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

Demystifying particle-based oral vaccines

Introduction: The oral route of vaccination is pain- and needle-free and can induce systemic and mucosal immunity. However, gastrointestinal barriers and antigen degradation impose significant hurdles in the development of oral vaccines. Live attenuated viruses and bacteria can overcome these barriers but at the risk of introducing safety concerns. As an alternative, particles have been investigated for antigen protection and delivery, yet there are no FDA-approved oral vaccines based on particle-based delivery systems. Our objective was to discover underlying determinants that can explain the current inadequacies and identify paradigms that can be implemented in future for successful development of oral vaccines relying on particle-based delivery systems.Areas covered: We reviewed literature related to the use of particles for oral vaccination and placed special emphasis on formulation characteristics and administration schedules to gain an insight into how these parameters impact production of antigen-specific antibodies in systemic and mucosal compartments.Expert opinion: Despite the long history of vaccines, particle-based oral vaccination is a relative new field with the first study published in 1989. Substantial variability exists between different studies with respect to dosing schedules, number of doses, and the amount of vaccine per dose. Most studies have not used adjuvants in the formulations. Better standardization in vaccination parameters is required to improve comparison between experiments, and adjuvants should be used to enhance the systemic and mucosal immune responses and to reduce the number of doses, which will make oral vaccines more attractive.

Chitosan-coated poly(lactic-co-glycolic) acid nanoparticles as an efficient delivery system for Newcastle disease virus DNA vaccine

We determined the efficacy and safety of chitosan (CS)-coated poly(lactic-co-glycolic) acid (PLGA) nanoparticles (NPs) as a delivery system for a vaccine to protect chickens against Newcastle disease virus (NDV). The newly constructed vaccine contained DNA (the F gene) of NDV. The Newcastle disease virus (NDV) F gene deoxyribonucleic acid (DNA) plasmid (pFDNA)-CS/PLGA-NPs were spherical (diameter =699.1±5.21 nm [mean ± standard deviation]) and smooth, with an encapsulation efficiency of 98.1% and a Zeta potential of +6.35 mV. An in vitro release assay indicated that CS controlled the burst release of plasmid DNA, such that up to 67.4% of the entire quantity of plasmid DNA was steadily released from the pFDNA-CS/PLGA-NPs. An in vitro expression assay indicated that the expression of nanoparticles (NPs) was maintained in the NPs. In an immunization test with specific pathogen-free chickens, the pFDNA-CS/PLGA-NPs induced stronger cellular, humoral, and mucosal immune responses than the plasmid DNA vaccine alone. The pFDNA-CS/PLGA-NPs did not harm 293T cells in an in vitro assay and did not harm chickens in an in vivo assay. Overall, the results indicated that CS-coated PLGA NPs can serve as an efficient and safe mucosal immune delivery system for NDV DNA vaccine.

Progress towards a needle-free hepatitis B vaccine

Hepatitis B virus (HBV) infection is a worldwide public health problem. Vaccination is the most efficient way to prevent hepatitis B. Despite the success of the currently available vaccine, there is a clear need for the development of new generation of HBV vaccines. Needle-free immunization is an attractive approach for mass immunization campaigns, since avoiding the use of needles reduces the risk of needle-borne diseases and prevents needle-stick injuries and pain, thus augmenting patient compliance and eliminating the need for trained medical personnel. Moreover, this kind of immunization was shown to induce good systemic as well as mucosal immunological responses, which is important for the creation of both a prophylactic and therapeutic vaccine. In order to produce a better, safer, more efficient and more suitable vaccine, adjuvants have been used. In this article, several adjuvants tested over the years for their potential to help create a needle-free vaccine against HBV are reviewed.

Mucosal vaccines: recent progress in understanding the natural barriers

It has long been known that protection against pathogens invading the organism via mucosal surfaces correlates better with the presence of specific antibodies in local secretions than with serum antibodies. The most effective way to induce mucosal immunity is to administer antigens directly to the mucosal surface. The development of vaccines for mucosal application requires antigen delivery systems and immunopotentiators that efficiently facilitate the presentation of the antigen to the mucosal immune system. This review provides an overview of the events within mucosal tissues that lead to protective mucosal immune responses. The understanding of those biological mechanisms, together with knowledge of the technology of vaccines and adjuvants, provides guidance on important technical aspects of mucosal vaccine design. Not being exhaustive, this review also provides information related to modern adjuvants, including polymeric delivery systems and immunopotentiators.

