Polylactide-coglycolide microspheres co-encapsulating recombinant tandem prion protein with CpG-oligonucleotide break self-tolerance to prion protein in wild-type mice and induce CD4 and CD8 T cell responses

Oral vaccination as a potential strategy to manage chronic wasting disease in wild cervid populations

Prion diseases are a novel class of infectious disease based in the misfolding of the cellular prion protein (PrPC) into a pathological, self-propagating isoform (PrPSc). These fatal, untreatable neurodegenerative disorders affect a variety of species causing scrapie in sheep and goats, bovine spongiform encephalopathy (BSE) in cattle, chronic wasting disease (CWD) in cervids, and Creutzfeldt-Jacob disease (CJD) in humans. Of the animal prion diseases, CWD is currently regarded as the most significant threat due its ongoing geographical spread, environmental persistence, uptake into plants, unpredictable evolution, and emerging evidence of zoonotic potential. The extensive efforts to manage CWD have been largely ineffective, highlighting the need for new disease management tools, including vaccines. Development of an effective CWD vaccine is challenged by the unique biology of these diseases, including the necessity, and associated dangers, of overcoming immune tolerance, as well the logistical challenges of vaccinating wild animals. Despite these obstacles, there has been encouraging progress towards the identification of safe, protective antigens as well as effective strategies of formulation and delivery that would enable oral delivery to wild cervids. In this review we highlight recent strategies for antigen selection and optimization, as well as considerations of various platforms for oral delivery, that will enable researchers to accelerate the rate at which candidate CWD vaccines are developed and evaluated.

Large animal models for chronic wasting disease

Chronic wasting disease (CWD) is a fatal neurodegenerative prion disease of cervid species including deer, elk, moose and reindeer. The disease has shown both geographic and species expansion since its discovery in the late 1960's and is now recognized in captive and free-ranging cervid populations in North America, Asia and Europe. The facile transmission of CWD is unique among prion diseases and has resulted in growing concern for cervid populations and human public health. The development of native cervid host models with longitudinal monitoring has revealed new insights about CWD pathogenesis and transmission dynamics. More than 20 years of experimental studies conducted in these models, using biologically relevant routes of infection, have led to better understanding of many aspect of CWD infections. This review addresses some of these insights, including: (i) the temporal intra-host trafficking of CWD prions in tissues and bodily fluids, (ii) the presence of infectivity shed in bodily excretions that may help explain the facile transmission of CWD, (iii) mother-to-offspring CWD transmission, (iv) the influence of some Prnp polymorphisms on CWD susceptibility, and (vi) continued development of vaccine strategies to mitigate CWD.

Immunization with Genetically Modified Trypanosomes Provides Protection against Transmissible Spongiform Encephalopathies

Transmissible spongiform encephalopathies are incurable neurodegenerative diseases, associated with the conversion of the physiological prion protein to its disease-associated counterpart. Even though immunization against transmissible spongiform encephalopathies has shown great potential, immune tolerance effects impede the use of active immunization protocols for successful prophylaxis. In this study, we evaluate the use of trypanosomes as biological platforms for the presentation of a prion antigenic peptide to the host immune system. Using the engineered trypanosomes in an immunization protocol without the use of adjuvants led to the development of a humoral immune response against the prion protein in wild type mice, without the appearance of adverse reactions. The immune reaction elicited with this protocol displayed in vitro therapeutic potential and was further evaluated in a bioassay where immunized mice were partially protected in a representative murine model of prion diseases. Further studies are underway to better characterize the immune reaction and optimize the immunization protocol.

Vaccination with Prion Peptide-Displaying Polyomavirus-Like Particles Prolongs Incubation Time in Scrapie-Infected Mice

Prion diseases like scrapie in sheep, bovine spongiform encephalopathy (BSE) in cattle or Creutzfeldt–Jakob disease (CJD) in humans are fatal neurodegenerative diseases characterized by the conformational conversion of the normal, mainly α-helical cellular prion protein (PrP^C) into the abnormal β-sheet rich infectious isoform PrP^Sc. Various therapeutic or prophylactic approaches have been conducted, but no approved therapeutic treatment is available so far. Immunisation against prions is hampered by the self-tolerance to PrP^C in mammalian species. One strategy to avoid this tolerance is presenting PrP variants in virus-like particles (VLPs). Therefore, we vaccinated C57/BL6 mice with nine prion peptide variants presented by hamster polyomavirus capsid protein VP1/VP2-derived VLPs. Mice were subsequently challenged intraperitoneally with the murine RML prion strain. Importantly, one group exhibited significantly increased mean survival time of 240 days post-inoculation compared with 202 days of the control group. These data show that immunisation with VLPs presenting PrP peptides may represent a promising strategy for an effective vaccination against transmissible spongiform encephalitis agents.

Immunotherapy against Prion Disease

The term "prion disease" encompasses a group of neurodegenerative diseases affecting both humans and animals. Currently, there is no effective therapy and all forms of prion disease are invariably fatal. Because of (a) the outbreak of bovine spongiform encephalopathy in cattle and variant Creutzfeldt-Jakob disease in humans; (b) the heated debate about the prion hypothesis; and (c) the availability of a natural prion disease in rodents, the understanding of the pathogenic process in prion disease is much more advanced compared to that of other neurodegenerative disorders, which inspired many attempts to develop therapeutic strategies against these fatal diseases. In this review, we focus on immunotherapy against prion disease. We explain our rationale for immunotherapy as a plausible therapeutic choice, review previous trials using either active or passive immunization, and discuss potential strategies for overcoming the hurdles in developing a successful immunotherapy. We propose that immunotherapy is a plausible and practical therapeutic strategy and advocate more studies in this area to develop effective measures to control and treat these devastating disorders.

