The generation and characterization of potentially therapeutic Abeta antibodies in mice: differences according to strain and immunization protocol

Development of an anti-tauopathy mucosal vaccine specifically targeting pathologic conformers

Alzheimer's disease (AD) and related tauopathies are associated with pathological tau protein aggregation, which plays an important role in neurofibrillary degeneration and dementia. Targeted immunotherapy to eliminate pathological tau aggregates is known to improve cognitive deficits in AD animal models. The tau repeat domain (TauRD) plays a pivotal role in tau-microtubule interactions and is critically involved in the aggregation of hyperphosphorylated tau proteins. Because TauRD forms the structural core of tau aggregates, the development of immunotherapies that selectively target TauRD-induced pathological aggregates holds great promise for the modulation of tauopathies. In this study, we generated recombinant TauRD polypeptide that form neurofibrillary tangle-like structures and evaluated TauRD-specific immune responses following intranasal immunization in combination with the mucosal adjuvant FlaB. In BALB/C mice, repeated immunizations at one-week intervals induced robust TauRD-specific antibody responses in a TLR5-dependent manner. Notably, the resulting antiserum recognized only the aggregated form of TauRD, while ignoring monomeric TauRD. The antiserum effectively inhibited TauRD filament formation and promoted the phagocytic degradation of TauRD aggregate fragments by microglia. The antiserum also specifically recognized pathological tau conformers in the human AD brain. Based on these results, we engineered a built-in flagellin-adjuvanted TauRD (FlaB-TauRD) vaccine and tested its efficacy in a P301S transgenic mouse model. Mucosal immunization with FlaB-TauRD improved quality of life, as indicated by the amelioration of memory deficits, and alleviated tauopathy progression. Notably, the survival of the vaccinated mice was dramatically extended. In conclusion, we developed a mucosal vaccine that exclusively targets pathological tau conformers and prevents disease progression.

Monoclonal antibodies against Aβ42 fibrils distinguish multiple aggregation state polymorphisms in vitro and in Alzheimer disease brain

Amyloidogenic proteins generally form intermolecularly hydrogen-bonded β-sheet aggregates, including parallel, in-register β-sheets (recognized by antiserum OC) or antiparallel β-sheets, β-solenoids, β-barrels, and β-cylindrins (recognized by antiserum A11). Although these groups share many common properties, some amyloid sequences have been reported to form polymorphic structural variants or strains. We investigated the humoral immune response to Aβ42 fibrils and produced 23 OC-type monoclonal antibodies recognizing distinct epitopes differentially associated with polymorphic structural variants. These mOC antibodies define at least 18 different immunological profiles represented in aggregates of amyloid-β (Aβ). All of the antibodies strongly prefer amyloid aggregates over monomer, indicating that they recognize conformational epitopes. Most of the antibodies react with N-terminal linear segments of Aβ, although many recognize a discontinuous epitope consisting of an N-terminal domain and a central domain. Several of the antibodies that recognize linear Aβ segments also react with fibrils formed from unrelated amyloid sequences, indicating that reactivity with linear segments of Aβ does not mean the antibody is sequence-specific. The antibodies display strikingly different patterns of immunoreactivity in Alzheimer disease and transgenic mouse brain and identify spatially and temporally unique amyloid deposits. Our results indicate that the immune response to Aβ42 fibrils is diverse and reflects the structural polymorphisms in fibrillar amyloid structures. These polymorphisms may contribute to differences in toxicity and consequent effects on pathological processes. Thus, a single therapeutic monoclonal antibody may not be able to target all of the pathological aggregates necessary to make an impact on the overall disease process.

Immunization therapy in Alzheimer's disease

Alzheimer's disease (AD) is a common and devastating neurodegenerative disease. The incidence of AD is increasing in Western societies. The current treatment of AD is mostly symptomatic and ineffective in stopping or reversing the cognitive impairment. One of the exciting and effective new treatments developed in experimental AD is immunization against amyloid-beta peptide. This article provides an overview of immunization therapy in AD and examines the future prospects of this therapeutic modality.

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.

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.

Amyloid beta-HSP60 peptide conjugate vaccine treats a mouse model of Alzheimer's disease

Active vaccination with amyloid beta peptide (Aβ) to induce beneficial antibodies was found to be effective in mouse models of Alzheimer's disease (AD), but human vaccination trials led to adverse effects, apparently caused by exuberant T-cell reactivity. Here, we sought to develop a safer active vaccine for AD with reduced T-cell activation. We treated a mouse model of AD carrying the HLA-DR DRB1*1501 allele, with the Aβ B-cell epitope (Aβ 1-15) conjugated to the self-HSP60 peptide p458. Immunization with the conjugate led to the induction of Aβ-specific antibodies associated with a significant reduction of cerebral amyloid burden and of the accompanying inflammatory response in the brain; only a mild T-cell response specific to the HSP peptide but not to the Aβ peptide was found. This type of vaccination, evoking a gradual increase in antibody titers accompanied by a mild T-cell response is likely due to the unique adjuvant and T-cell stimulating properties of the self-HSP peptide used in the conjugate and might provide a safer approach to effective AD vaccination.

Genetic background modifies neurodegeneration and neuroinflammation driven by misfolded human tau protein in rat model of tauopathy: implication for immunomodulatory approach to Alzheimer's disease

Background

Numerous epidemiological studies demonstrate that genetic background modifies the onset and the progression of Alzheimer's disease and related neurodegenerative disorders. The efficacious influence of genetic background on the disease pathway of amyloid beta has been meticulously described in rodent models. Since the impact of genetic modifiers on the neurodegenerative and neuroinflammatory cascade induced by misfolded tau protein is yet to be elucidated, we have addressed the issue by using transgenic lines expressing the same human truncated tau protein in either spontaneously hypertensive rat (SHR) or Wistar-Kyoto (WKY) genetic background.

Methods

Brains of WKY and SHR transgenic rats in the terminal stage of phenotype and their age-matched non-transgenic littermates were examined by means of immunohistochemistry and unbiased stereology. Basic measures of tau-induced neurodegeneration (load of neurofibrillary tangles) and neuroinflammation (number of Iba1-positive microglia, their activated morphology, and numbers of microglia immunoreactive for MHCII and astrocytes immunoreactive for GFAP) were quantified with an optical fractionator in brain areas affected by neurofibrillary pathology (pons, medulla oblongata). The stereological data were evaluated using two-way ANOVA and Student's t-test.

