Pathways towards an effective immunotherapy for Parkinson's disease

Dopaminergic regulation of inflammation and immunity in Parkinson's disease: friend or foe?

Parkinson's disease (PD) is a neurodegenerative disease affecting 7-10 million people worldwide. Currently, there is no treatment available to prevent or delay PD progression, partially due to the limited understanding of the pathological events which lead to the death of dopaminergic neurons in the substantia nigra in the brain, which is known to be the cause of PD symptoms. The current available treatments aim at compensating dopamine (DA) deficiency in the brain using its precursor levodopa, dopaminergic agonists and some indirect dopaminergic agents. The immune system is emerging as a critical player in PD. Therefore, immune-based approaches have recently been proposed to be used as potential antiparkinsonian agents. It has been well-known that dopaminergic pathways play a significant role in regulating immune responses in the brain. Although dopaminergic agents are the primary antiparkinsonian treatments, their immune regulatory effect has yet to be fully understood. The present review summarises the current available evidence of the immune regulatory effects of DA and its mimics and discusses dopaminergic agents as antiparkinsonian drugs. Based on the current understanding of their involvement in the regulation of neuroinflammation in PD, we propose that targeting immune pathways involved in PD pathology could offer a better treatment outcome for PD patients.

Evaluation of an Adoptive Cellular Therapy-Based Vaccine in a Transgenic Mouse Model of α-synucleinopathy

Aggregated α-synuclein, a major constituent of Lewy bodies plays a crucial role in the pathogenesis of α-synucleinopathies (SPs) such as Parkinson's disease (PD). PD is affected by the innate and adaptive arms of the immune system, and recently both active and passive immunotherapies targeted against α-synuclein are being trialed as potential novel treatment strategies. Specifically, dendritic cell-based vaccines have shown to be an effective treatment for SPs in animal models. Here, we report on the development of adoptive cellular therapy (ACT) for SP and demonstrate that adoptive transfer of pre-activated T-cells generated from immunized mice can improve survival and behavior, reduce brain microstructural impairment via magnetic resonance imaging (MRI), and decrease α-synuclein pathology burden in a peripherally induced preclinical SP model (M83) when administered prior to disease onset. This study provides preclinical evidence for ACT as a potential immunotherapy for LBD, PD and other related SPs, and future work will provide necessary understanding of the mechanisms of its action.

Harnessing the immune system for the treatment of Parkinson's disease

Current treatment options for Parkinson's disease (PD) typically aim to replace dopamine, and hence only provide symptomatic relief. However, in the long run, this approach alone loses its efficacy as it is associated with debilitating side effects. Hence there is an unmet clinical need for addressing levodopa resistant symptoms, and an urgency to develop therapies that can halt or prevent the course of PD. The premise that α-syn can transmit from cell-to-cell in a prion like manner has opened up the possibility for the use of immunotherapy in PD. There is evidence for inflammation in PD as is evidenced by microglial activation, as well as the involvement of the peripheral immune system in PD, and peripheral inflammation can exacerbate dopaminergic degeneration as seen in animal models of the disease. However, mechanisms that link the immune system with PD are not clear, and the sequence of immune responses with respect to PD are still unknown. Nevertheless, our present knowledge offers avenues for the development of immune-based therapies for PD. In order to successfully employ such strategies, we must comprehend the state of the peripheral immune system during the course of PD. This review describes the developments in the field of both active and passive immunotherapies in the treatment of PD, and highlights the crucial need for future research for clarifying the role of inflammation and immunity in this debilitating disease.

