Transplantation of neural progenitor cells into the human CNS

Cell therapy for neurological disorders

Cell therapies for neurological disorders are entering the clinic and present unique challenges and opportunities compared with conventional medicines. They have the potential to replace damaged nervous tissue and integrate into the brain or spinal cord to produce functional effects for the lifetime of the patient, which could revolutionize the way clinicians treat debilitating neurological disorders. The major challenge has been cell sourcing, which historically relied mainly on fetal brain tissue. This has largely been overcome with the advent of pluripotent stem cell technology and the ability to make almost any cell of the nervous system at scale. Furthermore, advances in gene editing now allow the generation of genetically modified cells that could perform better and evade the immune system. With all the remarkable new approaches to treat neurological disorders, we take a critical look at the state of current clinical trials and how challenges may be overcome with the evolving technology and innovation occurring in the stem cell field.

Regenerative medicine strategies for chronic complete spinal cord injury

Spinal cord injury is a condition in which the parenchyma of the spinal cord is damaged by trauma or various diseases. While rapid progress has been made in regenerative medicine for spinal cord injury that was previously untreatable, most research in this field has focused on the early phase of incomplete injury. However, the majority of patients have chronic severe injuries; therefore, treatments for these situations are of fundamental importance. The reason why the treatment of complete spinal cord injury has not been studied is that, unlike in the early stage of incomplete spinal cord injury, there are various inhibitors of neural regeneration. Thus, we assumed that it is difficult to address all conditions with a single treatment in chronic complete spinal cord injury and that a combination of several treatments is essential to target severe pathologies. First, we established a combination therapy of cell transplantation and drug-releasing scaffolds, which contributes to functional recovery after chronic complete transection spinal cord injury, but we found that functional recovery was limited and still needs further investigation. Here, for the further development of the treatment of chronic complete spinal cord injury, we review the necessary approaches to the different pathologies based on our findings and the many studies that have been accumulated to date and discuss, with reference to the literature, which combination of treatments is most effective in achieving functional recovery.

Human-induced pluripotent stem cell-derived neural stem/progenitor cell ex vivo gene therapy with synaptic organizer CPTX for spinal cord injury

The transplantation of neural stem/progenitor cells (NS/PCs) derived from human induced pluripotent stem cells (hiPSCs) has shown promise in spinal cord injury (SCI) model animals. Establishing a functional synaptic connection between the transplanted and host neurons is crucial for motor function recovery. To boost therapeutic outcomes, we developed an ex vivo gene therapy aimed at promoting synapse formation by expressing the synthetic excitatory synapse organizer CPTX in hiPSC-NS/PCs. Using an immunocompromised transgenic rat model of SCI, we evaluated the effects of transplanting CPTX-expressing hiPSC-NS/PCs using histological and functional analyses. Our findings revealed a significant increase in excitatory synapse formation at the transplantation site. Retrograde monosynaptic tracing indicated extensive integration of transplanted neurons into the surrounding neuronal tracts facilitated by CPTX. Consequently, locomotion and spinal cord conduction significantly improved. Thus, ex vivo gene therapy targeting synapse formation holds promise for future clinical applications and offers potential benefits to individuals with SCI.

Biohybrid neural interfaces: improving the biological integration of neural implants

Implantable neural interfaces (NIs) have emerged in the clinic as outstanding tools for the management of a variety of neurological conditions caused by trauma or disease. However, the foreign body reaction triggered upon implantation remains one of the major challenges hindering the safety and longevity of NIs. The integration of tools and principles from biomaterial design and tissue engineering has been investigated as a promising strategy to develop NIs with enhanced functionality and performance. In this Feature Article, we highlight the main bioengineering approaches for the development of biohybrid NIs with an emphasis on relevant device design criteria. Technical and scientific challenges associated with the fabrication and functional assessment of technologies composed of both artificial and biological components are discussed. Lastly, we provide future perspectives related to engineering, regulatory, and neuroethical challenges to be addressed towards the realisation of the promise of biohybrid neurotechnology.

In Vitro Models of Amyotrophic Lateral Sclerosis

Amyotrophic Lateral Sclerosis (ALS) is one of the commonest neurodegenerative diseases of adult-onset, which is characterized by the progressive death of motor neurons in the cerebral cortex, brain stem and spinal cord. The dysfunction and death of motor neurons lead to the progressive muscle weakness, atrophy, fasciculations, spasticity and ultimately the whole paralysis of body. Despite the identification of several genetic mutations associated with the pathogenesis of ALS, including mutations in chromosome 9 open reading frame 72 leading to the abnormal expansion of GGGGCC repeat sequence, TAR DNA-binding protein 43, fused in sarcoma/translocated in liposarcoma, copper/zinc superoxide dismutase 1 (SOD1) and TANK-binding kinase 1, the exact mechanisms underlying the specific degeneration of motor neurons that causes ALS remain incompletely understood. At present, since the transgenic model expressed SOD1 mutants was established, multiple in vitro models of ALS have been developed for studying the pathology, pathophysiology and pathogenesis of ALS as well as searching the effective neurotherapeutics. This review reviewed the details of present established in vitro models used in studying the pathology, pathophysiology and pathogenesis of ALS. Meanwhile, we also discussed the advantages, disadvantages, cost and availability of each models.

