An attenuated immune response is sufficient to enhance cognition in an Alzheimer's disease mouse model immunized with amyloid-beta derivatives

Prediction of the 3D conformation of a small peptide vaccine targeting Aβ42 oligomers

The original etiology of Alzheimer's disease (AD) is the deposition of amyloid-beta (Aβ) proteins, which starts from the aggregation of the Aβ oligomers. The optimal therapeutic strategy targeting Aβ oligomer aggregation is the development of AD vaccines. Despite the fact that positive progress has been made for experimental attempts at AD vaccines, the physicochemical and even structural properties of these AD vaccines remain unclear. In this study, through immunoinformatic and molecular dynamics (MD) simulations, we first designed and simulated an alternative of vaccine TAPAS and found that the structure of the alternative can reproduce the 3D conformation of TAPAS determined experimentally. Meanwhile, immunoinformatic methods were used to analyze the physicochemical properties of TAPAS, including immunogenicity, antigenicity, thermal stability, and solubility, which confirm well the efficacy and safety of the vaccine, and validate the scheme reliability of immunoinformatic and MD simulations in designing and simulating the TAPAS vaccine. Using the same scheme, we predicted the 3D conformation of the optimized ACI-24 peptide vaccine, an Aβ peptide with the first 15 residues of Aβ42 (Aβ1-15). The vaccine was verified once to be effective against both full-length Aβ1-42 and truncated Aβ4-42 aggregates, but an experimental 3D structure was absent. We have also explored the immune mechanism of the vaccine at the molecular level and found that the optimized ACI-24 and its analogues can block the growth of either full-length Aβ1-42 or truncated Aβ4-42 pentamer by contacting the hydrophobic residues within the N-terminus and β1 region on the contact surface of either pentamer. Additionally, residues (D1, D7, S8, H13, and Q15) were identified as the key residues of the vaccine to contact either of the two Aβ oligomers. This work provides a feasible implementation scheme of immunoinformatic and MD simulations for the development of AD small peptide vaccines, validating the power of the scheme as a parallel tool to the experimental approaches and injecting molecular-level information into the understanding and design of anti-AD vaccines.

Recent Advances in Targeting Transition Metals (Copper, Iron, and Zinc) in Alzheimer's Disease

Changes in the transition metal homeostasis in the brain are closely linked with Alzheimer's disease (AD), including intraneuronal iron accumulation and extracellular copper and zinc pooling in the amyloid plague. The brain copper, zinc, and iron surplus are commonly acknowledged characteristics of AD, despite disagreements among some. This has led to the theory that oxidative stress resulting from abnormal homeostasis of these transition metals may be a causative explanation behind AD. In the nervous system, the interaction of metals with proteins appears to be an essential variable in the development or suppression of neurodegeneration. Chelation treatment may be an option for treating neurodegeneration induced by transition metal ion dyshomeostasis. Some clinicians even recommend using chelating agents as an adjunct therapy for AD. The current review also looks at the therapeutic strategies that have been attempted, primarily with metal-chelating drugs. Metal buildup in the nervous system, as reported in the AD, could be the result of compensatory mechanisms designed to improve metal availability for physiological functions.

Attempts to Develop Vaccines Against Alzheimer's Disease: A Systematic Review of Ongoing and Completed Vaccination Trials in Humans

In this systematic review, we evaluate the safety, tolerability, and immunogenicity of vaccination efforts against Alzheimer's disease (AD) in human subjects from both ongoing and completed vaccination trials. Databases like PubMed, Embase, and Scopus were used to identify relevant articles on completed vaccination trials whereas the clinicaltrials.gov database was used for identifying ongoing clinical trials for vaccination against AD in humans until January 2022. Only interventional randomized or non-randomized clinical trials which reported on the safety and immunogenicity of vaccine against AD in humans were included. Cochrane risk of bias tool-2 (RoB-2) or risk of bias in non-randomized studies- of intervention (ROBINS-I) was used for risk of bias assessment as appropriate. A narrative descriptive synthesis of the findings was done. Sixteen randomized/non-randomized clinical trials (phase I: six and phase II: 10) for seven different types of vaccines against AD were identified comprising a total of 2080 participants. Apart from the development of meningoencephalitis in 6% of patients receiving AN1792 in an interrupted phase II trial, the rest of the trial reported promising results on the safety and immunogenicity of vaccines. While only a subset of reported adverse events was treatment related, none of the fatalities reported during the trial were considered related to vaccine administration. The serological response rate ranged from 100% (4/16 trials) to 19.7% in an interrupted trial. Although current trials show promising results, adequately powered phase III studies are needed to conclusively establish the safety, immunogenicity and therapeutic efficacy of vaccines.

Physiological β-amyloid clearance by the liver and its therapeutic potential for Alzheimer's disease

Cerebral amyloid-β (Aβ) accumulation due to impaired Aβ clearance is a pivotal event in the pathogenesis of Alzheimer's disease (AD). Considerable brain-derived Aβ is cleared via transporting to the periphery. The liver is the largest organ responsible for the clearance of metabolites in the periphery. Whether the liver physiologically clears circulating Aβ and its therapeutic potential for AD remains unclear. Here, we found that about 13.9% of Aβ42 and 8.9% of Aβ40 were removed from the blood when flowing through the liver, and this capacity was decreased with Aβ receptor LRP-1 expression down-regulated in hepatocytes in the aged animals. Partial blockage of hepatic blood flow increased Aβ levels in both blood and brain interstitial fluid. The chronic decline in hepatic Aβ clearance via LRP-1 knockdown specific in hepatocytes aggravated cerebral Aβ burden and cognitive deficits, while enhancing hepatic Aβ clearance via LRP-1 overexpression attenuated cerebral Aβ deposition and cognitive impairments in APP/PS1 mice. Our findings demonstrate that the liver physiologically clears blood Aβ and regulates brain Aβ levels, suggesting that a decline of hepatic Aβ clearance during aging could be involved in AD development, and hepatic Aβ clearance is a novel therapeutic approach for AD.

Amyloid-β targeting immunisation in aged non-human primate (Microcebus murinus)

Non-human primates have an important translational value given their close phylogenetic relationship to humans. Studies in these animals remain essential for evaluating efficacy and safety of new therapeutic approaches, particularly in aging primates that display Alzheimer's disease (AD) -like pathology. With the objective to improve amyloid-β (Aβ) targeting immunotherapy, we investigated the safety and efficacy of an active immunisation with an Aβ derivative, K6Aβ1-30-NH2, in old non-human primates. Thirty-two aged (4-10 year-old) mouse lemurs were enrolled in the study, and received up to four subcutaneous injections of the vaccine in alum adjuvant or adjuvant alone. Even though antibody titres to Aβ were not high, pathological examination of the mouse lemur brains showed a significant reduction in intraneuronal Aβ that was associated with reduced microgliosis, and the vaccination did not lead to microhemorrhages. Moreover, a subtle cognitive improvement was observed in the vaccinated primates, which was probably linked to Aβ clearance. This Aβ derivative vaccine appeared to be safe as a prophylactic measure based on the brain analyses and because it did not appear to have detrimental effects on the general health of these old animals.

