DNA immunization against amyloid beta 42 has high potential as safe therapy for Alzheimer's disease as it diminishes antigen-specific Th1 and Th17 cell proliferation

Neuroinflammation in Alzheimer's disease: insights from peripheral immune cells

Alzheimer's disease (AD) is a serious brain disorder characterized by the presence of beta-amyloid plaques, tau pathology, inflammation, neurodegeneration, and cerebrovascular dysfunction. The presence of chronic neuroinflammation, breaches in the blood-brain barrier (BBB), and increased levels of inflammatory mediators are central to the pathogenesis of AD. These factors promote the penetration of immune cells into the brain, potentially exacerbating clinical symptoms and neuronal death in AD patients. While microglia, the resident immune cells of the central nervous system (CNS), play a crucial role in AD, recent evidence suggests the infiltration of cerebral vessels and parenchyma by peripheral immune cells, including neutrophils, T lymphocytes, B lymphocytes, NK cells, and monocytes in AD. These cells participate in the regulation of immunity and inflammation, which is expected to play a huge role in future immunotherapy. Given the crucial role of peripheral immune cells in AD, this article seeks to offer a comprehensive overview of their contributions to neuroinflammation in the disease. Understanding the role of these cells in the neuroinflammatory response is vital for developing new diagnostic markers and therapeutic targets to enhance the diagnosis and treatment of AD patients.

Alterations in Immune Responses Are Associated with Dysfunctional Intracellular Signaling in Peripheral Blood Mononuclear Cells of Men and Women with Mild Cognitive Impairment and Alzheimer's disease

Deficits in the neuroendocrine-immune network in the periphery associated with the onset and progression of mild cognitive impairment (MCI) and Alzheimer's disease (AD) have not been extensively studied. The present study correlatively examines the association between cell-mediated immune responses, stress hormones, amyloid precursor protein (APP) expression, peripheral blood mononuclear cells (PBMC), and intracellular signaling molecules in the pathophysiology of MCI and AD compared to adults. Serum APP, lymphocyte proliferation, total cholinesterase (TChE), butyrylcholinesterase (BChE) activities, cytokines (IL-2, IFN-γ, IL-6, and TNF-α), and intracellular signaling molecules (p-ERK, p-CREB, and p-Akt) were measured in the PBMCs of adult, old, MCI, and AD men and women initially and after 3 years in the same population. An age- and disease-associated decline in mini-mental state examination (MMSE) scores and lymphocyte proliferation of MCI and AD men and women were observed. An age- and disease-related increase in serum APP, cortisol levels, and TChE activity were observed in men and women. Enhanced production of Th1 cytokine, IL-2, pro-inflammatory cytokines, and suppressed intracellular transcription factors may promote the inflammatory environment in MCI and AD patients. The expression of CREB and Akt was lower in MCI and AD men, while the expression of p-ERK was higher, and p-CREB was lower in MCI and AD women after 3 years. These results suggest that changes in specific intracellular signaling pathways may influence alterations in cell-mediated immunity to promote disease progression in MCI and AD patients.

DNA Aβ42 immunization via needle-less Jet injection in mice and rabbits as potential immunotherapy for Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia found in the elderly and disease progression is associated with accumulation of Amyloid beta 1-42 (Aβ42) in brain. An immune-mediated approach as a preventive intervention to reduce amyloid plaques without causing brain inflammation is highly desirable for future clinical use. Genetic immunization, in which the immunizing agent is DNA encoding Aβ42, has great potential because the immune response to DNA delivered into the skin is generally non-inflammatory, and thus differs quantitatively and qualitatively from immune responses elicited by peptides, which are inflammatory with production of IFNγ and IL-17 cytokines by activated T cells. DNA immunization has historically been proven difficult to apply to larger mammals. A potential barrier to use DNA immunization in large mammals is the method for delivery of the DNA antigen. We tested jet injection in mice and rabbits and found good antibody production and safe immune responses (no inflammatory cytokines). We found significant reduction of amyloid plaques and Aβ peptides in brains of the DNA Aβ42 immunized 3xTg-AD mouse model. This study was designed to optimize DNA delivery for possible testing of the DNA Aβ42 vaccine for AD prevention in a clinical trial.

Acquired immunity and Alzheimer's disease

Alzheimer's disease (AD) is an age-related neurodegenerative disease characterized by progressive cognitive defects. The role of the central immune system dominated by microglia in the progression of AD has been extensively investigated. However, little is known about the peripheral immune system in AD pathogenesis. Recently, with the discovery of the meningeal lymphatic vessels and glymphatic system, the roles of the acquired immunity in the maintenance of central homeostasis and neurodegenerative diseases have attracted an increasing attention. The T cells not only regulate the function of neurons, astrocytes, microglia, oligodendrocytes and brain microvascular endothelial cells, but also participate in the clearance of β-amyloid (Aβ) plaques. Apart from producing antibodies to bind Aβ peptides, the B cells affect Aβ-related cascades via a variety of antibody-independent mechanisms. This review systemically summarizes the recent progress in understanding pathophysiological roles of the T cells and B cells in AD.

Glial cell transcriptome analyses in 3xTg-AD mice: Effects of aging, disease progression, and anti-Aβ immunotherapy

Background

To investigate how changes in expression of glial genes relate to a progression of Alzheimer's disease (AD) pathology, and how anti-Aβ immunotherapy impact these changes, we conducted a transcriptomic analysis for brains from cohorts of 2-, 10-, and 20 month old 3xTg-AD mice, and a cross-sectional study in groups of 20 month-old mice treated with active DNA Aβ42 immunization, passive immunotherapy, untreated, and wild-type (wt) controls.

Methods

Twenty-four Formalin-Fixed Paraffin-Embedded (FFPE) mouse brain sections were used for the gene expression analyses (nanostring). Adjacent sections from these and additional mouse brains were stained for microglia using antibodies detecting IbaI and Gal3. For a semi-quantitative analysis of increased tau and amyloid pathology with aging and disease progression, a comparison of ELISA results from brains of 12 and 20 months old 3xTg-AD mice were shown.