Human iPSC-derived neural progenitor cells secreting GDNF provide protection in rodent models of ALS and retinal degeneration

Human induced pluripotent stem cells (iPSCs) are a renewable cell source that can be differentiated into neural progenitor cells (iNPCs) and transduced with glial cell line-derived neurotrophic factor (iNPC-GDNFs). The goal of the current study is to characterize iNPC-GDNFs and test their therapeutic potential and safety. Single-nuclei RNA-seq show iNPC-GDNFs express NPC markers. iNPC-GDNFs delivered into the subretinal space of the Royal College of Surgeons rodent model of retinal degeneration preserve photoreceptors and visual function. Additionally, iNPC-GDNF transplants in the spinal cord of SOD1G93A amyotrophic lateral sclerosis (ALS) rats preserve motor neurons. Finally, iNPC-GDNF transplants in the spinal cord of athymic nude rats survive and produce GDNF for 9 months, with no signs of tumor formation or continual cell proliferation. iNPC-GDNFs survive long-term, are safe, and provide neuroprotection in models of both retinal degeneration and ALS, indicating their potential as a combined cell and gene therapy for various neurodegenerative diseases.

Induced neural stem cells suppressed neuroinflammation by inhibiting the microglial pyroptotic pathway in intracerebral hemorrhage rats

Intracerebral hemorrhage usually manifests as strong neuroinflammation and neurological deficits. There is an urgent need to explore effective methods for the treatment of intracerebral hemorrhage. The therapeutic effect and the possible mechanism of induced neural stem cell transplantation in an intracerebral hemorrhage rat model are still unclear. Our results showed that transplantation of induced neural stem cells could improve neurological deficits by inhibiting inflammation in an intracerebral hemorrhage rat model. Additionally, induced neural stem cell treatment could effectively suppress microglial pyroptosis, which might occur through inhibiting the NF-κB signaling pathway. Induced neural stem cells could also regulate the polarization of microglia and promote the transition of microglia from pro-inflammatory phenotypes to anti-inflammatory phenotypes to exert their anti-inflammatory effects. Overall, induced neural stem cells may be a promising tool for the treatment of intracerebral hemorrhage and other neuroinflammatory diseases.

Neuroprotective Effects of Genome-Edited Human iPS Cell-Derived Neural Stem/Progenitor Cells on Traumatic Brain Injury

Despite developing neurosurgical procedures, few treatment options have achieved functional recovery from traumatic brain injury (TBI). Neural stem/progenitor cells (NS/PCs) may produce a long-term effect on neurological recovery. Although induced pluripotent stem cells (iPSCs) can overcome ethical and practical issues of human embryonic or fetal-derived tissues in clinical applications, the tumorigenicity of iPSC-derived populations remains an obstacle to their safe use in regenerative medicine. We herein established a novel treatment strategy for TBI using iPSCs expressing the enzyme-prodrug gene yeast cytosine deaminase-uracil phosphoribosyl transferase (yCD-UPRT). NS/PCs derived from human iPSCs displayed stable and high transgene expression of yCD-UPRT following CRISPR/Cas9-mediated genome editing. In vivo bioluminescent imaging and histopathological analysis demonstrated that NS/PCs concentrated around the damaged cortex of the TBI mouse model. During the subacute phase, performances in both beam walking test and accelerating rotarod test were significantly improved in the treatment group transplanted with genome-edited iPSC-derived NS/PCs compared with the control group. The injury area visualized by extravasation of Evans blue was smaller in the treatment group compared with the control group, suggesting the prevention of secondary brain injury. During the chronic phase, cerebral atrophy and ventricle enlargement were significantly less evident in the treatment group. Furthermore, after 5-fluorocytosine (5-FC) administration, 5-fluorouracil converted from 5-FC selectively eliminated undifferentiated NS/PCs while preserving the adjacent neuronal structures. NS/PCs expressing yCD-UPRT can be applied for safe regenerative medicine without the concern for tumorigenesis.

A review of regenerative therapy for spinal cord injury using human iPS cells

Spinal cord injury (SCI) has been considered to cause sudden, irreversible loss of function in patients. However, developments in stem cell biology and regenerative medicine are changing this conventional notion. Here we reviewed the overview of regenerative medicine of SCI. As a consequence of the establishment of human induced pluripotent stem cells (hiPSCs), hiPSC-based therapies for SCI, such as neural stem/progenitor cell (NS/PC) transplantation, have emerged as promising therapeutic modalities. Using several animal models, hiPSC-NS/PC transplantation into subacute injured spinal cords has been repeatedly demonstrated to improve locomotor function. Some biological mechanisms underlying this improvement have been proposed. In particular, combined with advanced neuroscience techniques such as designer receptors exclusively activated by designer drugs (DREADDs), neuronal relay theory, in which the transplanted cell-derived neurons reconstruct disrupted neuronal circuits, was proven to be involved histologically, pharmaceutically, electrophysiologically, and via in vivo bioimaging. Based on these findings, hiPSC-NS/PC transplantation for subacute SCI was moved ahead to a clinical study on human patients. At the same time, the search for effective treatments for chronic SCI is proceeding gradually, combining hiPSC-NS/PC transplantation with other treatment modalities such as rehabilitation, pharmaceutical interventions, or optimal scaffolds. In addition to NS/PCs, oligodendrocyte precursor cells (OPCs) are also a promising cell source for transplantation, as demyelinated axons affected by SCI can be repaired by OPCs. Therapies with OPCs derived from hiPSCs are still in preclinical studies but have shown favorable outcomes in animal models. In the future, several therapeutic options may be available according to the pathological conditions and the time period of SCI. Moreover, the application of regenerative therapy for the spinal cord could be broadened to degenerative disorders, such as spinal canal stenosis. Summary sentence: A historical review of human induced pluripotent stem cell (hiPSC) based cell transplantation therapy for spinal cord injury (SCI), in particular about footsteps of hiPSC-derived neural stem/progenitor cell transplantation, recent clinical study, and its future perspective.