Controlled release microparticles as a single dose hepatitis B vaccine: evaluation of immunogenicity in mice

Engineered drug delivery devices to address Global Health challenges

There is a dire need for innovative solutions to address global health needs. Polymeric systems have been shown to provide substantial benefit to all sectors of healthcare, especially for their ability to extend and control drug delivery. Herein, we review polymeric drug delivery devices for vaccines, tuberculosis, and contraception.

mPEG-PLA and PLA-PEG-PLA nanoparticles as new carriers for delivery of recombinant human Growth Hormone (rhGH)

mPEG-PLA and PLA-PEG-PLA copolymeric nanoparticles with three different PLA to PEG ratios are synthesized and used for encapsulation of recombinant human Growth hormone (rhGH). The structure and composition of the synthesized copolymers were analyzed by ¹H NMR and GPC techniques. Moreover, morphology, encapsulation efficiency (EE), cytotoxicity, release profile and stability of the encapsulated rhGH were measured. Structural analysis of the prepared copolymers showed that they were successfully synthesized with approximately expected molecular weight and relatively low size distribution. It was also revealed that by increasing amounts of PLA/PEG ratio, EE content and size of nanoparticles were increased. Release profile evaluation of rhGH from both formulations indicated that copolymeric nanoparticles of Di-B2 and Tri-B2 exhibited the best results among the synthesized nanospheres, by having initial burst release of 17.5% and 28% and then slow and constant release of rhGH up to 65% and 77% of the encapsulated drug, respectively. Furthermore, results of HPLC, SDS-PAGE and CD analyses showed stability of rhGH during encapsulation and release from nanoparticles. Finally, the results showed that these two formulations provided safe and efficient sustained release of rhGH for more than a month and they have the potential to do further studies under in vivo conditions.

Rational design and evaluation of HBsAg polymeric nanoparticles as antigen delivery carriers

The present work is focused on the development and evaluation of single dose sustained-release Hepatitis B surface antigen (HBsAg) loaded nanovaccine for Hepatitis B. The conventional treatment suffers from repeated administration and hence requires a booster dose. Therefore, polymeric nanovaccine of HBsAg was developed by double emulsion solvent evaporation technique, utilizing central composite design for formulation optimization. The effects of independent variables (like polymer amount, stabilizer concentration, aqueous/organic phase ratio and homogenizer speed) were also studied on critical quality attributes like particle size and entrapment efficiency. Nanovaccine was characterized in terms of physicochemical parameters, release, internalization and in vivo immunological evaluation in BALB/c mice after administration by different routes such as oral, sub-cutaneous, nasal and intramuscular. The designed nanovaccine demonstrated nanometric size with smooth surface, negative zeta potential, maximum entrapment, sustained release and better internalization in macrophage and MRC-5 cell line. The immune-stimulating activity of nanovaccine administered by different routes was evaluated by measuring anti-HBsAg titre like specific immunoglobulin IgG and IgA response and cytokine level (interleukin-2, interferon-Y) measurement. The results indicated that the nanovaccine administered by intramuscular route produced better humoral as well as cellular responses and potential carriers for antigen delivery at single dose administration via intramuscular route.

Nanovaccine for immunotherapy and reduced hepatitis-B virus in humanized model

Chronic Hepatitis B Virus (HBV) infections are severe with weak antiviral immune responses. The lack of an appropriate small animal model for chronic hepatitis, a major hurdle for studying the immunotolerance and immunopathogenesis induced by hepatitis B viral (HBV) infection. In this study, for enhancing the antibody production efficiency the prepared polymeric HBsAg-loaded nanoparticles (nanovaccine) will be tested in immune-deficit mice, which suffer from chronic Hepatitis B virus. Vaccination of Balb/c mice by this prepared nanoparticles that were engrafted with peripheral blood mononuclear cells (PBMCs), which was already lethally irradiated and transplanted by the bone marrow of NOD (knockout mice) mice. In the present study, after the vaccination detected the high frequencies of immunoglobulin G (IgG)-secreting B cells and mitogen-responsive interferon-Y (IFN-Y) secreting T cells in serum, determined by specific ELISA technique. During the entire observation period, unvaccinated animals showed lower concentration of specific IgG secreting B cells and IFN-Y secreting T cells found in comparison to vaccinated mice group. Chronic HBV carrier PBMCs transplanted into the chimera failed to produce antigen and increased the antibodies production due to vaccination. Furthermore, another advantage was that the viral gene expression and viral DNA replication was no longer observed in vaccinated group. This prepared nanovaccine formulations is better for the cure of Hepatitis B viral infection carrier. Therefore, specific memory responses were elicited by vaccination with Hepatitis B virus surface (HBsAg) antigen of chimeric mice transplanted with PBMCs derived from HBV donors.

Nasal vaccination with poly(β-amino ester)-poly(d,l-lactide-co-glycolide) hybrid nanoparticles

Mucosal vaccination stimulates both mucosal and systemic immunity. However, mucosal applications of vaccine antigens in their free form generally result in poor systemic immune responses and need adjuvantation. In this study, bovine serum albumin loaded, new hybridised poly(β-amino ester)-poly(d,l-lactide-co-glycolide) nanoparticles were prepared by double emulsion-solvent evaporation method, characterised and evaluated in vivo as nasal vaccine carriers. Cationic spherical particles with a mean size of 240nm, good physical stability and high encapsulation efficiency were obtained. Protein structure was not affected throughout preparation and minimal toxicity was shown in Calu-3 and A549 cells. Nasal vaccination with these nanoparticles revealed markedly higher humoral immune responses compared with free antigen following intranasal and subcutaneous immunisation. Mucosal immune response was also stimulated and cytokine titres indicated that Th1 and Th2 pathways were successfully activated. This study shows that the formulated hybrid nanoparticles can be a promising carrier for nasal immunisation of poor antigenic proteins.

