Translating cell therapies for neurodegenerative diseases: Huntington's disease as a model disorder.

There has been substantial progress in the development of regenerative medicine strategies for CNS disorders over the last decade, with progression to early clinical studies for some conditions. However, there are multiple challenges along the translational pipeline, many of which are common across diseases and pertinent to multiple donor cell types. These include defining the point at which the preclinical data are sufficiently compelling to permit progression to the first clinical studies; scaling-up, characterization, quality control and validation of the cell product; design, validation and approval of the surgical device; and operative procedures for safe and effective delivery of cell product to the brain. Furthermore, clinical trials that incorporate principles of efficient design and disease-specific outcomes are urgently needed (particularly for those undertaken in rare diseases, where relatively small cohorts are an additional limiting factor), and all processes must be adaptable in a dynamic regulatory environment. Here we set out the challenges associated with the clinical translation of cell therapy, using Huntington's disease as a specific example, and suggest potential strategies to address these challenges. Huntington's disease presents a clear unmet need, but, importantly, it is an autosomal dominant condition with a readily available gene test, full genetic penetrance and a wide range of associated animal models, which together mean that it is a powerful condition in which to develop principles and test experimental therapeutics. We propose that solving these challenges in Huntington's disease would provide a road map for many other neurological conditions. This white paper represents a consensus opinion emerging from a series of meetings of the international translational platforms Stem Cells for Huntington's Disease and the European Huntington's Disease Network Advanced Therapies Working Group, established to identify the challenges of cell therapy, share experience, develop guidance and highlight future directions, with the aim to expedite progress towards therapies for clinical benefit in Huntington's disease.

Single-Cell Transcriptomics Reveals Conserved Regulatory Networks in Human and Mouse Interneuron Development.

Inhibitory GABAergic interneurons originate in the embryonic medial ganglionic eminence (MGE) and control network activity in the neocortex. Dysfunction of these cells is believed to lead to runaway excitation underlying seizure-based neurological disorders such as epilepsy, autism, and schizophrenia. Despite their importance in heath and disease, our knowledge about the development of this diverse neuronal population remains incomplete. Here we conducted single-cell RNA sequencing (scRNA-seq) of human foetal MGE from 10 to 15 weeks post conception. These MGE tissues are composed of largely cycling progenitors and immature post-mitotic interneurons with characteristic regional marker expression. Analysis of integrated human and mouse MGE data revealed species-conserved transcriptomic profiles and regulatory programs. Moreover, we identified novel candidate transcription regulators for human interneuron differentiation. These findings provide a framework for in vitro modelling of interneuron development and a strategy for potentially enhancing interneuron production from human pluripotent stem cells.

Targeting Huntingtin Expression in Patients with Huntington's Disease.

BACKGROUND: Huntington's disease is an autosomal-dominant neurodegenerative disease caused by CAG trinucleotide repeat expansion in HTT, resulting in a mutant huntingtin protein. IONIS-HTTRx (hereafter, HTTRx) is an antisense oligonucleotide designed to inhibit HTT messenger RNA and thereby reduce concentrations of mutant huntingtin. METHODS: We conducted a randomized, double-blind, multiple-ascending-dose, phase 1-2a trial involving adults with early Huntington's disease. Patients were randomly assigned in a 3:1 ratio to receive HTTRx or placebo as a bolus intrathecal administration every 4 weeks for four doses. Dose selection was guided by a preclinical model in mice and nonhuman primates that related dose level to reduction in the concentration of huntingtin. The primary end point was safety. The secondary end point was HTTRx pharmacokinetics in cerebrospinal fluid (CSF). Prespecified exploratory end points included the concentration of mutant huntingtin in CSF. RESULTS: Of the 46 patients who were enrolled in the trial, 34 were randomly assigned to receive HTTRx (at ascending dose levels of 10 to 120 mg) and 12 were randomly assigned to receive placebo. Each patient received all four doses and completed the trial. Adverse events, all of grade 1 or 2, were reported in 98% of the patients. No serious adverse events were seen in HTTRx-treated patients. There were no clinically relevant adverse changes in laboratory variables. Predose (trough) concentrations of HTTRx in CSF showed dose dependence up to doses of 60 mg. HTTRx treatment resulted in a dose-dependent reduction in the concentration of mutant huntingtin in CSF (mean percentage change from baseline, 10% in the placebo group and -20%, -25%, -28%, -42%, and -38% in the HTTRx 10-mg, 30-mg, 60-mg, 90-mg, and 120-mg dose groups, respectively). CONCLUSIONS: Intrathecal administration of HTTRx to patients with early Huntington's disease was not accompanied by serious adverse events. We observed dose-dependent reductions in concentrations of mutant huntingtin. (Funded by Ionis Pharmaceuticals and F. Hoffmann-La Roche; ClinicalTrials.gov number, NCT02519036.).

