Intravenous immunoglobulin enhances the clearance of fibrillar amyloid-beta peptide

The immunology of B-1 cells: from development to aging

B-1 cells have intricate biology, with distinct function, phenotype and developmental origin from conventional B cells. They generate a B cell receptor with conserved germline characteristics and biased V(D)J recombination, allowing this innate-like lymphocyte to spontaneously produce self-reactive natural antibodies (NAbs) and become activated by immune stimuli in a T cell-independent manner. NAbs were suggested as "rheostats" for the chronic diseases in advanced age. In fact, age-dependent loss of function of NAbs has been associated with clinically-relevant diseases in the elderly, such as atherosclerosis and neurodegenerative disorders. Here, we analyzed comprehensively the ontogeny, phenotypic characteristics, functional properties and emerging roles of B-1 cells and NAbs in health and disease. Additionally, after navigating through the complexities of B-1 cell biology from development to aging, therapeutic opportunities in the field are discussed.

Engineered Antibodies to Improve Efficacy against Neurodegenerative Disorders

Antibodies that can selectively remove rogue proteins in the brain are an obvious choice to treat neurodegenerative disorders (NDs), but after decades of efforts, only two antibodies to treat Alzheimer's disease are approved, dozens are in the testing phase, and one was withdrawn, and the other halted, likely due to efficacy issues. However, these outcomes should have been evident since these antibodies cannot enter the brain sufficiently due to the blood-brain barrier (BBB) protectant. However, all products can be rejuvenated by binding them with transferrin, preferably as smaller fragments. This model can be tested quickly and at a low cost and should be applied to bapineuzumab, solanezumab, crenezumab, gantenerumab, aducanumab, lecanemab, donanemab, cinpanemab, and gantenerumab, and their fragments. This paper demonstrates that conjugating with transferrin does not alter the binding to brain proteins such as amyloid-β (Aβ) and α-synuclein. We also present a selection of conjugate designs that will allow cleavage upon entering the brain to prevent their exocytosis while keeping the fragments connected to enable optimal binding to proteins. The identified products can be readily tested and returned to patients with the lowest regulatory cost and delays. These engineered antibodies can be manufactured by recombinant engineering, preferably by mRNA technology, as a more affordable solution to meet the dire need to treat neurodegenerative disorders effectively.

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

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

Five-year outcomes after IVIG for mild cognitive impairment due to alzheimer disease

Background

The purpose of this study was to assess the five-year treatment effects of a short course of intravenous immunoglobulin (IVIG) in subjects with mild cognitive impairment (MCI) due to Alzheimer disease (AD).

Methods

Fifty subjects 50 to 84 years of age with MCI due to AD were administered 0.4 g/kg 10% IVIG or 0.9% saline every two weeks x five doses in a randomized double-blinded design as part of a two-year study. Twenty-seven subjects completed an additional three-year extension study. MRI brain imaging, cognitive testing, and conversion to dementia were assessed annually. Participants were stratified into early MCI (E-MCI) and late MCI (L-MCI). The primary endpoint was brain atrophy measured as annualized percent change in ventricular volume (APCV) annually for five years. ANOVA was used to compare annualized percent change in ventricular volume from baseline between the groups adjusting for MCI status (E-MCI, L-MCI).

Results

Differences in brain atrophy between the groups, which were statistically significant after one year, were no longer significant after five years. IVIG-treated L-MCI subjects did demonstrate a delay in conversion to dementia of 21.4 weeks.

Conclusion

An eight-week course of IVIG totaling 2 g/kg in MCI is safe but is not sufficient to sustain an initial reduction in brain atrophy or a temporary delay in conversion to dementia at five years. Other dosing strategies of IVIG in the early stages of AD should be investigated to assess more sustainable disease-modifying effects.

Trial registration ClinicalTrials.gov NCT01300728. Registered 23 February 2011.

Effects of a Multimerized Recombinant Autoantibody Against Amyloid-β

Alzheimer's disease (AD) is the most common neurodegenerative disease; thus, the search for a cure or causal therapy has become necessary. Despite intense research on this topic in recent decades, there is no curative therapy up today, and also no disease-modifying treatment has been approved. As promising approach passive immunization strategies have thereby come forth. In this study, we focused on naturally occurring autoantibodies against the AD-associated peptide amyloid-β. These antibodies have already reported to show beneficial functions in vitro and in mouse models of AD. However, their availability is limited due to their low abundance in peripheral blood. In a recent study, we were able to generate four recombinant antibodies against amyloid-β. In the present study, we tested these antibodies in ELISA and SPR assays for their binding behavior and by aggregation- and phagocytosis assays as functional evidences to characterize their amyloid-β-related neutralizing and clearance abilities. Further ex vivo assay on organotypic hippocampal slice cultures gave first evidence of microglial activation and inflammatory features. The tested recombinant antibodies in IgG format showed, in comparison to naturally occurring autoantibodies against amyloid-β, insufficient binding capacities and -affinities. However, after conversion of one antibody into a single chain format multimerization of the scFv-Fc construct, the investigated binding capacity and -affinity showed improvements. Further functional assays predict a protective effect of this antibody. Although, all four recombinant antibodies showed binding to amyloid-β, promising features were only detectable after conversion into a multimeric format. The multimeric scFv-Fc antibody exhibited thereby strong impact on amyloid-β clearance and inhibition of oligomerization.

Preventing dementia? Interventional approaches in mild cognitive impairment

Mild cognitive impairment (MCI) is defined as an intermediate state between normal cognitive aging and dementia. It describes a status of the subjective impression of cognitive decline and objectively detectible memory impairment beyond normal age-related changes. Activities of daily living are not affected. As the population ages, there is a growing need for early, proactive programs that can delay the consequences of dementia and improve the well-being of people with MCI and their caregivers. Various forms and approaches of intervention for older people with MCI have been suggested to delay cognitive decline. Pharmacological as well as non-pharmacological approaches (cognitive, physiological, nutritional supplementation, electric stimulation, psychosocial therapeutic) and multicomponent interventions have been proposed. Interventional approaches in MCI from 2009 to April 2019 concerning the cognitive performance are presented in this review.

Reduction of Amyloid in the Brain and Retina After Treatment With IVIG for Mild Cognitive Impairment

OBJECTIVE

To assess whether intravenous immunoglobulin (IVIG) in subjects with mild cognitive impairment (MCI) results in a reduction in amyloid in the central nervous system (CNS).