Protein misfolding, aggregation and mechanism of amyloid cytotoxicity: An overview and therapeutic strategies to inhibit aggregation

Protein and peptides are converted from their soluble forms into highly ordered fibrillar aggregates under various conditions inside the cell. Such transitions confer diverse neurodegenerative diseases including Alzheimer's disease, Huntington's disease Prion's disease, Parkinson's disease, polyQ and share abnormal folding of potentially cytotoxic protein species linked with degeneration and death of precise neuronal populations. Presently, major advances are made to understand and get detailed insight into the structural basis and mechanism of amyloid formation, cytotoxicity and therapeutic approaches to combat them. Here we highlight classifies and summarizes the detailed overview of protein misfolding and aggregation at their molecular level including the factors that promote protein aggregation under in vivo and in vitro conditions. In addition, we describe the recent technologies that aid the characterization of amyloid aggregates along with several models that might be responsible for amyloid induced cytotoxicity to cells. Overview on the inhibition of amyloidosis by targeting different small molecules (both natural and synthetic origin) have been also discussed, that provides important approaches to identify novel targets and develop specific therapeutic strategies to combat protein aggregation related neurodegenerative diseases.

Recombinant prion protein vaccination of transgenic elk PrP mice and reindeer overcomes self-tolerance and protects mice against chronic wasting disease

Chronic wasting disease (CWD) is a fatal neurodegenerative disease that affects cervids in North America and now Europe. No effective measures are available to control CWD. We hypothesized that active vaccination with homologous and aggregation-prone recombinant prion protein (PrP) could overcome self-tolerance and induce autoantibody production against the cellular isoform of PrP (PrP^C), which would be protective against CWD infection from peripheral routes. Five groups of transgenic mice expressing elk PrP (TgElk) were vaccinated with either the adjuvant CpG alone or one of four recombinant PrP immunogens: deer dimer (Ddi); deer monomer (Dmo); mouse dimer (Mdi); and mouse monomer (Mmo). Mice were then challenged intraperitoneally with elk CWD prions. All vaccinated mice developed ELISA-detectable antibody titers against PrP. Importantly, all four vaccinated groups survived longer than the control group, with the Mmo-immunized group exhibiting 60% prolongation of mean survival time compared with the control group (183 versus 114 days post-inoculation). We tested for prion infection in brain and spleen of all clinically sick mice. Notably, the attack rate was 100% as revealed by positive CWD signals in all tested tissues when assessed with Western blotting, real-time quaking-induced conversion, and immunohistochemistry. Our pilot study in reindeer indicated appreciable humoral immune responses to Mdi and Ddi immunogens, and the post-immune sera from the Ddi-vaccinated reindeer mitigated CWD propagation in a cell culture model (CWD-RK13). Taken together, our study provides very promising vaccine candidates against CWD, but further studies in cervids are required to investigate vaccine efficacy in the natural CWD hosts.

Immunization of cervidized transgenic mice with multimeric deer prion protein induces self-antibodies that antagonize chronic wasting disease infectivity in vitro

Chronic wasting disease (CWD) is the most contagious prion disease. It is expanding rapidly in North America, was found recently in Europe, and the potential for transmission to humans cannot be excluded yet. We hypothesized that it is possible to prevent peripheral CWD infection and CWD prion shedding by inducing auto-antibodies against the cellular prion protein (PrP^C) by active vaccination. Our objective is to overcome self-tolerance against PrP by using a multimeric recombinant PrP (recPrP) as an immunogen. We expressed in E. coli, purified and refolded four immunogens: cervid and murine recPrP in monomeric and dimeric form. Testing immunogenicity in sera of the vaccinated transgenic mice expressing cervid PrP revealed that all four immunogens effectively overcame self-tolerance against the prion protein as shown by high antibody titers. Confocal microscopy analysis revealed effective binding of post-immune sera to surface-located PrP^C in both murine and cervid PrP expressing cultured cells. Remarkably, the post-immune auto-antibodies effectively inhibited CWD-induced prion conversion in RT-QuIC assay when incubated with either PrP substrate or CWD seed. Furthermore, they mitigated prion propagation in CWD-infected cervid-PrP expressing RK13 cells. Together, multimeric recombinant cervid PrP effectively overcomes self-tolerance to PrP and induces auto-antibodies that interfere with CWD conversion in vitro.