Immunotherapies for Aging-Related Neurodegenerative Diseases-Emerging Perspectives and New Targets

Neurological disorders such as Alzheimer's disease (AD), Lewy body dementia (LBD), frontotemporal dementia (FTD), and vascular dementia (VCID) have no disease-modifying treatments to date and now constitute a dementia crisis that affects 5 million in the USA and over 50 million worldwide. The most common pathological hallmark of these age-related neurodegenerative diseases is the accumulation of specific proteins, including amyloid beta (Aβ), tau, α-synuclein (α-syn), TAR DNA-binding protein 43 (TDP43), and repeat-associated non-ATG (RAN) peptides, in the intra- and extracellular spaces of selected brain regions. Whereas it remains controversial whether these accumulations are pathogenic or merely a byproduct of disease, the majority of therapeutic research has focused on clearing protein aggregates. Immunotherapies have garnered particular attention for their ability to target specific protein strains and conformations as well as promote clearance. Immunotherapies can also be neuroprotective: by neutralizing extracellular protein aggregates, they reduce spread, synaptic damage, and neuroinflammation. This review will briefly examine the current state of research in immunotherapies against the 3 most commonly targeted proteins for age-related neurodegenerative disease: Aβ, tau, and α-syn. The discussion will then turn to combinatorial strategies that enhance the effects of immunotherapy against aggregating protein, followed by new potential targets of immunotherapy such as aging-related processes.

Dale Schenk One Year Anniversary: Fighting to Preserve the Memories

It has been a year since we lost Dale Schenk on September 30, 2016. Dale's visionary work resulted in the remarkable discovery in 1999 that an experimental amyloid-β (Aβ) vaccine reduced the neurodegeneration in a transgenic model of Alzheimer's disease (AD). Following Dale's seminal work, several active and passive immunotherapies have since been developed and tested in the clinic for AD, Parkinson's disease (PD), and other neurodegenerative disorders. Here we provide a brief overview of the current state of development of immunotherapy for AD, PD, and other neurodegenerative disorders in the context of this anniversary. The next steps in the development of immunotherapies will require combinatorial approaches mixing antibodies against various targets (e.g., Aβ, α-syn, Tau, and TDP43) with small molecules that block toxicity, aggregation, inflammation, and promote cell survival.

Immune Cell Activation in the Cerebrospinal Fluid of Patients With Parkinson's Disease

Background: Parkinson's disease (PD) is a common neurodegenerative disorder. The contribution of the immune system to its pathogenesis remains incompletely understood.

Methods: In this study, we performed comprehensive immune cell profiling in the cerebrospinal fluid (CSF) and peripheral blood (PB) of PD patients. Ten PD patients were diagnosed according to brain bank criteria and underwent detailed clinical examination, magnetic resonance imaging, PB and CSF immune cell profiling by multiparameter flow cytometry, and cytokine and chemokine measurements by bead-based arrays. Thirteen healthy elderly volunteers served as control population.

Results: The proportions of activated T-lymphocytes and non-classical monocytes in the CSF were increased in patients with PD compared to the control group. In accordance, we found increased levels of the pro-inflammatory cytokines IL-2, IL-6 and TNFα and of the monocyte chemoattractant protein 1 (MCP-1) in the CSF of the included PD patients.

Conclusions: Our data provide novel evidence for a response of the innate and adaptive immune system in the central nervous system of patients with PD.

Simvastatin as a Potential Disease-Modifying Therapy for Patients with Parkinson's Disease: Rationale for Clinical Trial, and Current Progress

Many now believe the holy grail for the next stage of therapeutic advance surrounds the development of disease-modifying approaches aimed at intercepting the year-on-year neurodegenerative decline experienced by most patients with Parkinson’s disease (PD). Based on recommendations of an international committee of experts who are currently bringing multiple, potentially disease-modifying, PD therapeutics into long-term neuroprotective PD trials, a clinical trial involving 198 patients is underway to determine whether Simvastatin provides protection against chronic neurodegeneration. Statins are widely used to reduce cardiovascular risk, and act as competitive inhibitors of HMG-CoA reductase. It is also known that statins serve as ligands for PPARα, a known arbiter for mitochondrial size and number. Statins possess multiple cholesterol-independent biochemical mechanisms of action, many of which offer neuroprotective potential (suppression of proinflammatory molecules & microglial activation, stimulation of endothelial nitric oxide synthase, inhibition of oxidative stress, attenuation of α-synuclein aggregation, modulation of adaptive immunity, and increased expression of neurotrophic factors). We describe the biochemical, physiological and pharmaceutical credentials that continue to underpin the rationale for taking Simvastatin into a disease-modifying trial in PD patients. While unrelated to the Simvastatin trial (because this conducted in patients who already have PD), we discuss conflicting epidemiological studies which variously suggest that statin use for cardiovascular prophylaxis may increase or decrease risk of developing PD. Finally, since so few disease-modifying PD trials have ever been launched (compared to those of symptomatic therapies), we discuss the rationale of the trial structure we have adopted, decisions made, and lessons learnt so far.

