Amyloid beta peptide as a vaccine for Alzheimer's disease involves receptor-mediated transport at the blood-brain barrier

Treating brain diseases using systemic parenterally-administered protein therapeutics: Dysfunction of the brain barriers and potential strategies

The parenteral administration of protein therapeutics is increasingly gaining importance for the treatment of human diseases. However, the presence of practically impermeable blood-brain barriers greatly restricts access of such pharmaceutics to the brain. Treating brain disorders with proteins thus remains a great challenge, and the slow clinical translation of these therapeutics may be largely ascribed to the lack of appropriate brain delivery system. Exploring new approaches to deliver proteins to the brain by circumventing physiological barriers is thus of great interest. Moreover, parallel advances in the molecular neurosciences are important for better characterizing blood-brain interfaces, particularly under different pathological conditions (e.g., stroke, multiple sclerosis, Parkinson's disease, and Alzheimer's disease). This review presents the current state of knowledge of the structure and the function of the main physiological barriers of the brain, the mechanisms of transport across these interfaces, as well as alterations to these concomitant with brain disorders. Further, the different strategies to promote protein delivery into the brain are presented, including the use of molecular Trojan horses, the formulation of nanosystems conjugated/loaded with proteins, protein-engineering technologies, the conjugation of proteins to polymers, and the modulation of intercellular junctions. Additionally, therapeutic approaches for brain diseases that do not involve targeting to the brain are presented (i.e., sink and scavenging mechanisms).

Targeting Tumor Necrosis Factor Alpha for Alzheimer's Disease

Alzheimer's disease (AD) affects an estimated 44 million individuals worldwide, yet no therapeutic intervention is available to stop the progression of the dementia. Neuropathological hallmarks of AD are extracellular deposits of amyloid beta (Aβ) peptides assembled in plaques, intraneuronal accumulation of hyperphosphorylated tau protein forming tangles, and chronic inflammation. A pivotal molecule in inflammation is the pro-inflammatory cytokine TNF-α. Several lines of evidence using genetic and pharmacological manipulations indicate that TNF-α signaling exacerbates both Aβ and tau pathologies in vivo. Interestingly, preventive and intervention anti-inflammatory strategies demonstrated a reduction in brain pathology and an amelioration of cognitive function in rodent models of AD. Phase I and IIa clinical trials suggest that TNF-α inhibitors might slow down cognitive decline and improve daily activities in AD patients. In the present review, we summarize the evidence pointing towards a beneficial role of anti-TNF-α therapies to prevent or slow the progression of AD. We also present possible physical and pharmacological interventions to modulate TNF-α signaling in AD subjects along with their limitations.

Blood–Brain Barrier Pathology in Alzheimer's and Parkinson's Disease: Implications for Drug Therapy

The blood–brain barrier (BBB) is a tightly regulated barrier in the central nervous system. Though the BBB is thought to be intact during neurodegenerative diseases such as Alzheimer's (AD) and Parkinson's disease (PD), recent evidence argues otherwise. Dysfunction of the BBB may be involved in disease progression, eliciting of peripheral immune response, and, most importantly, altered drug efficacy. In this review, we will give a brief overview of the BBB, its components, and their functions. We will critically evaluate the current literature in AD and PD BBB pathology resulting from insult, neuroinflammation, and neurodegeneration. Specifically, we will discuss alterations in tight junction, transport and endothelial cell surface proteins, and vascular density changes, all of which result in altered permeability. Finally, we will discuss the implications of BBB dysfunction in current and future therapeutics. Developing a better appreciation of BBB dysfunction in AD and PD may not only provide novel strategies in treatment, but will prove an interesting milestone in understanding neurodegenerative disease etiology and progression.

A carrier for non-covalent delivery of functional beta-galactosidase and antibodies against amyloid plaques and IgM to the brain

Background

Therapeutic intervention of numerous brain-associated disorders currently remains unrealized due to serious limitations imposed by the blood-brain-barrier (BBB). The BBB generally allows transport of small molecules, typically <600 daltons with high octanol/water partition coefficients, but denies passage to most larger molecules. However, some receptors present on the BBB allow passage of cognate proteins to the brain. Utilizing such receptor-ligand systems, several investigators have developed methods for delivering proteins to the brain, a critical requirement of which involves covalent linking of the target protein to a carrier entity. Such covalent modifications involve extensive preparative and post-preparative chemistry that poses daunting limitations in the context of delivery to any organ. Here, we report creation of a 36-amino acid peptide transporter, which can transport a protein to the brain after routine intravenous injection of the transporter-protein mixture. No covalent linkage of the protein with the transporter is necessary.