Artificial bacterial biomimetic nanoparticles synergize pathogen-associated molecular patterns for vaccine efficacy

Antigen-presenting cells (APCs) sense microorganisms via pathogen-associated molecular patterns (PAMPs) by both extra- and intracellular Toll-like Receptors (TLRs), initiating immune responses against invading pathogens. Bacterial PAMPs include extracellular lipopolysaccharides and intracellular unmethylated CpG-rich oligodeoxynucleotides (CpG). We hypothesized that a biomimetic approach involving antigen-loaded nanoparticles (NP) displaying Monophosphoryl Lipid A (MPLA) and encapsulating CpG may function as an effective "artificial bacterial" biomimetic vaccine platform. This hypothesis was tested in vitro and in vivo using NP assembled from biodegradable poly(lactic-co-glycolic acid) (PLGA) polymer, surface-modified with MPLA, and loaded with CpG and model antigen Ovalbumin (OVA). First, CpG potency, characterized by cytokine profiles, titers, and antigen-specific T cell responses, was enhanced when CpG was encapsulated in NP compared to equivalent concentrations of surface-presented CpG, highlighting the importance of biomimetic presentation of PAMPs. Second, NP synergized surface-bound MPLA with encapsulated CpG in vitro and in vivo, inducing greater pro-inflammatory, antigen-specific T helper 1 (Th1)-skewed cellular and antibody-mediated responses compared to single PAMPs or soluble PAMP combinations. Importantly, NP co-presentation of CpG and MPLA was critical for CD8(+) T cell responses, as vaccination with a mixture of NP presenting either CpG or MPLA failed to induce cellular immunity. This work demonstrates a rational methodology for combining TLR ligands in a context-dependent manner for synergistic nanoparticulate vaccines.

The potential of nanoparticles for the immunization against viral infections

Vaccination has a great impact on the prevention and control of infectious diseases. However, there are still many infectious diseases for which an effective vaccine is missing. Thirty years after the discovery of the AIDS-pathogen (human immunodeficiency virus, HIV) and intensive research, there is still no protective immunity against the HIV infection. Over the past decade, nanoparticulate systems such as virus-like particles, liposomes, polymers and inorganic nanoparticles have received attention as potential delivery vehicles which can be loaded or functionalized with active biomolecules (antigens and adjuvants). Here we compare the properties of different nanoparticulate systems and assess their potential for the development of new vaccines against a range of viral infections.

Dendritic cell-targeted vaccines

Despite significant effort, the development of effective vaccines inducing strong and durable T-cell responses against intracellular pathogens and cancer cells has remained a challenge. The initiation of effector CD8⁺ T-cell responses requires the presentation of peptides derived from internalized antigen on class I major histocompatibility complex molecules by dendritic cells (DCs) in a process called cross-presentation. A current strategy to enhance the effectiveness of vaccination is to deliver antigens directly to DCs. This is done via selective targeting of antigen using monoclonal antibodies directed against endocytic receptors on the surface of the DCs. In this review, we will discuss considerations relevant to the design of such vaccines: the existence of DC subsets with specialized functions, the impact of the antigen intracellular trafficking on cross-presentation, and the influence of maturation signals received by DCs on the outcome of the immune response.

Immunotherapeutic approaches in prion disease: progress, challenges and potential directions

Therapeutic trials utilizing animal models of prion disease have explored a variety of compounds and a number of approaches with varying success, including several immunotherapeutic strategies, such as passive immunization through the delivery of viruses carrying nucleic acid inserts encoding prion protein-specific immunoglobulin. Targeted, organ-specific cellular production of therapeutic proteins is a relatively unexplored approach in the treatment of neurodegeneration despite many successful experimental outcomes in animal models and human trials of other diseases of the CNS. Emphasizing studies utilizing mouse models of disease, this review outlines developments and limitations of immunological approaches to the treatment of prion diseases. In addition, the authors discuss the potential of an experimental therapeutic strategy, utilizing hybridoma cells injected directly into the CNS to establish long-term production of anti-prion antibodies in vivo within the organ associated with the greatest pathogenic change in prion disease, the brain.

Prolongation of prion disease-associated symptomatic phase relates to CD3+ T cell recruitment into the CNS in murine scrapie-infected mice

Prion diseases are caused by the transconformation of the host cellular prion protein PrP(c) into an infectious neurotoxic isoform called PrP(Sc). While vaccine-induced PrP-specific CD4(+) T cells and antibodies partially protect scrapie-infected mice from disease, the potential autoreactivity of CD8(+) cytotoxic T lymphocytes (CTLs) received little attention. Beneficial or pathogenic influence of PrP(c)-specific CTL was evaluated by stimulating a CD8(+) T-cell-only response against PrP in scrapie-infected C57BL/6 mice. To circumvent immune tolerance to PrP, five PrP-derived nonamer peptides identified using prediction algorithms were anchored-optimized to improve binding affinity for H-2D(b) and immunogenicity (NP-peptides). All of the NP-peptides elicited a significant number of IFNγ secreting CD8(+) T cells that better recognized the NP-peptides than the natives; three of them induced T cells that were lytic in vivo for NP-peptide-loaded target cells. Peptides 168 and 192 were naturally processed and presented by the 1C11 neuronal cell line. Minigenes encoding immunogenic NP-peptides inserted into adenovirus (rAds) vectors enhanced the specific CD8(+) T-cell responses. Immunization with rAd encoding 168NP before scrapie inoculation significantly prolonged the survival of infected mice. This effect was attributable to a significant lengthening of the symptomatic phase and was associated with enhanced CD3(+) T cell recruitment to the CNS. However, immunization with Ad168NP in scrapie-incubating mice induced IFNγ-secreting CD8(+) T cells that were not cytolytic in vivo and did not influence disease progression nor infiltrated the brain. In conclusion, the data suggest that vaccine-induced PrP-specific CD8(+) T cells interact with prions into the CNS during the clinical phase of the disease.

