Improvement of spatial learning and memory deficits by intranasal administration of human olfactory ecto-mesenchymal stem cells in an Alzheimer's disease rat model

Mesenchymal stem cells therapy provides a new perspective of therapeutic approaches in the treatment of neurodegenerative diseases. The present study aimed to investigate the effects of intranasally transplanted human "olfactory ecto-mesenchymal stem cells" (OE-MSCs) in Alzheimer's disease (AD) rats. In this study, we isolated OE-MSCs from human olfactory lamina propria and phenotypically characterized them using immunocytochemistry and flow cytometry. The undifferentiated OE-MSCs were transplanted either by intranasal (IN) or intrahippocampal (IH) injection to rat models of AD, which were induced by injecting amyloid-beta (Aβ) intrahippocampally. Behavioral, histological, and molecular assessments were performed after a three-month recovery period. Based on the results, intranasal administration of OE-MSCs significantly reduced Aβ accumulation and neuronal loss, improved learning and memory impairments, and increased levels of BDNF (brain-derived neurotrophic factor) and NMDAR (N-methyl-D-Aspartate receptors) in the AD rat model. These changes were more significant in animals who received OE-MSCs by intranasal injection. The results of this study suggest that OE-MSCs have the potential to enhance cognitive function in AD, possibly mediated by BDNF and the NMDA receptors.

Combining physical & cognitive training with iPSC-derived dopaminergic neuron transplantation promotes graft integration & better functional outcome in parkinsonian marmosets

Parkinson's disease (PD) is a relentlessly progressive and currently incurable neurodegenerative disease with significant unmet medical needs. Since PD stems from the degeneration of midbrain dopaminergic (DA) neurons in a defined brain location, PD patients are considered optimal candidates for cell replacement therapy. Clinical trials for cell transplantation in PD are beginning to re-emerge worldwide with a new focus on induced pluripotent stem cells (iPSCs) as a source of DA neurons since they can be derived from adult somatic cells and produced in large quantities under current good manufacturing practices. However, for this therapeutic strategy to be realized as a viable clinical option, fundamental translational challenges need to be addressed including the manufacturing process, purity and efficacy of the cells, the method of delivery, the extent of host reinnervation and the impact of patient-centered adjunctive interventions. In this study we report on the impact of physical and cognitive training (PCT) on functional recovery in the nonhuman primate (NHP) model of PD after cell transplantation. We observed that at 6 months post-transplant, the PCT group returned to normal baseline in their daily activity measured by actigraphy, significantly improved in their sensorimotor and cognitive tasks, and showed enhanced synapse formation between grafted cells and host cells. We also describe a robust, simple, efficient, scalable, and cost-effective manufacturing process of engraftable DA neurons derived from iPSCs. This study suggests that integrating PCT with cell transplantation therapy could promote optimal graft functional integration and better outcome for patients with PD.

Enriching new transplantable RGC-like cells from retinal organoids for RGC replacement therapy

Optic neuropathies, such as glaucoma, are due to progressive retinal ganglion cells (RGCs) degeneration, result in irreversible vision loss. The promising RGCs replacement therapy for restoring vision are impeded by insufficient RGC-like cells sources. The present work was enriched one new type RGC-like cells using two surface markers CD184 and CD171 from human induced pluripotent stem cells (hiPSCs) by FACS sorting firstly. These new kind cells have well proliferation ability and possessed passage tolerance in vitro 2D or 3D spheroids culture, which kept expressing Pax6, Brn3b and βIII-Tubulin and so on. The transplanted CD184+CD171+ RGC-like cells could survive and integrate into the normal and optic nerve crush (ONC) mice retina, especially they were more inclined to across the optic nerve head and extend to the damaged optic nerve. These data support the feasible application for cell replacement therapy in RGC degenerative diseases, as well as help to develop new commercial cells sorting reagents and establish good manufacturing practice (GMP) grade RGC-like donor cells for further clinical application.

Identifying secreted biomarkers of dopaminergic ventral midbrain progenitor cells

BACKGROUND

Ventral midbrain (VM) dopaminergic progenitor cells derived from human pluripotent stem cells have the potential to replace endogenously lost dopamine neurons and are currently in preclinical and clinical development for treatment of Parkinson's Disease (PD). However, one main challenge in the quality control of the cells is that rostral and caudal VM progenitors are extremely similar transcriptionally though only the caudal VM cells give rise to dopaminergic (DA) neurons with functionality relevant for cell replacement in PD. Therefore, it is critical to develop assays which can rapidly and reliably discriminate rostral from caudal VM cells during clinical manufacturing.

