Immunization with a soluble recombinant HIV protein entrapped in biodegradable microparticles induces HIV-specific CD8+ cytotoxic T lymphocytes and CD4+ Th1 cells

Novel approaches to reactivate pertussis immunity

INTRODUCTION

Whole cell and acellular pertussis vaccines have been very effective in decreasing the deaths of neonates and infants from Bordetella pertussis. Despite high vaccine coverage worldwide, pertussis remains one of the most common vaccine-preventable diseases, thus suggesting that new pertussis vaccination strategies are needed. Several candidates are currently under development, such as acellular pertussis vaccines that use genetically detoxified pertussis toxin, acellular pertussis vaccines delivered with new adjuvants or new delivery systems, or an intranasally delivered, live attenuated vaccine.

AREAS COVERED

This review discusses the different possibilities for improving current pertussis vaccines and the present state of knowledge on the pertussis vaccine candidates under development.

EXPERT OPINION

Until there is a safe, effective, and affordable alternative to the two types of existing vaccines, we should maintain sufficient childhood coverage and increase the vaccination of pregnant women, adolescents, and young adults.

Nanoparticles of Chitosan/Poly(D,L-Lactide-Co-Glycolide) Enhanced the Immune Responses of Haemonchus contortus HCA59 Antigen in Model Mice

Background

Hepatocellular carcinoma-associated antigen 59 (HCA59) from excretory/secretory products of Haemonchus contortus is known to have the ability to modulate the functions of host cells. However, its immunogenicities using different nanoparticles adjuvants remain poorly understood.

Purpose

The study aimed to select an efficient nanoparticle antigen delivery system, which could enhance the immune responses of Haemonchus contortus HCA59 in mice.

Methods

Here, the immune responses induced by the recombinant protein of HCA59 (rHCA59) with poly-D,L-lactide-co-glycolide (PLGA) nanoparticles, Chitosan nanoparticles, mixture of PLGA and Chitosan nanoparticles (rHCA59-Chitosan-PLGA), and Freund’s complete adjuvant were observed, respectively, in mice. Cytokine and antibody levels induced by different groups were detected by ELISA assay. The effects of lymphocyte proliferations on different groups were examined using CCK-8 kit. Phenotypes of T cells and dendritic cells were analyzed by flow cytometry.

Results

On day 14 post vaccination, levels of IgM, IgG1, IgG2a, IFN-γ, IL-4, and IL-17 were significantly increased in the groups immunized with rHCA59 encapsulated with nanoparticles. After mice were vaccinated with rHCA59 loaded with Chitosan/PLGA nanoparticles, lymphocytes proliferated significantly. Additionally, the percentages of CD4⁺ T cells (CD3⁺ CD4⁺), CD8⁺ T cells (CD3⁺ CD8⁺), and dendritic cells (CD11c⁺ CD83⁺, CD11c⁺ CD86⁺) were obviously up-regulated in the mice immunized with nanoparticles, especially in the rHCA59-Chitosan-PLGA antigen delivery system group.

Conclusion

The findings of this research demonstrated that rHCA59-Chitosan-PLGA antigen delivery system could induce higher immune responses in mice model and indicated that rHCA59 might be a good candidate molecule to develop nanovaccines against Haemonchus contortus in future study.

Nanoparticles (PLGA and Chitosan)-Entrapped ADP-Ribosylation Factor 1 of Haemonchus contortus Enhances the Immune Responses in ICR Mice

ADP-ribosylation factor 1 (HcARF1) is one of the Haemonchus contortus (H. contortus) excretory/secretory proteins involved in modulating the immune response of goat peripheral blood mononuclear cells (PBMC). Here, we evaluated the immunogenic potential of recombinant HcARF1 (rHcARF1) against H. contortus infection in Institute of Cancer Research (ICR) mice. Briefly, rHcARF1 was entrapped in poly (D, L-lactide-co-glycolide) (PLGA) and chitosan (CS) nanoparticles (NP) and injected into mice as a vaccine. Fifty-six ICR mice were assigned randomly into seven groups, with eight animals in each group, and they were vaccinated subcutaneously. At the end of the experiment (14th day), the blood and the spleen were collected from euthanized mice to detect lymphocyte proliferation, cytokine analysis, and the production of antigen-specific antibodies. Scanning electron microscope was used to determine the size, morphology, and zeta potential of nanoparticles. Flow cytometry was performed, which presented the increase percentages of CD4⁺ T cells (CD3e⁺CD4⁺), CD8⁺ T cells (CD3e⁺CD8⁺) and dendritic cells (CD11c⁺CD83⁺, CD11c⁺CD86⁺) in mice vaccinated with rHcARF1+PLGA NP. Immunoassay analysis show raised humoral (Immunoglobulin (Ig)G1, IgG2a, IgM) and cell-mediated immune response (Interleukin (IL)-4, IL-12, and IL-17, and Interferon (IFN)-γ) induced by rHcARF1+PLGA NP. Experimental groups that were treated with the antigen-loaded NP yield higher lymphocyte proliferation than the control groups. Based on these results, we could propose that the rHcARF1 encapsulated in NP could stimulate a strong immune response in mice rather than administering alone against the infection of H. contortus.