Single-injection vaccines: Progress, challenges, and opportunities

Currently, vaccination is the most efficient and cost-effective medical treatment for infectious diseases; however, each year 10 million infants remain underimmunized due to current vaccination schedules that require multiple doses to be administered across months or years. These dosing regimens are especially challenging in the developing world where limited healthcare access poses a major logistical barrier to immunization. Over the past four decades, researchers have attempted to overcome this issue by developing single-administration vaccines based on controlled-release antigen delivery systems. These systems can be administered once, but release antigen over an extended period of time to elicit both primary and secondary immune responses resulting in antigen-specific immunological memory. Unfortunately, unlike controlled release systems for drugs, single-administration vaccines have yet to be commercialized due to poor antigen stability and difficulty in obtaining unconventional release kinetics. This review discusses the current state of single-administration vaccination, challenges delaying the development of these vaccines, and potential strategies for overcoming these challenges.

Biodegradable polylactide microspheres enhance specific immune response induced by Hepatitis B surface antigen

Hepatitis B (HB) infection caused by Hepatitis B virus (HBV) is the most common liver disease in the world. HB vaccine, when administered in conjunction with alum adjuvants, induces Th2 immunity that confers protection against HBV. However, currently available vaccine formulations and adjuvants do not elicit adequate Th1 and CTL responses that are important for prevention of maternal transmission of the virus. Microspheres synthesized from poly (D, L-lactide-co-glycolide) (PLGA) or poly (D, L-lactide) (PLA) polymers have been considered as promising tools for in vivo delivery of antigens and drugs. Here we describe PLA microspheres synthesized by premix membrane emulsification method and their application in formulating a new microsphere based HB vaccine. To evaluate the immunogenicity of this microsphere vaccine, BALB/c mice were immunized with microsphere vaccine and a series of immunological assays were conducted. Results of Enzyme-linked ImmunoSpot (ELISPOT) assays revealed that the number of interferon-gamma (IFN-γ)-producing splenocytes and CD8(+) T cells increased significantly in the microsphere vaccine group. Microsphere vaccine group showed enhanced specific cell lysis when compared with HB surface antigen (HBsAg) only group in (51)Cr cytotoxicity assays. Moreover, microsphere vaccine elicited a comparable level of antibody production as that of HB vaccine administered with alum adjuvant. We show that phagocytosis of HBsAg by dendritic cells is more pronounced in microsphere vaccine group when compared with other control groups. These results clearly demonstrate the potential of using PLA microspheres as effective HB vaccine adjuvants for an enhanced Th1 immune response.

Next generation vaccines: single-dose encapsulated vaccines for improved global immunisation coverage and efficacy

OBJECTIVES

Vaccination is considered the most successful health intervention; yet incomplete immunisation coverage continues to risk outbreaks of vaccine preventable diseases worldwide. Vaccination coverage improvement through a single-dose prime-boost technology would revolutionise modern vaccinology, impacting on disease prevalence, significantly benefiting health care and lowering economic burden of disease.

KEY FINDINGS

Over the past 30 years, there have been efforts to develop a single-dose delayed release vaccine technology that could replace the repeated prime-boost immunisations required for many current vaccines. Biocompatible polymers have been employed to encapsulate model vaccines for delayed delivery in vivo, using either continuous or pulsed release. Biomaterial considerations, safety aspects, particle characteristics and immunological aspects of this approach are discussed in detail.

SUMMARY

Despite many studies showing the feasibility of vaccine encapsulation for single-dose prime-boost administration, none have been translated into convincing utility in animal models or human trials. Further development of the encapsulation technology, through optimising the particle composition, formulation, antigen loading efficacy and stability, could lead to the application of this important approach in vaccine deployment. If successful, this would provide a solution to better global vaccination coverage through a reduction in the number of immunisations needed to achieve protection against infectious diseases. This review provides an overview of single-dose vaccination in the context of today's vaccine needs and is derived from a body of literature that has not been reviewed for over a decade.

Development and characterization of surface modified PLGA nanoparticles for nasal vaccine delivery: effect of mucoadhesive coating on antigen uptake and immune adjuvant activity

In this study, the efficacy of mucoadhesive polymers, i.e., chitosan and glycol chitosan as a mucoadhesive coating material in nasal vaccine delivery was investigated. The Hepatitis B surface Antigen (HBsAg) encapsulated PLGA, chitosan coated PLGA (C-PLGA), and Glycol chitosan coated PLGA (GC-PLGA) nanoparticles (NPs) were prepared. The formulations were characterized for particle size, shape, surface charge, and entrapment efficiency. The mucoadhesive ability of coated and non-coated NPs was determined using in vitro mucoadhesion and nasal clearance test. In addition, the systemic uptake and bio-distribution were also evaluated to understand the fate of NPs following nasal delivery. The immuno-adjuvant ability of various formulations was compared by measuring specific antibody titer in serum and secretory. The results indicated that PLGA NPs exhibit negative surface charge, whereas C-PLGA and GC-PLGA NPs exhibited positive surface charge. The GC-PLGA NPs demonstrated lower clearance and better local and systemic uptake compared to chitosan coated and uncoated PLGA NPs. In vivo immunogenicity studies indicated that GC-PLGA NPs could induce significantly higher systemic and mucosal immune response compared to PLGA and C-PLGA NPs. In conclusion, GC-PLGA NPs could be a promising carrier adjuvant for the nasal vaccine delivery for inducing a potent immune response at mucosal surface(s) and systemic circulation.