METHODS

Five subjects with MCI underwent baseline Florbetapir positron emission tomography and retinal autofluorescent imaging. All were administered IVIG (Octagam 10%) at 0.4 g/kg every 14 days for a total of 5 infusions. After 3 months, standard uptake value ratio (SUVR) and amyloid retinal deposits were reassessed.

RESULTS

Three subjects had a reduction in amyloid SUVR and all 5 subjects had a reduction in amyloid retinal deposits in at least 1 eye.

CONCLUSIONS

A short course of IVIG over 2 months removes a measurable amount of amyloid from the CNS in persons with MCI.

Efficacy and Tolerability of Intravenous Immunoglobulin and Subcutaneous Immunoglobulin in Neurologic Diseases

PURPOSE

IV immunoglobulin (Ig) therapy has been widely used for the treatment of neurologic disorders, autoimmune diseases, immunodeficiency-related diseases, blood system diseases, and cancers. In this review, we summarize the efficacy and tolerability of IVIg and SCIg therapy in neurologic diseases.

METHODS

We summarized and analyzed the efficacy and tolerability of IVIg and SCIg in neurologic diseases, by analyzing the literature pertaining to the use of IVIg and SCIg to treat nervous system diseases.

FINDINGS

In clinical neurology practice, IVIg has been shown to be useful for the treatment of new-onset or recurrent immune diseases and for long-term maintenance treatment of chronic diseases. Moreover, IVIg may have applications in the management of intractable autoimmune epilepsy, paraneoplastic syndrome, autoimmune encephalitis, and neuromyelitis optica. SCIg is emerging as an alternative to IVIg treatment. Although SCIg has a composition similar to that of IVIg, the applications of this therapy are different. Notably, the bioavailability of SCIg is lower than that of IVIg, but the homeostasis level is more stable. Current studies have shown that these 2 therapies have pharmacodynamic equivalence.

IMPLICATIONS

In this review, we explored the efficacy of IVIg in the treatment of various neurologic disorders. IVIg administration still faces many challenges. Thus, it will be necessary to standardize the use of IVIg in the clinical setting. SCIg administration is a novel and feasible treatment option for neurologic and immune-related diseases, such as chronic inflammatory demyelinating polyradiculoneuropathy and idiopathic inflammatory myopathies. As our understanding of the mechanisms of action of IVIg improve, potential next-generation biologics can being developed.

Intravenous Immunoglobulin for Patients With Alzheimer's Disease: A Systematic Review and Meta-Analysis

AIM

To assess the efficacy and safety of intravenous immunoglobulin (IVIg) for patients with Alzheimer's disease (AD).

MATERIALS AND METHODS

We searched electronic databases and other sources for randomized controlled trials comparing IVIg with placebo or other treatment for adults with AD. Primary outcome was change from baseline in Alzheimer's Disease Assessment Scale-Cognitive subscale (ADAS-Cog).

RESULTS

Five placebo-controlled trials were included in the meta-analysis. Compared to placebo, IVIg 0.2 and 0.4 g/kg once every two weeks did not change ADAS-Cog score (weighted mean difference: 0.37, 95% confidence interval: -1.46 to 2.20 and 0.77, -1.34 to 2.88, respectively). Furthermore, except for an increase in the incidence of rash, IVIg did not affect the incidence of other adverse events.

CONCLUSION

IVIg, albeit safe, is inefficacious for treatment of patients with AD. Future trials targeting earlier stages of disease or applying different dosing regimens may be warranted to clarify its therapeutic potential.

Decreased immunoglobulin G in brain regions of elder female APOE4-TR mice accompany with Aβ accumulation

Background

Apolipoprotein E4 (APOE4) and ageing are the most important known risk factors for late-onset Alzheimer’s disease (AD). In the present study, we determined the alterations of IgG, CD19, and Aβ in various brain regions of uninfected male and female APOE3- and APOE4-TR mice at the age of 3 and 10 months to elucidate impacts of AD risk factors on alterations of brain IgG.

Results

Positive staining for IgG was distributed across the brain, including neocortex, entorhinal cortex, hippocampus, thalamus and cerebellum. IgG positive staining was mainly located on microglia, but not astrocytes. Some IgG positive neurons were also observed, but only in mediodorsal thalamic nucleus. Compared with APOE3-TR mice, 10-month-old female APOE4-TR mice had lower IgG level in AD susceptible brain regions such as neocortex, entorhinal cortex and hippocampus, but no significant changes in thalamus and cerebellum, two regions nearly intact in AD. In addition, the expression of CD19, a specific marker for mature B cells, was significantly reduced in the hippocampus of 10-month-old female APOE4-TR mice. Although there were no obvious differences in plasma IgG levels between APOE4- and age matched female APOE3-TR mice, significant decreased B cell amount in blood of 10-month-old female APOE4-TR mice have also been found. Moreover, more obvious positive staining for Aβ was observed in the cortex of 10-month-old female APOE4-TR mice than other groups.

Conclusions

Our study demonstrated that AD risk factors were associated with IgG alterations in various brain regions, which might result from the defects of humoral immunity and lead to the impairment of IgG-mediated clearance of Aβ by microglia, therefore facilitated AD progression.

Extending the functional characteristics of naturally occurring autoantibodies against β-Amyloid, Prion Protein and α-Synuclein

Background

Abnormal aggregation of proteins induces neuronal cell loss in neurodegenerative disorders such as Alzheimer’s Disease, Creutzfeldt-Jakob Disease and Parkinson’s Disease. Specific stimuli initialize conformational changes in physiological proteins, causing intra- or extracellular protein aggregation. We and other groups have identified naturally occurring autoantibodies (nAbs) as part of the human antibody pool that are able to prevent peptide fibrillation. These nAbs show a rescue effect following exposure of toxic aggregates on neurons, and they support microglial uptake of aggregated peptides.

Objective

Identification of a putative common epitope among the relevant proteins β-Amyloid, α-Synuclein and Prion Protein for the respective nAbs.

Material and methods

Binding affinity between the aforementioned proteins and nAbs was tested by Dot Blot, ELISA and SPR-technology. Furthermore, the functionality of the protein-nAbs-complexes was studied in Thioflavin-T assays and microglial uptake experiments to study dependent inhibition of protein aggregation and enhancement of Fcγ mediated uptake by microglial cells.