Sustained high body temperature exacerbates cognitive function and Alzheimer's disease-related pathologies

Global warming is a serious public health threat to people worldwide. High body temperature is one of the important risk factors for Alzheimer’s disease (AD), and the body temperature of AD patients has been found to be significantly higher than that of elderly control subjects. However, the effects of high body temperature on cognitive function and AD pathologies have not been completely elucidated. We report here that Tg2576 mice housed at a high ambient temperature of 30 °C for 13 months showed an increase in the body temperature, which is accompanied by memory impairment and an enhancement of amyloid-β peptides (Aβ) generation through the upregulation of β-site APP cleaving enzyme 1 (BACE1) level and decrease in the level of an Aβ-degrading enzyme, neprilysin (NEP) in the brain, compared with those of Tg2576 mice at 23 °C. High body temperature also increased the levels of heat shock proteins (HSPs), stress-stimulated kinases such as JNK, and total tau, leading to the enhancement of tau phosphorylation at 30 °C. Taken together, our findings suggest that high body temperature exacerbates cognitive function and AD pathologies, which provides a mechanistic insight for its prevention.

Abnormal amyloid beta metabolism in systemic abnormalities and Alzheimer's pathology: Insights and therapeutic approaches from periphery

Alzheimer's disease (AD) is an age-associated, multifactorial neurodegenerative disorder that is incurable. Despite recent success in treatments that partially improve symptomatic relief, they have failed in most clinical trials. Re-holding AD for accurate diagnosis and treatment is widely known as a challenging task. Lack of knowledge of basic molecular pathogenesis might be a possible reason for ineffective AD treatment. Historically, a majority of therapy-based studies have investigated the role of amyloid-β (Aβ peptide) in the central nervous system (CNS), whereas less is known about Aβ peptide in the periphery in AD. In this review, we provide a comprehensive summary of the current understanding of Aβ peptide metabolism (anabolism and catabolism) in the brain and periphery. We show that the abnormal metabolism of Aβ peptide is significantly linked with central-brain and peripheral abnormalities; the interaction between peripheral Aβ peptide metabolism and peripheral abnormalities affects central-brain Aβ peptide metabolism, suggesting the existence of significant communication between these two pathways of Aβ peptide metabolism. This close interaction between the central brain and periphery in abnormal Aβ peptide metabolism plays a key role in the development and progression of AD. In conclusion, we need to obtain a full understanding of the dynamic roles of Aβ peptide at the molecular level in both the brain and periphery in relation to the pathology of AD. This will not only provide new information regarding the complex disease pathology, but also offer potential new clues to improve therapeutic strategies and diagnostic biomarkers for the successful treatment of AD.

Review on Alzheimer's disease: Inhibition of amyloid beta and tau tangle formation

It is reported that approximately 40 million people are suffering from dementia, globally. Dementia is a group of symptoms that affect neurons and cause some mental disorders, such as losing memory. Alzheimer's disease (AD) which is known as the most common cause of dementia, is one of the top medical care concerns across the world. Although the exact sources of the disease are not understood, is it believed that aggregation of amyloid-beta (Aβ) outside of neuron cells and tau aggregation or neurofibrillary tangles (NFTs) formation inside the cell may play crucial roles. In this paper, we are going to review studies that targeted inhibition of amyloid plaque and tau protein tangle formation, to suppress or postpone AD.

Tauopathy Analysis in P301S Mouse Model of Alzheimer Disease Immunized With DNA and MVA Poxvirus-Based Vaccines Expressing Human Full-Length 4R2N or 3RC Tau Proteins

Alzheimer’s disease (AD) is a neurodegenerative disorder characterized by a progressive memory loss and cognitive decline that has been associated with an accumulation in the brain of intracellular neurofibrillary tangles (NFTs) formed by hyperphosphorylated tau protein, and extracellular senile plaques formed by β-amyloid peptides. Currently, there is no cure for AD and after the failure of anti β-amyloid therapies, active and passive tau immunotherapeutic approaches have been developed in order to prevent, reduce or ideally reverse the disease. Vaccination is one of the most effective approaches to prevent diseases and poxviruses, particularly modified vaccinia virus Ankara (MVA), are one of the most promising viral vectors used as vaccines against several human diseases. Thus, we present here the generation and characterization of the first MVA vectors expressing human tau genes; the full-length 4R2N tau protein or a 3RC tau fragment containing 3 tubulin-binding motifs and the C-terminal region (termed MVA-Tau4R2N and MVA-Tau3RC, respectively). Both MVA-Tau recombinant viruses efficiently expressed the human tau 4R2N or 3RC proteins in cultured cells, being detected in the cytoplasm of infected cells and co-localized with tubulin. These MVA-Tau vaccines impacted the innate immune responses with a differential recruitment of innate immune cells to the peritoneal cavity of infected mice. However, no tau-specific T cell or humoral immune responses were detected in vaccinated mice. Immunization of transgenic P301S mice, a mouse model for tauopathies, with a DNA-Tau prime/MVA-Tau boost approach showed no significant differences in the hyperphosphorylation of tau, motor capacity and survival rate, when compared to non-vaccinated mice. These findings showed that a well-established and potent protocol of T and B cell activation based on DNA/MVA prime/boost regimens using DNA and MVA vectors expressing tau full-length 4R2N or 3RC proteins is not sufficient to trigger tau-specific T and B cell immune responses and to induce a protective effect against tauopathy in this P301S murine model. In the pursuit of AD vaccines, our results highlight the need for novel optimized tau immunogens and additional modes of presentation of tau protein to the immune system.