Approach

A peptide transporter comprising sixteen lysine residues and 20 amino acids corresponding to the LDLR-binding domain of apolipoprotein E (ApoE) was synthesized. Transport of beta-galactosidase, IgG, IgM, and antibodies against amyloid plques to the brain upon iv injection of the protein-transporter mixture was evaluated through staining for enzyme activity or micro single photon emission tomography (micro-SPECT) or immunostaining. Effect of the transporter on the integrity of the BBB was also investigated.

Principal Findings

The transporter enabled delivery to the mouse brain of functional beta-galactosidase, human IgG and IgM, and two antibodies that labeled brain-associated amyloid beta plaques in a mouse model of Alzheimer's disease.

Significance

The results suggest the transporter is able to transport most or all proteins to the brain without the need for chemically linking the transporter to a protein. Thus, the approach offers an avenue for rapid clinical evaluation of numerous candidate drugs against neurological diseases including cancer. (299 words).

Immunization in Alzheimer's disease: naïve hope or realistic clinical potential?

There has been considerable recent interest in vaccination of patients by immunotherapy as a potentially clinically useful methodology for combating histopathological changes in Alzheimer's disease (AD). The focus of the majority of this research has been on (1) active immunotherapy using the pre-aggregated synthetic beta-amyloid (Abeta) 42 preparation AN1792 vaccine (QS-21), or (2) passive immunization using injections of already prepared polyclonal anti-Abeta antibodies (intravenous immunoglobulin). These two clinical approaches to the treatment of patients with AD represent the focus of this review. We conclude here that, with certain caveats, immunization offers further potential as a technique for the treatment (and possible prevention) of AD. New studies are seeking to develop and apply safer vaccines that do not result in toxicity and neuroinflammation. Nevertheless, caution is warranted, and future clinical investigations are required to tackle key outstanding issues. These include the need to demonstrate efficacy in humans as well as animal models (especially with respect to the potentially toxic side effects of immunotherapy), and fine-tuning in safely guiding the immune response. The issue of defining necessary and sufficient criteria for determining clinical efficacy remains an additional important issue for future immunization trials. The vaccination methodology appears to offer substantial current promise for clearing both soluble and aggregated amyloid in AD. However, it remains to be determined whether this approach will help to repair already damaged neural systems in the disease, and the extent to which vaccination-driven amyloid clearance will impact beneficially on patients' neurocognitive capacity and their functional status. The outcomes of future studies will be important both clinically and scientifically: an important further test of the validity of the amyloid hypothesis of AD is to evaluate the impact of an effective anti-amyloid strategy on the functional status of patients with this disease.

Peripheral and central biodistribution of (111)In-labeled anti-beta-amyloid autoantibodies in a transgenic mouse model of Alzheimer's disease

Active as well as passive immunization against beta-amlyoid (Abeta) has been proposed as a treatment to lower cerebral amyloid burden and stabilize cognitive decline in Alzheimer's disease (AD). To clarify the mechanism of action underlying passive immunization, the in vivo distribution (and sites of degradation) of peripherally administered radiolabeled human and mouse anti-Abeta antibodies were analyzed in a transgenic mouse model of AD. In APP23 mice, a model in which mutated human amyloid precursor protein is overexpressed, the biodistribution of intravenously applicated (111)indium-conjugated affinity-purified human polyclonal autoantibodies (NAbs-Abeta) was compared to that of monoclonal anti-Abeta(1-17) (6E10), anti-Abeta(17-24) antibodies (4G8) and anti-CD-20 (Rituximab), a non-Abeta targeting control. Blood clearance half-lives were 50+/-6h for Rituximab, 20-30h for NAbs-Abeta, 29+/-5h for 4G8 and 27+/-3h for 6E10. Blood activity was higher for 6E10 at 4h as compared to 4G8, Rituximab and NAbs-Abeta. At the 96h time point, Rituximab had the highest blood activity among the antibodies tested. As expected, all antibodies displayed hepatobiliary clearance. Additionally, NAbs-Abeta was excreted in the urinary tract. Liver and kidney uptake of NAbs-Abeta increased over time and was higher than in the monoclonal antibodies at 48h/96h. The brain-to-blood radioactivity ratio for NAbs-Abeta at later time points (>48h) was higher than that of 6E10, 4G8 and Rituximab. In addition, the distribution varied, with highest values found in the hippocampus. Our data indicate a cerebral accumulation of human NAbs-Abeta in the APP23 model. Further studies with human immunoglobulins and particularly with those that recognize different Abeta-epitopes are required in order to delineate in more detail the mode of action of NAbs-Abeta.