M-cell targeted delivery of recombinant hepatitis B surface antigen using cholera toxin B subunit conjugated bilosomes

The present study aims to improve upon our earlier findings with bilosomes as potential delivery vehicle through oral route for recombinant hepatitis B surface antigen (HBsAg). The work entails the conjugation of bilosomal system with cholera toxin B subunit (CTB) to increase transmucosal uptake via M-cell specific delivery approach. The study encompasses the development and characterization of HBsAg-loaded CTB-conjugated system for percent antigen entrapment, size, shape, and stability in SGF (USP, pH 1.2), SIF (USP, pH 7.5) and in bile salt solutions. Biological activity of CTB, subsequent to conjugation, was verified by hemagglutination test. Anti-HBsAg IgG response in serum and anti-HBsAg sIgA in various body secretions were estimated using ELISA, following oral immunization with 10 microg dose-loaded CTB-conjugated bilosomes (CTB2) and 20 microg dose-loaded CTB-conjugated bilosomes (CTB1) in BALB/c mice. The results showed that CTB1 produced anti-HBsAg IgG antibody titre response comparable to that of the intramuscular (i.m.) injection of 10 microg of alum-adsorbed HBsAg. Moreover, all the bilosomal preparations elicited measurable sIgA vis-à-vis negligible response with i.m. administered HBsAg. Thus, HBsAg-loaded CTB-conjugated bilosomes provide a promising potential for targeted oral immunization against hepatitis B.

Preparation, physiochemical characterization, and oral immunogenicity of Abeta(1-12), Abeta(29-40), and Abeta(1-42) loaded PLG microparticles formulations

Alzheimer's disease (AD) is caused by the deposition of beta-amyloid (Abeta) protein in brain. The current AD immunotherapy aims to prevent Abeta plaque deposition and enhance its degradation in the brain. In this work, the peptides B-cell epitope Abeta(1-12), T-cell epitope Abeta(29-40) and full-length Abeta(1-42) were loaded separately to the poly (D,L-lactide co-glycolide) (PLG) microparticles by using W/O/W double emulsion solvent evaporation method with entrapment efficacy of 70.46%, 60.93%, and 65.98%, respectively. The prepared Abeta PLG microparticles were smooth, spherical, individual, and nonporous in nature with diameters ranging from 2 to 12 microm. The cumulative in vitro release profiles of Abeta(1-12), Abeta(29-40), and Abeta(1-42) from PLG microparticles sustained for long periods and progressively reached to 73.89%, 69.29%, and 70.08% by week 15. In vitro degradation studies showed that the PLG microparticles maintained the surface integrity up to week 8 and eroded completely by week 16. Oral immunization of Abeta peptides loaded microparticles in mice elicited stronger immune response by inducing anti-Abeta antibodies for prolonged time (24 weeks). The physicochemical characterization and immunogenic potency of Abeta peptides incorporated PLG microparticles suggest that the microparticles formulation of Abeta can be a potential oral AD vaccine.

Mechanistic study of the adjuvant effect of biodegradable nanoparticles in mucosal vaccination

For oral vaccination, incorporation of antigens into nanoparticles has been shown to protect the antigen from degradation, but may also increase its uptake through the intestinal epithelium via M-cells. The aim of this study was to understand the mechanisms by which oral administration of antigen-loaded nanoparticles induces an immune response and to analyze the effect of the nanoparticle composition on these mechanisms. Nanoparticles made from chitosan (CS) and its N-trimethylated derivative, TMC, loaded with a model antigen ovalbumin (OVA) were prepared by ionic gelation with tripolyphosphate. Intraduodenal vaccination with OVA-loaded nanoparticles led to significantly higher antibody responses than immunization with OVA alone. TMC nanoparticles induced anti-OVA antibodies after only a priming dose. To explain these results, the interaction of nanoparticles with the intestinal epithelium was explored, in vitro, using a follicle associated epithelium model and visualized, ex vivo, using confocal laser scanning microscopy. The transport of FITC-OVA-loaded TMC nanoparticles by Caco-2 cells or follicle associated epithelium model was higher than FITC-OVA-loaded CS or PLGA nanoparticles. The association of nanoparticles with human monocyte derived dendritic cells and their effect on their maturation were determined with flow cytometry. TMC nanoparticles but not CS or PLGA nanoparticles had intrinsic adjuvant effect on DCs. In conclusion, depending on their composition, nanoparticles can increase the M-cell dependent uptake and enhance the association of the antigen with DC. In this respect, TMC nanoparticles are a promising strategy for oral vaccination.

Oral vaccine delivery: can it protect against non-mucosal pathogens?