Results

β-Amyloid and Prion Protein fragment showed considerable binding affinity and functional efficacy for all applied nAbs. Thereby, no significant difference within the different nAbs was detected. In contrast, α-Synuclein was bound exclusively by nAbs-α-Synuclein, which was reproduced in all binding studies. Surprisingly, functional assays with α-Synuclein revealed no significant effect of nAbs in comparison to IVIg treatment. However, all applied nAbs as well as IVIg show a minimal functionality on the microglial uptake of α-Synuclein.

Conclusion

nAbs-Aβ, nAbs-PrP possibly display comparable affinity to the same structural epitope within Aβ and PrP106-126 A117V whereas the epitope recognized by nAbs-α-Syn is only present in α-Syn. The structural similarity of Aβ and PrP fragment promotes the outline for an efficient antibody for the treatment of several neurodegenerative disorders and extend the functional characteristics of the investigated nAbs.

Vaccination strategies in tauopathies and synucleinopathies

Vaccination therapies constitute potential treatment options in neurodegenerative disorders such as Alzheimer disease or Parkinson disease. While a lot of research has been performed on vaccination against extracellular amyloid β, the focus recently shifted toward vaccination against the intracellular proteins tau and α-synuclein, with promising results in terms of protein accumulation reduction. In this review, we briefly summarize lessons to be learned from clinical vaccination trials in Alzheimer disease that target amyloid β. We then focus on tau and α-synuclein. For both proteins, we provide important data on protein immunogenicity, and put them into context with data available from both animals and human vaccination trials targeted at tau and α-synuclein. Together, we give a comprehensive overview about current clinical data, and discuss associated problems.

IVIG treatment of mild cognitive impairment due to Alzheimer's disease: a randomised double-blinded exploratory study of the effect on brain atrophy, cognition and conversion to dementia

OBJECTIVE

To determine the effect of intravenous immunoglobulin (IVIG) on brain atrophy and cognitive function in mild cognitive impairment (MCI) due to Alzheimer's disease (AD).

METHODS

50 participant 50-84 years of age with amnestic MCI were administered 0.4 g/kg 10% IVIG or 0.9% saline every 2 weeks for a total of 5 infusions (2 g/kg total dose) in a randomised double-blinded design. MRI brain was completed at baseline, 12  and 24 months. Cognitive testing was completed at baseline and every 4 months. Participants were stratified into early and late (LMCI) MCI stages. Average annualised per cent change in ventricular volume was computed as a measure of brain atrophy.

RESULTS

There was significantly less brain atrophy (p=0.037, adjusted for MCI status) in the IVIG group (5.87%) when compared with placebo (8.14%) at 12 months; at 24 months, the reduction in brain atrophy no longer reached statistical significance. The LMCI participants who received IVIG performed better on Alzheimer's Disease Assessment Scale-cognitive subscale (ADAS-Cog; p=0.011) and Mini-Mental State Examination (MMSE; p=0.004) at 1 year; these differences were not present after 2 years. There was no difference in conversion to AD dementia between the treatment and control groups after 2 years; however, at 1 year, there were fewer conversions from LMCI to AD dementia in the IVIG group (33.3%) when compared with control group (58.3%).

CONCLUSIONS

This exploratory study provides limited evidence that a short course of IVIG administered in the MCI stage of AD reduces brain atrophy, prevents cognitive decline in LMCI and delays conversion to AD dementia for at least 1 year; however, this effect of IVIG appears to wane by 2 years.

TRIAL REGISTRATION NUMBER

ClinicalTrials.gov, NCT01300728.

Aβ-Immunotherapeutic strategies: a wide range of approaches for Alzheimer's disease treatment

Current therapies to treat Alzheimer's disease (AD) are focused on ameliorating symptoms instead of treating the underlying causes of AD. The accumulation of amyloid β (Aβ) oligomers, whether by an increase in production or by a decrease in clearance, has been described as the seed that initiates the pathological cascade in AD. Developing therapies to target these species is a vital step in improving AD treatment. Aβ-immunotherapy, especially passive immunotherapy, is a promising approach to reduce the Aβ burden. Up to now, several monoclonal antibodies (mAbs) have been tested in clinical trials on humans, but none of them have passed Phase III. In all likelihood, these trials failed mainly because patients with mild-to-moderate AD were recruited, and thus treatment may have been too late to be effective. Therefore, many ongoing clinical trials are being conducted in patients at the prodromal stage. New structures based on antibody fragments have been engineered intending to improve efficacy and safety. This review presents the properties of this variety of developing treatments and provides a perspective on state-of-the-art of passive Aβ-immunotherapy in AD.

Demonstration of safety of intravenous immunoglobulin in geriatric patients in a long-term, placebo-controlled study of Alzheimer's disease

INTRODUCTION

We present safety results from a study of Gammagard Liquid intravenous immunoglobulin (IGIV) in patients with probable Alzheimer's disease.

METHODS

This was a placebo-controlled double-blind study. Subjects were randomized to 400 mg/kg (n = 127), 200 mg/kg (n = 135) IGIV, or to 0.25% human albumin (n = 121) administered every 2 weeks ± 7 days for 18 months.

RESULTS

Elevated risk ratios of IGIV versus placebo included chills (3.85) in 9.5% of IGIV-treated subjects (all doses), compared to 2.5% of placebo-treated subjects, and rash (3.08) in 15.3% of IGIV-treated subjects versus 5.0% of subjects treated with placebo. Subjects in the highest IGIV dose group had the lowest proportion of SAEs considered related to product (2 of 127 [1.6%]). Subjects treated with IGIV experienced a lower rate of respiratory and all other infections compared to placebo.

DISCUSSION

IGIV-treated subjects did not experience higher rates of renal failure, lung injury, or thrombotic events than the placebo group. There were no unexpected safety findings. IGIV was well tolerated throughout 18 months of treatment in subjects aged 50-89 years.

