A cGMP-applicable expansion method for aggregates of human neural stem and progenitor cells derived from pluripotent stem cells or fetal brain tissue

GMP-grade human neural progenitors delivered subretinally protect vision in rat model of retinal degeneration and survive in minipigs

BACKGROUND

Stem cell products are increasingly entering early stage clinical trials for treating retinal degeneration. The field is learning from experience about comparability of cells proposed for preclinical and clinical use. Without this, preclinical data supporting translation to a clinical study might not adequately reflect the performance of subsequent clinical-grade cells in patients.

METHODS

Research-grade human neural progenitor cells (hNPC) and clinical-grade hNPC (termed CNS10-NPC) were injected into the subretinal space of the Royal College of Surgeons (RCS) rat, a rodent model of retinal degeneration such as retinitis pigmentosa. An investigational new drug (IND)-enabling study with CNS10-NPC was performed in the same rodent model. Finally, surgical methodology for subretinal cell delivery in the clinic was optimized in a large animal model with Yucatan minipigs.

RESULTS

Both research-grade hNPC and clinical-grade hNPC can survive and provide functional and morphological protection in a dose-dependent fashion in RCS rats and the optimal cell dose was defined and used in IND-enabling studies. Grafted CNS10-NPC migrated from the injection site without differentiation into retinal cell phenotypes. Additionally, CNS10-NPC showed long-term survival, safety and efficacy in a good laboratory practice (GLP) toxicity and tumorigenicity study, with no observed cell overgrowth even at the maximum deliverable dose. Finally, using a large animal model with the Yucatan minipig, which has an eye size comparable to the human, we optimized the surgical methodology for subretinal cell delivery in the clinic.

CONCLUSIONS

These extensive studies supported an approved IND and the translation of CNS10-NPC to an ongoing Phase 1/2a clinical trial (NCT04284293) for the treatment of retinitis pigmentosa.

Transplantation of human neural progenitor cells secreting GDNF into the spinal cord of patients with ALS: a phase 1/2a trial

Amyotrophic lateral sclerosis (ALS) involves progressive motor neuron loss, leading to paralysis and death typically within 3–5 years of diagnosis. Dysfunctional astrocytes may contribute to disease and glial cell line-derived neurotrophic factor (GDNF) can be protective. Here we show that human neural progenitor cells transduced with GDNF (CNS10-NPC-GDNF) differentiated to astrocytes protected spinal motor neurons and were safe in animal models. CNS10-NPC-GDNF were transplanted unilaterally into the lumbar spinal cord of 18 ALS participants in a phase 1/2a study (NCT02943850). The primary endpoint of safety at 1 year was met, with no negative effect of the transplant on motor function in the treated leg compared with the untreated leg. Tissue analysis of 13 participants who died of disease progression showed graft survival and GDNF production. Benign neuromas near delivery sites were common incidental findings at post-mortem. This study shows that one administration of engineered neural progenitors can provide new support cells and GDNF delivery to the ALS patient spinal cord for up to 42 months post-transplantation.

A phase 1/2a study shows that human neural progenitor cells modified to release the growth factor GDNF are safely transplanted into the spinal cord of patients with ALS, with cell survival and GDNF production for over 3 years.

Cell Surface Proteins for Enrichment and In Vitro Characterization of Human Pluripotent Stem Cell-Derived Myogenic Progenitors

