A Brucella ovis antigenic complex bearing poly-epsilon-caprolactone microparticles confer protection against experimental brucellosis in mice

The immunostimulatory roles of gold nanoparticles in immunization and vaccination against Brucella abortus antigens

One effective antigen carrier proposed for use in immunization and vaccination is gold nanoparticles. Prior work has shown that gold nanoparticles themselves have adjuvant properties. Currently, gold nanoparticles are used to design new diagnostic tests and vaccines against viral, bacterial, and parasitic infections. We investigated the use of gold nanoparticles as immunomodulators in immunization and vaccination with an antigen isolated from Brucella abortus. Gold nanoparticles with a diameter of 15 nm were synthesized for immunization of animals and were then conjugated to the isolated antigen. The conjugates were used to immunize white BALB/c mice. As a result, high-titer (1:10240) antibodies were produced. The respiratory and proliferative activities of immune cells were increased, as were the serum interleukin concentrations. The minimum antigen amount detected with the produced antibodies was ∼ 0.5 pg. The mice immunized with gold nanoparticles complexed with the B. abortus antigen were more resistant to B. abortus strain 82 than were the mice immunized through other schemes. This fact indicates that animal immunization with this conjugate enhances the effectiveness of the immune response. The results of this study are expected to be used in further work to examine the protective effect of gold nanoparticles complexed with the B. abortus antigen on immunized animals and to develop test systems for diagnosing brucellosis in the laboratory and in the field.

Evaluation of the efficacy of polymeric antigen BLSOmp31 formulated in a new cage-like particle adjuvant (ISPA) administered by parenteral or mucosal routes against Brucella ovis in BALB/c mice

Brucella ovis is an economically important cause of epididymitis in rams worldwide. Polymeric BLSOmp31 was previously identified as a protective immunogen against this pathogen. In this study, BLSOmp31 was formulated with a modified version of ISCOMATRIX adjuvant called ISPA (BLSOmp31/ISPA) and was administered in BALB/C by the subcutaneous and ocular route. The systemic and mucosal immune responses, the opsonic activity of antibodies and the protection conferred against B. ovis were evaluated. BLSOmp31+ISPA injected subcutaneously or by ocular route induced significantly higher IgG antibody levels with a mixed Th1/Th2 profile compared to non-immunized mice. IgA and IgG were detected in sera and nasal, tracheobronchial, vaginal secretions, tears and faeces, from SC immunized mice while in the group immunized by the ocular route a slight increase in both isotypes was mainly observed in all secretions, except in vaginal fluid. Opsonic antibodies stimulated binding and increased uptake of PHrodo™ Green-labelled B. ovis by neutrophils and monocytes. BLSOmp31 administered subcutaneously induced the highest levels of IFN-ɣ. The ocular immunization not only produced significant levels of this cytokine but also IL-4 compared to non-immunized mice. Both, subcutaneous and ocular routes of immunization, significantly protected against B. ovis infection. These results indicate that BLSOmp31/ISPA administered parenterally or by ocular route is a safe and effective vaccine against B. ovis in the murine model.

Polymeric antigen BLSOmp31 formulated with class B CpG-ODN in a nanostructure (BLSOmp31/CpG-ODN/Coa-ASC16) administered by parenteral or mucosal routes confers protection against Brucella ovis in Balb/c mice

