to highlight the current state of stem cell therapy in the treatment of gliomas, exploring the different mechanistic approaches, clinical applicability, and the existing limitations.

Murine induced pluripotent stem cell-derived neuroimmune cell culture models emphasize opposite immune-effector functions of interleukin 13-primed microglia and macrophages in terms of neuroimmune toxicity

Cellular models of induced pluripotent stem cell (iPSC)-derived microglia and macrophages are an emerging toolbox to investigate neuroinflammation in vitro. We previously demonstrated that murine iPSC-microglia and iPSC-macrophages display phenotypical activation properties highly comparable to microglia and macrophages in vivo. Here we extended the characterization of iPSC-microglia and iPSC-macrophages with the analysis of their transcriptome profile. Next, these cellular models were employed to evaluate neuroimmune toxicity in vitro and to investigate the immune-modulatory properties of interleukin 13 (IL13), a cytokine known for its ability to protect against neuroinflammation-induced pathology by modulating microglia and macrophage activation. iPSC-microglia and iPSC-macrophages, in co-culture with astrocyte-committed neural stem cells (NSC), were (pre)treated with IL13 and stimulated with lipopolysaccharide (LPS) and interferon γ (IFNγ), to assess how IL13 modulates their inflammatory response. Additionally, the use of luciferase-expressing NSC (Luc-NSC) allowed real-time monitoring of immune-mediated neurotoxicity. Despite the known anti-inflammatory properties of IL13, iPSC-microglia primed with IL13 before LPS + IFNγ stimulation significantly increased NO secretion. This was associated with a marked reduction of the luminescence signal produced by Luc-NSC. Interestingly, we observed that IL13 signaling has a divergent functional outcome in microglia as compared to macrophages, as for the latter no major alterations in NO release and Luc-NSC viability were observed upon IL13 (pre)treatment. Finally, the striking IL13-induced upregulation of NO secretion by microglia under pro-inflammatory conditions was confirmed in vivo, where intracerebral delivery of IL13 increased inducible nitric oxide synthase mRNA expression. Concluding, we applied iPSC-derived neuroimmune cell culture models to identify distinct neuroimmune (toxicity) responses of microglia and macrophages to IL13-based immune modulation.

Recent advances of induced pluripotent stem cells application in neurodegenerative diseases

Stem cell is defined by its ability to self-renewal and generates differentiated functional cell types, which are derived from the embryo and various sources of postnatal animal. These cells can be divided according to their potential development into totipotent, unipotent, multipotent andpluripotent. Pluripotent is considered as the most important type due to its advantageous capability to create different cell types of the body in a similar behavior as embryonic stem cell. Induced pluripotent stem cells (iPSCs) are adult cells that maintain the characteristics of embryonic stem cells because it can be genetically reprogrammed to an embryonic stem cell-like state via express genes and transcription factors. Such cells provide an efficient pathway to explorehuman diseases and their corresponding therapy, particularly, neurodevelopmental disorders. Consequently, iPSCs can be investigated to check the specific mutations of neurodegenerative disease due to their unique ability to differentiate into neural cell types and/or neural organoids. The current review addresses the different neurodegenerative diseases model by using iPSCs approach such as Alzheimer's diseases (AD), Parkinson diseases (PD),multiplesclerosis(MS) and psychiatric disorders. We also highlight the importance of autophagy in neurodegenerative diseases.

Murine iPSC-derived microglia and macrophage cell culture models recapitulate distinct phenotypical and functional properties of classical and alternative neuro-immune polarisation

The establishment and validation of reliable induced pluripotent stem cell (iPSC)-derived in vitro models to study microglia and monocyte/macrophage immune function holds great potential for fundamental and translational neuro-immunology research. In this study, we first demonstrate that ramified CX₃CR1⁺ iPSC-microglia (cultured within a neural environment) and round-shaped CX₃CR1^- iPSC-macrophages can easily be differentiated from newly established murine CX₃CR1^eGFP/+CCR2^RFP/+ iPSC lines. Furthermore, we show that obtained murine iPSC-microglia and iPSC-macrophages are distinct cell populations, even though iPSC-macrophages may upregulate CX₃CR1 expression when cultured within a neural environment. Next, we characterized the phenotypical and functional properties of murine iPSC-microglia and iPSC-macrophages following classical and alternative immune polarisation. While iPSC-macrophages could easily be triggered to adopt a classically-activated or alternatively-activated phenotype following, respectively, lipopolysaccharide + interferon γ or interleukin 13 (IL13) stimulation, iPSC-microglia and iPSC-macrophages cultured within a neural environment displayed a more moderate activation profile as characterised by the absence of MHCII expression upon classical immune polarisation and the absence of Ym1 expression upon alternative immune polarisation. Finally, extending our preceding in vivo studies, this striking phenotypical divergence was also observed for resident microglia and infiltrating monocytes within highly inflammatory cortical lesions in CX₃CR1^eGFP/+CCR2^RFP/+ mice subjected to middle cerebral arterial occlusion (MCAO) stroke and following IL13-mediated therapeutic intervention thereon. In conclusion, our study demonstrates that the applied murine iPSC-microglia and iPSC-macrophage culture models are able to recapitulate in vivo microglia and monocyte/macrophage ontogeny and corresponding phenotypical/functional properties upon classical and alternative immune polarisation, and therefore represent a valuable in vitro platform to further study and modulate microglia and (infiltrating) monocyte immune responses under neuro-inflammatory conditions within a neural environment.