Human myogenic progenitors can be derived from pluripotent stem cells (PSCs) for use in modeling natural and pathological myogenesis, as well as treating muscle diseases. Transgene-free methods of deriving myogenic progenitors from different PSC lines often produce mixed populations that are heterogeneous in myogenic differentiation potential, yet detailed and accurate characterization of human PSC-derived myogenic progenitors remains elusive in the field. The isolation and purification of human PSC-derived myogenic progenitors is thus an important methodological consideration when we investigate the properties and behaviors of these cells in culture. We previously reported a transgene-free, serum-free floating sphere culture method for the derivation of myogenic progenitors from human PSCs. In this study, we first performed comprehensive cell surface protein profiling of the sphere culture cells through the screening of 255 antibodies. Next, we used magnetic activated cell sorting and enriched the cells according to the expression of specific surface markers. The ability of muscle differentiation in the resulting cells was characterized by immunofluorescent labeling and quantification of positively stained cells. Our results revealed that myotube-forming cells resided in the differentiated cultures of CD29+, CD56+, CD271+, and CD15– fractions, while thick and multinucleated myotubes were identified in the differentiated cultures from CD9+ and CD146+ fractions. We found that PAX7 localization to the nucleus correlates with myotube-forming ability in these sorted populations. We also demonstrated that cells in unsorted, CD271+, and CD15– fractions responded differently to cryopreservation and prolonged culture expansion. Lastly, we showed that CD271 expression is essential for terminal differentiation of human PSC-derived myogenic progenitors. Taken together, these cell surface proteins are not only useful markers to identify unique cellular populations in human PSC-derived myogenic progenitors but also functionally important molecules that can provide valuable insight into human myogenesis.

Modeling Psychomotor Retardation using iPSCs from MCT8-Deficient Patients Indicates a Prominent Role for the Blood-Brain Barrier

Inactivating mutations in the thyroid hormone (TH) transporter Monocarboxylate transporter 8 (MCT8) cause severe psychomotor retardation in children. Animal models do not reflect the biology of the human disease. Using patient-specific induced pluripotent stem cells (iPSCs), we generated MCT8-deficient neural cells that showed normal TH-dependent neuronal properties and maturation. However, the blood-brain barrier (BBB) controls TH entry into the brain, and reduced TH availability to neural cells could instead underlie the diseased phenotype. To test potential BBB involvement, we generated an iPSC-based BBB model of MCT8 deficiency, and we found that MCT8 was necessary for polarized influx of the active form of TH across the BBB. We also found that a candidate drug did not appreciably cross the mutant BBB. Our results therefore clarify the underlying physiological basis of this disorder, and they suggest that circumventing the diseased BBB to deliver active TH to the brain could be a viable therapeutic strategy.

Bringing Neural Cell Therapies to the Clinic: Past and Future Strategies

Cell replacement therapy in the nervous system has a rich history, with ∼40 years of research and ∼30 years of clinical experience. There is compelling evidence that appropriate cells can integrate and function in the dysfunctioning human nervous system, but the clinical results are mixed in practice. A number of factors conspire to vary patient outcome: the indication, cell source, patient selection, and team performing transplantation are all variables that can affect efficacy. Most early clinical trials have used fetal cells, a limited cell source that resists scale and standardization. Direct fetal cell transplantation creates significant challenges to commercialization that is the ultimate goal of an effective cell therapy. One approach to help scale and standardize fetal cell preparations is the expansion of neural cells in vitro. Expansion is achieved by transformation or through the application of mitogens before cryopreservation. Recently, neural cells derived from pluripotent stem cells have provided a scalable alternative. Pluripotent stem cells are desirable for manufacturing but present alternative concerns and manufacturing obstacles. All cell sources require robust and reproducible manufacturing to make nervous system cell replacement therapy an option for patients. Here, we discuss the challenges and opportunities for cell replacement in the nervous system. In this review, we give an overview of completed and ongoing neural cell transplantation clinical trials, and we discuss the challenges and opportunities for future cell replacement trials with a particular focus on pluripotent stem cell-derived therapies.

