Intravaginal immunization in sheep using a bioadhesive microsphere antigen delivery system

Evaluation of mucoadhesive property and the effect of Boswellia carteri gum on intranasal vaccination against small ruminant morbillivirus infection (PPR)

A study was conducted to evaluate mucoadhesive property and immunomodulatory effect of phytogenic gums from Boswellia frereana, Boswellia carteri andCommiphora myrrha on intranasal Peste des petits ruminants (PPR) vaccination in goats and sheep in an ex-vivo and in-vivo situations. Plant gums were purified, dried and compressed into 500gm tablets. Modified shear stress measurement technique was used on freshly excised trachea and intestine tissues of goat to measure peak adhesion time. Forty eight animals (24 goats and 24 sheep) were divided into eight groups (of 3 goats and 3 sheep) and immunized intranasally with gum-vaccine combinations in two ratios (1:1, 1:2). Antibody against PPR virus was measured on day 14, 28, 42 and 56 post vaccination using H-based PPR bELISA. The peak adhesion time of the different gums was transient. PPR virus antibodies were detected in all immunized goats and sheep but not in unvaccinated control. The best percentage inhibition was recorded for Boswellia carteri-vaccine combination group at a ratio of 1:1. Administration of Boswellia carteri-PPR vaccine combination through intranasal or subcutaneous route, elicited similar antibody titre, implying that the intranasal route may be used as a non-invasive alternative delivery in PPR vaccination of small ruminants.

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.

Vaccination Strategies against Malaria: novel carrier(s) more than a tour de force

The introduction of vaccine technology has facilitated an unprecedented multi-antigen approach to develop an effective vaccine against complex systemic inflammatory pathogens such as Plasmodium spp. that cause severe malaria. The capacity of multi subunit DNA vaccine encoding different stage Plasmodium antigens to induce CD8(+) cytotoxic T lymphocytes and interferon-γ responses in mice, monkeys and humans has been observed. Moreover, genetic vaccination may be capable of eliciting both cell mediated and humoral immune responses. The cytotoxic T cell responses are categorically needed against intracellular hepatic stage and humoral response with antibodies targeted against antigens from all stages of malaria parasite life cycle. Therefore, the key to success for any DNA based vaccine is to design a vector able to serve as a safe and efficient delivery system. This has encouraged the development of non-viral DNA-mediated gene transfer techniques such as liposome, virosomes, microsphere and nanoparticles. Efficient and relatively safe DNA transfection using lipoplexes makes them an appealing alternative to be explored for gene delivery. Also, liposome-entrapped DNA has been shown to enhance the potency of DNA vaccines, possibly by facilitating uptake of the plasmid by antigen-presenting cells (APC). Another recent technology using cationic lipids has been deployed and has generated substantial interest in this approach to gene transfer. In this review we discussed various aspects that could be decisive in the formulation of efficient and stable carrier system(s) for the development of malaria vaccine.

A chitosan lactate/poloxamer 407-based matrix containing Eudragit RS microparticles for vaginal delivery of econazole: design and in vitro evaluation

A matrix based on chitosan lactate and poloxamer 407 was evaluated as a delivery system for the vaginal administration of the antifungal drug econazole. The matrix was investigated both containing the pure drug and after introducing microparticles of Eudragit RS 100 containing econazole. Eudragit RS 100 microparticles were prepared using an emulsion-extraction method and dispersed in a solution containing chitosan lactate (2% w/w) and poloxamer 407 (1.7% w/w). The microparticles, obtained with a yield of 64% w/w and an encapsulation efficiency of 42% w/w, had a diameter of less than 2 μm and a drug loading of 13% w/w. The compressed matrices, characterized by DSC, swelling, erosion, release and mucoadhesion studies, had behaviours dependent on the relative amounts of the contained microparticles. The matrix without microparticles (MECN) showed zero-order release kinetics, with a maximum drug-release of 60% w/w, while those containing 50 or 75% w/w microparticles showed a diffusion controlled release up to 8 and 16 h, respectively, and a linear trend after those time intervals, caused by the erosion process, which allowed reaching a drug-release of approximately 100% w/w at 22 h. In in vitro experiments, the matrices were mucoadhesive and active in inhibiting the growth of Candida albicans 796.

