Induction of secretory immunity with bioadhesive poly (D,L-lactide-co-glycolide) microparticles containing Streptococcus sobrinus glucosyltransferase

A review: Gelatine as a bioadhesive material for medical and pharmaceutical applications

Bioadhesive polymers offer versatility to medical and pharmaceutical inventions. The incorporation of such materials to conventional dosage forms or medical devices may confer or improve the adhesivity of the bioadhesive systems, subsequently prolonging their residence time at the site of absorption or action and providing sustained release of actives with improved bioavailability and therapeutic outcomes. For decades, much focus has been put on scientific works to replace synthetic polymers with biopolymers with desirable functional properties. Gelatine has been considered one of the most promising biopolymers. Despite its biodegradability, biocompatibility and unique biological properties, gelatine exhibits poor mechanical and adhesive properties, limiting its end-use applications. The chemical modification and blending of gelatine with other biomaterials are strategies proposed to improve its bioadhesivity. Here we discuss the classical approaches involving a variety of polymer blends and composite systems containing gelatine, and gelatine modifications via thiolation, methacrylation, catechol conjugation, amination and other newly devised strategies. We highlight several of the latest studies on these strategies and their relevant findings.

Current advances in research and clinical applications of PLGA-based nanotechnology

Co-polymer poly(lactic-co-glycolic acid) (PLGA) nanotechnology has been developed for many years and has been approved by the US FDA for the use of drug delivery, diagnostics and other applications of clinical and basic science research, including cardiovascular disease, cancer, vaccine and tissue engineering. This article presents the more recent successes of applying PLGA-based nanotechnologies and tools in these medicine-related applications. It focuses on the possible mechanisms, diagnosis and treatment effects of PLGA preparations and devices. This updated information will benefit to both new and established research scientists and clinical physicians who are interested in the development and application of PLGA nanotechnology as new therapeutic and diagnostic strategies for many diseases.

Mutans streptococcal infection induces salivary antibody to virulence proteins and associated functional domains

The interplay between mucosal immune responses to natural exposure to mutans streptococci and the incorporation and accumulation of these cariogenic microorganisms in oral biofilms is unclear. An initial approach to explore this question would be to assess the native secretory immunity emerging as a consequence of Streptococcus mutans infection. To this end, we analyzed salivary immunoglobulin A (IgA) antibody to mutans streptococcal glucosyltransferase (Gtf) and glucan binding protein B (GbpB) and to domains associated with enzyme function and major histocompatibility complex (MHC) class II binding in two experiments. Salivas were collected from approximately 45-day-old Sprague-Dawley rats, which were then infected with S. mutans SJ32. Infection was verified and allowed to continue for 2 to 2.5 months. Salivas were again collected following the infection period. Pre- and postinfection salivas were then analyzed for IgA antibody activity using peptide- or protein-coated microsphere Luminex technology. S. mutans infection induced significant levels of salivary IgA antibody to Gtf (P < 0.002) and GbpB (P < 0.001) in both experiments, although the levels were usually far lower than the levels achieved when mucosal immunization is used. Significantly (P < 0.035 to P < 0.001) elevated levels of postinfection salivary IgA antibody to 6/10 Gtf peptides associated with either enzyme function or MHC binding were detected. The postinfection levels of antibody to two GbpB peptides in the N-terminal region of the six GbpB peptides assayed were also elevated (P < 0.031 and P < 0.001). Interestingly, the patterns of the rodent response to GbpB peptides were similar to the patterns seen in salivas from young children during their initial exposure to S. mutans. Thus, the presence of a detectable postinfection salivary IgA response to mutans streptococcal virulence-associated components, coupled with the correspondence between rat and human mucosal immune responsiveness to naturally presented Gtf and GbpB epitopes, suggests that the rat may be a useful model for defining mucosal responses that could be expected in humans. Under controlled infection conditions, such a model could prove to be helpful for unraveling relationships between the host response and oral biofilm development.