Results

Based on the different comparisons of transcript numbers found the 3xTg-AD age groups with the senescent 20 months old wt control mouse brains, and the 20 months old 3xTg-AD mouse brains with the 20 months old wt control mouse brains, genes were assigned as upregulated due to aging, or due to disease progression, or due to both. The immunohistochemistry of microglia markers revealed that Gal3 might be an important marker for phagocytosing microglia around amyloid plaques. The comparison of the two anti-Aβ immunotherapy approaches showed a differential downregulation of inflammatory glial genes.

Conclusion

These results are relevant for future clinical trials using active anti-amyloid immunotherapy.

A Review of Brain-Targeted Nonviral Gene-Based Therapies for the Treatment of Alzheimer's Disease

Diseases of the central nervous system (CNS) are difficult to treat owing to the complexity of the brain and the presence of a natural blood-brain-barrier (BBB). Alzheimer's disease (AD) is one of the major progressive and currently incurable neurodegenerative disorders of the CNS, which accounts for 60-80% of cases of dementia. The pathophysiology of AD involves the accumulation of amyloid beta (Aβ) plaques and neurofibrillary tangles (NFTs) in the brain. Additionally, synaptic loss and imbalance of neuronal signaling molecules are characterized as important markers of AD. Existing treatments of AD help in the management of its symptoms and aim toward the maintenance of cognitive functions, behavior, and attenuation of gradual memory loss. Over the past decade, nonviral gene therapy has attracted increasing interest due to its various advantages over its viral counterparts. Moreover, advancements in nonviral gene technology have led to their increasing contributions in clinical trials. However, brain-targeted nonviral gene delivery vectors come across various extracellular and intracellular barriers, limiting their ability to transfer the therapeutic gene into the target cells. Chief barriers to nonviral gene therapy have been discussed briefly in this review. We have also highlighted the rapid advancement of several nonviral gene therapies for AD, which are broadly categorized into physical and chemical methods. These methods aim to modulate Aβ, beta-site amyloid precursor protein (APP) cleaving enzyme 1 (BACE1), apolipoprotein E, or neurotrophic factors' expression in the CNS. Overall, this review discusses challenges and recent advancements of nonviral gene therapy for AD.

Changes in the brain transcriptome after DNA Aβ42 trimer immunization in a 3xTg-AD mouse model

Alzheimer's disease (AD) has been associated with accumulation of amyloid beta (Aβ) peptides in brain, and immunotherapy targeting Aβ provides potential for AD prevention. We have used a DNA Aβ42 trimer construct for immunization of 3xTg-AD mice and found previously significant reduction of amyloid and tau pathology due to the immunotherapy. We show here that DNA Aβ42 immunized 3xTg-AD mice showed better performance in nest building activities and had a higher 24 months survival rate compared to the non-treated AD controls. The analysis of differently expressed genes in brains from 24 months old mice showed significant increases transcript levels between non-immunized AD mice and wild-type controls for genes involved in microglia and astrocyte function, cytokine and inflammatory signaling, apoptosis, the innate and adaptive immune response and are consistent with an inflammatory phenotype in AD. Most of these upregulated genes were downregulated in the DNA Aβ42 immunized 3xTg-AD mice due to the vaccine. Transcript numbers for the immediate early genes, Arc, Bdnf, Homer1, Egr1 and cfos, involved in neuronal and neurotransmission pathways which were much lower in the non-immunized 3xTg-AD mice, were restored to wild-type mouse brain levels in DNA Aβ42 immunized 3xTg-AD mice indicating positive effects of DNA Aβ42 immunotherapy on synapse stability and plasticity. The immune response after immunization is complex, but the multitude of changes after DNA Aβ42 immunization shows that this response moves beyond the amyloid hypothesis and into direction of disease prevention.

Salidroside Attenuates Cognitive Dysfunction in Senescence-Accelerated Mouse Prone 8 (SAMP8) Mice and Modulates Inflammation of the Gut-Brain Axis

Background: Alzheimer's disease (AD) is a fatal neurodegenerative disease characterized by progressive cognitive decline and memory loss. However, several therapeutic approaches have shown unsatisfactory outcomes in the clinical setting. Thus, developing alternative therapies for the prevention and treatment of AD is critical. Salidroside (SAL) is critical, an herb-derived phenylpropanoid glycoside compound, has been shown to attenuate lipopolysaccharide (LPS)-induced cognitive impairment. However, the mechanism underlying its neuroprotective effects remains unclear. Here, we show that SAL has a therapeutic effect in the senescence-accelerated mouse prone 8 (SAMP8) strain, a reliable and stable mouse model of AD. Methods: SAMP8 mice were treated with SAL, donepezil (DNP) or saline, and cognitive behavioral impairments were assessed using the Morris water maze (MWM), Y maze, and open field test (OFT). Fecal samples were collected and analyzed by 16S rRNA sequencing on an Illumina MiSeq system. Brain samples were analyzed to detect beta-amyloid (Aβ) 1-42 (Aβ1-42) deposition by immunohistochemistry (IHC) and western blotting. The activation of microglia and neuroinflammatory cytokines was detected by immunofluorescence (IF), western blotting and qPCR. Serum was analyzed by a Mouse High Sensitivity T Cell Magnetic Bead Panel on a Luminex-MAGPIX multiplex immunoassay system. Results: Our results suggest that SAL effectively alleviated hippocampus-dependent memory impairment in the SAMP8 mice. SAL significantly 1) reduced toxic Aβ1-42 deposition; 2) reduced microglial activation and attenuated the levels of the proinflammatory factors IL-1β, IL-6, and TNF-α in the brain; 3) improved the gut barrier integrity and modified the gut microbiota (reversed the ratio of Bacteroidetes to Firmicutes and eliminated Clostridiales and Streptococcaceae, which may be associated with cognitive deficits); and 4) decreased the levels of proinflammatory cytokines, particularly IL-1α, IL-6, IL-17A and IL-12, in the peripheral circulation, as determined by a multiplex immunoassay. Conclusion: In summary, SAL reversed AD-related changes in SAMP8 mice, potentially by regulating the microbiota-gut-brain axis and modulating inflammation in both the peripheral circulation and central nervous system. Our results strongly suggest that SAL has a preventive effect on cognition-related changes in SAMP8 mice and highlight its value as a potential agent for drug development.

