Effective DNA epitope chimeric vaccines for Alzheimer's disease using a toxin-derived carrier protein as a molecular adjuvant

Amyloid-β-targeting immunotherapies for Alzheimer's disease

Recent advances in clinical passive immunotherapy have provided compelling evidence that eliminating amyloid-β (Aβ) slows cognitive decline in Alzheimer's disease (AD). However, the modest benefits and side effects observed in clinical trials indicate that current immunotherapy therapy is not a panacea, highlighting the need for a deeper understanding of AD mechanisms and the significance of early intervention through optimized immunotherapy or immunoprevention. This review focuses on the centrality of Aβ pathology in AD and summarizes recent clinical progress in passive and active immunotherapies targeting Aβ, discussing their lessons and failures to inform future anti-Aβ biotherapeutics design. Various delivery strategies to optimize Aβ-targeting immunotherapies are outlined, highlighting their benefits and drawbacks in overcoming challenges such as poor stability and limited tissue accessibility of anti-Aβ biotherapeutics. Additionally, the perspectives and challenges of immunotherapy and immunoprevention targeting Aβ are concluded in the end, aiming to guide the development of next-generation anti-Aβ immunotherapeutic agents towards improved efficacy and safety.

Improved synaptic and cognitive function in aged 3 × Tg-AD mice with reduced amyloid-β after immunotherapy with a novel recombinant 6Aβ15-TF chimeric vaccine

Alzheimer's disease (AD) is the most common progressive neurodegenerative disorder impairing memory and cognition. In this study, we describe the immunogenicity and protective efficacy of the novel recombinant 6Aβ15-TF chimeric antigen as a subunit protein vaccine for AD. Recombinant 6Aβ15-TF chimeric vaccine induced strong Aβ-specific humoral immune responses without Aβ-specific T cell immunity in C57/BL6 and 3 × Tg-AD mice at different ages. As an early immunotherapy model for AD, this vaccine induced high titers of long-lasting anti-Aβ42 antibodies in aged 3 × Tg-AD mice, which led to improve behavioral performance and markedly reduced the levels of insoluble and soluble Aβ and Aβ oligomers. In agreement with these findings, immunotherapy with 6Aβ15-TF prevented the Aβ-induced decrease of presynaptic and postsynaptic proteins in aged 3 × Tg-AD mice. Our results suggest that this novel and highly immunogenic recombinant 6Aβ15-TF chimeric vaccine provides neuroprotection in AD mice and can be considered an effective AD candidate vaccine.

Peripherally administered sera antibodies recognizing amyloid-β oligomers mitigate Alzheimer's disease-like pathology and cognitive decline in aged 3× Tg-AD mice

Active and passive immunotherapy targeting amyloid-β (Aβ) may be the most promising strategy to prevent or treat Alzheimer's disease (AD). Previously, immunization with the recombinant 6Aβ15-T antigen generated robust anti-Aβ serum antibodies that strongly recognized Aβ42 oligomers in different mice, markedly reduced the amyloid burden, and improved behavioral performance of immunized older AD mice. Here, we further determined that these anti-6Aβ15-T serum antibodies from different strains of mice displayed anti-Aβ antibody responses against the same epitopes in the Aβ1-15 region. Peripheral administration of anti-6Aβ15-T serum antibodies was also effective to mitigate AD-like pathology and cognitive decline in aged 3× Tg-AD mice. Specifically, the levels of Aβ and tau in the brains of 3× Tg-AD mice were significantly reduced after passive immunotherapy, which seemed necessary or beneficial to ameliorate memory impairment. In addition, our results showed that this immunotherapy also prevented presynaptic dynamin 1 degradation, which might help to further protect synaptic functions and allow functional recovery of cognition. Moreover, immunization with 6Aβ15-T in rabbits induced a similar antibody response as that in mice, and the rabbit serum antibodies reacted strongly with Aβ42 oligomers and inhibited oligomer-mediated neurotoxicity. We concluded that passive immunization with Aβ42 oligomer conformation-sensitive anti-6Aβ15-T serum antibodies is effective in providing potentially therapeutic effects in aged 3× Tg-AD mice by reducing Aβ and tau.

Co-immunization with DNA and protein mixture: a safe and efficacious immunotherapeutic strategy for Alzheimer's disease in PDAPP mice

Active immunotherapy targeting β-amyloid (Aβ) is the most promising strategy to prevent or treat Alzheimer's disease (AD). Based on pre-clinical studies and clinical trials, a safe and effective AD vaccine requires a delicate balance between providing therapeutically adequate anti-Aβ antibodies and eliminating or suppressing unwanted adverse T cell-mediated inflammatory reactions. We describe here the immunological characterization and protective efficacy of co-immunization with a 6Aβ15-T DNA and protein mixture without adjuvant as an AD immunotherapeutic strategy. Impressively, this co-immunization induced robust Th2-polarized Aβ-specific antibodies while simultaneously suppressed unwanted inflammatory T cell reactions and avoiding Aβ42-specific T cell-mediated autoimmune responses in immunized mice. Co-immunization with the DNA + protein vaccine could overcome Aβ42-associated hypo-responsiveness and elicit long-term Aβ-specific antibody responses, which helped to maintain antibody-mediated clearance of amyloid and accordingly alleviated AD symptoms in co-immunized PDAPP mice. Our DNA and protein combined vaccine, which could induce an anti-inflammatory Th2 immune response with high level Aβ-specific antibodies and low level IFN-γ production, also demonstrated the capacity to inhibit amyloid accumulation and prevent cognitive dysfunction. Hence, co-immunization with antigen-matched DNA and protein may represent a novel and efficacious strategy for AD immunotherapy to eliminate T cell inflammatory reactions while retaining high level antibody responses.