A Novel Immunosuppressor, (5R)-5-Hydroxytriptolide, Alleviates Movement Disorder and Neuroinflammation in a 6-OHDA Hemiparkinsonian Rat Model

Parkinson's disease (PD) is one of the most common age-related neurodegenerative diseases. Promising therapies for PD still need to be explored. Immune dysfunction has been found to be involved in PD pathogenesis. Here, a novel immunosuppressor, (5R)-5-hydroxytriptolide (LLDT8), was used to treat 6-hydroxydopamine (6-OHDA)-induced hemiparkinson rats. We found that oral administration of LLDT8 significantly alleviated apomorphine-induced rotations at a dose of 125 µg/kg, and improved performance in cylinder and rotarod tests at a lower dose of 31.25 µg/kg, in 6-OHDA hemiparkinsonian rats. Moreover, loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc) of the 6-OHDA rat was attenuated in response to LLDT8 treatment in a dose-dependent manner. In addition, inflammatory factors IL-1β, IL-6 and TNF-α, were significantly inhibited in LLDT8-treated hemiparkisonian rats, compared with vehicle. Notably, the level of dopamine (DA) in the striatum of PD rats was restored by LLDT8 treatment. Furthermore, we also detected that the disequilibrium of peripheral lymphocytes was reversed by LLDT8 administration. Taken together, the results imply that the immunosuppressor, LLDT8, can rescue dopaminergic neurodegeneration in 6-OHDA hemiparkinsonian rats, thus providing a potential therapeutic strategy for PD.

First-in-human assessment of PRX002, an anti-α-synuclein monoclonal antibody, in healthy volunteers

BACKGROUND

α-Synuclein is a major component of pathologic inclusions that characterize Parkinson's disease. PRX002 is an antibody that targets α-synuclein, and its murine parent antibody 9E4 has been shown in preclinical studies to reduce α-synuclein pathology and to protect against cognitive and motor deteriorations and progressive neurodegeneration in human α-synuclein transgenic mice.

METHODS

This first-in-human, randomized, double-blind, placebo-controlled, phase 1 study assessed the impact of PRX002 administered to 40 healthy participants in 5 ascending-dose cohorts (n = 8/cohort) in which participants were randomly assigned to receive a single intravenous infusion of study drug (0.3, 1, 3, 10, or 30 mg/kg; n = 6/cohort) or placebo (n = 2/cohort).

RESULTS

PRX002 demonstrated favorable safety, tolerability, and pharmacokinetic profiles at all doses tested, with no immunogenicity. No serious adverse events, discontinuations as a result of adverse events, or dose-limiting toxicities were reported. Serum PRX002 exposure was dose proportional; the average terminal half-life across all doses was 18.2 days. A significant dose-dependent reduction in free serum α-synuclein (unbound to PRX002) was apparent within 1 hour after PRX002 administration, whereas total α-synuclein (free plus bound) increased dose-dependently, presumably because of the expected change in kinetics following antibody binding.

CONCLUSIONS

This study demonstrates that serum α-synuclein can be safely modulated in a dose-dependent manner after single intravenous infusions of an anti-α-synuclein antibody. These findings support continued development of PRX002, including further characterization of its safety, tolerability, pharmacokinetics, and pharmacodynamic effects in the central nervous system in patients with Parkinson's disease. © 2016 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society.