Surface conjugation of EP67 to biodegradable nanoparticles increases the generation of long-lived mucosal and systemic memory T-cells by encapsulated protein vaccine after respiratory immunization and subsequent T-cell-mediated protection against respiratory infection

Encapsulation of protein vaccines in biodegradable nanoparticles (NP) increases T-cell expansion after mucosal immunization but requires incorporating a suitable immunostimulant to increase long-lived memory T-cells. EP67 is a clinically viable, host-derived peptide agonist of the C5a receptor that selectively activates antigen presenting cells over neutrophils. We previously found that encapsulating EP67-conjugated CTL peptide vaccines in NP increases long-lived memory subsets of CTL after respiratory immunization. Thus, we hypothesized that alternatively conjugating EP67 to the NP surface can increase long-lived mucosal and systemic memory T-cells generated by encapsulated protein vaccines. We found that respiratory immunization of naïve female C57BL/6 mice with LPS-free ovalbumin (OVA) encapsulated in PLGA 50:50 NP (∼380 nm diameter) surface-conjugated with ∼0.1 wt% EP67 through 2 kDa PEG linkers (i) increased T-cell expansion and long-lived memory subsets of OVA_323-339-specific CD4⁺ and OVA_257-264-specific CD8a⁺ T-cells in the lungs (CD44^HI/CD127/KLRG1) and spleen (CD44^HI/CD127/KLRG1/CD62L) and (ii) decreased peak CFU of OVA-expressing L. monocytogenes (LM-OVA) in the lungs, liver, and spleen after respiratory challenge vs. encapsulation in unmodified NP. Thus, conjugating EP67 to the NP surface is one approach to increase the generation of long-lived mucosal and systemic memory T-cells by encapsulated protein vaccines after respiratory immunization.

Controlled release of antigen and Toll-like receptor ligands from PLGA nanoparticles enhances immunogenicity

AIM

Dendritic cells rapidly capture nanoparticles and induce a potent cellular immune response. It is yet unknown whether the immunological response induced by slow release of encapsulated versus soluble antigen and adjuvant is superior.

MATERIALS & METHODS

The kinetics of poly(lactic-co-glycolic acid) PLGA nanoparticles antigen release was studied by the DQ-bovine serum albumin (BSA) self-quenching antigen model. The immunological response induced was evaluated by means of dendritic cell activation/maturation markers, cytokine production and their ability to drive antigen-specific T-cell proliferation.

RESULTS & CONCLUSION

PLGA-encapsulated antigen and adjuvant showed an enhanced T-cell response when compared with soluble vaccine components by increasing antigenicity and adjuvanticity. Although the kinetic profile followed the same pattern, encapsulation increased strength and duration of the response.

PLGA nano/micro particles encapsulated with pertussis toxoid (PTd) enhances Th1/Th17 immune response in a murine model

Poly(lactic-co-glycolic acid) (PLGA) based nano/micro particles were investigated as a potential vaccine platform for pertussis antigen. Presentation of pertussis toxoid as nano/micro particles (NP/MP) gave similar antigen-specific IgG responses in mice compared to soluble antigen. Notably, in cell line based assays, it was found that PLGA based nano/micro particles enhanced the phagocytosis of fluorescent antigen-nano/micro particles by J774.2 murine monocyte/macrophage cells compared to soluble antigen. More importantly, when mice were immunised with the antigen-nano/micro particles they significantly increased antigen-specific Th1 cytokines INF-γ and IL-17 secretion in splenocytes after in vitro re-stimulation with heat killed Bordetalla pertussis, indicating the induction of a Th1/Th17 response. Also, presentation of pertussis antigen in a NP/MP formulation is able to provide protection against respiratory infection in a murine model. Thus, the NP/MP formulation may provide an alternative to conventional acellular vaccines to achieve a more balanced Th1/Th2 immune response.

Preparation, characterization and immunological evaluation: canine parvovirus synthetic peptide loaded PLGA nanoparticles

BACKGROUND

Canine parvovirus 2 (CPV-2) remains a significant worldwide canine pathogen and the most common cause of viral enteritis in dogs. The 1 L15 and 7 L15 peptides overlap each other with QPDGGQPAV residues (7-15 of VP2 capsid protein of CPV) is shown to produce high immune response. PLGA nanoparticles were demonstrated to have special properties such as; controlled antigen release, protection from degradation, elimination of booster-dose and enhancing the cellular uptake by antigen presenting cells. Nevertheless, there is no study available in literature, about developing vaccine based on PLGA nanoparticles with adjuvant properties against CPV. Thus, the aim of the present study was to synthesize and characterize high immunogenic W-1 L19 peptide (from the VP2 capsid protein of CPV) loaded PLGA nanoparticle and to evaluate their in vitro immunogenic activity.

RESULTS

PLGA nanoparticles were produced with 5.26 ± 0.05 % loading capacity and high encapsulation efficiency with 81.2 ± 3.1 %. Additionally, it was evaluated that free NPs and W-1 L19 peptide encapsulated PLGA nanoparticles have Z-ave of 183.9 ± 12.1 nm, 221.7 ± 15.8 nm and polydispersity index of 0.107 ± 0.08, 0.135 ± 0.12 respectively. It was determined that peptide loaded PLGA nanoparticles were successfully phagocytized by macrophage cells and increased NO production at 2-folds (*P < 0.05) in contrast to free peptide, and 3-folds (*P < 0.01) in contrast to control.

CONCLUSION

In conclusion, for the first time, W-1 L19 peptide loaded PLGA nanoparticles were successfully synthesized and immunogenic properties evaluated. Obtained results showed that PLGA nanoparticles enhanced the capacity of W-1 L19 peptide to induce nitric oxide production in vitro due to its adjuvant properties. Depend on the obtained results, these nanoparticles can be accepted as potential vaccine candidate against Canine Parvovirus. Studies targeting PLGA nanoparticles based delivery system must be maintained in near future in order to develop new and more effective nano-vaccine formulations.

Implication of nanoparticles/microparticles in mucosal vaccine delivery

Although polymeric nanoparticles/microparticles are well established for the mucosal administration of conventional drugs, they have not yet been developed commercially for vaccine delivery. The limitation of the mucosal (particularly oral) route of delivery, including low pH, gastric enzymes, rapid transit and poor absorption of large molecules, has made mucosal vaccine delivery challenging. Nevertheless, several polymeric delivery systems for mucosal vaccine delivery are currently being evaluated. The polymer-based approaches are designed to protect the antigen in the gut, to target the antigen to the gut-associated lymphoid tissue or to increase the residence time of the antigen in the gut through bioadhesion. M-cell targeting is a potential approach for mucosal vaccine delivery, which can be achieved using M-cell-specific lectins, microbial adhesins or immunoglobulins. While many hurdles must be overcome before targeted mucosal vaccine delivery becomes a practical reality, this is a potential area of research that has important implications for future vaccine development. This review comprises various aspects that could be decisive in the development of polymer based mucosal vaccine delivery systems.