The Critical Role of Nurr1 as a Mediator and Therapeutic Target in Alzheimer's Disease-related Pathogenesis

Several studies have revealed that the transcription factor nuclear receptor related 1 (Nurr1) plays several roles not only in the regulation of gene expression related to dopamine synthesis, but also in alternative splicing, and miRNA targeting. Moreover, it regulates cognitive functions and protects against inflammation-induced neuronal death. In particular, the role of Nurr1 in the pathogenesis of Parkinson's disease (PD) has been well investigated; for example, it has been shown that it restores behavioral and histological impairments in PD models. Although many studies have evaluated the connection between Nurr1 and PD pathogenesis, the role of Nurr1 in Alzheimer's disease (AD) remain to be studied. There have been several studies describing Nurr1 protein expression in the AD brain. However, only a few studies have examined the role of Nurr1 in the context of AD. Therefore, in this review, we highlight the overall effects of Nurr1 under the neuropathologic conditions related to AD. Furthermore, we suggest the possibility of using Nurr1 as a therapeutic target for AD or other neurodegenerative disorders.

An Overview of the Intrinsic Role of Citrullination in Autoimmune Disorders

A protein undergoes many types of posttranslation modification. Citrullination is one of these modifications, where an arginine amino acid is converted to a citrulline amino acid. This process depends on catalytic enzymes such as peptidylarginine deiminase enzymes (PADs). This modification leads to a charge shift, which affects the protein structure, protein-protein interactions, and hydrogen bond formation, and it may cause protein denaturation. The irreversible citrullination reaction is not limited to a specific protein, cell, or tissue. It can target a wide range of proteins in the cell membrane, cytoplasm, nucleus, and mitochondria. Citrullination is a normal reaction during cell death. Apoptosis is normally accompanied with a clearance process via scavenger cells. A defect in the clearance system either in terms of efficiency or capacity may occur due to massive cell death, which may result in the accumulation and leakage of PAD enzymes and the citrullinated peptide from the necrotized cell which could be recognized by the immune system, where the immunological tolerance will be avoided and the autoimmune disorders will be subsequently triggered. The induction of autoimmune responses, autoantibody production, and cytokines involved in the major autoimmune diseases will be discussed.

Active full-length DNA Aβ42 immunization in 3xTg-AD mice reduces not only amyloid deposition but also tau pathology

Background

Alzheimer’s disease (AD) is the most well-known and most common type of age-related dementia. Amyloid deposition and hyperphosphorylation of tau protein are both pathological hallmarks of AD. Using a triple-transgenic mouse model (3xTg-AD) that develops plaques and tangles in the brain similar to human AD, we provide evidence that active full-length DNA amyloid-β peptide 1–42 (Aβ₄₂) trimer immunization leads to reduction of both amyloid and tau aggregation and accumulation.

Methods

Immune responses were monitored by enzyme-linked immunosorbent assay (ELISA) (antibody production) and enzyme-linked immunospot (cellular activation, cytokine production). Brains from 20-month-old 3x Tg-AD mice that had received DNA Aβ₄₂ immunotherapy were compared with brains from age- and gender-matched transgenic Aβ₄₂ peptide-immunized and control mice by histology, Western blot analysis, and ELISA. Protein kinase activation and kinase levels were studied in Western blots from mouse hemibrain lysates.

Results

Quantitative ELISA showed a 40% reduction of Aβ₄₂ peptide and a 25–50% reduction of total tau and different phosphorylated tau molecules in the DNA Aβ₄₂ trimer-immunized 3xTg-AD mice compared with nonimmunized 3xTg-AD control animals. Plaque and Aβ peptide reductions in the brain were due to the anti-Aβ antibodies generated following the immunizations. Reductions of tau were likely due to indirect actions such as less Aβ in the brain resulting in less tau kinase activation.

Conclusions

The significance of these findings is that DNA Aβ₄₂ trimer immunotherapy targets two major pathologies in AD—amyloid plaques and neurofibrillary tangles—in one vaccine without inducing inflammatory T-cell responses, which carry the danger of autoimmune inflammation, as found in a clinical trial using active Aβ₄₂ peptide immunization in patients with AD (AN1792).

Intradermal active full-length DNA Aβ42 immunization via electroporation leads to high anti-Aβ antibody levels in wild-type mice

Aβ immunotherapies with anti-Aβ antibody responses have high potential as possible prevention treatment for Alzheimer's disease. We have previously shown that active DNA Aβ1-42 immunization via gene gun delivery led to a non-inflammatory immune response resulting in decreased Aβ levels in brains of an immunized AD mouse model. To make DNA vaccination more applicable for clinical use, we used here intradermal electroporation. With fine tuning of the electropulse parameters, high antibody levels and low levels of inflammatory cytokines in the cellular immunoassays were observed. Full-length DNA Aβ1-42 immunization delivered via electroporation has potential to be used in the clinical setting.