Results

Tau neurodegeneration (neurofibrillary tangles (NFTs), axonopathy) and neuroinflammation (microgliosis, astrocytosis) appeared in both WKY and SHR transgenic rats. Although identical levels of transgene expression in both lines were present, terminally-staged WKY transgenic rats displayed significantly lower final NFT loads than their SHR transgenic counterparts. Interestingly, microglial responses showed a striking difference between transgenic lines. Only 1.6% of microglia in SHR transgenic rats expressed MHCII in spite of having a robust phagocytic phenotype, whereas in WKY transgenic rats, 23.2% of microglia expressed MHCII despite displaying a considerably lower extent of transformation into phagocytic phenotype.

Conclusions

These results show that the immune response represents a pivotal and genetically variable modifying factor that is able to influence vulnerability to neurodegeneration. Therefore, targeted immunomodulation could represent a prospective therapeutic approach to Alzheimer's disease.

Virus-like peptide vaccines against Abeta N-terminal or C-terminal domains reduce amyloid deposition in APP transgenic mice without addition of adjuvant

Immunotherapy against the Abeta peptide is increasingly viewed as an effective means of preventing and even decreasing Abeta deposition in transgenic mouse models and human cases of Alzheimer's disease. A prior active immunization trial was halted due to adverse events which occurred subsequent to a change in the adjuvant used in the vaccine preparation. Although widely used in experimental studies, adjuvants available for use in vaccines intended for humans are limited. We compared two vaccine preparations in which an immunogenic bacteriophage was conjugated with either an N-terminal (Abeta1-9) or C-terminal (Abeta28-40) peptide sequence from the Abeta molecule. We found that both produced significant antibody titers without use of additional adjuvants. Surprisingly, the response to the N terminal sequence was comprised largely of a stable IgM response, while the C-terminal vaccine produced an IgG response with minimal IgM reactivity. Both of these immunogens reduced Abeta levels when tissues were examined 8 months after the first inoculation. These data demonstrate that (a) C-terminal specific vaccines can effectively lower Abeta and (b) IgM antibodies against Abeta may be capable of lowering Abeta, possibly through action in the brain rather than the periphery.

HLA-DR alleles in amyloid beta-peptide autoimmunity: a highly immunogenic role for the DRB1*1501 allele

Active amyloid beta-peptide (Abeta) immunization of patients with Alzheimer's disease (AD) caused meningoencephalitis in approximately 6% of immunized patients in a clinical trial. In addition, long-term studies of AD patients show varying degrees of Abeta Ab responses, which correlate with the extent of Abeta clearance from the brain. In this study, we examined the contribution of various HLA-DR alleles to these immune-response variations by assessing Abeta T cell reactivity, epitope specificity, and immunogenicity. Analysis of blood samples from 133 individuals disclosed that the abundant DR haplotypes DR15 (found in 36% of subjects), DR3 (in 18%), DR4 (12.5%), DR1 (11%), and DR13 (8%) were associated with Abeta-specific T cell responses elicited via distinct T cell epitopes within residues 15-42 of Abeta. Because the HLA-DRB1*1501 occurred most frequently, we examined the effect of Abeta challenge in humanized mice bearing this allele. The observed T cell response was remarkably strong, dominated by secretion of IFN-gamma and IL-17, and specific to the same T cell epitope as that observed in the HLA-DR15-bearing humans. Furthermore, following long-term therapeutic immunization of an AD mouse model bearing the DRB1*1501 allele, Abeta was effectively cleared from the brain parenchyma and brain microglial activation was reduced. The present study thus characterizes HLA-DR alleles directly associated with specific Abeta T cell epitopes and demonstrates the highly immunogenic properties of the abundant allele DRB1*1501 in a mouse model of AD. This new knowledge enables us to explore the basis for understanding the variations in naturally occurring Abeta-reactive T cells and Abeta immunogenicity among humans.

Preparation, physiochemical characterization, and oral immunogenicity of Abeta(1-12), Abeta(29-40), and Abeta(1-42) loaded PLG microparticles formulations

Alzheimer's disease (AD) is caused by the deposition of beta-amyloid (Abeta) protein in brain. The current AD immunotherapy aims to prevent Abeta plaque deposition and enhance its degradation in the brain. In this work, the peptides B-cell epitope Abeta(1-12), T-cell epitope Abeta(29-40) and full-length Abeta(1-42) were loaded separately to the poly (D,L-lactide co-glycolide) (PLG) microparticles by using W/O/W double emulsion solvent evaporation method with entrapment efficacy of 70.46%, 60.93%, and 65.98%, respectively. The prepared Abeta PLG microparticles were smooth, spherical, individual, and nonporous in nature with diameters ranging from 2 to 12 microm. The cumulative in vitro release profiles of Abeta(1-12), Abeta(29-40), and Abeta(1-42) from PLG microparticles sustained for long periods and progressively reached to 73.89%, 69.29%, and 70.08% by week 15. In vitro degradation studies showed that the PLG microparticles maintained the surface integrity up to week 8 and eroded completely by week 16. Oral immunization of Abeta peptides loaded microparticles in mice elicited stronger immune response by inducing anti-Abeta antibodies for prolonged time (24 weeks). The physicochemical characterization and immunogenic potency of Abeta peptides incorporated PLG microparticles suggest that the microparticles formulation of Abeta can be a potential oral AD vaccine.

Prevention of age-associated dementia

The advancement of medical sciences during the last century has resulted in a considerable increase in life expectancy. As more people live to old age, one of the most fundamental questions of the 21st century is whether the number of individuals suffering from dementia will also continue to increase. Alzheimer's disease (AD) accounts for the majority of cases of dementia in the elderly, but there is currently no curative treatment available. Several strategies have been introduced for treatment, the most recent strategy of which was the immunization of patients using antibodies against Abeta, which is a naturally occurring, even though misfolded peptide in the AD brain. Both active and passive immunization routes have been shown to reduce the pathology associated with Abeta accumulation in brains of genetically designed animal models. However, despite tremendous efforts, no unequivocal proof of therapeutic efficacy could be shown in AD patients. Particularly, the persistence of the neurofibrillary tangles in immunized brains and the issue of inducing cerebral amyloid angiopathy are major limiting factors of antibody therapy. Furthermore, physical activity, a healthy immune system and nutritional habits are suggested to protect against the onset of age-associated dementia. Thus, accumulative evidence suggests that an early integrated strategy, combining pharmacological, immunological, nutritional and life-style factors, is the most pragmatic approach to delay the onset and progression of age-associated dementia.