Combination vaccines: synergistic simultaneous induction of antibody and T-cell immunity

Vaccines have traditionally been designed to induce antibody responses and have been licensed on their capacity to induce high titers of circulating antibody to the pathogen. With our increased knowledge of host-pathogen interactions, it became apparent that induction of the cellular arm of the immune response is crucial to the efficacy of vaccines against intracellular pathogens and for providing appropriate help for antibody induction. Diverging strategies emerged that concentrate on developing candidate vaccines that solely induce either cellular or humoral responses. As most microbes reside at some point in the infectious cycle in the extracellular as well as intracellular space, and there is interplay between antibody and T cells, it is now apparent that both arms of immunity are essential to effectively control and eliminate the infection. It is, therefore, necessary to develop vaccines that can effectively induce a broad adaptive immune response. For vaccines targeted at diseases of the developing world, such as HIV, tuberculosis and malaria, it is imperative that these vaccines are simple to deliver and cost effective, that is,that optimum T-cell and antibody immunity is achieved with the minimum number of vaccinations. Combination vaccines, where an antibody-inducing subunit protein vaccine is coadministered with a T-cell-inducing poxvirus-based vaccine fulfill these requirements and induce sterile immunity to pathogen challenge.

Nanotechnological Approaches for Genetic Immunization

Genetic immunization is one of the important findings that provide multifaceted immunological response against infectious diseases. With the advent of r-DNA technology, it is possible to construct vector with immunologically active genes against specific pathogens. Nevertheless, site-specific delivery of constructed genetic material is an important contributory factor for eliciting specific cellular and humoral immune response. Nanotechnology has demonstrated immense potential for the site-specific delivery of biomolecules. Several polymeric and lipidic nanocarriers have been utilized for the delivery of genetic materials. These systems seem to have better compatibility, low toxicity, economical and capable to delivering biomolecules to intracellular site for the better expression of desired antigens. Further, surface engineering of nanocarriers and targeting approaches have an ability to offer better presentation of antigenic material to immunological cells. This chapter gives an overview of existing and emerging nanotechnological approaches for the delivery of genetic materials.

Enhancing immunogenicity and cross-reactivity of HIV-1 antigens by in vivo targeting to dendritic cells

Current retroviral treatments have reduced AIDS to a chronic disease for most patients. However, given drug-related side effects, the emergence of drug-resistant strains and the persistence of viral replication, the development of alternative treatments is a pressing need. This review focuses on recent developments in HIV immunotherapy treatments, with particular emphasis on current vaccination strategies for optimizing the induction of an effective immune response by the recruitment of dendritic cells. In addition to cell-based therapies, targeted strategies aiming to deliver synthetic HIV peptides to dendritic cell-specific receptors in vivo will be discussed.

Local and systemic immune responses in mice to intranasal delivery of peptides representing bovine respiratory syncytial virus epitopes encapsulated in poly (DL-lactide-co-glycolide) microparticles

The potential of a microparticulate vaccine delivery system in eliciting a specific mucosal antibody response in the respiratory tract of mice was evaluated. Two vaccine candidate peptides representing epitopes from the G attachment and F fusion antigens from bovine respiratory syncytial virus (BRSV) were encapsulated into poly(DL-lactide co-glycolide) biodegradable microparticles. The encapsulation process did not denature the entrapped peptides as verified by detection of peptide-specific antibodies in mucosal secretions by ELISA using peptide as antigen. Following intranasal immunisation, the encapsulated peptides induced stronger upper and lower respiratory tract specific-IgA responses, respectively, than the soluble peptide forms. Moreover, a strong peptide-specific cell-mediated immune response was measured in splenocytes in vitro from the mice inoculated with the encapsulated peptides compared to their soluble form alone indicating that migration of primed T cells had taken place from the site of mucosal stimulation in the upper respiratory tract to the spleen. These results act as a foundation for vaccine efficacy studies in large animal BRSV challenge models.

PLGA-polymer encapsulating tumor antigen and CpG DNA administered into the tumor microenvironment elicits a systemic antigen-specific IFN-γ response and enhances survival

Critical to the generation of an effective therapeutic antitumor immune response is the elicitation of effective antigen presentation coupled with overcoming tumor-immune escape mechanisms. Towards this end, we aimed to understand the therapeutic effectiveness of a polymer based vaccine approach at enhancing the anti-tumor responses in a tumor-bearing mouse model. While we and others have previously demonstrated the effectiveness of PLGA based systems in delivering antigen etc., studies scarcely focus on understanding the immunological mechanisms of polymer based therapies in tumor bearing treatment models. Considering tumors modulate the immune system and consequently the efficacy of therapies, understanding treatment mechanisms in the presence of tumor will help lead to more efficacious treatment options. We demonstrate here that a poly(lactic-co-glycolic acid) (PLGA) based delivery system encapsulating tumor antigen (OVA) and the TLR9 agonist CpG motif DNA administered into the tumor microenvironment initiates an effective type 1 mediated (IFN-γ producing) anti-tumor response in a syngeneic murine model of T cell lymphoma (E.G7-OVA). Although E.G7-OVA tumors spontaneously generate antigen specific CTLs in draining lymph nodes (LN), tumors progress rapidly. Modulation of the tumor microenvironment via local PLGA based therapy led to the generation of a systemic antigen specific Th1 response, absent in the non-polymer delivery method, subsequently associated with reduced tumor growth and prolongation of survival. These studies provide further insight into the use of a PLGA-based therapeutic approach at modulating the tumor microenvironment and highlight the need for analyzing the treatment effects in a tumor bearing model.