CNS delivery via adsorptive transcytosis

Adsorptive-mediated transcytosis (AMT) provides a means for brain delivery of medicines across the blood-brain barrier (BBB). The BBB is readily equipped for the AMT process: it provides both the potential for binding and uptake of cationic molecules to the luminal surface of endothelial cells, and then for exocytosis at the abluminal surface. The transcytotic pathways present at the BBB and its morphological and enzymatic properties provide the means for movement of the molecules through the endothelial cytoplasm. AMT-based drug delivery to the brain was performed using cationic proteins and cell-penetrating peptides (CPPs). Protein cationization using either synthetic or natural polyamines is discussed and some examples of diamine/polyamine modified proteins that cross BBB are described. Two main families of CPPs belonging to the Tat-derived peptides and Syn-B vectors have been extensively used in CPP vector-mediated strategies allowing delivery of a large variety of small molecules as well as proteins across cell membranes in vitro and the BBB in vivo. CPP strategy suffers from several limitations such as toxicity and immunogenicity--like the cationization strategy--as well as the instability of peptide vectors in biological media. The review concludes by stressing the need to improve the understanding of AMT mechanisms at BBB and the effectiveness of cationized proteins and CPP-vectorized proteins as neurotherapeutics.

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.

Selective contrast enhancement of individual Alzheimer's disease amyloid plaques using a polyamine and Gd-DOTA conjugated antibody fragment against fibrillar Abeta42 for magnetic resonance molecular imaging

PURPOSE

The lack of an in vivo diagnostic test for AD has prompted the targeting of amyloid plaques with diagnostic imaging probes. We describe the development of a contrast agent (CA) for magnetic resonance microimaging that utilizes the F(ab')2 fragment of a monoclonal antibody raised against fibrillar human Abeta42

METHODS

This fragment is polyamine modified to enhance its BBB permeability and its ability to bind to amyloid plaques. It is also conjugated with a chelator and gadolinium for subsequent imaging of individual amyloid plaques

RESULTS

Pharmacokinetic studies demonstrated this 125I-CA has higher BBB permeability and lower accumulation in the liver and kidney than F(ab')2 in WT mice. The CA retains its ability to bind Abeta40/42 monomers/fibrils and also binds to amyloid plaques in sections of AD mouse brain. Intravenous injection of 125I-CA into the AD mouse demonstrates targeting of amyloid plaques throughout the cortex/hippocampus as detected by emulsion autoradiography. Incubation of AD mouse brain slices in vitro with this CA resulted in selective enhancement on T1-weighted spin-echo images, which co-register with individual plaques observed on spatially matched T2-weighted spin-echo image

CONCLUSIONS

Development of such a molecular probe is expected to open new avenues for the diagnosis of AD.

Antibody against C-terminal Abeta selectively elevates plasma Abeta

Accumulation of amyloid beta in the brain is a pathological hallmark of Alzheimer's disease, and the reduction of amyloid beta has been proposed as a primary therapeutic target. Mice immunized against amyloid beta and mice infused with anti-amyloid beta antibody (active and passive immunization, respectively) have reduced brain amyloid beta levels, and two mechanisms have been proposed: microglial phagocytosis in the brain and enhancement of amyloid beta efflux by antibodies present in the periphery (sequestration). The optimal antibody for microglial phagocytosis has been shown to be N-terminal-specific antibody; however, the potency of C-terminal-specific antibody in sequestration remains unclear. In this study, we found that anti-amyloid beta 40-specific antibody induces amyloid beta sequestration. These results indicate that C-terminal antibodies may be useful in amyloid beta sequestration therapy.

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.

IgG marker of optic-spinal multiple sclerosis binds to the aquaporin-4 water channel

Neuromyelitis optica (NMO) is an inflammatory demyelinating disease that selectively affects optic nerves and spinal cord. It is considered a severe variant of multiple sclerosis (MS), and frequently is misdiagnosed as MS, but prognosis and optimal treatments differ. A serum immunoglobulin G autoantibody (NMO-IgG) serves as a specific marker for NMO. Here we show that NMO-IgG binds selectively to the aquaporin-4 water channel, a component of the dystroglycan protein complex located in astrocytic foot processes at the blood-brain barrier. NMO may represent the first example of a novel class of autoimmune channelopathy.