Intramembranous fragment of amyloid-beta: A potential immunogen for Alzheimer's disease immunotherapy

Immunotherapy holds great promise for Alzheimer's disease (AD), but meningoencephalitis observed in the first AD vaccination trial, which accompanied T-lymphocytic infiltration, needs to be overcome. This study was aimed to investigate alternative approaches for a safer vaccine to treat AD. We used intramembranous fragment of amyloid-beta (IF-Abeta) to immunize Kunming mice for up to 2.5 months and then evaluated the immunization efficacy and potential adverse effects. Immunization of mice with IF-Abeta plus Freund's adjuvant resulted in moderate levels of Abeta antibodies (IgG), and the anti-sera were able to neutralize Abeta1-42-neurotoxicity in cultured primary cortical neurons. IF-Abeta itself did not show neurotoxicity, and immunization with IF-Abeta did not cause behavioral deficits in Morris water maze or any abnormalities by histological examinations of major organs including the brain. We conclude that vaccination with IF-Abeta may be a potentially safe and effective treatment for AD.

Immunotherapy as treatment for Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that is characterized pathologically by the deposition of beta-amyloid (A beta)-containing extracellular neuritic plaques, intracellular neurofibrillary tangles and neuronal loss. Much evidence supports the hypothesis that A beta peptide aggregation contributes to AD pathogenesis, however, currently approved therapeutic treatments do nothing to stop or reverse A beta deposition. The success of active and passive anti-A beta immunotherapies in both preventing and clearing parenchymal amyloid in transgenic mouse models led to the initiation of an active anti-A beta vaccination (AN1792) trial in human patients with mild-to-moderate AD, but was prematurely halted when 6% of inoculated patients developed aseptic meningoencephalitis. Autopsy results from the brains of four individuals treated with AN1792 revealed decreased plaque burden in select brain areas, as well as T-cell lymphocytes in three of the patients. Furthermore, antibody responders showed some improvement in memory task measures. These findings indicated that anti-A beta therapy might still be a viable option for the treatment of AD, if potentially harmful proinflammatory processes can be avoided. Over the past 6 years, this target has led to the development of novel experimental immunization strategies, including selective A beta epitope targeting, antibody and adjuvant modifications, as well as alternative routes and mechanisms of vaccine delivery, to generate anti-A beta antibodies that selectively target and remove specific A beta species without evoking autoimmunity. Results from the passive vaccination AD clinical trials that are currently underway will provide invaluable information about both the effectiveness of newly improved anti-A beta vaccines in clinical treatment, as well as the role of the A beta peptide in the pathogenesis of the disease.

Dendrimeric Aβ1–15 is an effective immunogen in wildtype and APP-tg mice

Immunization of humans and APP-tg mice with full-length beta-amyloid (Abeta) results in reduced cerebral Abeta levels. However, due to adverse events in the AN1792 trial, alternative vaccines are required. We investigated dendrimeric Abeta1-15 (dAbeta1-15), which is composed of 16 copies of Abeta1-15 peptide on a branched lysine core and thus, includes an Abeta-specific B cell epitope but lacks the reported T cell epitope. Immunization by subcutaneous, transcutaneous, and intranasal routes of B6D2F1 wildtype mice led to anti-Abeta antibody production. Antibody isotypes were mainly IgG1 for subcutaneous or transcutaneous immunization and IgG2b for intranasal immunization, suggestive of a Th2-biased response. All Abeta antibodies preferentially recognized an epitope in Abeta1-7. Intranasal immunization of J20 APP-tg mice resulted in a robust humoral immune response with a corresponding significant reduction in cerebral plaque burden. Splenocyte proliferation against Abeta peptide was minimal indicating the lack of an Abeta-specific cellular immune response. Anti-Abeta antibodies bound monomeric, oligomeric, and fibrillar Abeta. Our data suggest that dAbeta1-15 may be an effective and potentially safer immunogen for Alzheimer's disease (AD) vaccination.

In vivo targeting of antibody fragments to the nervous system for Alzheimer’s disease immunotherapy and molecular imaging of amyloid plaques

Targeting therapeutic or diagnostic proteins to the nervous system is limited by the presence of the blood-brain barrier. We report that a F(ab')(2) fragment of a monoclonal antibody against fibrillar human Abeta42 that is polyamine (p)-modified has increased permeability at the blood-brain barrier, comparable binding to the antigen, and comparable in vitro binding to amyloid plaques in Alzheimer's disease (AD) transgenic mouse brain sections. Intravenous injection of the pF(ab')(2)4.1 in the AD transgenic mouse demonstrated efficient targeting to amyloid plaques throughout the brain, whereas the unmodified fragment did not. Removal of the Fc portion of this antibody derivative will minimize the inflammatory response and cerebral hemorrhaging associated with passive immunization and provide increased therapeutic potential for treating AD. Coupling contrast agents/radioisotopes might facilitate the molecular imaging of amyloid plaques with magnetic resonance imaging/positron emission tomography. The efficient delivery of immunoglobulin G fragments may also have important applications to other neurodegenerative disorders or for the generalized targeting of nervous system antigens.