METHODS

We performed shotgun proteomics on cell culture supernatants from rostral and caudal VM progenitor cells to search for novel secreted biomarkers specific to DA progenitors from the caudal VM. Key hits were validated by qRT-PCR and ELISA.

RESULTS

We identified and validated novel secreted markers enriched in caudal VM progenitor cultures (CPE, LGI1 and PDGFC), and found these markers to correlate strongly with the expression of EN1, which is a predictive marker for successful graft outcome in DA cell transplantation products. Other markers (CNTN2 and CORIN) were found to conversely be enriched in the non-dopaminergic rostral VM cultures. Key novel ELISA markers were further validated on supernatant samples from GMP-manufactured caudal VM batches.

CONCLUSION

As a non-invasive in-process quality control test for predicting correctly patterned batches of caudal VM DA cells during clinical manufacturing, we propose a dual ELISA panel measuring LGI1/CORIN ratios around day 16 of differentiation.

Human pluripotent stem cell-derived β cells: Truly immature islet β cells for type 1 diabetes therapy?

A century has passed since the Nobel Prize winning discovery of insulin, which still remains the mainstay treatment for type 1 diabetes mellitus (T1DM) to this day. True to the words of its discoverer Sir Frederick Banting, “insulin is not a cure for diabetes, it is a treatment”, millions of people with T1DM are dependent on daily insulin medications for life. Clinical donor islet transplantation has proven that T1DM is curable, however due to profound shortages of donor islets, it is not a mainstream treatment option for T1DM. Human pluripotent stem cell derived insulin-secreting cells, pervasively known as stem cell-derived β cells (SC-β cells), are a promising alternative source and have the potential to become a T1DM treatment through cell replacement therapy. Here we briefly review how islet β cells develop and mature in vivo and several types of reported SC-β cells produced using different ex vivo protocols in the last decade. Although some markers of maturation were expressed and glucose stimulated insulin secretion was shown, the SC-β cells have not been directly compared to their in vivo counterparts, generally have limited glucose response, and are not yet fully matured. Due to the presence of extra-pancreatic insulin-expressing cells, and ethical and technological issues, further clarification of the true nature of these SC-β cells is required.

Stem cell sources and characterization in the development of cell-based products for treating retinal disease: An NEI Town Hall report

National Eye Institute recently issued a new Strategic Plan outlining priority research areas for the next 5 years. Starting cell source for deriving stem cell lines is as an area with gaps and opportunities for making progress in regenerative medicine, a key area of emphasis within the NEI Strategic Plan. There is a critical need to understand how starting cell source affects the cell therapy product and what specific manufacturing capabilities and quality control standards are required for autologous vs allogeneic stem cell sources. With the goal of addressing some of these questions, in discussion with the community-at-large, NEI hosted a Town Hall at the Association for Research in Vision and Ophthalmology annual meeting in May 2022. This session leveraged recent clinical advances in autologous and allogeneic RPE replacement strategies to develop guidance for upcoming cell therapies for photoreceptors, retinal ganglion cells, and other ocular cell types. Our focus on stem cell-based therapies for RPE underscores the relatively advanced stage of RPE cell therapies to patients with several ongoing clinical trials. Thus, this workshop encouraged lessons learned from the RPE field to help accelerate progress in developing stem cell-based therapies in other ocular tissues. This report provides a synthesis of the key points discussed at the Town Hall and highlights needs and opportunities in ocular regenerative medicine.

Implantation of human olfactory ecto-mesenchymal stem cells restores locomotion in a rat model of Parkinson's disease

One of the complex neurodegenerative disorders is Parkinson disease (PD). PD is mainly caused by dopaminergic (DAergic) neuron degeneration in the midbrain. The loss of DAergic neurons is considered as a key reason of motor functional defects in PD patients. Cell replacement strategies are considered as an alternative remedy to effectively address neurodegeneration in PD. In this report, we evaluated the restorative effect of human olfactory ecto-mesenchymal stem cells (OE-MSCs) in rat models of PD. Accordingly, human OE-MSCs were isolated and phenotypically characterized by flow cytometry and immunocytochemistry. Next, the undifferentiated OE-MSCs were unilaterally transplanted into the striatum of 6-hydroxydopamine (6-OHDA)-lesioned rat models, followed by molecular and histological analyzes as well as assessment of motor skills. Our results displayed that the grafting of OE-MSCs increased the expression of DAergic markers namely dopamine transporter (DAT), tyrosine hydroxylase (TH), nuclear receptor related-1 (Nurr1) in a 6-OHDA model compared with that of control, detected by immunohistochemical staining and western blot. Moreover, noticeable improvements in motor coordination, muscle activity and locomotor performance were observed in 6-OHDA model of PD following OE-MSCs transplantation. Taken together, our finding indicates that undifferentiated OE-MSCs might be counted as an appropriate source for cell replacement therapy particularly aimed at PD.