Mucoadhesive drug delivery systems

Mucoadhesion is commonly defined as the adhesion between two materials, at least one of which is a mucosal surface. Over the past few decades, mucosal drug delivery has received a great deal of attention. Mucoadhesive dosage forms may be designed to enable prolonged retention at the site of application, providing a controlled rate of drug release for improved therapeutic outcome. Application of dosage forms to mucosal surfaces may be of benefit to drug molecules not amenable to the oral route, such as those that undergo acid degradation or extensive first-pass metabolism. The mucoadhesive ability of a dosage form is dependent upon a variety of factors, including the nature of the mucosal tissue and the physicochemical properties of the polymeric formulation. This review article aims to provide an overview of the various aspects of mucoadhesion, mucoadhesive materials, factors affecting mucoadhesion, evaluating methods, and finally various mucoadhesive drug delivery systems (buccal, nasal, ocular, gastro, vaginal, and rectal).

Preparation and in vivo study of dry powder microspheres for nasal immunization

The immunoadjuvant potential of alginate microspheres as delivery system, and cross-linked dextran microspheres (CDM) as absorption enhancer and excipient for powder of alginate microspheres, were evaluated. Alginate microspheres were prepared by emulsification method. Microspheres encapsulated with tetanus toxoid (TT) or Quillaja saponin (QS) were nasally administered to rabbits, three times in 2 weeks interval and serum IgG and nasal lavage sIgA titers were determined by ELISA. The mean diameter of microspheres was about 1.5 mum. Release of TT and QS was 13.1 +/- 1.4% and 31.8 +/- 4.3% after 4 h. The serum IgG titer induced with (TT)(ALG) microspheres was higher than TT solution (P<0.001). Addition of QS or CDM adjuvant, in separate, to (TT)(ALG) microspheres could not significantly increase the immune responses (P>0.05), but the highest systemic IgG titers induced with (TT+QS)(ALG)+CDM (P<0.01). The sIgA titer induced with (TT)(ALG) microspheres was higher than TT solution (P<0.05). The highest mucosal sIgA titers were seen in animals immunized with (TT)(ALG)+CDM (P<0.05). Co-encapsulation of QS and TT in microspheres did not increase the sIgA titers. When CDM was added to alginate microspheres encapsulated with TT or TT+QS, the highest mucosal and systemic responses were observed.

Dextran microspheres could enhance immune responses against PLGA nanospheres encapsulated with tetanus toxoid and Quillaja saponins after nasal immunization in rabbit

Potent immunoadjuvants are needed to elicit responses following mucosal delivery. PLGA (poly[D,L-lactic-co-glycolic acid]) nanospheres, Quillaja saponin (QS) and cross-linked dextran microspheres (CDM) as drug delivery and absorption enhancer adjuvants were evaluated. PLGA nanospheres were prepared by solvent evaporation method. Particulate characteristics of nanospheres were studied by optical and scanning electron microscopes and dynamic light scattering technique. The mean diameter of nanospheres encapsulated with TT and TT + QS determined as 425 and 390 nm. Loadings of TT and QS were 30 ± 1.9% and 23 ± 2.8%. Nanospheres encapsulated with TT or QS were intranasally administered to rabbits, three times in two-week intervals and the serum IgG and nasal lavage IgA titers were determined by ELISA. The serum IgG titer induced with (TT)(PLGA) nanospheres was higher than TT solution (P < 0.001). IgG titers induced with (TT + QS)(PLGA) was higher than (TT)(PLGA) (P < 0.0001). When (TT)(PLGA) and (TT + QS)(PLGA) nanospheres were mixed with CDM, higher IgG titers were induced (P < 0.001). The highest mucosal sIgA titers were seen in animals immunized with (TT + QS)(PLGA) + CDM. Co-encapsulation of QS and TT in PLGA nanospheres increased sIgA titers. In conclusion, the highest immune responses were observed by concomitant use of three adjuvants.

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.