Structure-dependent immunostimulatory effect of CpG oligodeoxynucleotides and their delivery system

Unmethylated cytosine-phosphate-guanosine (CpG) oligodeoxynucleotides (ODNs) are recognized by Toll-like receptor 9 (TLR9) found in antigen-presenting cells and B cells and can activate the immune system. Using CpG ODNs as an adjuvant has been found to be effective for treating infectious diseases, cancers, and allergies. Because natural ODNs with only a phosphodiester backbone are easily degraded by nuclease (deoxyribonuclease [DNase]) in serum, CpG ODNs with a phosphorothioate backbone have been studied for clinical application. CpG ODNs with a phosphorothioate backbone have raised concern regarding undesirable side effects; however, several CpG ODNs with only a phosphodiester backbone have been reported to be stable in serum and to show an immunostimulatory effect. In recent years, research has been conducted on delivery systems for CpG ODNs using nanoparticles (NPs). The advantages of NP-based delivery of CpG ODN include (1) it can protect CpG ODN from DNase, (2) it can retain CpG ODN inside the body for a long period of time, (3) it can improve the cellular uptake efficiency of CpG ODN, and (4) it can deliver CpG ODN to the target tissues. Because the target cells of CpG ODN are cells of the immune system and TLR9, the receptor of CpG ODN is localized in endolysosomes, CpG ODN delivery systems are required to have qualities different from other nucleic acid drugs such as antisense DNA and small interfering RNA. Studies until now have reported various NPs as carriers for CpG ODN delivery. This review presents DNase-resistant CpG ODNs with various structures and their immunostimulatory effects and also focuses on delivery systems of CpG ODNs that utilize NPs. Because CpG ODNs interact with TLR9 and activate both the innate and the adaptive immune system, the application of CpG ODNs for the treatment of cancers, infectious diseases, and allergies holds great promise.

PLGA nanoparticle-mediated delivery of tumor antigenic peptides elicits effective immune responses

The peptide vaccine clinical trials encountered limited success because of difficulties associated with stability and delivery, resulting in inefficient antigen presentation and low response rates in patients with cancer. The purpose of this study was to develop a novel delivery approach for tumor antigenic peptides in order to elicit enhanced immune responses using poly(DL-lactide-co-glycolide) nanoparticles (PLGA-NPs) encapsulating tumor antigenic peptides. PLGA-NPs were made using the double emulsion-solvent evaporation method. Artificial antigen-presenting cells were generated by human dendritic cells (DCs) loaded with PLGA-NPs encapsulating tumor antigenic peptide(s). The efficiency of the antigen presentation was measured by interferon-γ ELISpot assay (Vector Laboratories, Burlingame, CA). Antigen-specific cytotoxic T lymphocytes (CTLs) were generated and evaluated by CytoTox 96^® Non-Radioactive Cytotoxicity Assay (Promega, Fitchburg, WI). The efficiency of the peptide delivery was compared between the methods of emulsification in incomplete Freund’s adjuvant and encapsulation in PLGA-NPs. Our results showed that most of the PLGA-NPs were from 150 nm to 500 nm in diameter, and were negatively charged at pH 7.4 with a mean zeta potential of −15.53 ± 0.71 mV; the PLGA-NPs could be colocalized in human DCs in 30 minutes of incubation. Human DCs loaded with PLGA-NPs encapsulating peptide induced significantly stronger CTL cytotoxicity than those pulsed with free peptide, while human DCs loaded with PLGA-NPs encapsulating a three-peptide cocktail induced a significantly greater CTL response than those encapsulating a two-peptide cocktail. Most importantly, the peptide dose encapsulated in PLGA-NPs was 63 times less than that emulsified in incomplete Freund’s adjuvant, but it induced a more powerful CTL response in vivo. These results demonstrate that the delivery of peptides encapsulated in PLGA-NPs is a promising approach to induce effective antitumor CTL responses in vivo.

Quantitative determination of the composition of multi-shell calcium phosphate-oligonucleotide nanoparticles and their application for the activation of dendritic cells

Biodegradable calcium phosphate nanoparticles as carriers for the immunoactive toll-like receptor ligands CpG and polyinosinic-polycytidylic acid for the activation of dendritic cells (DC) combined with the viral antigen hemagglutinin (HA) were prepared. A purification method based on ultracentrifugation and ultrasonication was developed to separate the nanoparticles from dissolved biomolecules. The number of biomolecules, i.e., oligonucleotides and peptide, incorporated into the nanoparticles was quantitatively determined by UV-spectroscopy, using fluorescent derivatives of the biomolecules. The immunostimulatory effects of purified calcium phosphate nanoparticles on DC were studied, i.e., cytokine production and activation of the cells in terms of the upregulation of surface molecules. Purified calcium phosphate nanoparticles, i.e., without dissolved biomolecules, are capable of inducing adaptive immunity by activation of DC. Immunostimulatory effects of purified calcium phosphate nanoparticles on DC were demonstrated by increased expression of co-stimulatory molecules and MHC II and by cytokine secretion. In addition, DC treated with purified functionalized calcium phosphate nanoparticles induced an antigen-specific T-cell response in vitro.