Human Neural Progenitor Transplantation Rescues Behavior and Reduces α-Synuclein in a Transgenic Model of Dementia with Lewy Bodies

Synucleinopathies are a group of neurodegenerative disorders sharing the common feature of misfolding and accumulation of the presynaptic protein α‐synuclein (α‐syn) into insoluble aggregates. Within this diverse group, Dementia with Lewy Bodies (DLB) is characterized by the aberrant accumulation of α‐syn in cortical, hippocampal, and brainstem neurons, resulting in multiple cellular stressors that particularly impair dopamine and glutamate neurotransmission and related motor and cognitive function. Recent studies show that murine neural stem cell (NSC) transplantation can improve cognitive or motor function in transgenic models of Alzheimer's and Huntington's disease, and DLB. However, examination of clinically relevant human NSCs in these models is hindered by the challenges of xenotransplantation and the confounding effects of immunosuppressant drugs on pathology and behavior. To address this challenge, we developed an immune‐deficient transgenic model of DLB that lacks T‐, B‐, and NK‐cells, yet exhibits progressive accumulation of human α‐syn (h‐α‐syn)‐laden inclusions and cognitive and motor impairments. We demonstrate that clinically relevant human neural progenitor cells (line CNS10‐hNPCs) survive, migrate extensively and begin to differentiate preferentially into astrocytes following striatal transplantation into this DLB model. Critically, grafted CNS10‐hNPCs rescue both cognitive and motor deficits after 1 and 3 months and, furthermore, restore striatal dopamine and glutamate systems. These behavioral and neurochemical benefits are likely achieved by reducing α‐syn oligomers. Collectively, these results using a new model of DLB demonstrate that hNPC transplantation can impact a broad array of disease mechanisms and phenotypes and suggest a cellular therapeutic strategy that should be pursued. Stem Cells Translational Medicine2017;6:1477–1490

Cell freezing protocol suitable for ATAC-Seq on motor neurons derived from human induced pluripotent stem cells

In recent years, the assay for transposase-accessible chromatin using sequencing (ATAC-Seq) has become a fundamental tool of epigenomic research. However, it is difficult to perform this technique on frozen samples because freezing cells before extracting nuclei can impair nuclear integrity and alter chromatin structure, especially in fragile cells such as neurons. Our aim was to develop a protocol for freezing neuronal cells that is compatible with ATAC-Seq; we focused on a disease-relevant cell type, namely motor neurons differentiated from induced pluripotent stem cells (iMNs) from a patient affected by spinal muscular atrophy. We found that while flash-frozen iMNs are not suitable for ATAC-Seq, the assay is successful with slow-cooled cryopreserved cells. Using this method, we were able to isolate high quality, intact nuclei, and we verified that epigenetic results from fresh and cryopreserved iMNs quantitatively agree.

Human neural progenitors differentiate into astrocytes and protect motor neurons in aging rats

Age-associated health decline presents a significant challenge to healthcare, although there are few animal models that can be used to test potential treatments. Here, we show that there is a significant reduction in both spinal cord motor neurons and motor function over time in the aging rat. One explanation for this motor neuron loss could be reduced support from surrounding aging astrocytes. Indeed, we have previously shown using in vitro models that aging rat astrocytes are less supportive to rat motor neuron function and survival over time. Here, we test whether rejuvenating the astrocyte niche can improve the survival of motor neurons in an aging spinal cord. We transplanted fetal-derived human neural progenitor cells (hNPCs) into the aging rat spinal cord and found that the cells survive and differentiate into astrocytes with a much higher efficiency than when transplanted into younger animals, suggesting that the aging environment stimulates astrocyte maturation. Importantly, the engrafted astrocytes were able to protect against motor neuron loss associated with aging, although this did not result in an increase in motor function based on behavioral assays. We also transplanted hNPCs genetically modified to secrete glial cell line-derived neurotrophic factor (GDNF) into the aging rat spinal cord, as this combination of cell and protein delivery can protect motor neurons in animal models of ALS. During aging, GDNF-expressing hNPCs protected motor neurons, though to the same extent as hNPCs alone, and again had no effect on motor function. We conclude that hNPCs can survive well in the aging spinal cord, protect motor neurons and mature faster into astrocytes when compared to transplantation into the young spinal cord. While there was no functional improvement, there were no functional deficits either, further supporting a good safety profile of hNPC transplantation even into the older patient population.