Various carrier system(s)- mediated genetic vaccination strategies against malaria

The introduction of vaccine technology has facilitated an unprecedented multiantigen approach to develop an effective vaccine against complex pathogens, such as Plasmodium spp., that cause severe malaria. The capacity of multisubunit DNA vaccines encoding different stage Plasmodium antigens to induce CD8(+) cytotoxic T lymphocytes and IFN-gamma responses in mice, monkeys and humans has been observed. Moreover, genetic vaccination may be multi-immune (i.e., capable of eliciting more than one type of immune response, including cell-mediated and humoral). In the case of malaria parasites, a cytotoxic T-lymphocyte response is categorically needed against the intracellular hepatocyte stage while a humoral response, with antibodies targeted against antigens from all stages of the life cycle, is also needed. Therefore, the key to success for any DNA-based therapy is to design a vector able to serve as a safe and efficient delivery system. This has encouraged the development of nonviral DNA-mediated gene-transfer techniques, such as liposomes, virosomes, microspheres and nanoparticles. Efficient and relatively safe DNA transfection using lipoplexes makes them an appealing alternative to be explored for gene delivery. In addition, liposome-entrapped DNA has been shown to enhance the potency of DNA vaccines, possibly by facilitating uptake of the plasmid by antigen-presenting cells. Another recent technology using cationic lipids has been deployed and has generated substantial interest in this approach to gene transfer. This review comprises various aspects that could be decisive in the formulation of efficient and stable carrier system(s) for the development of malaria vaccines.

Induction of high antitoxin titers against tetanus toxoid in rabbits by intranasal immunization with dextran microspheres

Poor absorption of protein antigens through the mucosal membranes necessitates the use of mucoadhesive delivery systems. Regarding the advantages of mucosal immunization and also the penetration enhancement potential of dextran microspheres, in this study the adjuvant potential of these microspheres was compared with CpG-ODN. Cross-linked dextran microspheres (CDMs) were loaded with tetanus toxoid (TT). In vitro release studies were performed in a model, simulating the nasal cavity. The immunoreactivity of encapsulated TT was assayed by ELISA. Membrane toxicity and local irritating potential of CDM was examined by erythrocyte hemolysis and nasal administration to human nose, respectively. The various formulations were nasally administered to rabbits (n=4). Alum-adsorbed TT (AATT) was injected as the positive control. The serum IgG and nasal lavage sIgA titers were determined by ELISA method. Serum antitoxin titers were determined by toxin neutralization (TN) bioassay method. Mean diameter of CDM was 128.1+/-25.8 microm. Mean encapsulation efficiency was 20.3+/-3.2% (n=3). Antigenicity of encapsulated TT was 90.5+/-1.8% (n=3) that of original TT. Hemolysis studies showed no membrane disruption by CDM and none of the human subjects reported nasal irritation. Among the nasally immunized animals, the highest antitoxin titers was seen in the group immunized with CDM+TT (P<0.0001). The serum IgG titers of the CDM+TT group was higher than the TT solution group (P<0.05). The adjuvant potentials of CDM and CpG-ODN in inducing IgG titers was not significantly different (P>0.05). The lowest sIgA titers in the bronchial lavage were seen in the group of animals received AATT parenterally. Considering the proper release characteristics, desirable preservation of the antigen activity of TT, good mucoadhesion properties and also safety of CDM+TT, these microspheres could be regarded as an efficient mucosal adjuvant and antigen delivery system. These microspheres could induce very high antitoxin titers following nasal administration, while the CpG-ODN could not induce such titers. The antitoxin titers induced by CDM+TT was 175 times higher than the protective levels.

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.

Intranasal delivery of vaccines against HIV

HIV poses a serious health threat in the world. Mucosal transmission of HIV through the genitourinary tract may be the most important route of transmission. Intranasal immunisations induce vaginal and systemic immune responses. Various protein-, DNA- and RNA-based immunopotentiating adjuvants/delivery systems and live bacterial and viral vectors are available for intranasal immunisations, and these systems may differ in their ability to induce a specific type of immune response (e.g., a cytotoxic T cell versus an antibody response). As the protection against HIV may require both cytotoxic T cell and antibodies, a combination of adjuvants/delivery systems for combinations of mucosal and parenteral immunisations may be required in order to develop a protective anti-HIV vaccine.