Human stem cell models of polyglutamine diseases: Sources for disease models and cell therapy

Polyglutamine (polyQ) diseases are a group of neurodegenerative disorders involving expanded CAG repeats in pathogenic genes that are translated into extended polyQ tracts and lead to progressive neuronal degeneration in the affected brain. To date, there is no effective therapy for these diseases. Due to the complex pathologic mechanisms of these diseases, intensive research on the pathogenesis of their progression and potential treatment strategies is being conducted. However, animal models cannot recapitulate all aspects of neuronal degeneration. Pluripotent stem cells (PSCs), such as induced pluripotent stem cells (iPSCs) and embryonic stem cells (ESCs), can be used to study the pathological mechanisms of polyQ diseases, and the ability of autologous stem cell transplantation to treat these diseases. Differentiated PSCs, neuronal precursor cells/neural progenitor cells (NPCs) and mesenchymal stem cells (MSCs) are valuable resources for preclinical and clinical cell transplantation therapies. Here, we discuss diverse stem cell models and their ability to generate neurons involved in polyQ diseases, such as medium spiny neurons (MSNs), cortical neurons, cerebellar Purkinje cells (PCs) and motor neurons. In addition, we discuss potential therapeutic approaches, including stem cell replacement therapy and gene therapy.

In vitro platform establishes antigen-specific CD8+ T cell cytotoxicity to encapsulated cells via indirect antigen recognition

The curative potential of non-autologous cellular therapy is hindered by the requirement of anti-rejection therapy. Cellular encapsulation within nondegradable biomaterials has the potential to inhibit immune rejection, but the efficacy of this approach in robust preclinical and clinical models remains poor. While the responses of innate immune cells to the encapsulating material have been characterized, little attention has been paid to the contributions of adaptive immunity in encapsulated graft destabilization. Avoiding the limitations of animal models, we established an efficient, antigen-specific in vitro platform capable of delineating direct and indirect host T cell recognition to microencapsulated cellular grafts and evaluated their consequential impacts. Using ovalbumin (OVA) as a model antigen, we determined that alginate microencapsulation abrogates direct CD8⁺ T cell activation by interrupting donor-host interaction; however, indirect T cell activation, mediated by host antigen presenting cells (APCs) primed with shed donor antigens, still occurs. These activated T cells imparted cytotoxicity on the encapsulated cells, likely via diffusion of cytotoxic solutes. Overall, this platform delivers unique mechanistic insight into the impacts of hydrogel encapsulation on host adaptive immune responses, comprehensively addressing a long-standing hypothesis of the field. Furthermore, it provides an efficient benchtop screening tool for the investigation of new encapsulation methods and/or synergistic immunomodulatory agents.

Oxygen generating biomaterial improves the function and efficacy of beta cells within a macroencapsulation device

Tissue-engineered devices have the potential to significantly improve human health. A major impediment to the success of clinically scaled transplants, however, is insufficient oxygen transport, which leads to extensive cell death and dysfunction. To provide in situ supplementation of oxygen within a cellular implant, we developed a hydrolytically reactive oxygen generating material in the form of polydimethylsiloxane (PDMS) encapsulated solid calcium peroxide, termed OxySite. Herein, we demonstrate, for the first time, the successful implementation of this in situ oxygen-generating biomaterial to support elevated cellular function and efficacy of macroencapsulation devices for the treatment of type 1 diabetes. Under extreme hypoxic conditions, devices supplemented with OxySite exhibited substantially elevated beta cell and islet viability and function. Furthermore, the inclusion of OxySite within implanted macrodevices resulted in the significant improvement of graft efficacy and insulin production in a diabetic rodent model. Translating to human islets at elevated loading densities further validated the advantages of this material. This simple biomaterial-based approach for delivering a localized and controllable oxygen supply provides a broad and impactful platform for improving the therapeutic efficacy of cell-based approaches.