In Vivo Tracking of Human Neural Progenitor Cells in the Rat Brain Using Magnetic Resonance Imaging Is Not Enhanced by Ferritin Expression

Rapid growth in the field of stem cell research has generated a lot of interest in their therapeutic use, especially in the treatment of neurodegenerative diseases. Specifically, human neural progenitor cells (hNPCs), unique in their capability to differentiate into cells of the neural lineage, have been widely investigated due to their ability to survive, thrive, and migrate toward injured tissues. Still, one of the major roadblocks for clinical applicability arises from the inability to monitor these cells following transplantation. Molecular imaging techniques, such as magnetic resonance imaging (MRI), have been explored to assess hNPC transplant location, migration, and survival. Here we investigated whether inducing hNPCs to overexpress ferritin (hNPCs(Fer)), an iron storage protein, is sufficient to track these cells long term in the rat striatum using MRI. We found that increased hypointensity on MRI images could establish hNPC(Fer) location. Unexpectedly, however, wild-type hNPC transplants were detected in a similar manner, which is likely due to increased iron accumulation following transplantation-induced damage. Hence, we labeled hNPCs with superparamagnetic iron oxide (SPIO) nanoparticles to further increase iron content in an attempt to enhance cell contrast in MRI. SPIO-labeling of hNPCs (hNPCs-SPIO) achieved increased hypointensity, with significantly greater area of decreased T2* compared to hNPC(Fer) (p < 0.0001) and all other controls used. However, none of the techniques could be used to determine graft rejection in vivo, which is imperative for understanding cell behavior following transplantation. We conclude that in order for cell survival to be monitored in preclinical and clinical settings, another molecular imaging technique must be employed, including perhaps multimodal imaging, which would utilize MRI along with another imaging modality.

A Subsequent Human Neural Progenitor Transplant into the Degenerate Retina Does Not Compromise Initial Graft Survival or Therapeutic Efficacy

PURPOSE

Stem and progenitor cell transplantation provides a promising clinical application for treating degenerative retinal diseases, including age-related macular degeneration (AMD) and retinitis pigmentosa (RP). Our previous studies have shown that a single subretinal injection of human cortical-derived neural progenitor cells (hNPCctx) into cyclosporine-treated Royal College of Surgeons (RCS) rats preserved both photoreceptors and visual function. However, it is still unknown whether nonautologous progenitor cell readministration for sustained vision is efficacious and safe in terms of the initial graft initiating an immune response to a subsequent graft.

METHODS

A cell suspension containing 3×104 hNPCctx into one eye of cyclosporine-treated RCS rats at postnatal day 21 (P21), followed by a second transplantation at P95 into the previously untreated fellow eye.

RESULTS

hNPCctx delayed photoreceptor degeneration and preserved visual function, as measured by electroretinography (ERG), optokinetic response (OKR), and luminance threshold recordings (LTRs). Visual function and photoreceptors of the initially treated eye were still preserved 6 weeks after hNPCctx were injected into the second eye. Antibodies against T-cell markers showed that CD3, CD4, and CD8 T cells were not detected at P90 and P140 in most cases. No detectable level of anti-nestin antibody was found in serum by enzyme-linked immunosorbent assay (ELISA).

CONCLUSIONS

This xenograft study with cyclosporine-treated animals demonstrates that readministration of hNPCctx into the fellow eye did not induce anti-graft immune responses or lower therapeutic efficacy of hNPCctx in preserving vision. Thus, readministration of progenitor cells to sustain long-term efficacy may be an option for long-term therapies of retinal degeneration.

TRANSLATIONAL RELEVANCE

Redosing neural progenitors do not affect the efficacy of the initial grafts in protecting vision or induce unwanted immune responses.