Progress in the active immunotherapeutic approach to Alzheimer's disease: clinical investigations into AN1792-associated meningoencephalitis

Immunotherapeutic approaches for Alzheimer's disease: Exploring active and passive vaccine progress

Alzheimer's disease (AD) is the most common neurodegeneration having non-effective treatments. Vaccines or monoclonal antibodies are two typical immunotherapies for AD. Due to Aβ neurotoxicity, most of the treatments target its generation and deposition. However, therapies that specifically target tau protein are also being investigated. UB311 vaccine generates N-terminal anti-Aβ antibodies, that neutralize Aβ toxicity and promote plaque clearance. It is designed to elicit specific B-cell and wide T-cell responses. ACC001 or PF05236806 vaccine has the same Aβ fragment and QS21 as an adjuvant. CAD106 stimulates response against Aβ1-6. However, Nasopharyngitis and injection site erythema are its side effects. AN1792, the first-generation vaccine was formulated in proinflammatory QS21 adjuvant. However, T-cell epitopes are omitted from the developed epitope AD vaccine with Aβ1-42B-cell epitopes. The first-generation vaccine immune response was immensely successful in clearing Aβ, but it was also sufficient to provoke meningoencephalitis. Immunotherapies have been at the forefront of these initiatives in recent years. The review covers the recent updates on active and passive immunotherapy for AD.

Three major effects of APOEε4 on Aβ immunotherapy induced ARIA

The targeting of amyloid-beta (Aβ) plaques therapeutically as one of the primary causes of Alzheimer's disease (AD) dementia has been an ongoing effort spanning decades. While some antibodies are extremely promising and have been moved out of clinical trials and into the clinic, most of these treatments show similar adverse effects in the form of cerebrovascular damage known as amyloid-related imaging abnormalities (ARIA). The two categories of ARIA are of major concern for patients, families, and prescribing physicians, with ARIA-E presenting as cerebral edema, and ARIA-H as cerebral hemorrhages (micro- and macro-). From preclinical and clinical trials, it has been observed that the greatest genetic risk factor for AD, APOEε4, is also a major risk factor for anti-Aβ immunotherapy-induced ARIA. APOEε4 carriers represent a large population of AD patients, and, therefore, limits the broad adoption of these therapies across the AD population. In this review we detail three hypothesized mechanisms by which APOEε4 influences ARIA risk: (1) reduced cerebrovascular integrity, (2) increased neuroinflammation and immune dysregulation, and (3) elevated levels of CAA. The effects of APOEε4 on ARIA risk is clear, however, the underlying mechanisms require more research.

Immunotherapy: An emerging treatment option for neurodegenerative diseases

Accumulation of misfolded proteins and protein aggregates leading to degeneration of neurons is a hallmark of several neurodegenerative diseases. Therapy mostly relies on symptomatic relief. Immunotherapy offers a promising approach for the development of disease-modifying routes. Such strategies have shown remarkable results in oncology, and this promise is increasingly being realized for neurodegenerative diseases in advanced preclinical and clinical studies. This review highlights cases of passive and active immunotherapies in Parkinson's and Alzheimer's diseases. The reasons for success and failure, wherever available, and strategies to cross the blood-brain barrier, are discussed. The need for conditional modulation of the immune response is also reflected on.

Passive immunotherapy for Alzheimer's disease

Alzheimer's disease (AD) is the most common neurodegenerative disease characterized by cognitive impairment with few therapeutic options. Despite many failures in developing AD treatment during the past 20 years, significant advances have been achieved in passive immunotherapy of AD very recently. Here, we review characteristics, clinical trial data, and mechanisms of action for monoclonal antibodies (mAbs) targeting key players in AD pathogenesis, including amyloid-β (Aβ), tau and neuroinflammation modulators. We emphasized the efficacy of lecanemab and donanemab on cognition and amyloid clearance in AD patients in phase III clinical trials and discussed factors that may contribute to the efficacy and side effects of anti-Aβ mAbs. In addition, we provided important information on mAbs targeting tau or inflammatory regulators in clinical trials, and indicated that mAbs against the mid-region of tau or pathogenic tau have therapeutic potential for AD. In conclusion, passive immunotherapy targeting key players in AD pathogenesis offers a promising strategy for effective AD treatment.

Accelerating Alzheimer's therapeutic development: The past and future of clinical trials

Alzheimer's disease (AD) research has entered a new era with the recent positive phase 3 clinical trials of the anti-Aβ antibodies lecanemab and donanemab. Why did it take 30 years to achieve these successes? Developing potent therapies for reducing fibrillar amyloid was key, as was selection of patients at relatively early stages of disease. Biomarkers of the target pathologies, including amyloid and tau PET, and insights from past trials were also critical to the recent successes. Moving forward, the challenge will be to develop more efficacious therapies with greater efficiency. Novel trial designs, including combination therapies and umbrella and basket protocols, will accelerate clinical development. Better diversity and inclusivity of trial participants are needed, and blood-based biomarkers may help to improve access for medically underserved groups. Incentivizing innovation in both academia and industry through public-private partnerships, collaborative mechanisms, and the creation of new career paths will be critical to build momentum in these exciting times.

Antibody-Mediated Clearance of Brain Amyloid-β: Mechanisms of Action, Effects of Natural and Monoclonal Anti-Aβ Antibodies, and Downstream Effects

Immunotherapeutic efforts to slow the clinical progression of Alzheimer's disease (AD) by lowering brain amyloid-β (Aβ) have included Aβ vaccination, intravenous immunoglobulin (IVIG) products, and anti-Aβ monoclonal antibodies. Neither Aβ vaccination nor IVIG slowed disease progression. Despite conflicting phase III results, the monoclonal antibody Aducanumab received Food and Drug Administration (FDA) approval for treatment of AD in June 2021. The only treatments unequivocally demonstrated to slow AD progression to date are the monoclonal antibodies Lecanemab and Donanemab. Lecanemab received FDA approval in January 2023 based on phase II results showing lowering of PET-detectable Aβ; phase III results released at that time indicated slowing of disease progression. Topline results released in May 2023 for Donanemab's phase III trial revealed that primary and secondary end points had been met. Antibody binding to Aβ facilitates its clearance from the brain via multiple mechanisms including promoting its microglial phagocytosis, activating complement, dissolving fibrillar Aβ, and binding of antibody-Aβ complexes to blood-brain barrier receptors. Antibody binding to Aβ in peripheral blood may also promote cerebral efflux of Aβ by a peripheral sink mechanism. According to the amyloid hypothesis, for Aβ targeting to slow AD progression, it must decrease downstream neuropathological processes including tau aggregation and phosphorylation and (possibly) inflammation and oxidative stress. This review discusses antibody-mediated mechanisms of Aβ clearance, findings in AD trials involving Aβ vaccination, IVIG, and anti-Aβ monoclonal antibodies, downstream effects reported in those trials, and approaches which might improve the Aβ-clearing ability of monoclonal antibodies.