Restorative Mechanism of Neural Progenitor Cells Overexpressing Arginine Decarboxylase Genes Following Ischemic Injury

Cell replacement therapy using neural progenitor cells (NPCs) following ischemic stroke is a promising potential therapeutic strategy, but lacks efficacy for human central nervous system (CNS) therapeutics. In a previous in vitro study, we reported that the overexpression of human arginine decarboxylase (ADC) genes by a retroviral plasmid vector promoted the neuronal differentiation of mouse NPCs. In the present study, we focused on the cellular mechanism underlying cell proliferation and differentiation following ischemic injury, and the therapeutic feasibility of NPCs overexpressing ADC genes (ADC-NPCs) following ischemic stroke. To mimic cerebral ischemia in vitro , we subjected the NPCs to oxygen-glucose deprivation (OGD). The overexpressing ADC-NPCs were differentiated by neural lineage, which was related to excessive intracellular calcium-mediated cell cycle arrest and phosphorylation in the ERK1/2, CREB, and STAT1 signaling cascade following ischemic injury. Moreover, the ADC-NPCs were able to resist mitochondrial membrane potential collapse in the increasingly excessive intracellular calcium environment. Subsequently, transplanted ADC-NPCs suppressed infarct volume, and promoted neural differentiation, synapse formation, and motor behavior performance in an in vivo tMCAO rat model. The results suggest that ADC-NPCs are potentially useful for cell replacement therapy following ischemic stroke.

Corneal cell therapy: with iPSCs, it is no more a far-sight

Human-induced pluripotent stem cells (hiPSCs) provide a personalized approach to study conditions and diseases including those of the eye that lack appropriate animal models to facilitate the development of novel therapeutics. Corneal disease is one of the most common causes of blindness. Hence, significant efforts are made to develop novel therapeutic approaches including stem cell-derived strategies to replace the diseased or damaged corneal tissues, thus restoring the vision. The use of adult limbal stem cells in the management of corneal conditions has been clinically successful. However, its limited availability and phenotypic plasticity necessitate the need for alternative stem cell sources to manage corneal conditions. Mesenchymal and embryonic stem cell-based approaches are being explored; nevertheless, their limited differentiation potential and ethical concerns have posed a significant hurdle in its clinical use. hiPSCs have emerged to fill these technical and ethical gaps to render clinical utility. In this review, we discuss and summarize protocols that have been devised so far to direct differentiation of human pluripotent stem cells (hPSCs) to different corneal cell phenotypes. With the summarization, our review intends to facilitate an understanding which would allow developing efficient and robust protocols to obtain specific corneal cell phenotype from hPSCs for corneal disease modeling and for the clinics to treat corneal diseases and injury.

Stem Cell Derived Retinal Pigment Epithelium: The Role of Pigmentation as Maturation Marker and Gene Expression Profile Comparison with Human Endogenous Retinal Pigment Epithelium

In age-related macular degeneration (AMD) the retinal pigment epithelium (RPE) deteriorates, leading to photoreceptor decay and severe vision loss. New therapeutic strategies aim at RPE replacement by transplantation of pluripotent stem cell (PSC)-derived RPE. Several protocols to generate RPE have been developed where appearance of pigmentation is commonly used as indicator of RPE differentiation and maturation. It is, however, unclear how different pigmentation stages reflect developmental stages and functionality of PSC-derived RPE cells. We generated human embryonic stem cell-derived RPE (hESC-RPE) cells and investigated their gene expression profiles at early pigmentation (EP) and late pigmentation (LP) stages. In addition, we compared the hESC-RPE samples with human endogenous RPE. We used a common reference design microarray (44 K). Our analysis showed that maturing hESC-RPE, upon acquiring pigmentation, expresses markers specific for human RPE. Interestingly, our analysis revealed that EP and LP hESC-RPE do not differ much in gene expression. Our data further showed that pigmented hESC-RPE has a significant lower expression than human endogenous RPE in the visual cycle and oxidative stress pathways. In contrast, we observed a significantly higher expression of pathways related to the process adhesion-to-polarity model that is typical of developing epithelial cells. We conclude that, in vitro, the first appearance of pigmentation hallmarks differentiated RPE. However, further increase in pigmentation does not result in much significant gene expression changes and does not add important RPE functionalities. Consequently, our results suggest that the time span for obtaining differentiated hESC-RPE cells, that are suitable for transplantation, may be greatly reduced.