Effective anti-Alzheimer Aβ therapy involves depletion of specific Aβ oligomer subtypes

BACKGROUND

Recent studies have implicated specific assembly subtypes of β-amyloid (Aβ) peptide, specifically soluble oligomers (soAβ) as disease-relevant structures that may underlie memory loss in Alzheimer disease. Removing existing soluble and insoluble Aβ assemblies is thought to be essential for any attempt at stabilizing brain function and slowing cognitive decline in Alzheimer disease. IV immunoglobulin (IVIg) therapies have been shown to contain naturally occurring polyclonal antibodies that recognize conformational neoepitopes of soluble or insoluble Aβ assemblies including soAβ. These naturally occurring polyclonal antibodies have been suggested to underlie the apparent clinical benefits of IVIg. However, direct evidence linking anti-Aβ antibodies to the clinical bioactivity of IVIg has been lacking.

METHODS

Five-month-old female Dutch APP E693Q mice were treated for 3 months with neat IVIg or with IVIg that had been affinity-depleted over immobilized Aβ conformers in 1 of 2 assembly states. Memory was assessed in a battery of tests followed by quantification of brain soAβ levels using standard anti-soAβ antibodies.

RESULTS

We provide evidence that NU4-type soAβ (NU4-soAβ) assemblies accumulate in the brains of Dutch APP E693Q mice and are associated with defects in memory, even in the absence of insoluble Aβ plaques. Memory benefits were associated with depletion from APP E693Q mouse brain of NU4-soAβ and A11-soAβ but not OC-type fibrillar Aβ oligomers.

CONCLUSIONS

We propose that targeting of specific soAβ assembly subtypes may be an important consideration in the therapeutic and/or prophylactic benefit of anti-Aβ antibody drugs.

Should development of Alzheimer's disease-specific intravenous immunoglobulin be considered?

Recent phase II and III studies with intravenous immunoglobulin (IVIG) in patients with Alzheimer's disease (AD) did not find evidence for the slowing of AD progression compared to placebo-treated patients, in contrast to encouraging results in pilot studies. An additional phase III trial is ongoing. If negative results are found, then further AD studies with IVIG are unlikely unless a manufacturer opts for a trial with high-dose IVIG, which would increase its anti-inflammatory effects but also the risk for adverse events. An alternative approach could be an AD-specific IVIG, supplementing IVIG with higher concentrations of selected antibodies purified from it or produced via recombinant polyclonal antibody technology. These antibodies could include those to amyloid-beta (Aβ, tau protein, inflammatory cytokines, complement activation proteins, and the receptor for advanced glycation end products. IgG fragment crystallizable (Fc) fragments containing terminal sialic acid could be added to increase anti-inflammatory effects. While this product might be more effective in slowing AD clinical progression than current IVIG, there are difficulties with this approach. Preclinical studies would be required to determine which of the antibodies of interest for supplementing current IVIG (for example, antibodies to phosphorylated or oligomeric tau) are actually present (and, therefore, available for purification) in IVIG, and the effects of the product in mouse models of AD. An Investigational New Drug application for an AD-specific IVIG would require United States Food and Drug Administration approval. If the drug would be found to benefit AD patients, meeting the increased demand for IVIG would be challenging.

Safety and tolerability of immune globulin intravenous (human), 10% solution in Japanese subjects with mild to moderate Alzheimer's disease

BACKGROUND

Immune globulin intravenous (IGIV), 10% is a donor-derived polyclonal human immunoglobulin G antibody mixture that has potent immune modulatory properties and contains conformation selective anti-amyloid antibodies. We evaluated the safety and tolerability of multiple doses of IGIV, 10% in Japanese patients with mild to moderate Alzheimer's disease.

METHODS

Among the 16 subjects, 12 subjects were assigned to the IGIV group and 4 subjects to the placebo group. Subjects received a total of six infusions of either IGIV at a dose of 0.2 or 0.4 g/kg, or placebo every 2 weeks.

RESULTS

A total of 33 treatment-emergent adverse events (TEAE) occurred in 14 subjects: 13 TEAE in five subjects in both the IGIV 0.2 and 0.4 g/kg groups, and 7 TEAE in four subjects in the placebo group. The most common TEAE in the IGIV subjects were nasopharyngitis, injection-site swelling, and erythema. All 26 TEAE in the IGIV group were considered to be mild. Only one mild TEAE (rash) was considered to be possibly related to the study drug. There were no significant differences in incidence of TEAE between the treatment groups. Four serious TEAE were reported, and all of these were considered to be unrelated to the study treatment. Other assessments related to safety revealed neither clinically significant abnormal values nor findings in the study.

CONCLUSION

IGIV is generally safe and well tolerated with multiple intravenous infusions at doses of 0.2 g/kg and 0.4 g/kg in Japanese patients with mild to moderate Alzheimer's disease.

Beta-amyloid auto-antibodies are reduced in Alzheimer's disease

Accumulation and cytotoxicity of amyloid beta (Aβ) are understood as the major cause of Alzheimer's disease (AD). There is evidence that naturally occurring antibodies against amyloid beta (Aβ) protein play a role in Aβ-clearance, and such a mechanism appears to be impaired in AD. In the present study, the anti-Aβ antibodies in the serum from individuals with and without late onset AD were measured using ELISA and dot-blot methods. Aβ auto-antibodies in serum were mainly targeted to Aβ1-15 epitope and its titer was significantly lower in AD patients than elderly non-AD controls (NC). The dot-blot analysis further demonstrated that auto-antibodies against fibrillar Aβ42, Aβ1-15 and Aβ16-30 epitopes were all in a lower level in AD than in NC. The isotypes of the auto-antibodies were mainly non-inflammatory IgG2 type. We also analyzed the relationship of auto-Aβ antibody levels with the genotypes of apolipoprotein E (ApoE) and ANKK1/DRD2 gene.

Immunomodulation and AD--down but not out

Alzheimer's disease (AD) is a progressive neurodegenerative disorder and is the most common cause of dementia in the elderly. Interventions that remove existing fibrillar and oligomeric amyloid-β (Aβ) are believed to be essential for the success of any attempt at stabilization of brain function and mitigation of cognitive decline. Many of these strategies have focused on Aβ vaccination and administration of anti-Aβ antibodies. Both active and passive immunotherapies have been successful in mouse models, but both have had limited effect in clinical trials. Intravenous immunoglobulin (IVIG) has been proposed as a potential treatment for AD following evidence for behavioral benefit in AD models and cognitive benefit in early phase 1 and phase 2 clinical trials. A phase 3 trial IVIG trial failed to meet its primary outcomes. While there was a statistically significant benefit in moderate stage AD patients who carried an APOE ε4 allele, this stabilization of cognition was evident only on neuropsychological examination. No benefit on activities of daily living was evident, therefore failing to qualify AD as a new indication for IVIG. Identifying the biologically active component (s) responsible for the neuropsychological benefit in APOE ε4-positive AD patients could enable the development of a compound with greater potency that would qualify for FDA (US Food and Drug Administration) registration.