Method for measurement of the blood-brain barrier permeability in the perfused mouse brain: application to amyloid-beta peptide in wild type and Alzheimer's Tg2576 mice

The role of transport exchanges of neuroactive solutes across the blood-brain barrier (BBB) is increasingly recognized. To take full advantage of genetically altered mouse models of neurodegenerative disorders for BBB transport studies, we adapted a brain perfusion technique to the mouse. During a carotid brain perfusion with a medium containing sheep red blood cells and mock plasma, the physiological parameters in the arterial inflow, regional cerebral blood flow (14C-iodoantipyrine autoradiography), ultrastructural integrity of the tissue, barrier to lanthanum, brain water content, energy metabolites and lactate levels remain unchanged. Amyloid-beta peptides (Abeta) were iodinated by lactoperoxidase method. Non-oxidized mono-iodinated Abeta monomers were separated by HPLC (as confirmed by MALDI-TOF spectrometry) and used in transport measurements. Transport of intact 125I-Abeta40 across the BBB was time- and concentration-dependent in contrast to negligible 14C-inulin uptake. In 5-6 months old Alzheimer's Tg2576 mice, Abeta40 BBB transport was increased by >eight-fold compared to age-matched littermate controls, and was mediated via the receptor for advanced glycation endproducts. We conclude the present arterial brain perfusion method provides strictly controlled environment in cerebral microcirculation suitable for examining transport of rapidly and slowly penetrating molecules across the BBB in normal and transgenic mice.

Anti-A?: The good, the bad, and the unforeseen

Alzheimer's disease (AD) is characterized in part by the deposition of amyloid beta protein (Abeta) in compact fibrillar plaques. These structures can induce an innate immune response in the brain, which triggers progressive inflammation, neuronal loss, and further acceleration of Abeta plaque formation. Compared with the case in normal individuals, the T and B lymphocytes in AD patients and murine models are hyporesponsive to Abeta. However, depending on the route of delivery, tolerance can be overcome by vaccination, with the induction of an anti-Abeta-mediated immune response. Through mechanisms that are incompletely understood, immunized APP transgenic animals show markedly reduced Abeta deposition, preservation of normal neuronal architecture, and improved performance in memory and spatial learning tasks. In human trials, Abeta vaccination stabilized cognition and slowed the progression of dementia. Neuropathologic examination of a vaccinated subject showed reduced cortical Abeta without changes in other AD-associated pathology. However, in some patients, vaccination induced severe meningoencephalitis, causing the trial to be terminated. Thus, vaccination appears to activate both beneficial and deleterious anti-Abeta immunity, suggesting that the vaccine can have potent clinical utility if an appropriate immunologic response can be generated.

Nonsteroidal anti-inflammatory drug use and the risk for Alzheimer's disease: dissecting the epidemiological evidence

Inflammation is hypothesised to contribute to the genesis of pathology causing or contributing to Alzheimer's disease (AD). As a part of the immune response in the brain, the prostaglandin pathway is induced; this pathway is the target for NSAIDs, the most widely used anti-inflammatory medication. There are many epidemiological studies, which are reviewed here, suggesting NSAIDs reduce the risk for AD. The most recent of these studies suggest NSAIDs should be taken for at least 2 years. There are little data in humans about whether one type of NSAID is more effective than another. To date, randomised, double-blind, clinical trials in patients with AD have been negative. There is one prevention trial that will yield valuable information about the efficacy of NSAIDs in slowing down the progression of, or preventing, AD. At present, no recommendations can be made concerning the when, what, who and for how long a person should take an NSAID to reduce his or her risk for AD.

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

Recent studies in murine models of Alzheimer's disease (AD) have found that active immunisation with amyloid-beta peptide (Abeta) or passive immunisation with Abeta antibodies can lessen the severity of Abeta-induced neuritic plaque pathology through the activation of microglia. These antibodies can be detected in the serum and CSF. Whether they slow down or speed up the development and progression of AD has not been determined. Furthermore, the conditions that induce formation of such antibodies are unknown, or how specific they are to AD. However, the evidence suggests at least a potential beneficial role for some features of neuroinflammation in AD. A clinical phase II study of an active immunisation approach with AN1792 was started in 2001, but was recently suspended after some patients developed serious adverse events. These were most likely caused by the activation of the proinflammatory cascade. Immunotherapy approaches represent fascinating ways to test the amyloid hypothesis and may offer genuine opportunities to modify disease progression. This review focuses on immunisation strategies and details of the pathways involved in antibody clearance of Abeta.