IL-17A and IL-23: plausible risk factors to induce age-associated inflammation in Alzheimer's disease

Background: Aging and its complications such as Alzheimer's disease (AD) are associated with chronic low-grade inflammation entitled age-associated inflammation. However, the main mechanisms whichinduce age-associated inflammation in aging and AD are yet to beclarified. L-23/IL-17A axis plays important roles in the induction of inflammation and consequently autoimmune disease. This review evaluates the main roles played by IL-17A, IL-23, and IL-17A/IL-23 axis in the pathogenesis of age-associated inflammation in AD patients. Result: IL-23/IL-17A axis, is an important factor participate in the pathogenesis of age-associated inflammation. The genetic variations and microbial infection can be considered as the most important candidates to induce AD via upregulation of IL-17A. IL-17A also deteriorates AD via induction by amyloid-β. IL-17A participates in the induction of AD by increasing neutrophils infiltration to brain, induction of neuroinflammation, increase in FASL, and amyloid-βdeposition as well as activation of microglia. Conclusions: Due to the important roles played by IL-23/IL-17A axis in AD pathogenesis, it can be considered as a target for immunotherapy against AD. Abbreviations: Aβ: β-Amyloid; AD: Alzheimer's disease; CD: cluster of differentiation; DAMPs: Damage-associated molecular patterns; DCs: dendritic cells; HLA: human leukocyte antigen; NF-κB: nuclear factor kappa-light-chain-enhancer of activated B cells; RAR: retinoic-acid receptor; RORγt: RAR-related orphan receptor gamma t; SAMP8: senescence-accelerated mouse prone 8 strain; TGF-β: tumor growth factor-β; TLRs: toll-like receptors.

Imbalance of Circulating Th17 and Regulatory T Cells in Alzheimer's Disease: A Case Control Study

The neuropathological hallmarks of Alzheimer's disease (AD), i.e., neuritic plaques and neurofibrillary tangles, consist of beta amyloid peptides (Aβ) and hyperphosphorylated Tau. These are accompanied by reactive microglia and astrocytes in the vicinity of the neuritic plaques and by changes to the peripheral immune system, e.g., an increase of the pro-inflammatory cytokines IL-1β, IL-6, and TNF-α in the peripheral blood. To address a potential involvement of peripheral T helper cell (T_h) subsets in AD, we conducted a case control study with 54 individuals with AD dementia (n = 14), with mild cognitive impairment (MCI) due to AD (MCI_AD, n = 14), with MCI unlikely due to AD (MCI_other, n = 13), and controls without cognitive impairment (controls, n = 13). The proportions of CD3⁺CD8^-IL-17A⁺IFNγ^- Th17 cells, CD3⁺CD8^-IL-17A^-IFNγ⁺ Th1 cells, and CD4⁺CD127^lowCD25⁺ regulatory T cells (T_regs) were assessed by flow cytometry. In addition, the correlations of the proportions of T_h subsets to cerebrospinal fluid biomarkers were studied. CD3⁺CD8^-IL-17A⁺IFNγ^- Th17 cells were significantly increased in subjects with MCI_AD compared to age- and sex-matched subjects with MCI_other and controls (MCI_AD mean = 1.13, SD = 0.77; MCI_other mean = 0.58, SD = 0.28; and controls mean = 0.52, SD = 0.22; p = 0.008). The proportion of CD4⁺CD127^lowCD25⁺ T_regs was not altered between the different groups, but it significantly positively related with the levels of total Tau and pTau181 (r_{Treg|totalTau} = 0.43, p = 0.021, n = 28; r_Treg|pTau181 = 0.46; p = 0.024, n = 28) in subjects with AD but not in nonAD controls (r_{Treg|totalTau =} -0.51, p = 0.007, n = 26). The increase of circulating CD3⁺CD8^-IL-17A⁺IFNγ^- Th17 cells in the early stages of AD and the association of CD4⁺CD127^lowCD25⁺ T_regs with neurodegeneration marker Tau may indicate that the adaptive immune system relates to neuropathological changes in AD.

Cathepsin S Is Involved in Th17 Differentiation Through the Upregulation of IL-6 by Activating PAR-2 after Systemic Exposure to Lipopolysaccharide from Porphyromonas gingivalis

Positive links have been found between periodontitis and numerous diseases in humans via persistent inflammation throughout the body. However, the main factors responsible for maintaining this pro-inflammatory condition are poorly understood. The spleen, the largest secondary immune organ, is a central hub regulating the immune response/inflammation due to the dendritic cell (DC) response to CD4⁺ T cell subtype differentiation, and lysosomal proteinase cathepsin S (CatS) is known to be involved in DC functions. In the present study, we found that CatS-induced IL-6 production by splenic DCs subsequently promotes Th17 differentiation, in response to systemic exposure to lipopolysaccharide derived from Porphyromonas gingivalis (PgLPS). The population of CD11c⁺ DCs was significantly increased in the splenic marginal zone (MZ) locally of wild-type (DBA/2) mice with splenomegaly but not in that of CatS deficient (CatS^-/-) mice after systemic exposure to PgLPS for 7 consecutive days (5 mg/kg/day, intraperitoneal). Similarly, the population of Th17⁺CD4⁺ T cells was also significantly increased in the splenic MZ of wild-type mice but not in that of CatS^-/- mice after PgLPS exposure. Furthermore, the increase in the Th17⁺ CD4⁺ T cell population paralleled increases in the levels of CatS and IL-6 in CD11c⁺ cells in the splenic MZ. In isolated primary splenic CD11c⁺ cells, the mRNA expression and the production of IL-6 was dramatically increased in wild-type mice but not in CatS^-/- mice after direct stimulation with PgLPS (1 μg/ml), and this PgLPS-induced increase in the IL-6 expression was completely abolished by pre-treatment with Z-Phe-Leu-COCHO (Z-FL), the specific inhibitor of CatS. The PgLPS activated protease-activated receptor (PAR) 2 in the isolated splenic CD11c⁺ cells was also significantly inhibited by CatS deficiently. In addition, the PgLPS-induced increase in the IL-6 production by splenic CD11c⁺ cells was completely abolished by pre-treatment with FSLLRY-NH₂, a PAR2 antagonist, as well as Akti, a specific inhibitor of Akt. These findings indicate that CatS plays a critical role in driving splenic DC-dependent Th17 differentiation through the upregulation of IL-6 by activating PAR2 after exposure to components of periodontal bacteria. Therefore, CatS-specific inhibitors may be effective in alleviating periodontitis-related immune/inflammation.