Human B-1 cells take the stage

B-1 cells play critical roles in defending against microbial invasion and in housekeeping removal of cellular debris. B-1 cells secrete natural antibody and manifest functions that influence T cell expansion and differentiation and in these and other ways differ from conventional B-2 cells. B-1 cells were originally studied in mice where they are easily distinguished from B-2 cells, but their identity in the human system remained poorly defined for many years. Recently, functional criteria for human B-1 cells were established on the basis of murine findings, and reverse engineering resulted in identification of the phenotypic profile, CD20(+)CD27(+)CD43(+)CD70(-), for B-1 cells found in both umbilical cord blood and adult peripheral blood. Human B-1 cells may contribute to multiple disease states through production of autoantibody and stimulation/modulation of T cell activity. Human B-1 cells could be a rich source of antibodies useful in treating diseases present in elderly populations where natural antibody protection may have eroded. Manipulation of human B-1 cell numbers and/or activity may be a new avenue for altering T cell function and treating immune dyscrasias.

Intravenous immunoglobulin and Alzheimer's disease: what now?

Intravenous immunoglobulin (IVIG) products are prepared from purified plasma immunoglobulins from large numbers of healthy donors. Pilot studies with the IVIG preparations Octagam and Gammagard in individuals with mild-to-moderate Alzheimer’s disease (AD) suggested stabilization of cognitive functioning in these patients, and a phase II trial with Gammagard reported similar findings. However, subsequent reports from Octagam’s phase II trial and Gammagard’s phase III trial found no evidence for slowing of AD progression. Although these recent disappointing results have reduced enthusiasm for IVIG as a possible treatment for AD, it is premature to draw final conclusions; a phase III AD trial with the IVIG product Flebogamma is still in progress. IVIG was the first attempt to use multiple antibodies to treat AD. This approach should be preferable to administration of single monoclonal antibodies in view of the multiple processes that are thought to contribute to AD neuropathology. Development of “AD-specific” preparations with higher concentrations of selected human antibodies and perhaps modified in other ways (such as increasing their anti-inflammatory effects and/or ability to cross the blood–brain barrier) should be considered. Such preparations, if generated with recombinant technology, could overcome the problems of high cost and limited supplies, which have been major concerns relating to the possible widespread use of IVIG in AD patients. This review summarizes the recent AD IVIG trials and discusses the major issues relating to possible use of IVIG for treating AD, as well as the critical questions which remain.

Intravenous immunglobulin binds beta amyloid and modifies its aggregation, neurotoxicity and microglial phagocytosis in vitro

Intravenous Immunoglobulin (IVIG) has been proposed as a potential therapeutic for Alzheimer's disease (AD) and its efficacy is currently being tested in mild-to-moderate AD. Earlier studies reported the presence of anti-amyloid beta (Aβ) antibodies in IVIG. These observations led to clinical studies investigating the potential role of IVIG as a therapeutic agent in AD. Also, IVIG is known to mediate beneficial effects in chronic inflammatory and autoimmune conditions by interfering with various pathological processes. Therefore, we investigated the effects of IVIG and purified polyclonal Aβ -specific antibodies (pAbs-Aβ) on aggregation, toxicity and phagocytosis of Aβ in vitro, thus elucidating some of the potential mechanisms of action of IVIG in AD patients. We report that both IVIG and pAbs-Aβ specifically bound to Aβ and inhibited its aggregation in a dose-dependent manner as measured by Thioflavin T assay. Additionally, IVIG and the purified pAbs-Aβ inhibited Aβ-induced neurotoxicity in the SH-SY5Y human neuroblastoma cell line and prevented Aβ binding to rat primary cortical neurons. Interestingly, IVIG and pAbs-Aβ also increased the number of phagocytosing cells as well as the amount of phagocytosed fibrillar Aβ by BV-2 microglia. Phagocytosis of Aβ depended on receptor-mediated endocytosis and was accompanied by upregulation of CD11b expression. Importantly, we could also show that Privigen dose-dependently reversed Aβ-mediated LTP inhibition in mouse hippocampal slices. Therefore, our in vitro results suggest that IVIG may have an impact on different processes involved in AD pathogenesis, thereby promoting further understanding of the effects of IVIG observed in clinical studies.

Mechanisms of action of naturally occurring antibodies against β-amyloid on microglia

BACKGROUND

Naturally occurring autoantibodies against amyloid-β (nAbs-Aβ) have been shown to exert beneficial effects on transgenic Alzheimer's disease (AD) animals in vivo and on primary neurons in vitro. Not much is known about their effect on microglial cells. Our aim was to investigate the effect of nAbs-Aβ on amyloid-β (Aβ)-treated microglial cells in vitro with respect to cell viability, stress pathways, cytokine production and phagocytotic abilities and whether these effects can be conveyed to neurons.

METHODS

Primary microglial cells isolated from Swiss Webster mouse mesencephalons on embryonic day 13.5 were pretreated with nAbs-Aβ and then treated with Aβ oligomers. After 3 hours, phagocytosis as well as western blot analysis were evaluated to measure the amount of phagocytized Aβ. Cell viability was analyzed using an MTT assay 24 hours after treatment. Pro-inflammatory cytokines in the supernatants were analyzed with ELISAs and then we treated primary neuronal cells with these conditioned microglia supernatants. Twenty-four hours later we did a MTT assay of the treated neurons. We further investigated the effect of a single nAbs-Aβ administration on Tg2576 mice in vivo.

RESULTS

Upon co-administration of Aβ and nAbs-Aβ no change in microglia viability was observed. However, there was an increase in phosphorylated p38 protein level, an increase in the pro-inflammatory cytokines TNF-α and IL-6 and an increase in Aβ uptake by microglial cells. Treatment of primary neurons with conditioned microglia medium led to a 10% improvement in cell viability when nAbs-Aβ were co-administered compared to Aβ-treated cells alone. We were unable to detect changes in cytokine production in brain lysates of Tg2576 mice.

