Subacute meningoencephalitis in a subset of patients with AD after Abeta42 immunization

[Ethical questions in clinical research with the mentally ill]

The review deals with present problems of protecting mentally ill patients who are incompetent to give informed consent to participating in clinical research, and of assessment of the capacity to consent. 1. Clinical trials of drugs on efficacy and safety in incompetent patients are ethically justified and legally admissible if the investigational drug can be expected to exert a direct potential individual benefit and if such trials will be performed under defined criteria to protect these vulnerable patients. In Germany it is questionable how far these prescriptions of the German Drug Law (AMG) are transferable to other than drug research. 2. Research with no direct potential individual benefit or only a group-specific benefit in incompetent patients is controversially discussed. However, it may be ethically justified as an exception, and is in Germany legally admissible only in minors, but not in adults. 3. However, internationally there exists a wide range of legal regulations, terms, interpretations, and practices of research with vulnerable persons. In the past years a shift seems to have developed from normatively oriented discussions to more empirically based investigations. Especially vague but clinically relevant terms in protection declarations or guidelines have been better specified, put in concrete form by anchor examples, and empirically studied. 4. In general the criteria of protecting the dignity and, even if impaired, the autonomy of incompetent patients as subjects for research appear to guarantee a high standard of protection. However, the application of these criteria must be improved by practicable procedures. This is valid particularly for the assessment of the basic criterion whether a patient is capable of consenting or not. 5. Open Questions are formulated as need of research.

Nonviral DNA vaccination augments microglial phagocytosis of beta-amyloid deposits as a major clearance pathway in an Alzheimer disease mouse model

Immunotherapies markedly reduce beta-amyloid (Abeta) burden and reverse behavioral impairment in mouse models of Alzheimer disease. We previously showed that new Abeta DNA vaccines reduced Abeta deposits in Alzheimer disease model mice without detectable side effects. Although they are effective, the mechanisms of Abeta reduction by the DNA vaccines remain to be elucidated. Here, we analyzed vaccinated and control Alzheimer disease model mice from 4 months to 15 months of age to assess which of several proposed mechanisms may underlie the beneficial effects of this vaccination. Immunohistochemical analysis revealed that activated microglial numbers increased significantly in the brains of vaccinated mice after DNA vaccination both around Abeta plaques and in areas remote from them. Microglia in treated mice phagocytosed Abeta debris more frequently than they did in untreated mice. Although microglia had an activated morphological phenotype, they did not produce significant amounts of tumor necrosis factor. Amyloid plaque immunoreactivity and Abeta concentrations in plasma increased slightly in vaccinated mice compared with controls at 9 but not at 15 months of age. Collectively, these data suggest that phagocytosis of Abeta deposits by microglia plays a central role in Abeta reduction after DNA vaccination.

DNA epitope vaccine containing complement component C3d enhances anti-amyloid-beta antibody production and polarizes the immune response towards a Th2 phenotype

We have engineered a DNA epitope vaccine that expresses 3 self-B cell epitopes of Abeta(42) (3Abeta(1-11)), a non-self T helper (Th) cell epitope (PADRE), and 3 copies of C3d (3C3d), a component of complement as a molecular adjuvant, designed to safely reduce CNS Abeta. Immunization of mice with 3Abeta(1-11)-PADRE epitope vaccine alone generated only moderate levels of anti-Abeta antibodies and a pro-inflammatory T helper (Th1 phenotype) cellular immune response. However, the addition of 3C3d to the vaccine construct significantly augmented the anti-Abeta humoral immune response and, importantly, shifted the cellular immune response towards the potentially safer anti-inflammatory Th2 phenotype.

Immune defects in Alzheimer's disease: new medications development

Alzheimer's disease (AD) is a neurodegenerative disease characterized by the accumulation of intracellular and extracellular aggregates. According to the amyloid beta (Aβ) hypothesis, amyloidosis occurring in the brain is a leading cause of neurodegeneration in AD. Defects in the innate immune system may decrease the clearance of Aβ in the brain. Macrophages of most AD patients do not transport Aβ into endosomes and lysosomes, and monocytes from AD patients do not efficiently clear Aβ from AD brain. After stimulation with Aβ, mononuclear cells of normal subjects display up-regulated transcription of MGAT3, which encodes β-1,4-mannosyl-glycoprotein 4-β-N-acetylglucosaminyltransferase, and Toll-like receptor (TLR) genes. Monocytes of AD patients generally down-regulate these genes. A commonly used, naturally occurring material from a spice that enhances certain key functions defective in cells of innate immunity of many AD patients has shown epidemiologic rationale for use in AD treatment. Bisdemethoxycurcumin, a natural curcumin, is a minor constituent of turmeric (curry), and it enhances phagocytosis and clearance of Aβ in cells from most AD patients. We confirmed the effectiveness of a synthetic version of the same compound. In mononuclear cells of most AD patients, bisdemethoxycurcumin enhanced defective phagocytosis of Aβ and increased the transcription of MGAT3 and TLR genes. The potency of bisdemethoxycurcumin as a highly purified compound in facilitating the clearance of Aβ in mononuclear cells suggests the promise of enhanced effectiveness compared to curcuminoid mixtures. Bisdemethoxycurcumin appears to enhance immune function in mononuclear cells of AD patients and may provide a novel approach to AD immunotherapy.

Drug therapy in Alzheimer disease: an update for the oral health care provider

Alzheimer disease (AD) is a progressive neurologic disorder that manifests as memory loss, personality changes, global cognitive dysfunction, and functional impairment. As the United States population continues to age, the prevalence of AD will rise. Accordingly, oral health care providers will be more likely to treat patients affected by this disease; therefore, it is necessary to understand the pharmacologic agents used for the management of AD. This article provides an update of the available drug therapies for AD and discusses their implications on the oral and dental health of patients.

Mouse models of Alzheimer's dementia: current concepts and new trends

It is lay knowledge now that Alzheimer's dementia (AD) is one of the most devastating diseases afflicting our societies. A major thrust in search for a cure has relied in the development of animal models of the disease. Thanks to progress in the genetics of the rare inherited forms of AD, various transgenic mouse models harboring human mutated proteins were developed, yielding very significant advancements in the understanding of pathological pathways. Although these models led to testing many different new therapies, none of the preclinical successes have translated yet into much needed therapeutic improvements. Further insight into the metabolic disturbances that are probably associated with the onset of the disease may also rely on new animal models of AD involving insulin/IGF-I signaling that could mimic the far most common sporadic forms of AD associated with old age. Combination of models of familial AD that develop severe amyloidosis with those displaying defects in insulin/IGF-I signaling may help clarify the link between putative initial metabolic disturbances and mechanisms of pathological progression.

Pharmacotherapeutic targets in Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder which is characterized by an increasing impairment in normal memory and cognitive processes that significantly diminishes a person's daily functioning. Despite decades of research and advances in our understanding of disease aetiology and pathogenesis, there are still no effective disease-modifying drugs available for the treatment of AD. However, numerous compounds are currently undergoing pre-clinical and clinical evaluations. These candidate pharma-cotherapeutics are aimed at various aspects of the disease, such as the microtubule-associated τ-protein, the amyloid-β (Aβ) peptide and metal ion dyshomeostasis – all of which are involved in the development and progression of AD. We will review the way these pharmacological strategies target the biochemical and clinical features of the disease and the investigational drugs for each category.