Vaccination is an efficient and cost-effective form of preventing infectious diseases. However, most currently available vaccines are delivered by injection, which makes mass immunization more costly and less safe, particularly in resource-poor developing countries. Oral vaccines have several attractive features compared with parenteral vaccines, but studies on their use have been limited almost exclusively to protection against mucosally transmitted pathogens. Their potential for controlling non-mucosally transmitted diseases has not yet been appreciated in general. In this article, we provide evidence that oral immunization is a feasible alternative for preventing infections transmitted through non-mucosal routes, including infections such as malaria, Japanese encephalitis and hepatitis B. Although there are still hurdles to overcome before such approaches can be deployed widely, recent progress in the oral vaccination field and the availability of a range of delivery systems offers hope for the development of a larger number of oral vaccines.

Micro- and nanoparticle-based vaccines for hepatitis B

The incredible success of vaccinations in contributing to public health is undeniable. In fact, vaccines are the most cost-effective public health tool for disease prevention because their cost is less than the combined costs of treatment, hospitalization, and time loss from work. However, despite the availability of vaccines, cost per dose is a factor limiting the success of global vaccination campaigns, as are the limitations imposed by the need of delivering multiple vaccine doses. A number of approaches are being tested particularly for the delivery of subunit vaccines, and in recent years, a number of groups have devoted their efforts to develop nano/microparticles prepared from biodegradable and biocompatible polymers as vaccine delivery systems with the goal of inducing both humoral and cellular immune responses. Some important properties of biodegradable polymers are their documented safety history, biocompatibility, and an ability to provide controlled time/rate of antigen release and polymer degradation. The most extensively studied polymer used for encapsulating vaccine antigens is poly (lactide-co-glycolide acid) (PLGA). This chapter deals in brief with efforts targeting the use of PLGA micro-and nanoparticles for the delivery of hepatitis B surface antigen.

Oral vaccination: where we are?

As early as 900 years ago, the Bedouins of the Negev desert were reported to kill a rabid dog, roast its liver and feed it to a dog-bitten person for three to five days according to the size and number of bites [1] . In sixteenth century China, physicians routinely prescribed pills made from the fleas collected from sick cows, which purportedly prevented smallpox. One may dismiss the wisdom of the Bedouins or Chinese but the Nobel laureate, Charles Richet, demonstrated in 1900 that feeding raw meat can cure tuberculous dogs - an approach he termed zomotherapy. Despite historical clues indicating the feasibility of oral vaccination, this particular field is notoriously infamous for the abundance of dead-end leads. Today, most commercial vaccines are delivered by injection, which has the principal limitation that recipients do not like needles. In the last few years, there has been a sharp increase in interest in needle-free vaccine delivery; new data emerges almost daily in the literature. So far, there are very few licensed oral vaccines, but many more vaccine candidates are in development. Vaccines delivered orally have the potential to take immunization to a fundamentally new level. In this review, the authors summarize the recent progress in the area of oral vaccines.

Viral peptide immunogens: current challenges and opportunities

Synthetic peptide vaccines have potential to control viral infections. Successful experimental models using this approach include the protection of mice against the lethal Sendai virus infection by MHC class I binding CTL peptide epitope. The main benefit of vaccination with peptide epitopes is the ability to minimize the amount and complexity of a well-defined antigen. An appropriate peptide immunogen would also decrease the chance of stimulating a response against self-antigens, thereby providing a safer vaccine by avoiding autoimmunity. In general, the peptide vaccine strategy needs to dissect the specificity of antigen processing, the presence of B-and T-cell epitopes and the MHC restriction of the T-cell responses. This article briefly reviews the implications in the design of peptide vaccines and discusses the various approaches that are applied to improve their immunogenicity.

Evaluation of the immune response following a short oral vaccination schedule with hepatitis B antigen encapsulated into alginate-coated chitosan nanoparticles

The purpose of this work was to assess the ability of recombinant hepatitis B vaccine, encapsulated in alginate-coated chitosan nanoparticles, to induce local and systemic immune responses following oral vaccination. The antigen was administered either alone or in combination with the immunopotentiator, synthetic oligodeoxynucleotide containing immunostimulatory CpG motif (CpG ODN) as adjuvant, and associated or not with the alginate-coated chitosan nanoparticles. After two immunizations the group I (HBsAg associated with nanoparticles) and the group VI (HBsAg and CpG, both associated with nanoparticles) showed enhanced immune responses. Both groups showed significant higher values of the CD69 expression in CD4+ and CD8+ T-lymphocytes and lower values of this marker in B lymphocytes. Moreover, a strongest proliferative response of the splenocytes, ex vivo stimulated with concanavalin A, was observed in the same groups. Although with a presence of non-responder mice within the groups, only mice of the groups I and VI elicited the generation of anti-HBsAg antibodies detected in serum (IgG) and in the intestinal washings (sIgA). The results demonstrated that coated chitosan nanoparticles might have potential for being used as a deliver system for oral vaccination with the recombinant hepatitis B surface antigen.