Immunization with a new DNA vaccine for Alzheimer's disease elicited Th2 immune response in BALB/c mice by in vivo electroporation

Induction of an effective anti-Amyloid-β humoral response in aged mice

Aging-related decline in immune functions, termed immunosenescence, is a primary cause of reduced protective responses to vaccines in the elderly, due to impaired induction of cellular and humoral responses to new antigens (Ag), especially if the response is T cell dependent. The result is a more severe morbidity following infections, more prolonged and frequent hospitalization, and a higher mortality rate than in the general population. Therefore, there is an increasing need to develop vaccination strategies that overcome immunosenescence, especially for aging-related diseases such as Alzheimer's disease (AD). Here we report a new vaccination strategy harnessing memory-based immunity, which is less affected by aging. We found that aged C57BL/6 and 5xFAD mice exhibit a dramatic reduction in anti-Amyloid-β (Aβ) antibody (Ab) production. We aimed to reverse this process by inducing memory response at a young age. To this end, young mice were primed with the vaccine carrier Hepatitis B surface antigen (HBsAg). At an advanced age, these mice were immunized with an Aβ_1-11 fused to HBsAg. This vaccination scheme elicited a markedly higher Aβ-specific antibody titer than vaccinating aged unprimed mice with the same construct. Importantly, this vaccine strategy more efficiently reduced cerebral Aβ levels and altered microglial phenotype. Overall, we provide evidence that priming with an exogenous Ag carrier can overcome impaired humoral responses to self-antigens in the elderly, paving the route for a potent immunotherapy to AD.

Immunopotentiator Thymosin Alpha-1 Promotes Neurogenesis and Cognition in the Developing Mouse via a Systemic Th1 Bias

In early life, the immune system plays an essential role in brain development. In our study, the immunopotentiator thymosin alpha-1 (Ta1) was peripherally administered to neonatal mice to explore whether the peripheral immunopotentiator affects neurodevelopment and cognition, and to further investigate the relevant mechanism. Compared with the control group, the Ta1 mice displayed better cognitive abilities in early life. The numbers of 5-bromodeoxyuridine (BrdU)+, nestin+, T-box transcription factor 2 (Tbr2)+, BrdU+/doublecortin (DCX)+, BrdU+/ionized calcium-binding adaptor molecule 1 (Iba1)+, and BrdU+/neuronal nuclei (NeuN)+ cells in the hippocampus were increased in the Ta1 group, accompanied by increased interleukin-4 (IL-4), interferon-gamma, brain-derived neurotrophic factor, nerve growth factor, and insulin-like growth factor-1 as well as decreased IL-6 and tumor necrosis factor-α. Furthermore, the Ta1-group showed a Th1-polarized immune response, and the neurotrophic factors were positively associated with the Th1/Th2 ratio. More importantly, administration of Ta1 blocked lipopolysaccharide-induced impairment of hippocampal neurogenesis in early life. These findings suggest that peripheral Ta1 contributes to neurogenesis and cognition probably through a systemic Th1 bias, as well as neuroprotection against LPS infection by Ta1.

Impact of aging immune system on neurodegeneration and potential immunotherapies

The interaction between the nervous and immune systems during aging is an area of avid interest, but many aspects remain unclear. This is due, not only to the complexity of the aging process, but also to a mutual dependency and reciprocal causation of alterations and diseases between both the nervous and immune systems. Aging of the brain drives whole body systemic aging, including aging-related changes of the immune system. In turn, the immune system aging, particularly immunosenescence and T cell aging initiated by thymic involution that are sources of chronic inflammation in the elderly (termed inflammaging), potentially induces brain aging and memory loss in a reciprocal manner. Therefore, immunotherapeutics including modulation of inflammation, vaccination, cellular immune therapies and "protective autoimmunity" provide promising approaches to rejuvenate neuroinflammatory disorders and repair brain injury. In this review, we summarize recent discoveries linking the aging immune system with the development of neurodegeneration. Additionally, we discuss potential rejuvenation strategies, focusing aimed at targeting the aging immune system in an effort to prevent acute brain injury and chronic neurodegeneration during aging.