Dopaminergic Receptors on CD4+ T Naive and Memory Lymphocytes Correlate with Motor Impairment in Patients with Parkinson's Disease

Parkinson’s disease (PD) is characterized by loss of dopaminergic neurons in substantia nigra pars compacta, α-synuclein (α-syn)-rich intraneuronal inclusions (Lewy bodies), and microglial activation. Emerging evidence suggests that CD4+ T lymphocytes contribute to neuroinflammation in PD. Since the mainstay of PD treatment is dopaminergic substitution therapy and dopamine is an established transmitter connecting nervous and immune systems, we examined CD4+ T naive and memory lymphocytes in PD patients and in healthy subjects (HS), with specific regard to dopaminergic receptor (DR) expression. In addition, the in vitro effects of α-syn were assessed on CD4+ T naive and memory cells. Results showed extensive association between DR expression in T lymphocytes and motor dysfunction, as assessed by UPDRS Part III score. In total and CD4+ T naive cells expression of D₁-like DR decrease, while in T memory cells D₂-like DR increase with increasing score. In vitro, α-syn increased CD4+ T memory cells, possibly to a different extent in PD patients and in HS, and affected DR expression with cell subset-specific patterns. The present results support the involvement of peripheral adaptive immunity in PD, and may contribute to develop novel immunotherapies for PD, as well as to better use of current dopaminergic antiparkinson drugs.

An update on potential therapeutic strategies for Parkinson's disease based on pathogenic mechanisms

INTRODUCTION

Parkinson's disease is a common neurodegenerative disorder mainly caused by the loss of nigral dopaminergic neurons, of which the pathogenesis remains essentially unknown. Current therapeutic strategies help manage signs and symptoms but have no effect in disease modification. Over the past several decades, scientists have devoted a lot of effort to clarifying the pathological mechanism and searching for new targets for Parkinson's disease treatment.

AREAS COVERED

Treatment of Parkinson's disease. Expert Commentary: Illustrated in this review are newly found discoveries and evidence that contribute to the understanding of Parkinson's disease pathogenic mechanism. Also discussed are potential therapeutic strategies that are being studied, including disease-modifying and genetically mediated small molecule compounds, cell- and gene-based therapeutic strategies, immunization strategies and anti-diabetic therapy, which may be very promising therapeutic methods in the future.

Immunotherapeutic Approaches Targeting Amyloid-β, α-Synuclein, and Tau for the Treatment of Neurodegenerative Disorders

Disease-modifying alternatives are sorely needed for the treatment of neurodegenerative disorders, a group of diseases that afflict approximately 50 million Americans annually. Immunotherapy is one of the most developed approaches in this direction. Vaccination against amyloid-β, α-synuclein, or tau has been extensively explored, specially as the discovery that these proteins may propagate cell-to-cell and be accessible to antibodies when embedded into the plasma membrane or in the extracellular space. Likewise, the use of passive immunization approaches with specific antibodies against abnormal conformations of these proteins has also yielded promising results. The clinical development of immunotherapies for Alzheimer’s disease, Parkinson’s disease, frontotemporal dementia, dementia with Lewy bodies, and other neurodegenerative disorders is a field in constant evolution. Results to date suggest that immunotherapy is a promising therapeutic approach for neurodegenerative diseases that progress with the accumulation and prion-like propagation of toxic protein aggregates. Here we provide an overview of the most novel and relevant immunotherapeutic advances targeting amyloid-β in Alzheimer’s disease, α-synuclein in Alzheimer’s disease and Parkinson’s disease, and tau in Alzheimer’s disease and frontotemporal dementia.

A Perspective on Roles Played by Innate and Adaptive Immunity in the Pathobiology of Neurodegenerative Disorders

Aberrant innate and adaptive immune responses are neurodegenerative disease effectors. Disease is heralded by a generalized, but subtle immune activation orchestrated by the release of extracellular prion-like aggregated and oxidized or otherwise modified proteins. These are responsible for an inflammatory neurotoxic cascade. The perpetrators of such events include effector T cells and activated microglia. What ensues are Alzheimer's and Parkinson's disease, amyotrophic lateral sclerosis and stroke with changed frequencies of effector T cell and reduced numbers or function of regulatory lymphocytes. The control of such immune responses could lead to new therapeutic strategies and the means to effectively combat a composite of diseases that have quite limited therapeutic options.