Genomics of Alzheimer Disease: A Review

IMPORTANCE

To provide a comprehensive review of knowledge of the genomics of Alzheimer disease (AD) and DNA amyloid β 42 (Aβ42) vaccination as a potential therapy.

OBSERVATIONS

Genotype-phenotype correlations of AD are presented to provide a comprehensive appreciation of the spectrum of disease causation. Alzheimer disease is caused in part by the overproduction and lack of clearance of Aβ protein. Oligomer Aβ, the most toxic species of Aβ, causes direct injury to neurons, accompanied by enhanced neuroinflammation, astrocytosis and gliosis, and eventually neuronal loss. The strongest genetic evidence supporting this hypothesis derives from mutations in the amyloid precursor protein (APP) gene. A detrimental APP mutation at the β-secretase cleavage site linked to early-onset AD found in a Swedish pedigree enhances Aβ production, in contrast to a beneficial mutation 2 residues away in APP that reduces Aβ production and protects against the onset of sporadic AD. A number of common variants associated with late-onset AD have been identified including apolipoprotein E, BIN1, ABC7, PICALM, MS4A4E/MS4A6A, CD2Ap, CD33, EPHA1, CLU, CR1, and SORL1. One or 2 copies of the apolipoprotein E ε4 allele are a major risk factor for late-onset AD. With DNA Aβ42 vaccination, a Th2-type noninflammatory immune response was achieved with a downregulation of Aβ42-specific effector (Th1, Th17, and Th2) cell responses at later immunization times. DNA Aβ42 vaccination upregulated T regulator cells (CD4+, CD25+, and FoxP3+) and its cytokine interleukin 10, resulting in downregulation of T effectors.

CONCLUSIONS AND RELEVANCE

Mutations in APP and PS-1 and PS-2 genes that are associated with early-onset, autosomal, dominantly inherited AD, in addition to the at-risk gene polymorphisms responsible for late-onset AD, all indicate a direct and early role of Aβ in the pathogenesis of AD. A translational result of genomic research has been Aβ-reducing therapies including DNA Aβ42 vaccination as a promising approach to delay or prevent this disease.

Evaluation of a DNA Aβ42 vaccine in adult rhesus monkeys (Macaca mulatta): antibody kinetics and immune profile after intradermal immunization with full-length DNA Aβ42 trimer

Background

Aggregated amyloid-β peptide 1–42 (Aβ42), derived from the cellular amyloid precursor protein, is one of the pathological hallmarks of Alzheimer’s disease (AD). Although active immunization against Aβ42 peptide was successful in AD mouse models and led to removal of plaques and improved memory, a similar clinical trial in humans (Aβ42 peptide immunization with QS-21 adjuvant) was stopped in phase II, when 6% of the treated patients developed encephalitis. Currently ongoing passive immunizations with the injection of preformed monoclonal antibodies against different epitopes within the Aβ_1–42 peptide, which do not lead to activation of the immune system, have shown some effects in slowing AD pathology. Active DNA Aβ42 immunizations administered with the gene gun into the skin are noninflammatory because they activate a different T-cell population (Th2) with different cytokine responses eliciting a different humoral immune response. We present our findings in rhesus macaques that underwent the DNA Aβ42 immunization via gene gun delivery into the skin.

Methods

Six rhesus monkeys received two different doses of a DNA Aβ42 trimer vaccine. The humoral immune response was analyzed from blood throughout the study, and cellular immune responses were determined in peripheral blood mononuclear cells (PBMCs) after three and six immunizations.

Results

DNA Aβ42 trimer immunization led to high titer antibody responses in the nonhuman primate (NHP) model. Antibodies generated in the rhesus monkeys following DNA Aβ42 immunization detected amyloid plaques consisting of human Aβ42 peptide in the brain of the triple-transgenic AD mouse model. T-cell responses showed no interferon (IFN)-γ- and interleukin (IL)-17-producing cells from PBMCs in Enzyme-Linked ImmunoSpot assays after three immunization time points. At six immunization time points, IFN-γ- and IL-17-producing cells were found in immunized animals as well as in control animals and were thus considered nonspecific and not due to the immunization regimen. IFN-γ and IL-17 secretion in response to Aβ42 peptide restimulation became undetectable after a 3-month rest period.

Conclusions

Intradermal DNA Aβ42 immunization delivered with the gene gun produces a high antibody response in NHPs and is highly likely to be effective and safe in a clinical AD prevention trial in patients.

Two decades of new drug discovery and development for Alzheimer's disease

Alzheimer's disease is a progressive and irreversible neurodegenerative disease, associated with a decreased cognitive function and severe behavioral abnormalities.

Evaluation of a DNA Aβ42 Vaccine in Aged NZW Rabbits: Antibody Kinetics and Immune Profile after Intradermal Immunization with Full-Length DNA Aβ42 Trimer

A pathological hallmark of Alzheimer's disease (AD) are amyloid plaques in the brain consisting of aggregated amyloid-β 42 peptide (Aβ42) derived from cellular amyloid-β protein precursor (AβPP). Based on successful experiments in mouse AD models, active immunization with Aβ42 peptide and passive immunizations with anti-Aβ42 antibodies were started in clinical trials. Active Aβ42 peptide immunization in humans had led to an inflammatory autoimmune response, and the trial was stopped. Passive immunizations had shown some effects in slowing AD pathology. Active DNA Aβ42 immunizations administered with the gene gun into the skin elicits a different immune response and is non-inflammatory. While in rodents, good responses had been found for this type of immunization, positive results in larger mammals are missing. We present here results from sixteen New Zealand White Rabbits, which underwent intradermal DNA Aβ42 immunization via gene gun. The humoral immune response was analyzed from blood throughout the study, and cellular immune responses were determined from spleens at the end of the study. A good anti-Aβ antibody response was found in the rabbit model. The T cell response after re-stimulation in cell culture showed no IFNγ producing cells when ELISPOT assays were analyzed from PBMC, but low numbers of IFNγ and IL-17 producing cells were found in ELISPOTS from spleens (both 5 immunizations). Brains from immunized rabbits showed no signs of encephalitis. Based on these results, DNA Aβ42 immunization is highly likely to be safe and effective to test in a possible clinical AD prevention trial in patients.