Preconditioning of Human Dental Pulp Stem Cells with Leukocyte- and Platelet-Rich Fibrin-Derived Factors Does Not Enhance Their Neuroregenerative Effect

Pathologies of the central nervous system are characterized by loss of brain tissue and neuronal function which cannot be adequately restored by endogenous repair processes. This stresses the need for novel treatment options such as cell-based therapies that are able to restore damaged tissue or stimulate repair. This study investigated the neuroregenerative potential of the conditioned medium of human dental pulp stem cells (CM-hDPSCs) on neural stem cell (NSC) proliferation and migration as well as on neurite outgrowth of primary cortical neurons (pCNs). Additionally, the effect of leukocyte- and platelet-rich fibrin (L-PRF) priming on the neuroregenerative potential of the hDPSC secretome on NSCs and pCNs was evaluated. L-PRF contains factors that enhance stem cell-induced regeneration, but its effect on hDPSC-mediated neuroregeneration is unknown. This study demonstrated that CM-hDPSCs enhanced neuritogenesis. Moreover, CM-hDPSCs had a chemoattractant effect on NSCs. Although priming hDPSCs with L-PRF increased brain-derived neurotrophic factor secretion, no additional effects on the paracrine-mediated repair mechanisms were observed. These data support the neuroregenerative potential of hDPSCs, and although priming had no additional effect, the potential of L-PRF-primed hDPSCs on distinct regenerative mechanisms remains to be clarified.

Tracking Neural Progenitor Cell Migration in the Rodent Brain Using Magnetic Resonance Imaging

The study of neurogenesis and neural progenitor cells (NPCs) is important across the biomedical spectrum, from learning about normal brain development and studying disease to engineering new strategies in regenerative medicine. In adult mammals, NPCs proliferate in two main areas of the brain, the subventricular zone (SVZ) and the subgranular zone, and continue to migrate even after neurogenesis has ceased within the rest of the brain. In healthy animals, NPCs migrate along the rostral migratory stream (RMS) from the SVZ to the olfactory bulb, and in diseased animals, NPCs migrate toward lesions such as stroke and tumors. Here we review how MRI-based cell tracking using iron oxide particles can be used to monitor and quantify NPC migration in the intact rodent brain, in a serial and relatively non-invasive fashion. NPCs can either be labeled directly in situ by injecting particles into the lateral ventricle or RMS, where NPCs can take up particles, or cells can be harvested and labeled in vitro, then injected into the brain. For in situ labeling experiments, the particle type, injection site, and image analysis methods have been optimized and cell migration toward stroke and multiple sclerosis lesions has been investigated. Delivery of labeled exogenous NPCs has allowed imaging of cell migration toward more sites of neuropathology, which may enable new diagnostic and therapeutic opportunities for as-of-yet untreatable neurological diseases.

Loss of Neuroglobin Expression Alters Cdkn1a/Cdk6-Expression Resulting in Increased Proliferation of Neural Stem Cells

In the quest to unravel its functional significance, neuroglobin (Ngb), a brain-specific neuroprotective protein, has recently been proposed as an actor in neurodevelopment. As neural stem cells (NSCs) are fundamental during brain development, the present study aimed at investigating the role of Ngb in the growth and proliferation of NSCs by comparing an Ngb-floxed (Ngb_fl-)NSC line, equivalent to the wild-type cellular situation, with an in-house created Ngb knockout (Ngb_KO-)NSC line. Ngb_KO-NSCs were characterized by an increased growth and proliferation capacity in vitro, supported by RNA sequencing and western blot results reporting the downregulation of Cdkn1a and the upregulation of Cdk6, both enhancing the cell cycle. Based on additional gene ontology enrichment and pathway analyses, we hypothesize that the loss of Ngb affects multiple cellular signaling pathways with the most important being the Akt-Tp53 axis.

Immune remodelling of stromal cell grafts in the central nervous system: therapeutic inflammation or (harmless) side-effect?

Over the past two decades, several cell types with fibroblast-like morphology, including mesenchymal stem/stromal cells, but also other adult, embryonic and extra-embryonic fibroblast-like cells, have been brought forward in the search for cellular therapies to treat severe brain injuries and/or diseases. Although current views in regenerative medicine are highly focused on the immune modulating and regenerative properties of stromal cell transplantation in vivo, many open questions remain regarding their true mode of action. In this perspective, this study integrates insights gathered over the past 10 years to formulate a unifying model of the cellular events that accompany fibroblast-like cell grafting in the rodent brain. Cellular interactions are discussed step-by-step, starting from the day of implantation up to 10 days after transplantation. During the short period that precedes stable settlement of autologous/syngeneic stromal cell grafts, there is a complex interplay between hypoxia-mediated cell death of grafted cells, neutrophil invasion, microglia and macrophage recruitment, astrocyte activation and neo-angiogenesis within the stromal cell graft site. Consequently, it is speculated that regenerative processes following cell therapeutic intervention in the CNS are not only modulated by soluble factors secreted by grafted stromal cells (bystander hypothesis), but also by in vivo inflammatory processes following stromal cell grafting. Copyright © 2016 John Wiley & Sons, Ltd.