Generation of Human Neural Stem Cells by Direct Phenotypic Conversion

Human neural stem cells (hNSC) are multipotent adult stem cells. Various studies are underway worldwide to identify new methods for treatment of neurological diseases using hNSC. This chapter summarizes the latest research trends in and fields for application of patient-specific hNSC using direct phenotypic conversion technology. The aim of the study was to analyze the advantages and disadvantages of current technology and to suggest relevant directions for future hNSC research.

Concise Review: The Use of Stem Cells for Understanding and Treating Huntington's Disease

Two decades ago, researchers identified that a CAG expansion mutation in the huntingtin (HTT) gene was involved in the pathogenesis of Huntington's disease (HD). However, since the identification of the HTT gene, there has been no advance in the development of therapeutic strategies to prevent or reduce the progression of HD. With the recent advances in stem cell biology and human cell reprogramming technologies, several novel and exciting pathways have emerged allowing researchers to enhance their understanding of the pathogenesis of HD, to identify and screen potential drug targets, and to explore alternative donor cell sources for cell replacement therapy. This review will discuss the role of compensatory neurogenesis in the HD brain, the use of stem cell-based therapies for HD to replace or prevent cell loss, and the recent advance of cell reprogramming to model and/or treat HD. These new technologies, coupled with advances in genome editing herald a promising new era for HD research with the potential to identify a therapeutic strategy to alleviate this debilitating disorder. Stem Cells 2018;36:146-160.

Precise immune tolerance for hPSC derivatives in clinical application

Human pluripotent stem cells (hPSCs) promise a foreseeing future for regeneration medicine and cell replacement therapy with their abilities to produce almost any types of somatic cells of the body. The complicated immunogenicity of hPSC derivatives and context dependent responses in variable transplantations greatly hurdle the practical application of hPSCs in clinic. Especially for applications of hPSCs, induction of immune tolerance at the same time increases the risks of tumorigenesis. Over the past few years, thanks to the progress in immunology and practices in organ transplantation, endeavors on exploring strategies to induce long term protection of allogeneic transplants have shed light on overcoming this barrier. Novel genetic engineering techniques also allow to precisely cradle the immune response of transplantation. Here we reviewed the current understanding on immunogenicity, and efforts have been attempted on inducing immune tolerance for hPSC derivatives, with extra focus on modifying the graft cells. We also glimpse on employing cutting-edge genome editing technologies for this purpose, which will potentially endow hPSC derivatives with the nature of wide spectrum drugs for therapy.

Engineered hydrogels increase the post-transplantation survival of encapsulated hESC-derived midbrain dopaminergic neurons

Cell replacement therapies have broad biomedical potential; however, low cell survival and poor functional integration post-transplantation are major hurdles that hamper clinical benefit. For example, following striatal transplantation of midbrain dopaminergic (mDA) neurons for the treatment of Parkinson's disease (PD), only 1-5% of the neurons typically survive in preclinical models and in clinical trials. In general, resource-intensive generation and implantation of larger numbers of cells are used to compensate for the low post-transplantation cell-survival. Poor graft survival is often attributed to adverse biochemical, mechanical, and/or immunological stress that cells experience during and after implantation. To address these challenges, we developed a functionalized hyaluronic acid (HA)-based hydrogel for in vitro maturation and central nervous system (CNS) transplantation of human pluripotent stem cell (hPSC)-derived neural progenitors. Specifically, we functionalized the HA hydrogel with RGD and heparin (hep) via click-chemistry and tailored its stiffness to encourage neuronal maturation, survival, and long-term maintenance of the desired mDA phenotype. Importantly, ∼5 times more hydrogel-encapsulated mDA neurons survived after transplantation in the rat striatum, compared to unencapsulated neurons harvested from commonly used 2D surfaces. This engineered biomaterial may therefore increase the therapeutic potential and reduce the manufacturing burden for successful neuronal implantation.

Regenerative medicine for Parkinson's disease using differentiated nerve cells derived from human buccal fat pad stem cells