Vessel ultrastructure in APP23 transgenic mice after passive anti-Aβ immunotherapy and subsequent intracerebral hemorrhage

Passive immunization of amyloid precursor protein (APP) transgenic mice with anti-amyloid beta (Abeta) antibodies was shown to reduce Abeta-deposition in brain and to improve cognition. However, immunotherapy may also be accompanied by a significant increase in the frequency of intracerebral hemorrhages. Because hemorrhages are associated with amyloid-laden vessels, this raises the question whether high concentrations of anti-Abeta antibodies may directly or indirectly lead to a structural destabilization of the vessel wall. To address this point, transmission electron microscopy was performed and the ultrastructure of bleeding and non-bleeding vessels in immunized and non-immunized APP23 transgenic animals was analyzed. To localize bleeding vessels, hemosiderin-positive macrophages were visualized by pre-embedding Perl's Berlin Blue histochemistry. Vessels were analyzed morphologically, anomalies evaluated and quantified. Bleeding vessels were, furthermore, reconstructed in three dimensions to analyze the spatial distribution of amyloid deposits and other pathological changes of the vessel wall. This in-depth morphological analysis revealed that bleeding vessels in immunized as well as in non-immunized APP23 mice were surrounded by a higher number of macrophages compared to non-bleeding vessels in the same animals. However, no differences in the number of macrophages or other structural parameters, such as amyloid deposition, were observed between bleeding vessels of immunized and non-immunized mice. No pathologies which may indicate impending bleeding were observed in the vascular wall of non-bleeding vessels. We conclude, that the increased hemorrhage frequency observed after passive immunization with anti-Abeta antibodies does not lead to overt structural changes in the vessel wall of APP23 transgenic mice. Minor structural alterations of the vessel wall, however, cannot be excluded due to the sample size of our study and the high complexity of the three-dimensional vessel wall ultrastructure.

Conformation-sensitive antibodies against alzheimer amyloid-beta by immunization with a thioredoxin-constrained B-cell epitope peptide

Immunotherapy against the amyloid-beta (Abeta) peptide is a valuable potential treatment for Alzheimer disease (AD). An ideal antigen should be soluble and nontoxic, avoid the C-terminally located T-cell epitope of Abeta, and yet be capable of eliciting antibodies that recognize Abeta fibrils and neurotoxic Abeta oligomers but not the physiological monomeric species of Abeta. We have described here the construction and immunological characterization of a recombinant antigen with these features obtained by tandem multimerization of the immunodominant B-cell epitope peptide Abeta1-15 (Abeta15) within the active site loop of bacterial thioredoxin (Trx). Chimeric Trx(Abeta15)n polypeptides bearing one, four, or eight copies of Abeta15 were constructed and injected into mice in combination with alum, an adjuvant approved for human use. All three polypeptides were found to be immunogenic, yet eliciting antibodies with distinct recognition specificities. The anti-Trx(Abeta15)4 antibody, in particular, recognized Abeta42 fibrils and oligomers but not monomers and exhibited the same kind of conformational selectivity against transthyretin, an amyloidogenic protein unrelated in sequence to Abeta. We have also demonstrated that anti-Trx(Abeta15)4, which binds to human AD plaques, markedly reduces Abeta pathology in transgenic AD mice. The data indicate that a conformational epitope shared by oligomers and fibrils can be mimicked by a thioredoxin-constrained Abeta fragment repeat and identify Trx(Abeta15)4 as a promising new tool for AD immunotherapy.

Vaccination Strategies for Alzheimer???s Disease

The pathological hallmarks of Alzheimer's disease (AD) include beta-amyloid (Abeta) plaques, dystrophic neurites and neurofibrillary pathology, which eventually result in the degeneration of neurons and subsequent dementia. In 1999, international interest in a new therapeutic approach to the treatment of AD was ignited following transgenic mouse studies that indicated that it might be possible to immunise against the pathological alterations in Abeta that lead to aggregation of this protein in the brain. A subsequent phase I human trial for safety, tolerability and immunogenicity using an active immunisation strategy against Abeta had a positive outcome. However, phase IIA human trials involving active immunisation were halted following the diagnosis of aseptic meningoencephalitis in 6% of immunised subjects. Research into immunisation strategies involving transgenic AD mouse models has subsequently been refocused to determine the mechanisms by which plaque clearance and reduced memory deficits are attained, and to establish safer therapeutic approaches that may reduce potentially harmful brain inflammation. The vigour of international research on immunotherapy for AD provides significant hope for a strong therapeutic lead for the escalating number of individuals who will develop this otherwise incurable condition.

Amelioration of amyloid load by anti-Abeta single-chain antibody in Alzheimer mouse model

Parenteral immunization of transgenic mouse models of Alzheimer disease (AD) with synthetic amyloid beta-peptide (Abeta) prevented or reduced Abeta deposits and attenuated their memory and learning deficits. A clinical trial of immunization with synthetic Abeta, however, was halted due to brain inflammation, presumably induced by a toxic Abeta, T-cell- and/or Fc-mediated immune response. Another issue relating to such immunizations is that some AD patients may not be able to raise an adequate immune response to Abeta vaccination due to immunological tolerance or age-associated decline. Because peripheral administration of antibodies against Abeta also induced clearance of amyloid plaques in the model mice, injection of humanized Abeta antibodies has been proposed as a possible therapy for AD. By screening a human single-chain antibody (scFv) library for Abeta immunoreactivity, we have isolated a scFv that specifically reacts with oligomeric Abeta as well as amyloid plaques in the brain. The scFv inhibited Abeta amyloid fibril formation and Abeta-mediated cytotoxicity in vitro. We have tested the efficacy of the human scFv in a mouse model of AD (Tg2576 mice). Relative to control mice, injections of the scFv into the brain of Tg2576 mice reduced Abeta deposits. Because scFvs lack the Fc portion of the immunoglobulin molecule, human scFvs against Abeta may be useful to treat AD patients without eliciting brain inflammation.

Boosting with intranasal dendrimeric Abeta1-15 but not Abeta1-15 peptide leads to an effective immune response following a single injection of Abeta1-40/42 in APP-tg mice

Background

Immunotherapy for Alzheimer's disease (AD) is emerging as a potential treatment. However, a clinical trial (AN1792) was halted after adverse effects occurred in a small subset of subjects, which may have been caused by a T cell-mediated immunological response. In general, aging limits the humoral immune response, therefore, immunogens and vaccination regimes are required that induce a strong antibody response with less potential for an adverse immune response.

Method

In the current study, we immunized both wildtype and J20 APP-tg mice with a priming injection of Aβ1–40/42, followed by multiple intranasal boosts with the novel immunogen dAβ1–15 (16 copies of Aβ1–15 on a lysine tree), Aβ1–15 peptide or Aβ1–40/42 full length peptide.