Current and future therapeutic strategies for Alzheimer's disease: an overview of drug development bottlenecks

Alzheimer's disease (AD) is the most common chronic neurodegenerative disease worldwide. It causes cognitive dysfunction, such as aphasia and agnosia, and mental symptoms, such as behavioral abnormalities; all of which place a significant psychological and economic burden on the patients' families. No specific drugs are currently available for the treatment of AD, and the current drugs for AD only delay disease onset and progression. The pathophysiological basis of AD involves abnormal deposition of beta-amyloid protein (Aβ), abnormal tau protein phosphorylation, decreased activity of acetylcholine content, glutamate toxicity, autophagy, inflammatory reactions, mitochondria-targeting, and multi-targets. The US Food and Drug Administration (FDA) has approved five drugs for clinical use: tacrine, donepezil, carbalatine, galantamine, memantine, and lecanemab. We have focused on the newer drugs that have undergone clinical trials, most of which have not been successful as a result of excessive clinical side effects or poor efficacy. Although aducanumab received rapid approval from the FDA on 7 June 2021, its long-term safety and tolerability require further monitoring and confirmation. In this literature review, we aimed to explore the possible pathophysiological mechanisms underlying the occurrence and development of AD. We focused on anti-Aβ and anti-tau drugs, mitochondria-targeting and multi-targets, commercially available drugs, bottlenecks encountered in drug development, and the possible targets and therapeutic strategies for future drug development. We hope to present new concepts and methods for future drug therapies for AD.

Safety, tolerability, immunogenicity, and efficacy of UB-311 in participants with mild Alzheimer's disease: a randomised, double-blind, placebo-controlled, phase 2a study

BACKGROUND

Anti-amyloid vaccines may offer a convenient, affordable, and accessible means of preventing and treating Alzheimer's disease. UB-311 is an anti-amyloid-β active immunotherapeutic vaccine shown to be well-tolerated and to have a durable antibody response in a phase 1 trial. This phase 2a study assessed the safety, immunogenicity, and preliminary efficacy of UB-311 in participants with mild Alzheimer's disease.

METHODS

A 78-week, randomised, double-blind, placebo-controlled, parallel-group, multicentre, phase 2a study was conducted in Taiwan. Participants were randomised in a 1:1:1 ratio to receive seven intramuscular injections of UB-311 (Q3M arm), or five doses of U311 with two doses of placebo (Q6M arm), or seven doses of placebo (placebo arm). The primary endpoints were safety, tolerability, and immunogenicity of UB-311. Safety was assessed in all participants who received at least one dose of investigational product. This study was registered at ClinicalTrials.gov (NCT02551809).

FINDINGS

Between 7 December 2015 and 28 August 2018, 43 participants were randomised. UB-311 was safe, well-tolerated, and generated a robust immune response. The three treatment-emergent adverse events (TEAEs) with the highest incidence were injection-site pain (14 TEAEs in seven [16%] participants), amyloid-related imaging abnormality with microhaemorrhages and haemosiderin deposits (12 TEAEs in six [14%] participants), and diarrhoea (five TEAEs in five [12%] participants). A 97% antibody response rate was observed and maintained at 93% by the end of the study across both UB-311 arms.

INTERPRETATION

These results support the continued development of UB-311.

FUNDING

Vaxxinity, Inc. (Formerly United Neuroscience Ltd.).

Recent Trends in Active and Passive Immunotherapies of Alzheimer's Disease

In the elderly, a debilitating condition known as dementia, which is a major health concern, is caused by Alzheimer's disease (AD). Despite promising advances by researchers, there is currently no way to completely cure this devastating disease. It is illustrated by the deposition of amyloid β-peptide (Aβ) plaques that are followed by neural dysfunction and cognitive decline. Responses against AD activate an immune system that contributes to and accelerates AD pathogenesis. Potential efforts in the field of pathogenesis have prompted researchers to explore novel therapies such as active and passive vaccines against Aβ proteins (Aβ immunotherapy), intravenous immunoglobulin, and tau immunotherapy, as well as targets that include microglia and several cytokines for the treatment of AD. Aims are now underway by experts to begin immunotherapies before the clinical manifestation, which is made possible by improving the sensitivity of biomarkers used for the diagnosis of AD to have better outcome measures. This review provides an overview of approved immunotherapeutic strategies for AD and those currently being investigated in clinical trials. We examine their mechanisms of action and discuss the potential perspectives and challenges associated with immunotherapies for AD.

Review of Advanced Drug Trials Focusing on the Reduction of Brain Beta-Amyloid to Prevent and Treat Dementia

Alzheimer disease (AD) is the most common neurodegenerative disease and typically affects patients older than age 65. Around this age, the number of neurons begins to gradually decrease in healthy brains, but brains of patients with AD show a marked increase in neuron death, often resulting in a significant loss of cognitive abilities. Cognitive skills affected include information retention, recognition capabilities, and language skills. At present, AD can be definitively diagnosed only through postmortem brain biopsies via the detection of extracellular amyloid beta (Aβ) plaques and intracellular hyperphosphorylated tau neurofibrillary tangles. Because the levels of both Aβ plaques and tau tangles are increased, these 2 proteins are thought to be related to disease progression. Although relatively little is known about the cause of AD and its exact pathobiological development, many forms of treatment have been investigated to determine an effective method for managing AD symptoms by targeting Aβ. These treatments include but are not limited to using small molecules to alter the interactions of Aβ monomers, reducing hyperactivation of neuronal circuits altering Aβ's molecular pathway of synthesis, improving degradation of Aβ, employing passive immunity approaches, and stimulating patients' active immunity to target Aβ. This review summarizes the current therapeutic interventions in Phase II/III of clinical development or higher that are capable of reducing abnormal brain Aβ levels to determine which treatments show the greatest likelihood of clinical efficacy. We conclude that, in the near future, the most promising therapeutic interventions for brain Aβ pathology will likely be passive immunotherapies, with aducanumab and donanemab leading the way, and that these drugs may be combined with antidepressants and acetylcholine esterase inhibitors, which can modulate Aβ synthesis.

Conformational Essentials Responsible for Neurotoxicity of Aβ42 Aggregates Revealed by Antibodies against Oligomeric Aβ42

Soluble aggregation of amyloid β-peptide 1-42 (Aβ42) and deposition of Aβ42 aggregates are the initial pathological hallmarks of Alzheimer's disease (AD). The bipolar nature of Aβ42 molecule results in its ability to assemble into distinct oligomers and higher aggregates, which may drive some of the phenotypic heterogeneity observed in AD. Agents targeting Aβ42 or its aggregates, such as anti-Aβ42 antibodies, can inhibit the aggregation of Aβ42 and toxicity of Aβ42 aggregates to neural cells to a certain extent. However, the epitope specificity of an antibody affects its binding affinity for different Aβ42 species. Different antibodies target different sites on Aβ42 and thus elicit different neuroprotective or cytoprotective effects. In the present review, we summarize significant information reflected by anti-Aβ42 antibodies in different immunotherapies and propose an overview of the structure (conformation)-toxicity relationship of Aβ42 aggregates. This review aimed to provide a reference for the directional design of antibodies against the most pathogenic conformation of Aβ42 aggregates.