Cytokine-mediated inhibition of fibrillar amyloid-beta peptide degradation by human mononuclear phagocytes

Vaccination therapy of AD animal models and patients strongly suggests an active role of brain mononuclear phagocytes in immune-mediated clearance of amyloid-beta peptides (Abeta) in brain. Although Abeta uptake by macrophages can be regulated by pro- and anti-inflammatory cytokines, their effects on macrophage-mediated Abeta degradation are poorly understood. To better understand this mechanism of degradation, we examined whether pro- and anti-inflammatory cytokines affect the degradation of Abeta using primary cultured human monocyte-derived macrophages (MDM) and microglia using pulse-chase analysis of fibrillar and oligomer (125)I-Abeta40 and Abeta42. Initial uptake of fibrillar Abeta40 and Abeta42 was 40% and its degradation was saturated by 120 h in both MDM and microglia, compared with an initial uptake of oligomeric Abeta less than 0.5% and saturation of degradation within 24 h. IFN-gamma increased the intracellular retention of fibrillar Abeta40 and Abeta42 by inhibiting degradation, whereas IL-4, IL-10, and TGF-beta1, but not IL-13 and IL-27, enhanced degradation. Fibrillar Abeta degradation in MDM is sensitive to lysosomal and insulin degrading enzyme inhibitors but insensitive to proteasomal and neprilysin inhibitors. IFN-gamma and TNF-alpha directly reduced the expression of insulin degrading enzyme and chaperone molecules (heat shock protein 70 and heat shock cognate protein 70), which are involved in refolding of aggregated proteins. Coculture of MDM with activated, but not naive T cells, suppressed Abeta degradation in MDM, which was partially blocked by a combination of neutralizing Abs against proinflammatory cytokines. These data suggest that proinflammatory cytokines suppress Abeta degradation in MDM, whereas select anti-inflammatory and regulatory cytokines antagonize these effects.

Neuroinflammation and tumor necrosis factor signaling in the pathophysiology of Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that affects nearly one in two individuals over 90 years of age. Its neuropathological hallmarks are accumulation of extraneuronal plaques of amyloid-beta (Aβ), the presence of neurofibrillary tangles formed by aberrantly hyperphosphorylated tau, progressive synaptic loss, and neurodegeneration which eventually results in decline of memory and cognitive faculties. Although the etiology of sporadic AD in humans is unknown, mutations in amyloid precursor protein or components of its processing machinery (β-secretase and γ-secretase) result in overproduction of Aβ1-40 and 1-42 peptides and are sufficient to cause disease. In this review, we highlight the experimental and clinical evidence that suggests a close association between neuro-inflammation and AD pathogenesis. Overproduction of inflammatory mediators in the brain occurs when microglia, which are often found in close physical association with amyloid plaques in AD brains, become chronically activated. It has been proposed that elevated levels of pro-inflammatory cytokines, including tumor necrosis factor (TNF), may inhibit phagocytosis of Aβ in AD brains thereby hindering efficient plaque removal by resident microglia. In support of this idea, the bacterial endotoxin lipopolysaccharide, a potent trigger of inflammation that elicits production of TNF and many other cytokines, can accelerate the appearance and severity of AD pathology in several animal models of AD. We review the evidence implicating TNF signaling in AD pathology and discuss how TNF-dependent processes may contribute to cognitive dysfunction and accelerated progression of AD. We conclude by reviewing the observations that provide compelling rationale to investigate the extent to which new therapeutic approaches that selectively target the TNF pathway modify progression of neuropathology in pre-clinical models of AD as well as the promising findings with the use of nonsteroidal anti-inflammatory drugs and recent clinical trials with Aβ immunotherapy.

[Current immune therapy for Alzheimer's disease]

New treatment strategies have developed since publication in 1991 of the amyloid hypothesis on the pathogenesis of Alzheimer's disease. In contrast to previous methods, these strategies are not for countering the effects of neuronal loss at the transmitter level. Instead, they are meant to influence the neurodegenerative process itself. They incorporate amyloid precursor protein-splitting proteases (secretase inhibitors), substances for reducing the aggregation of beta-amyloid 42 (Abeta42) and stimulating specific immune reactions against it. Particularly Abeta42 and the clinical research are examined. Ethical and economic questions resulting from successful immunization against Abeta are discussed.

[Innovative treatment approaches for Alzheimer's disease. Immunotherapy]

Immunotherapeutic approaches for treating Alzheimer's disease were first described in 1999. A clinical trial using an active immunization with Abeta1-42 was initiated shortly thereafter, but it was halted early because of serious safety issues (acute meningoencephalitis in 6% of the treated patients). Despite this drawback, encouraging data from preclinical and clinical data were available, prompting researchers to seek alternative approaches for safer active and passive immunization. Currently, several passive and active immunotherapeutic approaches are being tested in clinical trials. However, our understanding of the mechanisms behind immunization in neurodegenerative disorders is still incomplete. In this review we present the current status of the different approaches in relation to Alzheimer's disease as well as to other neurodegenerative disorders.

Consequence of Abeta immunization on the vasculature of human Alzheimer's disease brain

A major feature of Alzheimer's disease is the accumulation of amyloid-beta peptide (Abeta) in the brain both in the form of plaques in the cerebral cortex and in blood vessel as cerebral amyloid angiopathy (CAA). Experimental models and human clinical trials have shown that accumulation of Abeta plaques can be reversed by immunotherapy. In this study, we hypothesized that Abeta in plaques is solubilized by antibodies generated by immunization and drains via the perivascular pathway, detectable as an increase in cerebrovascular Abeta. We have performed a follow up study of Alzheimer's disease patients immunized against Abeta42. Neuropathological examination was performed on nine patients who died between four months and five years after their first immunization. Immunostaining for Abeta40 and Abeta42 was quantified and compared with that in unimmunized Alzheimer's disease controls (n = 11). Overall, compared with these controls, the group of immunized patients had approximately 14 times as many blood vessels containing Abeta42 in the cerebral cortex (P<0.001) and seven times more in the leptomeninges (P = 0.013); among the affected blood vessels in the immunized cases, most of them had full thickness and full circumference involvement of the vessel wall in the cortex (P = 0.001), and in the leptomeninges (P = 0.015). There was also a significantly higher level of cerebrovascular Abeta40 in the immunized cases than in the unimmunized cases (cortex: P = 0.009 and leptomeninges: P = 0.002). In addition, the immunized patients showed a higher density of cortical microhaemorrhages and microvascular lesions than the unimmunized controls, though none had major CAA-related intracerebral haemorrhages. The changes in cerebral vascular Abeta load did not appear to substantially influence the structural proteins of the blood vessels. Unlike most of the immunized patients, two of the longest survivors, four to five years after first immunization, had virtually complete absence of both plaques and CAA, raising the possibility that, given time, Abeta is eventually cleared from the cerebral vasculature. The findings are consistent with the hypothesis that Abeta immunization results in solubilization of plaque Abeta42 which, at least in part, exits the brain via the perivascular pathway, causing a transient increase in the severity of CAA. The extent to which these vascular alterations following Abeta immunization in Alzheimer's disease are reflected in changes in cognitive function remains to be determined.