Mutation-related magnetization-transfer, not axon density, drives white matter differences in premanifest Huntington disease: Evidence from in vivo ultra-strong gradient MRI.

White matter (WM) alterations have been observed in Huntington disease (HD) but their role in the disease-pathophysiology remains unknown. We assessed WM changes in premanifest HD by exploiting ultra-strong-gradient magnetic resonance imaging (MRI). This allowed to separately quantify magnetization transfer ratio (MTR) and hindered and restricted diffusion-weighted signal fractions, and assess how they drove WM microstructure differences between patients and controls. We used tractometry to investigate region-specific alterations across callosal segments with well-characterized early- and late-myelinating axon populations, while brain-wise differences were explored with tract-based cluster analysis (TBCA). Behavioral measures were included to explore disease-associated brain-function relationships. We detected lower MTR in patients' callosal rostrum (tractometry: p = .03; TBCA: p = .03), but higher MTR in their splenium (tractometry: p = .02). Importantly, patients' mutation-size and MTR were positively correlated (all p-values < .01), indicating that MTR alterations may directly result from the mutation. Further, MTR was higher in younger, but lower in older patients relative to controls (p = .003), suggesting that MTR increases are detrimental later in the disease. Finally, patients showed higher restricted diffusion signal fraction (FR) from the composite hindered and restricted model of diffusion (CHARMED) in the cortico-spinal tract (p = .03), which correlated positively with MTR in the posterior callosum (p = .033), potentially reflecting compensatory mechanisms. In summary, this first comprehensive, ultra-strong gradient MRI study in HD provides novel evidence of mutation-driven MTR alterations at the premanifest disease stage which may reflect neurodevelopmental changes in iron, myelin, or a combination of these.

Cell therapy in Huntington's disease: Taking stock of past studies to move the field forward.

Huntington's disease (HD) is a rare inherited neurodegenerative disease that manifests mostly in adulthood with progressive cognitive, behavioral, and motor dysfunction. Neuronal loss occurs predominantly in the striatum but also extends to other brain regions, notably the cortex. Most patients die around 20 years after motor onset, although there is variability in the rate of progression and some phenotypic heterogeneity. The most advanced experimental therapies currently are huntingtin-lowering strategies, some of which are in stage 3 clinical trials. However, even if these approaches are successful, it is unlikely that they will be applicable to all patients or will completely halt continued loss of neural cells in all cases. On the other hand, cellular therapies have the potential to restore atrophied tissues and may therefore provide an important complementary therapeutic avenue. Pilot studies of fetal cell grafts in the 2000s reported the most dramatic clinical improvements yet achieved for this disease, but subsequent studies have so far failed to identify methodology to reliably reproduce these results. Moving forward, a major challenge will be to generate suitable donor cells from (nonfetal) cell sources, but in parallel there are a host of procedural and trial design issues that will be important for improving reliability of transplants and so urgently need attention. Here, we consider findings that have emerged from clinical transplant studies in HD to date, in particular new findings emerging from the recent multicenter intracerebral transplant HD study, and consider how these data may be used to inform future cell therapy trials.