CONCLUSIONS

We provide evidence on the mechanism of action of nAbs-Aβ on microglia in vitro. Interestingly, our in vivo data indicate that nAbs-Aβ administration should be considered as a therapeutic strategy in AD, since there is no inflammatory reaction.

Amyloid and Alzheimer's disease: inside and out

Alzheimer's disease (AD) is poised to become the most serious healthcare issue of our generation. The leading theory of AD pathophysiology is the Amyloid Cascade Hypothesis, and clinical trials are now proceeding based on this hypothesis. Here, we review the original evidence for the Amyloid Hypothesis, which was originally focused on the extracellular deposition of beta amyloid peptides (Aβ) in large fibrillar aggregates, as well as how this theory has been extended in recent years to focus on highly toxic small soluble amyloid oligomers. We will also examine emerging evidence that Aβ may actually begin to accumulate intracellularly in lysosomes, and the role for intracellular Aβ and lysosomal dysfunction may play in AD pathophysiology. Finally, we will review the clinical implications of these findings.

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

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

Effects of human intravenous immunoglobulin on amyloid pathology and neuroinflammation in a mouse model of Alzheimer's disease

BACKGROUND

Human intravenous immunoglobulin (hIVIG) preparation is indicated for treating primary immunodeficiency disorders associated with impaired humoral immunity. hIVIG is known for its anti-inflammatory properties and a decent safety profile. Therefore, by virtue of its constituent natural anti-amyloid beta antibodies and anti-inflammatory effects, hIVIG is deemed to mediate beneficial effects to patients of Alzheimer's disease (AD). Here, we set out to explore the effects of hIVIG in a mouse model of AD.

METHODS

We treated APP/PS1dE9 transgenic and wild-type mice with weekly injections of a high hIVIG dose (1 g/kg) or saline for 3 or 8 months. Treatment effect on brain amyloid pathology and microglial reactivity was assessed by ELISA, immunohistochemistry, RT-PCR, and confocal microscopy.

RESULTS

We found no evidence for reduction in Aβ pathology; instead 8 months of hIVIG treatment significantly increased soluble levels of Aβ40 and Aβ42. In addition, we noticed a significant reduction in CD45 and elevation of Iba-1 markers in specific sub-populations of microglial cells. Long-term hIVIG treatment also resulted in significant suppression of TNF-α and increase in doublecortin positive adult-born neurons in the dentate gyrus.

CONCLUSIONS

Our data indicate limited ability of hIVIG to impact amyloid burden but shows changes in microglia, pro-inflammatory gene expression, and neurogenic effects. Immunomodulation by hIVIG may account for its beneficial effect in AD patients.

Solanezumab for the treatment of mild-to-moderate Alzheimer's disease

Solanezumab (LY2062430) is a humanized monoclonal antibody that binds to the central region of β-amyloid, a peptide believed to play a key role in the pathogenesis of Alzheimer's disease (AD). Eli Lilly & Co is developing an intravenous formulation of solanezumab for the treatment of mild-to-moderate AD. Acute and subchronic treatment with solanezumab of transgenic mice attenuated or reversed memory deficits with no effects on incidence or severity of cerebral amyloid angiopathy-associated microhemorrhages, a severe side effect associated with bapineuzumab, another monoclonal antibody. Phase II studies in AD patients have shown a good safety profile with encouraging indications on cerebrospinal and plasma biomarkers. The drug is currently being investigated in Phase III trials. While there is a strong hope that solanezumab may represent the first effective passive vaccine for AD treatment, skepticism still exists on the ability of the drug to slow the rate of deterioration in patients with fully established disease.

Animal Models of Alzheimer's Disease: Utilization of Transgenic Alzheimer's Disease Models in Studies of Amyloid Beta Clearance

Glial cells in Alzheimer’s disease (AD) have been shown to be capable of clearing or at least restricting the accumulation of toxic amyloid beta (Aβ) deposits. Recently, bone marrow (BM)–derived monocytic cells have been recognized in experimental studies to be superior in their phagocytic properties when compared to their brain endogenous counterparts. In human AD, BM-derived monocytic cells may have deficiencies in their capacity to restrict plaque growth. Therefore, enhancement of phagocytic properties of cells of monocyte origin, both brain endogenous microglia and BM-derived monocytic cells, offers an attractive therapeutic approach to fight off AD. Transgenic mouse models with aberrant Aβ deposition offer a valuable tool for discovery of novel pathways to facilitate cell-mediated Aβ uptake. This article reviews the most recent findings on the phagocytic capacity of cells with monocytic origin in various transgenic AD models and describes the methods to study phagocytic activity of these cells.

Naturally occurring autoantibodies against β-Amyloid

Naturally occurring antibodies (NAbs) have been described for more than 30 years. Recently, NAbs against β-Amyloid and against other proteins involved in neurodegenerative disorders have been detected in humans. Based on the current evidence, it is hypothesized that anti-Aβ NAbs can inhibit the fibrillation and toxicity of β-aymloid, can improve cognition in a transgenic mouse model and interfere with oligomers of Aβ. Different functions of these NAbs have been described in the current literature. Based on the results of the diverse studies a Phase-III study using IVIG has been initiated in patients with AD. The results will show whether the application of NAbs will change the fate of the disease. This chapter summarizes our current knowledge on NAbs against Aβ.

ELISA measurement of specific non-antigen-bound antibodies to Aβ1-42 monomer and soluble oligomers in sera from Alzheimer's disease, mild cognitively impaired, and noncognitively impaired subjects

Background

The literature contains conflicting results regarding the status of serum anti-Aβ antibody concentrations in Alzheimer's disease (AD). Reduced levels of these antibodies have been suggested to contribute to the development of this disorder. The conflicting results may be due to polyvalent antibodies, antibody "masking" due to Aβ binding, methodological differences, and/or small sample sizes. The objectives of this pilot study were to compare serum anti-Aβ antibody concentrations between AD, mild cognitive impairment (MCI), and elderly noncognitively impaired (NCI) subjects while addressing these issues, and to perform power analyses to determine appropriate group sizes for future studies employing this approach.