Granulocyte Colony Stimulating Factor Enhances Reward Learning through Potentiation of Mesolimbic Dopamine System Function

Deficits in motivation and cognition are hallmark symptoms of multiple psychiatric diseases. These symptoms are disruptive to quality of life and often do not improve with available medications. In recent years there has been increased interest in the role of the immune system in neuropsychiatric illness, but to date no immune-related treatment strategies have come to fruition. The cytokine granulocyte-colony stimulating factor (G-CSF) is known to have trophic and neuroprotective properties in the brain, and we recently identified it as a modulator of neuronal and behavioral plasticity. By combining operant tasks that assess discrete aspects of motivated behavior and decision-making in male mice and rats with subsecond dopamine monitoring via fast-scan cyclic voltammetry, we defined the role of G-CSF in these processes as well as the neural mechanism by which it modulates dopamine function to exert these effects. G-CSF enhanced motivation for sucrose as well as cognitive flexibility as measured by reversal learning. These behavioral outcomes were driven by mesolimbic dopamine system plasticity, as systemically administered G-CSF increased evoked dopamine release in the nucleus accumbens independent of clearance mechanisms. Importantly, sustained increases in G-CSF were required for these effects as acute exposure did not enhance behavioral outcomes and decreased dopamine release. These effects seem to be a result of the ability of G-CSF to alter local inflammatory signaling cascades, particularly tumor necrosis factor α. Together, these data show G-CSF as a potent modulator of the mesolimbic dopamine circuit and its ability to appropriately attend to salient stimuli.SIGNIFICANCE STATEMENT Emerging evidence has highlighted the importance of the immune system in psychiatric diseases states. However, the effects of peripheral cytokines on motivation and cognitive function are largely unknown. Here, we report that granulocyte-colony stimulating factor (G-CSF), a pleiotropic cytokine with known trophic and neuroprotective properties in the brain, acts directly on dopaminergic circuits to enhance their function. These changes in dopaminergic dynamics enhance reward learning and motivation for natural stimuli. Together, these results suggest that targeting immune factors may provide a new avenue for therapeutic intervention in the multiple psychiatric disorders that are characterized by motivational and cognitive deficits.

Prophylactic Active Tau Immunization Leads to Sustained Reduction in Both Tau and Amyloid-β Pathologies in 3xTg Mice

Amyloid-β (Aβ) and tau pathologies are intertwined in Alzheimer's disease, and various immunotherapies targeting these hallmarks are in clinical trials. To determine if tau pathology influences Aβ burden and to assess prophylactic benefits, 3xTg and wild-type mice received tau immunization from 2-6 months of age. The mice developed a high IgG titer that was maintained at 22 months of age. Pronounced tau and Aβ pathologies were primarily detected in the subiculum/CA1 region, which was therefore the focus of analysis. The therapy reduced histopathological tau aggregates by 70-74% overall (68% in males and 78-86% in females), compared to 3xTg controls. Likewise, western blot analysis revealed a 41% clearance of soluble tau (38-76% in males and 48% in females) and 42-47% clearance of insoluble tau (47-58% in males and 49% in females) in the immunized mice. Furthermore, Aβ burden was reduced by 84% overall (61% in males and 97% in females). These benefits were associated with reductions in microgliosis and microhemorrhages. In summary, prophylactic tau immunization not only prevents tau pathology but also Aβ deposition and related pathologies in a sustained manner, indicating that tau pathology can promote Aβ deposition, and that a short immunization regimen can have a long-lasting beneficial effect.

Antibody Therapeutics Targeting Aβ and Tau

The astonishing findings that active and passive immunization against amyloid-β (Aβ) in mouse models of Alzheimer's disease (AD) dramatically decreased amyloid burden led to a rapid initiation of human clinical trials with much enthusiasm. However, methodological issues and adverse effects relating to these clinical trials arose, challenging the effectiveness and safety of these reagents. Efforts are now underway to develop safer immunotherapeutic approaches toward Aβ and the treatment of individuals at risk for AD before or in the earliest stages of cognitive decline with new hopes. Furthermore, several studies have shown tau as a potential immunotherapeutic target for the treatment of tauopathy-related diseases including frontotemporal lobar dementia (FTLD). Both active and passive immunization targeting tau in mouse models of tauopathy effectively decreased tau pathology while improving cognitive performance. These preclinical studies have highlighted tau as an alternative target with much anticipation of clinical trials to be undertaken.

Production of Monoclonal Antibodies to Pathologic β-sheet Oligomeric Conformers in Neurodegenerative Diseases

We describe a novel approach to produce conformational monoclonal antibodies selected to specifically react with the β-sheet secondary structure of pathological oligomeric conformers, characteristic of many neurodegenerative diseases. Contrary to past and current efforts, we utilize a mammalian non-self-antigen as an immunogen. The small, non-self peptide selected was covalently polymerized with glutaraldehyde until it reached a high β-sheet secondary structure content, and species between 10–100kDa that are immunogenic, stable and soluble (p13Bri). Inoculation of p13Bri in mice elicited antibodies to the peptide and the β-sheet secondary structure conformation. Hybridomas were produced and clones selected for their reactivity with at least two different oligomeric conformers from Alzheimer’s, Parkinson and/or Prion diseases. The resulting conformational monoclonals are able to detect pathological oligomeric forms in different human neurodegenerative diseases by ELISA, immunohistochemistry and immunoblots. This technological approach may be useful to develop tools for detection, monitoring and treatment of multiple misfolding disorders.

Sex and Immunogen-Specific Benefits of Immunotherapy Targeting Islet Amyloid Polypeptide in Transgenic and Wild-Type Mice

Type 2 diabetes mellitus is characterized by the deposition of islet amyloid polypeptide (IAPP) as amyloid in islets, a process thought to be toxic to β-cells. To determine the feasibility of targeting these aggregates therapeutically, we vaccinated transgenic (Tg) mice that overexpress human IAPP and were fed a high-fat diet to promote their diabetic phenotype. Our findings indicate that prophylactic vaccination with IAPP and its derivative IAPP7-19-TT, protects wild-type female mice, but not males, from obesity-induced early mortality, and the derivative showed a strong trend for prolonging the lifespan of Tg females but not males. Furthermore, IAPP7-19-TT-immunized Tg females cleared a glucose bolus more efficiently than controls, while IAPP-immunized Tg females showed an impaired ability to clear a glucose bolus compared to their adjuvant injected Tg controls. Interestingly, IAPP or IAPP7-19-TT treatments had no effect on glucose clearance in Tg males. Overall, these beneficial effects of IAPP targeted immunization depend on Tg status, sex, and immunogen. Hence, future studies in this field should carefully consider these variables that clearly affect the therapeutic outcome. In conclusion, IAPP targeting immunotherapy may have benefits in patients with type 2 diabetes.

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.

Impact of amyloid β aggregate maturation on antibody treatment in APP23 mice

Introduction

The deposition of the amyloid β protein (Aβ) in the brain is a hallmark of Alzheimer's disease (AD). Removal of Aβ by Aβ-antibody treatment has been developed as a potential treatment strategy against AD. First clinical trials showed neither a stop nor a reduction of disease progression. Recently, we have shown that the formation of soluble and insoluble Aβ aggregates in the human brain follows a hierarchical sequence of three biochemical maturation stages (B-Aβ stages). To test the impact of the B-Aβ stage on Aβ immunotherapy, we treated transgenic mice expressing human amyloid precursor protein (APP) carrying the Swedish mutation (KM670/671NL; APP23) with the Aβ-antibody β1 or phosphate-buffered saline (PBS) beginning 1) at 3 months, before the onset of dendrite degeneration and plaque deposition, and 2) at 7 months, after the start of Aβ plaque deposition and dendrite degeneration.