Influence of microparticle formulation on immunogenicity of SYI, a synthetic peptide derived from Streptococcus mutans GbpB

Subcutaneous immunization with SYI, a peptide construct based on Streptococcus mutans glucan binding protein B (GbpB) residues 113-132, significantly reduces experimental dental caries. Since mucosal immunization may be preferred for human vaccine applications, the present objective was to determine what formulation of SYI combined with polylactide-coglycolide microparticles could give rise to significant levels of salivary IgA antibody reactive with the native GbpB protein. A comparison of the SYI construct, loaded into or mixed with polylactide-coglycolide revealed the SYI-loaded microparticles to induce significant and sustainable levels of salivary and nasal wash IgA antibody to the peptide and the native protein. SYI mixed with unloaded microparticles was less effective in mucosal antibody response induction. These studies indicate that mucosal immunization with the SYI construct can induce salivary IgA antibody to a pathogenesis-associated component of S. mutans if delivered within polylactide-coglycolide microparticles, suggesting that this approach could successfully induce protective salivary immunity to dental caries caused by S. mutans.

Remote glucosyltransferase-microparticle vaccine delivery induces protective immunity in the oral cavity

Intranasally administered dental caries vaccines show significant promise for human application. Alternate mucosal routes may be required, however, to induce caries-protective salivary IgA antibody in children with respiratory diseases. Since rectal mucosa contains inductive lymphoid tissue, we hypothesized that the rectal route could be used to induce salivary immunity to mutans streptococcal glucosyltransferase (GTF), resulting in protective immunity to experimental dental caries. We first explored the ability of glucosyltransferase, incorporated into polylactide-co-glycolide (PLGA) microparticles (MP), and administered rectally together with mucosal adjuvant, to induce a salivary IgA antibody response. Groups of Sprague-Dawley rats (6/group) were immunized rectally on days 0, 7, 14 and 21 with a) GTF-MP alone, b) GTF-MP with cholera toxin, c) GTF-MP with detoxified mutant Escherichia coli toxin (dLT), or d) sham immunized with PLGA and cholera toxin. An additional group was immunized intranasally with GTF-MP alone. Saliva and nasal washes of all intranasally immunized rats contained IgA antibody to glucosyltransferase on day 28. Salivary IgA antibody was also detected in 7/12 rats rectally immunized with GTF-MP and cholera toxin or dLT, although responses were lower than those obtained by intranasal immunization. Most fecal extracts from rectally delivered GTF-MP plus cholera toxin or dLT rats contained IgA antibody to GTF-MP. Low levels of fecal IgA antibody were detected in 3/6 intranasally immunized rats and 2/6 rats rectally immunized with GTF-MP alone. We then examined the extent to which salivary IgA antibody induced by the rectal route could be protective. At 25, 31 and 38 days of age, two groups of female Sprague-Dawley rats (13/group) were rectally immunized with GTF-MP and cholera toxin or with empty microparticles and cholera toxin (sham group). A third group was intranasally immunized with GTF-MP alone. After demonstrating salivary IgA responses to GTF in most GTF-immunized rats, all animals were infected with streptomycin-resistant Streptococcus sobrinus and placed on diet 2000. After 79 days of infection, total caries on molar surfaces were lower in both rectally (7.9 +/- 1.0) and intranasally (7.1 +/- 0.9; P < 0.0.03) immunized groups compared with the sham-immunized group (11.9 +/- 1.6). Smooth surface caries were significantly lower (P < 0.05) in both rectally and intranasally immunized groups. These results support the interconnectedness of the mucosal immune system and indicate that rectal immunization with GTF-MP, together with adjuvant, or intranasal immunization with GTF-MP alone, can induce protective levels of salivary antibody in rats.