Anti-oligomeric Abeta single-chain variable domain antibody blocks Abeta-induced toxicity against human neuroblastoma cells

The Amyloid-beta (Abeta) peptide is a major component of the amyloid plaques associated with Alzheimer's disease (AD). Recent studies suggest that the most toxic forms of Abeta are small, soluble oligomeric aggregates. Here, we report the isolation and characterization of a single-chain variable domain (scFv) antibody isolated against oligomeric Abeta using a protocol developed in our laboratory that combines phage display technology and atomic force microscopy (AFM). Starting with a randomized, single framework phage display library, after three rounds of selection against oligomeric Abeta, we identified an scFv that bound oligomeric Abeta specifically, but not monomeric or fibrillar forms. The anti-oligomeric scFv inhibits Abeta aggregation and toxicity, and reduces the toxicity of preformed oligomeric Abeta towards human neuroblastoma cells. When used to probe samples of human brain tissue, the scFv reacted with AD tissue but not a healthy control or Parkinson's disease brain samples. The anti-oligomeric Abeta scFv therefore has potential therapeutic and diagnostic applications in specifically targeting or identifying the toxic morphologies of Abeta in AD brains.

Developing new treatments for Alzheimer's disease: the who, what, when, and how of biomarker-guided therapies

This synthetic review presents an approach to the use of biomarkers for the development of new treatments for Alzheimer's disease (AD). After reviewing the process of translation as applied to AD, the paper provides a general update on what is known about the biology of the disease, and highlights currently available treatments. This is followed by a discussion of future drug development for AD emphasizing the roles that biomarkers are likely to play in this process: (1) define patients who are going to progress rapidly for the purpose of trial enrichment; (2) differentiate disease and therapeutically relevant AD subtypes; (3) assess the potential activity of specific therapies in vivo or ex vivo; and (4) measure the underlying disease state, so as to (a) detect disease and assess drug response in asymptomatic patients, (b) serve as a secondary outcome measure in clinical trials of symptomatic patients, and (c) decide if further development of a treatment should be stopped if not likely to be effective. Several examples are used to illustrate each biomarker utility in the AD context.

Mannan-Abeta28 conjugate prevents Abeta-plaque deposition, but increases microhemorrhages in the brains of vaccinated Tg2576 (APPsw) mice

Background

New pre-clinical trials in AD mouse models may help to develop novel immunogen-adjuvant configurations with the potential to avoid the adverse responses that occurred during the clinical trials with AN-1792 vaccine formulation. Recently, we have pursued an alternative immunization strategy that replaces QS21 the Th1 type adjuvant used in the AN-1792 clinical trial with a molecular adjuvant, mannan that can promote a Th2-polarized immune response through interactions with mannose-binding and CD35/CD21 receptors of the innate immune system. Previously we established that immunization of wild-type mice with mannan-Aβ₂₈ conjugate promoted Th2-mediated humoral and cellular immune responses. In the current study, we tested the efficacy of this vaccine configuration in amyloid precursor protein (APP) transgenic mice (Tg2576).

Methods

Mannan was purified, activated and chemically conjugated to Aβ₂₈ peptide. Humoral immune responses induced by the immunization of mice with mannan-Aβ₂₈ conjugate were analyzed using a standard ELISA. Aβ₄₂ and Aβ₄₀ amyloid burden, cerebral amyloid angiopathy (CAA), astrocytosis, and microgliosis in the brain of immunized and control mice were detected using immunohistochemistry. Additionally, cored plaques and cerebral vascular microhemorrhages in the brains of vaccinated mice were detected by standard histochemistry.

Results

Immunizations with low doses of mannan-Aβ₂₈ induced potent and long-lasting anti-Aβ humoral responses in Tg2576 mice. Even 11 months after the last injection, the immunized mice were still producing low levels of anti-Aβ antibodies, predominantly of the IgG1 isotype, indicative of a Th2 immune response. Vaccination with mannan-Aβ₂₈ prevented Aβ plaque deposition, but unexpectedly increased the level of microhemorrhages in the brains of aged immunized mice compared to two groups of control animals of the same age either injected with molecular adjuvant fused with an irrelevant antigen, BSA (mannan-BSA) or non-immunized mice. Of note, mice immunized with mannan-Aβ₂₈ showed a trend toward elevated levels of CAA in the neocortex and in the leptomeninges compared to that in mice of both control groups.

Conclusion

Mannan conjugated to Aβ₂₈ provided sufficient adjuvant activity to induce potent anti-Aβ antibodies in APP transgenic mice, which have been shown to be hyporesponsive to immunization with Aβ self-antigen. However, in old Tg2576 mice there were increased levels of cerebral microhemorrhages in mannan-Aβ₂₈ immunized mice. This effect was likely unrelated to the anti-mannan antibodies induced by the immunoconjugate, because control mice immunized with mannan-BSA also induced antibodies specific to mannan, but did not have increased levels of cerebral microhemorrhages compared with non-immunized mice. Whether these anti-mannan antibodies increased the permeability of the blood brain barrier thus allowing elevated levels of anti-Aβ antibodies entry into cerebral perivascular or brain parenchymal spaces and contributed to the increased incidence of microhemorrhages remains to be investigated in the future studies.

Active and passive immunotherapy for neurodegenerative disorders

Immunotherapeutic strategies to combat neurodegenerative disorders have galvanized the scientific community since the first dramatic successes in mouse models recreating aspects of Alzheimer disease (AD) were reported. However, initial human trials of active amyloid-beta (Abeta) vaccination were halted early because of a serious safety issue: meningoencephalitis in 6% of subjects. Nonetheless, some encouraging preliminary data were obtained, and rapid progress has been made toward developing alternative, possibly safer active and passive immunotherapeutic approaches for several neurodegenerative conditions. Many of these are currently in human trials for AD. Despite these advances, our understanding of the essential mechanisms underlying the effects seen in preclinical models and human subjects is still incomplete. Antibody-induced phagocytosis of pathological protein deposits, direct antibody-mediated disruption of aggregates, neutralization of toxic soluble proteins, a shift in equilibrium toward efflux of specific proteins from the brain, cell-mediated immune responses, and other mechanisms may all play roles depending on the specific immunotherapeutic scenario.

Developing injectable immunoglobulins to treat cognitive impairment in Alzheimer's disease

BACKGROUND

Alzheimer's disease is a devastating disorder, clinically characterized by a comprehensive cognitive decline. The novel strategy of anti-amyloid-beta immunotherapy has been suggested following encouraging results obtained in murine models of Alzheimer's disease, in non-human primates, and in small-scale clinical trials.

OBJECTIVE

To examine the choice between active or passive anti-amyloid-beta immunization and the choice of the molecule to which the immune machinery should be targeted, which are central issues in future immune therapy of Alzheimer's disease.

METHODS

Research into the new area of Alzheimer's disease immune therapy is primarily based on in vivo and in vitro studies of murine models of Alzheimer's disease. The studies are hence limited to defined genetic deficiencies.

RESULTS/CONCLUSIONS

In humans, infusion of anti-amyloid-beta antibodies is considered a safer approach than active anti-amyloid-beta vaccination. Alzheimer's-disease-protective anti-amyloid-beta monoclonal antibodies should target specific epitopes within the amyloid beta(1 42) peptide, avoiding possibly harmful binding to the ubiquitous normal amyloid precursor protein. Since Alzheimer's disease immunotherapy requires repeated infusion of antibodies over a prolonged period of time, Alzheimer's disease patients will tolerate such antibodies provided the latter are exclusively of human origin. Human monoclonal antibodies that correspond to ubiquitous anti-amyloid-beta, present in all healthy humans, might bear important protective characteristics.