Results

At 5 months of age, first Aβ aggregates in APP23 brain consisted of non-modified Aβ (representing B-Aβ stage 1) whereas mature Aβ-aggregates containing N-terminal truncated, pyroglutamate-modified Aβ_N3pE and phosphorylated Aβ (representing B-Aβ stage 3) were found at 11 months of age in both β1- and PBS-treated animals. Protective effects on commissural neurons with highly ramified dendritic trees were observed only in 3-month-old β1-treated animals sacrificed at 5 months. When treatment started at 7 months of age, no differences in the numbers of healthy commissural neurons were observed between β1- and PBS-treated APP23 mice sacrificed with 11 months.

Conclusions

Aβ antibody treatment was capable of protecting neurons from dendritic degeneration as long as Aβ aggregation was absent or represented B-Aβ stage 1 but had no protective or curative effect in later stages with mature Aβ aggregates (B-Aβ stage 3). These data indicate that the maturation stage of Aβ aggregates has impact on potential treatment effects in APP23 mice.

Electronic supplementary material

The online version of this article (doi:10.1186/s40478-015-0217-z) contains supplementary material, which is available to authorized users.

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.

Interaction between therapeutic interventions for Alzheimer's disease and physiological Aβ clearance mechanisms

Most therapeutic agents are designed to target a molecule or pathway without consideration of the mechanisms involved in the physiological turnover or removal of that target. In light of this and in particular for Alzheimer’s disease, a number of therapeutic interventions are presently being developed/investigated which target the amyloid-β peptide (Aβ). However, the literature has not adequately considered which Aβ physiological clearance pathways are necessary and sufficient for the effective action of these therapeutics. In this review, we evaluate the therapeutic strategies targeting Aβ presently in clinical development, discuss the possible interaction of these treatments with pathways that under normal physiological conditions are responsible for the turnover of Aβ and highlight possible caveats. We consider immunization strategies primarily reliant on a peripheral sink mechanism of action, small molecules that are reliant on entry into the CNS and thus degradation pathways within the brain, as well as lifestyle interventions that affect vascular, parenchymal and peripheral degradation pathways. We propose that effective development of Alzheimer’s disease therapeutic strategies targeting Aβ peptide will require consideration of the age- and disease-specific changes to endogenous Aβ clearance mechanisms in order to elicit maximal efficacy.

Doubly Phosphorylated Peptide Vaccines to Protect Transgenic P301S Mice against Alzheimer's Disease Like Tau Aggregation

Intracellular neurofibrillary tangles and extracellular senile plaques are potential targets for active and passive immunotherapies. In this study we used the transgenic mouse model P301S for active immunizations with peptide vaccines composed of a double phosphorylated tau neoepitope (pSer202/pThr205, pThr212/pSer214, pThr231/pSer235) and an immunomodulatory T cell epitope from the tetanus toxin or tuberculosis antigen Ag85B. Importantly, the designed vaccine combining Alzheimer’s disease (AD) specific B cell epitopes with foreign (bacterial) T cell epitopes induced fast immune responses with high IgG₁ titers after prophylactic immunization that subsequently decreased over the observation period. The effectiveness of the immunization was surveyed by evaluating the animal behavior, as well as the pathology in the brain by biochemical and histochemical techniques. Immunized mice clearly lived longer with reduced paralysis than placebo-treated mice. Additionally, they performed significantly better in rotarod and beam walk tests at the age of 20 weeks, indicating that the disease development was slowed down. Forty-eight weeks old vaccinated mice passed the beam walk test significantly better than control animals, which together with the increased survival rates undoubtedly prove the treatment effect. In conclusion, the data provide strong evidence that active immune therapies can reduce toxic effects of deposits formed in AD.

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.

Plasma protein profiling of Mild Cognitive Impairment and Alzheimer's disease using iTRAQ quantitative proteomics

BACKGROUND

With the promise of disease modifying treatments, there is a need for more specific diagnosis and prognosis of Alzheimer's disease (AD) and mild cognitive impairment (MCI). Plasma biomarkers are likely to be utilised to increase diagnostic accuracy and specificity of AD and cognitive decline.

METHODS

Isobaric tags (iTRAQ) and proteomic methods were used to identify potential plasma biomarkers of MCI and AD. Relative protein expression level changes were quantified in plasma of 411 cognitively normal subjects, 19 AD patients and 261 MCI patients. Plasma was pooled into 4 groups including normal control, AD, amnestic single and multiple domain MCI (aMCI), and nonamnestic single and multiple domain MCI (nMCI). Western-blotting was used to validate iTRAQ data. Integrated function and protein interactions were explored using WEB based bioinformatics tools (DAVID v6.7 and STRING v9.0).

RESULTS

In at least two iTRAQ replicate experiments, 30 proteins were significantly dysregulated in MCI and AD plasma, relative to controls. These proteins included ApoA1, ApoB100, complement C3, C4b-binding protein, afamin, vitamin D-binding protein precursor, isoform 1 of Gelsolin actin regulator, Ig mμ chain C region (IGHM), histidine-rich glycoprotein and fibrinogen β and γ chains. Western-blotting confirmed that afamin was decreased and IGHM was increased in MCI and AD groups. Bioinformatics results indicated that these dysregulated proteins represented a diversity of biological processes, including acute inflammatory response, cholesterol transport and blood coagulation.

CONCLUSION

These findings demonstrate that expression level changes in multiple proteins are observed in MCI and AD plasma. Some of these, such as afamin and IGHM, may be candidate biomarkers for AD and the predementia condition of MCI.

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.

Immunotherapy for Alzheimer's disease: DNA- and protein-based epitope vaccines

Active immunotherapy for Alzheimer's disease (AD) is aimed to induce antibodies specific to amyloid-beta (Aβ) that are capable to reduce the level of Aβ in the CNS of Alzheimer's disease patients. First clinical trial AN-1792 that was based on vaccination with full-length Aβ42 showed that safe and effective AD vaccine should induce high titers of anti-Aβ antibodies without activation of harmful autoreactive T cells. Replacement of self-T cell epitope with foreign epitope, keeping self-B cell epitope intact, may allow to induce high titers of anti-Aβ antibodies while avoiding the activation of T cells specific to Aβ. Here we describe the protocols for evaluation of AD DNA- or multiple antigenic peptide (MAP)-based epitope vaccines composed of Aβ(1-11) B cell epitope fused to synthetic T cell epitope PADRE (Aβ(1-11)-PADRE). All protocols could be used for testing any epitope vaccine constructed in your lab and composed of other T cell epitopes using the appropriate peptides in tests for evaluation of humoral and cellular immune responses.