Immunostimulatory CpG-DNA and PSA-peptide vaccination elicits profound cytotoxic T cell responses

OBJECTIVE

Novel strategies for the treatment of advanced prostate cancer (CaP), including immunotherapy or gene therapy, are currently under evaluation with Sipuleucel-T as first FDA-approved immunotherapeutic. Here, we examine cytosine-phosphorothioate-guanine (CpG)-DNA oligonucleotides (ODN) to boost cytokine responses and costimulatory molecule expression on murine bone marrow-derived dendritic cells (mBMDC). Furthermore, we evaluate the potency of a PSA-peptide based vaccine in combination with CpG-DNA to elicit specific cytotoxic T cell (CTL) responses.

MATERIALS AND METHODS

mBMDC were stimulated with CpG-DNA (1668: 5'-TCCATGACGTTCCTGATGCT-3') or non-stimulatory control-ODN (1720: 5'-TCCATGAGCTTCCTGATGCT-3'). Subsequently, expression of the costimulatory molecules CD40 and CD86 and induction of proinflammatory cytokines (interleukin (IL)-6 and IL-12) were analyzed. For induction of PSA-peptide specific CTL, female C57BL/6 mice were immunized with PSA-peptide 65-73 (HCIRNKSVI) alone or in combination with 1668 or 1720-ODN. In vivo cytotoxicity assay determined PSA-peptide specific cytotoxicity 1 week after vaccination.

RESULTS

Treatment of mBMDC with stimulatory CpG-DNA ODN resulted in pronounced up-regulation of costimulatory molecule expression on mBMDC in a dose-dependent manner. CpG-ODN significantly increased production of IL-6 and IL-12 in mBMDC (P < 0.001). Induction of PSA-peptide specific CTL responses in mice immunized with PSA-peptide and CpG-DNA were significantly greater than those of PSA-peptide and control-ODN immunized mice or PSA-peptide only vaccination.

CONCLUSIONS

CpG-DNA acts as potent adjuvant for vaccination therapies and elicits profound PSA-peptide specific CTL responses in combination with an immunodominant PSA-peptide. CpG-ODN mediated immunotherapy represents a potentially inexpensive, safe, easy-to-produce, and easy-to-handle treatment alternative. Therefore, further evaluation of CpG-DNA in immunization therapies against CaP is warranted.

Formulation of sustained-release microspheres of granulocyte macrophage colony stimulating factor by freezing-induced phase separation with dextran and encapsulation with blended polymers

This study aimed to assess the potential merits of formulating sustained-release microspheres of recombinant human granulocyte macrophage colony stimulating factor (rhGM-CSF) via freezing-induced phase separation (FIPS) of the protein with dextran followed by encapsulation with binary mixture of poly(lactic-co-glycolic acid) (PLGA) 2A (MW∼12K) and 3A (MW∼47K) or of PLGA2A and polylactic acid (PLA; MW∼83K). The formulated dextran particles and microspheres were characterized in vitro for loading, aggregation, bioactivity and release behavior of the protein where appropriate. rhGM-CSF retained about 60% of bioactivity with no significant aggregation after each formulation step. Encapsulation of protein-loaded dextran particles attained only 80% with the PLGA2A and PLGA3A blend, but 100% with the PLGA2A and PLA mixture. The former formulation exhibited a triphasic in-vitro release profile typical of PLGA microspheres while the latter revealed a much lower initial burst followed by a steady and complete release of rhGM-CSF with preserved bioactivity over a 15-day period.

Robust IgG responses to nanograms of antigen using a biomimetic lipid-coated particle vaccine

New subunit vaccine formulations with increased potency are of interest to improve immune responses against poorly immunogenic antigens, to avoid vaccine shortages in pandemic situations, and to promote dose-sparing of potent adjuvant molecules that can cause unacceptable side effects in prophylactic vaccination. Here we report strong class-switched, high avidity humoral immune responses elicited by a vaccine system based on poly(lactide-co-glycolide) micro- or nano-particles enveloped by PEGylated phospholipid bilayers, with protein antigens covalently anchored to the lipid surface and lipophilic adjuvants inserted in the bilayer coating. Strikingly, these particles elicited high endpoint antigen-specific IgG titers (>10(6)) sustained for over 100 days after two immunizations with as little as 2.5 ng of antigen. At such low doses, the conventional adjuvant alum or the molecular adjuvants monophosphoryl lipid A (MPLA) or α-galactosylceramide (αGC) failed to elicit responses. Co-delivery of antigen with MPLA or αGC incorporated into the particle bilayers in a pathogen-mimetic fashion further enhanced antibody titers by ~12-fold. MPLA provided the highest sustained IgG titers at these ultra-low antigen doses, while αGC promoted a rapid rise in serum IgG after one immunization, which may be valuable in emergencies such as disease pandemics. The dose of αGC required to boost the antibody response was also spared by particulate delivery. Lipid-enveloped biodegradable micro- and nano-particles thus provide a potent dose-sparing platform for vaccine delivery.