Results

J20 APP-tg mice primed with Aβ1–40/42 subcutaneously and subsequently boosted intranasally with Aβ1–15 peptide did not generate a cellular or humoral immune response. In contrast, J20 APP-tg mice boosted intranasally with dAβ1–15 or full length Aβ1–40/42 produced high levels of anti-Aβ antibodies. Splenocyte proliferation was minimal in mice immunized with dAβ1–15. Wildtype littermates of the J20 APP-tg mice produced higher amounts of anti-Aβ antibodies compared to APP-tg mice but also had low T cell proliferation. The anti-Aβ antibodies were mainly composed of IgG2b and directed to an epitope within the Aβ1–7 region, regardless of the immunogen. Examination of the brain showed a significant reduction in Aβ plaque burden in the J20 APP-tg mice producing antibodies compared to controls. Biochemically, Aβ40 or Aβ42 were also reduced in brain homogenates and elevated in plasma but the changes did not reach significance.

Conclusion

Our results demonstrate that priming with full length Aβ40/42 followed by boosting with dAβ1–15 but not Aβ1–15 peptide led to a robust humoral immune response with a minimal T cell response in J20 APP-tg mice. In addition, Aβ plaque burden was reduced in mice producing anti-Aβ antibodies. Interestingly, wildtype mice produced higher levels of anti-Aβ antibodies, indicating that immune tolerance may be present in J20 APP-tg mice. Together, these data suggest that dAβ1–15 but not Aβ1–15 peptide may be useful as a boosting immunogen in an AD vaccination regime.

Role of fibrillar Abeta25-35 in the inflammation induced rat model with respect to oxidative vulnerability

The major pathological ramification of Alzheimer's disease (AD) is accumulation of beta-Amyloid (Abeta) peptides in the brain. An emerging therapeutic approach for AD is elimination of excessive Ass peptides and preventing its re-accumulation. Immunization is the most effective strategy in removing preexisting cerebral Abetas and improving the cognitive capacity as shown in transgenic mice model of AD. However, active immunization is associated with adverse effect such as encephalitis with perivascular inflammation and hemorrhage. Details about the mechanistic aspects of propagation of these toxic effects are matter of intense enquiry as this knowledge is essential for the understanding of the AD pathophysiology. The present work aimed to study the oxidative vulnerability in the plasma, liver and brain of the inflammation-induced rats subjected to Ass immunization. Induction of inflammation was performed by subcutaneous injection of 0.5?ml of 2% silver nitrate. Our present result shows that the proinflammatory cytokines such as IL1alpha and TNFalpha are increased significantly in the inflammation-induced, Abeta1-42, Abeta25-35 treated groups and inflammation with Abeta25-35 treated group when compared to control, complete Freund's adjuvant and Abeta35-25 treated groups. These increased proinflammatory cytokines concurrently releases significant amount of free radicals in the astrocytes of respected groups. The present result shows that nitric oxide (NO) level was significantly higher (P<0.001) in plasma, liver and brain of the rat subjected to inflammation, Abeta1-42, Abeta25-35 and inflammation with Abeta25-35 injected groups when compared to control. The increased level of lipid peroxides (LPO) (P<0.001) and decreased antioxidant status (P<0.05) were observed in the plasma, liver and brain of inflammation-induced group when compared to control. Our result shows that significant oxidative vulnerability was observed in the inflammation with Ass treated rats when compared to other groups. Based on our results, we suggest that immunization of AD patients with Ass should be done with caution as the increase in Ass could trigger the brain inflammation in uncontrollable level.

Abeta-induced meningoencephalitis is IFN-gamma-dependent and is associated with T cell-dependent clearance of Abeta in a mouse model of Alzheimer's disease

Vaccination against amyloid beta-peptide (Abeta) has been shown to be successful in reducing Abeta burden and neurotoxicity in mouse models of Alzheimer's disease (AD). However, although Abeta immunization did not show T cell infiltrates in the brain of these mice, an Abeta vaccination trial resulted in meningoencephalitis in 6% of patients with AD. Here, we explore the characteristics and specificity of Abeta-induced, T cell-mediated encephalitis in a mouse model of the disease. We demonstrate that a strong Abeta-specific T cell response is critically dependent on the immunizing T cell epitope and that epitopes differ depending on MHC genetic background. Moreover, we show that a single immunization with the dominant T cell epitope Abeta10-24 induced transient meningoencephalitis only in amyloid precursor protein (APP)-transgenic (Tg) mice expressing limited amounts of IFN-gamma under an myelin basic protein (MBP) promoter. Furthermore, immune infiltrates were targeted primarily to sites of Abeta plaques in the brain and were associated with clearance of Abeta. Immune infiltrates were not targeted to the spinal cord, consistent with what was observed in AD patients vaccinated with Abeta. Using primary cultures of microglia, we show that IFN-gamma enhanced clearance of Abeta, microglia, and T cell motility, and microglia-T cell immunological synapse formation. Our study demonstrates that limited expression of IFN-gamma in the brain, as observed during normal brain aging, is essential to promote T cell-mediated immune infiltrates after Abeta immunization and provides a model to investigate both the beneficial and detrimental effects of Abeta-specific T cells.

Induction of anti-inflammatory immune response by an adenovirus vector encoding 11 tandem repeats of Abeta1-6: toward safer and effective vaccines against Alzheimer's disease

Induction of an immune response to amyloid beta-protein (Abeta) is effective in treating animal models of Alzheimer's disease. Human clinical trials of vaccination with synthetic Abeta (AN1792), however, were halted due to brain inflammation, presumably induced by T cell-mediated immune responses. We have developed an adenovirus vector as a "possibly safer" vaccine. Here, we show that an adenovirus vector encoding 11 tandem repeats of Abeta1-6 can induce an immune response against amyloid beta-protein. Much higher titers against amyloid beta-protein were observed when an adenovirus vector encoding GM-CSF was co-administered. Immunoglobulin isotyping revealed a predominant IgG1 response, indicating anti-inflammatory Th2 type. Immunohistochemical analysis revealed no inflammation-related pathology in the brain of mice immunized with the adenovirus vector. Induced antibodies strongly reacted with amyloid plaques in the brain, demonstrating functional activity of the antibodies. Thus, the adenovirus vector encoding 11 tandem repeats of Abeta1-6 may be a safer alterative to peptide-based vaccines.