Peptides and proteins in plasma and cerebrospinal fluid as biomarkers for the prediction, diagnosis, and monitoring of therapeutic efficacy of Alzheimer's disease

Alzheimer's disease (AD) affects millions of persons worldwide. Earlier detection and/or diagnosis of AD would permit earlier intervention, which conceivably could delay progression of this dementing disorder. In order to accomplish this goal, reliable and specific biomarkers are needed. Biomarkers are multidimensional and have the potential to aid in various facets of AD such as diagnostic prediction, assessment of disease stage, discrimination from normally cognitive controls as well as other forms of dementia, and therapeutic efficacy of AD drugs. To date, biomarker research has focused on plasma and cerebrospinal fluid (CSF), two bodily fluids believed to contain the richest source of biomarkers for AD. CSF is the fluid surrounding the central nervous system (CNS), and is the most indicative obtainable fluid of brain pathology. Blood plasma contains proteins that affect brain processes from the periphery, as well as proteins/peptides exported from the brain; this fluid would be ideal for biomarker discovery due to the ease and non-invasive process of sample collection. However, it seems reasonable that biomarker discovery will result in combinations of CSF, plasma, and other fluids such as urine, to serve the aforementioned purposes. This review focuses on proteins and peptides identified from CSF, plasma, and urine that may serve as biomarkers in AD.

Biomarkers for early diagnosis of Alzheimer disease: 'ALZheimer ASsociated gene'--a new blood biomarker?

Simple, non-invasive tests for an early detection of degenerative dementia by use of biomarkers are urgently required. However, up to the present, no validated extracerebral diagnostic markers (plasma/serum, platelets, urine, connective tissue) for the early diagnosis of Alzheimer disease (AD) are available. In disease stages with evident cognitive disturbances, the clinical diagnosis of probable AD is made with around 90% accuracy using modern clinical, neuropsychological and imaging methods. Diagnostic sensitivity and specificity even in early disease stages are improved by CSF markers, in particular combined tau and amyloid beta peptides (Abeta) and plasma markers (eg, Abeta-42/Abeta-40 ratio). Recently, a novel gene/protein--ALZAS (Alzheimer Associated Protein)--with a 79 amino acid sequence, containing the amyloid beta-42 fragment (Abeta-42), the amyloid precursor protein (APP) transmembrane signal and a 12 amino acid C-terminal, not present in any other known APP alleles, has been discovered on chromosome 21 within the APP region. Reverse transcriptase-PCR revealed the expression of the transcript of this protein in the cortex and hippocampal regions as well as in lymphocytes of human AD patients. The expression of ALZAS is mirrored by a specific autoimmune response in AD patients, directed against the ct-12 end of the ALZAS-peptide but not against the Abeta-sequence. ELISA studies of plasma detected highest titers of ALZAS in patients with mild cognitive impairment (presymptomatic AD), but only moderately increased titers in autopsy-confirmed AD, whereas low or undetectable ct-12 titers were found in cognitively intact age-matched subjects and young controls. The antigen, ALZAS protein, was detected in plasma in later clinical stages of AD. It is suggested that ALZAS represents an indicator in a dynamic equilibrium between both peripheral and brain degenerative changes in AD and may become a useful "non-invasive" diagnostic marker via a simple blood test.

Present and prospective clinical therapeutic regimens for Alzheimer's disease

Alzheimer's disease (AD) is an incurable neurodegenerative disorder that produces cognitive impairments that increase in severity as the disease progresses. The clinical symptoms are related to the presence of neuritic plaques and neurofibrillary tangles in the cerebral cortex which represent the pathophysiological hallmarks of AD. The debilitating nature of the disease can result in clinical burden for the patient, emotional strain for those that care for patients with Alzheimer's, and significant financial burden to society. The goals of current treatments, such as cholinesterase inhibitors and N-methyl-D-aspartate receptor antagonist, are to reduce the severity or slow the progression of cognitive symptoms. Although these treatments have demonstrated modest clinical benefit, they are unable to prevent, prohibit, or reverse the underlying pathophysiology of AD. Considerable progress has been made toward the development of disease-modifying treatments. Treatments currently under development mainly target the production, aggregation, and removal of existing amyloid beta-peptide aggregates which are believed to instigate the overall development of the neuropathology. Additional strategies that target tau pathology are being studied to promote neural protection against AD pathology. The current research has continued to expand our knowledge toward the development of disease modifying Alzheimer's therapies; however, no specific treatment strategy capable of demonstrating empirical efficacy and safety has yet to emerge.

Animal models of Alzheimer's disease and frontotemporal dementia

Insoluble protein aggregates have been linked to Alzheimer's disease (AD) and frontotemporal dementia (FTD). Recent work in transgenic mice has shed light on the role of these aggregates by identifying soluble oligomeric species that may interfere with essential cellular mechanisms at an early disease stage. This review summarizes what we have learned about the roles of these proteins from transgenic mice and invertebrate species such as flies and worms. Proteomic and transcriptomic analyses of tissue from these animal models have identified new molecules with crucial roles in disease. Moreover, transgenic animals have been instrumental in defining drug targets and designing novel therapeutic strategies. With advanced imaging techniques that can be used in both humans and mice an early, preclinical diagnosis of AD and FTD could be within reach.

Long-term effects of Abeta42 immunisation in Alzheimer's disease: follow-up of a randomised, placebo-controlled phase I trial

BACKGROUND

Immunisation of patients with Alzheimer's disease with full-length amyloid-beta peptide (Abeta(42)) can clear amyloid plaques from the brain. Our aim was to assess the relation between Abeta(42) immune response, degree of plaque removal, and long-term clinical outcomes.

METHODS

In June, 2003, consent for long-term clinical follow-up, post-mortem neuropathological examination, or both, was sought from 80 patients (or their carers) who had entered a phase I randomised, placebo-controlled trial of immunisation with Abeta(42) (AN1792, Elan Pharmaceuticals) in September, 2000. The follow-up study was completed in September, 2006. Plaques were assessed in terms of the percentage area of the cortex with Abeta immunostaining (Abeta load) and in terms of characteristic histological features reflecting plaque removal. Survival of all 80 individuals until severe dementia or death was assessed with a Cox proportional hazard model.

FINDINGS

20 participants--15 in the AN1792 group, five in the placebo group--died before follow-up started. A further 22 patients--19 in the AN1792 group, three in the placebo group--died during follow-up. Nine of the deceased patients, all in the AN1792 group, had given consent for post-mortem analysis; one of these who did not die with Alzheimer's disease was excluded. In the remaining eight participants who received immunisation and who were examined neuropathologically, mean Abeta load was lower than in an unimmunised control group that was matched for age at death (2.1% [SE 0.7] in treated participants vs 5.1% [0.9] in controls; mean difference 3.0%, 95% CI 0.6-5.4; p=0.02). Although there was considerable variation in Abeta load and degree of plaque removal among immunised participants, the degree of plaque removal varied significantly with mean antibody response attained during the treatment study period (Kruskal-Wallis p=0.02). Seven of the eight immunised patients who underwent post-mortem assessment, including those with virtually complete plaque removal, had severe end stage dementia before death. In the whole cohort, there was no evidence of improved survival (hazard ratio 0.93, 95% CI 0.43-3.11; p=0.86) or of an improvement in the time to severe dementia (1.18, 0.45-3.11; p=0.73) in the AN1792 group versus the placebo group.