The role of stem cell therapy in multiple sclerosis: An overview of the current status of the clinical studies

The complexity of multiple sclerosis (MS) and the incompetence of a large number of promised treatments for MS urge us to plan new and more effective therapeutic approaches that aim to suppress ongoing autoimmune responses and induction of local endogenous regeneration. Emerging data propose that hematopoietic, mesenchymal, and neural stem cells have the potential to restore self-tolerance, provide in situ immunomodulation and neuroprotection, as well as promote regeneration. Thus, in this article, we will first provide an overview of the cell sources for proposed mechanisms that contribute to the beneficial effects of stem cell transplantation, the ideal route and/or timing of stem cell-based therapies for each main stem cell group, and finally, an overview of the current status of stem cell research in clinical trial stages in MS by comparable and healthy therapeutic effects of different stem cell therapies for MS patients.

Neural and mesenchymal stem cells in animal models of Huntington's disease: past experiences and future challenges

Huntington's disease (HD) is an inherited disease that causes progressive nerve cell degeneration. It is triggered by a mutation in the HTT gene that strongly influences functional abilities and usually results in movement, cognitive and psychiatric disorders. HD is incurable, although treatments are available to help manage symptoms and to delay the physical, mental and behavioral declines associated with the condition. Stem cells are the essential building blocks of life, and play a crucial role in the genesis and development of all higher organisms. Ablative surgical procedures and fetal tissue cell transplantation, which are still experimental, demonstrate low rates of recovery in HD patients. Due to neuronal cell death caused by accumulation of the mutated huntingtin (mHTT) protein, it is unlikely that such brain damage can be treated solely by drug-based therapies. Stem cell-based therapies are important in order to reconstruct damaged brain areas in HD patients. These therapies have a dual role: stem cell paracrine action, stimulating local cell survival, and brain tissue regeneration through the production of new neurons from the intrinsic and likely from donor stem cells. This review summarizes current knowledge on neural stem/progenitor cell and mesenchymal stem cell transplantation, which has been carried out in several animal models of HD, discussing cell distribution, survival and differentiation after transplantation, as well as functional recovery and anatomic improvements associated with these approaches. We also discuss the usefulness of this information for future preclinical and clinical studies in HD.

Early Inflammatory Responses following Cell Grafting in the CNS Trigger Activation of the Subventricular Zone: A Proposed Model of Sequential Cellular Events

While multiple rodent preclinical studies, and to a lesser extent human clinical trials, claim the feasibility, safety, and potential clinical benefit of cell grafting in the central nervous system (CNS), currently only little convincing knowledge exists regarding the actual fate of the grafted cells and their effect on the surrounding environment (or vice versa). Our preceding studies already indicated that only a minor fraction of the initially grafted cell population survives the grafting process, while the surviving cell population becomes invaded by highly activated microglia/macrophages and surrounded by reactive astrogliosis. In the current study, we further elaborate on early cellular and inflammatory events following syngeneic grafting of eGFP mouse embryonic fibroblasts (mEFs) in the CNS of immunocompetent mice. Based on obtained quantitative histological data, we here propose a detailed mathematically derived working model that sequentially comprises hypoxia-induced apoptosis of grafted mEFs, neutrophil invasion, neoangiogenesis, microglia/macrophage recruitment, astrogliosis, and eventually survival of a limited number of grafted mEFs. Simultaneously, we observed that the cellular events following mEF grafting activates the subventricular zone neural stem and progenitor cell compartment. This proposed model therefore further contributes to our understanding of cell graft-induced cellular responses and will eventually allow for successful manipulation of this intervention.

Intranasal delivery of stem cells as therapy for central nervous system disease

Stem cells, upon entering the CNS, can preferentially migrate into disease foci, where they exert therapeutic effects that compensate for lost tissue, reconstructing damaged neuronal circuitry and establishing in the brain a new microenvironment suitable for cell survival. However, the route of stem cell delivery into the CNS remains a challenge: with systemic administration (e.g., intravenous injection), a fraction of cells may be trapped in other organs than the CNS, while direct CNS injections, e.g., intracerebroventricular or transcranial, are invasive. Intranasal (i.n.) delivery of stem cells, in contrast, can effectively bypass the blood-brain barrier, rapidly enter the CNS, and minimize systemic distribution. I.n. delivery of stem cells may therefore be a safe and non-invasive way of targeting the CNS and would thus be a promising therapeutic option for CNS disease. In this review we discuss the i.n. route for stem cell delivery into the CNS, and the perspectives of i.n. stem cell-based therapy in CNS disease.

Neural stem/progenitor cells induce conversion of encephalitogenic T cells into CD4+-CD25+- FOXP3+ regulatory T cells

An immune role of neural stem/progenitor cells (NSPCs) has been proposed in many recent studies; however much still remains to be elucidated. In the current investigation, we report that NSPCs possess the ability to convert encephalitogenic T cells into CD4(+)-CD25(+)-FOXP3(+) regulatory T cells (T(reg)). Encephalitogenic and nonencephalitogenic T cells isolated from sham and Japanese encephalitis virus (JEV) infected animals were co-cultured with mouse NSPCs. Post co-culture, significant increase in the number of T(regs) was observed from encephalitogenic T cells co-cultured with NSPCs. This increased conversion was found to be dependent on direct contact between T cells and NSPCs. Neutralization of TGF-β and IFN-γ in NSPC cultures abrogated this increased conversion of encephalitogenic T cells into T(regs). Flow cytometric, quantitative RT-PCR, and immunoblot analysis of both T cells and NSPCs revealed surface and intracellular changes post co-culture. Co-stimulatory molecules (B7) and ICAM-1 were increased on NSPCs post co-culture; levels of TGFβ, IFNγ, and TGFβR1 were also increased in NSPCs. This study provides a basic insight into the interaction between CNS-infiltrating encephalitogenic T cells and NSPCs during viral encephalitis. Conversion of encephalitogenic T cells into CD4(+)-CD25(+)-FOXP3(+) T(regs) through interaction with NSPCs indicates an attempt in regulation of excessive inflammation in the CNS.