Activation of antigen-specific T cell-responses by mannan-decorated PLGA nanoparticles

PURPOSE

Mannosylation of vaccines is a promising strategy to selectively target vaccine antigens to the mannose receptor expressed on dendritic cells (DCs). The purpose of this study was to investigate the effect of mannan (MN) chemically conjugated to poly(D, L-lactide-co-glycolic acid) (PLGA) nanoparticles (NPs) on antigen-specific T-cell responses elicited by a model antigen (ovalbumin, OVA) loaded in PLGA-NPs.

METHODS

In vitro T-cell proliferation assay was done to assess the ability of DCs treated with OVA-NPs (±MN decoration) to induce antigen-specific T-cell activation. The efficacy of this vaccination strategy was further evaluated in vivo, where T-cell proliferation was performed to evaluate activation of T-cell responses in lymph nodes and spleens isolated from the vaccinated mice.

RESULTS

Our results demonstrate that MN-decorated antigen-loaded PLGA-NPs simultaneously enhanced antigen-specific CD4+ and CD8+ T-cell responses compared to non-decorated NPs.

CONCLUSIONS

MN decoration of PLGA-NPs is a promising strategy for enhancing antigen-specific T-cell responses.

Harnessing dendritic cells for immunotherapy

Dendritic cells (DC) are the antigen presenting cells that initiate and direct adaptive immune responses, capable of inducing protective adaptive immune responses and tolerance. They sample their surroundings, internalizing, processing and presenting antigens to T cells. They distinguish between self and foreign antigens with a wide array of microbial sensors, and induce immunity when antigen is captured in the presence of microbial products or inflammatory stimuli, but tolerance in the absence of these signals. However, not all DCs are identical. There are distinct DC subsets spread throughout the body, and although they share common features, they also have specialized functions. As a consequence, the outcome of the immune response is determined by the context in which the antigen is acquired, and also by the DC subset(s) involved. Here we discuss the features of the DC subsets, their handling of antigens for MHCI- and MHCII-restricted presentation, how their functions are regulated by foreign and endogenous signals, the consequences on the type of immune response induced, and how they provide insights on the design of immunotherapy.

The impact of nanoparticle ligand density on dendritic-cell targeted vaccines

Dendritic-cell (DC) targeted antigen delivery systems hold promise for enhancing vaccine efficacy and delivery of therapeutics. However, it is not known how the number and density of targeting ligands on such systems may affect DC function and subsequent T cell response. We modified the surface of biodegradable nanoparticles loaded with antigen with different densities of the mAb to the DC lectin DEC-205 receptor and assessed changes in the cytokine response of DCs and T cells. DEC-205 targeted nanoparticles unexpectedly induced a differential cytokine response that depended on the density of ligands on the surface. Strikingly, nanoparticle surface density of DEC-205 mAb increased the amount of anti-inflammatory, IL-10, produced by DCs and T cells. Boosting mice with DEC-205 targeted OVA-nanoparticles after immunization with an antigen in CFA induced a similar pattern of IL-10 response. The correlation between DC production of IL-10 as a function of the density of anti-DEC-205 is shown to be due to cross-linking of the DEC-205 receptor. Cross-linking also increased DC expression of the scavenger receptor CD36, and blockade of CD36 largely abrogated the IL-10 response. Our studies highlight the importance of target ligand density in the design of vaccine delivery systems.

In vitro analysis of acetalated dextran microparticles as a potent delivery platform for vaccine adjuvants

Toll-like receptor (TLR) agonists induce potent innate immune responses and can be used in the development of novel vaccine adjuvants. However, access to TLRs can be challenging as exemplified by TLR 7, which is located intracellularly in endosomal compartments. To increase recognition and subsequent stimulatory effects of TLR 7, imiquimod was encapsulated in acetalated dextran (Ac-DEX) microparticles. Ac-DEX, a water-insoluble and biocompatible polymer, is relatively stable at pH 7.4, but degrades rapidly under acidic conditions, such as those found in lysosomal vesicles. To determine the immunostimulatory capacity of encapsulated imiquimod, we compared the efficacy of free versus encapsulated imiquimod in activating RAW 264.7 macrophages, MH-S macrophages, and bone marrow derived dendritic cells. Encapsulated imiquimod significantly increased IL-1 beta, IL-6, and TNF-alpha cytokine expression in macrophages relative to the free drug. Furthermore, significant increases were observed in classic macrophage activation markers (iNOS, PD1-L1, and NO) after treatment with encapsulated imiquimod over the free drug. Also, bone marrow derived dendritic cells produced significantly higher levels of IL-1 beta, IL-6, IL-12p70, and MIP-1 alpha as compared to their counterparts receiving free imiquimod. These results suggest that encapsulation of TLR ligands within Ac-DEX microparticles results in increased immunostimulation and potentially better protection from disease when used in conjunction with vaccine formulations.