Current Efforts on Generation of Optimal Immune Responses against HIV through Mucosal Immunisations

Currently, over 40 million HIV-infected individuals are found around the globe, with an additional 15,000 daily infections. There is a general consensus that the most effective way to prevent new infections is to introduce a prophylactic vaccine. It is also generally agreed that both cytotoxic T lymphocytes (CTLs) and neutralising antibodies are important to mediate protection. The neutralising antibodies must be broadly reactive to neutralise multiple primary isolates. There is also increasing agreement that CTLs and neutralising antibodies should be present at mucosal sites of HIV entry, the draining lymph nodes and systemically. The route of immunisation is important when determining the site where protection is desired, i.e. the female genitourinary tract versus the male or female rectum versus systemic tissues, as are the type of HIV-related antigens, immunopotentiating adjuvants and delivery systems. Finally, multiple vaccine delivery systems may be required to be administered through both mucosal and parenteral routes to induce optimal immune responses and protection against HIV infection through rectal, vaginal or systemic routes of transmission. This review discusses current efforts on the generation of optimal immune responses against HIV in the genitourinary and intestinal tracts using mucosal immunisations alone or combinations of mucosal and parenteral immunisations.

Starch microparticles as vaccine adjuvant

The demand for new vaccine adjuvants is well documented. New purified antigens from parasites, bacterial or viral pathogens, as well as recombinant subunit antigens and synthetic peptides, are often inherently weak immunogens; therefore, they need some kind of adjuvant to help initiate an immune response. In addition, there are very few adjuvants using the potential of the mucosal immune system, which may play an important role in the defence against air- and food-borne infections. Starch is a natural biocompatible and biodegradable polymer that is suitable for the production of various particulate adjuvant formulations, which can induce mucosal as well as systemic immune responses. This review gives an account of the different starch adjuvants used in immunisation studies. In particular, the properties of polyacryl starch microparticles as an oral vaccine adjuvant that induce protective immune responses in mice challenge experiments are summarised. In addition, a diphtheria booster vaccine has been proposed to be used to proving the concept in man and the possibilities to design an efficient vaccine formulation for human use are discussed.

Bioadhesive microspheres as a controlled drug delivery system

The concept of controlled drug delivery has been traditionally used to obtain specific release rates or spatial targeting of active ingredients. The phenomenon of bioadhesion, introduced by Park and Robinson [Park, K., Robinson, J.R., 1984. Bioadhesive polymers as platforms for oral controlled drug delivery: method to study bioadhesion. Int. J. Pharm. 198, 107-127], has been studied extensively in the last decade and applied to improve the performance of these drug delivery systems. Recent advances in polymer science and drug carrier technologies have promulgated the development of novel drug carriers such as bioadhesive microspheres that have boosted the use of "bioadhesion" in drug delivery. This article presents the spectrum of potential applications of bioadhesive microspheres in controlled drug delivery ranging from the small molecules, to peptides, and to the macromolecular drugs such as proteins, oligonucleotides and even DNA. The development of mucus or cell-specific bioadhesive polymers and the concepts of cytoadhesion and bioinvasion provide unprecedented opportunities for targeting drugs to specific cells or intracellular compartments. Developments in the techniques for in vitro and in vivo evaluation of bioadhesive microspheres have also been discussed.

Microparticles for intranasal immunization

Of the several routes available for mucosal immunization, the nasal route is particularly attractive because of ease of administration and the induction of potent immune responses, particularly in the respiratory and genitourinary tracts. However, adjuvants and delivery systems are required to enhance immune responses following nasal immunization. This review focuses on the use of microparticles as adjuvants and delivery systems for protein and DNA vaccines for nasal immunization. In particular we discuss our own work on poly(lactide co-glycolide) (PLG) microparticles with entrapped protein or adsorbed DNA as a vaccine delivery system. The possible mechanisms involved in the enhancement of immune responses through the use of DNA adsorbed onto PLG microparticles are also discussed.