An MDS Evidence-Based Review on Treatments for Huntington's Disease.

BACKGROUND: Huntington's disease (HD) is a rare neurodegenerative disorder with protean clinical manifestations. Its management is challenging, consisting mainly of off-label treatments. OBJECTIVES: The International Parkinson and Movement Disorder Society commissioned a task force to review and evaluate the evidence of available therapies for HD gene expansion carriers. METHODS: We followed the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach. Eligible randomized controlled trials were identified via an electronic search of the CENTRAL, MEDLINE, and EMBASE databases. All eligible trials that evaluated one or more of 33 predetermined clinical questions were included. Risk of bias was evaluated using the Cochrane Risk of Bias tool. A framework was adapted to allow for efficacy and safety conclusions to be drawn from the balance between the GRADE level of evidence and the importance of the benefit/harm of the intervention. RESULTS: Twenty-two eligible studies involving 17 interventions were included, providing data to address 8 clinical questions. These data supported a likely effect of deutetrabenazine on motor impairment, chorea, and dystonia and of tetrabenazine on chorea. The data did not support a disease-modifying effect for premanifest and manifest HD. There was no eligible evidence to support the use of specific treatments for depression, psychosis, irritability, apathy, or suicidality. Similarly, no evidence was eligible to support the use of physiotherapy, occupational therapy, exercise, dietary, or surgical treatments. CONCLUSIONS: Data for therapeutic interventions in HD are limited and support only the use of VMAT2 inhibitors for specific motor symptoms. © 2021 International Parkinson and Movement Disorder Society.

Induced pluripotent stem cells derived from the developing striatum as a potential donor source for cell replacement therapy for Huntington disease.

BACKGROUND: Cell replacement therapy (CRT) for Huntington disease (HD) requires a source of striatal (STR) progenitors capable of restoring the function lost due to STR degeneration. Authentic STR progenitors can be collected from the fetal putative striatum, or whole ganglionic eminence (WGE), but these tissues remain impractical for widespread clinical application, and alternative donor sources are required. Here we begin exploring the possibility that induced pluripotent stem cells (iPSC) derived from WGE may retain an epigenetic memory of their tissue of origin, which could enhance their ability to differentiate into STR cells. RESULTS: We generate four iPSC lines from human WGE (hWGE) and establish that they have a capacity similar to human embryonic stem cells with regard to their ability to differentiate toward an STR phenotype, as measured by expression and demethylation of key STR genes, while maintaining an overall different methylome. Finally, we demonstrate that these STR-differentiated hWGE iPSCs share characteristics with hWGE (i.e., authentic STR tissues) both in vitro and following transplantation into an HD model. Overall, iPSCs derived from human WGE show promise as a donor source for CRT for HD.

Neural modeling of antisaccade performance of healthy controls and early Huntington's disease patients.

Huntington's disease (HD), a genetically determined neurodegenerative disease, is positively correlated with eye movement abnormalities in decision making. The antisaccade conflict paradigm has been widely used to study response inhibition in eye movements, and reliable performance deficits in HD subjects have been observed, including a greater number and timing of direction errors. We recorded the error rates and response latencies of early HD patients and healthy age-matched controls performing the mirror antisaccade task. HD participants displayed slower and more variable antisaccade latencies and increased error rates relative to healthy controls. A competitive accumulator-to-threshold neural model was then employed to quantitatively simulate the controls' and patients' reaction latencies and error rates and uncover the mechanisms giving rise to the observed HD antisaccade deficits. Our simulations showed that (1) a more gradual and noisy rate of accumulation of evidence by HD patients is responsible for the observed prolonged and more variable antisaccade latencies in early HD; (2) the confidence level of early HD patients making a decision is unaffected by the disease; and (3) the antisaccade performance of healthy controls and early HD patients is the end product of a neural lateral competition (inhibition) between a correct and an erroneous decision process, and not the end product of a third top-down stop signal suppressing the erroneous decision process as many have speculated.

