Deglycosylated anti-Abeta antibody dose-response effects on pathology and memory in APP transgenic mice

A pentavalent peptide vaccine elicits Aβ and tau antibodies with prophylactic activity in an Alzheimer's disease mouse model

Amyloid-β (Aβ) and hyperphosphorylated tau protein are targets for Alzheimer's Disease (AD) immunotherapies, which are generally focused on single epitopes within Aβ or tau. However, due to the complexity of both Aβ and tau in AD pathogenesis, a multipronged approach simultaneously targeting multiple epitopes of both proteins could overcome limitations of monotherapies. Herein, we propose an active AD immunotherapy based on a nanoparticle vaccine comprising two Aβ peptides (1-14 and pyroglutamate pE3-14) and three tau peptides (centered on phosphorylated pT181, pT217 and pS396/404). These correspond to both soluble and aggregated targets and are displayed on the surface of immunogenic liposomes in an orientation that maintains reactivity with epitope-specific monoclonal antibodies. Intramuscular immunization of mice with individual epitopes resulted in minimally cross-reactive antibody induction, while simultaneous co-display of 5 antigens ("5-plex") induced antibodies against all epitopes without immune interference. Post-immune sera recognized plaques and neurofibrillary tangles from human AD brain tissue. Vaccine administration to 3xTg-AD mice using a prophylactic dosing schedule inhibited tau and amyloid pathologies and resulted in improved cognitive function. Immunization was well tolerated and did not induce antigen-specific cellular responses or persistent inflammatory responses in the peripheral or central nervous system. Antibody levels could be reversed by halting monthly vaccinations. Altogether, these results indicate that active immune therapies based on nanoparticle formulations of multiple Aβ and tau epitopes warrant further study for treating early-stage AD.

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.

Emerging Promise of Immunotherapy for Alzheimer's Disease: A New Hope for the Development of Alzheimer's Vaccine

BACKGROUND

Alzheimer's disease (AD) is a chronic neurodegenerative disorder and the characteristics of this devastating disorder include the progressive and disabling deficits in the cognitive functions including reasoning, attention, judgment, comprehension, memory, and language.

OBJECTIVE

In this article, we have focused on the recent progress that has been achieved in the development of an effective AD vaccine.

SUMMARY

Currently, available treatment options of AD are limited to deliver short-term symptomatic relief only. A number of strategies targeting amyloid-beta (Aβ) have been developed in order to treat or prevent AD. In order to exert an effective immune response, an AD vaccine should contain adjuvants that can induce an effective anti-inflammatory T helper 2 (Th2) immune response. AD vaccines should also possess the immunogens which have the capacity to stimulate a protective immune response against various cytotoxic Aβ conformers. The induction of an effective vaccine's immune response would necessitate the parallel delivery of immunogen to dendritic cells (DCs) and their priming to stimulate a Th2-polarized response. The aforesaid immune response is likely to mediate the generation of neutralizing antibodies against the neurotoxic Aβ oligomers (AβOs) and also anti-inflammatory cytokines, thus preventing the AD-related inflammation.

CONCLUSION

Since there is an age-related decline in the immune functions, therefore vaccines are more likely to prevent AD instead of providing treatment. AD vaccines might be an effective and convenient approach to avoid the treatment-related huge expense.

Decoding the synaptic dysfunction of bioactive human AD brain soluble Aβ to inspire novel therapeutic avenues for Alzheimer's disease

Pathologic, biochemical and genetic evidence indicates that accumulation and aggregation of amyloid β-proteins (Aβ) is a critical factor in the pathogenesis of Alzheimer's disease (AD). Several therapeutic interventions attempting to lower Aβ have failed to ameliorate cognitive decline in patients with clinical AD significantly, but most such approaches target only one or two facets of Aβ production/clearance/toxicity and do not consider the heterogeneity of human Aβ species. As synaptic dysfunction may be among the earliest deficits in AD, we used hippocampal long-term potentiation (LTP) as a sensitive indicator of the early neurotoxic effects of Aβ species. Here we confirmed prior findings that soluble Aβ oligomers, much more than fibrillar amyloid plaque cores or Aβ monomers, disrupt synaptic function. Interestingly, not all (84%) human AD brain extracts are able to inhibit LTP and the degree of LTP impairment by AD brain extracts does not correlate with Aβ levels detected by standard ELISAs. Bioactive AD brain extracts also induce neurotoxicity in iPSC-derived human neurons. Shorter forms of Aβ (including Aβ_1-37, Aβ_1-38, Aβ_1-39), pre-Aβ APP fragments (- 30 to - 1) and N-terminally extended Aβs (- 30 to + 40) each showed much less synaptotoxicity than longer Aβs (Aβ_1-42 - Aβ_1-46). We found that antibodies which target the N-terminus, not the C-terminus, efficiently rescued Aβ oligomer-impaired LTP and oligomer-facilitated LTD. Our data suggest that preventing soluble Aβ oligomer formation and targeting their N-terminal residues with antibodies could be an attractive combined therapeutic approach.