Development and characterization of LTA-appended chitosan nanoparticles for mucosal immunization against hepatitis B

The present study was aimed at exploring the targeting potential of LTA-anchored chitosan nanoparticles (CH-NP) specifically to M cell following oral immunization. The lectinized CH-NP exhibited 7-29% coupling capacity depending upon the amount of glutaraldehyde added. Induction of the mucosal immunity was assessed by estimating secretory IgA level in the salivary, intestinal and vaginal secretions, and cytokine (IL-2 and IFN-γ) levels in the spleen homogenates. The results demonstrated that LTA-anchored CH-NP elicited strong humoral and cellular responses and hence could be a competent carrier-adjuvant delivery system for oral mucosal immunization against Hepatitis B.

Antibody nanoparticle dispersions formed with mixtures of crowding molecules retain activity and in vivo bioavailability

Monoclonal antibodies continue to command a large market for treatment of a variety of diseases. In many cases, the doses required for therapeutic efficacy are large, limiting options for antibody delivery and administration. We report a novel formulation strategy based on dispersions of antibody nanoclusters that allows for subcutaneous injection of highly concentrated antibody (≈ 190 mg/mL). A solution of monoclonal antibody 1B7 was rapidly frozen and lyophilized using a novel spiral-wound in-situ freezing technology to generate amorphous particles. Upon gentle stirring, a translucent dispersion of approximately 430 nm protein clusters with low apparent viscosity (≈ 24 cp) formed rapidly in buffer containing the pharmaceutically acceptable crowding agents such as trehalose, polyethylene glycol, and n-methyl-2-pyrrolidone. Upon in vitro dilution of the dispersion, the nanoclusters rapidly reverted to monomeric protein with full activity, as monitored by dynamic light scattering and antigen binding. When administered to mice as an intravenous solution, subcutaneous solution, or subcutaneous dispersion at similar (4.6-7.3 mg/kg) or ultra-high dosages (51.6 mg/kg), the distribution and elimination kinetics were within error and the protein retained full activity. Overall, this method of generating high-concentration, low-viscosity dispersions of antibody nanoclusters could lead to improved administration and patient compliance, providing new opportunities for the biotechnology industry.

Protective effect of recombinant staphylococcal enterotoxin A entrapped in polylactic-co-glycolic acid microspheres against Staphylococcus aureus infection

Staphylococcus aureus is an important cause of nosocomial and community-acquired infections in humans and animals, as well as the cause of mastitis in dairy cattle. Vaccines aimed at preventing S. aureus infection in bovine mastitis have been studied for many years, but have so far been unsuccessful due to the complexity of the bacteria, and the lack of suitable vaccine delivery vehicles. The current study developed an Escherichia coli protein expression system that produced a recombinant staphylococcal enterotoxin A (rSEA) encapsulated into biodegradable microparticles generated by polylactic-co-glycolic acid (PLGA) dissolved in methylene chloride and stabilized with polyvinyl acetate. Antigen loading and surface properties of the microparticles were investigated to optimize particle preparation protocols. The prepared PLGA-rSEA microspheres had a diameter of approximately 5 μm with a smooth and regular surface. The immunogenicity of the PLGA-rSEA vaccine was assessed using mice as an animal model and showed that the vaccine induced a strong humoral immune response and increased the percent survival of challenged mice and bacterial clearance. Histological analysis showed moderate impairment caused by the pathogen upon challenge afforded by immunization with PLGA-rSEA microspheres. Antibody titer in the sera of mice immunized with PLGA-rSEA microparticles was higher than in vaccinated mice with rSEA. In conclusion, the PLGA-rSEA microparticle vaccine developed here could potentially be used as a vaccine against enterotoxigenic S. aureus.

The long-term potential of biodegradable poly(lactide-co-glycolide) microparticles as the next-generation vaccine adjuvant

Biodegradable polymeric microparticles of poly(lactide-co-glycolide) (PLG) have been extensively evaluated for drug delivery and vaccine applications over the last three decades. Despite a wealth of studies on the use of PLG microparticles in vaccines through controlled release of antigens, there is no commercial PLG-based vaccine as yet. The key challenge that prevented the development of PLG microparticles as commercial vaccines was the instability of encapsulated antigen. Over the years, advancements were made towards maintaining antigen integrity during PLG microparticle preparation and sterilization. In parallel and independently, development of PLG microparticles as therapeutic commercial products established PLG with an excellent safety record in humans, and as a suitable candidate for next-generation vaccines. Through the combination of Toll-like receptor agonist encapsulation and surface adsorption of antigen, PLG microparticles can be used as a vaccine adjuvant to address unmet medical needs, such as vaccines against HIV, malaria and TB. With strategic development of PLG-based vaccines, PLG microparticles can offer advantages over the conventional vaccine adjuvants allowing commercial development of this adjuvant.