Exacerbation of cerebral amyloid angiopathy-associated microhemorrhage in amyloid precursor protein transgenic mice by immunotherapy is dependent on antibody recognition of deposited forms of amyloid beta

Passive immunization with an antibody directed against the N terminus of amyloid beta (Abeta) has recently been reported to exacerbate cerebral amyloid angiopathy (CAA)-related microhemorrhage in a transgenic animal model. Although the mechanism responsible for the deleterious interaction is unclear, a direct binding event may be required. We characterized the binding properties of several monoclonal anti-Abeta antibodies to deposited Abeta in brain parenchyma and CAA. Biochemical analyses demonstrated that the 3D6 and 10D5, two N-terminally directed antibodies, bound with high affinity to deposited forms of Abeta, whereas 266, a central domain antibody, lacked affinity for deposited Abeta. To determine whether 266 or 3D6 would exacerbate CAA-associated microhemorrhage, we treated aged PDAPP mice with either antibody for 6 weeks. We observed an increase in both the incidence and severity of CAA-associated microhemorrhage when PDAPP transgenic mice were treated with the N-terminally directed 3D6 antibody, whereas mice treated with 266 were unaffected. These results may have important implications for future immune-based therapeutic strategies for Alzheimer's disease.

Beyond the signal sequence: protein routing in health and disease

Receptors, hormones, enzymes, ion channels, and structural components of the cell are created by the act of protein synthesis. Synthesis alone is insufficient for proper function, of course; for a cell to operate effectively, its components must be correctly compartmentalized. The mechanism by which proteins maintain the fidelity of localization warrants attention in light of the large number of different molecules that must be routed to distinct subcellular loci, the potential for error, and resultant disease. This review summarizes diseases known to have etiologies based on defective protein folding or failure of the cell's quality control apparatus and presents approaches for therapeutic intervention.

Antibodies from a DNA peptide vaccination decrease the brain amyloid burden in a mouse model of Alzheimer's disease

The neuropathology of Alzheimer's disease(AD) is characterized by the accumulation of amyloid peptide Abeta in the brain derived from proteolytic cleavage of the amyloid precursor protein (APP). Vaccination of mice with plasmid DNA coding for the human Abeta42 peptide together with low doses of preaggregated peptide induced antibodies with detectable titers after only 2 weeks. One serum was directed against the four aminoterminal amino acids DAEF and differs from previously described ones. Both immune sera and monoclonal antibodies solubilized preformed aggregates of Abeta42 in vitro and recognized amyloid plaques in brain sections of mice transgenic for human APP. Passive immunization of transgenic AD mice caused a significant and rapid reduction in brain amyloid plaques within 24 h. The combined DNA peptide vaccine may prove useful for active immunization with few inoculations and low peptide dose which may prevent the recently described inflammatory reactions inpatients. The monoclonal antibodies are applicable for passive immunization studies and may lead to a therapy of AD.

Induction of a Th2 immune response by co-administration of recombinant adenovirus vectors encoding amyloid β-protein and GM-CSF

Lines of experimental evidence indicate that induction of humoral immune responses in transgenic mouse models of Alzheimer disease (AD) by repeated injection of synthetic amyloid beta-protein (Abeta) is effective in prevention and clearance of deposits of Abeta aggregates in the brain of the mice. We have tested a non-injection modality whereby replication-defective adenovirus vectors encoding Abeta or the 99-amino acid carboxyl terminal fragment of Abeta precursor were intranasally administered to mice to elicit immune responses against Abeta. When mice were immunized only with the adenovirus vectors, immune responses against Abeta were negligible. By co-immunization with an adenovirus vector encoding granulocyte-macrophage colony stimulating factor (GM-CSF), the adenovirus vector encoding Abeta effectively elicited an immune response against Abeta. Immunoglobulin isotyping demonstrated a predominant IgG1 and IgG2b response, suggesting a Th2 anti-inflammatory type. Thus, adjuvantation is essential for induction of an immune response against Abeta by adenovirus-mediated nasal vaccination.

The protective role of dl-α-lipoic acid in biogenic amines catabolism triggered by Aβ amyloid vaccination in mice

The major pathological consequence of Alzheimer disease (AD) is accumulation of beta-amyloid (Abeta) peptide fibrillar plaque in the brain and subsequent inflammatory reaction associated with the surrounding cells due to the presence of these aggregates. Inflammation is the major complication associated with Abeta peptide vaccination. Abeta peptide activated T-helper cells are shown to enhance the existing-inflammatory conditions in the brain and other organs of AD patients. Hence systematic studies on potential approaches that will prevent inflammation during the vaccination are highly desired. DL-alpha-lipoic acid (LA), an antioxidant with known function as cofactor in mitochondrial dehydrogenase reactions, will be a good candidate to annul the oxidative damage due to vaccination triggered inflammation. For the first time, levels of principal neurotransmitters and their major metabolites in hippocampus and neocortex regions of brain are quantified to find out the level of inflammation. We have used high performance liquid chromatography with electro chemical detection (HPLC-EC) for monitoring neurotransmitter levels. We have shown a significant (p<0.05) reduction of 5-hydroxytryptamine (5-HT), dopamine (DA) and norepinephrine (NE) in the systemic inflammation induced (SI), vaccinated (VA) and inflammation induced vaccinated (IV) mice. Nevertheless their metabolites such as 5-hydroxyindole acetic acid (5-HIAA) and homovanillic acid (HVA) are significantly (p<0.05) increased when compared with control. Interestingly, antioxidant LA treated mice with systemic inflammation (IL), vaccinated (VL) and inflammation induced vaccinated (IVL) mice exhibited enhanced level of 5-HT, DA and NE and the concentration of 5-HIAA and HVA gradually returned to normal. These results suggest a possible new way for monitoring and modifying the inflammation and thereby preventing Abeta vaccination mediated tissue damage.