A novel bioadhesive intranasal delivery system for inactivated influenza vaccines

The aim of the current studies was to evaluate a bioadhesive delivery system for intranasal administration of a flu vaccine, in combination with a mucosal adjuvant (LTK63). A commercially available influenza vaccine, containing hemagglutinin (HA) from influenza/A Johannesberg H1N1 1996, and LTK63 or LTR72 adjuvants, which are genetically detoxified derivatives of heat labile enterotoxin from Escherichia coli, were administered IN in a bioadhesive delivery system, which comprised esterified hyaluronic acid (HYAFF) microspheres, to mice, rabbits and micro-pigs at days 0 and 28. For comparison, additional groups of animals were immunized intranasally with the HA vaccine alone, with soluble HA+LTK63, or IM with HA. In all three species, the groups of animals receiving IN immunization with the bioadhesive microsphere formulations, including LT mutants, showed significantly enhanced serum IgG responses (P<0.05) and higher hemagglutination inhibition (HI) titers in comparison to the other groups. In addition, the bioadhesive formulation also showed a significantly enhanced nasal wash IgA response (P<0.05). Most encouragingly, in pigs, the bioadhesive microsphere vaccine delivery system induced serum immune responses following IN immunization, which were significantly more potent than those induced by traditional IM immunization at the same vaccine dose (P<0.05).

Production of antibodies to Staphylococcus aureus serotypes 5, 8, and 336 using poly(DL-lactide-co-glycolide) microspheres

Staphylococcus aureus is responsible for a major portion of the economic losses due to mastitis. Attempts to produce a vaccine to prevent S. aureus mastitis have been hampered by the low immunogenicity of the polysaccharide, which forms on the surface of the organism when it enters the mammary gland. The polysaccharide inhibits phagocytosis and destruction of the organism by neutrophils. This study was conducted to determine if S. aureus polysaccharide serotypes 5, 8, and 336 conjugated to a protein and incorporated in poly(DL-lactide-co-glycolide) microspheres would enhance the production of opsonizing antibodies to the polysaccharide. Cows were immunized with either polysaccharide conjugates emulsified in Freund's incomplete adjuvant or polysaccharide conjugates encapsulated in poly (DL-lactide-co-glycolide) microspheres emulsified in Freund's incomplete adjuvant. All cows produced sustained antibody titers to the three polysaccharide serotypes. Cows immunized with microspheres had higher antibody titers. Cows in both groups produced increased concentrations of IgG1 and IgG2 antibodies; neither group produced an increase in IgM. Immune sera from cows immunized with conjugates alone increased phagocytosis, which decreased at the end of the study. Sera from cows immunized with conjugates in microspheres increased phagocytosis, which was sustained at the end of the study. Immune sera from both groups decreased bacterial adherence to bovine mammary epithelial cells. These data showed that a single injection of antigen in microspheres produced higher titers and more sustained enhancement of phagocytosis, which could aid in the defense of the cow against S. aureus infections.

Neutrophil activation by plasma opsonized polymeric microspheres: inhibitory effect of pluronic F127

The phagocytosis of drug-loaded polymeric microspheres by white blood cells, such as neutrophils or mononuclear cells, represents the major clearance mechanism by which this foreign material is eliminated from the body. The process of phagocytosis requires the activation of the white blood cells by the microsphere surface, followed by binding and engulfment. Phagocytosis may result in the removal of the microspheres from the blood or the disease site and an inflammatory response. Therefore, we have studied the level of neutrophil activation by microspheres ( +/- opsonization) manufactured from various biomaterials or polymers. Polymer microspheres with equivalent size distributions were made from poly (DL-lactic acid) (PLA), poly(epsilon-caprolactone) (PCL), poly(methyl methacrylate) (PMMA) or a 50 : 50 blend of PLA: poly(ethylene-co-vinyl acetate) (PLA: EVA). Neutrophils were isolated from human blood and activation of these cells by microspheres was measured by chemiluminescence (CL). All four types of microspheres induced only low levels of CL, however these levels were enhanced significantly if the microspheres were pretreated with plasma or IgG suggesting an opsonization effect. The adsorption of IgG or proteins from plasma was confirmed by polyacrylamide gel electrophoresis (SDS-PAGE). The poloxamer Pluronic F127 inhibited the opsonization effect of IgG and plasma on all four types of microspheres and inhibited protein adsorption as measured by SDS-PAGE. Since neutrophil activation is part of the inflammation process in vivo, these in vitro data suggest that all four types of microspheres are likely to be inflammatory if injected into body compartments containing plasma-derived fluids. Pretreatment of the microspheres with Pluronic F127 may reduce the inflammatory potential of the microspheres.