TLR9-targeted biodegradable nanoparticles as immunization vectors protect against West Nile encephalitis

Vaccines that activate humoral and cell-mediated immune responses are urgently needed for many infectious agents, including the flaviviruses dengue and West Nile (WN) virus. Vaccine development would be greatly facilitated by a new approach, in which nanoscale modules (Ag, adjuvant, and carrier) are assembled into units that are optimized for stimulating immune responses to a specific pathogen. Toward that goal, we formulated biodegradable nanoparticles loaded with Ag and surface modified with the pathogen-associated molecular pattern CpG oligodeoxynucleotides. We chose to evaluate our construct using a recombinant envelope protein Ag from the WN virus and tested the efficiency of this system in eliciting humoral and cellular responses and providing protection against the live virus. Animals immunized with this system showed robust humoral responses polarized toward Th1 immune responses compared with predominately Th2-biased responses with the adjuvant aluminum hydroxide. Immunization with CpG oligodeoxynucleotide-modified nanoparticles resulted in a greater number of circulating effector T cells and greater activity of Ag-specific lymphocytes than unmodified nanoparticles or aluminum hydroxide. Ultimately, compared with alum, this system offered superior protection in a mouse model of WN virus encephalitis.

Biomaterial-based technologies for brain anti-cancer therapeutics and imaging

Treating malignant brain tumors represents one of the most formidable challenges in oncology. Contemporary treatment of brain tumors has been hampered by limited drug delivery across the blood-brain barrier (BBB) to the tumor bed. Biomaterials are playing an increasingly important role in developing more effective brain tumor treatments. In particular, polymer (nano)particles can provide prolonged drug delivery directly to the tumor following direct intracerebral injection, by making them physiochemically able to cross the BBB to the tumor, or by functionalizing the material surface with peptides and ligands allowing the drug-loaded material to be systemically administered but still specifically target the tumor endothelium or tumor cells themselves. Biomaterials can also serve as targeted delivery devices for novel therapies including gene therapy, photodynamic therapy, anti-angiogenic and thermotherapy. Nanoparticles also have the potential to play key roles in the diagnosis and imaging of brain tumors by revolutionizing both preoperative and intraoperative brain tumor detection, allowing early detection of pre-cancerous cells, and providing real-time, longitudinal, non-invasive monitoring/imaging of the effects of treatment. Additional efforts are focused on developing biomaterial systems that are uniquely capable of delivering tumor-associated antigens, immunotherapeutic agents or programming immune cells in situ to identify and facilitate immune-mediated tumor cell killing. The continued translation of current research into clinical practice will rely on solving challenges relating to the pharmacology of nanoparticles but it is envisioned that novel biomaterials will ultimately allow clinicians to target tumors and introduce multiple, pharmaceutically relevant entities for simultaneous targeting, imaging, and therapy in a unique and unprecedented manner.

In vivo studies on the effect of co-encapsulation of CpG DNA and antigen in acid-degradable microparticle vaccines

Protein-based vaccines have been explored as a safer alternative to traditional weakened or killed whole organism based vaccination strategies and have been investigated for their ability to activate the immune system against certain cancers. For optimal stimulation of T lymphocytes, protein-based vaccines should deliver protein antigens to antigen presenting cells in the context of appropriate immunostimulatory signals, thus mimicking actual pathogens. In this report, we describe the synthesis, characterization, and biological evaluation of immunostimulatory acid-degradable microparticles, which are suitable delivery vehicles for use in protein-based vaccines and cancer immunotherapy. Using a 3' conjugation strategy, we optimized the attachment of immunostimulatory CpG DNA to our vaccine carriers and demonstrated that under acidic conditions similar to those found in endosomal compartments, these new particles were capable of simultaneously releasing a model protein antigen and a CpG DNA adjuvant. We found in an in vivo cytotoxicity assay that the co-encapsulation of ovalbumin, a model antigen, and immunostimulatory agent in the same particle led to superior cytotoxic T lymphocyte activity compared to particles coadministered with adjuvant in an unbound form. In addition, we investigated the ability of these acid-degradable particles to induce protective immunity in the MO5 murine melanoma model and found that they were effective until tumor escape, which appeared to result from a loss of antigen expression by the cancer cells due to in vivo selection pressure.

A prime-boost vaccination protocol optimizes immune responses against the nucleocapsid protein of the SARS coronavirus

Severe acute respiratory syndrome (SARS) is a serious infectious disease caused by the SARS coronavirus. We assessed the potential of prime-boost vaccination protocols based on the nucleocapsid (NC) protein co-administered with a derivative of the mucosal adjuvant MALP-2 or expressed by modified Vaccinia virus Ankara (MVA–NC) to stimulate humoral and cellular immune responses at systemic and mucosal levels. The obtained results demonstrated that strong immune responses can be elicited both at systemic and mucosal levels following a heterologous prime-boost vaccination protocol consisting in priming with NC protein add-mixed with MALP-2 by intranasal route and boosting with MVA–NC by intramuscular route.

The immunogenicity of CpG-antigen conjugates

Compared to "live" vaccines the immunogenicity of "split" vaccines is notably poor, because exogeneous antigens (Ag) insufficiently access the MHC class I processing pathway needed for cross-presentation. Here we review our evidence that targeting ligands of endosomally expressed Toll-like Receptors (TLRs), together with exogeneous Ag to endosomes of dendritic cells (DCs) conveys immunogenicity to Ag similar in magnitude as "live" vaccines that produce Ag. We explored the consequences of enforced endocytosis of "Ag plus TLR ligands" either by crosslinking Ag and CpG-Oligonucleotides (CpG-Ag conjugates) or by co-encapsulating Ag plus endosomally expressed TLR ligands in biodegradable microspheres (MP). While both approaches equally well yielded in effective cross-priming of MHC class I restricted CD8 T effector cells, our data recommend MP as a generally applicable endosomal delivery device to vaccinate for protective and therapeutic CD4 and CD8 T cell immunity. Furthermore, our data suggest that functional inactivation of Foxp3(+) regulatory T cells further enhances the immunogenicity of "split vaccines".