Immune response after oral administration of the encapsulated malaria synthetic peptide SPf66

The synthetic peptide SPf66 adsorbed on alum is one of the few Plasmodium falciparum vaccines which have been tested in field trials. We previously reported that subcutaneous administration of SPf66 loaded PLGA microparticles (MP) enhances the antibody response to this antigen compared to the conventional alum formulation. We now evaluate the suitability of polymeric formulations to obtain systemic immune responses by gastric intubation of Balb/c mice. Formulations composed of 1:1 mixtures of PLGA 50:50 and 75:25 (lactic:glycolic) microparticles were administered by the oral route, and when animals were boosted 3 weeks later significant systemic IgG antibody responses were elicited, comparable to alum triple shot and superior to the aqueous vaccine given by the oral route. The finding of IgG2a isotype for PLGA-vaccinated mice compared to the absent levels of this isotype for the alum-vaccinated group could be interpreted as a sign of Th1-like immune response and cellular immune response activation. Our results confirm that using the appropriate schedule the oral administration of PLGA particles is suitable to obtain systemic immune responses to the carried antigen.

Dental caries vaccines: prospects and concerns

Dental caries remains one of the most common infectious diseases of mankind. Cariogenic micro-organisms enter the dental biofilm early in life and can subsequently emerge, under favorable environmental conditions, to cause disease. In oral fluids, adaptive host defenses aroused by these infections are expressed in the saliva and gingival crevicular fluid. This review will focus on methods by which mucosal host defenses can be induced by immunization to interfere with dental caries caused by mutans streptococci. The natural history of mutans streptococcal colonization is described in the context of the ontogeny of mucosal immunity to these and other indigenous oral streptococci. Molecular targets for dental caries vaccines are explored for their effectiveness in intact protein and subunit (synthetic peptide, recombinant and conjugate) vaccines in pre-clinical studies. Recent progress in the development of mucosal adjuvants and viable and non-viable delivery systems for dental caries vaccines is described. Finally, the results of clinical trials are reviewed, followed by a discussion of the prospects and concerns of human application of the principles presented.

Size dependent immune response after subcutaneous, oral and intranasal administration of BSA loaded nanospheres

BSA was entrapped in particles of different sizes (200, 500 and 1000 nm) prepared from poly(D,L-lactic-co-glycolic) acid by a double emulsion method. The particles were given, either intranasally, orally or subcutaneously, to Balb/c mice and the serum IgG, IgG1 and IgG2a response elicited was compared to that obtained by the subcutaneous administration of either free antigen, free antigen emulsified 1:1 with Freund's Complete Adjuvant (FCA), or free antigen administered with Al(OH)(3). The administration of 1000 nm particles generally elicited a higher serum IgG response than that obtained with the administration of 500 or 200 nm sized nanospheres, the immune response for 500 nm particles being similar than that obtained with 200 nm by the subcutaneous and the oral route, and higher by the intranasal route. PLGA nanoparticles can elicit serum IgG2a responses by the three routes studied. No significant differences on the serum IgG2a/IgG1 ratios were found after the subcutaneous, the oral and the intranasal administration of the different spheres but those were in general higher compared to the administration of either free antigen or free antigen adsorbed to alum. The route of administration influences the serum IgG2a/IgG1 ratio after the administration of free antigen, but not after the administration of the particles. Therefore, differences on the total serum IgG response induced by particles of different sizes do not result in differences on the IgG1 or IgG2a-type immune responses, suggesting that the antigen processing and presentation is similar in all cases tested for PLGA particles.