Bioadhesive-based dosage forms: the next generation

Prolonged contact time of a drug with a body tissue, through the use of a bioadhesive polymer, can significantly improve the performance of many drugs. These improvements range from better treatment of local pathologies to improved drug bioavailability and controlled release to enhanced patient compliance. There are abundant examples in the literature over the past 15 years of these improvements using first generation or "off-the-shelf" bioadhesive polymers. The present mini-review will remind us of the success achieved with these first-generation polymers and focus on proposals for the next-generation polymers and attendant benefits likely to occur with these improved polymeric systems.

Intranasal immunization against influenza virus using polymeric particles

The aim of this study was to evaluate the potential of poly(D,L-lactide-co-glycolide) nano-and microspheres, with a mean diameter of 220 nm and 8 microm, respectively, to enhance the nasal and systemic immune responses against influenza virus antigen. High encapsulation levels of antigen were achieved in all cases. Neither the molecular weight nor the antigenicity of the entrapped antigen were affected by the encapsulation procedure. Following nasal immunization, the nasal washes IgA and the serum IgG responses were evaluated. With the soluble antigen, relatively high immune responses were observed. With nanospheres, nasal washes IgA levels were significantly lower (p<0.01) and serum IgG levels were not significantly different (p>0.05) from those obtained with the soluble antigen. With microspheres, both nasal washes IgA and serum IgG levels were significantly lower (p<0.01 and <0.05, respectively) as compared to the levels found for the soluble antigen. In addition, fluorescent microspheres administered intranasally failed to reach the nasal-associated lymphoid tissue (NALT). This lack of particle uptake by NALT and the high immunogenicity of the antigen used in this study, could explain the absence of enhancement of the immune responses by the polymeric particles.

Engineering the gram-positive cell surface for construction of bacterial vaccine vectors

A genetic system for surface display of heterologous proteins has been developed in Streptococcus gordonii, a gram-positive human oral commensal that is naturally competent for genetic transformation. Our approach is based on chromosomal integration downstream from a resident promoter and translational fusion to an M6 protein. Using this strategy a variety of proteins, of different origin and size, were displayed on the cell surface and were shown to be stably expressed both in vitro and in vivo. Animal models of mucosal colonization (oral and vaginal) and intragastric immunization with recombinant S. gordonii were developed and the local and systemic immune responses were studied. Here we report the techniques for the construction of recombinant bacteria, use of animal models, and analysis of the immune response.

Poly-DL-lactide-co-glycolide microspheres as a controlled release antigen delivery system

Successful vaccine application means maximum protection with minimal number of administrations. A rational development of vaccines involves studies of the nature of the antigen as well as of the adjuvant to be used to improve the immune responses. This has provided the impetus for studies to design the degradable devices and for different approaches to antigen delivery by different routes of administration. The development of controlled release systems based on polymeric devices that permit a sustained or pulsed release of encapsulated antigens has attracted much interest. Polymeric delivery systems consist of polymers that release their content continuously in a controlled manner over a period of time. The development of a biocompatible delivery system for parenteral administration offers several advantages in terms of immunoadjuvanticity over other compounds. It was found that, in contrast to other carriers, microspheres are more stable, thus permitting administration by the oral or parenteral route. In the present study, we describe the main characteristics and potentialities of this new immunoadjuvant for oral and parenteral administration.

Polymer-grafted starch microparticles for oral and nasal immunization

Microparticle delivery systems for oral vaccine administration are receiving considerable attention. A novel silicone polymer-grafted starch microparticle system was developed that is efficacious both orally and intranasally. Unlike most other microparticle systems, this novel system does not appear to retard the release of antigen or to protect antigen from degradation. The results indicate that a unique physiochemical relationship occurs between protein antigen and silicone in a starch matrix that facilitates the mucosal immunogenicity of antigen. This leads to predominance of Th2 antibody response. Taken together, these findings indicate that this novel microparticle system may be advantageous for the delivery of small quantities of antigen, especially intranasally, and may be useful for the induction of oral tolerance.