Continuous vaccinations of 4Aβ1-15 induces specific fluctuation of inflammatory factors accompany with pathologic alterations alleviation in APP/PS1 mice

The common pathological hallmark of Alzheimer's disease (AD) is β-amyloid plaques deposition. Immunotherapy is a revolutionary pharmacological treatment for AD, aiming at improving plaque clearance while concomitantly decreasing inflammation. Our previous study prepared antigen 4Aβ1-15 and found that it could alleviate pathologic alterations in APP/PS1 transgenic mice. The objective of our study was to research the changing processes induced by immunotherapy, including the inflammatory factor levels and microglial activation that is closely associated with Aβ burdens clearance. APP/PS1 mice were injected with 4Aβ1-15 6 times. Each time, the inflammatory factors in sera were detected, and a specific fluctuation that first increased and then decreased was found, in which there was a turning point after the third injection. It prompted us to further detect the indicators in the brains after the third injection and the sixth injection. The results showed that the therapeutic effects for Aβ burdens and behaviors were continuously improved during the whole immune processes, whereas the inflammatory factor levels and microglial activation experienced similar specific fluctuations. The novel discovery may provide convenient methods for further detection and evaluation of immunotherapy in disease courses.

Active Immunization with DNA Vaccine Reduced Cerebral Inflammation and Improved Cognitive Ability in APP/PS1 Transgenic Mice by In Vivo Electroporation

The aggregation of amyloid β-peptide (Aβ) is thought to play a pivotal role in the disease progression of Alzheimer's disease (AD). Amyloid β directed immunotherapy has been considered an alternative AD treatment. In this study, we constructed a DNA vaccine, p(Aβ3-10)10-mIL-4, encoding ten tandem repeats of Aβ3-10 fused with mouse IL-4. Eight-month-old APP/PS1 transgenic mice were injected intramuscularly with p(Aβ3-10)10-mIL-4 followed by in vivo electroporation. Immunization with the vaccine induced high-titer anti-Aβ antibodies and attenuated the behavior impairment. Immunoglobulin isotyping revealed a predominantly IgG1 response and ex vivo cultured splenocytes exhibited a low IFN-γ and high IL-4 response, indicating a Th2 anti-inflammatory response. Immunohistochemical analysis revealed that p(Aβ3-10)10-mIL-4 immunization decreased Aβ deposition, and the microglial attraction significantly decreased accompanied by the clearance of Aβ. There was no microhemorrhage in the brain of the immunized mice. These results suggest that the immunization potentially reduced the inflammation in brain of transgenic mice and therefore improved their cognitive ability. This novel DNA vaccine p(Aβ3-10)10-mIL-4 may be an effective immunization method as therapy for AD.

An optimized, synthetic DNA vaccine encoding the toxin A and toxin B receptor binding domains of Clostridium difficile induces protective antibody responses in vivo

Clostridium difficile-associated disease (CDAD) constitutes a large majority of nosocomial diarrhea cases in industrialized nations and is mediated by the effects of two secreted toxins, toxin A (TcdA) and toxin B (TcdB). Patients who develop strong antitoxin antibody responses can clear C. difficile infection and remain disease free. Key toxin-neutralizing epitopes have been found within the carboxy-terminal receptor binding domains (RBDs) of TcdA and TcdB, which has generated interest in developing the RBD as a viable vaccine target. While numerous platforms have been studied, very little data describes the potential of DNA vaccination against CDAD. Therefore, we created highly optimized plasmids encoding the RBDs from TcdA and TcdB in which any putative N-linked glycosylation sites were altered. Mice and nonhuman primates were immunized intramuscularly, followed by in vivo electroporation, and in these animal models, vaccination induced significant levels of both anti-RBD antibodies (blood and stool) and RBD-specific antibody-secreting cells. Further characterization revealed that sera from immunized mice and nonhuman primates could detect RBD protein from transfected cells, as well as neutralize purified toxins in an in vitro cytotoxicity assay. Mice that were immunized with plasmids or given nonhuman-primate sera were protected from a lethal challenge with purified TcdA and/or TcdB. Moreover, immunized mice were significantly protected when challenged with C. difficile spores from homologous (VPI 10463) and heterologous, epidemic (UK1) strains. These data demonstrate the robust immunogenicity and efficacy of a TcdA/B RBD-based DNA vaccine in preclinical models of acute toxin-associated and intragastric, spore-induced colonic disease.