A multitude of signaling pathways associated with Alzheimer's disease and their roles in AD pathogenesis and therapy

The exact molecular mechanisms associated with Alzheimer's disease (AD) pathology continue to represent a mystery. In the past decades, comprehensive data were generated on the involvement of different signaling pathways in the AD pathogenesis. However, the utilization of signaling pathways as potential targets for the development of drugs against AD is rather limited due to the immense complexity of the brain and intricate molecular links between these pathways. Therefore, finding a correlation and cross-talk between these signaling pathways and establishing different therapeutic targets within and between those pathways are needed for better understanding of the biological events responsible for the AD-related neurodegeneration. For example, autophagy is a conservative cellular process that shows link with many other AD-related pathways and is crucial for maintenance of the correct cellular balance by degrading AD-associated pathogenic proteins. Considering the central role of autophagy in AD and its interplay with many other pathways, the finest therapeutic strategy to fight against AD is the use of autophagy as a target. As an essential step in this direction, this comprehensive review represents recent findings on the individual AD-related signaling pathways, describes key features of these pathways and their cross-talk with autophagy, represents current drug development, and introduces some of the multitarget beneficial approaches and strategies for the therapeutic intervention of AD.

Bacille Calmette-Guérin attenuates vascular amyloid pathology and maximizes synaptic preservation in APP/PS1 mice following active amyloid-β immunotherapy

Despite effective clearance of parenchymal amyloid-β (Aβ) in patients with Alzheimer's disease, Aβ immunotherapy exacerbates the vascular Aβ (VAβ)-associated pathology in the brain. We have previously shown that BCG immunization facilitates protective monocyte recruitment to the brain of APP/PS1 mice. Here, we confirmed that the 4Aβ1-15 vaccine exacerbates VAβ deposits in this model, which coincides with a decrease in the number of cerebrovascular endothelial cells and pericytes, infiltration of neutrophils into the brain, and induction of cerebral microhemorrhage. Moreover, combined 4Aβ1-15/BCG treatment abrogates the development of the VAβ-associated pathology. In addition, BCG treatment is required for the upregulation of interleukin-10 in the brain. Notably, BCG treatment selectively enhances Aβ phagocytosis by recruited macrophages. Furthermore, combined 4Aβ1-15/BCG treatment is more effective than 4Aβ1-15 monotherapy in synaptic preservation and the enhancement of the learning efficiency. Overall, our study suggests that the combination of Aβ-targeted therapy with an immunomodulatory strategy may improve the efficacy of Aβ vaccine in Alzheimer's disease.

Vaccination against β-Amyloid as a Strategy for the Prevention of Alzheimer's Disease

Vaccination relies on the phenomenon of immunity, a long-term change in the immunological response to subsequent encounters with the same pathogen that occurs after the recovery from some infectious diseases. However, vaccination is a strategy that can, in principle, be applied also to non-infectious diseases, such as cancer or neurodegenerative diseases, if an adaptive immune response can prevent the onset of the disease or modify its course. Immunization against β-amyloid has been explored as a vaccination strategy for Alzheimer's disease for over 20 years. No vaccine has been licensed so far, and immunotherapy has come under considerable criticism following the negative results of several phase III clinical trials. In this narrative review, we illustrate the working hypothesis behind immunization against β-amyloid as a vaccination strategy for Alzheimer's disease, and the outcome of the active immunization strategies that have been tested in humans. On the basis of the lessons learned from preclinical and clinical research, we discuss roadblocks and current perspectives in this challenging enterprise in translational immunology.

Nanoliposomes as a Therapeutic Tool for Alzheimer's Disease

The accumulation of extracellular amyloid-beta (Aβ), denoted as senile plaques, and intracellular neurofibrillary tangles (formed by hyperphosphorylated Tau protein) in the brain are two major neuropathological hallmarks of Alzheimer's disease (AD). The current and most accepted hypothesis proposes that the oligomerization of Aβ peptides triggers the polymerization and accumulation of amyloid, which leads to the senile plaques. Several strategies have been reported to target Aβ oligomerization/polymerization. Since it is thought that Aβ levels in the brain and peripheral blood maintain equilibrium, it has been hypothesized that enhancing peripheral clearance (by shifting this equilibrium towards the blood) might reduce Aβ levels in the brain, known as the sink effect. This process has been reported to be effective, showing a reduction in Aβ burden in the brain as a consequence of the peripheral reduction of Aβ levels. Nanoparticles (NPs) may have difficulty crossing the blood-brain barrier (BBB), initially due to their size. It is not clear whether particles in the range of 50-100 nm should be able to cross the BBB without being specifically modified for it. Despite the size limitation of crossing the BBB, several NP derivatives may be proposed as therapeutic tools. The purpose of this review is to summarize some therapeutic approaches based on nanoliposomes using two complementary examples: First, unilamellar nanoliposomes containing Aβ generic ligands, such as sphingolipids, gangliosides or curcumin, or some sphingolipid bound to the binding domain of ApoE; and second, nanoliposomes containing monoclonal antibodies against Aβ. Following similar rationale NPs of poly(lactide-co-glycolide)-poly (ethylene glycol) conjugated with curcumin-derivate (PLGA-PEG-B6/Cur) were reported to improve the spatial learning and memory capability of APP/PS1 mice, compared with native curcumin treatment. Also, some new nanostructures such as exosomes have been proposed as a putative therapeutic and prevention strategies of AD. Although the unquestionable interest of this issue is beyond the scope of this review article. The potential mechanisms and significance of nanoliposome therapies for AD, which are still are in clinical trials, will be discussed.

Peripheral Immunity, Immunoaging and Neuroinflammation in Parkinson's Disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder among elderly population, characterized by the progressive degeneration of dopaminergic neurons in the midbrain. To date, exact cause remains unknown and the mechanism of neurons death uncertain. It is typically considered as a disease of central nervous system (CNS). Nevertheless, numerous evidence has been accumulated in several past years testifying undoubtedly about the principal role of neuroinflammation in progression of PD. Neuroinflammation is mainly associated with presence of activated microglia in brain and elevated levels of cytokine levels in CNS. Nevertheless, active participation of immune system as well has been noted, such as, elevated levels of cytokine levels in blood, the presence of auto antibodies, and the infiltration of T cell in CNS. Moreover, infiltration and reactivation of those T cells could exacerbate neuroinflammation to greater neurotoxic levels. Hence, peripheral inflammation is able to prime microglia into pro-inflammatory phenotype, which can trigger stronger response in CNS further perpetuating the on-going neurodegenerative process. In the present review, the interplay between neuroinflammation and the peripheral immune response in the pathobiology of PD will be discussed. First of all, an overview of regulation of microglial activation and neuroinflammation is summarized and discussed. Afterwards, we try to collectively analyze changes that occurs in peripheral immune system of PD patients, suggesting that these peripheral immune challenges can exacerbate the process of neuroinflammation and hence the symptoms of the disease. In the end, we summarize some of proposed immunotherapies for treatment of PD.