Anti-Aβ antibodies incapable of reducing cerebral Aβ oligomers fail to attenuate spatial reference memory deficits in J20 mice

Compelling genetic evidence links the amyloid precursor protein (APP) to Alzheimer's disease (AD). A leading hypothesis proposes that a small amphipathic fragment of APP, the amyloid β-protein (Aβ), self-associates to form soluble assemblies loosely referred to as "oligomers" and that these are primary mediators of synaptic dysfunction. As such, Aβ, and specifically Aβ oligomers, are targets for disease modifying therapies. Currently, the most advanced experimental treatment for AD relies on the use of anti-Aβ antibodies. In this study, we tested the ability of the monomer-preferring antibody, m266 and a novel aggregate-preferring antibody, 1C22, to attenuate spatial reference memory impairments in J20 mice. Chronic treatment with m266 resulted in a ~70-fold increase in Aβ detected in the bloodstream, and a ~50% increase in water-soluble brain Aβ--and in both cases Aβ was bound to m266. In contrast, 1C22 increased the levels of free Aβ in the bloodstream, and bound to amyloid deposits in J20 brain. However, neither 1C22 nor m266 attenuated the cognitive deficits evident in 12month old J20 mice. Moreover, both antibodies failed to alter the levels of soluble Aβ oligomers in J20 brain. These results suggest that Aβ oligomers may mediate the behavioral deficits seen in J20 mice and highlight the need for the development of aggregate-preferring antibodies that can reach the brain in sufficient levels to neutralize bioactive Aβ oligomers. Aside from the lack of positive effect of m266 and 1C22 on cognition, a substantial number of deaths occurred in m266- and 1C22-immunized J20 mice. These fatalities were specific to anti-Aβ antibodies and to the J20 mouse line since treatment of wild type or PDAPP mice with these antibodies did not cause any deaths. These and other recent results indicate that J20 mice are particularly susceptible to targeting of the APP/Aβ/tau axis. Notwithstanding the specificity of fatalities for J20 mice, it is worrying that the murine precursor (m266) of a lead experimental therapeutic, Solanezumab, did not engage with putatively pathogenic Aβ oligomers.

Treatment effects in a transgenic mouse model of Alzheimer's disease: a magnetic resonance spectroscopy study after passive immunization

Despite the enormous public health impact of Alzheimer's disease (AD), no disease-modifying treatment has yet been proven to be efficacious in humans. A rate-limiting step in the discovery of potential therapies for humans is the absence of efficient non-invasive methods of evaluating drugs in animal models of disease. Magnetic resonance spectroscopy (MRS) provides a non-invasive way to evaluate the animals at baseline, at the end of treatment, and serially to better understand treatment effects. In this study, MRS was assessed as potential outcome measure for detecting disease modification in a transgenic mouse model of AD. Passive immunization with two different antibodies, which have been previously shown to reduce plaque accumulation in transgenic AD mice, was used as intervention. Treatment effects were detected by MRS, and the most striking finding was attenuation of myo-inositol (mIns) increases in APP-PS1 mice with both treatments. Additionally, a dose-dependent effect was observed with one of the treatments for mIns. MRS appears to be a valid in vivo measure of anti-Aβ therapeutic efficacy in pre-clinical studies. Because it is noninvasive, and can detect treatment effects, use of MRS-based endpoints could substantially accelerate drug discovery.