Towards tailored vaccine delivery: needs, challenges and perspectives

The ideal vaccine is a simple and stable formulation which can be conveniently administered and provides life-long immunity against a given pathogen. The development of such a vaccine, which should trigger broad and strong B-cell and T-cell responses against antigens of the pathogen in question, is highly dependent on tailored vaccine delivery approaches. This review addresses vaccine delivery in its broadest scope. We discuss the needs and challenges in the area of vaccine delivery, including restrictions posed by specific target populations, potentials of dedicated stable formulations and devices, and the use of adjuvants. Moreover, we address the current status and perspectives of vaccine delivery via several routes of administration, including non- or minimally invasive routes. Finally we suggest possible directions for future vaccine delivery research and development.

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.

Antibody response to polyhistidine-tagged peptide and protein antigens attached to liposomes via lipid-linked nitrilotriacetic acid in mice

Particulate delivery systems enhance antibody responses to subunit antigens. However, covalent attachment of protein antigens can disrupt protein structure and mask critical epitopes, altering the antibody response to the antigen. In this report, we evaluate noncovalent metal chelation via nitrilotriacetic acid (NTA) as a nondestructive method to attach peptide and protein antigens to liposomes. Two model antigens, ovalbumin (OVA) and a peptide derived from the membrane-proximal region of HIV-1 gp41 (N-MPR), were polyhistidinylated and attached to liposomes via monovalent NTA (mono-NTA; K(D) [equilibrium dissociation constant], ∼10 μM), trivalent NTA (tris-NTA; K(D), ∼1 nM), or a covalent linkage. Attachment of N-MPR, but not OVA, to liposomes via an NTA lipid elicited stronger antibody responses in BALB/c mice than a formulation in which unassociated antigen was simply admixed with control liposomes lacking NTA. However, the tris-NTA linkage did not increase antibody responses to either N-MPR or OVA compared to the level for the mono-NTA linkage, despite the greater liposomal association of the antigen. For both antigens, covalently attaching them to a lipid elicited significantly stronger antibody responses than NTA-anchored antigens (OVA titer, 3.4 × 10(6) versus 1.4 × 10(6) to 1.6 × 10(6) [P < 0.001]; N-MPR titer, 4.4 × 10(4) versus 5.5 × 10(2) to 7.6 × 10(2) [P < 0.003]). The data indicate that NTA linkages may increase antibody titers to weak antigens such as N-MPR, but NTA-mediated attachment remains inferior to covalent conjugation. Moreover, enhancements in antigen-liposome affinity do not result in increased antibody titers. Thus, additional improvements of NTA-mediated conjugation technology are necessary to achieve an effective, nondestructive method for increasing the humoral response to antigens in particulate vaccines.

Innovative strategies for co-delivering antigens and CpG oligonucleotides

Cytosine-phosphorothioate-guanine oligodeoxynucleotides (CpG ODN) is a recent class of immunostimulatory adjuvants that includes unmethylated CpG dinucleotide sequences similar to those commonly found in bacterial DNA. CpG ODN specifically triggers toll like receptor 9 (TLR9), which is found within phagoendosomes of antigen presenting cells (APCs) such as dendritic cells (DCs). CpG ODN triggers activation and maturation of DCs and helps to increase expression of antigens. CpG ODN can be used to induce polarized Th1 type immune responses. Several studies have shown that antigens and CpG ODN must be co-localized in the same APC to generate the most potent therapeutic antigen-specific immune responses. Delivery vehicles can be utilized to ensure co-delivery of antigens and CpG ODN to the same APCs and to significantly increase uptake by APCs. These strategies can result in antigen-specific immune responses that are 5 to 500-fold greater than administration of antigen alone. In this review, we discuss several recent and innovative strategies to co-delivering antigens and CpG ODN adjuvants to APCs. These approaches include the utilization of conjugate molecules, multi-component nanorods, liposomes, biodegradable microparticles, pulsatile release chips and cell-microparticle hybrids.

Enhancement of immune response of HBsAg loaded poly (L-lactic acid) microspheres against Hepatitis B through incorporation of alum and chitosan

PURPOSE

Poly (L-lactic acid) (PLA) microparticles encapsulating Hepatitis B surface antigen (HBsAg) with alum and chitosan were investigated for their potential as a vaccine delivery system.

METHODS

The microparticles, prepared using a water-in-oil-in-water (w/o/w) double emulsion solvent evaporation method with polyvinyl alcohol (PVA) or chitosan as the external phase stabilising agent showed a significant increase in the encapsulation efficiency of the antigen.

RESULTS

PLA-Alum and PLA-chitosan microparticles induced HBsAg serum specific IgG antibody responses significantly higher than PLA only microparticles and free antigen following subcutaneous administration. Chitosan not only imparted a positive charge to the surface of the microparticles but was also able to increase the serum specific IgG antibody responses significantly.

CONCLUSIONS

The cytokine assays showed that the serum IgG antibody response induced is different according to the formulation, indicated by the differential levels of interleukin 4 (IL-4), interleukin 6 (IL-6) and interferon gamma (IFN-gamma). The microparticles eliciting the highest IgG antibody response did not necessarily elicit the highest levels of the cytokines IL-4, IL-6 and IFN-gamma.