Induction of secretory and serum antibody responses following oral administration of antigen with bioadhesive degradable starch microparticles

Bioadhesive degradable starch microparticles were used to deliver antigen and immunoglobulin A (IgA)-enhancing cytokines to the oral mucosa. Degradable starch microparticle immunization groups consisted of rats dosed topically at the sublingual epithelium of the oral cavity, by subcutaneous injection in the vicinity of the major salivary glands or by oral intubation with degradable starch microparticles containing dinitrophenyl-bovine serum albumin +/- IL-5/IL-6 +/- penetration enhancer (alpha-lysophosphatidylcholine). Dinitrophenyl-bovine serum albumin was also adsorbed onto alum for salivary gland vicinity injection and administered to the oral cavity in soluble form. Animals were subjected to 3 immunization cycles, and sequential samples were assayed by radioimmunoassay for salivary IgA, tear IgA and serum IgG anti-dinitrophenyl antibodies after secondary and tertiary immunization. Salivary IgA responses were highest in degradable starch microparticle groups receiving penetration enhancer at 71 days post-secondary immunization and continued in one degradable starch microparticle((oral cavity) and two injected (salivary gland vicinity) groups for up to 88 days post-tertiary immunization. Long-term tear responses were also observed in degradable starch microparticle groups receiving penetration enhancer, but they dissipated before the salivary gland-alum responses following tertiary immunization. Serum IgG responses were most pronounced in salivary gland groups, but long-term low level responses were detectable in oral cavity groups receiving degradable starch microparticle formulations with penetration enhancer. Inclusion of IL-5 and IL-6 in oral cavity-delivered degradable starch microparticle formulations consistently enhanced tear IgA while only upregulating salivary IgA antibody responses at early time points post immunization. IL-5 and IL-6 did not enhance serum IgG antibodies in any group. These data indicate that bioadhesive degradable starch microparticles can be used as a vehicle to deliver antigen and cytokine signals to the oral cavity and, when delivered in combination with a penetration enhancer, can potentiate long-term salivary IgA responses.

New advances in microsphere-based single-dose vaccines

Polymer microspheres have shown great potential as a next generation adjuvant to replace or complement existing aluminum salts for vaccine potentiation. Microsphere-based systems can now be made to deliver subunit protein and peptide antigens in their native form in a continuous or pulsatile fashion for periods of weeks to months with reliable and reproducible kinetics, often obviating the need for booster immunizations in animal models. Microspheres have also shown potential as carriers for oral vaccine delivery due to their protective effects on encapsulated antigens and their ability to be taken up by the Peyer's patches in the intestine. The potency of these optimal depot formulations for antigen may be enhanced by the co-delivery of vaccine adjuvants, including cytokines, that are either entrapped in the polymer matrix or, alternatively, incorporated into the backbone of the polymer itself and released concomitantly with antigen as the polymer degrades. In this article we review the use of polymer microspheres for single-step immunization and discuss future applications for the improvement of vaccines and immunotherapies by utilizing encapsulation technology.

Commensal bacteria as vectors for mucosal vaccines against sexually transmitted diseases: vaginal colonization with recombinant streptococci induces local and systemic antibodies in mice

There is a need to develop vaccines to control the spread of sexually transmitted diseases (STDs). Novel immunization strategies that elicit a mucosal immune response in the genital tract, may show improved protection by preventing or at least limiting entry of the pathogenic micro-organism. However, it has proven difficult to obtain a local immune response in the vaginal mucosa. Our approach is based on the use of recombinant bacteria capable of colonizing mucosal surfaces as live vaccine vectors. The human commensal Streptococcus gordonii, engineered to express the E7 protein of human papillomavirus type 16, was used for intravaginal immunization of mice. A single inoculum of recombinant bacteria was sufficient to establish colonization of the murine vagina and therefore induce papillomavirus-specific vaginal IgA and serum IgG. Evidence that mucosal colonization with recombinant commensal bacteria can induce a local immune response in the female genital tract represents a significant step toward the development of new vaccines against STDs.