Gene-based vaccines and immunotherapeutic strategies against neurodegenerative diseases: Potential utility and limitations

There has been a recent expansion of vaccination and immunotherapeutic strategies from controlling infectious diseases to the targeting of non-infectious conditions including neurodegenerative disorders. In addition to conventional vaccine and immunotherapeutic modalities, gene-based methods that express antigens for presentation to the immune system by either live viral vectors or non-viral naked DNA plasmids have been developed and evaluated. This mini-review/commentary summarizes the advantages and disadvantages, as well as the research findings to date, of both of these gene-based vaccination approaches in terms of how they can be targeted against appropriate antigens within the Alzheimer and Parkinson disease pathogenesis processes as well as potentially against targets in other neurodegenerative diseases. Most recently, the novel utilization of these viral vector and naked DNA gene-based technologies includes the delivery of immunoglobulin genes from established biologically active monoclonal antibodies. This modified passive immunotherapeutic strategy has recently been applied to deliver passive antibody immunotherapy against the pathologically relevant amyloid β protein in Alzheimer disease. The advantages and disadvantages of this technological application of gene-based immune interventions, as well as research findings to date are also summarized. In sum, it is suggested that further evaluation of gene based vaccines and immunotherapies against neurodegenerative diseases are warranted to determine their potential clinical utility.

Bacterial spores as particulate carriers for gene gun delivery of plasmid DNA

Bacillus subtilis spores represent a suitable platform for the adsorption of proteins, enzymes and viral particles at physiological conditions. In the present work, we demonstrate that purified spores can also adsorb DNA on their surface after treatment with cationic molecules. In addition, we demonstrate that DNA-coated B. subtilis spores can be used as particulate carriers and act as an alternative to gold microparticles for the biolistic (gene gun) administration of plasmid DNA in mice. Gene gun delivery of spores pre-treated with DODAB (dioctadecyldimethylammonium bromide) allowed efficient plasmid DNA absorption and induced protein expression levels similar to those obtained with gold microparticles. More importantly, we demonstrated that a DNA vaccine adsorbed on spores can be loaded into biolistic cartridges and efficiently delivered into mice, which induced specific cellular and antibody responses. Altogether, these data indicate that B. subtilis spores represent a simple and low cost alternative for the in vivo delivery of DNA vaccines by the gene gun technology.

Matrine improves cognitive impairment and modulates the balance of Th17/Treg cytokines in a rat model of Aβ1-42-induced Alzheimer's disease

Matrine (MAT) has been reported for its anti-inflammatory and neuroprotective effects. However, little is known about its effects on Th17/Treg cytokines and cognitive impairment in Alzheimer's disease (AD). In the present study, we injected Aβ_1-42 to the hippocampus of the rat to induce AD. Three groups of the AD rats were treated with MAT (25, 100 or 200 mg/kg/day, respectively) by intraperitoneal injection for 5 weeks. Levels of Th17 cell cytokines [interleukin (IL)-17A and IL-23] and regulatory T (Treg) cell cytokines [transforming growth factor β (TGF-β) and IL-35] in homogenates of the brain cortex and hippocampus were measured using enzyme-linked immunosorbent assay (ELISA) kits. The mRNA expressions of Th17 cell specific transcription factor RORγt and Treg cell specific transcription factor Foxp3 in the brain cortex and hippocampus were quantified by real-time RT-PCR. Learning and memory ability of the rats were evaluated by Morris water maze test and novel object recognition test. ELISA detections showed the AD rats had increased levels of IL-17A and IL-23 as well as decreased levels of TGF-β and IL-35. Matrine (100 and 200 mg/kg/day) significantly reversed the alternations of Th17/Treg cytokines induced by Aβ_1-42 injection, decreased RORγt mRNA expression, increased Foxp3 mRNA expression and improved the learning and memory ability in the AD rats. The findings demonstrated that the AD rats had imbalance of Th17/Treg cytokines in the brain. MAT could dose-dependently restore the balance of Th17/Treg cytokines and attenuate the cognitive impairment in AD rats.

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.

Linking T cells to Alzheimer's disease: from neurodegeneration to neurorepair

The overly-simplistic view that inflammatory and anti-inflammatory influences in the brain were respectively detrimental and advantageous in Alzheimer's disease (AD) is being challenged by advances in methodologies, and a debate relating to immune surveillance mechanisms in the brain. In contrast with previous findings, increasing interleukin (IL)-4 and IL-10 in brain by a recently-developed adenoviral delivery method, had detrimental effects in an animal model of AD, and the ability to isolate the choroid plexus has opened the debate on the role of this specialized tissue in immune surveillance. Delivery of polarized T cells to animal models of AD by different routes has yielded contrasting results; analysis of these diverse responses is vital to understand the role of T cells in the brain in AD, first reported over 25 years ago.

T Cells-Protective or Pathogenic in Alzheimer's Disease?