Thrombin receptor agonist peptide entrapped in poly(D,L)-lactide-co-glycolide microparticles: Preparation and characterization

Thrombin receptor agonist peptide (TRAP-6) could advantageously replace thrombin in terms of accelerating wound healing being less expensive and more stable. To promote TRAP-6 pharmacological action as a tissue reconstruction stimulator this study investigated its entrapment within poly(D,L)-lactide-co-glycolide (PLGA) microparticles. Due to its low molecular weight and water solubility, TRAP-6 microencapsulated form is expected to be more useful. This paper reports TRAP-6 microencapsulation by a double (w/o/w) emulsion-evaporation technique. TRAP-6 release kinetics were evaluated by both chemical (HPLC) and biological assays in vitro. The results revealed a high level of TRAP-6 sensitivity to physico-chemical events during the microencapsulation. The surface morphology difference between control microparticles (without TRAP-6) and microparticles with entrapped TRAP-6 during in vitro degradation highlighted a particular role of TRAP-6. The results can allow one to optimize the microencapsulation procedure and to encounter a new promising approach to development of biodegradable polymer drug delivery systems for wound healing.

Novel nanoparticles for the delivery of recombinant hepatitis B vaccine

We describe the use of methoxypolyethylene glycol-poly(lactide-co-glycolide) nanoparticles as a delivery system for recombinant hepatitis B surface antigen (HBsAg). Evaluation of the stability and release kinetics of nanoencapsulated HBsAg in vitro in serum revealed an initial burst effect and a subsequent slower release of the antigen. Importantly the antigenicity was not destroyed by the encapsulation process, because upon release it was able to react with an anti-HBs antibody. Bone marrow-derived dendritic cells showed efficient uptake of the nanoparticle vaccine as visualized by confocal imaging. To determine whether nano-encapsulated HBsAg was capable of eliciting an immune response in the absence of an adjuvant, mice were immunized with the nanoparticle vaccine or with nonencapsulated recombinant HBsAg. In mice immunized with the nanoparticle vaccine, anti-HBs antibodies were detected at significantly earlier time points than in mice immunized with the nonencapsulated recombinant HBsAg.

CpG oligonucleotides accelerate and boost the immune response elicited by AVA, the licensed anthrax vaccine

Synthetic oligodeoxynucleotides (ODN) containing unmethylated CpG motifs act as immune adjuvants, improving the immune response elicited by coadministered vaccines. Combining CpG ODN with anthrax vaccine adsorbed (AVA), the licensed human vaccine, can increase the speed, magnitude and avidity of the resultant anti-anthrax response in mice, rhesus macaques and humans. Adsorbing the CpG ODN onto cationic poly(actide-coglycolides) microparticles further boosts immunity to coadministered AVA. The antibody response induced by CpG ODN plus AVA confers protection against systemic anthrax challenge in multiple animal models. These findings suggest that CpG ODN, alone or in combination with other adjuvants and delivery strategies, may support the development of prophylactic and therapeutic vaccines against biothreat pathogens.

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.

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.

Lectin anchored stabilized biodegradable nanoparticles for oral immunization 1. Development and in vitro evaluation

The investigation comprises development of a stable and targeted formulation of HBsAg for the oral immunization against Hepatitis B. PLGA nanoparticles bearing HBsAg was prepared by double emulsion method. The antigen was protected from organic/aqueous interface by using protein stabilizer, trehalose. The acidic environment generated within PLGA nanoparticles was neutralized by co-encapsulation of a basic additive, Mg(OH)(2) which provides an additional stabilization to the antigen especially against acid induced antigen inactivation. Furthermore, lectin from Arachis hypogaea (PNA) was anchored on to the surface of the HBsAg loaded nanoparticles in order to enhance their affinity towards the antigen presenting cells of the Peyer's patches. The developed system was characterized for shape, size and loading efficiency. The antigen integrity was assessed by using SDS-PAGE followed by isoelectric focusing analysis. Bovine submaxillary mucin (BSM) was used as a biological model for in vitro ligand affinity determination and activity studies. The lectin anchored nanoparticles exhibited 52.18+/-4.73% loading while ligand density was estimated to be of 17.90+/-1.14 microg/mg. The results suggest that HBsAg can be successfully stabilized by co-encapsulation of an appropriate protein stabilizer, i.e. trehalose and a basic additive, Mg(OH)(2). The ligand-coupled nanoparticles demonstrated approximately four folds increase in degree interaction with the BSM as compared to plain nanoparticles. Additionally, the nanoparticles maintained their intrinsic sugar specificity as associated due to lectin (PNA).

Pharmaceutical and immunological evaluation of a single-dose hepatitis B vaccine using PLGA microspheres

The objective of the study was to investigate the feasibility of a single-dose hepatitis B vaccine based on three kinds of poly (D, L)-lactide-co-glicolide acid (PLGA) microspheres. PLGA microspheres loaded with recombinant hepatitis B surface antigen (HBsAg) were formulated using a double emulsion microencapsulation technique. The pharmaceutical characteristics of size, surface morphology, protein loading efficiency, antigen integrity, release of HBsAg-loaded PLGA microspheres and degradation of the polymer in vitro were evaluated. The degradation of the polymer corresponded with the composition of the polymer (lactide/glycolide ratio), molecular weight of the polymer (viscosity) and morphology of the microspheres. These PLGA microspheres were able to continuously release antigen under conditions that mimic the environment in vivo. The single subcutaneous injection of HBsAg-loaded PLGA50/50 microspheres, PLGA75/25 microspheres and a mixture of PLGA50/50, PLGA75/25, and PLGA50/50-COOH microspheres in mice resulted in comparable serum antibody titers to those of three injections of the conventional aluminum adjuvant formulated HBsAg vaccine. Based on these findings in vitro and in vivo, it was concluded that HBsAg was successfully loaded into the PLGA microspheres, which can auto-boost an immune response, and the HBsAg-loaded PLGA microsphere is a promising candidate for the controlled delivery of a vaccine.