Endothelial Progenitor Cells Derived From Wharton's Jelly of Human Umbilical Cord Attenuate Ischemic Acute Kidney Injury by Increasing Vascularization and Decreasing Apoptosis, Inflammation, and Fibrosis

Ischemia-reperfusion (I/R) injury to the kidney, a major cause of acute renal failure in humans, is associated with a high mortality, and the development of a new therapeutic strategy is therefore highly desirable. In this study, we examined the therapeutic potential of implantation of endothelial progenitor cells (EPCs) isolated from Wharton's jelly of human umbilical cords in the treatment of renal I/R injury in mice. To visualize the localization of the transplanted EPCs, the cells were labeled with Q-tracker before injection into the renal capsule. Mice with renal I/R injury showed a significant increase in blood urea nitrogen and creatinine levels, and these effects were decreased by EPC transplantation. The kidney injury score in the mice with I/R injury was also significantly decreased by EPC transplantation. EPC transplantation increased the microvascular density, and some of the EPCs surrounded and were incorporated into microvessels. In addition, EPC transplantation inhibited the I/R-induced cell apoptosis of endothelial, glomerular, and renal tubular cells, as demonstrated by TUNEL staining, and significantly reduced reactive oxygen species production and the expression of the inflammatory chemokines macrophage inflammatory protein-2 and keratinocyte-derived cytokine, as shown by immunostaining and ELISA. Moreover, EPC transplantation reduced I/R-induced fibrosis, as demonstrated by immunostaining for S100A4, a fibroblast marker, and by Jones silver staining. To our knowledge, this is the first report that transplantation of EPCs from Wharton's jelly of human umbilical cords might provide a novel therapy for ischemic acute kidney injury by promoting angiogenesis and inhibiting apoptosis, inflammation, and fibrosis.

Tackling the physiological barriers for successful mesenchymal stem cell transplantation into the central nervous system

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.

Immunopharmacological intervention for successful neural stem cell therapy: New perspectives in CNS neurogenesis and repair

The pharmacological support and stimulation of endogenous and transplanted neural stem cells (NSCs) is a major challenge in brain repair. Trauma to the central nervous system (CNS) results in a distinct inflammatory response caused by local and infiltrating immune cells. This makes NSC-supported regeneration difficult due to the presence of inhibitory immune factors which are upregulated around the lesion site. The continual and dual role of the neuroinflammatory response leaves it difficult to decipher upon a single modulatory strategy. Therefore, understanding the influence of cytokines upon regulation of NSC self-renewal, proliferation and differentiation is crucial when designing therapies for CNS repair. There is a plethora of partially conflicting data in vitro and in vivo on the role of cytokines in modulating the stem cell niche and the milieu around NSC transplants. This is mainly due to the pleiotropic role of many factors. In order for cell-based therapy to thrive, treatment must be phase-specific to the injury and also be personalized for each patient, i.e. taking age, sex, neuroimmune and endocrine status as well as other key parameters into consideration. In this review, we will summarize the most relevant information concerning interleukin (IL)-1, IL-4, IL-10, IL-15, IFN-γ, the neuropoietic cytokine family and TNF-α in order to extract promising therapeutic approaches for further research. We will focus on the consequences of neuroinflammation on endogenous brain stem cells and the transplantation environment, the effects of the above cytokines on NSCs, as well as immunopharmacological manipulation of the microenvironment for potential therapeutic use.

Injury-dependent retention of intraportally administered mesenchymal stromal cells following partial hepatectomy of steatotic liver does not lead to improved liver recovery

The aim of this study was to evaluate the effect of bone marrow-derived mesenchymal stromal cell (BM-MSC) administration on liver function following partial hepatectomy (PHx) of methionine/choline-deficient (MCD) diet induced steatotic livers in rodents. Here we identified and validated serum cholinesterase (CHE) and triglyceride (TG) levels as non-invasive markers to longitudinally monitor rat liver function. Using in vivo bioluminescence imaging, retention of BM-MSC in the liver was observed following intraportal administration, but not after intravenous administration. Therefore, BM-MSC were intraportally delivered to investigate the effect on liver recovery and/or regeneration after PHx. However, despite recovery to normal body weight, liver weight and NAS score, both serum CHE and TG levels of non-treated and cell-treated rats with PHx after MCD diet remained significantly lower as compared to those of control rats. Importantly, serum CHE levels, but not TG levels, of cell-treated rats remained significantly lower as compared to those of non-treated rats, thereby warranting that certain caution should be considered for future clinical application of IP BM-MSC administration in order to promote liver regeneration and/or function.

Similarities between inherited demyelinating neuropathies and Wallerian degeneration: an old repair program may cause myelin and axon perturbation under nonlesion conditions

Wallerian degeneration (WD) and inherited demyelinating neuropathies of the Charcot-Marie-Tooth type 1 (CMT1) appear to represent completely distinct events. CMT1-like diseases are chronic disorders of peripheral nerves that are genetically caused and lead to secondary neurodegenerative events, resulting in usually non-treatable disabilities, whereas WD is an acute, usually transient, reaction on injuries, aiming to allow peripheral nerve regeneration. Despite these differences, there are some striking similarities regarding molecular characteristics of neural cells in the affected peripheral nerves. The most conspicuous similarities might comprise the inflammatory component in both situations, as identified in appropriate mouse models. However, although inflammation is a beneficial component in WD, leading to removal of regrowth-repellent myelin debris, inflammation in CMT1 mouse models causes damage of initially intact nerve fibers. We hypothesize that, in CMT1 models, molecular pathways are activated that are shared with an important repair program after peripheral nerve injury, but lead to neural perturbation when activated under nonlesion conditions, as is the case in CMT1. These novel insights into the pathogenesis of CMT1 might be instrumental for the development of new therapeutic options in humans.