Dendritic cell-mediated-immunization with xenogenic PrP and adenoviral vectors breaks tolerance and prolongs mice survival against experimental scrapie

In prion diseases, PrP^c, a widely expressed protein, is transformed into a pathogenic form called PrP^Sc, which is in itself infectious. Antibodies directed against PrP^c have been shown to inhibit PrP^c to PrP^Sc conversion in vitro and protect in vivo from disease. Other effectors with potential to eliminate PrPSc-producing cells are cytotoxic T cells directed against PrP-derived peptides but their ability to protect or to induce deleterious autoimmune reactions is not known. The natural tolerance to PrP^c makes difficult to raise efficient adaptive responses. To break tolerance, adenovirus (Ad) encoding human PrP (hPrP) or control Ad were administered to wild-type mice by direct injection or by transfer of Ad-transduced dendritic cells (DCs). Control Ad-transduced DCs from Tg650 mice overexpressing hPrP were also used for immunization. DC-mediated but not direct administration of AdhPrP elicited antibodies that bound to murine native PrP^c. Frequencies of PrP-specific IFNγ-secreting T cells were low and in vivo lytic activity only targeted cells strongly expressing hPrP. Immunohistochemical analysis revealed that CD3⁺ T cell infiltration was similar in the brain of vaccinated and unvaccinated 139A-infected mice suggesting the absence of autoimmune reactions. Early splenic PrP^Sc replication was strongly inhibited ten weeks post infection and mean survival time prolonged from 209 days in untreated 139A-infected mice to 246 days in mice vaccinated with DCs expressing the hPrP. The efficacy appeared to be associated with antibody but not with cytotoxic cell-mediated PrP-specific responses.

Targeting prion proteins in neurodegenerative disease

BACKGROUND

Spongiform neurodegeneration is the pathological hallmark of individuals suffering from prion disease. These disorders, whose manifestation is sporadic, familial or acquired by infection, are caused by accumulation of the aberrantly folded isoform of the cellular prion protein (PrP(c)), termed PrP(Sc). Although usually rare, prion disorders are inevitably fatal and transferrable by infection.

OBJECTIVE

Pathology is restricted to the central nervous system and premortem diagnosis is usually not possible. Yet, promising approaches towards developing therapeutic regimens have been made recently.

METHODS

The biology of prion proteins and current models of neurotoxicity are discussed and prophylactic and therapeutic concepts are introduced.

RESULTS/CONCLUSIONS

Although various promising drug candidates with antiprion activity have been identified, this proof-of-concept cannot be transferred into translational medicine yet.

Contribution of antibody and T cell-specific responses to the progression of 139A-scrapie in C57BL/6 mice immunized with prion protein peptides

Prion diseases are associated with the conversion of the normal host cellular prion protein to an abnormal protease-resistant (PrPres) associated with infectivity. No specific immune response against prions develops during infection due to the strong tolerance to cellular prion protein. We examined the protective potential on prion diseases of immune responses elicited in C57BL/6 mice with PrP peptides 98-127 (P5) or 158-187 (P9) with CpG. After immunization, P5-treated mice developed high titer and long-lasting Abs, and P9-treated mice developed transient IFN-gamma secreting T cells and poor and variable Ab responses. Both treatments impaired early accumulation of PrPres in the spleen and prolonged survival of mice infected with 139A scrapie. Additional P9 boosts after 139A infection sustained the T cell response and partially inhibited PrPres early accumulation but did not improve the survival. Surprisingly, when P9 injections were started 1 mo after infection and repeated subsequently, specific T cell and Ab responses were impaired and no beneficial effect on prion disease was observed. After a single injection of P9, the number of IFN-gamma secreting CD4+ T cells was also reduced in mice 8- to 10-wk postinfection compared with healthy mice. In vivo and in vitro removal of CD4+CD25+ T cells restored the T cell response to P9 in infected mice. In conclusion, CD4+ T cells as well as Abs might participate to the protection against scrapie. Of importance, the peripheral accumulation of PrPres during infection negatively interferes with the development of T and B cell responses to PrP and regulatory T cells might contribute to this phenomenon.

TLR ligands and antigen need to be coencapsulated into the same biodegradable microsphere for the generation of potent cytotoxic T lymphocyte responses

Dendritic cells phagocytose pathogens leading to maturation and cross-presentation on MHC class I. We found that the efficiency of cross-priming in mice after vaccination with biodegradable poly(D,L-lactide-co-glycolide) microspheres (MSs) was enhanced when ovalbumin was coencapsulated together with either a CpG oligonucleotide or polyI:C as compared to co-inoculation of ovalbumin-bearing MS with soluble or separately encapsulated adjuvants. A single immunization with MS containing coencaspsulated CpG and ovalbumin yielded 9% SIINFEKL/H-2K(b) tetramer positive CTLs, production of IFN-gamma, efficient cytolysis, and protection from vaccinia virus infection. Taken together, coencapsulation of adjuvant and antigen is an important paradigm for the generation of potent CTL responses.