Prophylaxis and treatment of Alzheimer's disease by delivery of an adeno-associated virus encoding a monoclonal antibody targeting the amyloid Beta protein

We previously reported on a monoclonal antibody (mAb) that targeted amyloid beta (Aß) protein. Repeated injection of that mAb reduced the accumulation of Aß protein in the brain of human Aß transgenic mice (Tg2576). In the present study, cDNA encoding the heavy and light chains of this mAb were subcloned into an adeno-associated virus type 1 (AAV) vector with a 2A/furin adapter. A single intramuscular injection of 3.0×10¹⁰ viral genome of these AAV vectors into C57BL/6 mice generated serum anti-Aß Ab levels up to 0.3 mg/ml. Anti-Aß Ab levels in excess of 0.1 mg/ml were maintained for up to 64 weeks. The effect of AAV administration on Aß levels in vivo was examined. A significant decrease in Aß levels in the brain of Tg2576 mice treated at 5 months (prophylactic) or 10 months (therapeutic) of age was observed. These results support the use of AAV vector encoding anti-Aß Ab for the prevention and treatment of Alzheimer's disease.

Efficacy of a therapeutic vaccine using mutated β-amyloid sensitized dendritic cells in Alzheimer's mice

Despite FDA suspension of Elan's AN-1792 amyloid beta (Aβ) vaccine in phase IIb clinical trials, the implications of this study are the guiding principles for contemporary anti-Aβ immunotherapy against Alzheimer's disease (AD). AN-1792 showed promising results with regards to Aβ clearance and cognitive function improvement, but also exhibited an increased risk of Th1 mediated meningoencephalitis. As such, vaccine development has continued with an emphasis on eliciting a notable anti-Aβ antibody titer, while avoiding the unwanted Th1 pro-inflammatory response. Previously, we published the first report of an Aβ sensitized dendritic cell vaccine as a therapeutic treatment for AD in BALB/c mice. Our vaccine elicited an anti-Aβ titer, with indications that a Th1 response was not present. This study is the first to investigate the efficacy and safety of our dendritic cell vaccine for the prevention of AD in transgenic mouse models (PDAPP) for AD. We also used Immunohistochemistry to characterize the involvement of LXR, ABCA1, and CD45 in order to gain insight into the potential mechanisms through which this vaccine may provide benefit. The results indicate that (1) the use of mutant Aβ1-42 sensitized dendritic cell vaccine results in durable antibody production, (2) the vaccine provides significant benefits with regards to cognitive function without the global (Th1) inflammation seen in prior Aβ vaccines, (3) histological studies showed an overall decrease in Aβ burden, with an increase in LXR, ABCA1, and CD45, and (4) the beneficial results of our DC vaccine may be due to the LXR/ABCA1 pathway. In the future, mutant Aβ sensitized dendritic cell vaccines could be an efficacious and safe method for the prevention or treatment of AD that circumvents problems associated with traditional anti-Aβ vaccines.

Amyloid-related imaging abnormalities in amyloid-modifying therapeutic trials: recommendations from the Alzheimer's Association Research Roundtable Workgroup

Amyloid imaging related abnormalities (ARIA) have now been reported in clinical trials with multiple therapeutic avenues to lower amyloid-β burden in Alzheimer's disease (AD). In response to concerns raised by the Food and Drug Administration, the Alzheimer's Association Research Roundtable convened a working group to review the publicly available trial data, attempts at developing animal models, and the literature on the natural history and pathology of related conditions. The spectrum of ARIA includes signal hyperintensities on fluid attenuation inversion recoverysequences thought to represent "vasogenic edema" and/or sulcal effusion (ARIA-E), as well as signal hypointensities on GRE/T2* thought to represent hemosiderin deposits (ARIA-H), including microhemorrhage and superficial siderosis. The etiology of ARIA remains unclear but the prevailing data support vascular amyloid as a common pathophysiological mechanism leading to increased vascular permeability. The workgroup proposes recommendations for the detection and monitoring of ARIA in ongoing AD clinical trials, as well as directions for future research.

Immunotherapy for Alzheimer's disease

In the year 1999, a vaccine approach was found to reduce amyloid deposits in transgenic mice overproducing the amyloid precursor protein. This was followed closely by demonstrations that vaccines or passive immunotherapy could rescue memory deficits in these mice. Initial human clinical trials revealed apparent autoimmune reactions in a subset of patients, but also some cases of cognitive benefit and amyloid clearance. Further work with passive immunotherapy in mouse models confirmed exceptional clearing abilities of anti-amyloid antibodies even in older mice. However, in parallel with parenchymal amyloid clearance was the appearance of microhaemorrhages and increased vascular amyloid deposition. Additional clinical trials with passive immunotherapy confirmed occasional appearance of microhaemorrhage and occurrence of vasogenic oedema in some patients, particularly those with the apolipoprotein E4 genotype. Recent data with positron emission tomography demonstrates trial participants passively immunized with anti-Aß antibodies have reduced signals with amyloid binding ligands after 18 months of therapy. Several anti-Aß immunotherapies have reached phase 3 testing, and immunotherapy is likely to be the first test of the amyloid hypothesis of Alzheimer's disease. Identifying antibody variants that retain amyloid clearance with fewer adverse reactions remains a major focus of translational research in this area.