Delayed diagnosis of spinal cord injuries in Huntington's disease.

Huntington's disease is a neurodegenerative disorder, characterised by progressive cognitive, motor and psychiatric symptoms. Patients with advanced disease presenting to emergency medical services can pose a diagnostic and management challenge for physicians unfamiliar with the condition. We describe two patients with Huntington's disease in whom the diagnosis of traumatic spinal cord injury was delayed, discuss the role that cognitive bias and other factors played in this delay, and the lessons we can learn.

A Critical Review of White Matter Changes in Huntington's Disease.

Huntington's disease is a genetic neurodegenerative disorder. White matter alterations have recently been identified as a relevant pathophysiological feature of Huntington's disease, but their etiology and role in disease pathogenesis and progression remain unclear. Increasing evidence suggests that white matter changes in this disorder are attributed to alterations in myelin-associated biological processes. This review first discusses evidence from neurochemical studies lending support to the demyelination hypothesis of Huntington's disease, demonstrating aberrant myelination and changes in oligodendrocytes in the Huntington's brain. Next, evidence from neuroimaging studies is reviewed, the limitations of the described methodologies are discussed, and suggested interpretations of findings from published studies are challenged. Although our understanding of Huntington's associated pathological changes in the brain will increasingly rely on neuroimaging techniques, the shortcomings of these methodologies must not be forgotten. Advances in magnetic resonance imaging techniques and tissue modeling will enable a better in vivo, longitudinal characterization of the biological properties of white matter microstructure. This in turn will facilitate identification of disease-related biomarkers and the specification of outcome measures in clinical trials. © 2020 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society.

Hypertension, Antihypertensive Use and the Delayed-Onset of Huntington's Disease.

BACKGROUND: Hypertension is a modifiable cardiovascular risk factor implicated in neurodegeneration and dementia risk. In Huntington's disease, a monogenic neurodegenerative disease, autonomic and vascular abnormalities have been reported. This study's objective was to examine the relationship between hypertension and disease severity and progression in Huntington's disease. METHODS: Using longitudinal data from the largest worldwide observational study of Huntington's disease (n = 14,534), we assessed the relationship between hypertension, disease severity, and rate of clinical progression in Huntington's disease mutation carriers. Propensity score matching was used to statistically match normotensive and hypertensive participants for age, sex, body mass index, ethnicity, and CAG length. RESULTS: Huntington's disease patients had a lower prevalence of hypertension compared with age-matched gene-negative controls. Huntington's disease patients with hypertension had worse cognitive function, a higher depression score, and more marked motor progression over time compared with Huntington's disease patients without hypertension. However, hypertensive patients taking antihypertensive medication had less motor, cognitive, and functional impairment than Huntington's disease patients with untreated hypertension and a later age of clinical onset compared with untreated hypertensive patients and normotensive individuals with Huntington's disease. CONCLUSIONS: We report the novel finding that hypertension and antihypertensive medication use are associated with altered disease severity, progression, and clinical onset in patients with Huntington's disease. These findings have implications for the management of hypertension in Huntington's disease and suggest that prospective studies of the symptomatic or disease-modifying potential of antihypertensives in neurodegenerative diseases are warranted. © 2020 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society.

Outcome of cell suspension allografts in a patient with Huntington's disease.

For patients with incurable neurodegenerative disorders such as Huntington's (HD) and Parkinson's disease, cell transplantation has been explored as a potential treatment option. Here, we present the first clinicopathological study of a patient with HD in receipt of cell-suspension striatal allografts who took part in the NEST-UK multicenter clinical transplantation trial. Using various immunohistochemical techniques, we found a discrepancy in the survival of grafted projection neurons with respect to grafted interneurons as well as major ongoing inflammatory and immune responses to the grafted tissue with evidence of mutant huntingtin aggregates within the transplant area. Our results indicate that grafts can survive more than a decade post-transplantation, but show compromised survival with inflammation and mutant protein being observed within the transplant site. Ann Neurol 2018;84:950-956.