The protective role of DL-?-lipoic acid in the oxidative vulnerability triggered by A?-amyloid vaccination in mice

Recent reports indicate that beta-amyloid peptide (Abeta) vaccine based therapy for Alzheimer's disease (AD) may be on the horizon. There are however, concerns about the safety of this approach. Immunization with Abeta has several disadvantages, because it crosses the blood brain barrier and cause inflammation and neurotoxicity. The present work is aimed to study the protective effective of alpha-lipoic acid (LA) in the oxidative vulnerability of beta-amyloid in plasma, liver, spleen and brain, when Abeta fibrils are given intraperitoneally in inflammation induced mice. Result shows that reactive oxygen species (ROS) in the astrocytes of inflammation induced mice along with Abeta (IA) has shown 2.5-fold increase when compared with LA treated mice. The increased level of lipid peroxidase (LPO) (p < 0.05) and decreased antioxidant status (p < 0.05) were observed in the plasma, liver, spleen and brain of LA induced mice when compared with LA treated mice. Data shows that there were no significant changes observed between the control and LA treated mice. Our biochemical and histological results highlight that significant oxidative vulnerability was observed in IA treated mice, which was prevented by LA therapy. Our findings suggest that the antioxidant effect of LA when induced with Abeta may serve as a potent therapeutic tool for inflammatory AD models.

Mimotopes of conformational epitopes in fibrillar beta-amyloid

In Alzheimer's disease (AD) beta-amyloid peptide accumulates in the brain in different forms including fibrils. Amyloid fibrils could be recognized as foreign by the mature immune system since they are not present during its development. Thus, using mouse antisera raised against the fibrillar form of Abeta42, we have screened two phage peptide libraries for the presence of foreign conformational mimotopes of Abeta. Antisera from wild type animals recognized predominately peptides with the EFRH motif from Abeta42 sequence, whereas amyloid precursor protein (APP) transgenic mice recognized mainly phage clones that mimic epitopes (mimotopes) within the fibrillar Abeta42 but lack sequence homology with this peptide.

Immunization of Alzheimer model mice with adenovirus vectors encoding amyloid β-protein and GM-CSF reduces amyloid load in the brain

Induction of anti-amyloid beta-protein (Abeta) antibodies in transgenic mouse models of Alzheimer disease (AD) by repeated injection of synthetic Abeta was shown to be effective in preventing and removing deposition of Abeta aggregates in the brain. Here, we have tested a non-invasive modality whereby a replication-defective adenovirus vector encoding Abeta was intranasally administered to mice to elicit immune responses against Abeta. Intranasal immunization only with the adenovirus vector failed to induce significant immune responses. When an adenovirus vector encoding granulocyte/macrophage-colony stimulating factor (GM-CSF) was used as an adjuvant in conjunction with the adenovirus encoding Abeta, a marked immune response was elicited against Abeta. Immunoglobulin isotyping revealed that the induced anti-Abeta antibodies are predominantly of the IgG2b and IgG1 isotypes, suggesting a Th-2 anti-inflammatory type. Furthermore, amyloid load in the brain of AD model mice (Tg2576) vaccinated with adenovirus vectors encoding Abeta and GM-CSF was much smaller than that in control Tg2576 mice. Thus, intranasal administration of adenovirus vectors encoding Abeta and GM-CSF may be effective in prevention and treatment of AD.

Alzheimer's disease abeta vaccine reduces central nervous system abeta levels in a non-human primate, the Caribbean vervet

Amyloid beta (Abeta) protein immunotherapy lowers cerebral Abeta and improves cognition in mouse models of Alzheimer's disease (AD). Here we show that Caribbean vervet monkeys (Chlorocebus aethiops, SK) develop cerebral Abeta plaques with aging and that these deposits are associated with gliosis and neuritic dystrophy. Five aged vervets were immunized with Abeta peptide over 10 months. Plasma and cerebral spinal fluid (CSF) samples were collected periodically from the immunized vervets and five aged controls; one monkey per group expired during the study. By Day 42, immunized animals generated plasma Abeta antibodies that labeled Abeta plaques in human, AD transgenic mouse and vervet brains; bound Abeta1-7; and recognized monomeric and oligomeric Abeta but not full-length amyloid precursor protein nor its C-terminal fragments. Low anti-Abeta titers were detected in CSF. Abetax-40 levels were elevated approximately 2- to 5-fold in plasma and decreased up to 64% in CSF in immunized vervets. Insoluble Abetax-42 was decreased by 66% in brain homogenates of the four immunized animals compared to archival tissues from 13 age-matched control vervets. Abeta42-immunoreactive plaques were detected in frontal cortex in 11 of the 13 control animals, but not in six brain regions examined in each of the four immunized vervets. No T cell response or inflammation was observed. Our study is the first to demonstrate age-related Abeta deposition in the vervet monkey as well as the lowering of cerebral Abeta by Abeta vaccination in a non-human primate. The findings further support Abeta immunotherapy as a potential prevention and treatment of AD.

Lessons from the AN 1792 Alzheimer vaccine: lest we forget

Recent clinical and neuropathological data show that the AN 1792 vaccine enhanced the production of Abeta antibodies in the sera of Alzheimer's disease (AD) patients, but it appears to have been ineffective at stimulating the removal of Abeta deposits from the brain or at slowing the rate of cognitive decline. The 19 cases of meningoencephalitis were not linked in an obvious way to serum antibody titre, but they may have been linked to infiltration of the brain by antibodies and/or T-cells. Brain imaging indicated that oedema associated with the neuroinflammation did not reflect the typical distribution of neuritic plaques in AD. These outcomes were not anticipated by experiments on transgenic mice because compared to humans, these mice have less genetic variability, and their plaques have a different chemical composition, making them far more soluble and easier to remove. Furthermore, the consequences of vaccination are different. Vaccination of transgenic mice removes superfluous human Abeta while leaving endogenous mouse Abeta intact, whereas in humans the immune response is directed against an endogenous target that occurs naturally and is present in healthy brain tissue. The most important lesson to be learned from the AN 1792 trials is that new strategies for treating AD should not be tested on humans until they have been extensively tested on non-murine species.