Abeta immunization and anti-Abeta antibodies: potential therapies for the prevention and treatment of Alzheimer's disease

Amyloid-beta (Abeta) is a normally soluble 39-43 amino peptide. Genetic and biochemical data strongly suggest that the conversion of Abeta from soluble to insoluble forms with high beta-sheet content and its buildup in the brain is a key step in the pathogenesis of Alzheimer's disease (AD) and cerebral amyloid angiopathy (CAA). Prevention and/or reversal of this process may serve as a treatment. Methods to prevent or reverse Abeta deposition and its toxic effects would include decreasing its production, preventing its conversion to insoluble forms (e.g. inhibit beta-sheet formation) or in changing the dynamics of extracellular brain Abeta, either locally within the brain or by altering net flux of Abeta between the central nervous system (CNS) and plasma compartment. Transgenic mouse models of AD that develop age-dependent Abeta deposition, damage to the neuropil, and behavioral deficits have enabled researchers to test whether different manipulations can influence these AD-like changes. Recently, active immunization with different forms of the Abeta peptide has been shown to decrease brain Abeta deposition and improve cognitive performance in mouse models of AD. Certain peripherally administered anti-Abeta antibodies have similar effects. The mechanism(s) by which anti-Abeta antibodies result in these effects is just beginning to be elucidated. Abeta-related immune therapies in humans are an exciting new area of AD research. Understanding their detailed mechanism(s) of action and their potential usefulness awaits the results of future animal and human studies.

Vascular disorder in Alzheimer's disease: role in pathogenesis of dementia and therapeutic targets

It is not clear whether Alzheimer's Disease (AD) is primarily a neurodegenerative disorder or not. A body of evidence suggests that vascular disorder in brains of individuals with AD contributes to the extremes of this disease. This raises a question whether Alzheimer's dementia is secondary to vascular dysfunction in the central nervous system (CNS) and, therefore, the neurodegeneration that follows is a consequence of inadequate cerebral blood flow, altered brain metabolism and failure in physiological functions of brain endothelium which represents a site at the blood-brain barrier (BBB). In this paper the evidence for a primary role of the CNS vascular system in pathogenesis of Alzheimer's dementia is reviewed to show how alterations in transport across the BBB contribute to development of cerebral beta-amyloidosis in AD. In addition, vascularly-based therapeutic strategies to limit the development of beta-amyloidosis and to remove amyloid and plaques from the CNS of AD individuals are discussed.

Generation of antibodies specific for beta-amyloid by vaccination of patients with Alzheimer disease

To characterize antibodies produced in humans in response to Abeta42 vaccination, we carried out immunohistochemical examinations of the brains of both transgenic mice and human patients with beta-amyloid pathology. We collected sera from patients with Alzheimer disease who received a primary injection of pre-aggregated Abeta42 followed by one booster injection in a placebo-controlled study. Antibodies in immune sera recognized beta-amyloid plaques, diffuse Abeta deposits and vascular beta-amyloid in brain blood vessels. The antibodies did not cross-react with native full-length beta-amyloid precursor protein or its physiological derivatives, including soluble Abeta42. These findings indicate that vaccination of AD patients with Abeta42 induces antibodies that have a high degree of selectivity for the pathogenic target structures. Whether vaccination to produce antibodies against beta-amyloid will halt the cognitive decline in AD will depend upon clinical assessments over time.

A safer vaccine for Alzheimer's disease?

Recent reports indicate that amyloid-beta (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 Abeta1-42 may not be appropriate in humans because it crosses the blood-brain barrier, can seed fibril formation, and is highly fibrillogenic. Abeta1-42 fibrils can in turn cause inflammation and neurotoxicity. This issue is of a particular concern in the elderly who often do not mount an adequate immune response to vaccines. Our findings show that vaccination with nonamyloidogenic/nontoxic Abeta derivative may be a safer therapeutic approach to impede the progression of Abeta-related histopathology in AD. Although the site of action of the anti-Abeta antibodies has been suggested to be within the brain, peripheral clearance of Abeta may have a greater role in reducing cerebral amyloid plaques in these animals and eventually in AD patients. Antibodies in general are predominantly found outside the central nervous system (CNS) and will, therefore, primarily clear systemic Abeta compared to brain Abeta. This disruption of the equilibrium between central and peripheral Abeta should then result in efflux of Abeta out of the brain, and subsequent removal of plaques. Abeta therapy can be targeted to the periphery, which may result in fewer CNS side effects, such as inflammation. Future Abeta derived vaccines should include T(h) epitopes, carriers and/or lipid moieties to enhance antibody production in the elderly, the population predominantly affected by AD.