Influence of particle size, antigen load, dose and additional adjuvant on the immune response from antigen loaded PLA microparticles

Polylactide (PLA) polymer particles entrapping tetanus toxoid (TT) were evaluated in terms of particle size, antigen load, dose and additional adjuvant for achieving high and sustained anti-TT antibody titer from single point intramuscular immunization. Admixture of polymer entrapped TT and alum improved the immune response in comparison to particle-based immunization. High and long lasting antibody titer was achieved upon immunization with 2-8 microm size particles. Microparticles within the size range 50-150 microm elicited very low serum antibody response. Immunization with very small particles (<2 microm) and with intermediate size range particles (10-70 microm) elicited comparable antibody response from single point immunization but lower in comparison to that achieved while immunizing with 2-8 microm size particles. Potentiation of antibody response on immunization of admixture of microparticles and alum was also dependent on particle size. These results indicate the need of optimal particle sizes in micron ranges for improved humoral response from single point immunization. Increasing antigen load on polymer particles was found to have positive influence on generation of antibody titers from particle based immunization. Maximum peak antibody titer of approximately 300 microg/mL was achieved on day 50 upon immunization with particles having highest load of antigen (94 microg/mg of polymer). Increase in dose of polymer entrapped antigen resulted in concomitant increase in peak antibody titers indicating the importance of antigen stability, particle size and load on generating reproducible immune response. Optimization of particle size, antigen load, dose and use of additional adjuvant resulted in high and sustained anti-TT antibody titers over a period of more than 250 days from single point immunization. Serum anti-TT antibody titers from single point immunization of admixrure of PLA particles and alum was comparable with immunization from two divided doses of alum adsorbed TT.

Lipid microparticles for mucosal immunization against hepatitis B

Parenteral administration of vaccines often does not lead to optimal or long lasting protection against disease causing organisms particularly those that are inhaled, ingested or sexually transmitted. For optimal mucosal protection induction of immune response via mucosal routes is therefore highly desirable. Double emulsion-solvent evaporation (w/o/w) method best suited for water-soluble bioactives was selected for the preparation of hepatitis B surface antigen (HBsAg) loaded lipid microparticles. Intranasal route was considered for mucosal administration and hence to prepare the delivery system biocompatible and least irritable, soyalecithin (phospholipid) was taken instead of polymer because phosphatidylcholine is the major component of endogenous lung surfactant. The studies performed in present work included antigen characterization, development of lipid microparticles, stability studies of the prepared lipid microparticle formulations, percent mucoadhesion, ex vivo cellular uptake studies and in vivo studies. The general order obtained from in vivo studies for mucosal immune response (IgA) followed the sequence: LMST-HBsAg (IN)>LM-HBsAg (IN)>alum-HBsAg (IN)>LMST-HBsAg (IM)>alum-HBsAg (IM)>or=LM-HBsAg (IM)>plain HBsAg (IN)>plain HBsAg (IM).

Immunization by particle bombardment of antigen-loaded poly-(DL-lactide-co-glycolide) microspheres in mice

In the present study, we investigated whether poly-(DL-lactide-co-glycolide) (50:50) microspheres (PLG MS) containing a model antigen, ovalbumin (OVA), were delivered into mouse skin and the immune responses induced using a microparticulate bombardment system, Helios gene gun system, which can painlessly deliver the powdered drug through the stratum corneum to the epidermal-dermal interface using a high velocity supersonic flow of helium gas to accelerate the particles. The introduction of OVA-loaded PLG MS shows helium pressure-dependence, so that improved introduction can be achieved by a higher helium pressure used, thereby inducing sufficient anti-OVA IgG level. Moreover, in order to determine the type of immune system induced using particle bombardment, we investigated helper T-cell response characterized by the cytokine production in the isolated splenocytes 6 weeks after immunization and consequent production of the anti-OVA IgG subclasses in the serum in mice. As a result, IL-4 production in splenocytes and anti-OVA IgG1 level were preferentially elicited by particle bombardment with OVA-loaded PLG MS compared with IFN-gamma and anti-OVA IgG2a level. It seemed likely that particle bombardment using this system led to a Th-2 type immune response, i.e. a humoral immune response. In conclusion, this microparticulate bombardment system is a promising immunization method, expected to become an alternative to needle injection used to administer a broad range of vaccines for the treatment of various diseases.

Microparticles for oral delivery of vaccines

Nonreplicating antigens are poorly immunogenic when given orally, either due to their degradation in the gastrointestinal tract or because they are not efficiently taken up in the gut. Studies in laboratory animals have clearly demonstrated that microparticles can significantly improve the immunogenicity of orally administered antigens. However, the oral delivery of vaccines using microparticles has not been explored extensively in humans and large animals. In this article the progress in oral microparticle antigen delivery will be reviewed and, where possible, studies in humans and large animals will be highlighted. In addition, possible approaches that have the potential to significantly improve microparticle delivery of oral vaccines will be suggested.