Tissue compatibility of two biodegradable tubular scaffolds implanted adjacent to skin or buccal mucosa in mice

Radiation therapy for cancer in the head and neck region leads to a marked loss of salivary gland parenchyma, resulting in a severe reduction of salivary secretions. Currently, there is no satisfactory treatment for these patients. To address this problem, we are using both tissue engineering and gene transfer principles to develop an orally implantable, artificial fluid-secreting device. In the present study, we examined the tissue compatibility of two biodegradable substrata potentially useful in fabricating such a device. We implanted in Balb/c mice tubular scaffolds of poly-L-lactic acid (PLLA), poly-glycolic acid coated with PLLA (PGA/PLLA), or nothing (sham-operated controls) either beneath the skin on the back, a site widely used in earlier toxicity and biocompatibility studies, or adjacent to the buccal mucosa, a site quite different functionally and immunologically. At 1, 3, 7, 14, and 28 days postimplantation, implant sites were examined histologically, and systemic responses were assessed by conventional clinical chemistry and hematology analyses. Inflammatory responses in the connective tissue were similar regardless of site or type of polymer implant used. However, inflammatory reactions were shorter and without epithelioid and giant cells in sham-operated controls. Also, biodegradation proceeded more slowly with the PLLA tubules than with the PGA/PLLA tubules. No significant changes in clinical chemistry and hematology were seen due to the implantation of tubular scaffolds. These results indicate that the tissue responses to PLLA and PGA/PLLA scaffolds are generally similar in areas subjacent to skin in the back and oral cavity. However, these studies also identified several potentially significant concerns that must be addressed prior to initiating any clinical applications of this device.

Immunization against dental caries

Dental caries is one of the most common infectious diseases. Of the oral bacteria, mutans streptococci, such as Streptococcus mutans and S. sobrinus, are considered to be causative agents of dental caries in humans. There have been numerous studies of the immunology of mutans streptococci. To control dental caries, dental caries vaccines have been produced using various cell-surface antigens of these organisms. Progress in recombinant DNA technology and peptide synthesis has been applied to the development of recombinant and synthetic peptide vaccines to control dental caries. Significant protective effects against dental caries have been shown in experimental animals, such as mice, rats and monkeys, which have been subcutaneously, orally, or intranasally immunized with these antigens. Only a few studies, however, have examined the efficacy of dental caries vaccines in humans. Recently, local passive immunization using murine monoclonal antibodies, transgenic plant antibodies, egg-yolk antibodies, and bovine milk antibodies to antigens of mutans streptococci have been used to control the colonization of the organisms and the induction of dental caries in human. Such immunization procedures may be a safer approach for controlling human dental caries than active immunization.

Facilitated intranasal induction of mucosal and systemic immunity to mutans streptococcal glucosyltransferase peptide vaccines

Synthetic peptide vaccines which are derived from functional domains of Streptococcus mutans glucosyltransferases (GTF) have been shown to induce protective immunity in Sprague-Dawley rats after subcutaneous injection in the salivary gland region. Since mucosal induction of salivary immunity would be preferable in humans, we explored methods to induce mucosal antibody in the rat to the GTF peptide vaccines HDS and HDS-GLU after intranasal administration. Several methods of facilitation of the immune response were studied: the incorporation of peptides in bioadhesive poly(D,L-lactide-coglycolide) (PLGA) microparticles, the use of monoepitopic (HDS) or diepitopic (HDS-GLU) peptide constructs, or the use of mucosal adjuvants. Salivary immunoglobulin A (IgA) responses were not detected after intranasal administration of diepitopic HDS-GLU peptide constructs in alum or after incorporation into PLGA microparticles. However, significant primary and secondary salivary IgA and serum IgG antibody responses to HDS were induced in all rats when cholera holotoxin (CT) or a detoxified mutant Escherichia coli heat-labile enterotoxin (R192G LT) were intranasally administered with HDS peptide constructs in PLGA. Coadministration of LT with HDS resulted in predominantly IgG2a responses in the serum, while coadministration with CT resulted in significant IgG1 and IgG2a responses to HDS. Serum IgG antibody, which was induced to the HDS peptide construct by coadministration with these adjuvants, also bound intact mutans streptococcal GTF in an enzyme-linked immunosorbent assay and inhibited its enzymatic activity. Thus, immune responses which are potentially protective for dental caries can be induced to peptide-based GTF vaccines after mucosal administration if combined with the CT or LT R192G mucosal adjuvant.