Amyloid beta immunization worsens iron deposits in the choroid plexus and cerebral microbleeds

Anti-amyloid beta (Aβ) immunotherapy provides potential benefits in Alzheimer's disease patients. Nevertheless, strategies based on Aβ1-42 peptide induced encephalomyelitis and possible microhemorrhages. These outcomes were not expected from studies performed in rodents. It is critical to determine if other animal models better predict side effects of immunotherapies. Mouse lemur primates can develop amyloidosis with aging. Here we used old lemurs to study immunotherapy based on Aβ1-42 or Aβ-derivative (K6Aβ1-30). We followed anti-Aβ40 immunoglobulin G and M responses and Aβ levels in plasma. In vivo magnetic resonance imaging and histology were used to evaluate amyloidosis, neuroinflammation, vasogenic edema, microhemorrhages, and brain iron deposits. The animals responded mainly to the Aβ1-42 immunogen. This treatment induced immune response and increased Aβ levels in plasma and also microhemorrhages and iron deposits in the choroid plexus. A complementary study of untreated lemurs showed iron accumulation in the choroid plexus with normal aging. Worsening of iron accumulation is thus a potential side effect of Aβ-immunization at prodromal stages of Alzheimer's disease, and should be monitored in clinical trials.

MER5101, a novel Aβ1-15:DT conjugate vaccine, generates a robust anti-Aβ antibody response and attenuates Aβ pathology and cognitive deficits in APPswe/PS1ΔE9 transgenic mice

Active amyloid-β (Aβ) immunotherapy is under investigation to prevent or treat early Alzheimer's disease (AD). In 2002, a Phase II clinical trial (AN1792) was halted due to meningoencephalitis in ∼6% of the AD patients, possibly caused by a T-cell-mediated immunological response. Thus, generating a vaccine that safely generates high anti-Aβ antibody levels in the elderly is required. In this study, MER5101, a novel conjugate of Aβ1-15 peptide (a B-cell epitope fragment) conjugated to an immunogenic carrier protein, diphtheria toxoid (DT), and formulated in a nanoparticular emulsion-based adjuvant, was administered to 10-month-old APPswe/PS1ΔE9 transgenic (Tg) and wild-type (Wt) mice. High anti-Aβ antibody levels were observed in both vaccinated APPswe/PS1ΔE9 Tg and Wt mice. Antibody isotypes were mainly IgG1 and IgG2b, suggesting a Th2-biased response. Restimulation of splenocytes with the Aβ1-15:DT conjugate resulted in a strong proliferative response, whereas proliferation was absent after restimulation with Aβ1-15 or Aβ1-40/42 peptides, indicating a cellular immune response against DT while avoiding an Aβ-specific T-cell response. Moreover, significant reductions in cerebral Aβ plaque burden, accompanied by attenuated microglial activation and increased synaptic density, were observed in MER5101-vaccinated APPswe/PS1ΔE9 Tg mice compared with Tg adjuvant controls. Last, MER5101-immunized APPswe/PS1ΔE9 Tg mice showed improvement of cognitive deficits in both contextual fear conditioning and the Morris water maze. Our novel, highly immunogenic Aβ conjugate vaccine, MER5101, shows promise for improving Aβ vaccine safety and efficacy and therefore, may be useful for preventing and/or treating early AD.

Amyloid-β plaque reduction, endogenous antibody delivery and glial activation by brain-targeted, transcranial focused ultrasound

Noninvasive, targeted drug delivery to the brain can be achieved using transcranial focused ultrasound (FUS), which transiently increases the permeability of the blood-brain barrier (BBB) for localized delivery of therapeutics from the blood to the brain. Previously, we have demonstrated that FUS can deliver intravenously-administered antibodies to the brain of a mouse model of Alzheimer's disease (AD) and rapidly reduce plaques composed of amyloid-β peptides (Aβ). Here, we investigated two potential effects of transcranial FUS itself that could contribute to a reduction of plaque pathology, namely the delivery of endogenous antibodies to the brain and the activation of glial cells. We demonstrate that transcranial FUS application leads to a significant reduction in plaque burden four days after a single treatment in the TgCRND8 mouse model of AD and that endogenous antibodies are found bound to Aβ plaques. Immunohistochemical and western blot analyses showed an increase in endogenous immunoglobulins within the FUS-targeted cortex. Subsequently, microglia and astrocytes in FUS-treated cortical regions show signs of activation through increases in protein expression and changes in glial size, without changes in glial cell numbers. Enhanced activation of glia correlated with increased internalization of Aβ in microglia and astrocytes. Together these data demonstrate that FUS improved the bioavailability of endogenous antibodies and led to a temporal activation of glial cells, providing evidence towards antibody- and glia-dependent mechanisms of FUS-mediated plaque reduction.

Immunogenicity, efficacy, safety, and mechanism of action of epitope vaccine (Lu AF20513) for Alzheimer's disease: prelude to a clinical trial

The Alzheimer's disease (AD) process is understood to involve the accumulation of amyloid plaques and tau tangles in the brain. However, attempts at targeting the main culprits, neurotoxic Aβ peptides, have thus far proven unsuccessful for improving cognitive function. Recent clinical trials with passively administrated anti-Aβ antibodies failed to slow cognitive decline in mild to moderate AD patients, but suggest that an immunotherapeutic approach could be effective in patients with mild AD. Using an AD mouse model (Tg2576), we tested the immunogenicity (cellular and humoral immune responses) and efficacy (AD-like pathology) of clinical grade Lu AF20513 vaccine. We found that Lu AF20513 induces robust "non-self" T-cell responses and the production of anti-Aβ antibodies that reduce AD-like pathology in the brains of Tg2576 mice without inducing microglial activation and enhancing astrocytosis or cerebral amyloid angiopathy. A single immunization with Lu AF20513 induced strong humoral immunity in mice with preexisting memory T-helper cells. In addition, Lu AF20513 induced strong humoral responses in guinea pigs and monkeys. These data support the translation of Lu AF20513 to the clinical setting with the aims of: (1) inducing therapeutically potent anti-Aβ antibody responses in patients with mild AD, particularly if they have memory T-helper cells generated after immunizations with conventional tetanus toxoid vaccine, and (2) preventing pathological autoreactive T-cell responses.