Development of a single-dose stabilized poly(D,L-lactic-co-glycolic acid) microspheres-based vaccine against hepatitis B

The purpose of this study was to develop a stable single-dose vaccine based on recombinant hepatitis B surface antigen (HBsAg) in poly(D,L-lactic-co-glycolic acid) (PLGA) microspheres, in which HBsAg was stabilized by a protein stabilizer (trehalose) and an antacid (Mg(OH)2). The microspheres were prepared by the double emulsion method and characterized by scanning electron microscopy. To neutralize the acids liberated by the biodegradable lactic/glycolic acid based polymer, we coincorporated into the polymer an antacid, Mg(OH)2, which neutralized the acidity during degradation of the polymer and also prevented HBsAg structural losses and aggregation. The antigen integrity after encapsulation was examined by sodium dodecyl sulfate polyacrylamide gel electrophoresis followed by silver staining, isoelectric focusing and Western blotting techniques, which confirmed that antigen remained intact after encapsulation. In-vitro release experiments were performed in phosphate-buffered saline (pH 7.4) and the release of antigen was found to be improved by the protein stabilizer (trehalose). In stability studies, performed at 37 degrees C, the microspheres were found to be stable for 16 days. The immunogenicity of stable microsphere formulations bearing HBsAg was compared with the conventional alum-absorbed HBsAg vaccine in a guinea-pig model. The antibody titre indicated that a single injection of stabilized HBsAg-PLGA microspheres produced a better immune response than two injections of alum-formulated HBsAg vaccine. The findings suggest that recombinant HBsAg can be stabilized by use of a protein stabilizer and antacid during entrapment, and this stabilized preparation can be useful for antigen delivery.

CpG oligodeoxynucleotides adsorbed onto polylactide-co-glycolide microparticles improve the immunogenicity and protective activity of the licensed anthrax vaccine

To reduce the biothreat posed by anthrax, efforts are under way to improve the protection afforded by vaccination. This work examines the ability of immunostimulatory CpG oligodeoxynucleotides (ODN) adsorbed onto cationic polylactide-co-glycolide (PLG) microparticles (CpG ODN-PLG) to accelerate and boost the protective immunity elicited by Anthrax Vaccine Adsorbed (AVA, the licensed human anthrax vaccine). The results indicate that coadministering CpG ODN-PLG with AVA induces a stronger and faster immunoglobulin G response against the protective antigen of anthrax than AVA alone. Immunized mice were protected from lethal anthrax challenge within 1 week of vaccination with CpG ODN-PLG plus AVA, with the level of protection correlating with serum immunoglobulin G anti-protective antigen titers.

High cell density cultivation of probiotics and lactic acid production

The commercial interest in functional foods that contain live microorganisms, also named probiotics, is paralleled by the increasing scientific attention to their functionality in the digestive tract. This is especially true of yogurts that contain strains of lactic-acid bacteria of intestinal origin, among these, Lactobacillus delbrueckii ssp. bulgaricus is extensively used in the dairy industry and it has been demonstrated to be a probiotic strain. In this work we describe high cell density cultivations of this microorganism also focusing on the stereospecific production of lactic acid. Key parameters such as medium composition (bactocasitone concentration) and diverse aeration conditions were explored. The results showed that the final concentration of biomass in anaerobic fermentation was lower than the one obtained in microaerophilic conditions, while it gave a very high productivity of lactic acid which was present as a racemic mixture in the permeate. Fermentation experiments carried out with air sparging, even at very low flow-rate, led to the production of the sole L(+) lactic acid giving sevenfold increase in biomass yield in respect to the batch cultivation. Finally, a mathematical model was developed to describe the microfiltration bioprocess applied in this research considering an inhibition kinetic and enucleating a suitable mathematical description for the decrease of the transmembrane flux.

Poly-D,L-lactide-co-poly(ethylene glycol) microspheres as potential vaccine delivery systems

Adjuvants aimed at increasing the immunogenicity of recombinant antigens remain a focus in vaccine development. Worldwide, there is currently considerable care for the development of biodegradable microspheres as controlled release of vaccines, since the major disadvantage of several currently available vaccines is the need for repeated administration. Microspheres prepared from the biodegradable and biocompatible polymers, the polylactide (PLA) or polylactide-co-glycolide (PLGA), have been shown to be effective adjuvants for a number of antigens. This review mainly focuses on polylactide-co-poly(ethylene glycol) (PELA) microspheres adjuvant as vaccine delivery systems by summarizing our and other research groups' investigation on properties of the microspheres formulation encapsulating several kinds of antigens. The results indicate that compared with the commonly used PLA and PLGA, PELA showed several potentials in vaccine delivery systems, which may be due to the block copolymer have its capability to provide a biomaterial having a broad range of amphiphilic structure. PELA microspheres can control the rate of release of entrapped antigens and therefore, offer potential for the development of single-dose vaccines. The PELA microspheres have shown great potential as a next generation adjuvant to replace or complement existing aluminum salts for vaccine potential. The review mainly aims to promote the investigation of PELA microspheres adjuvant for antigens for worldwide researcher.