Methods

Serum antibodies to Aβ1-42 monomer and soluble oligomers in AD, MCI, and NCI subjects (10/group) were measured by ELISA, subtracting polyvalent antibody binding and dissociating antibody-antigen complexes. Differences in mean antibody levels were assessed for significance with repeated measures ANOVA using restricted maximum likelihood estimation, using Tukey-Kramer tests and confidence intervals for multiple comparisons. Spearman's rank correlation was used to determine associations between anti-monomer and anti-oligomer antibody concentrations. Estimated sample sizes required to detect effects of various sizes were calculated.

Results

There were no significant differences between groups for mean anti-Aβ antibody levels, although these tended to be higher in AD than NCI specimens. Estimated group sizes of 328 and 150 for anti-Aβ monomer and oligomer antibodies, respectively, would have been required for 80% power for significance at 0.05 for a 25% increase in the AD mean relative to the NCI mean. Serum antibody concentrations to Aβ monomer and oligomers were strongly associated (correlations: 0.798 for undissociated sera, 0.564 for dissociated sera). Antibody-antigen dissociation significantly increased anti-Aβ monomer but not anti-Aβ oligomer antibody levels.

Conclusions

The findings in this pilot study are consistent with relatively similar concentrations of specific, non-antigen-bound antibodies to Aβ1-42 monomer and soluble oligomers in AD, MCI, and NCI sera. The differences between groups for these antibodies would have required approximate group sizes of 328 and 150, respectively, for a high probability for statistical significance. These findings do not support the hypothesis that reduced levels of anti-Aβ antibodies might contribute to AD's pathogenesis.

Human intravenous immunoglobulin provides protection against Aβ toxicity by multiple mechanisms in a mouse model of Alzheimer's disease

Background

Purified intravenous immunoglobulin (IVIG) obtained from the plasma of healthy humans is indicated for the treatment of primary immunodeficiency disorders associated with defects in humoral immunity. IVIG contains naturally occurring auto-antibodies, including antibodies (Abs) against β-amyloid (Aβ) peptides accumulating in the brains of Alzheimer's disease (AD) patients. IVIG has been shown to alleviate AD pathology when studied with mildly affected AD patients. Although its mechanisms-of-action have been broadly studied, it remains unresolved how IVIG affects the removal of natively formed brain Aβ deposits by primary astrocytes and microglia, two major cell types involved in the neuroinflammatory responses.

Methods

We first determined the effect of IVIG on Aβ toxicity in primary neuronal cell culture. The mechanisms-of-action of IVIG in reduction of Aβ burden was analyzed with ex vivo assay. We studied whether IVIG solubilizes natively formed Aβ deposits from brain sections of APP/PS1 mice or promotes Aβ removal by primary glial cells. We determined the role of lysosomal degradation pathway and Aβ Abs in the IVIG-promoted reduction of Aβ. Finally, we studied the penetration of IVIG into the brain parenchyma and interaction with brain deposits of human Aβ in a mouse model of AD in vivo.

Results

IVIG was protective against Aβ toxicity in a primary mouse hippocampal neuron culture. IVIG modestly inhibited the fibrillization of synthetic Aβ1-42 but did not solubilize natively formed brain Aβ deposits ex vivo. IVIG enhanced microglia-mediated Aβ clearance ex vivo, with a mechanism linked to Aβ Abs and lysosomal degradation. The IVIG-enhanced Aβ clearance appears specific for microglia since IVIG did not affect Aβ clearance by astrocytes. The cellular mechanisms of Aβ clearance we observed have potential relevance in vivo since after peripheral administration IVIG penetrated to mouse brain tissue reaching highest concentrations in the hippocampus and bound selectively to Aβ deposits in co-localization with microglia.

Conclusions

Our results demonstrate that IVIG promotes recognition and removal of natively formed brain Aβ deposits by primary microglia involving natural Aβ Abs in IVIG. These findings may have therapeutic relevance in vivo as IVIG penetrates through the blood-brain barrier and specifically binds to Aβ deposits in brain parenchyma.

Anti-amyloidogenic activity of IgGs contained in normal plasma

INTRODUCTION

We have previously shown that a subpopulation of naturally occurring human IgGs has therapeutic potential for the amyloid-associated disorders. These molecules cross-react with conformational epitopes on amyloidogenic assemblies, including amyloid beta (Abeta) protein fibrils that are a pathological hallmark of Alzheimer's disease.

MATERIALS AND METHODS

Using our europium-linked immunosorbant assay, we established that approximately 95% of 260 screened donor plasma samples had amyloid fibril-reactive IgGs and Abeta conformer-reactive IgGs with minimal binding to Abeta monomers. Anti-amyloidogenic reactivity was diverse and attributed to Abeta targeting multiple fibril-related binding sites and/or variations in multidentate binding.

RESULTS AND DISCUSSION

There was no correlation between anti-fibril and anti-oligomer reactivity and donor age (19 to 60 years old) or gender. These findings demonstrate the inherent but diverse anti-amyloidogenic activity of natural IgGs contained in normal plasma.

CONCLUSION

Our studies provide support for investigating the clinical significance and physiological function of this novel class of antibodies.

Immunological origin and functional properties of catalytic autoantibodies to amyloid beta peptide

OBJECTIVES

Objectives The objectives of this study are to (1) evaluate the ability of the immune system to synthesize specific antibodies that catalyze the degradation of amyloid beta peptide (Abeta) and to (2) evaluate the prospect of developing a catalytic IVIG (CIVIG) formulation for therapy of Alzheimer's disease (AD).

CONCLUSIONS

Polyclonal autoantibodies from humans without dementia hydrolyzed Abeta specifically. The catalytic activity improved as a function of age. Patients with AD produced catalytic antibodies at increased levels. IgM-class antibodies expressed the activity at levels superior to IgGs. Production of catalytic autoantibodies appears to be an innate immunity function with adaptive improvements occurring upon Abeta overexpression, which suggests a beneficial function of the catalytic activity. The catalytic autoantibodies impeded Abeta aggregation, dissolved preformed Abeta aggregates, and inhibited Abeta cytotoxicity in tissue culture. Recombinant catalytic antibodies from a human library have been identified, validating the phenomenon of antibody-catalyzed Abeta cleavage. As a single catalyst molecule inactivates multiple Abeta molecules, catalytic antibodies may clear Abeta efficiently. IVIG did not cleave Abeta, indicating the importance of purification procedures that maintain catalytic site integrity. Traditional Abeta-binding antibodies form immune complexes that can induce inflammatory reaction and vascular dysfunction. Catalysts do not form stable immune complexes, minimizing these risks. Criteria appropriate for developing a CIVIG formulation with potential therapeutic utility are discussed, including isolation of the Abeta-specific catalytic subsets present in IgM and IgG from human blood.