Alzheimer's disease (AD) is the most common cause of dementia, and is characterised by deposits of amyloid β (Aβ), neurofibrillary tangles and neuronal loss. Neuroinflammatory changes have been identified as a feature of the disease, and recent studies have suggested a potential role for the peripheral immune system in driving these changes and, ultimately, the associated neuronal degeneration. A number of reports have detailed changes in the activation state and subtype of T cells in the circulation and CSF of AD patients and there is evidence of T cell infiltration into the brain. In this review, we examine the possible impact of T cell infiltration in the progression of pathology in AD and consider the data obtained from animal models of the disease. We consider how these cells infiltrate the brain, particularly in AD, and discuss whether the presence of T cells in the AD brain is protective or pathogenic. Finally we evaluate the current therapies, particularly those that involve immunization.

A noninflammatory immune response in aged DNA Aβ42-immunized mice supports its safety for possible use as immunotherapy in AD patients

Aging in the immune system results in tendency to proinflammatory responses. Intradermal DNA immunization showed Th2 polarized noninflammatory immune responses. We tested here 18-month-old mice which were immunized with Aβ42 peptide, DNA Aβ42 trimer, or 2 different prime boost protocols identical to previous experiments. High Aβ42 antibody levels were found in aged mice which had received peptide immunizations (900 μg/mL plasma), and in mice which had received peptide prime and DNA boost immunizations (500 μg/mL), compared with antibodies in DNA Aβ42 immunized mice with 50 μg/mL. Although we found T-cell proliferation and inflammatory cytokines in mice which had received peptide or prime boost immunization, these were not found in DNA-immunized mice. The results are concordant with proinflammatory responses because of immunosenescence and contraindicate the use of Aβ42 peptide immunizations or prime boost immunization protocols for the use in elderly Alzheimer's disease patients. DNA Aβ42 immunization only on the other hand does lead to effective levels of antibodies without inflammatory cytokine or T-cell responses in the aged animal model tested.

Co-stimulation with TNF receptor superfamily 4/25 antibodies enhances in-vivo expansion of CD4+CD25+Foxp3+ T cells (Tregs) in a mouse study for active DNA Aβ42 immunotherapy

The study was designed to test DNA Aβ42 immunization in mice as alternative approach for possible active immunotherapy in Alzheimer patients. As results, we found polarized Th2 immune responses, efficient Aβ42 antibody levels, and disappearance of antigen specific T cells. In-vivo TNFRSF4/25 antibody co-stimulation enhanced Aβ42 specific T cell responses with initial Th2 expansion and subsequent development of Aβ42 specific CD4+CD25+Foxp3+ cells. It showed that Th2 biased responses due to gene gun immunizations propagate the development of regulatory T cells. In conclusion, full-length DNA Aβ42 immunization into skin results in a regulatory response with minimal risk of inflammation and autoimmunity.

Active immunotherapy options for Alzheimer's disease

Alzheimer's disease (AD) is the most common cause of dementia and a major contributor to disability and dependency among older people. AD pathogenesis is associated with the accumulation of amyloid-beta protein (Aβ) and/or hyperphosphorylated tau protein in the brain. At present, current therapies provide temporary symptomatic benefit, but do not treat the underlying disease. Recent research has thus focused on investigating the molecular and cellular pathways and processes involved in AD pathogenesis to support the development of effective disease-modifying agents. In accordance with the existing Aβ-cascade hypothesis for AD pathogenesis, immunotherapy has been the most extensively studied approach in Aβ-targeted therapy. Both passive and active immunotherapies have been shown to effectively reduce Aβ accumulation and prevent downstream pathology in preclinical models. Following AN1792, second-generation active immunotherapies have shown promising results in terms of antibody response and safety. Comparatively, tau immunotherapy is not as advanced, but preclinical data support its development into clinical trials. Results from active amyloid-based immunotherapy studies in preclinical models indicate that intervention appears to be more effective in early stages of amyloid accumulation, highlighting the importance of diagnosing AD as early as possible and undertaking clinical trials at this stage. This strategy, combined with improving our understanding of the complex AD pathogenesis, is imperative to the successful development of these disease-modifying agents. This paper will review the active immunotherapies currently in development, including the benefits and challenges associated with this approach.

Anti-amyloid beta to tau - based immunization: Developments in immunotherapy for Alzheimer disease

Immunotherapy might provide an effective treatment for Alzheimer’s disease (AD). A unique feature of AD immunotherapies is that an immune response against a self-antigen needs to be elicited without causing adverse autoimmune reactions. Current research is focused on two possible targets in this regard. One is the inhibition of accumulation and deposition of amyloid beta 1–42 (Aβ42), which is one of the major peptides found in senile plaques, and the second target is hyperphosphorylated tau, which forms neurofibrillary tangles inside the nerve cell and shows association with the progression of dementia. Mouse models have shown that immunotherapy targeting Aβ42 as well as tau with the respective anti-Aβ or anti-tau antibodies can provide significant improvements in these mice. While anti-Aβ immunotherapy (active and passive immunizations) is already in several stages of clinical trials, tau-based immunizations have been analyzed only in mouse models. Recently, as a significant correlation of progression of dementia and levels of phosphorylated tau have been found, high interest has again focused on further development of tau-based therapies. While Aβ immunotherapy might delay the onset of AD, immunotherapy targeting tau might provide benefits in later stages of this disease. Last but not least, targeting Aβ and tau simultaneously with immunotherapy might provide additional therapeutic effects, as these two pathologies are likely synergistic; this is an approach that has not been tested yet. In this review, we will summarize animal models used to test possible therapies for AD, some of the facts about Aβ42 and tau biology, and present an overview on halted, ongoing, and upcoming clinical trials together with ongoing preclinical studies targeting tau or Aβ42.