Anti-human α-synuclein N-terminal peptide antibody protects against dopaminergic cell death and ameliorates behavioral deficits in an AAV-α-synuclein rat model of Parkinson's disease

The protein α-synuclein (α-Syn) has a central role in the pathogenesis of Parkinson’s disease (PD) and immunotherapeutic approaches targeting this molecule have shown promising results. In this study, novel antibodies were generated against specific peptides from full length human α-Syn and evaluated for effectiveness in ameliorating α-Syn-induced cell death and behavioral deficits in an AAV-α-Syn expressing rat model of PD. Fisher 344 rats were injected with rAAV vector into the right substantia nigra (SN), while control rats received an AAV vector expressing green fluorescent protein (GFP). Beginning one week after injection of the AAV-α-Syn vectors, rats were treated intraperitoneally with either control IgG or antibodies against the N-terminal (AB1), or central region (AB2) of α-Syn. An unbiased stereological estimation of TH+, NeuN+, and OX6 (MHC-II) immunostaining revealed that the α-Syn peptide antibodies (AB1 and AB2) significantly inhibited α-Syn-induced dopaminergic cell (DA) and NeuN+ cell loss (one-way ANOVA (F (3, 30) = 5.8, p = 0.002 and (F (3, 29) = 7.92, p = 0.002 respectively), as well as decreasing the number of activated microglia in the ipsilateral SN (one-way ANOVA F = 14.09; p = 0.0003). Antibody treated animals also had lower levels of α-Syn in the ipsilateral SN (one-way ANOVA F (7, 37) = 9.786; p = 0.0001) and demonstrated a partial intermediate improvement of the behavioral deficits. Our data suggest that, in particular, an α-Syn peptide antibody against the N-terminal region of the protein can protect against DA neuron loss and, to some extent behavioral deficits. As such, these results may be a potential therapeutic strategy for halting the progression of PD.

Vaccination strategies for Parkinson disease: induction of a swift attack or raising tolerance?

Parkinson disease is the second most common neurodegenerative disease in the world, but there is currently no available cure for it. Current treatments only alleviate some of the symptoms for a few years, but they become ineffective in the long run and do not stop the disease. Therefore it is of outmost importance to develop therapeutic strategies that can prevent, stop, or cure Parkinson disease. A very promising target for these therapies is the peripheral immune system due to its probable involvement in the disease and its potential as a tool to modulate neuroinflammation. But for such strategies to be successful, we need to understand the particular state of the peripheral immune system during Parkinson disease in order to avoid its weaknesses. In this review we examine the available data regarding how dopamine regulates the peripheral immune system and how this regulation is affected in Parkinson disease; the specific cytokine profiles observed during disease progression and the alterations documented to date in patients' peripheral blood mononuclear cells. We also review the different strategies used in Parkinson disease animal models to modulate the adaptive immune response to salvage dopaminergic neurons from cell death. After analyzing the evidence, we hypothesize the need to prime the immune system to restore natural tolerance against α-synuclein in Parkinson disease, including at the same time B and T cells, so that T cells can reprogram microglia activation to a beneficial pattern and B cell/IgG can help neurons cope with the pathological forms of α-synuclein.

Immunity and inflammation in neurodegenerative diseases

Immune reactions inside the central nervous system are finely regulated, thanks to the presence of several checkpoints that have the fundamental purpose to preserve this fragile tissue form harmful events. The current knowledge on the role of neuroinflammation and neuro-immune interactions in the fields of multiple sclerosis, Alzheimer's disease and Parkinson's disease is reviewed. Moreover, a focus on the potential role of both active and passive immunotherapy is provided. Finally, we propose a common perspective, which implies that, under pathological conditions, inflammation may exert both detrimental and protective functions, depending on local factors and the timing of immune activation and shutting-off systems.