The purpose of this study was to evaluate the utility of human adipose stem cells derived from the buccal fat pad (hBFP-ASCs) for nerve regeneration. Parkinson's disease (PD) is a neurodegenerative disorder characterized by progressive death of dopaminergic neurons. PD is a candidate disease for cell replacement therapy because it has no fundamental therapeutic methods. We examined the properties of neural-related cells induced from hBFP-ASCs as a cell source for PD treatment. hBFP-ASCs were cultured in neurogenic differentiation medium for about 2 weeks. After the morphology of hBFP-ASCs changed to neural-like cells, the medium was replaced with neural maintenance medium. Cells differentiated from hBFP-ASCs showed neuron-like structures and expressed neuron markers (β3-tubulin, neurofilament 200, and microtubule-associated protein 2), an astrocyte marker (glial fibrillary acidic protein), or dopaminergic neuron-related marker (tyrosine hydroxylase). Induced neural cells were transplanted into a 6-hydroxydopamine (6-OHDA)-lesioned rat hemi-parkinsonian model. At 4 weeks after transplantation, 6-OHDA-lesioned rats were subjected to apomorphine-induced rotation analysis. The transplanted cells survived in the brain of rats as dopaminergic neural cells. No tumor formation was found after cell transplantation. We demonstrated differentiation of hBFP-ASCs into neural cells, and that transplantation of these neural cells improved the symptoms of model rats. Our results suggest that neurons differentiated from hBFP-ASCs would be applicable to cell replacement therapy of PD.

White paper on guidelines concerning enteric nervous system stem cell therapy for enteric neuropathies

Over the last 20 years, there has been increasing focus on the development of novel stem cell based therapies for the treatment of disorders and diseases affecting the enteric nervous system (ENS) of the gastrointestinal tract (so-called enteric neuropathies). Here, the idea is that ENS progenitor/stem cells could be transplanted into the gut wall to replace the damaged or absent neurons and glia of the ENS. This White Paper sets out experts' views on the commonly used methods and approaches to identify, isolate, purify, expand and optimize ENS stem cells, transplant them into the bowel, and assess transplant success, including restoration of gut function. We also highlight obstacles that must be overcome in order to progress from successful preclinical studies in animal models to ENS stem cell therapies in the clinic.

Induced Pluripotent Stem Cells in Huntington's Disease: Disease Modeling and the Potential for Cell-Based Therapy

Huntington's disease (HD) is an incurable neurodegenerative disorder that is characterized by motor dysfunction, cognitive impairment, and behavioral abnormalities. It is an autosomal dominant disorder caused by a CAG repeat expansion in the huntingtin gene, resulting in progressive neuronal loss predominately in the striatum and cortex. Despite the discovery of the causative gene in 1993, the exact mechanisms underlying HD pathogenesis have yet to be elucidated. Treatments that slow or halt the disease process are currently unavailable. Recent advances in induced pluripotent stem cell (iPSC) technologies have transformed our ability to study disease in human neural cells. Here, we firstly review the progress made to model HD in vitro using patient-derived iPSCs, which reveal unique insights into illuminating molecular mechanisms and provide a novel human cell-based platform for drug discovery. We then highlight the promises and challenges for pluripotent stem cells that might be used as a therapeutic source for cell replacement therapy of the lost neurons in HD brains.

Stem cell transplantation therapy in Parkinson's disease

Ineffective therapeutic treatments and inadequate repair ability in the central nervous system are disturbing problems for several neurological diseases. Fortunately, the development of clinically applicable populations of stem cells has provided an avenue to overcome the failure of endogenous repair systems and substitute new cells into the damaged brain. However, there are still several existing obstacles to translating into clinical application. Here we review the stem-cell based therapies for Parkinson’s disease and discuss the potential advantages and drawbacks. We hope this review may provide suggestions for viable strategies to overcome the current technical and biological issues associated with the application of stem cells in Parkinson’s disease.

Cell replacement therapy: lessons from teleost fish

Many disorders of the CNS are characterized by a massive loss of neurons. A promising therapeutic strategy to cure such conditions is based on the activation of endogenous stem cells. Implementation of this strategy will benefit from a better understanding of stem cell dynamics and the local CNS microenvironment in regeneration-competent vertebrate model systems. Using a spinal cord injury paradigm in zebrafish larvae, Briona and Dorsky (2014) have provided evidence for the existence of two distinct neural stem cell populations. One population has the characteristics of radial glia and expresses the homeobox transcription factor Dbx. The other lacks Dbx but expresses Olig2. These results are placed in the context of other studies that also support the notion of heterogeneity of adult stem cells in the CNS. The implication that differences among stem cell populations, in combination with specific factors from the local cellular microenvironment, might have a decisive impact on the fate choices of the new cells, is discussed. Reviewed evidence suggests that rather few modifications in the signaling pathways involved in the control of stem cell behavior have led, in the course of evolution, to the pronounced differences between mammals and regeneration-competent organisms. As a consequence, rather minor pharmacological manipulations may be sufficient to reactivate the hidden neurogenic potential of the mammalian CNS, and thus make it available for therapeutic applications.