Cell size and velocity of injection are major determinants of the safety of intracarotid stem cell transplantation

Intracarotid transplantation has shown potential for efficient stem cell delivery to the brain. However, reported complications, such as compromised cerebral blood flow (CBF), prompted us to perform further safety studies. Glial-restricted precursors (GRPs) and mesenchymal stem cells (MSCs) were transplanted into the internal carotid artery of rats (n=99), using a microcatheter. Magnetic resonance imaging was used to detect post-transplantation complications, including the development of stroke, for the following experimental variables: cell size, cell dose, cell infusion velocity, delay between artery occlusion and cell infusion, discordant versus concordant xenografting, and intracarotid transplantation with preserved versus compromised blood flow. Immunocompatibility and delayed infusion did not affect the number of complications. An infusion velocity over 1 mL/minute often resulted in stroke (27 out of 44 animals), even with an infusion of vehicle, whereas a lower velocity (0.2 mL/minute) was safe for the infusion of both vehicle and smaller cells (GRPs, diameter=15 μm). Infusion of larger cells (MSCs, diameter=25 μm) resulted in a profound decrease (75±17%) in CBF. Stroke lesions occurred frequently (12 out of 15 animals) when injecting 2 × 10(6) MSCs, but not after lowering the dose to 1 × 10(6) cells. The present results show that cell size and infusion velocity are critical factors in developing safe protocols for intracarotid stem cell transplantation.

Intranasal Delivery of Neural Stem Cells: A CNS-specific, Non-invasive Cell-based Therapy for Experimental Autoimmune Encephalomyelitis

The therapeutic potential of adult neural stem cells (aNSCs) has been shown in EAE, an animal model of MS, administered by either i.c.v. or i.v. injection. However, i.c.v. is an invasive approach, while the i.v. route of aNSCs is associated with a non-specific immune suppression in the periphery. Here we demonstrate that intranasal (i.n.) delivery of fluorescently labeled aNSCs resulted in their appearance in the olfactory bulb, cortex, hippocampus, striatum, brainstem, and spinal cord. These cells induce functional recovery from ongoing EAE similar to that achieved with i.v. injected aNSCs, with comparable anti-inflammatory and remeylination effects in CNS inflammatory foci. Importantly, unlike the peripheral immune suppression brought about by i.v. NSCs, intranasal delivery did not influence peripheral immune responses. We conclude that aNSCs can be reliably delivered to the CNS via the nasal route to induce functional recovery and confer immunomodulation and remyelination in EAE. Intranasal administration of NSCs provides a highly promising, noninvasive and CNS-specific alternative to current cell-based approaches in treating EAE.

Quantitative evaluation of stem cell grafting in the central nervous system of mice by in vivo bioluminescence imaging and postmortem multicolor histological analysis

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.

Spatiotemporal evolution of early innate immune responses triggered by neural stem cell grafting

Introduction

Transplantation of neural stem cells (NSCs) is increasingly suggested to become part of future therapeutic approaches to improve functional outcome of various central nervous system disorders. However, recently it has become clear that only a small fraction of grafted NSCs display long-term survival in the (injured) adult mouse brain. Given the clinical invasiveness of NSC grafting into brain tissue, profound characterisation and understanding of early post-transplantation events is imperative to claim safety and efficacy of cell-based interventions.

Methods

Here, we applied in vivo bioluminescence imaging (BLI) and post-mortem quantitative histological analysis to determine the localisation and survival of grafted NSCs at early time points post-transplantation.

Results

An initial dramatic cell loss (up to 80% of grafted cells) due to apoptosis could be observed within the first 24 hours post-implantation, coinciding with a highly hypoxic NSC graft environment. Subsequently, strong spatiotemporal microglial and astroglial cell responses were initiated, which stabilised by day 5 post-implantation and remained present during the whole observation period. Moreover, the increase in astrocyte density was associated with a high degree of astroglial scarring within and surrounding the graft site. During the two-week follow up in this study, the NSC graft site underwent extensive remodelling with NSC graft survival further declining to around 1% of the initial number of grafted cells.

Conclusions

The present study quantitatively describes the early post-transplantation events following NSC grafting in the adult mouse brain and warrants that such intervention is directly associated with a high degree of cell loss, subsequently followed by strong glial cell responses.

Multimodal in vivo imaging reveals limited allograft survival, intrapulmonary cell trapping and minimal evidence for ischemia-directed BMSC homing

Background

Despite positive reports on the efficacy of stem cell therapy for the treatment of cardiovascular disease, the nature of stem cell homing to ischemic tissues remains elusive.