Vaccine Development against the Renin-Angiotensin System for the Treatment of Hypertension

Hypertension is a global public health issue and the most important preventable cause of cardiovascular diseases. Despite the clinical availability of many antihypertensive drugs, many hypertensive patients have poor medication adherence and blood pressure control due, at least partially, to the asymptomatic and chronic characteristics of hypertension. Immunotherapeutic approaches have the potential to improve medication adherence in hypertension because they induce prolonged therapeutic effects and need a low frequency of administration. The first attempts to reduce blood pressure by using vaccines targeting the renin-angiotensin system were made more than half a century ago; however, at the time, a poor understanding of immunology and the mechanisms of hypertension and a lack of optimal vaccine technologies such as suitable antigen design, proper adjuvants, and effective antigen delivery systems meant that attempts to develop antihypertensive vaccines failed. Recent advances in immunology and vaccinology have provided potential therapeutic immunologic approaches to treat not only infectious diseases but also cancers and other noncommunicable diseases. One important biotechnology that has had a major impact on modern vaccinology is virus-like particle technology, which can efficiently deliver vaccine antigens without the need for artificial adjuvants. A human clinical trial that indicated the effectiveness and safety of a virus-like particle-based antiangiotensin II vaccine marked a turning point in the field of therapeutic antihypertensive vaccines. Here, we review the history of the development of immunotherapies for the treatment of hypertension and discuss the current perspectives in the field.

Anti-Aβ Antibodies and Cerebral Amyloid Angiopathy Complications

Cerebral amyloid angiopathy (CAA) corresponds to the deposition of amyloid material in the cerebral vasculature, leading to structural modifications of blood vessel walls. The most frequent form of sporadic CAA involves fibrillar β-amyloid peptide (Aβ) deposits, mainly the 40 amino acid form (Aβ_1-40), which are commonly found in the elderly with or without Alzheimer's disease. Sporadic CAA usually remains clinically silent. However, in some cases, acute complications either hemorrhagic or inflammatory can occur. Similar complications occurred after active or passive immunization against Aβ in experimental animal models exhibiting CAA, and in subjects with Alzheimer's disease during clinical trials. The triggering of these adverse events by active immunization and monoclonal antibody administration in CAA-bearing individuals suggests that analogous mechanisms could be involved during spontaneous CAA complications, drawing particular attention to the role of anti-Aβ antibodies. However, antibodies that react with several monomeric and aggregated forms of Aβ spontaneously occur in virtually all human individuals, hence being part of the "natural antibody" repertoire. Natural antibodies are usually described as having low-affinity and high cross-reactivity toward microbial components and autoantigens. Although frequently of the IgM class, they also belong to IgG and IgA isotypes. They likely display homeostatic functions and protective roles in aging. Until recently, the peculiar properties of these natural antibodies have hindered proper analysis of the Aβ-reactive antibody repertoire and the study of their implication in CAA complications. Herein, we review and comment the evidences of an auto-immune nature of spontaneous CAA complications, and discuss implications for forthcoming research and clinical practice.

Identifying the Pathological Domain of Alpha- Synuclein as a Therapeutic for Parkinson's Disease

Alpha-synuclein is considered the major pathological protein associated with Parkinson's disease, but there is still no effective immunotherapy which targets alpha-synuclein. In order to create a safer and more effective therapy against PD, we are targeting an epitope of alpha-synuclein rather than full-length alpha-synuclein. We have selected several antigenic domains (B-cell epitope) through antigenicity prediction, and also made several recombinant protein fragments from alpha-synuclein upon antigenicity prediction in an E. coli system. We then tested the function of each of the peptides and recombinant fragments in aggregation, their toxicity and antigenicity. We have discovered that the full-length recombinant (aa1-140) can aggregate into oligomers or even fibrils, and fragment aa15-65 can promote the aggregation of aa1-140. It is worth noting that it not only promotes whole protein aggregation, but also self-aggregates as seen by western blotting and silver staining assays. We have tested all candidates on primary neurons for their toxicity and discovered that aa15-65 is the most toxic domain compared to all other fragments. The antibody targeting this domain also showed both anti-aggregation activity and some therapeutic effect. Therefore, we believe that we have identified the most potent therapeutic domain of alpha synuclein as a therapeutic target.

Active immunization with norovirus P particle-based amyloid-β chimeric protein vaccine induces high titers of anti-Aβ antibodies in mice

BACKGROUND

Active immunotherapy targeting amyloid-β (Aβ) is a promising treatment for Alzheimer's disease (AD). Numerous preclinical studies and clinical trials demonstrated that a safe and effective AD vaccine should induce high titers of anti-Aβ antibodies while avoiding the activation of T cells specific to Aβ.

RESULTS

An untagged Aβ1-6 chimeric protein vaccine against AD based on norovirus (NoV) P particle was expressed in Escherichia coli and obtained by sequential chromatography. Analysis of protein characteristics showed that the untagged Aβ1-6 chimeric protein expressed in soluble form exhibited the highest particle homogeneity, with highest purity and minimal host cell protein (HCP) and residual DNA content. Importantly, the untagged Aβ1-6 chimeric soluble protein could induce the strongest Aβ-specific humoral immune responses without activation of harmful Aβ-specific T cells in mice.

CONCLUSIONS

The untagged Aβ1-6 chimeric protein vaccine is safe and highly immunogenic. Further research will determine the efficacy in cognitive improvement and disease progression delay.

Hepatitis B core VLP-based mis-disordered tau vaccine elicits strong immune response and alleviates cognitive deficits and neuropathology progression in Tau.P301S mouse model of Alzheimer's disease and frontotemporal dementia

Background

Truncated mis-disordered tau protein plays an important role in the pathogenesis of Alzheimer’s disease (AD) and frontotemporal dementia (FTD). Tau_294–305, an epitope in the truncated tau, is essential for pathological tau-tau interaction and aggregation. A tau_294–305-targeted approach may have beneficial effects in the treatment of AD and FTD.

Methods

In this study, we genetically fused tau_294–305 epitope to the hepatitis B virus core protein (HBc) major immunodominant region (MIR) (with the resultant protein termed T294-HBc), and we subcutaneously immunized a Tau.P301S transgenic mouse model of FTD and AD with T294-HBc four times. The levels and characteristics of antibodies induced by T294-HBc were determined by enzyme-linked immunosorbent assay. The effect of T294-HBc on the cognitive deficits of Tau.P301S mice was tested using the Morris water maze test, novel object recognition, and a Y-maze test. Western blot analysis and IHC were applied to measure the effect of T294-HBc on tau pathologies and neuroinflammation in the mouse brains.

Results

The results showed that T294-HBc self-assembled into HBc chimeric virus-like particles (VLPs) with tau_294–305 displayed on the surface and that it induced high antibody titers specifically against the mis-disordered truncated tau. Further investigation showed that these antibodies simultaneously bound to microtubule-binding regions 1–4 (MTBR1–4) [tau_263–274, tau_294–305, tau_325–336, tau_357–368 and tau_294–305(P301S)]. Moreover, T294-HBc VLP vaccination significantly ameliorated memory and cognitive decline; reduced the levels of AT8-positive tau, truncated tau monomer, and oligomer; attenuated microgliosis and astrogliosis; and rescued synaptic deficits in Tau.P301S transgenic mice.

Conclusions

T294-HBc VLP vaccine elicited strong immune response and alleviated cognitive deficits and neuropathology progression in Tau.P301S mice, indicating that the T294-HBc VLP vaccine has promising therapeutic potential for the treatment of AD and FTD.