INTERPRETATION

Although immunisation with Abeta(42) resulted in clearance of amyloid plaques in patients with Alzheimer's disease, this clearance did not prevent progressive neurodegeneration.

Parenchymal and vascular Abeta-deposition and its effects on the degeneration of neurons and cognition in Alzheimer's disease

The deposition of the amyloid beta-protein (Abeta) is one of the pathological hallmarks of Alzheimer's disease (AD). Abeta-deposits show the morphology of senile plaques and cerebral amyloid angiopathy (CAA). Senile plaques and vascular Abeta-deposits occur first in neocorti-cal areas. Then, they expand hierarchically into further brain regions. The distribution of Abeta plaques throughout the entire brain, thereby correlates with the clinical status of the patients. Imaging techniques for Abeta make use of the hierarchical distribution of Abeta to distinguish AD patients from non-AD patients. However, pathology seen in AD patients represents a late stage of a pathological process starting 10-30 years earlier in cognitively normal individuals. In addition to the fibrillar amyloid of senile plaques, oligomeric and monomeric Abeta is found in the brain. Recent studies revealed that oligomeric Abeta is presumably the most toxic Abeta-aggregate, which interacts with glutamatergic synapses. In doing so, dendrites are presumed to be the primary target for Abeta-toxicity. In addition, vascular Abeta-deposits can lead to capillary occlusion and blood flow disturbances presumably contributing to the alteration of neurons in addition to the direct neurotoxic effects of Abeta. All these findings point to an important role of Abeta and its aggregates in the neurodegenerative process of AD. Since there is already significant neuron loss in AD patients, treatment strategies aimed at reducing the amyloid load will presumably not cure the symptoms of dementia but they may stop disease progression. Therefore, it seems to be necessary to protect the brain from Abeta-toxicity already in stages of the disease with minor neuron loss before the onset of cognitive symptoms.

The role of the immune system in clearance of Abeta from the brain

In Alzheimer's disease (AD), there is abnormal accumulation of Abeta and tau proteins in the brain. There is an associated immunological response, but it is still unclear whether this is beneficial or harmful. Inflammation in AD, specifically in the form of microglial activation, has, for many years, been considered to contribute to disease progression. However, two types of evidence suggest that it may be appropriate to revise this view: first, the disappointing results of prospective clinical trials of anti-inflammatory agents and, second, the observation that microglia can clear plaques in AD following Abeta immunization. Although Abeta immunization alters AD pathology, there is limited evidence so far of benefit to cognitive function. Immunization against microorganisms is almost always used as a method of disease prevention rather than to treat a disease process that has already started. In animal models, immunotherapy at an early age can protect against Abeta accumulation and it will be interesting to see if this can usefully be applied to humans to prevent AD.

DNA vaccine therapy for Alzheimer's disease: present status and future direction

Alzheimer's disease is the most common cause of dementia characterized by progressive neurodegeneration. Based on the amyloid cascade hypothesis, a vaccine therapy for Alzheimer's disease (AD) was developed as a curative treatment. In 1999, the amyloid beta (Abeta) reduction in AD model transgenic mice with active vaccination with Abeta peptide was first reported. Although the clinical trials of active vaccination for AD patients were halted due to the development of meningoencephalitis in some patients, from the analysis of the clinical and pathological findings of treated patients, the vaccine therapy is thought to be effective. Based on such information, the vaccines for clinical application of human AD have been improved to control excessive immune reaction. Recently, we have developed non-viral DNA vaccines and obtained substantial Abeta reduction in transgenic mice without side effects. DNA vaccines have many advantages over conventional active or passive immunization. In this article, we review conventional vaccine therapies and further explain our non-viral DNA vaccine therapy. Finally, we show some data regarding the mechanisms of Abeta reduction after administration of DNA vaccines. DNA vaccination may open up new avenues of vaccine therapy for AD.

Targeting beta-amyloid pathology in Alzheimer's disease with Abeta immunotherapy

More than 10 clinical trials of Abeta immunotherapy are currently underway in patients with Alzheimer's disease (AD). The aim is to identify safe approaches for the efficacious antibody-mediated removal of brain beta-amyloid or its neurotoxic oligomeric precursors consisting of aggregated amyloid beta-peptide (Abeta). Initial experimental and neuro-pathological evidence for clearance of brain beta-amyloid in response to Abeta immunotherapy is associated with structural and functional rescue of neurons, as well as initial signs of clinical stabilization and reduced rates of dementia progression. For the next steps in the future improvement of Abeta immunotherapy, major challenges in pharmacokinetics, safety, and tolerability need to be addressed. These include the low penetrations rates of IgG molecules through the blood-brain barrier, possible reductions in brain volume, the possibility of autoimmune disease related to unwanted cross-reactivity with endogenous antigens on physiological structures, micro-hemorrhages related to cross-reaction with pre-existing vascular amyloid pathology, possible relocalization of Abeta from beta-amyloid plaques to brain blood vessels resulting in increased amyloid angiopathy, and the lacking activity of Abeta antibodies on pre-existing neurofibrillary tangle pathology, as well as the lacking molecular identification of the forms of Abeta to be therapeutically targeted. The solutions to these problems will be guided by the fine lines between tolerance and immunity against physiological and pathological structures, respectively, as well as by the understanding of the pathogenic transition of soluble Abeta into toxic oligomeric aggregation intermediates in the dynamic equilibrium of beta-amyloid fibril assembly. Provided that the ongoing and planned clinical trials address these issues in a timely manner, there is a good chance for Abeta immunotherapy to be one of the first disease-modifying therapies of Alzheimer's disease to be introduced into clinical practice.

Effect of intraventricular infusion of anti-prion protein monoclonal antibodies on disease progression in prion-infected mice

It is well known that anti-prion protein (PrP) monoclonal antibodies (mAbs) inhibit abnormal isoform PrP (PrPSc) formation in cell culture. Additionally, passive immunization of anti-PrP mAbs protects the animals from prion infection via peripheral challenge when mAbs are administered simultaneously or soon after prion inoculation. Thus, anti-PrP mAbs are candidates for the treatment of prion diseases. However, the effects of mAbs on disease progression in the middle and late stages of the disease remain unclear. This study carried out intraventricular infusion of mAbs into prion-infected mice before and after clinical onset to assess their ability to delay disease progression. A 4-week infusion of anti-PrP mAbs initiated at 120 days post-inoculation (p.i.), which is just after clinical onset, reduced PrPSc levels to 70-80 % of those found in mice treated with a negative-control mAb. Spongiform changes, microglial activation and astrogliosis in the hippocampus and thalamus appeared milder in mice treated with anti-PrP mAbs than in those treated with a negative-control mAb. Treatment with anti-PrP mAb prolonged the survival of mice infected with Chandler or Obihiro strain when infusion was initiated at 60 days p.i., at which point PrPSc is detectable in the brain. In contrast, infusion initiated after clinical onset prolonged the survival time by about 8 % only in mice infected with the Chandler strain. Although the effects on survival varied for different prion strains, the anti-PrP mAb could partly prevent disease progression, even after clinical onset, suggesting immunotherapy as a candidate for treatment of prion diseases.