Results

We used a mouse model of peripheral tissue ischemia to study the survival and homing capacity of dual reporter gene (eGFP/Luciferase) expressing bone marrow-derived stromal cells (BMSC). Cell homing and survival were studied in the presence and absence of ciclosporin A (CsA) immunosuppression using bioluminescence imaging (BLI) together with confocal endomicroscopy. Different injection strategies were applied: central venous (CV), intra-arterial (IA) and intramuscular (IM). BLI and confocal endomicroscopy evidenced complete rejection of the IM injected allogeneic BMSC transplant within 5 to 10 days. Immunosuppression with CsA could only marginally prolong graft survival. IM injected BMSC did not migrate to the site of the arterial ligation. CV injection of BMSC resulted in massive pulmonary infarction, leading to respiratory failure and death. Intrapulmonary cell trapping was evidenced by confocal endomicroscopy, BLI and fluorescence microscopy. IA injection of BMSC proved to be a feasible and safe strategy to bypass the lung circulation. During the follow-up period, neither BLI nor confocal endomicroscopy revealed any convincing ischemia-directed homing of BMSC.

Conclusions

BLI and confocal endomicroscopy are complementary imaging techniques for studying the in vivo biology of dual reporter gene-expressing BMSC. Allogeneic BMSC survival is limited in an immunocompetent host and cannot be preserved by CsA immunosuppression alone. We did not find substantial evidence for ischemia-directed BMSC homing and caution against CV injection of BMSC, which can lead to massive pulmonary infarction.

Making the brain glow: in vivo bioluminescence imaging to study neurodegeneration

Bioluminescence imaging (BLI) takes advantage of the light-emitting properties of luciferase enzymes, which produce light upon oxidizing a substrate (i.e., D-luciferin) in the presence of molecular oxygen and energy. Photons emitted from living tissues can be detected and quantified by a highly sensitive charge-coupled device camera, enabling the investigator to noninvasively analyze the dynamics of biomolecular reactions in a variety of living model organisms such as transgenic mice. BLI has been used extensively in cancer research, cell transplantation, and for monitoring of infectious diseases, but only recently experimental models have been designed to study processes and pathways in neurological disorders such as Alzheimer disease, Parkinson disease, or amyotrophic lateral sclerosis. In this review, we highlight recent applications of BLI in neuroscience, including transgene expression in the brain, longitudinal studies of neuroinflammatory responses to neurodegeneration and injury, and in vivo imaging studies of neurogenesis and mitochondrial toxicity. Finally, we highlight some new developments of BLI compounds and luciferase substrates with promising potential for in vivo studies of neurological dysfunctions.

Intranasal delivery of neural stem/progenitor cells: a noninvasive passage to target intracerebral glioma

Stem cell-based therapies for neurological disorders, including brain tumors, advance continuously toward clinical trials. Optimized cell delivery to the central nervous system remains a challenge since direct intracerebral injection is an invasive method with low transplantation efficiency. We investigated the feasibility of intranasal administration of neural stem/progenitor cells (NSPCs) as an alternative, noninvasive, and direct passage for the delivery of stem cells to target malignant gliomas. Tumor-targeting and migratory pathways of murine and human NSPCs were investigated by intravital magnetic resonance imaging and in histological time course analyses in the intracerebral U87, NCE-G55T2, and syngenic Gl261 glioblastoma models. Intranasally administered NSPCs displayed a rapid, targeted tumor tropism with significant numbers of NSPCs accumulating specifically at the intracerebral glioma site within 6 hours after intranasal delivery. Histological time series analysis revealed that NSPCs migrated within the first 24 hours mainly via olfactory pathways but also by systemic distribution via the microvasculature of the nasal mucosa. Intranasal application of NSPCs leads to a rapid, targeted migration of cells toward intracerebral gliomas. The directional distribution of cells accumulating intra- and peritumorally makes the intranasal delivery of NSPCs a promising noninvasive and convenient alternative delivery method for the treatment of malignant gliomas with the possibility of multiple dosing regimens.

Stem cell therapy for multiple sclerosis: preclinical evidence beyond all doubt?

Stem cell transplantation holds great promise for restoration of neural function in various neurodegenerative disorders, including multiple sclerosis (MS). However, many questions remain regarding the true efficacy and precise mode of action of stem cell-based therapeutic approaches. Therefore, in this article, we will first discuss the ideal route and/or timing of stem cell-based therapies for experimental autoimmune encephalomyelitis (EAE), the most used preclinical animal model for MS. Next, we will provide an overview of the proposed mechanisms that contribute to the beneficial effects of stem cell transplantation observed during the treatment of rodent EAE. Reviews of current and past literature clearly demonstrate conceptual changes in the development of stem cell-based approaches for EAE/MS, leading to the identification of several major challenges to be tackled before (stem) cell therapy for rodent EAE can be safely and successfully translated to human therapy for MS.

Quantitative and phenotypic analysis of mesenchymal stromal cell graft survival and recognition by microglia and astrocytes in mouse brain

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.

Current challenges for the advancement of neural stem cell biology and transplantation research

Transplantation of neural stem cells (NSC) is hoped to become a promising primary or secondary therapy for the treatment of various neurodegenerative disorders of the central nervous system (CNS), as demonstrated by multiple pre-clinical animal studies in which functional recovery has already been demonstrated. However, for NSC therapy to be successful, the first challenge will be to define a transplantable cell population. In the first part of this review, we will briefly discuss the main features of ex vivo culture and characterisation of NSC. Next, NSC grafting itself may not only result in the regeneration of lost tissue, but more importantly has the potential to improve functional outcome through many bystander mechanisms. In the second part of this review, we will briefly discuss several pre-clinical studies that contributed to a better understanding of the therapeutic potential of NSC grafts in vivo. However, while many pre-clinical animal studies mainly report on the clinical benefit of NSC grafting, little is known about the actual in vivo fate of grafted NSC. Therefore, the third part of this review will focus on non-invasive imaging techniques for monitoring cellular grafts in the brain under in vivo conditions. Finally, as NSC transplantation research has evolved during the past decade, it has become clear that the host micro-environment itself, either in healthy or injured condition, is an important player in defining success of NSC grafting. The final part of this review will focus on the host environmental influence on survival, migration and differentiation of grafted NSC.