Structural characterization by NMR of a double phosphorylated chimeric peptide vaccine for treatment of Alzheimer's disease

Rational design of peptide vaccines becomes important for the treatment of some diseases such as Alzheimer's disease (AD) and related disorders. In this study, as part of a larger effort to explore correlations of structure and activity, we attempt to characterize the doubly phosphorylated chimeric peptide vaccine targeting a hyperphosphorylated epitope of the Tau protein. The 28-mer linear chimeric peptide consists of the double phosphorylated B cell epitope Tau₂₂₉₋₂₃₇[pThr231/pSer235] and the immunomodulatory T cell epitope Ag85B₂₄₁₋₂₅₅ originating from the well-known antigen Ag85B of the Mycobacterium tuberculosis, linked by a four amino acid sequence -GPSL-. NMR chemical shift analysis of our construct demonstrated that the synthesized peptide is essentially unfolded with a tendency to form a β-turn due to the linker. In conclusion, the -GPSL- unit presumably connects the two parts of the vaccine without transferring any structural information from one part to the other. Therefore, the double phosphorylated epitope of the Tau peptide is flexible and accessible.

Treatment strategies targeting amyloid β-protein

With the advent of the key discovery in the mid-1980s that the amyloid β-protein (Aβ) is the core constituent of the amyloid plaque pathology found in Alzheimer disease (AD), an intensive effort has been underway to attempt to mitigate its role in the hope of treating the disease. This effort fully matured when it was clarified that the Aβ is a normal product of cleavage of the amyloid precursor protein, and well-defined proteases for this process were identified. Further therapeutic options have been developed around the concept of anti-Aβ aggregation inhibitors and the surprising finding that immunization with Aβ itself leads to reduction of pathology in animal models of the disease. Here we review the progress in this field toward the goal of targeting Aβ for treatment and prevention of AD and identify some of the major challenges for the future of this area of medicine.

Therapeutic interventions targeting Beta amyloid pathogenesis in an aging dog model

Aged dogs and humans share complex cognitive and pathological responses to aging. Specifically, dogs develop Alzheimer's Disease (AD) like beta-amyloid (Aβ) that are associated with cognitive deficits. Currently, therapeutic approaches to prevent AD are targeted towards reduced production, aggregation and increased clearance of Aβ. The current review discusses cognition and neuropathology of the aging canine model and how it has and continues to be useful in further understanding the safety and efficacy of potential AD prevention therapies targeting Aβ.

Enhancement of cognitive function in models of brain disease through environmental enrichment and physical activity

This review will provide an overview of the non-drug based approaches that have been demonstrated to enhance cognitive function of the compromised brain, primarily focussed on the two most widely adopted paradigms of environmental enrichment and enhanced physical exercise. Environmental enrichment involves the generation of novelty and complexity in animal housing conditions which facilitates enhanced sensory and cognitive stimulation as well as physical activity. In a wide variety of animal models of brain disorders, environmental enrichment and exercise have been found to have beneficial effects, including cognitive enhancement, delayed disease onset, enhanced cellular plasticity and associated molecular processes. Potential cellular and molecular mechanisms will also be discussed, which have relevance for the future development of 'enviromimetics', drugs which could mimic or enhance the beneficial effects of environmental stimulation. This article is part of a Special Issue entitled 'Cognitive Enhancers'.

Could immunomodulation be used to prevent prion diseases?

All prion diseases are currently without effective treatment and are universally fatal. The underlying pathogenesis of prion diseases (prionoses) is related to an autocatalytic conformational conversion of PrP(C) (C for cellular) to a pathological and infectious conformer known as PrP(Sc) (Sc for scrapie) or PrP(Res) (Res for proteinase K resistant). The past experience with variant Creutzfeldt-Jakob disease, which originated from bovine spongiform encephalopathy, as well as the ongoing epidemic of chronic wasting disease has highlighted the necessity for effective prophylactic and/or therapeutic approaches. Human prionoses are most commonly sporadic, and hence therapy is primarily directed to stop progression; however, in animals the majority of prionoses are infectious and, as a result, the emphasis is on prevention of transmission. These infectious prionoses are most commonly acquired via the alimentary tract as a major portal of infectious agent entry, making mucosal immunization a potentially attractive method to produce a local immune response that can partially or completely prevent prion entry across the gut barrier, while at the same time producing a modulated systemic immunity that is unlikely to be associated with toxicity. A critical factor in any immunomodulatory methodology that targets a self-antigen is the need to delicately balance an effective humoral immune response with potential autoimmune inflammatory toxicity. The ongoing epidemic of chronic wasting disease affecting the USA and Korea, with the potential to spread to human populations, highlights the need for such immunomodulatory approaches.

Immunotherapy for Alzheimer's disease: from anti-β-amyloid to tau-based immunization strategies

The exact mechanisms leading to Alzheimer's disease (AD) are largely unknown, limiting the identification of effective disease-modifying therapies. The two principal neuropathological hallmarks of AD are extracellular β-amyloid (Aβ), peptide deposition (senile plaques) and intracellular neurofibrillary tangles containing hyperphosphorylated tau protein. During the last decade, most of the efforts of the pharmaceutical industry were directed against the production and accumulation of Aβ. The most innovative of the pharmacological approaches was the stimulation of Aβ clearance from the brain of AD patients via the administration of Aβ antigens (active vaccination) or anti-Aβ antibodies (passive vaccination). Several active and passive anti-Aβ vaccines are under clinical investigation. Unfortunately, the first active vaccine (AN1792, consisting of preaggregate Aβ and an immune adjuvant, QS-21) was abandoned because it caused meningoencephalitis in approximately 6% of treated patients. Anti-Aβ monoclonal antibodies (bapineuzumab and solanezumab) are now being developed. The clinical results of the initial studies with bapineuzumab were equivocal in terms of cognitive benefit. The occurrence of vasogenic edema after bapineuzumab, and more rarely brain microhemorrhages (especially in Apo E ε4 carriers), has raised concerns on the safety of these antibodies directed against the N-terminus of the Aβ peptide. Solanezumab, a humanized anti-Aβ monoclonal antibody directed against the midregion of the Aβ peptide, was shown to neutralize soluble Aβ species. Phase II studies showed a good safety profile of solanezumab, while studies on cerebrospinal and plasma biomarkers documented good signals of pharmacodynamic activity. Although some studies suggested that active immunization may be effective against tau in animal models of AD, very few studies regarding passive immunization against tau protein are currently available. The results of the large, ongoing Phase III trials with bapineuzumab and solanezumab will tell us if monoclonal anti-Aβ antibodies may slow down the rate of deterioration of AD. Based on the new diagnostic criteria of AD and on recent major failures of anti-Aβ drugs in mild-to-moderate AD patients, one could argue that clinical trials on potential disease-modifying drugs, including immunological approaches, should be performed in the early stages of AD.