Association of interleukin-4 genetic polymorphisms with sporadic Alzheimer's disease in Chinese Han population

Cytokine interleukin-4 (IL-4) is thought to play a role in the pathogenesis of Alzheimer's disease (AD). This study aimed to evaluate the potential association between single nucleotide polymorphisms (SNP) of IL-4 gene and AD susceptibility. This case-control study was conducted in Chinese Han populations consisting of 203 AD patients and 205 controls. Three common SNPs of IL-4 gene, including -590C>T (rs2243250), -33C>T (rs2070874), and -1098T>G (rs2243248), were determined by the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and verified using DNA sequencing methods. Our data show that -590C and -1098G alleles of IL-4 were more common in AD patients (30.5% vs 22.2% p=0.007; 14.3% vs 3.4% p<0.0001) and significantly associated with elevated risk for AD (OR=1.51 95% CI 1.05-2.23; OR=4.78 95% CI 2.37-7.67). Haplotype analysis revealed five common haplotypes CCG (OR=4.41), CCT (OR=1.22), TTT (OR=1.02), CTT (OR=0.7), and TCT (OR=0.14), from highest to lowest risk for AD. None of the associations appeared to be modified by APOE ɛ4 genetic variant. Bioinformatic analysis shows that -590C>T and -1098T>G have a linkage disequilibrium (LD) with multiple potentially functional SNPs inside IL-4 gene. Our findings indicate that the -590C and -1098G alleles located in the promoter of IL-4 may increase the susceptibility to AD among the Han Chinese and might be used as molecular markers for AD risk evaluation.

Perspectives in molecular imaging using staging biomarkers and immunotherapies in Alzheimer's disease

Sporadic Alzheimer's disease (AD) is an emerging chronic illness characterized by a progressive pleiotropic pathophysiological mode of actions triggered during the senescence process and affecting the elderly worldwide. The complex molecular mechanisms of AD not only are supported by cholinergic, beta-amyloid, and tau theories but also have a genetic basis that accounts for the difference in symptomatology processes activation among human population which will evolve into divergent neuropathological features underlying cognitive and behaviour alterations. Distinct immune system tolerance could also influence divergent responses among AD patients treated by immunotherapy. The complexity in nature increases when taken together the genetic/immune tolerance with the patient's brain reserve and with neuropathological evolution from early till advance AD clinical stages. The most promising diagnostic strategies in today's world would consist in performing high diagnostic accuracy of combined modality imaging technologies using beta-amyloid 42 peptide-cerebrospinal fluid (CSF) positron emission tomography (PET), Pittsburgh compound B-PET, fluorodeoxyglucose-PET, total and phosphorylated tau-CSF, and volumetric magnetic resonance imaging hippocampus biomarkers for criteria evaluation and validation. Early diagnosis is the challenge task that needs to look first at plausible mechanisms of actions behind therapies, and combining them would allow for the development of efficient AD treatment in a near future.

In vivo molecular imaging and histological analysis of changes induced by electric pulses used for plasmid DNA electrotransfer to the skin: a study in a dorsal window chamber in mice

Electropermeabilization/electroporation (EP) is a physical method that by application of electric pulses to cells increases cell membrane permeability and enables the introduction of molecules into the cells. One of the uses of EP in vivo is plasmid DNA electrotransfer to the skin for DNA vaccination. EP of tissues induces reduction of blood flow and, in combination with plasmid DNA, induction of an immune response. One of the EP protocols for plasmid DNA electrotransfer to the skin is a combination of high-voltage (HV) and low-voltage (LV) pulses. However, the effects of this pulse combination on skin-vessel blood flow are not known. Therefore, using intravital microscopy in a dorsal window chamber in mice and fluorescently labeled dextrans, the effects of one HV and eight LV pulses on skin vasculature were investigated. In addition, a detailed histological analysis was performed. Image analysis of fluorescence intensity changes demonstrated that EP induces a transient constriction and increased permeability of blood vessels as well as a “vascular lock.” Histological analysis revealed rounding up of endothelial cells and stacking up of erythrocytes at 1 h after EP. In addition, extravasation of erythrocytes and leukocyte infiltration accompanied by edema were determined up to 24 h after EP. In conclusion, our results show that blood flow modifying effects of EP in skin contribute to the infiltration of immune cells in the exposed area. When combined with plasmid DNA for vaccination, this could enable the initial and prolonged contact of immune cells with encoded therapeutic proteins.