Multimodal imaging of stem cell implantation in the central nervous system of mice

During the past decade, stem cell transplantation has gained increasing interest as primary or secondary therapeutic modality for a variety of diseases, both in preclinical and clinical studies. However, to date results regarding functional outcome and/or tissue regeneration following stem cell transplantation are quite diverse. Generally, a clinical benefit is observed without profound understanding of the underlying mechanism(s). Therefore, multiple efforts have led to the development of different molecular imaging modalities to monitor stem cell grafting with the ultimate aim to accurately evaluate survival, fate and physiology of grafted stem cells and/or their micro-environment. Changes observed in one or more parameters determined by molecular imaging might be related to the observed clinical effect. In this context, our studies focus on the combined use of bioluminescence imaging (BLI), magnetic resonance imaging (MRI) and histological analysis to evaluate stem cell grafting. BLI is commonly used to non-invasively perform cell tracking and monitor cell survival in time following transplantation, based on a biochemical reaction where cells expressing the Luciferase-reporter gene are able to emit light following interaction with its substrate (e.g. D-luciferin). MRI on the other hand is a non-invasive technique which is clinically applicable and can be used to precisely locate cellular grafts with very high resolution, although its sensitivity highly depends on the contrast generated after cell labeling with an MRI contrast agent. Finally, post-mortem histological analysis is the method of choice to validate research results obtained with non-invasive techniques with highest resolution and sensitivity. Moreover end-point histological analysis allows us to perform detailed phenotypic analysis of grafted cells and/or the surrounding tissue, based on the use of fluorescent reporter proteins and/or direct cell labeling with specific antibodies. In summary, we here visually demonstrate the complementarities of BLI, MRI and histology to unravel different stem cell- and/or environment-associated characteristics following stem cell grafting in the CNS of mice. As an example, bone marrow-derived stromal cells, genetically engineered to express the enhanced Green Fluorescent Protein (eGFP) and firefly Luciferase (fLuc), and labeled with blue fluorescent micron-sized iron oxide particles (MPIOs), will be grafted in the CNS of immune-competent mice and outcome will be monitored by BLI, MRI and histology (Figure 1).

Comparative study on the therapeutic potential of neurally differentiated stem cells in a mouse model of multiple sclerosis

BACKGROUND

Transplantation of neural stem cells (NSCs) is a promising novel approach to the treatment of neuroinflammatory diseases such as multiple sclerosis (MS). NSCs can be derived from primary central nervous system (CNS) tissue or obtained by neural differentiation of embryonic stem (ES) cells, the latter having the advantage of readily providing an unlimited number of cells for therapeutic purposes. Using a mouse model of MS, we evaluated the therapeutic potential of NSCs derived from ES cells by two different neural differentiation protocols that utilized adherent culture conditions and compared their effect to primary NSCs derived from the subventricular zone (SVZ).

METHODOLOGY/PRINCIPAL FINDINGS

The proliferation and secretion of pro-inflammatory cytokines by antigen-stimulated splenocytes was reduced in the presence of SVZ-NSCs, while ES cell-derived NSCs exerted differential immunosuppressive effects. Surprisingly, intravenously injected NSCs displayed no significant therapeutic impact on clinical and pathological disease outcomes in mice with experimental autoimmune encephalomyelitis (EAE) induced by recombinant myelin oligodendrocyte glycoprotein, independent of the cell source. Studies tracking the biodistribution of transplanted ES cell-derived NSCs revealed that these cells were unable to traffic to the CNS or peripheral lymphoid tissues, consistent with the lack of cell surface homing molecules. Attenuation of peripheral immune responses could only be achieved through multiple high doses of NSCs administered intraperitoneally, which led to some neuroprotective effects within the CNS.

CONCLUSION/SIGNIFICANCE

Systemic transplantation of these NSCs does not have a major influence on the clinical course of rMOG-induced EAE. Improving the efficiency at which NSCs home to inflammatory sites may enhance their therapeutic potential in this model of CNS autoimmunity.

Cell type-associated differences in migration, survival, and immunogenicity following grafting in CNS tissue

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 control-cell 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.

Intraventricularly injected Olig2-NSCs attenuate established relapsing-remitting EAE in mice