Long-Term Extensions of Randomized Vaccination Trials of ACC-001 and QS-21 in Mild to Moderate Alzheimer's Disease

OBJECTIVES

Long-term safety and tolerability of ACC-001 (vanutide cridificar), an antiamyloid- beta therapeutic vaccine, was evaluated in subjects with mild to moderate Alzheimer's disease.

DESIGN

Phase 2a extension studies of randomized parent trials were conducted in the United States, European Union, and Japan.

METHODS

Four immunizations of ACC-001 were administered at the same 3 dose levels (3, 10, and 30 μg) to subjects randomized in the parent studies; ACC-001 was administered with QS-21 adjuvant. Safety, tolerability, and immunogenicity were assessed during active treatment and 6-month follow-up.

RESULTS

ACC-001 + QS-21 was well tolerated in the United States (N=110) and European Union (N=50), and Japan (N=53) extension studies; safety profile was similar to that observed in the parent studies, and no new safety signals were identified. Overall, injection site reactions were the most common adverse event in these studies. Anti-amyloid antibody titers were elicited in all groups, with the highest titers observed in subjects who received ACC-001 + QS-21 in both the parent and extension studies.

CONCLUSIONS

Long-term exposure to ACC-001 + QS-21 was well tolerated in subjects with Alzheimer's disease, suggesting that side effects do not pose a principal limitation for anti-amyloid active immunotherapy. The highest anti-amyloid-beta IgG titers are elicited during long-term therapy with ACC-001 + QS-21 compared with other regimens.

Two Phase 2 Multiple Ascending-Dose Studies of Vanutide Cridificar (ACC-001) and QS-21 Adjuvant in Mild-to-Moderate Alzheimer's Disease

Vanutide cridificar (ACC-001), an immunotherapeutic vaccine, is a potentially disease-modifying therapy that aims to reduce brain amyloid-β (Aβ) plaques in patients with Alzheimer's disease (AD). ACC-001 was evaluated in two phase 2a, multicenter, randomized, third party-unblinded, placebo-controlled, multiple ascending-dose studies of ACC-001 (3μg, 10μg, 30μg) with and without QS-21 adjuvant that enrolled patients with mild-to-moderate AD (n = 245). Patients were treated with up to five doses of study vaccine or placebo and followed for safety and tolerability (primary objective) and anti-Aβ IgG immunogenicity (secondary objective) up to 12 months after the last vaccination. Exploratory assessments included cognitive/functional measures, brain magnetic resonance imaging (MRI) volumetry, and pharmacodynamic markers in plasma and cerebrospinal fluid (CSF). The most frequent treatment-emergent adverse events (≥10%) were local injection reactions and headache. Amyloid-related imaging abnormalities with vasogenic edema occurred in two (0.8%) patients (ACC-001 30μg + QS-21; ACC-001 10μg). ACC-001 + QS-21 elicited consistently higher peak and sustained anti-Aβ IgG titers compared with ACC-001 alone. Plasma Aβx-40 was significantly higher in all ACC-001 + QS-21 groups versus placebo (weeks 16-56), with no evidence of dose response. Exploratory cognitive evaluations, volumetric brain MRI, and CSF biomarkers did not show differences or trends between treatment groups and placebo. ACC-001 with or without QS-21 adjuvant has an acceptable safety profile in patients with mild-to-moderate AD.

Immunotherapy targeting pyroglutamate-3 Aβ: prospects and challenges

Immunization against amyloid-β (Aβ) peptides deposited in Alzheimer’s disease (AD) has shown considerable therapeutic effect in animal models however, the translation into human Alzheimer’s patients is challenging. In recent years, a number of promising Aβ immunotherapy trials failed to reach primary study endpoints. Aside from uncertainties in the selection of patients and the start and duration of treatment, these results also suggest that the mechanisms underlying AD are still not fully understood. Thorough characterizations of protein aggregates in AD brain have revealed a conspicuous heterogeneity of Aβ peptides enabling the study of the toxic potential of each of the major forms. One such form, amino-terminally truncated and modified pyroglutamate (pGlu)-3 Aβ peptide appears to play a seminal role for disease initiation, qualifying it as novel target for immunotherapy approaches.

Vaccination induced changes in pro-inflammatory cytokine levels as an early putative biomarker for cognitive improvement in a transgenic mouse model for Alzheimer disease

Several pieces of experimental evidence suggest that administration of anti-β amyloid (Aβ) vaccines, passive anti-Aβ antibodies or anti-inflammatory drugs can reduce Aβ deposition as well as associated cognitive/behavioral deficits in an Alzheimer disease (AD) transgenic (Tg) mouse model and, as such, may have some efficacy in human AD patients as well. In the investigation reported here an Aβ 1-42 peptide vaccine was administered to 16-month old APP+PS1 transgenic (Tg) mice in which Aβ deposition, cognitive memory deficits as well as levels of several pro-inflammatory cytokines were measured in response to the vaccination regimen. After vaccination, the anti-Aβ 1-42 antibody-producing mice demonstrated a significant reduction in the sera levels of 4 pro-inflammatory cytokines (TNF-α, IL-6, IL-1 α, and IL-12). Importantly, reductions in the cytokine levels of TNF-α and IL-6 were correlated with cognitive/behavioral improvement in the Tg mice. However, no differences in cerebral Aβ deposition in these mice were noted among the different control and experimental groups, i.e., Aβ 1-42 peptide vaccinated, control peptide vaccinated, or non-vaccinated mice. However, decreased levels of pro-inflammatory cytokines as well as improved cognitive performance were noted in mice vaccinated with the control peptide as well as those immunized with the Aβ 1-42 peptide. These findings suggest that reduction in pro-inflammatory cytokine levels in these mice may be utilized as an early biomarker for vaccination/treatment induced amelioration of cognitive deficits and are independent of Aβ deposition and, interestingly, antigen specific Aβ 1-42 vaccination. Since cytokine changes are typically related to T cell activation, the results imply that T cell regulation may have an important role in vaccination or other immunotherapeutic strategies in an AD mouse model and potentially in AD patients. Overall, these cytokine changes may serve as a predictive marker for AD development and progression as well as having potential therapeutic implications.

Developing therapeutic vaccines against Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia worldwide. It is characterized by an imbalance between the production and clearance of amyloid β (Aβ) and tau proteins. In AD these normal proteins accumulate, leading to aggregation and a conformational change forming oligomeric and fibrillary species with a high β-sheet content. Active and passive immunotherapeutic approaches result in dramatic reduction of Aβ pathology in AD animal models. However, there is much more limited evidence in human studies of significant clinical benefits from these strategies and it is becoming apparent that they may only be effective very early in AD. Vaccination targeting only tau pathology has shown benefits in some mouse studies but human studies are limited. Greater therapeutic efficacy for the next generation of vaccine approaches will likely benefit from specifically targeting the most toxic species of Aβ and tau, ideally simultaneously.

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.