Tau-based treatment strategies in neurodegenerative diseases

Neurofibrillary tangles are a characteristic hallmark of Alzheimer's and other neurodegenerative diseases, such as Pick's disease (PiD), progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), and frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17). These diseases are summarized as tauopathies, because neurofibrillary tangles are composed of intracellular aggregates of the microtubule-associated protein tau. The molecular mechanisms of tau-mediated neurotoxicity are not well understood; however, pathologic hyperphosphorylation and aggregation of tau play a central role in neurodegeneration and neuronal dysfunction. The present review, therefore, focuses on therapeutic approaches that aim to inhibit tau phosphorylation and aggregation or to dissolve preexisting tau aggregates. Further experimental therapy strategies include the enhancement of tau clearance by activation of proteolytic, proteasomal, or autophagosomal degradation pathways or anti-tau directed immunotherapy. Hyperphosphorylated tau does not bind microtubules, leading to microtubule instability and transport impairment. Pharmacological stabilization of microtubule networks might counteract this effect. In several tauopathies there is a shift toward four-repeat tau isoforms, and interference with the splicing machinery to decrease four-repeat splicing might be another therapeutic option.

Therapeutic strategies for Alzheimer's disease

Therapeutic approaches for Alzheimer's disease (AD) are guided by four disease characteristics: amyloid plaques, neurofibrillar tangles (NFT), neurodegeneration, and dementia. Amyloid plaques are composed largely of 4 kDa beta-amyloid (Abeta) peptides, with the more amyloidogenic, 42 amino acid form (Abeta42) as the primary species. Because multiple, rare mutations that cause early-onset, familial AD lead to increased production or aggregation of Abeta42, amyloid therapeutics aim to reduce the amount of toxic Abeta42 aggregates. Amyloid-based therapies include gamma-secretase inhibitors and modulators, BACE inhibitors, aggregation blockers, catabolism inducers, and anti-Abeta biologics. Tangles are composed of paired helical filaments of hyperphosphorylated tau protein. Tau-based therapeutics include kinase inhibitors, microtubule stabilizers, and catabolism inducers. Therapeutic strategies for neurodegeneration target multiple mechanisms, including excitotoxicity, mitochondrial dysfunction, oxidative damage, and inflammation or stimulation of neuronal viability. Although not disease modifying, cognition enhancers are important to treat the symptom of dementia. Strategies for cognition enhancement include cholinesterase inhibitors, and other approaches to enhance the signaling of cholinergic and glutamatergic neurons. In summary, plaques, tangles, neurodegeneration and dementia guide the development of multiple therapeutic approaches for AD and are the subject of this review.

The safety and tolerability of an HIV-1 DNA prime-protein boost vaccine (DP6-001) in healthy adult volunteers

This report describes the safety observations following administration of a polyvalent DNA prime-protein boost HIV-1 vaccine formulated with adjuvant QS21. Local injection site reactions were the most common (65% of subjects), and included type IV delayed-type hypersensitivity (DTH) reactions at prior DNA inoculation sites in 12 of 28 (43%) subjects following protein vaccination. Systemic reactions revealed two cases of vasculitis temporally related to inoculation with recombinant Env protein+QS21 adjuvant. Questions remain regarding the cause of the vasculitis, but the unique DTH observation may have contributed to the high level of immune responses previously reported for this vaccine.

Vaccination of Alzheimer's model mice with adenovirus vector containing quadrivalent foldable Abeta(1-15) reduces Abeta burden and behavioral impairment without Abeta-specific T cell response

Active amyloid beta (Abeta) vaccination has been shown to be effective in clearing cerebral Abeta and improving cognitive function in mouse models of Alzheimer's disease (AD). The meningoencephalitis observed in AD vaccination trial was likely related to excessive T cell-mediated immunity caused by the immunogen Abeta(1-42). To avoid this toxicity, previous researchers have been using synthetic truncated Abeta derivatives that promote humoral immunity. In this study, we develop a novel adenovirus vaccine, which can express quadrivalent foldable Abeta(1-15) (4 x Abeta(15)) and gene adjuvant GM-CSF in vivo. Importantly, the 4 x Abeta(15) sequence includes an Abeta-specific B cell epitope but lacks the reported T cell epitope. The 4 x Abeta(15) adenovirus vaccine induces an Abeta-specific IgG1 predominant humoral immune response, and reduces brain Abeta deposition and cognition deficits in Tg2576 mice. Detection of IL-4 and IFN-gamma in restimulated splenocytes shows a significant Th2-polarized immune response. Stimulation of splenocytes with 4 x Abeta(15) peptides results in robust proliferative responses, whereas proliferation is absent after stimulation with full-length Abeta, which indicates that the 4 x Abeta(15) adenovirus vaccine does not induce Abeta-specific T cellular immune response. Thus, our results raise the possibility that adenovirus vector encoding 4 x Abeta(15) would be a promising candidate for future AD vaccination program.

Can the immune system be harnessed to repair the CNS?

Experimental and clinical data have demonstrated that activating the immune system in the CNS can be destructive. However, other studies have shown that enhancing an immune response can be therapeutic, and several clinical trials have been initiated with the aim of boosting immune responses in the CNS of individuals with spinal cord injury, multiple sclerosis and Alzheimer's disease. Here, we evaluate the controversies in the field and discuss the remaining scientific challenges that are associated with enhancing immune function in the CNS to treat neurological diseases.

Vaccine approaches to prevent and treat prion infection : progress and challenges

Prion diseases are transmissible neurodegenerative diseases of humans and animals. The prion agent consists of a misfolded protein, PrPSc (prion protein, scrapie form), of a glycosylphosphatidylinositol-anchored host protein, PrPC (PrP cellular form) of unknown function. During prion replication, PrPSc induces host PrPC to adopt its pathogenic conformation. Some PrPSc may aggregate to microscopically visible, extracellular prion plaques that stain for amyloid. The development of antiprion vaccines presents some challenges. While there is strong self-tolerance to an endogenous antibody response to PrPC and PrPSc, highly potent monoclonal antibodies (mAbs) have been raised in mice in which the prion protein gene has been deleted by gene targeting. These mAbs have been demonstrated to be antiprion-active in permanently scrapie-infected neuroblastoma (ScN2a) cells, primarily when bound to one of four epitopes (the octarepeat region, the region around codons 90-110, helix 1 region codons 145-160, and the extreme C-terminal codons 210-220). The mAbs directed against codon regions 90-110 or 145-160 are also antiprion-active in vivo, but only after intraperitoneal infection with prions, not intracerebral infection, suggesting their blood-brain barrier (BBB) impermeability. The challenge will be to make antibodies, or recombinant derivatives thereof, BBB permeable; this is preferably achieved by monovalent antibody fragments since divalent ones were found to be neurotoxic. Self-tolerance of wild-type animals to PrP immunizations was found to be of extrathymic origin. Even though antibodies raised in wild-type mice were found to display antiprion activity in ScN2a cells, these mice did not have significant extensions of incubation times when challenged intraperitoneally with prions. A general low affinity of these antibody responses to native surface-bound PrPC may account for this. Since wild-type mice were found to develop sufficient T-cell responses to codon regions 145-160 and 210-220, we believe that there is a theoretical chance of a successful vaccination therapy. The influence of the way the immunogen is presented has already been shown to be of major importance for the ensuing immune response, in that presentation of PrP with CpG oligodeoxynucleotides as adjuvant or viral packaging improved antibody responses. Major progress for active immunizations may therefore be expected in this field. Eradication programs will be one of the most important uses of active immunization protocols. For this purpose, vaccines will have to be inexpensive, easy to handle, and effective. In the short term, passive immunizations will likely be most promising for therapy of prion disease, including for human medical interventions. Active immunization protocols are less likely to succeed quickly, and will take years if not decades to be validated for domestic or free-ranging animals.