Advances in the development of vaccines for Alzheimer's disease

One of the challenges of our society is to find a treatment or cure for Alzheimer's disease (AD). AD is the leading form of age-related dementia and with the increase of life expectancy worldwide, the social and economic burden from this disease will increase dramatically. It is a progressive and, in regard to clinical scores, a highly variable disease. AD pathogenesis has been associated with the accumulation, aggregation, and deposition of amyloid beta (Abeta) peptides in the brain. Hallmarks of AD are the amyloid plaques consisting of fibrillar Abeta and neurofibrillary tangles which are intracellular fibrils of hyperphosphorylated tau protein that develop later in this disease. The amyloid cascade hypothesis postulates that Abeta deposition is an initial event in the multifactorial pathogenesis and Abeta deposition may precede AD symptoms in some patients by at least 20 years. Amyloid beta therapy with active and passive immunizations against Abeta has a high possibility to be effective in removing Abeta from brain and might thus prevent the downstream pathology. Since 2000 a number of clinical trials for AD immunotherapy have started, have failed, and are continuing to be pursued. This article will review these clinical trials and ongoing research in this regard.

Nimodipine inhibits IL-1β release stimulated by amyloid β from microglia

BACKGROUND AND PURPOSE

There is growing evidence that inflammation plays a major role in the pathogenesis of neural damage caused by deposition of amyloid β (Aβ) in the brain. Nimodipine has received attention as a drug that might improve learning and reduce cognitive deficits in Alzheimer's disease, but the mechanism of action is poorly known. In this study, we tested the hypothesis that nimodipine inhibited Aβ-stimulated IL-1β release from microglia.

EXPERIMENTAL APPROACH

Cultures of N13 microglia cells or primary mouse microglia were treated with nimodipine, and intracellular accumulation and release of IL-1β in response to Aβ or to the P2 receptor agonists ATP and benzoyl ATP (BzATP) were measured. Accumulation of IL-1β was measured in vivo after intrahippocampal inoculation of Aβ in the absence or presence of nimodipine. The effect of nimodipine on Aβ-triggered cytotoxicity was also investigated.

KEY RESULTS

We show here that nimodipine dose-dependently inhibited Aβ-stimulated IL-1β synthesis and release from primary microglia and microglia cell lines. Furthermore, nimodipine also inhibited Aβ-induced IL-1βin vivo accumulation at concentrations known to be reached in the CNS. Finally, nimodipine protected microglia from Aβ-dependent cytotoxicity.

CONCLUSION AND IMPLICATIONS

These data suggest that alleviation of symptoms of Alzheimer's disease following nimodipine administration might be due to an anti-inflammatory effect and point to a novel role for nimodipine as a centrally acting anti-inflammatory drug.

Translational research in neurology: dementia

Dementia disorders are characterized by clinicopathological criteria. Molecular understandings of these disorders, based on immunohistochemical studies, biochemical investigations, genetic approaches, and animal models, have resulted in advances in diagnosis. Likewise, translational research has allowed us to apply our increasing basic scientific knowledge of neurodegeneration to the rational development of new investigational therapies based on our current understanding of disease pathogenesis. This review discusses the application of translational research to both diagnosis and treatment of dementia disorders. The development of biomarkers has yielded imaging and biochemical methods that assist the physician more than ever in the diagnosis of neurodegenerative dementias, especially Alzheimer disease. New diagnostic criteria for disease are based on these molecular-based techniques. And these biomarkers are of potential use in monitoring disease activity during therapeutic trials. Translational investigations likewise have led toward new avenues in targeted dementia research. This is particularly so in the development and testing of disease-modifying treatments that might slow or deter progressive deterioration. Recent clinical trials have not been based on empirical trials of established drugs but, rather, on trials of drugs shown, through experiments in biochemical, cell culture, and animal models, to interfere with known elements of the pathogenetic cascade of Alzheimer disease.

A peptide prime-DNA boost immunization protocol provides significant benefits as a new generation Aβ42 DNA vaccine for Alzheimer disease

Immunotherapy has the potential to provide a possible treatment therapy to prevent or delay Alzheimer disease. In a clinical trial (AN1792) in which patients received this immunotherapy and received active Aβ1-42 peptide immunizations, treatment was stopped when 6% of patients showed signs of meningoencephalitis. Follow up on these patients led to the conclusion that the antibody response was beneficial in removing Aβ1-42 from brain but an accompanying inflammatory Th1 T cell response was harmful. As a safe alternative treatment targeting the same self protein, Aβ1-42, in brain, we and others are working on a DNA Aβ1-42 immunization protocol as the immune response to DNA immunizations differs in many aspects from immunizations with peptide antigens. Because the immune response to DNA vaccination has different kinetics and has a significantly lower antibody production, we evaluated two different prime boost regimens, Aβ1-42 DNA prime/Aβ1-42 peptide boost and Aβ1-42 peptide prime/Aβ1-42 DNA boost for their effectiveness in antibody production and possible side effects due to inflammatory T cell responses. While both boost regimes significantly enhanced the specific antibody production with comparable antibody concentrations, the absence of the Aβ1-42 T cell response (no proliferation and no cytokine production) is consistent with our previous findings using this DNA Aβ1-42 trimer immunization and greatly enhances the safety aspect for possible clinical use.

Active DNA Aβ42 vaccination as immunotherapy for Alzheimer disease

As a neurodegenerative disorder, Alzheimer disease (AD) is the most common form of dementia found in the aging population. Immunotherapy with passive or active immunizations targeting amyloid beta (Aβ) build-up in the brain may provide a possible treatment option and may help prevent AD from progressing. A number of passive immunizations with anti-Aβ42 antibodies are in different phases of clinical trials. One active immunization approach, AN-1792, was stopped after the development of autoimmune encephalitis in 6% of patients and a second one, CAD106, in which a small Aβ epitope is used, is currently in safety and tolerability studies. Besides active immunizations with proteins or peptides, active immunizations using DNA which codes for the protein against which the immune response will be directed, so called genetic immunizations, provide additional safety as the immune response in DNA immunizations differs quantitatively and qualitatively from the response elicited by peptide immunizations. In this review, we summarize our data using DNA Aβ42 immunizations in mouse models and discuss the results together with the results presented by other groups working on a DNA vaccine as treatment option for AD.