Aging and cerebrovascular dysfunction: contribution of hypertension, cerebral amyloid angiopathy, and immunotherapy

Age-related cerebrovascular dysfunction contributes to ischemic stroke, intracerebral hemorrhages (ICHs), microbleeds, cerebral amyloid angiopathy (CAA), and cognitive decline. Importantly, there is increasing recognition that this dysfunction plays a critical secondary role in many neurodegenerative diseases, including Alzheimer's disease (AD). Atherosclerosis, hypertension, and CAA are the most common causes of blood-brain barrier (BBB) lesions. The accumulation of amyloid beta (Aβ) in the cerebrovascular system is a significant risk factor for ICH and has been linked to endothelial transport failure and blockage of perivascular drainage. Moreover, recent anti-Aβ immunotherapy clinical trials demonstrated efficient clearance of parenchymal amyloid deposits but have been plagued by CAA-associated adverse events. Although management of hypertension and atherosclerosis can reduce the incidence of ICH, there are currently no approved therapies for attenuating CAA. Thus, there is a critical need for new strategies that improve BBB function and limit the development of β-amyloidosis in the cerebral vasculature.

An amyloid-beta protofibril-selective antibody prevents amyloid formation in a mouse model of Alzheimer's disease

Human genetics link Alzheimer's disease pathogenesis to excessive accumulation of amyloid-beta (Abeta) in brain, but the symptoms do not correlate with senile plaque burden. Since soluble Abeta aggregates can cause synaptic dysfunctions and memory deficits, these species could contribute to neuronal dysfunction and dementia. Here we explored selective targeting of large soluble aggregates, Abeta protofibrils, as a new immunotherapeutic strategy. The highly protofibril-selective monoclonal antibody mAb158 inhibited in vitro fibril formation and protected cells from Abeta protofibril-induced toxicity. When the mAb158 antibody was administered for 4 months to plaque-bearing transgenic mice with both the Arctic and Swedish mutations (tg-ArcSwe), Abeta protofibril levels were lowered while measures of insoluble Abeta were unaffected. In contrast, when treatment began before the appearance of senile plaques, amyloid deposition was prevented and Abeta protofibril levels diminished. Therapeutic intervention with mAb158 was however not proven functionally beneficial, since place learning depended neither on treatment nor transgenicity. Our findings suggest that Abeta protofibrils can be selectively cleared with immunotherapy in an animal model that display highly insoluble Abeta deposits, similar to those of Alzheimer's disease brain.

Immunotherapy, vascular pathology, and microhemorrhages in transgenic mice

Alzheimer's disease (AD) is a progressive, neurodegenerative disorder that results in severe cognitive decline. Amyloid plaques are a principal pathology found in AD and are composed of aggregated amyloid-beta (Abeta) peptides. According to the amyloid hypothesis, Abeta peptides initiate the other pathologies characteristic for AD including cognitive deficits. Immunotherapy against Abeta is a potential therapeutic for the treatment of humans with AD. While anti-Abeta immunotherapy has been shown to reduce amyloid burden in both mouse models and in humans, immunotherapy also exacerbates vascular pathologies. Cerebral amyloid angiopathy (CAA), that is, the accumulation of amyloid in the cerebrovasculature, is increased with immunotherapy in humans with AD and in mouse models of amyloid deposition. CAA persists in the brains of clinical trial patients that show removal of parenchymal amyloid. Mouse model studies also show that immunotherapy results in multiple small bleeds in the brain, termed microhemorrhages. The neurovascular unit is a term used to describe the cerebrovasculature and its associated cells-astrocytes, neurons, pericytes and microglia. CAA affects brain perfusion and there is now evidence that the neurovascular unit is affected in AD when CAA is present. Understanding the type of damage to the neurovascular unit caused by CAA in AD and the underlying cause of microhemorrhage after immunotherapy is essential to the success of therapeutic vaccines as a treatment for AD.