Fluid Biomarkers in Clinical Trials of Alzheimer's Disease Therapeutics

With the demographic shift of the global population toward longer life expectancy, the number of people living with Alzheimer’s disease (AD) has rapidly expanded and is projected to triple by the year 2050. Current treatments provide symptomatic relief but do not affect the underlying pathology of the disease. Therapies that prevent or slow the progression of the disease are urgently needed to avoid this growing public health emergency. Insights gained from decades of research have begun to unlock the pathophysiology of this complex disease and have provided targets for disease-modifying therapies. In the last decade, few therapeutic agents designed to modify the underlying disease process have progressed to clinical trials and none have been brought to market. With the focus on disease modification, biomarkers promise to play an increasingly important role in clinical trials. Six biomarkers have now been included in diagnostic criteria for AD and are regularly incorporated into clinical trials. Three biomarkers are neuroimaging measures – hippocampal atrophy measured by magnetic resonance imaging (MRI), amyloid uptake as measured by Pittsburg compound B positron emission tomography (PiB-PET), and decreased fluorodeoxyglucose (18F) uptake as measured by PET (FDG-PET) – and three are sampled from fluid sources – cerebrospinal fluid levels of amyloid β42 (Aβ42), total tau, and phosphorylated tau. Fluid biomarkers are important because they can provide information regarding the underlying biochemical processes that are occurring in the brain. The purpose of this paper is to review the literature regarding the existing and emerging fluid biomarkers and to examine how fluid biomarkers have been incorporated into clinical trials.

Autophagy is involved in oral rAAV/Aβ vaccine-induced Aβ clearance in APP/PS1 transgenic mice

The imbalance between ß-amyloid (Aß) generation and clearance plays a fundamental role in the pathogenesis of Alzheimer's disease (AD). The sporadic form of AD is characterized by an overall impairment in Aß clearance. Immunotherapy targeting Aß clearance is believed to be a promising approach and is under active clinical investigation. Autophagy is a conserved pathway for degrading abnormal protein aggregates and is crucial for Aß clearance. We previously reported that oral vaccination with a recombinant AAV/Aß vaccine increased the clearance of Aß from the brain and improved cognitive ability in AD animal models, while the underlying mechanisms were not well understood. In this study, we first demonstrated that oral vaccination with rAAV/Aß decreased the p62 level and up-regulated the LC3B-II/LC3B-I ratio in APP/PS1 mouse brain, suggesting enhanced autophagy. Further, inhibition of the Akt/mTOR pathway may account for autophagy enhancement. We also found increased anti-Aß antibodies in the sera of APP/PS1 mice with oral vaccination, accompanied by elevation of complement factors C1q and C3 levels in the brain. Our results indicate that autophagy is closely involved in oral vaccination-induced Aß clearance, and modulating the autophagy pathway may be an important strategy for AD prevention and intervention.

A fresh perspective from immunologists and vaccine researchers: active vaccination strategies to prevent and reverse Alzheimer's disease

Traditional vaccination against infectious diseases relies on generation of cellular and humoral immune responses that act to protect the host from overt disease even though they do not induce sterilizing immunity. More recently, attempts have been made with mixed success to generate therapeutic vaccines against a wide range of noninfectious diseases including neurodegenerative disorders. After the exciting first report of successful vaccine prevention of progression of an Alzheimer's disease (AD) animal model in 1999, various epitope-based vaccines targeting amyloid beta (Aβ) have proceeded to human clinical trials, with varied results. More recently, AD vaccines based on tau protein have advanced into clinical testing too. This review seeks to put perspective to the mixed results obtained so far in clinical trials of AD vaccines and discusses the many pitfalls and misconceptions encountered on the path to a successful AD vaccine, including better standardization of immunologic efficacy measures of antibodies, immunogenicity of platform/carrier and adjuvants.

Alzheimer's Disease: Lessons Learned from Amyloidocentric Clinical Trials

Alzheimer's disease (AD) is one of the most debilitating neurodegenerative diseases and is predicted to affect 1 in 85 people by 2050. Despite much effort to discover a therapeutic strategy to prevent progression or to cure AD, to date no effective disease-modifying agent is available that can prevent, halt, or reverse the cognitive and functional decline of patients with AD. Several underlying etiologies to this failure are proposed. First, accumulating evidence from past trials suggests a preventive as opposed to therapeutic paradigm, and the precise temporal and mechanistic relationship of β-amyloid (Aβ) and tau protein should be elucidated to confirm this hypothesis. Second, we are in urgent need of revised diagnostic criteria to support future trials. Third, various technical and methodological improvements are required, based on the lessons learned from previous failed trials.

Immunotherapeutic approaches for Alzheimer's disease

Alzheimer's disease (AD) is the most prevalent form of dementia worldwide and is an emerging global epidemic. It is characterized by an imbalance between production and clearance of amyloid β (Aβ) and tau proteins. Oligomeric forms of Aβ and tau are believed to be the most toxic. Dramatic results from AD animal models showed great promise for active and passive immune therapies targeting Aβ. However, there is very limited evidence in human studies of the clinical benefits from these approaches. Immunotherapies targeting only tau pathology have had some success but are limited so far to mouse models. The majority of current methods is based on immunological targeting of a self-protein; hence, benefits need to be balanced against risks of stimulating excessive autoimmune toxic inflammation. For greater efficacy the next generation of vaccines needs to focus more on concurrently targeting all the intermediate toxic conformers of oligomeric Aβ and tau species.

Proteinopathies, a core concept for understanding and ultimately treating degenerative disorders?

The current review covers proteinopathies an umbrella term for neurodegenerative disorders that are characterized by the accumulation of specific proteins within neurons or in the brain parenchyma. Most prevalent examples for typical proteinopathies are Alzheimer's disease and Parkinson's disease. In healthy brain, these proteins are unstructured as a monomer, serving most likely as the physiological form. In a disease condition, the unstructured proteins experience a conformational change leading to small oligomers that eventually will aggregate into higher order structures. Prion disease is an exception within the family of proteinopathies as the aggregated prion protein is highly infectious and can self-aggregate and propagate. Recent reports might implicate a prion-like spread of misfolded proteins in Alzheimer's and Parkinson's disease; however there are evident differences in comparison to prion diseases. As proteinopathies are caused by the aggregation of disease-typical proteins with an ordered structure, active and passive immunization protocols have been used to expose model systems to therapeutic antibodies that bind to the aggregates thereby inhibiting the prolongation into higher ordered fibrils or dissolving the existing fibrillar structure. While most of the immunization treatments have been only carried out in preclinical model systems overexpressing the disease-relevant aggregating protein, other approaches are already in clinical testing. Taking the core concept of proteinopathies with conformationally altered protein aggregates into account, immunization appears to be a very promising therapeutic option for neurodegenerative disorders.

A comparative evaluation of a novel vaccine in APP/PS1 mouse models of Alzheimer's disease

Immunization against amyloid-beta-peptide (Aβ) has been widely investigated as a potential immunotherapeutic approach for Alzheimer's disease (AD). With the aim of developing an active immunogenic vaccine without need of coadjuvant modification for human trials and therefore avoiding such side effects, we designed the Aβ_1–42 vaccine (EB101), delivered in a liposomal matrix, that based on our previous studies significantly prevents and reverses the AD neuropathology, clearing Aβ plaques while markedly reducing neuronal degeneration, behavioral deficits, and minimizing neuroinflammation in APP/PS1 transgenic mice. Here, the efficacy of our immunogenic vaccine EB101 was compared with the original immunization vaccine cocktail Aβ₄₂ + CFA/IFA (Freund's adjuvant), in order to characterize the effect of sphingosine-1-phosphate (S1P) in the immunotherapeutic response. Quantitative analysis of amyloid burden showed a notable decrease in the neuroinflammation reaction against Aβ plaques when S1P was compared with other treatments, suggesting that S1P plays a key role as a neuroprotective agent. Moreover, EB101 immunized mice presented a protective immunogenic reaction resulting in the increase of Aβ-specific antibody response and decrease of reactive glia in the affected brain areas, leading to a Th2 immunological reaction.