Antibodies to potato virus Y bind the amyloid beta peptide: immunohistochemical and NMR studies

Studies in transgenic mice bearing mutated human Alzheimer disease (AD) genes show that active vaccination with the amyloid beta (Abeta) protein or passive immunization with anti-Abeta antibodies has beneficial effects on the development of disease. Although a trial of Abeta vaccination in humans was halted because of autoimmune meningoencephalitis, favorable effects on Abeta deposition in the brain and on behavior were seen. Conflicting results have been observed concerning the relationship of circulating anti-Abeta antibodies and AD. Although these autoantibodies are thought to arise from exposure to Abeta, it is also possible that homologous proteins may induce antibody synthesis. We propose that the long-standing presence of anti-Abeta antibodies or antibodies to immunogens homologous to the Abeta protein may produce protective effects. The amino acid sequence of the potato virus Y (PVY) nuclear inclusion b protein is highly homologous to the immunogenic N-terminal region of Abeta. PVY infects potatoes and related crops worldwide. Here, we show through immunocytochemistry, enzyme-linked immunosorbent assay, and NMR studies that mice inoculated with PVY develop antibodies that bind to Abeta in both neuritic plaques and neurofibrillary tangles, whereas antibodies to material from uninfected potato leaf show only modest levels of background immunoreactivity. NMR data show that the anti-PVY antibody binds to Abeta within the Phe4-Ser8 and His13-Leu17 regions. Immune responses generated from dietary exposure to proteins homologous to Abeta may induce antibodies that could influence the normal physiological processing of the protein and the development or progression of AD.

Reducing AD-like pathology in 3xTg-AD mouse model by DNA epitope vaccine - a novel immunotherapeutic strategy

BACKGROUND

The development of a safe and effective AD vaccine requires a delicate balance between providing an adequate anti-Abeta antibody response sufficient to provide therapeutic benefit, while eliminating an adverse T cell-mediated proinflammatory autoimmune response. To achieve this goal we have designed a prototype chemokine-based DNA epitope vaccine expressing a fusion protein that consists of 3 copies of the self-B cell epitope of Abeta(42) (Abeta(1-11)) , a non-self T helper cell epitope (PADRE), and macrophage-derived chemokine (MDC/CCL22) as a molecular adjuvant to promote a strong anti-inflammatory Th2 phenotype.

METHODS AND FINDINGS

We generated pMDC-3Abeta(1-11)-PADRE construct and immunized 3xTg-AD mouse model starting at age of 3-4 months old. We demonstrated that prophylactic immunizations with the DNA epitope vaccine generated a robust Th2 immune response that induced high titers of anti-Abeta antibody, which in turn inhibited accumulation of Abeta pathology in the brains of older mice. Importantly, vaccination reduced glial activation and prevented the development of behavioral deficits in aged animals without increasing the incidence of microhemorrhages.

CONCLUSIONS

Data from this transitional pre-clinical study suggest that our DNA epitope vaccine could be used as a safe and effective strategy for AD therapy. Future safety and immunology studies in large animals with the goal to achieve effective humoral immunity without adverse effects should help to translate this study to human clinical trials.

A two-year study with fibrillar beta-amyloid (Abeta) immunization in aged canines: effects on cognitive function and brain Abeta

Aged canines (dogs) accumulate human-type beta-amyloid (Abeta) in diffuse plaques in the brain with parallel declines in cognitive function. We hypothesized that reducing Abeta in a therapeutic treatment study of aged dogs with preexisting Abeta pathology and cognitive deficits would lead to cognitive improvements. To test this hypothesis, we immunized aged beagles (8.4-12.4 years) with fibrillar Abeta(1-42) formulated with aluminum salt (Alum) for 2.4 years (25 vaccinations). Cognitive testing during this time revealed no improvement in measures of learning, spatial attention, or spatial memory. After extended treatment (22 vaccinations), we observed maintenance of prefrontal-dependent reversal learning ability. In the brain, levels of soluble and insoluble Abeta(1-40) and Abeta(1-42) and the extent of diffuse plaque accumulation was significantly decreased in several cortical regions, with preferential reductions in the prefrontal cortex, which is associated with a maintenance of cognition. However, the amount of soluble oligomers remained unchanged. The extent of prefrontal Abeta was correlated with frontal function and serum anti-Abeta antibody titers. Thus, reducing total Abeta may be of limited therapeutic benefit to recovery of cognitive decline in a higher mammalian model of human brain aging and disease. Immunizing animals before extensive Abeta deposition and cognitive decline to prevent oligomeric or fibrillar Abeta formation may have a greater impact on cognition and also more directly evaluate the role of Abeta on cognition in canines. Alternatively, clearing preexisting Abeta from the brain in a treatment study may be more efficacious for cognition if combined with a second intervention that restores neuron health.

Immunotherapy of malignant brain tumors

Despite aggressive multi-modality therapy including surgery, radiation, and chemotherapy, the prognosis for patients with malignant primary brain tumors remains very poor. Moreover, the non-specific nature of conventional therapy for brain tumors often results in incapacitating damage to surrounding normal brain and systemic tissues. Thus, there is an urgent need for the development of therapeutic strategies that precisely target tumor cells while minimizing collateral damage to neighboring eloquent cerebral cortex. The rationale for using the immune system to target brain tumors is based on the premise that the inherent specificity of immunologic reactivity could meet the clear need for more specific and precise therapy. The success of this modality is dependent on our ability to understand the mechanisms of immune regulation within the central nervous system (CNS), as well as counter the broad defects in host cell-mediated immunity that malignant gliomas are known to elicit. Recent advances in our understanding of tumor-induced and host-mediated immunosuppressive mechanisms, the development of effective strategies to combat these suppressive effects, and a better understanding of how to deliver immunologic effector molecules more efficiently to CNS tumors have all facilitated significant progress toward the realization of true clinical benefit from immunotherapeutic treatment of malignant gliomas.

Neuroprotective and neurotoxic properties of glial cells in the pathogenesis of Alzheimer's disease

Alzheimer's disease (AD) affects more than 18 million people worldwide and is characterized by progressive memory deficits, cognitive impairment and personality changes. The main cause of AD is generally attributed to the increased production and accumulation of amyloid-β (Aβ), in association with neurofibrillary tangle (NFT) formation. Increased levels of pro-inflammatory factors such as cytokines and chemokines, and the activation of the complement cascade occurs in the brains of AD patients and contributes to the local inflammatory response triggered by senile plaque. The existence of an inflammatory component in AD is now well known on the basis of epidemiological findings showing a reduced prevalence of the disease upon long-term medication with anti-inflammatory drugs, and evidence from studies of clinical materials that shows an accumulation of activated glial cells, particularly microglia and astrocytes, in the same areas as amyloid plaques. Glial cells maintain brain plasticity and protect the brain for functional recovery from injuries. Dysfunction of glial cells may promote neurodegeneration and, eventually, the retraction of neuronal synapses, which leads to cognitive deficits. The focus of this review is on glial cells and their diversity properties in AD.