Salivary, gut, vaginal and nasal antibody responses after oral immunization with biodegradable microparticles

The aims of this study were to determine whether oral immunization with microparticles might lead to a common mucosal response including vaginal secretions. Female Balb/c mice were immunized orally with microparticles containing ovalbumin at 0 and 4 weeks or with soluble antigen. Antibody responses were assayed by ELISA in saliva, gut washings, vaginal washings and serum, and antibody producing cells were assayed by ELISPOT in salivary glands and nasal cavity. After primary immunization, IgA antibodies were detected in vaginal washings, saliva and in gut washings which were significantly greater than those detected with soluble antigen (P < 0.01). After secondary immunization, greatly enhanced antibody titres were found in three fluids. The specific activity (antibody per microgram IgA) of antibodies in vaginal fluid and saliva was significantly greater than in serum or gut wash (P < 0.01). Oral immunization also resulted in the development of antibody forming cells in salivary glands and in nasal associated mucosal tissue. Immunization with microparticles containing antigen should prove useful in immunization against infections affecting a number of different mucosal surfaces.

Nasal lymphoid tissue, intranasal immunization, and compartmentalization of the common mucosal immune system

Mucosal application of vaccines with an appropriate adjuvant can induce immune responses at both systemic and mucosal sites, and therefore may prevent not only infectious disease, but also colonization of mucosal surfaces. Intranasal is more effective than intragastric immunization at generating earlier and stronger mucosal immune response. Nasal lymphoid tissue (NALT) and its local draining lymph nodes may retain long-term immune memory. IgA isotype switching, and the differentiation and maturation of IgA antibody-secreting cells (ASC) may occur before these cells migrate out of NALT, whereas IgG ASC responses require passage of the cells through draining lymph nodes of the NALT. Knowledge of whether immune memory cells can recirculate to and reside in the inductive sites other than their origin after encountering antigen will be helpful for understanding the compartmentalization of the common mucosal immune system as well as for determining the best route for delivering a mucosal vaccine against a particular pathogen.

Formulation of poly(DL-lactide-co-glycolide) microspheres and their ingestion by bovine leukocytes

This study determined optimal parameters for producing controlled-release microspheres and examined their suitability for vaccines via ingestion by bovine leukocytes. Microspheres elicit an immune response when ingested by antigen-presenting cells and provide sustained exposure of antigen to sensitized cells. Ingestion of microspheres is determined by their size (< 10 microns), and antigen release is governed by composition. Poly(DL-lactide-co-glycolide) microspheres were prepared using different polymer concentrations, stir rates, emulsifier concentrations, and emulsifier molecular masses. Microspheres that were < 10 microns were prepared using a 6% 50:50 lactide to glycolide polymer solution emulsified at 12,000 rpm in a low molecular mass, 5% polyvinyl alcohol solution. Microspheres that were > 20 microns were prepared using a 10% 85:15 lactide to glycolide polymer solution emulsified at 1200 rpm in a low molecular mass, 3% polyvinyl alcohol solution. Small microspheres released 90% of the antigen after 7 d, and large microspheres released only 24% of the antigen after 56 d. Both monocytes and neutrophils selectively ingested small microspheres that were opsonized with normal bovine serum (heated and unheated). Ingestion of microspheres that had been opsonized with fetal bovine serum (heated and unheated) was minimal. Lymphocytes did not ingest microspheres. Ingestion of small microspheres by bovine monocytes and sustained release of antigen by large microspheres suggested that microspheres have the ability to produce a sustained immune response with a single injection.

Immunoglobulin G antibodies in human vaginal secretions after parenteral vaccination

The induction of antibodies in vaginal secretions by systemic (intramuscular) immunization in humans was investigated by using the tetanus toxoid vaccine. Five women, 30 to 40 years old, were injected with a currently used dose of toxoid (40 IU), and serum, saliva, and vaginal secretion samples were collected on day 0 and on day 6 or day 10. All of these subjects had been previously vaccinated at least 5 years before; four were in good health, whereas one suffered from AIDS in clinical category B3. In most cases, analysis of specific antibodies in the vaginal wash showed a dramatic rise after boosting. These antibodies were primarily of the immunoglobulin G (IgG) isotype. The specific activity (ratio of antibody titer to IgG concentration) was shown to increase after the booster injection, irrespective of variations in the IgG level during the menstrual cycle. Comparison between serum and genital antibodies showed no difference in terms of both specific activity and level of avidity. These results demonstrate that parenteral injections can induce a systemic-derived antibody release in the vaginal fluid. Hence, systemic vaccinations can be efficient at the genital level and thus could reinforce or even replace a local vaccine.