Insensitivity to loss predicts apathy in huntington's disease.

BACKGROUND: Apathy is a deficit in goal-directed behavior that significantly affects quality of life and function. It is common in Huntington's disease and other disorders affecting corticostriatal pathways. Deficits in processing of reward, altered effort, and executive dysfunction are associated with apathy in other disorders, but the cognitive processes leading to apathy in Huntington's disease remain largely unknown. A previously reported deficit in learning from losses in Huntington's disease raises the possibility of a hitherto unrecognized mechanism leading to apathy. This study's objective was to delineate the cognitive processes associated with apathy in HD. METHODS: We tested 51 Huntington's disease participants and 26 controls on a battery of novel and established measures to assess the contribution to apathy in Huntington's disease of executive function, reward value, reward-effort calculations, instrumental learning, and response to reward and loss. RESULTS: Huntington's disase participants had deficits in instrumental learning with impaired response to loss, but no evidence to suggest altered reward-related behavior or effort. We also saw an executive dysfunction contribution to apathy in Huntington's disease. DISCUSSION: We report the novel finding that apathy in Huntington's disease is associated with blunted responses to losses and impaired instrumental learning. This association is consistent with the known early degeneration of the indirect pathway and amygdala involvement in apathy in Huntington's disease, but is previously unreported in any disorder. In keeping with the comparative preservation of the ventral striatum and orbitofrontal cortex in Huntington's disease, reward valuation and reward-effort calculations did not contribute to apathy. © 2019 International Parkinson and Movement Disorder Society.

Kv7 channels are upregulated during striatal neuron development and promote maturation of human iPSC-derived neurons.

Kv7 channels determine the resting membrane potential of neurons and regulate their excitability. Even though dysfunction of Kv7 channels has been linked to several debilitating childhood neuronal disorders, the ontogeny of the constituent genes, which encode Kv7 channels (KNCQ), and expression of their subunits have been largely unexplored. Here, we show that developmentally regulated expression of specific KCNQ mRNA and Kv7 channel subunits in mouse and human striatum is crucial to the functional maturation of mouse striatal neurons and human-induced pluripotent stem cell-derived neurons. This demonstrates their pivotal role in normal development and maturation, the knowledge of which can now be harnessed to synchronise and accelerate neuronal differentiation of stem cell-derived neurons, enhancing their utility for disease modelling and drug discovery.

Activin A directs striatal projection neuron differentiation of human pluripotent stem cells.

The efficient generation of striatal neurons from human embryonic stem cells (hESCs) and induced pluripotent stem cells (hiPSCs) is fundamental for realising their promise in disease modelling, pharmaceutical drug screening and cell therapy for Huntington's disease. GABAergic medium-sized spiny neurons (MSNs) are the principal projection neurons of the striatum and specifically degenerate in the early phase of Huntington's disease. Here we report that activin A induces lateral ganglionic eminence (LGE) characteristics in nascent neural progenitors derived from hESCs and hiPSCs in a sonic hedgehog-independent manner. Correct specification of striatal phenotype was further demonstrated by the induction of the striatal transcription factors CTIP2, GSX2 and FOXP2. Crucially, these human LGE progenitors readily differentiate into postmitotic neurons expressing the striatal projection neuron signature marker DARPP32, both in culture and following transplantation in the adult striatum in a rat model of Huntington's disease. Activin-induced neurons also exhibit appropriate striatal-like electrophysiology in vitro. Together, our findings demonstrate a novel route for efficient differentiation of GABAergic striatal MSNs from human pluripotent stem cells.

A hyperbranched dopamine-containing PEG-based polymer for the inhibition of α-synuclein fibrillation.