Intranasal administration of influenza vaccines: current status

AbstractThis review article focuses on intranasal immunisation against influenza,although it also encompasses antigen uptake and processing in the nasopharyngealpassages, host defence from influenza and current influenza vaccination practices.Improvement of current vaccination strategies is clearly required; current proceduresinvolve repeated annual injections that sometimes fail to protect the recipient. It isenvisaged that nonpercutaneous immunisation would be more attractive to potentialvaccinees, thus improving uptake and coverage. As well as satisfying noninvasivecriteria, intranasal influenza immunisation has a number of perceived immunologicaladvantages over current procedures. Perhaps one of the greatest attributes of thisapproach is its potential to evoke the secretion of haemagglutinin-specific IgAantibodies in the upper respiratory tract, the main site of viral infection. Inactivated influenza vaccines have the advantage that they have a long historyof good tolerability as injected immunogens, and in this respect are possibly morelikely to be licensed than attenuated viruses. Inert influenza vaccines are poormucosal immunogens, requiring several administrations, or prior immunologicalpriming, in order to engender significant antibody responses. The use of vaccinedelivery systems or mucosal adjuvants serves to appreciably improve theimmunogenicity of mucosally applied inactivated influenza vaccines. As is the casewhen they are introduced parenterally, inactivated influenza vaccines are relativelypoor stimulators of virus-specific cytotoxic T lymphocyte activity following nasalinoculation. Live attenuated intranasal influenza vaccines are at a far moreadvanced stage of clinical readiness (phase III versus phase I). With the use of liveattenuated vaccines, it is possible to stimulate mucosal and cell-mediatedimmunological responses of a similar kind to those elicited by natural influenzainfection. In children, recombinant live attenuated cold-adapted influenza viruses arewell tolerated. Moreover, cold-adapted influenza viruses usually stimulate protectiveimmunity following only a single nasal inoculation. Safety of recombinant liveattenuated cold-adapted influenza viruses has also been demonstrated in high riskindividuals with cystic fibrosis, asthma, cardiovascular disease and diabetes mellitus.They are not suitable for immunising immunocompromised patients, however, andare poorly efficacious in individuals with pre-existing immunity to strains closelyantigenically matched with the recombinant virus. According to the reviewedliterature, it is apparent that intranasal administration of vaccine as an aerosol issuperior to administration as nose drops. The information reviewed in this papersuggests that nasally administered influenza vaccines could make a substantialimpact on the human and economic cost of influenza.

Vaccine adjuvants - Current status and prospects on controlled release adjuvancity

The strategy of World Health Organization is to develop efficient and inexpensive vaccine against various infectious diseases amongst children's population. Vaccination is considered as the most cost effective health intervention known to public. Since 90 years various substances have been added in vaccine formulation but still alum is considered as the safest adjuvant for human use licensed by United States Food and Drug Administration. MF 59 and ASO4 are the adjuvants were developed recently and approved for human use. Due to poor adjuvancity, conventional vaccines require multiple recall injection at approximately time intervals to attain optimal immune response. For past approximately two decades the vaccine research has been focused towards the alternation of alum type of adjuvant in order to increase the immunogenicity. The development of new vaccines, is more efficacious or easier to deliver, or both have become an area of research that can certainly benefit from controlled release technology. Especially, the conversion of multiple administration vaccine into single administration vaccine may represent an improved advancement towards the betterment of human health care and welfare. Biodegradable polymer microparticles have been evaluated for delivering antigens in native form, sustained release keeping in mind the safety aspects. In this article we review the overall concept of adjuvants in vaccine technology with special focus towards the prospects of controlled release antigens.

Immunization with PCEP microparticles containing pertussis toxoid, CpG ODN and a synthetic innate defense regulator peptide induces protective immunity against pertussis

We investigated the efficacy of a novel microparticle (MP) based vaccine formulation consisting of pertussis toxoid (PTd), polyphosphazene (PCEP), CpG ODN 10101 and synthetic cationic innate defense regulator peptide 1002 (IDR) against Bordetella pertussis in mice. We studied whether encapsulation of these IDR-CpG ODN complexes into polyphosphazene-based microparticles further enhanced their immunomodulatory activity compared to soluble formulations containing PCEP (SOL), or without PCEP (AQ). In vitro stimulation of murine macrophages showed MP induced significantly higher levels of pro-inflammatory cytokines. When assessed in a B. pertussis infection challenge model, a single immunization with MP formulation led to significantly lower bacterial loads compared to other formulations and non-vaccinated animals. ELISPOT of splenocytes showed that MP group mice had significantly higher number of antigen-specific IL-17 secreting cells. The cytokine profile in lung homogenates of MP group mice after challenge showed significantly higher amounts of MCP-1, TNF-α, IFN-γ, IL-12 and IL-17 and significantly lowered IL-10 levels suggesting a strong Th1 shift. Protection was observed against challenge infection with B. pertussis. On the other hand protective immune responses elicited in Quadracel(®) immunized mice were Th2 skewed. Hence, we conclude that formulation of PTd, PCEP, CpG ODN and IDR into MP generates a protective immune response in mice against pertussis emphasizing the potential of MP as a delivery vehicle for the potential development of single-shot vaccines.

Particulate vaccines: on the quest for optimal delivery and immune response

Subunit vaccines offer a safer alternative to traditional organism-based vaccines, but their immunogenicity is impaired. This hurdle might be overcome by the use of micro- and nanodelivery systems carrying the antigen(s). This review discusses the rationale for the use of particulate vaccines and provides an overview of antigen-delivery vehicles currently under investigation. It further highlights the cellular uptake, antigen processing and the presentation by antigen-presenting cells because these processes are partially governed by particle characteristics and eventually determine the immunological outcome. Finally, we address the attractive concept of concomitant delivery of antigens and immunopotentiators. The condensed knowledge could be an asset for rationally designing antigen-delivery vehicles to obtain safe and efficacious vaccines.