Enhanced Th2 immunity after DNA prime-protein boost immunization with amyloid beta (1-42) plus CpG oligodeoxynucleotides in aged rats

Generation and accumulation of fibrillar amyloid beta (Abeta) is widely considered as the pathogenic basis of neurodegeneration in Alzheimer's disease (AD). Both active immunization with fibrillar Abeta and passive immunization with anti-Abeta antibodies in transgenic mouse models of AD result in prevention/dissociation of Abeta plaque formation and restoration of cognitive functions. However, similar immunization studies in humans had to be halted because 6% of the AD patients developed acute meningoencephalitis, likely due to anti-Abeta specific autoimmune Th1 cells. Hence, making Abeta immunotherapy successful requires production of strong antibody responses without Th1-type immunity. In an attempt to develop safer vaccines, we examined the influence of oligodeoxynucleotides as adjuvant on the Th1 and Th2 immune response to Abeta in aged rats. We further investigated whether a DNA prime-protein boost strategy could elicit a more robust Th2 response. The results of the present study showed that all the animals injected with either Abeta peptide alone or Abeta encoding plasmid alone or plasmid DNA prime followed by peptide boost have elicited specific anti-Abeta antibodies. When co-administered, synthetic oligodeoxynucleotides (ODN) further enhanced the anti-Abeta titres. More importantly, the IgG subclasses of the antibodies generated by DNA prime-peptide boost regimen with ODN as adjuvant were primarily of IgG2b and IgG1 isotypes, suggesting that heterologous immunization strategy along with ODN would be advantageous in eliciting more beneficial Th2-type humoral immune response.

Reduced pathology and improved behavioral performance in Alzheimer's disease mice vaccinated with HSV amplicons expressing amyloid-beta and interleukin-4

Immunotherapeutics designed to dissolve existing amyloid plaques or to interrupt amyloid-beta (Abeta) accumulation may be feasible for treatment and/or prevention of Alzheimer's disease (AD). "Shaping" the immune responses elicited against Abeta is requisite toward generating an efficacious and safe outcome; this can be achieved by minimizing the possibility of deleterious inflammatory reactions in the brain as observed in clinical testing of Abeta peptide/adjuvant-based modalities. Herpes simplex virus (HSV)-based amplicons can coexpress multiple antigens and/or immunomodulatory genes due to their large genetic size capacity, thereby facilitating antigen-specific immune response shaping. We have constructed an amplicon (HSV(IE)Abeta(CMV)IL-4) that co-delivers Abeta(1-42) with interleukin-4 (IL-4), a cytokine that promotes the generation of Th2-like T-cell responses, which are favored in the setting of AD immunotherapy. Triple-transgenic AD (3xTg-AD) mice, which progressively develop both amyloid and neurofibrillary tangle pathology, were vaccinated thrice with HSV(IE)Abeta(CMV)IL-4, or a set of control amplicon vectors. Increased Th2-related, Abeta-specific antibodies, improved learning and functioning of memory, and prevention of AD-related amyloid and tau pathological progression were observed significantly more in the HSV(IE)Abeta(CMV)IL-4 vaccinated mice as compared to the other experimental groups. Our study underscores the potential of Abeta immunotherapy for AD and highlights the potency of amplicons in facilitating the immune response modulation to a disease-relevant antigen.

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

BACKGROUND

In a phase 2a clinical trial of AN1792 (Study 201), a potential immunotherapeutic agent for use in Alzheimer's disease (AD), approximately 6% of the treated AD patients (18/300) developed meningoencephalitis (ME).

OBJECTIVE

To elucidate potential immune mechanisms of treatment-induced ME.

METHODS

Peripheral blood mononuclear cells obtained from patients who received AN1792 were stimulated in vitro either with beta-amyloid (Abeta) or various overlapping peptides of Abeta(1-42), followed by quantification of cytokine-secreting cells by enzyme-linked immunosorbent spot assay.

RESULTS

A significant difference in the quality of the T-cell responses between patients in Study 201 and those in earlier studies of AN1792 was noted. T-cell responses specific to the carboxy terminus of Abeta elicited from patients' peripheral blood mononuclear cells in an earlier multiple dose study (Study 102) were Th2 biased, while those from Study 201 were biased toward a proinflammatory Th1 response. Antibody responses in both studies were quantitatively and qualitatively similar (as determined by epitope mapping). The addition of polysorbate 80 to the formulation used in Study 201 is the most likely explanation for the difference in the T-cell response.

CONCLUSION

ME following injection of AN1792 may be related to immune response differences driven by a formulation change. To address this, a novel peptide-carrier protein conjugate using an amino-terminal fragment of Abeta (ACC-001) has been developed to avoid potentially harmful T-cell responses, while maintaining a similar antibody response to that of AN1792. Immunotherapeutic trials using this treatment approach in AD patients are in progress.

Plasma antibodies to Abeta40 and Abeta42 in patients with Alzheimer's disease and normal controls

Antibodies to amyloid beta protein (Abeta) are present naturally or after Abeta vaccine therapy in human plasma. To clarify their clinical role, we examined plasma samples from 113 patients with Alzheimer's disease (AD) and 205 normal controls using the tissue amyloid plaque immunoreactivity (TAPIR) assay. A high positive rate of TAPIR was revealed in AD (45.1%) and age-matched controls (41.2%), however, no significance was observed. No significant difference was observed in the MMS score or disease duration between TAPIR-positive and negative samples. TAPIR-positive plasma reacted with the Abeta40 monomer and dimer, and the Abeta42 monomer weakly, but not with the Abeta42 dimer. TAPIR was even detected in samples from young normal subjects and young Tg2576 transgenic mice. Although the Abeta40 level and Abeta40/42 ratio increased, and Abeta42 was significantly decreased in plasma from AD groups when compared to controls, no significant correlations were revealed between plasma Abeta levels and TAPIR grading. Thus an immune response to Abeta40 and immune tolerance to Abeta42 occurred naturally in humans without a close relationship to the Abeta burden in the brain. Clarification of the mechanism of the immune response to Abeta42 is necessary for realization of an immunotherapy for AD.

Developing preventive therapies for chronic diseases: lessons learned from Alzheimer's disease

A remarkable rise in life expectancy during the past century has made Alzheimer's disease (AD) the most common form of progressive intellectual failure in humans. Patients with AD lose their most human qualities-reasoning, abstraction, language, and memory. The brain plaques that Alois Alzheimer first described 100 years ago have inspired the search for genetic alterations that underlie AD. Four genes have been unequivocally implicated to date in inherited forms of AD, where mutations or natural variations in these genes cause excessive accumulation of the amyloid beta-protein, the building block of amyloid plaques. This aggregation leads to subsequent neuronal degeneration in brain regions important for memory and cognition. The discovery of the genes involved in the mechanisms of amyloid beta-protein build-up in AD, coupled with cell culture and animal models of their involved pathways, has led to the development of specific pharmacological strategies to lower amyloid beta-protein levels as a way of treating or preventing all forms of the disease. While hard work lies ahead, the movement from basic research to the clinic in AD represents a triumph of reductionist biology applied to the most complex of all biological systems, the human cerebral cortex.