Lymphocytes and autoimmunity after spinal cord injury

Over the past 15 years an immense amount of data has accumulated regarding the infiltration and activation of lymphocytes in the traumatized spinal cord. Although the impact of the intraspinal accumulation of lymphocytes is still unclear, modulation of the adaptive immune response via active and passive vaccination is being evaluated for its preclinical efficacy in improving the outcome for spinal-injured individuals. The complexity of the interaction between the nervous and the immune systems is highlighted in the contradictions that appear in response to these modulations. Current evidence regarding augmentation and inhibition of the adaptive immune response to spinal cord injury is reviewed with an aim toward reconciling conflicting data and providing consensus issues that may be exploited in future therapies. Opportunities such an approach may provide are highlighted as well as the obstacles that must be overcome before such approaches can be translated into clinical trials.

Alzheimer's disease: is a vaccine possible?

The cause of Alzheimer's disease is still unknown, but the disease is distinctively characterized by the accumulation of β-amyloid plaques and neurofibrillary tangles in the brain. These features have become the primary focus of much of the research looking for new treatments for the disease, including immunotherapy and vaccines targeting β-amyloid in the brain. Adverse effects observed in a clinical trial based on the β-amyloid protein were attributed to the presence of the target antigen and emphasized the relevance of finding safer antigen candidates for active immunization. For this kind of approach, different vaccine formulations using DNA, peptide, and heterologous prime-boost immunization regimens have been proposed. Promising results are expected from different vaccine candidates encompassing B-cell epitopes of the β-amyloid protein. In addition, recent results indicate that targeting another protein involved in the etiology of the disease has opened new perspectives for the effective prevention of the illness. Collectively, the evidence indicates that the idea of finding an effective vaccine for the control of Alzheimer's disease, although not without challenges, is a possibility.

Immunogenicity of DNA- and recombinant protein-based Alzheimer disease epitope vaccines

Alzheimer disease (AD) process involves the accumulation of amyloid plaques and tau tangles in the brain, nevertheless the attempts at targeting the main culprits, neurotoxic β-amyloid (Aβ) peptides, have thus far proven unsuccessful for improving cognitive function. Important lessons about anti-Aβ immunotherapeutic strategies were learned from the first active vaccination clinical trials. AD progression could be safely prevented or delayed if the vaccine (1) induces high titers of antibodies specific to toxic forms of Aβ; (2) does not activate the harmful autoreactive T cells that may induce inflammation; (3) is initiated before or at least at the early stages of the accumulation of toxic forms of Aβ. Data from the recent passive vaccination trials with bapineuzumab and solanezumab also indicated that anti-Aβ immunotherapy might be effective in reduction of the AD pathology and even improvement of cognitive and/or functional performance in patients when administered early in the course of the disease. For the prevention of AD the active immunization strategy may be more desirable than passive immunotherapy protocol and it can offer the potential for sustainable clinical and commercial advantages. Here we discuss the active vaccine approaches, which are still in preclinical development and vaccines that are already in clinical trials.

Pharmacogenomics of Alzheimer's disease: novel therapeutic strategies for drug development

Alzheimer's disease (AD) is a major problem of health and disability, with a relevant economic impact on our society. Despite important advances in pathogenesis, diagnosis, and treatment, its primary causes still remain elusive, accurate biomarkers are not well characterized, and the available pharmacological treatments are not cost-effective. As a complex disorder, AD is a polygenic and multifactorial clinical entity in which hundreds of defective genes distributed across the human genome may contribute to its pathogenesis. Diverse environmental factors, cerebrovascular dysfunction, and epigenetic phenomena, together with structural and functional genomic dysfunctions, lead to amyloid deposition, neurofibrillary tangle formation, and premature neuronal death, the major neuropathological hallmarks of AD. Future perspectives for the global management of AD predict that genomics and proteomics may help in the search for reliable biomarkers. In practical terms, the therapeutic response to conventional drugs (cholinesterase inhibitors, multifactorial strategies) is genotype-specific. Genomic factors potentially involved in AD pharmacogenomics include at least five categories of gene clusters: (1) genes associated with disease pathogenesis; (2) genes associated with the mechanism of action of drugs; (3) genes associated with drug metabolism (phase I and II reactions); (4) genes associated with drug transporters; and (5) pleiotropic genes involved in multifaceted cascades and metabolic reactions. The implementation of pharmacogenomic strategies will contribute to optimize drug development and therapeutics in AD and related disorders.