Nanoparticle vaccines against respiratory viruses

Influenza virus, respiratory syncytial virus (RSV), and parainfluenza type 3 virus (PI-3V) are the major viral agents which are consistently involved in causing lower respiratory tract disease in humans and animals. The virus infection begins in the upper respiratory tract, where immune responses are initiated, and then progresses to the lower respiratory tract where destruction of cells and tissues leads to bronchitis, bronchiolitis, and pneumonia, which is occasionally fatal. Nanoparticle vaccines, incorporating antigenic components from influenza, RSV, or PI-3V have been shown to be capable of stimulating mucosal and systemic immune responses, which can prevent the spread of infection to the lower respiratory tract. The encapsulation of viral proteins within nanoparticles may also facilitate production of respiratory vaccines which are efficacious in infants, where presence of maternally derived antibodies can reduce vaccine efficacy.

Vaccine adjuvants: current challenges and future approaches

For humans, companion animals, and food producing animals, vaccination has been touted as the most successful medical intervention for the prevention of disease in the twentieth century. However, vaccination is not without problems. With the development of new and less reactogenic vaccine antigens, which take advantage of molecular recombinant technologies, also comes the need for more effective adjuvants that will facilitate the induction of adaptive immune responses. Furthermore, current vaccine adjuvants are successful at generating humoral or antibody mediated protection but many diseases currently plaguing humans and animals, such as tuberculosis and malaria, require cell mediated immunity for adequate protection. A comprehensive discussion is presented of current vaccine adjuvants, their effects on the induction of immune responses, and vaccine adjuvants that have shown promise in recent literature.

Poly(lactide-co-glycolide) microspheres: a potent oral delivery system to elicit systemic immune response against inactivated rabies virus

Rabies is an endemic, fatal zoonotic disease in the developing countries. Oral vaccination strategies are suitable for rabies control in developing countries. Studies were performed to investigate the suitability of poly(lactide-co-glycolide) (PLG) microspheres as an oral delivery system for beta-propiolactone inactivated concentrated rabies virus (CRV). Immune responses induced by encapsulated (PLG+CRV) and un-encapsulated inactivated rabies virus after oral and intraperitoneal route administrations were compared. The anti-rabies virus IgG antibody titer, virus neutralizing antibody (VNA) titers obtained by mouse neutralization test (MNT) and IgG2a and IgG1 titers of mice group immunized orally with PLG+CRV showed significantly (p<0.001) higher response than the group immunized orally with un-encapsulated CRV. There was no significant difference (p>0.05) between groups inoculated by intraperitoneal route. The stimulation index (SI) obtained by lymphoproliferation assay of PLG+CRV oral group also showed significantly (p<0.001) higher response than the group immunized orally with un-encapsulated CRV, suggesting that oral immunization activates Th1-mediated cellular immunity. Immunized mice of all experimental groups were challenged intracerebrally with a lethal dose of virulent rabies virus Challenge Virus Standard (CVS). The survival rates of mice immunized orally with PLG+CRV and CRV alone were 75% and 50%, respectively, whereas intraperitoneally immunized groups showed 100% protection. The overall results of humoral, cellular immune response and survival rates of mice immunized orally with PLG+CRV were significantly (p<0.001) higher than those of mice immunized orally with CRV alone. These data suggest that the PLG encapsulated inactivated rabies virus can be used for oral immunization against rabies.

Past, present, and future technologies for oral delivery of therapeutic proteins

Biological drugs are usually complex proteins and cannot be orally delivered due to problems related to degradation in the acidic and protease-rich environment of the gastrointestinal (GI) tract. The high molecular weight of these drugs often results in poor absorption into the periphery when administered orally. The most common route of administration for these therapeutic proteins is injection. Most of these proteins have short serum half-lives and need to be administered frequently or in high doses to be effective. So, difficulties in the administration of protein-based drugs provides the motivation for developing drug delivery systems (DDSs) capable of maintaining therapeutic drug levels without side effects as well as traversing the deleterious mucosal environment. Employing a polymer as an entrapment matrix is a common feature among the different types of systems currently being pursued for protein delivery. Protein release from these matrices can occur through various mechanisms, such as diffusion through or erosion of the polymer matrix, and sometimes a combination of both. Encapsulation of proteins in liposomes has also been a widely investigated technology for protein delivery. All of these systems have merit and our worthy of pursuit.

Intranasal vaccination with poly(lactide-co-glycolide) microparticles containing a peptide T of Ole e 1 prevents mice against sensitization

BACKGROUND

Biodegradable microparticles, in particular poly(lactide-co-glycolide) (PLGA), have been shown as potential delivery vehicles for intranasal (i.n.) vaccines in animal models.

OBJECTIVES

To evaluate whether i.n. administration of PLGA microparticles containing a peptide with the major T cell epitope of Ole e 1, the main allergen of olive pollen, prevented mice from allergic sensitization to the whole protein.

METHODS

Peptide-PLGA microparticles were prepared by a solvent evaporation double emulsion method. Microparticles in a size range of 0.8 mum were evaluated for peptide loading and in vitro antigen release. Stability and immunogenicity of the entrapped peptide were retained, as determined by dot blot and ELISA inhibition. BALB/c mice were intranasally treated with peptide-PLGA microparticles for 3 consecutive days, 1 week before sensitization/challenge to Ole e 1. Blood, lungs and spleen were collected and analysed for immune response. Biodistribution of microparticles was investigated using confocal microscopy.

RESULTS

I.n. pretreatment of BALB/c mice with peptide-PLGA microparticles before sensitization to Ole e 1 led to a significant inhibition of serum allergen-specific IgE and IgG1 antibody levels, but a marked increase of specific IgG2a antibodies as compared with sham-pretreated mice. Moreover, IL-5 and IL-10 levels in spleen cell cultures were suppressed in peptide-PLGA pretreated mice. The airway histopathologic parameters associated with inflammation were significantly suppressed by the pretreatment.

CONCLUSION

These results demonstrate that i.n. immunization with peptide T-PLGA microparticles is effective in preventing subsequent allergic sensitization to Ole e 1. Our data indicate that peptide-PLGA microparticles may be promising candidates for the design of nasal vaccines against allergic diseases in humans.