Alzheimer's therapeutics: translation of preclinical science to clinical drug development

Over the past three decades, significant progress has been made in understanding the neurobiology of Alzheimer's disease. In recent years, the first attempts to implement novel mechanism-based treatments brought rather disappointing results, with low, if any, drug efficacy and significant side effects. A discrepancy between our expectations based on preclinical models and the results of clinical trials calls for a revision of our theoretical views and questions every stage of translation-from how we model the disease to how we run clinical trials. In the following sections, we will use some specific examples of the therapeutics from acetylcholinesterase inhibitors to recent anti-Aβ immunization and γ-secretase inhibition to discuss whether preclinical studies could predict the limitations in efficacy and side effects that we were so disappointed to observe in recent clinical trials. We discuss ways to improve both the predictive validity of mouse models and the translation of knowledge between preclinical and clinical stages of drug development.

Passive immunization targeting pathological phospho-tau protein in a mouse model reduces functional decline and clears tau aggregates from the brain

Targeting hyperphosphorylated tau by immunotherapy is emerging as a promising approach to treat tauopathies such as Alzheimer's disease and frontotemporal dementia. We have previously reported that active tau immunization clears tau aggregates from the brain and attenuates or prevents functional impairments in two different tangle mouse models. Here, we assessed the efficacy of passive immunization with the PHF1 antibody, which targets a phospho-epitope within one of our active immunogens. Homozygous female tangle mice (JNPL3, 2-3 months) were injected intraperitoneally once per week with PHF1 or pooled mouse IgG (250 μg/125 μL; n = 10 per group) for a total of 13 injections. Their behavior was assessed at 5-6 months of age and brain tissue was subsequently harvested for analyses of treatment efficacy. The treated mice performed better than controls on the traverse beam task (p < 0.03), and had 58% less tau pathology in the dentate gyrus of the hippocampus (p = 0.02). As assessed by western blots, the antibody therapy reduced the levels of insoluble pathological tau by 14-27% (PHF1, p < 0.05; PHF1/total tau, p < 0.0001) and 34-45% (CP13 or CP13/total tau, p < 0.05). Levels of soluble tau and sarkosyl soluble tau were unchanged, compared with controls, as well as total tau levels in all the fractions. Plasma levels of PHF1 correlated inversely with tau pathology in the brainstem (p < 0.01), with a strong trend in the motor cortex (p < 0.06) as well as with insoluble total tau levels (p < 0.02), indicating that higher dose of antibodies may have a greater therapeutic effect. Significant correlation was also observed between performance on the traverse beam task and PHF1 immunoreactivity in the dentate gyrus (p < 0.05) as well as with insoluble PHF1/total tau ratio on western blots (p < 0.04). These results show that passive immunization with tau antibodies can decrease tau pathology and functional impairments in the JNPL3 model. Future studies will determine the feasibility of this approach with other monoclonals and in different tangle models in which thorough cognitive assessment can be performed.

Immunotherapy for tauopathies

Pathological tau protein is found in Alzheimer's disease and related tauopathies. The protein is hyperphosphorylated and/or mutated which leads to aggregation and neurotoxicity. Because cognitive functions correlate well with the degree of tau pathology, clearing these aggregates is a promising therapeutic approach. Studies pioneered by our laboratory and confirmed by others have shown that both active and passive immunizations targeting disease-related tau epitopes successfully reduce tau aggregates in vivo and slow or prevent behavioral impairments in mouse models of tauopathy. Here, we summarize recent advances in this new field.

Transgenic rice expressing amyloid β-peptide for oral immunization

Various vaccine therapies for Alzheimer's disease (AD) have been investigated. Here we report transgenic rice expressing amyloid β-peptide (Aβ). The Aβ42 gene fused with a green fluorescent protein gene was introduced into rice using the Agrobacterium method. When transgenic brown rice expressing Aβ was orally administered to mice, serum anti-Aβ antibody titers were elevated. The same results were observed when mice were fed boiled, transgenic brown rice. The results indicate that an edible vaccine against AD using rice may be feasible. A vaccine derived from rice would be far cheaper than existing medical vaccines.

Immunomodulation for prion and prion-related diseases

Prion diseases are a unique category of illness, affecting both animals and humans, where the underlying pathogenesis is related to a conformational change of a normal self protein called cellular prion protein to a pathological and infectious conformer known as scrapie prion protein (PrP(Sc)). Currently, all prion diseases lack effective treatment and are universally fatal. Past experiences with bovine spongiform encephalopathy and variant Creutzfeldt-Jakob disease mainly in Europe, as well as the current epidemic of chronic wasting disease in North America, have highlighted the need to develop prophylactic and/or therapeutic approaches. In Alzheimer's disease that, like prion disease, is a conformational neurodegenerative disorder, both passive and active immunization has been shown to be highly effective in model animals at preventing disease and cognitive deficits, with emerging data from human trials suggesting that this approach is able to reduce amyloid-related pathology. However, any immunomodulatory approach aimed at a self-antigen has to finely balance an effective humoral immune response with potential autoimmune toxicity. The prion diseases most commonly acquired by infection typically have the alimentary tract as a portal of infectious agent entry. This makes mucosal immunization a potentially attractive method to produce a local immune response that partially or completely prevents prion entry across the gut barrier, while at the same time producing modulated systemic immunity that is unlikely to be associated with toxicity. Our results using an attenuated Salmonella vaccine strain expressing the prion protein showed that mucosal vaccination can protect against prion infection from a peripheral source, suggesting the feasibility of this approach. It is also possible to develop active and/or passive immunomodulatory approaches that more specifically target PrP(Sc) or target the shared pathological conformer found in numerous conformational disorders. Such approaches could have a significant impact on many of the common age-associated dementias.

Immunotherapy targeting pathological tau prevents cognitive decline in a new tangle mouse model

Harnessing the immune system to clear protein aggregates is emerging as a promising approach to treat various neurodegenerative diseases. In Alzheimer's disease (AD), several clinical trials are ongoing using active and passive immunotherapy targeting the amyloid-β (Aβ) peptide. Limited emphasis has been put into clearing tau/tangle pathology, another major hallmark of the disease. Recent findings from the first Aβ vaccination trial suggest that this approach has limited effect on tau pathology and that Aβ plaque clearance may not halt or slow the progression of dementia in individuals with mild-to-moderate AD. To assess within a reasonable timeframe whether targeting tau pathology with immunotherapy could prevent cognitive decline, we developed a new model with accelerated tangle development. It was generated by crossing available strains that express all six human tau isoforms and the M146L presenilin mutation. Here, we show that this unique approach completely prevents severe cognitive impairment in three different tests. This remarkable effect correlated well with extensive clearance of abnormal tau within the brain. Overall, our findings indicate that immunotherapy targeting pathological tau is very feasible for tauopathies, and should be assessed in clinical trials in the near future.