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

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

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

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

Amyloid-modifying therapies for Alzheimer's disease: therapeutic progress and its implications

Alzheimer's disease (AD) is the most prevalent form of dementia, affecting an estimated 4.8 million people in North America. For the past decade, the amyloid cascade hypothesis has dominated the field of AD research. This theory posits that the deposition of amyloid-beta protein (Abeta) in the brain is the key pathologic event in AD, which induces a series of neuropathological changes that manifest as cognitive decline and eventual dementia. Based on this theory, interventions that reduce Abeta burden in the brain would be expected to alleviate both the neuropathological changes and dementia, which characterize AD. Several diverse pharmacological strategies have been developed to accomplish this. These include inhibiting the formation of Abeta, preventing the aggregation of Abeta into insoluble aggregates, preventing the entry of Abeta into the brain from the periphery and enhancing the clearance of Abeta from the central nervous system. To date, no amyloid-modifying therapy has yet been successful in phase 3 clinical trials; however, several trials are currently underway. This article provides a review of the status of amyloid-modifying therapies and the implications for the amyloid cascade hypothesis.

Measurement of anti-beta amyloid antibodies in human blood

The human IgG repertoire contains endogenous antibodies against beta amyloid (Aβ) that may be relevant to the pathogenesis and treatment of Alzheimer's disease. There have been widely disparate estimates of the levels of these antibodies in human plasma. We identify factors that have contributed to these disparities and describe improved methods for measuring anti-Aβ antibodies in blood. These methods include isolating immunoglobulin by thiophilic chromatography and using chaotropic salts to dislodge weakly bound antibodies without significantly reducing the binding of specific anti-Aβ antibodies. Using these methods, we show that human blood contains polyvalent IgG antibodies that bind to Aβ with relatively low avidity and specificity, as well as IgG antibodies that bind to linear and conformational epitopes on amyloid monomers and aggregates with moderate to high avidity.

Amyloid-beta immunotherapy for Alzheimer's disease

Alzheimer's disease (AD) is a progressive, degenerative disorder of the brain and the most common form of dementia among the elderly. As the population grows and lifespan is extended, the number of AD patients will continue to rise. Current clinical therapies for AD provide partial symptomatic benefits for some patients; however, none of them modify disease progression. Amyloid-beta (Abeta) peptide, the major component of senile plaques in AD patients, is considered to play a crucial role in the pathogenesis of AD thereby leading to Abeta as a target for treatment. Abeta immunotherapy has been shown to induce a marked reduction in amyloid burden and an improvement in cognitive function in animal models. Although preclinical studies were successful, the initial human clinical trial of an active Abeta vaccine was halted due to the development of meningoencephalitis in approximately 6% of the vaccinated AD patients. Some encouraging outcomes, including signs of cognitive stabilization and apparent plaque clearance, were obtained in subset of patients who generated antibody titers. These promising preliminary data support further efforts to refine Abeta immunotherapy to produce highly effective and safer active and passive vaccines for AD. Furthermore, some new human clinical trials for both active and passive Abeta immunotherapy are underway. In this review, we will provide an update of Abeta immunotherapy in animal models and in human beings, as well as discuss the possible mechanisms underlying Abeta immunotherapy for AD.

Can Alzheimer disease be prevented by amyloid-beta immunotherapy?

Alzheimer disease (AD) is the most common form of dementia. The amyloid-beta (Abeta) peptide has become a major therapeutic target in AD on the basis of pathological, biochemical and genetic evidence that supports a role for this molecule in the disease process. Active and passive Abeta immunotherapies have been shown to lower cerebral Abeta levels and improve cognition in animal models of AD. In humans, dosing in the phase II clinical trial of the AN1792 Abeta vaccine was stopped when approximately 6% of the immunized patients developed meningoencephalitis. However, some plaque clearance and modest clinical improvements were observed in patients following immunization. As a result of this study, at least seven passive Abeta immunotherapies are now in clinical trials in patients with mild to moderate AD. Several second-generation active Abeta vaccines are also in early clinical trials. On the basis of preclinical studies and the limited data from clinical trials, Abeta immunotherapy might be most effective in preventing or slowing the progression of AD when patients are immunized before or in the very earliest stages of disease onset. Biomarkers for AD and imaging technology have improved greatly over the past 10 years and, in the future, might be used to identify presymptomatic, at-risk individuals who might benefit from Abeta immunization.

Inherent anti-amyloidogenic activity of human immunoglobulin gamma heavy chains

We have previously shown that a subpopulation of naturally occurring human IgGs were cross-reactive against conformational epitopes on pathologic aggregates of Abeta, a peptide that forms amyloid fibrils in the brains of patients with Alzheimer disease, inhibited amyloid fibril growth, and dissociated amyloid in vivo. Here, we describe similar anti-amyloidogenic activity that is a general property of free human Ig gamma heavy chains. A gamma(1) heavy chain, F1, had nanomolar binding to an amyloid fibril-related conformational epitope on synthetic oligomers and fibrils as well as on amyloid-laden tissue sections. F1 did not bind to native Abeta monomers, further indicating the conformational nature of its binding site. The inherent anti-amyloidogenic activity of Ig gamma heavy chains was demonstrated by nanomolar amyloid fibril and oligomer binding by polyclonal and monoclonal human heavy chains that were isolated from inert or weakly reactive antibodies. Most importantly, the F1 heavy chain prevented in vitro fibril growth and reduced in vivo soluble Abeta oligomer-induced impairment of rodent hippocampal long term potentiation, a cellular mechanism of learning and memory. These findings demonstrate that free human Ig gamma heavy chains comprise a novel class of molecules for developing potential therapeutics for Alzheimer disease and other amyloid disorders. Moreover, establishing the molecular basis for heavy chain-amyloidogenic conformer interactions should advance understanding on the types of interactions that these pathologic assemblies have with biological molecules.

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.