Induction of potent CD8+ T-cell responses by novel biodegradable nanoparticles carrying human immunodeficiency virus type 1 gp120

The mainstream of recent anti-AIDS vaccines is a prime/boost approach with multiple doses of the target DNA of human immunodeficiency virus type 1 (HIV-1) and recombinant viral vectors. In this study, we have attempted to construct an efficient protein-based vaccine using biodegradable poly(gamma-glutamic acid) (gamma-PGA) nanoparticles (NPs), which are capable of inducing potent cellular immunity. A significant expansion of CD8+ T cells specific to the major histocompatibility complex class I-restricted gp120 epitope was observed in mice intranasally immunized once with gp120-carrying NPs but not with gp120 alone or gp120 together with the B-subunit of cholera toxin. Both the gp120-encapsulating and -immobilizing forms of NPs could induce antigen-specific spleen CD8+ T cells having a functional profile of cytotoxic T lymphocytes. Long-lived memory CD8+ T cells could also be elicited. Although a substantial decay in the effector memory T cells was observed over time in the immunized mice, the central memory T cells remained relatively constant from day 30 to day 238 after immunization. Furthermore, the memory CD8+ T cells rapidly expanded with boosting with the same immunogen. In addition, gamma-PGA NPs were found to be a much stronger inducer of antigen-specific CD8+ T-cell responses than nonbiodegradable polystyrene NPs. Thus, gamma-PGA NPs carrying various HIV-1 antigens may have great potential as a novel priming and/or boosting tool in current vaccination regimens for the induction of cellular immune responses.

Bacterial ghosts as adjuvant particles

The development of more advanced and effective vaccines is of great interest in modern medicine. These new-generation vaccines, based on recombinant proteins or DNA, are often less reactogenic and immunogenic than traditional vaccines. Thus, there is an urgent need for the development of new and improved adjuvants. Besides many other immunostimulatory components, the bacterial ghost (BG) system is currently under investigation as a potent vaccine delivery system with intrinsic adjuvant properties. BGs are nonliving cell envelope preparations from Gram-negative cells, devoid of cytoplasmic contents, while their cellular morphology and native surface antigenic structures remain preserved. Owing to the particulate nature of BGs and the fact that they contain many well known immune-stimulating compounds, BGs have the potential to enhance immune responses against ghost-delivered target antigens.

Putting microbes to work: Dairy fermentation, cell factories and bioactive peptides. Part I: Overview

A variety of milk-derived biologically active peptides have been shown to exert both functional and physiological roles in vitro and in vivo, and because of this are of particular interest for food science and nutrition applications. Biological activities associated with such peptides include immunomodulatory, antibacterial, anti-hypertensive and opioid-like properties. Milk proteins are recognized as a primary source of bioactive peptides, which can be encrypted within the amino acid sequence of dairy proteins, requiring proteolysis for release and activation. Fermentation of milk proteins using the proteolytic systems of lactic acid bacteria (LAB) is an attractive approach for generation of functional foods enriched in bioactive peptides given the low cost and positive nutritional image associated with fermented milk drinks and yoghurt. In this review, we discuss the exploitation of such fermentation towards the development of functional foods conferring specific health benefits to the consumer beyond basic nutrition. In particular, in Part I, we focus on the release of encrypted bioactive peptides from a range of food protein sources, as well as the use of LAB as cell factories for the de novo generation of bioactivities.

Development of Vaccine Adjuvants Using Polymeric Nanoparticles and Their Potential Applications for Anti-HIV Vaccine

The development of a prophylactic/therapeutic HIV-1 vaccine based on recombinant proteins is needed for the control of the worldwide AIDS epidemic. Subunit protein and peptide vaccines are generally very safe, with well-defined components. However, these antigens are often poorly immunogenic, and thus require the use of adjuvants to induce adequate immunity. Particulate adjuvants (e.g. micro/nanoparticles, emulsions, ISCOMS, liposomes, virosomes, and virus-like particles) have been widely investigated as HIV-1 vaccine delivery systems. Antigen uptake by antigen-presenting cells (APC) is enhanced by the association of the antigens with polymeric micro/nanoparticles. The adjuvant effect of micro/nanoparticles appears to largely be a consequence of their uptake into APC. More importantly, particulate antigens have been shown to be more efficient than soluble antigens for the induction of immune responses. Over the past two decades, we have studied the synthesis and clinical applications of core-corona polymeric nanospheres composed of hydrophobic polystyrene and hydrophilic macromonomers. Core-corona type polymeric nanospheres have applications in various technological and biomedical fields, because their chemical structures and particle size can be easily controlled. In this study, we focused on the development of a HIV-1 vaccine using polymeric nanoparticles. We evaluated the immunization strategies for HIV-1-capturing core-corona type polystyrene nanospheres that would efficiently induce HIV-1-specific IgA responses in female mice and the macaque genital tract. Moreover, based on this research, we attempted to develop novel biodegradable nanoparticles composed of poly (gamma-glutamic acid) (gamma-PGA) for protein-based vaccine delivery. These HIV-1-capturing nanospheres and protein-loaded gamma-PGA nanoparticles have shown unique potential as vaccine carriers.

Microparticle-based technologies for vaccines

Microparticles have been effectively used for many years as delivery systems for drugs and therapeutic proteins. Their application to the delivery of vaccines is not as extensive, but is growing. Utility has been demonstrated for the delivery of various types of vaccines (e.g., recombinant proteins, plasmid DNA, and peptides) and other vaccine components (e.g., immune potentiators). With respect to delivery of immune potentiators, synergistic effects are often observed whereby much more potent immune responses are induced with a combination than with either component alone. Hence, the prospects for broad application of microparticle-based delivery systems for vaccines are excellent.

Preparation and Characterization of Nickel Nanoparticles for Binding to His-tag Proteins and Antigens

PURPOSE

The purpose of these studies was to prepare nanoparticles (NPs) with a small amount of surface-chelated nickel for obtaining enhanced binding of histidine-tagged (his-tag) proteins compared to non-histidine-tagged protein binding to charged nanoparticles.

