Prediction of the 3D conformation of a small peptide vaccine targeting Aß42 oligomers.

The original etiology of Alzheimer's disease (AD) is the deposition of amyloid-beta (Aß) proteins, which starts from the aggregation of the Aß oligomers. The optimal therapeutic strategy targeting Aß oligomer aggregation is the development of AD vaccines. Despite the fact that positive progress has been made for experimental attempts at AD vaccines, the physicochemical and even structural properties of these AD vaccines remain unclear. In this study, through immunoinformatic and molecular dynamics (MD) simulations, we first designed and simulated an alternative of vaccine TAPAS and found that the structure of the alternative can reproduce the 3D conformation of TAPAS determined experimentally. Meanwhile, immunoinformatic methods were used to analyze the physicochemical properties of TAPAS, including immunogenicity, antigenicity, thermal stability, and solubility, which confirm well the efficacy and safety of the vaccine, and validate the scheme reliability of immunoinformatic and MD simulations in designing and simulating the TAPAS vaccine. Using the same scheme, we predicted the 3D conformation of the optimized ACI-24 peptide vaccine, an Aß peptide with the first 15 residues of Aß42 (Aß1-15). The vaccine was verified once to be effective against both full-length Aß1-42 and truncated Aß4-42 aggregates, but an experimental 3D structure was absent. We have also explored the immune mechanism of the vaccine at the molecular level and found that the optimized ACI-24 and its analogues can block the growth of either full-length Aß1-42 or truncated Aß4-42 pentamer by contacting the hydrophobic residues within the N-terminus and ß1 region on the contact surface of either pentamer. Additionally, residues (D1, D7, S8, H13, and Q15) were identified as the key residues of the vaccine to contact either of the two Aß oligomers. This work provides a feasible implementation scheme of immunoinformatic and MD simulations for the development of AD small peptide vaccines, validating the power of the scheme as a parallel tool to the experimental approaches and injecting molecular-level information into the understanding and design of anti-AD vaccines.

Norovirus P particle-based active Aß immunotherapy elicits sufficient immunogenicity and improves cognitive capacity in a mouse model of Alzheimer's disease.

Disease-modifying immunotherapies focusing on reducing amyloid-beta (Aß) deposition are the main treatment for Alzheimer's disease (AD). However, none of the Aß immunotherapies has produced clinically meaningful results to date. The main reason for this lack of efficacy is that the vaccine induces insufficiently high antibody titers, as it contains small B-cell epitope of Aß to avoid Aß42-specific T-cell activation. With the aim of generating a potent AD vaccine, we designed the protein PP-3copy-Aß1-6-loop123, comprising three copies of Aß1-6 inserted into three loops of a novel vaccine platform, the norovirus P particle, which could present Aß at its surface and remarkably enhance the immunogenicity of the vaccine. We demonstrated that PP-3copy-Aß1-6-loop123 was able to elicit high antibody titers against Aß42, without causing T-cell activation, in AD mice regardless of their age. Importantly, PP-3copy-Aß1-6-loop123 treatment successfully reduced amyloid deposition, rescued memory loss, and repaired hippocampus damage in AD mice. The Aß antibodies induced by this active immunotherapy reacted with and disrupted aggregated Aß, reducing its cellular toxicity. In addition, our results suggested PP-3copy-Aß1-6-loop123 immunization could restore Aß42 homeostasis in both the serum and brain. Thus, the P particle-based Aß epitope vaccine is a sufficiently immunogenic and safe immunotherapeutic intervention for Alzheimer's disease.

Design and development of non-fibrillar amyloid beta as a potential Alzheimer vaccine.

Alzheimer's disease (AD) is the most common cause of dementia affecting the elderly. Treatment for effective cure of this complex neurodegenerative disease does not yet exist. In AD, otherwise soluble, monomeric form of amyloid beta (Abeta) peptide converts into toxic, fibrillar form rich in beta-sheet content. Several immunological approaches that prevent this conversion of Abeta into pathological form or that accelerate its clearance are being actively pursued worldwide. As part of these attempts, we report here, the design and characterization of a non-amyloidogenic homologue of Abeta (Abeta-KEK). We demonstrate that this peptide is helical in nature and retains the immunoneutralizing epitopes of native Abeta. More importantly, Fab fragments of the polyclonal anti-Abeta-KEK antibodies interfere with formation of Abeta fibrils as well as dissociate the preformed Abeta aggregates in vitro. These results suggest that non-amyloidogenic Abeta-KEK may serve as a safer alternative vaccine for Alzheimer's disease.

Immunodominant epitope and properties of pyroglutamate-modified Abeta-specific antibodies produced in rabbits.

N-truncated and N-modified forms of amyloid beta (Abeta) peptide are found in diffused and dense core plaques in Alzheimer's disease (AD) and Down's syndrome patients as well as transgenic mouse models of AD. Although the pathological significance of these shortened forms Abeta is not completely understood, previous studies have demonstrated that these peptides are significantly more resistant to degradation, aggregate more rapidly in vitro and exhibit similar or, in some cases, increased toxicity in hippocampal neuronal cultures compared to the full length peptides. In the present study we further investigated the mechanisms of toxicity of one of the most abundant N-truncated/modified Abeta peptide bearing amino-terminal pyroglutamate at position 3 (AbetaN3(pE)). We demonstrated that AbetaN3(pE) oligomers induce phosphatidyl serine externalization and membrane damage in SH-SY5Y cells. Also, we produced AbetaN3(pE)-specific polyclonal antibodies in rabbit and identified an immunodominant epitope recognized by anti-AbetaN3(pE) antibodies. Our results are important for developing new immunotherapeutic compounds specifically targeting AbetaN3(pE) aggregates since the most commonly used immunogens in the majority of vaccines for AD have been shown to induce antibodies that recognize the N-terminal immunodominant epitope (EFRH) of the full length Abeta, which is absent in N-amino truncated peptides.

Alzheimer's disease peptide epitope vaccine reduces insoluble but not soluble/oligomeric Abeta species in amyloid precursor protein transgenic mice.

Active vaccination of elderly Alzheimer's disease (AD) patients with fibrillar amyloid-beta peptide (Abeta42), even in the presence of a potent Th1 adjuvant, induced generally low titers of antibodies in a small fraction (approximately 20% responders) of those that received the AN-1792 vaccine. To improve the immunogenicity and reduce the likelihood of inducing adverse autoreactive T-cells specific for Abeta42, we previously tested in wild-type mice an alternative approach for active immunization: an epitope vaccine that selectively initiate B cell responses toward an immunogenic self-epitope of Abeta in the absence of anti-Abeta T cell responses. Here, we describe a second generation epitope vaccine composed of two copies of Abeta(1-11) fused with the promiscuous nonself T cell epitope, PADRE (pan human leukocyte antigen DR-binding peptide) that completely eliminates the autoreactive T cell responses and induces humoral immune responses in amyloid precursor protein transgenic 2576 mice with pre-existing AD-like pathology. Based on the titers of anti-Abeta(1-11) antibody experimental mice were divided into low, moderate and high responders, and for the first time we report a positive correlation between the concentration of anti-Abeta(1-11) antibody and a reduction of insoluble, cerebral Abeta plaques. The reduction of insoluble Abeta deposition was not associated with adverse events, such as CNS T cell or macrophage infiltration or microhemorrhages. Surprisingly, vaccination did not alter the levels of soluble Abeta. Alternatively, early protective immunization before substantial neuropathology, neuronal loss and cognitive deficits have become firmly established may be more beneficial and safer for potential patients, especially if they can be identified in a preclinical stage by the development of antecedent biomarkers of AD.