Disease-Modifying Treatments for Progressive Supranuclear Palsy

In recent years, research has focused on the development of disease-modifying treatments for PSP, targeting mainly at tau dysfunction. However, the glycogen synthase kinase 3 inhibitor, tideglusib, and the microtubuli stabilizer, davunetide, both failed to show efficacy in recent double-blind, placebo-controlled studies. Despite these results, further agents targeting tau dysfunction, tau post-translational modifications, or aiming at mictorubuli stabilization are currently being investigated. Further approaches under development include agents to reduce tau levels extracellularly by active or passive immunization, antisense oligonucleotides to reduce tau concentrations, and small interfering RNAs to suppress human tau expression. However, the major limitation on the way to find disease-modifying treatments for PSP still remains the lack of biomarkers. Indeed, for all of these potential therapeutic modalities, a well-designed human trial would require validated biomarkers, without which the results of negative efficacy trials will be difficult to interpret. In this regard, PET imaging using tau-specific ligands may be proven useful in the near future. There is great hope that the next decade will bring the first effective therapy for PSP.

Tailoring the antibody response to aggregated Aß using novel Alzheimer-vaccines

Recent evidence suggests Alzheimer-Disease (AD) to be driven by aggregated Aß. Capitalizing on the mechanism of molecular mimicry and applying several selection layers, we screened peptide libraries for moieties inducing antibodies selectively reacting with Aß-aggregates. The technology identified a pool of peptide candidates; two, AFFITOPES AD01 and AD02, were assessed as vaccination antigens and compared to Aβ1-6, the targeted epitope. When conjugated to Keyhole Limpet Hemocyanin (KLH) and adjuvanted with aluminum, all three peptides induced Aß-targeting antibodies (Abs). In contrast to Aß1-6, AD01- or AD02-induced Abs were characterized by selectivity for aggregated forms of Aß and absence of reactivity with related molecules such as Amyloid Precursor Protein (APP)/ secreted APP-alpha (sAPPa). Administration of AFFITOPE-vaccines to APP-transgenic mice was found to reduce their cerebral amyloid burden, the associated neuropathological alterations and to improve their cognitive functions. Thus, the AFFITOME-technology delivers vaccines capable of inducing a distinct Ab response. Their features may be beneficial to AD-patients, a hypothesis currently tested within a phase-II-study.

Alum and squalene-oil-in-water emulsion enhance the titer and avidity of anti-Aβ antibodies induced by multimeric protein antigen (1-11)E2, preserving the Igg1-skewed isotype distribution

The development of active immunotherapy for Alzheimer's disease (AD) requires the identification of immunogens that can ensure a high titer antibody response toward Aβ, while minimizing the risks of adverse reactions. Multimeric protein (1–11)E2 induces a robust and persistent antibody response to Aβ in mice, when formulated in Freund's adjuvant. The goal of this translational study was to evaluate the immunogenicity of (1–11)E2 formulated in alum (Alhydrogel 2%), or in a squalene oil-in-water emulsion (AddaVax), or without adjuvant. A IgG1-skewed isotype distribution was observed for the anti-Aβ antibodies generated in mice immunized with either the non-adjuvanted or the adjuvanted vaccine, indicating that (1–11)E2 induces a Th2-like response in all tested conditions. Both Alhydrogel 2% and AddaVax enhanced the titer and avidity of the anti-Aβ response elicited by (1–11)E2. We conclude that (1–11)E2 is a promising candidate for anti-Aβ immunization protocols that include alum or squalene-oil-in-water emulsion, or no adjuvant.

Clinical trials: past, current, and future for atypical Parkinsonian syndromes

There are currently no effective Food and Drug Administration-approved treatments for atypical parkinsonian disorders such as progressive supranuclear palsy, corticobasal degeneration, dementia with Lewy bodies, or multiple system atrophy. Previous treatment trials for these disorders were focused on symptomatic support and did not affect disease progression. Recent breakthroughs in neuropathology and pathophysiology have allowed a new understanding of these disorders and investigation into potentially disease modifying therapies. Randomized, placebo-controlled clinical trials of these disorders will be reviewed here. Suggestions for future therapeutic targets and clinical trial design (with a focus on progressive supranuclear palsy) will also be provided.

Immunotherapy for Alzheimer's disease

Alzheimer's disease (AD) is the most common cause of dementia worldwide. In AD the normal soluble amyloid β (sAβ) peptide is converted into oligomeric/fibrillar Aβ. The oligomeric forms of Aβ are thought to be the most toxic, while fibrillar Aβ becomes deposited as amyloid plaques and congophilic angiopathy, which serve as neuropathological markers of the disease. In addition the accumulation of abnormally phosphorylated tau as soluble toxic oligomers and as neurofibrillary tangles is a critical part of the pathology. Numerous therapeutic interventions are under investigation to prevent and treat AD. Among the more exciting and advanced of these approaches is vaccination. Active and passive Immunotherapy targeting only Aβ has been successful in many AD model animal trials; however, the more limited human data has shown much less benefit so far, with encephalitis occurring in a minority of patients treated with active immunization and vasogenic edema or amyloid-related imaging abnormalities (ARIA) being a complication in some passive immunization trials. Therapeutic intervention targeting only tau has been tested only in mouse models; and no approaches targeting both pathologies concurrently has been attempted, until very recently. The immune approaches tried so far were targeting a self-protein, albeit in an abnormal conformation; however, effective enhanced clearance of the disease associated conformer has to be balanced with the potential risk of stimulating excessive toxic inflammation. The design of future more effective immunomodulatory approaches will need to target all aspects of AD pathology, as well as specifically targeting pathological oligomeric conformers, without the use of any self-antigen.

Novel immunological approaches for the treatment of Alzheimer's disease

Alzheimer's disease (AD), the most prevalent form of dementia worldwide, can be deemed as the next global health epidemic. The biochemistry underlying deposition of amyloid beta (A β) and hyperphosphorylated tau aggregates in AD has been extensively studied. The oligomeric forms of A β that are derived from the normal soluble A β peptides are believed to be the most toxic. However, it is the fibrillar Aβ form that aggregates as amyloid plaques and cerebral amyloid angiopathy, which serve as pathological hallmarks of AD. Moreover, deposits of abnormally phosphorylated tau that form soluble toxic oligomers and then accumulate as neurofibrillary tangles are an essential part of AD pathology. Currently, many strategies are being tested that either inhibit, eradicate or prevent the development of plaques in AD. An exciting new approach on the horizon is the immunization approach. Dramatic results from AD animal models have shown promise for active and passive immune therapies targeting A β. However, there is very limited data in humans that suggests a clear benefit. Some hurdles faced with these studies arise from complications noted with therapy. Encephalitis has been reported in trials of active immunization and vasogenic edema or amyloid - related imaging abnormalities (ARIA) has been reported with passive immunization in a minority of patients. As yet, therapies targeting only tau are still limited to mouse models with few studies targeting both pathologies. As the majority of approaches tried so far are based on targeting a self - protein, though in an abnormal conformation, benefits of therapy need to be balanced against the possible risks of stimulating excessive toxic inflammation. For better efficacy, future strategies will need to focus on the toxic oligomers and targeting all aspects of AD pathology.