Hepatitis B surface antigen (HBsAg) derived from yeast cells (Hansenula polymorpha) used to establish an influence of antigenic subtype (adw2, adr, ayw3) in measuring the immune response after vaccination

As a product of western world biotechnology the yeast (Saccharomyces cerevisiae) hepatitis B vaccine was introduced as antigenic subtype adw2. However, an HBsAg/adw2-vaccine may provide a good but not "optimal" immunologic response for infection with heterologous virus strains. The availability of the yeast Hansenula polymorpha HBsAg in three different antigenic forms (adw2, ayw3 and adr) enabled us to investigate the influence of variant amino acids in the binding of immune anti-HBs after vaccination. Hansenula-derived HBsAg was standardised on the basis of protein content at >95% purity. Standardisation was controlled by monoclonal anti-HBs binding in a well-conserved region. Sera were obtained after immunisation with type adw, ayw and adr vaccines. Direct binding of immune antibodies to homologous antigen (in EIA) was higher than to heterologous antigen except for the adr-related antibodies. Since the binding of the WHO reference anti-HBs was strongly reduced for the ayw and adr compared to the adw antigen, a similar binding profile for the three antigens on protein basis could result in 2-3-fold different anti-HBs level expressed in IU/l. Inhibition of Hansenula-derived HBsAg binding to solid phase monoclonal anti-HBs in enzyme immunoassays after incubation with serum anti-HBs confirmed the differential binding of serum anti-HBs with variant Hansenula-derived HBsAg. This variant (antigenic subtype) dependent reactivity of anti-HBs in immunoassays in combination with a variant specific WHO standard may limit the application of the threshold levels of 10 and 100 IU/l for seroconversion and seroprotection.

Pharmaceutical and immunological evaluation of a single-shot hepatitis B vaccine formulated with PLGA microspheres

A single-shot Hepatitis B vaccine formulation using poly(d,l)-lactide-co-glycolide acid (PLGA) microspheres as a delivery system was examined using a variety of biophysical and biochemical techniques as well as immunological evaluation in C3H mice. PLGA microsphere encapsulation of the Hepatitis B surface antigen (HBsAg), a lipoprotein particle, resulted in good recoveries of protein mass, protein particle conformational integrity, and in vitro antigenicity. Some partial delipidation of the HBsAg, however, was observed. The loading and encapsulation efficiency of HBsAg into the PLGA microspheres were measured along with the morphology and size distribution of the vaccine-loaded PLGA microspheres. The in vitro release kinetics of HBsAg from the PLGA microspheres was evaluated and found to be affected by experimental conditions such as stirring rate. HBsAg showed enhanced storage stability at 37 degrees C in the slightly acidic pH range reported to be found inside PLGA microspheres; thus, the antigen is relatively stable under conditions of temperature and pH that may mimic in vivo conditions. The immunogenicity of the microsphere formulations of HBsAg was compared with conventional aluminum adjuvant formulated HBsAg vaccine in C3H mice. Comparisons were made between aluminum formulations (one and two injections), PLGA microsphere formulations (single injection), and a mixture of aluminum and PLGA microsphere formulations (single injection). The nine-month serum antibody titers indicate that a single injection of a mixture of aluminum and PLGA-formulated HBsAg results in equal or better immune responses than two injections of aluminum-formulated HBsAg vaccine. Based on these in vitro and in vivo studies, it is concluded that HBsAg can be successfully encapsulated and recovered from the PLGA microspheres and a mixture of aluminum-adjuvanted and PLGA-formulated HBsAg can auto-boost an immune response in manner comparable to multiple injections of an aluminum-formulated vaccine.

The application of biodegradable collagen minipellets as vaccine delivery vehicles in mice and sheep

Collagen minipellets are injectable delivery vehicles that release antigen and adjuvant over several days in a first-order release profile. In vaccination experiments in mice, secondary antibody responses induced by minipellets formulated with avidin and IL-1beta as adjuvant were equivalent to those induced by a conventional immunization with avidin in alum. When no adjuvant was used, anti-avidin responses induced by minipellets were 10-20-fold higher than those induced by injection of avidin in saline. In sheep, conventional vaccination with avidin in alum induced antibody responses initially exceeding that induced by minipellets formulated with avidin and IL-1beta, while following a secondary vaccination, the minipellet antibody response was equal to or greater than the alum-adjuvanted control groups. Increasing levels of IL-1beta adjuvant resulted in enhanced persistence of the antibody response. When clostridial vaccine antigens were incorporated into the minipellets, total antibody responses induced in sheep were equivalent to those induced by vaccination with the clostridial antigens in alum. Neutralizing antibody titres exceeded those induced by conventional vaccination. No adverse site reactions were observed at the implant site, with immunohistological study showing that the cellular infiltrate was dominated by a transient influx of neutrophils. This is a typical response to delivery of bioactive IL-1beta. The minipellets were completely degraded within 35 days of implantation.

Tetanus toxoid loaded 'preformed microspheres' of cross-linked dextran

The conformation of an antigen and hence its biological activity may get compromised when encapsulated in controlled release microspheres during formulation. In order to obviate the need for exposure of the antigen to the inactivating conditions, such as exposure to organic solvent and the high shear stress of emulsification required for microencapsulation, an alternate strategy was employed. 'Pre-formed' microspheres (20--340 microm in size) made of cross-linked dextran (Dex) were employed as matrix for conjugation of tetanus toxoid (TT) under aqueous conditions. The native immunoreactivity of TT was completely retained after conjugation, as checked by immunofluorescence and quantitative ELISA. Immunogenicity of Dex--TT conjugate was tested in rodents. No untoward mortality or adverse effects of immunization with the test material were observed on histopathology of the site of injection. A single immunization with the long-acting depot formulation elicited anti-TT antibody response lasting for 1 year without any need of booster. The titres were comparable after 12 weeks with those obtained using the conventional alum adsorbed toxoid.