MATERIALS AND METHODS

NPs were prepared from oil-in-water microemulsion precursors using emulsifying wax, 3 mM Brij 78 and 0.1 mM DOGS-NTA-Ni lipid (referred to as Ni-NPs). The amount of lipid entrapped in the NPs was quantitated by atomic emission spectroscopy (AES). The Ni-NPs were investigated for binding to two his-tag proteins, green fluorescent protein (GFP) and his-tag HIV-1 Gag p24. In vivo studies in mice were carried out to evaluate the immune responses obtained to his-tag Gag p24 bound to Ni-NPs.

RESULTS

AES studies demonstrated that approximately 5% of the DOGS-NTA-Ni lipid used was entrapped in the NPs. The optimal binding ratio his-tag GFP and his-tag Gag p24 to Ni-NPs was found to be 1:33.7 and 1:35.4 w/w, respectively. This interaction was stable at 37 degrees C in PBS, pH 7.4 over 4 h and the interaction of his-tag GFP with the Ni-NPs was enhanced compared to control NPs prepared with no Ni on the surface (NTA-NPs). The in vivo studies demonstrated enhanced serum IgG and IgG2a responses to his-tag Gag p24 bound to Ni-NPs compared to protein adjuvanted with Alum or adsorbed on the surface of control NTA-NPs.

CONCLUSIONS

Ni-NPs can be used to bind strongly to his-tag proteins. This system was demonstrated to have potential applications in vaccine delivery for enhancing immune responses to protein-based vaccines.

The role of adjuvants in the development of mucosal vaccines

It is well-established that most pathogens that cause infectious diseases enter the host via mucosal membranes of the respiratory, digestive and genital tracts. Some parenterally administered vaccines induce protection against mucosal pathogens. However, there is increasing evidence that mucosal protection is better afforded by mucosal vaccination, particularly for the induction of memory responses. Mucosal vaccines must pass several difficult hurdles before entering the host and inducing an effective and protective immune response. This review deals with present and past efforts in devising effective mucosal vaccines using delivery systems and immunopotentiating adjuvants for protein-based vaccines. The paper will conclude with the authors' opinion on how the field will or should progress in the future and what will be the required components of ideal future mucosal vaccines that can induce immunological memory.

Development of hepatitis B oral vaccine using B-cell epitope loaded PLG microparticles

Oral hepatitis B vaccine formulation was prepared by successful encapsulation of immunogenic peptide representing residues 127-145 of the immunodominant B-cell epitope of hepatitis B surface antigen (HBsAg) in poly(D,L-lactide co-glycolide) (PLG) microparticles. The smooth, spherical PLG microparticles with a diameter of around 10 microm was prepared by using W/O/W double emulsion solvent evaporation method. The entrapment efficiency of B-cell epitope peptide (BCEP) into PLG microparticles was 64%. In vitro studies showed B-cell epitope loaded PLG microparticles (BCEM) released the peptide in sustained profile and reached 64.9% efficiency by Day 25. Single oral immunization of mice with BCEM led to the significant induction of specific serum IgG and IgM anti-HB antibodies. After the termination of antibody induction, the orally immunized mice were infected with HBsAg, which resulted in the rapid production of antibodies against HBsAg as a result of secondary immune response. PLG microparticles formulation approach may have potential in increasing the efficacy of microparticulate systems for the oral administration of hepatitis B vaccine.

Enhanced and prolonged cross-presentation following endosomal escape of exogenous antigens encapsulated in biodegradable nanoparticles

CD8(+) T-cell responses are critical in the immunological control of tumours and infectious diseases. To prime CD8(+) T cells against these cell-associated antigens, exogenous antigens must be cross-presented by professional antigen-presenting cells (APCs). While cross-presentation of soluble antigens by dendritic cells is detectable in vivo, the efficiency is low, limiting the clinical utility of protein-based vaccinations. To enhance the efficiency of presentation, we generated nanoparticles from a biodegradable polymer, poly(D,L-lactide-co-glycolide) (PLGA), to deliver antigen into the major histocompatibility complex (MHC) class I antigen presentation pathway. In primary mouse bone marrow-derived dendritic cells (BMDCs), the MHC class I presentation of PLGA-encapsulated ovalbumin (OVA) stimulated T cell interleukin-2 secretion at 1000-fold lower concentration than soluble antigen and 10-fold lower than antigen-coated latex beads. The microparticles also served as an intracellular antigen reservoir, leading to sustained MHC class I presentation of OVA for 72 hr, decreasing by only 20% after 96 hr, a time at which the presentation of soluble and latex bead-associated antigens was undetectable. Cytosol extraction demonstrated that antigen delivery via PLGA particles increased the amount of protein that escaped from endosomes into the cytoplasm, thereby increasing the access of exogenous antigen to the classic MHC class I loading pathway. These data indicate that the unique properties of PLGA particle-mediated antigen delivery dramatically enhance and sustain exogenous antigen presentation by MHC class I, potentially facilitating the clinical use of these particles in vaccination.

Induction of dendritic cell-mediated immune responses against HIV-1 by antigen-capturing nanospheres in mice

Prophylactic vaccines, designed to elicit potent humoral and cellular immune responses to human immunodeficiency virus type 1 (HIV-1) antigens in mucosa, are the important approach to the protection of individuals against HIV-1 infection, since HIV-1 transmission is largely a result of sexual contact. In this study, a novel strategy has been developed to induce HIV-1-specific immune responses, which involves inactivated HIV-1-caputring concanavalin A (Con A)-immobilized nanospheres (HIV-NS) and their interaction with bone marrow (BM)-derived dendritic cells. HIV-NS were taken up by dendritic cells via cytoskeleton-dependent but mannose-binding site-independent phagocytosis. Serial stimulations to unprimed T-cells with HIV-1 gp120-capturing NS-pulsed dendritic cells could induce antigen-specific T-cell response. Intranasal administration of fluorescein isothiocyanate-labeled nanospheres (NS) in mice proved that the particles were taken up into pulmonary dendritic cells. Analysis of mice receiving intranasal immunizations with HIV-NS revealed that the mice efficiently induced the antibodies against HIV-1 in the genital tract and specific cytotoxic T-cells in the spleen. These results suggest that the use of HIV-1-NS may provide a novel and promising approach for the induction of humoral and cellular immune responses to HIV-1.