Active and passive immunization strategies based on the SDPM1 peptide demonstrate pre-clinical efficacy in the APPswePSEN1dE9 mouse model for Alzheimer's disease

Recent clinical and pre-clinical studies suggest that both active and passive immunization strategies targeting Aβ amyloid may have clinical benefit in Alzheimer's disease. Here, we demonstrate that vaccination of APPswePSEN1dE9 mice with SDPM1, an engineered non-native Aβ amyloid-specific binding peptide, lowers brain Aβ amyloid plaque burden and brain Aβ1-40 and Aβ1-42 peptide levels, improves cognitive learning and memory in Morris water maze tests and increases the expression of synaptic brain proteins. This was the case in young mice immunized prior to development of significant brain amyloid burden, and in older mice, where brain amyloid was already present. Active immunization was optimized using ALUM as an adjuvant to stimulate production of anti-SDPM1 and anti-Aβ amyloid antibodies. Intracerebral injection of P4D6, an SDPM1 peptide-mimotope antibody, also lowered brain amyloid plaque burden in APPswePSEN1dE9 mice. Additionally, P4D6 inhibited Aβ amyloid-mediated toxicity in cultured neuronal cells. The protein sequence of the variable domain within the P4D6 heavy chain was found to mimic a multimer of the SDPM1 peptide motif. These data demonstrate the efficacy of active and passive vaccine strategies to target Aβ amyloid oligomers using an engineered peptide-mimotope strategy.

Efficacy and safety of a liposome-based vaccine against protein Tau, assessed in tau.P301L mice that model tauopathy

Progressive aggregation of protein Tau into oligomers and fibrils correlates with cognitive decline and synaptic dysfunction, leading to neurodegeneration in vulnerable brain regions in Alzheimer's disease. The unmet need of effective therapy for Alzheimer's disease, combined with problematic pharmacological approaches, led the field to explore immunotherapy, first against amyloid peptides and recently against protein Tau. Here we adapted the liposome-based amyloid vaccine that proved safe and efficacious, and incorporated a synthetic phosphorylated peptide to mimic the important phospho-epitope of protein Tau at residues pS396/pS404. We demonstrate that the liposome-based vaccine elicited, rapidly and robustly, specific antisera in wild-type mice and in Tau.P301L mice. Long-term vaccination proved to be safe, because it improved the clinical condition and reduced indices of tauopathy in the brain of the Tau.P301L mice, while no signs of neuro-inflammation or other adverse neurological effects were observed. The data corroborate the hypothesis that liposomes carrying phosphorylated peptides of protein Tau have considerable potential as safe and effective treatment against tauopathies, including Alzheimer's disease.

AL amyloid imaging and therapy with a monoclonal antibody to a cryptic epitope on amyloid fibrils

The monoclonal antibody 2A4 binds an epitope derived from a cleavage site of serum amyloid protein A (sAA) containing a -Glu-Asp- amino acid pairing. In addition to its reactivity with sAA amyloid deposits, the antibody was also found to bind amyloid fibrils composed of immunoglobulin light chains. The antibody binds to synthetic fibrils and human light chain (AL) amyloid extracts with high affinity even in the presence of soluble light chain proteins. Immunohistochemistry with biotinylated 2A4 demonstrated positive reaction with ALκ and ALλ human amyloid deposits in various organs. Surface plasmon resonance analyses using synthetic AL fibrils as a substrate revealed that 2A4 bound with a K_D of ∼10 nM. Binding was inhibited in the presence of the –Glu-Asp- containing immunogen peptide. Radiolabeled 2A4 specifically localized with human AL amyloid extracts implanted in mice (amyloidomas) as evidenced by single photon emission (SPECT) imaging. Furthermore, co-localization of the radiolabeled mAb with amyloid was shown in biodistribution and micro-autoradiography studies. Treatment with 2A4 expedited regression of ALκ amyloidomas in mice, likely mediated by the action of macrophages and neutrophils, relative to animals that received a control antibody. These data indicate that the 2A4 mAb might be of interest for potential imaging and immunotherapy in patients with AL amyloidosis.

TLR4- and TRIF-dependent stimulation of B lymphocytes by peptide liposomes enables T cell-independent isotype switch in mice

Immunoglobulin class switching from IgM to IgG in response to peptides is generally T cell-dependent and vaccination in T cell-deficient individuals is inefficient. We show that a vaccine consisting of a dense array of peptides on liposomes induced peptide-specific IgG responses totally independent of T-cell help. Independency was confirmed in mice lacking T cells and in mice deficient for MHC class II, CD40L, and CD28. The IgG titers were high, long-lived, and comparable with titers obtained in wild-type animals, and the antibody response was associated with germinal center formation, expression of activation-induced cytidine deaminase, and affinity maturation. The T cell-independent (TI) IgG response was strictly dependent on ligation of TLR4 receptors on B cells, and concomitant TLR4 and cognate B-cell receptor stimulation was required on a single-cell level. Surprisingly, the IgG class switch was mediated by TIR-domain-containing adapter inducing interferon-β (TRIF), but not by MyD88. This study demonstrates that peptides can induce TI isotype switching when antigen and TLR ligand are assembled and appropriately presented directly to B lymphocytes. A TI vaccine could enable efficient prophylactic and therapeutic vaccination of patients with T-cell deficiencies and find application in diseases where induction of T-cell responses contraindicates vaccination, for example, in Alzheimer disease.

Pathways towards an effective immunotherapy for Parkinson's disease

Immunizations that target specific types of immune responses are used commonly to prevent microbial infections. However, a range of immune responses may prove necessary to combat the ravages of neurodegenerative diseases. The goal is to eliminate the 'root' cause of neurodegenerative disorders, misfolded aggregated proteins, while harnessing adaptive immune responses to promote neural repair. However, immunization strategies used to elicit humoral immune responses against aberrant brain proteins have yielded mixed success. While specific proteins can be cleared, the failures in halting disease progression revolve, in measure, around adaptive immune responses that promote autoreactive T cells and, as such, induce a meningoencephalitis, accelerating neurodegeneration. Thus, alternative approaches for protein clearance and neural repair are desired. To this end, our laboratories have sought to transform autoreactive adaptive immune responses into regulatory neuroprotective cells in Parkinson's disease. In this context, induction of immune responses against modified brain proteins serves to break immunological tolerance, while eliciting adaptive immunity to facilitate neuronal repair. How to harness the immune response in the setting of Parkinson's disease requires a thorough understanding of the role of immunity in human disease and the ways to modify such immune responses to elicit therapeutic gain. These are discussed in this review.