Bapineuzumab: anti-β-amyloid monoclonal antibodies for the treatment of Alzheimer’s disease

In the last decade, new therapeutic approaches targeting β-amyloid (Aβ) have been discovered and developed with the hope of modifying the natural history of Alzheimer’s disease (AD). The most revolutionary of these approaches consists in the removal of brain Aβ via anti-Aβ antibodies. After an active vaccine (AN1792) was discontinued in 2002 due to occurrence of meningoencephalitis in approximately 6% of patients, several other second-generation active Aβ vaccines and passive Aβ immunotherapies have been developed and are under clinical investigation with the aim of accelerating Aβ clearance from the brain of AD patients. The most advanced of these immunological approaches is bapineuzumab, which is composed of humanized anti-Aβ monoclonal antibodies that has been tested in two Phase II trials. Bapineuzumab has been shown to reduce Aβ burden in the brain of AD patients. However, its preliminary cognitive efficacy appears uncertain, particularly in ApoE ε4 carriers, and vasogenic edema may limit its clinical use. The results of four ongoing large Phase III trials on bapineuzumab will provide answers regarding whether passive anti-Aβ immunization is able to alter the course of this devastating disease.

Immunomodulation targeting abnormal protein conformation reduces pathology in a mouse model of Alzheimer's disease

Many neurodegenerative diseases are characterized by the conformational change of normal self-proteins into amyloidogenic, pathological conformers, which share structural properties such as high β-sheet content and resistance to degradation. The most common is Alzheimer's disease (AD) where the normal soluble amyloid β (sAβ) peptide is converted into highly toxic oligomeric Aβ and fibrillar Aβ that deposits as neuritic plaques and congophilic angiopathy. Currently, there is no highly effective treatment for AD, but immunotherapy is emerging as a potential disease modifying intervention. A major problem with most active and passive immunization approaches for AD is that both the normal sAβ and pathogenic forms are equally targeted with the potential of autoimmune inflammation. In order to avoid this pitfall, we have developed a novel immunomodulatory method that specifically targets the pathological conformations, by immunizing with polymerized British amyloidosis (pABri) related peptide which has no sequence homology to Aβ or other human proteins. We show that the pABri peptide through conformational mimicry induces a humoral immune response not only to the toxic Aβ in APP/PS1 AD transgenic mice but also to paired helical filaments as shown on AD human tissue samples. Treated APP/PS1 mice had a cognitive benefit compared to controls (p<0.0001), associated with a reduction in the amyloid burden (p = 0.0001) and Aβ40/42 levels, as well as reduced Aβ oligomer levels. This type of immunomodulation has the potential to be a universal β-sheet disrupter, which could be useful for the prevention or treatment of a wide range of neurodegenerative diseases.

Murine models of Alzheimer's disease and their use in developing immunotherapies

Alzheimer's disease (AD) is one of the categories of neurodegenerative diseases characterized by a conformational change of a normal protein into a pathological conformer with a high beta-sheet content that renders it resistant to degradation and neurotoxic. In AD, the normal soluble amyloid beta (sAbeta) peptide is converted into oligomeric/fibrillar Abeta. The oligomeric forms of Abeta are thought to be the most toxic, while fibrillar Abeta becomes deposited as amyloid plaques and congophilic angiopathy, which both serve as neuropathological markers of the disease. An additional important feature of AD is the accumulation of abnormally phosphorylated tau as soluble toxic oligomers and as neurofibrillary tangles. Many therapeutic interventions are under investigation to prevent and treat AD. The testing of these diverse approaches to ameliorate AD pathology has been made possible by the existence of numerous transgenic mouse models which each mirror specific aspects of AD pathology. None of the current murine models is a perfect match of the human disease. Perhaps the most exciting of the therapeutic approaches being developed is immunomodulation targeting the aggregating proteins, Abeta and tau. This type of AD therapy is currently being assessed in many transgenic mouse models, and promising findings have led to clinical trials. However, there is a discrepancy between results in murine models and ongoing clinical trials, which highlight the limitations of these models and also of our understanding of the underlying etiology and pathogenesis of AD. Because of these uncertainties, Tg models for AD are continuously being refined with the aim to better understand the disease and to enhance the predictive validity of potential treatments such as immunotherapies.

Diminished amyloid-beta burden in Tg2576 mice following a prophylactic oral immunization with a salmonella-based amyloid-beta derivative vaccine

Immunotherapy holds great promise for Alzheimer's disease (AD) and other conformational disorders but certain adverse reactions need to be overcome. Prior to the side effects in the first Elan/Wyeth AD vaccine trial, we proposed using amyloid-beta (Abeta) derivatives as a safer approach. The route of administration may also affect vaccine safety. To assess the feasibility of oral immunization that promotes mucosal immunity, Tg2576 AD model mice were treated prophylactically three times over 6 weeks starting at 3-5 months of age with a Salmonella vaccine expressing K6Abeta(1-30). At 22-24 months of age, cortical Abeta plaque burden and total Abeta(40/42) levels were reduced by 48-75% in the immunized mice compared to controls, which received unmodified Salmonella. Plaque clearance was not associated with increased microglial activation, which may be explained by the long treatment period. Furthermore, cerebral microhemorrhages were not increased in the treated mice in contrast to several passive Abeta antibody studies. These results further support our findings with this immunogen delivered subcutaneously and demonstrate its efficacy when given orally, which may provide added benefits for human use.

Neuropathology after active Abeta42 immunotherapy: implications for Alzheimer's disease pathogenesis

The amyloid cascade hypothesis of Alzheimer's disease (AD) is testable: it implies that interference with Abeta aggregation and plaque formation may be therapeutically useful. Abeta42 immunisation of amyloid precursor protein (APP) transgenic mice prevented plaque formation and caused removal of existing plaques. The first clinical studies of Abeta immunisation in AD patients (AN1792, Elan Pharmaceuticals) were halted when some patients suffered side effects. Since our confirmation that Abeta immunisation can prompt plaque removal in human AD, we have performed a clinical and neuropathological follow up of AD patients in the initial Elan Abeta immunisation trial. In immunised AD patients, we found: a lower Abeta load, with evidence that plaques had been removed; a reduced tau load in neuronal processes, but not in cell bodies; and no evidence of a beneficial effect on synapses. There were pathological "side effects" including: increased microglial activation; increased cerebral amyloid angiopathy; and there is some evidence for increased soluble/oligomeric Abeta. A pathophysiological mechanism involving effects on the cerebral vasculature is proposed for the clinical side effects observed with some active and passive vaccine protocols. Our current knowledge of the effects of Abeta immunotherapy is based on functional information from the early clinical trials and a few post mortem cases. Several further clinical studies are underway using a variety of protocols and important clinical, imaging and neuropathological data will become available in the near future. The information obtained will be important in helping to understand the pathogenesis not only of AD but also of other neurodegenerative disorders associated with protein aggregation.