In multiple sclerosis (MS), a chronic inflammatory relapsing demyelinating disease, failure to control or repair damage leads to progressive neurological dysfunction and neurodegeneration. Implantation of neural stem cells (NSCs) has been shown to promote repair and functional recovery in the acute experimental autoimmune encephalomyelitis (EAE) animal model for MS; the major therapeutic mechanism of these NSCs appeared to be immune regulation. In the present study, we examined the efficacy of intraventricularly injected NSCs in chronic relapsing experimental autoimmune encephalomyelitis (CREAE), the animal disease model that is widely accepted to mimic most closely recurrent inflammatory demyelination lesions as observed in relapsing-remitting MS. In addition, we assessed whether priming these NSCs to become oligodendrocyte precursor cells (OPCs) by transient overexpression of Olig2 would further promote functional recovery, for example, by contributing to actual remyelination. Upon injection at the onset of the acute phase or the relapse phase of CREAE, NSCs as well as Olig2-NSCs directly migrated toward active lesions in the spinal cord as visualized by in vivo bioluminescence and biofluorescence imaging, and once in the spinal cord, the majority of Olig2-NSCs, in contrast to NSCs, differentiated into OPCs. The survival of Olig2-NSCs was significantly higher than that of injected control NSCs, which remained undifferentiated. Nevertheless, both Olig2-NSCs and NSC significantly reduced the clinical signs of acute and relapsing disease and, in case of Olig2-NSCs, even completely abrogated relapsing disease when administered early after onset of acute disease. We provide the first evidence that NSCs and in particular NSC-derived OPCs (Olig2-NSCs) ameliorate established chronic relapsing EAE in mice. Our experimental data in established neurological disease in mice indicate that such therapy may be effective in relapsing-remitting MS preventing chronic progressive disease.

Evaluation of intracellular labeling with micron-sized particles of iron oxide (MPIOs) as a general tool for in vitro and in vivo tracking of human stem and progenitor cells

Magnetic resonance imaging (MRI)-based tracking is increasingly attracting attention as a means of better understanding stem cell dynamics in vivo. Intracellular labeling with micrometer-sized particles of iron oxide (MPIOs) provides a practical MRI-based approach due to superior detectability relative to smaller iron oxide particles. However, insufficient information is available about the general utility across cell types and the effects on cell vitality of MPIO labeling of human stem cells. We labeled six human cell types from different sources: mesenchymal stem cells derived from bone marrow (MSCs), mesenchymal stem cells derived from adipose tissue (ASCs), presumptive adult neural stem cells (ad-NSCs), fetal neural progenitor cells (f-NPCs), a glioma cell line (U87), and glioblastoma tumor stem cells (GSCs), with two different sizes of MPIOs (0.9 and 2.84 µm). Labeling and uptake efficiencies were highly variable among cell types. Several parameters of general cell function were tested in vitro. Only minor differences were found between labeled and unlabeled cells with respect to proliferation rate, mitotic duration, random motility, and capacity for differentiation to specific phenotypes. In vivo behavior was tested in chicken embryos and severe combined immunodeficient (SCID) mice. Postmortem histology showed that labeled cells survived and could integrate into various tissues. MRI-based tracking over several weeks in the SCID mice showed that labeled GSCs and f-NPCs injected into the brain exhibited translocations similar to those seen for unlabeled cells and as expected from migratory behavior described in previous studies. The results support MPIO-based cell tracking as a generally useful tool for studies of human stem cell dynamics in vivo.

Spontaneous ocular and neurologic deficits in transgenic mouse models of multiple sclerosis and noninvasive investigative modalities: a review

Multiple sclerosis (MS) is an autoimmune, inflammatory, neurodegenerative, demyelinating disease of the central nervous system, predominantly involving myelinated neurons of the brain, spinal cord, and optic nerve. Optic neuritis is frequently associated with MS and often precedes other neurologic deficits associated with MS. A large number of patients experience visual defects and have abnormalities concomitant with neurologic abnormalities. Transgenic mice manifesting spontaneous neurologic and ocular disease are unique models that have revolutionized the study of MS. Spontaneous experimental autoimmune encephalomyelitis (sEAE) presents with spontaneous onset of demyelination, without the need of an injectable immunogen. This review highlights the various models of sEAE, their disease characteristics, and applicability for future research. The study of optic neuropathy and neurologic manifestations of demyelination in sEAE will expand our understanding of the pathophysiological mechanisms underlying MS. Early and precise diagnosis of MS with different noninvasive methods has opened new avenues in managing symptoms, reducing morbidity, and limiting disease burden. This review discusses the spectrum of available noninvasive techniques, such as electrophysiological and behavioral assessment, optical coherence tomography, scanning laser polarimetry, confocal scanning laser ophthalmoscopy, pupillometry, magnetic resonance imaging, positron emission tomography, gait, and cardiovascular monitoring, and their clinical relevance.

Meeting report of the first conference of the International Placenta Stem Cell Society (IPLASS)

The International Placenta Stem Cell Society (IPLASS) was founded in June 2010. Its goal is to serve as a network for advancing research and clinical applications of stem/progenitor cells isolated from human term placental tissues, including the amnio-chorionic fetal membranes and Wharton's jelly. The commitment of the Society to champion placenta as a stem cell source was realized with the inaugural meeting of IPLASS held in Brescia, Italy, in October 2010. Officially designated as an EMBO-endorsed scientific activity, international experts in the field gathered for a 3-day meeting, which commenced with "Meet with the experts" sessions, IPLASS member and board meetings, and welcome remarks by Dr. Ornella Parolini, President of IPLASS. The evening's highlight was a keynote plenary lecture by Dr. Diana Bianchi. The subsequent scientific program consisted of morning and afternoon oral and poster presentations, followed by social events. Both provided many opportunities for intellectual exchange among the 120 multi-national participants. This allowed a methodical and deliberate evaluation of the status of placental cells in research in regenerative and reparative medicine. The meeting concluded with Dr. Parolini summarizing the meeting's highlights. This further prepared the fertile ground on which to build the promising potential of placental cell research. The second IPLASS meeting will take place in September 2012 in Vienna, Austria. This meeting report summarizes the thought-provoking lectures delivered at the first meeting of IPLASS.