Aggregation of α-synuclein is believed to play an important role in Parkinson's disease and in other neurodegenerative maladies. Small molecule inhibitors of this process are among the most promising drug candidates for neurodegenerative diseases. Dendrimers have also been studied for anti-fibrillation applications but they can be difficult and expensive to synthetize. Here we show that RAFT polymerization can be used to produce a hyperbranched polyethylene glycol structure via a one-pot reaction. This polymer included a dopamine moiety, a known inhibitor of α-synuclein fibril formation. Dopamine within the polymer structure was capable of aggregation inhibition, although not to the same degree as free dopamine. This result opens up new avenues for the use of controlled radical polymerizations as a means of preparing hyperbranched polymers for anti-fibrillation activity, but shows that the incorporation of functional groups from known small molecules within polymers may alter their biological activity.

Development and Delivery of a Physical Activity Intervention for People With Huntington Disease: Facilitating Translation to Clinical Practice.

BACKGROUND AND PURPOSE: We studied the development and delivery of a 14-week complex physical activity intervention for people with Huntington disease, where detailed information about the intervention was fully embedded in the trial design process. METHODS: Intervention Development: The intervention was developed through a series of focus groups. The findings from the focus groups informed the development of a logic model for the physical activity intervention that was broadly consistent with the framework of self-determination theory. Intervention Delivery: Key components underpinning the delivery of the intervention were implemented including a defined coach training program and intervention fidelity assessment methods. Training of coaches (physical therapists, occupational therapists, research nurses, and exercise trainers) was delivered via group and 1:1 training sessions using a detailed coach's manual, and with ongoing support via video calls, and e-mail communication as needed. Detailed documentation was provided to determine costs of intervention development and coach training. RESULTS: Intervention delivery coaches at 8 sites across the United Kingdom participated in the face-to-face training. Self-report checklists completed by each of the coaches indicated that all components of the intervention were delivered in accordance with the protocol. Mean (standard deviation) intervention fidelity scores (n = 15), as measured using a purpose-developed rating scale, was 11 (2.4) (out of 16 possible points). Coaches' perceptions of intervention fidelity were similarly high. The total cost of developing the intervention and providing training was £30,773 ($47,042 USD). DISCUSSION AND CONCLUSIONS: An important consideration in promoting translation of clinical research into practice is the ability to convey the detailed components of how the intervention was delivered to facilitate replication if the results are favorable. This report presents an illustrative example of a physical activity intervention, including the development and the training required to deliver it. This approach has the potential to facilitate reproducibility, evidence synthesis, and implementation in clinical practice.Video Abstract available for more insights from the authors (see Supplemental Digital Content 1, http://links.lww.com/JNPT/A122).

Tackling Cell Transplantation Anoikis: An Injectable, Shape Memory Cryogel Microcarrier Platform Material for Stem Cell and Neuronal Cell Growth.

Highly macroporous semisynthetic cryogel microcarriers can be synthesized for culturing stem cells and neuronal type cells. Growth factors loaded to heparin-containing microcarriers show near zero-order release kinetics and cell-loaded microcarriers can be injected through a fine gauge cannula without negative effect on the cells. These carriers can be applied for cell transplantation applications.

Ethyl-eicosapentaenoic acid treatment in Huntington's disease: A placebo-controlled clinical trial.

BACKGROUND: It has been suggested that treatment with ethyl-eicosapentaenoic acid (EPA) may improve motor function in patients with Huntington's disease (HD) with cytosine-adenine-guanine repeat numbers of <45. METHODS: This multicenter, randomized, double-blind, placebo-controlled 6-month trial compared the effects of ethyl-EPA versus placebo on 290 subjects with mild-to-moderate HD. The primary endpoint was the change from baseline to 6 months in the Total Motor Score 4 (TMS-4) component of the Unified Huntington's Disease Rating Scale (UHDRS). Secondary endpoints included change from baseline in UHDRS subscores and Clinical Global Impression (CGI). RESULTS: No significant differences in TMS-4 scores were noted between treatment groups. Similarly, there were no significant differences between groups on any of the UHDRS subscores or CGI scores. CONCLUSION: Ethyl-EPA was not beneficial in patients with HD during 6 months of placebo-controlled evaluation.