Synergism between active listeriolysin O and dimethyldioctadecylammonium bromide to activate CD8+ T cells

Purified recombinant listeriolysin O (LLO) was assessed for its ability to induce T cell responses in mice. Intraperitoneal immunisation with LLO, as a fusion with glutathione-S-transferase (GST), induced the production of LLO-specific CD8(+) T cells, but not LLO-specific CD4(+) T cells. The generation of this response could be blocked by pre-treatment with cholesterol, indicating a requirement for LLO pore formation. An increase in the LLO-specific response of both CD8(+) and CD4(+) T cells could be detected following the addition of dimethyldioctadecylammonium bromide (DDA), although the generation of this response was not dependent upon LLO pore formation, suggesting that DDA might change the presentation pathway of LLO leading to activation of the CD8(+) T cells. However, this response was dependent upon the presence of structurally intact LLO, suggesting a requirement for the innate recognition of LLO in the activation of the CD4(+) and CD8(+) T cells. Therefore, DDA and LLO can act synergistically to induce the production of a CD8(+) T cell response.

Development of a CTL vaccine for Her-2/neu using peptide-microspheres and adjuvants

With the ultimate goal of developing a therapeutic cancer vaccine, we encapsulated the Her-2/neu peptide p369-377 in poly(lactide-co-glycolide) microspheres. This formulation was found to effectively elicit CD8+ cytotoxic T cell (CTL) responses in an HLA-A*0201 transgenic mouse model. In contrast, immunization with either peptide alone or peptide formulated in incomplete Freund's adjuvant (IFA) failed to elicit such CTL responses. Responses induced by the peptide-microsphere formulation were found to peak at approximately 6 weeks post-immunization, and were enhanced by delivering increased doses of peptide and with repeated administrations over time. Co-administration of the peptide-microspheres with adjuvants, including granulocyte-macrophage colony stimulating factor, MPL adjuvant and select synthetic Toll-Like Receptor 4 ligands, the aminoalkyl glucosaminide-4 phosphates, significantly augmented CTL responses. These studies provide important guidance for the design of human clinical trials of microsphere vaccines in terms of optimal peptide-microsphere formulation, vaccination regimen, vaccine dose, and adjuvant selection.

Novel approaches to vaccine delivery

Although the currently available vaccines represent an outstanding success story in modern medicine and have had a dramatic effect on morbidity and mortality worldwide, it is clear that improvements are required in the current vaccine delivery technologies. Improvements are required to enable the successful development of vaccines against infectious diseases that have so far proven difficult to control with conventional approaches. Improvements may include the addition of novel injectable adjuvants or the use of novel routes of delivery, including mucosal immunization. Mucosal delivery may be required to provide protection against pathogens that infect at mucosal sites, including sexually transmitted diseases. Alternatively, novel approaches to delivery, including mucosal administration, may be used to improve compliance for existing vaccines. Of particular interest for safer mass immunization campaigns are needle-free delivery devices, which would avoid problems due to needle re-use in many parts of the world and would avoid needle-stick injuries.

Childhood and malaria vaccines combined in biodegradable microspheres produce immunity with synergistic interactions

Biodegradable microspheres may represent a potential tool for the delivery of combination vaccines. We demonstrate strong immunogenicity of five co-encapsulated antigens after a single subcutaneous inoculation in guinea pigs. Tetanus- and diphtheria-specific antibodies were not significantly affected by the presence of either antigen or by the presence of pertussis or Haemophilus influenzae type b (Hib) antigens. Microsphere formulations gave better protection against diphtheria toxin than did two injections of a licensed tetravalent vaccine. Finally, a synthetic malaria peptide antigen (PfCS) also encapsulated in PLGA microspheres increased diphtheria and tetanus-specific immunity and improved protection against diphtheria. These findings demonstrate the potential of microspheres as an alternative and promising strategy for combination vaccines with a further aptitude in reducing the number of inoculations required to gain functional immunity.

Mucosal adjuvants and delivery systems for protein-, DNA- and RNA-based vaccines

Almost all vaccinations today are delivered through parenteral routes. Mucosal vaccination offers several benefits over parenteral routes of vaccination, including ease of administration, the possibility of self-administration, elimination of the chance of injection with infected needles, and induction of mucosal as well as systemic immunity. However, mucosal vaccines have to overcome several formidable barriers in the form of significant dilution and dispersion; competition with a myriad of various live replicating bacteria, viruses, inert food and dust particles; enzymatic degradation; and low pH before reaching the target immune cells. It has long been known that vaccination through mucosal membranes requires potent adjuvants to enhance immunogenicity, as well as delivery systems to decrease the rate of dilution and degradation and to target the vaccine to the site of immune function. This review is a summary of current approaches to mucosal vaccination, and it primarily focuses on adjuvants as immunopotentiators and vaccine delivery systems for mucosal vaccines based on protein, DNA or RNA. In this context, we define adjuvants as protein or oligonucleotides with immunopotentiating properties co-administered with pathogen-derived antigens, and vaccine delivery systems as chemical formulations that are more inert and have less immunomodulatory effects than adjuvants, and that protect and deliver the vaccine through the site of administration. Although vaccines can be quite diverse in their composition, including inactivated virus, virus-like particles and inactivated bacteria (which are inert), protein-like vaccines, and non-replicating viral vectors such as poxvirus and adenovirus (which can serve as DNA delivery systems), this review will focus primarily on recombinant protein antigens, plasmid DNA, and alphavirus-based replicon RNA vaccines and delivery systems. This review is not an exhaustive list of all available protein, DNA and RNA vaccines, with related adjuvants and delivery systems, but rather is an attempt to highlight many of the currently available approaches in immunopotentiation of mucosal vaccines.