Transgenic animal models of Alzheimer's disease and related disorders: histopathology, behavior and therapy

Alzheimer's disease (AD) is a devastating neurodegenerative disease that affects more than 15 million people worldwide. Within the next generation, these numbers will more than double. To assist in the elucidation of pathogenic mechanisms of AD and related disorders, such as frontotemporal dementia (FTDP-17), genetically modified mice, flies, fish and worms were developed, which reproduce aspects of the human histopathology, such as beta-amyloid-containing plaques and tau-containing neurofibrillary tangles (NFT). In mice, the tau pathology caused selective behavioral impairment, depending on the distribution of the tau aggregates in the brain. Beta-amyloid induced an increase in the numbers of NFT, whereas the opposite was not observed in mice. In beta-amyloid-producing transgenic mice, memory impairment was associated with increased levels of beta-amyloid. Active and passive beta-amyloid-directed immunization caused the removal of beta-amyloid plaques and restored memory functions. These findings have since been translated to human therapy. This review aims to discuss the suitability and limitations of the various animal models and their contribution to an understanding of the pathophysiology of AD and related disorders.

Therapeutic approaches to protein-misfolding diseases

Several sporadic and genetic diseases are caused by protein misfolding. These include cystic fibrosis and other devastating diseases of childhood as well as Alzheimer's, Parkinson's and other debilitating maladies of the elderly. A unified view of the molecular and cellular pathogenesis of these conditions has led to the search for chemical chaperones that can slow, arrest or revert disease progression. Molecules are now emerging that link our biophysical insights with our therapeutic aspirations.

Immunotherapeutic approaches to Alzheimer's disease

Although neurodegenerative diseases such as Alzheimer's disease are not classically considered mediated by inflammation or the immune system, in some instances the immune system may play an important role in the degenerative process. Furthermore, it has become clear that the immune system itself may have beneficial effects in nervous system diseases considered neurodegenerative. Immunotherapeutic approaches designed to induce a humoral immune response have recently been developed for the treatment of Alzheimer's disease. These studies have led to human trials that resulted in both beneficial and adverse effects. In animal models, it has also been shown that immunotherapy designed to induce a cellular immune response may be of benefit in central nervous system injury, although T cells may have either a beneficial or detrimental effect depending on the type of T cell response induced. These areas provide a new avenue for exploring immune system-based therapy of neurodegenerative diseases and will be discussed here with a primary focus on Alzheimer's disease. We will also discuss how these approaches affect microglia activation, which plays a key role in therapy of such diseases.

Vaccines for Alzheimer's disease: how close are we?

Alzheimer's disease is a neurodegenerative disorder characterised by a progressive loss of cognitive function. Despite the considerable progress being made, a complete description of the molecular pathology of this disease has yet to be elucidated. The evidence indicates that abnormal processing and extracellular deposition of the longer form of the beta-amyloid (Abeta) peptide (Abeta(1-42), a proteolytic derivative of the amyloid precursor protein [APP]) is implicated in the pathogenesis of Alzheimer's disease. In this respect, recent use of experimental mouse models, in which the mice develop some aspects of Alzheimer's disease in a reproducible fashion, has provided a new opportunity for a multidisciplinary and invasive analysis of mechanisms behind the amyloid pathology and its role in Alzheimer's disease. It has been demonstrated, using a single transgenic mouse model system that overexpresses the human mutated APP gene, that an immunisation against Abeta(1-42) causes a marked reduction in the amyloid burden in the brain. The follow-up research provided more evidence that both active and passive Abeta immunisation also reduces cognitive dysfunction in transgenic mouse models of Alzheimer's disease. Other studies using different approaches - such as secretase, cholesterol and Abeta metalloprotein inhibitors or NSAIDs - but all targeting the abnormal metabolism of Abeta have confirmed in each case that a significant reduction of amyloid plaque burden can be achieved in transgenic mouse models of Alzheimer's disease. This research strongly supports the notion that abnormal Abeta processing is essential to the pathogenesis of Alzheimer's disease and provides a crucial platform for the development and detailed testing of potential treatments in experimental models before each of these approaches can be proposed as a therapy for Alzheimer's disease. Although the first clinical trial of active immunisation with a pre-aggregated synthetic Abeta(42) preparation (AN-1792 vaccine) met with some setbacks and was discontinued after several patients experienced meningoencephalitis, the follow-up analysis of the effect of immunisation against Abeta in humans revealed a powerful effect of vaccination in the clearance of amyloid plaques from the cerebral cortex.

Amyloid-beta immunization in Alzheimer's disease transgenic mouse models and wildtype mice

Alzheimer's disease is the most prevalent form of dementia worldwide. Therapies are desperately needed to prevent and cure the disease. Mouse models of amyloid-beta deposition [APP and PSAPP transgenic (tg) mice] have been useful in determining the role of amyloid-beta (A beta) in both the pathogenesis and cognitive changes in AD. In addition, they have allowed scientists to investigate potential AD therapies in living animals. Active and passive A beta immunizations have been employed successfully in APP and PSAPP tg mice to lower cerebral A beta levels and improve cognition. Optimization of immunization protocols and characterization of immune responses in wildtype mice have been reported. Based on the promising results of A beta immunization studies in mice, a clinical trial was initiated for A beta vaccination in humans with AD. Although no adverse effects were reported in the Phase I safety trials, about 5% of AD patients in the phase II clinical trial developed meningoencephalitis, ending the trial prematurely in March 2002. Studies in AD mouse models and wildtype mice may help elucidate the mechanism for these unwanted side effects and will be useful for testing newer, safer vaccines for future use in human clinical trials.

Immunotherapy for Alzheimer's disease: will vaccination work?

Active or passive immunization against the beta-amyloid peptide (Abeta) has been proposed as a method for preventing and/or treating Alzheimer's disease (AD). In addition to lowering brain Abeta and amyloid burden in transgenic mouse models of AD, a beneficial effect of immunization on previously characterized memory impairment(s) has also been reported in these mice. Whether these preclinical data will predict efficacy in AD patients remains to be seen. A clinical trial of active immunization (vaccination) was halted, owing to a serious adverse event (meningoencephalitis), raising questions about the safety of this approach. Two recent reports suggest that immunotherapy-based approaches to treating and preventing AD will require careful antigen and antibody selection, to maximize efficacy and minimize serious adverse events. However, given the potential efficacy of this approach, we believe that immunotherapy for AD should not be prematurely abandoned.