Recent advancements toward therapeutic vaccines against Alzheimer's disease.

INTRODUCTION: Alzheimer's disease (AD) is a devastating neurodegenerative disease characterized by protein aggregates of amyloid ß (Aß) and tau. These proteins have normal physiological functions, but in AD, they undergo a conformational change and aggregate as toxic oligomeric and fibrillar species with a high ß-sheet content. AREAS COVERED: Active and passive immunotherapeutic approaches are among the most attractive methods for targeting misfolded Aß and tau. Promising preclinical testing of various immunotherapeutic approaches has yet to translate to cognitive benefits in human clinical trials. Knowledge gained from these past failures has led to the development of second-generation Aß-active immunotherapies, anti-Aß monoclonal antibodies targeting a wide array of Aß conformations, and to a number of immunotherapies targeting pathological tau. This review covers the more recent advances in vaccine development for AD from 2016 to present. EXPERT COMMENTARY: Due to the complex pathophysiology of AD, greatest clinical efficacy will most likely be achieved by concurrently targeting the most toxic forms of both Aß and tau.

Immunotherapy to improve cognition and reduce pathological species in an Alzheimer's disease mouse model.

BACKGROUND: Alzheimer's disease (AD) is characterized by physiologically endogenous proteins amyloid beta (Aß) and tau undergoing a conformational change and accumulating as soluble oligomers and insoluble aggregates. Tau and Aß soluble oligomers, which contain extensive ß-sheet secondary structure, are thought to be the most toxic forms. The objective of this study was to determine the ability of TWF9, an anti-ß-sheet conformation antibody (aßComAb), to selectively recognize pathological Aß and phosphorylated tau in AD human tissue compared with cognitively normal age-matched controls and to improve the performance of old 3xTg-AD mice with advanced pathology in behavioral testing after acute treatment with TWF9. METHODS: In this study, we used immunohistochemistry, immunoprecipitation, and enzyme-linked immunosorbent assay (ELISA) to characterize TWF9 specificity. We further assessed cognitive performance in old (18-22 months) 3xTg-AD mice using both a Barnes maze and novel object recognition after intraperitoneal administration of TWF9 (4 mg/kg) biweekly for 2 weeks before the start of behavioral testing. Injections continued for the duration of the behavioral testing, which lasted 2 weeks. RESULTS: Histological analysis of TWF9 in formalin-fixed paraffin-embedded human control and AD (ABC score: A3B3C3) brain tissue revealed preferential cytoplasmic immunoreactivity in neurons in the AD tissue compared with controls (p < 0.05). Furthermore, ELISA using oligomeric and monomeric Aß showed a preferential affinity for oligomeric Aß. Immunoprecipitation studies showed that TWF9 extracted both phosphorylated tau (p < 0.01) and Aß (p < 0.01) from fresh frozen brain tissues. Results show that treated old 3xTg-AD mice have an enhanced novel object recognition memory (p < 0.01) and Barnes maze performance (p = 0.05) compared with control animals. Overall plaque burden, neurofibrillary tangles, microgliosis, and astrocytosis remained unchanged. Soluble phosphorylated tau was significantly reduced in TWF9-treated mice (p < 0.05), and there was a trend for a reduction in soluble Aß levels in the brain homogenates of female 3xTg-AD mice (p = 0.06). CONCLUSIONS: This study shows that acute treatment with an aßComAb can effectively improve performance in behavioral testing without reduction of amyloid plaque burden, and that peripherally administered IgG can affect levels of pathological species in the brain.

Anti-ß-sheet conformation monoclonal antibody reduces tau and Aß oligomer pathology in an Alzheimer's disease model.

BACKGROUND: Oligomeric forms of amyloid-ß (Aß) and tau are increasing being recognized as key toxins in the pathogenesis of Alzheimer's disease (AD). METHODS: We developed a novel monoclonal antibody (mAb), GW-23B7, that recognizes ß-sheet secondary structure on pathological oligomers of neurodegenerative diseases. RESULTS: The pentameric immunoglobulin M kappa chain (IgMκp) we developed specifically distinguishes intra- and extracellular pathology in human AD brains. Purified GW-23B7 showed a dissociation constant in the nanomolar range for oligomeric Aß and did not bind monomeric Aß. In enzyme-linked immunosorbent assays, it recognized oligomeric forms of both Aß and hyperphosphorylated tau. Aged triple-transgenic AD mice with both Aß and tau pathology infused intraperitoneally for 2 months showed IgMκp in the soluble brain homogenate, peaking at 24 h postinoculation. Treated mice exhibited significant cognitive rescue on radial arm maze testing compared with vehicle control-infused mice. Immunohistochemically, treatment resulted in a significant decrease of extracellular pathology. Biochemically, treatment resulted in significant reductions of oligomeric forms of Aß and tau. CONCLUSIONS: These results suggest that GW-23B7, an anti-ß-sheet conformational mAb humanized for clinical trials, may be an effective therapeutic agent for human AD.

Production of Monoclonal Antibodies to Pathologic ß-sheet Oligomeric Conformers in Neurodegenerative Diseases.

We describe a novel approach to produce conformational monoclonal antibodies selected to specifically react with the ß-sheet secondary structure of pathological oligomeric conformers, characteristic of many neurodegenerative diseases. Contrary to past and current efforts, we utilize a mammalian non-self-antigen as an immunogen. The small, non-self peptide selected was covalently polymerized with glutaraldehyde until it reached a high ß-sheet secondary structure content, and species between 10-100kDa that are immunogenic, stable and soluble (p13Bri). Inoculation of p13Bri in mice elicited antibodies to the peptide and the ß-sheet secondary structure conformation. Hybridomas were produced and clones selected for their reactivity with at least two different oligomeric conformers from Alzheimer's, Parkinson and/or Prion diseases. The resulting conformational monoclonals are able to detect pathological oligomeric forms in different human neurodegenerative diseases by ELISA, immunohistochemistry and immunoblots. This technological approach may be useful to develop tools for detection, monitoring and treatment of multiple misfolding disorders.

Immunomodulation targeting of both Aß and tau pathological conformers ameliorates Alzheimer's disease pathology in TgSwDI and 3xTg mouse models.

BACKGROUND: Central to the pathogenesis of Alzheimer's disease (AD) and many other neurodegenerative diseases is the conformational change of a normal self-protein into toxic oligomeric species and amyloid deposits. None of these disorders have an effective therapy, but immunization approaches hold great promise. We have previously shown that active immunization with a novel peptide when polymerized into a stable oligomeric conformation, pBri, induced a humoral immune response to toxic Aß species in an AD model, APP/PS1 transgenic (Tg) mice, reducing plaque deposits. pBri is a glutaraldehyde polymerized form of the carboxyl fragment of an amyloidogenic protein, which is deposited in the brains of patients with a rare autosomal dominant disease due to a missense mutation in a stop codon, resulting in the translation of an intronic sequence, with no known sequence homology to any mammalian protein. METHODS: In the current study we tested whether pBri-peptide-based immunomodulation is effective at reducing both vascular amyloid deposits and tau-related pathology using TgSwDI mice with extensive congophilic angiopathy and 3xTg mice with tau pathology. RESULTS: Our results indicate that this immunomodulation approach, which produces a humoral response to proteins in a pathological conformation, is effective at reducing both Aß and tau-related pathologies. CONCLUSIONS: This immunomodulatory approach has the advantage of using a non-self-immunogen that is less likely to be associated with autoimmune toxicity. Furthermore we found that it is able to target all the cardinal features of AD concurrently.