Previously, we demonstrated that the chimera BLSOmp31 formulated in chitosan microspheres or Poloxamer407-Chitosan administered via the nasal and the ocular mucosa conferred partial protection in sheep against B. ovis. In this work, we tested a new delivery system for mucosal immunization with BLSOmp31 in the murine model to improve the efficacy of previously used formulations. First, we evaluated the protective efficacy against B. ovis induced by BLSOmp31 administered by the subcutaneous route using either BLSOmp31 alone, co-administered with immunostimulatory synthetic oligodeoxynucleotides containing unmethylated cytosine-guanine motifs (CpG-ODN) or with CpG-ODN in a nanostructure called Coa-ASC16 compared with BLSOmp31 emulsified in Incomplete Freund Adjuvant. Then, we evaluated the protection conferred by the best performing formulation (BLSOmp31/CpG-ODN/Coa-ASC16) administered by both subcutaneous and ocular routes. BLSOmp31/CpG-ODN/Coa-ASC16 injected subcutaneously did not induce higher IgG antibody levels compared to BLSOmp31 alone or BLSOmp31/CpG-ODN but it did stimulate a mixed immune Th1-Th2 response with the highest levels of IFN-ɣ and conferred significant protection against the B. ovis challenge. Although ocular instillation of BLSOmp31/CpG-ODN/Coa-ASC16 showed a similar degree of protection compared to the parenteral route (3.66 and 3.60 logs of protection, respectively), it induced lower levels in serum of specific IgG (with mixed IgG1/IgG2a) and IgA antibodies and, less IFN-ɣ and IL-4 than the subcutaneous route. No antibodies were detected in vaginal lavages or saliva. Fecal antigen-specific IgA was slightly higher in mice immunized with BLSOmp31/CpG-ODN/Coa-ASC16 subcutaneously compared with the ocular route. These results indicate that BLSOmp31/CpG-ODN/Coa-ASC16 was a safe and effective vaccine against B. ovis in mice.

Poly-ϵ-caprolactone/chitosan nanoparticles provide strong adjuvant effect for hepatitis B antigen

Aim: This work aims to investigate the adjuvant effect of poly-ϵ-caprolactone/chitosan nanoparticles (NPs) for hepatitis B surface antigen (HBsAg) and the plasmid DNA encoding HBsAg (pRC/CMV-HBs). Methods: Both antigens were adsorbed onto preformed NPs. Vaccination studies were performed in C57BL/6 mice. Transfection efficiency was investigated in A549 cell line. Results: HBsAg-adsorbed NPs generated strong anti-HBsAg IgG titers, mainly of IgG1 isotype, and induced antigen-specific IFN-γ and IL-17 secretion by spleen cells. The addition of pRC/CMV-HBs to the HBsAg-adsorbed NPs inhibited IL-17 secretion but had minor effect on IFN-γ levels. Lastly, pRC/CMV-HBs-loaded NPs generated a weak serum antibody response. Conclusion: Poly-ϵ-caprolactone/chitosan NPs provide a strong humoral adjuvant effect for HBsAg and induce a Th1/Th17-mediated cellular immune responses worth explore for hepatitis B virus vaccination.

Meta-Analysis and Advancement of Brucellosis Vaccinology

Background/Objectives

In spite of all the research effort for developing new vaccines against brucellosis, it remains unclear whether these new vaccine technologies will in fact become widely used. The goal of this study was to perform a meta-analysis to identify parameters that influence vaccine efficacy as well as a descriptive analysis on how the field of Brucella vaccinology is advancing concerning type of vaccine, improvement of protection on animal models over time, and factors that may affect protection in the mouse model.

Methods

A total of 117 publications that met the criteria were selected for inclusion in this study, with a total of 782 individual experiments analyzed.

Results

Attenuated (n = 221), inactivated (n = 66) and mutant (n = 102) vaccines provided median protection index above 2, whereas subunit (n = 287), DNA (n = 68), and vectored (n = 38) vaccines provided protection indexes lower than 2. When all categories of experimental vaccines are analyzed together, the trend line clearly demonstrates that there was no improvement of the protection indexes over the past 30 years, with a low negative and non significant linear coefficient. A meta-regression model was developed including all vaccine categories (attenuated, DNA, inactivated, mutant, subunit, and vectored) considering the protection index as a dependent variable and the other parameters (mouse strain, route of vaccination, number of vaccinations, use of adjuvant, challenge Brucella species) as independent variables. Some of these variables influenced the expected protection index of experimental vaccines against Brucella spp. in the mouse model.

Conclusion

In spite of the large number of publication over the past 30 years, our results indicate that there is not clear trend to improve the protective potential of these experimental vaccines.

PLGA (85:15) nanoparticle based delivery of rL7/L12 ribosomal protein in mice protects against Brucella abortus 544 infection: A promising alternate to traditional adjuvants

There is a compelling need for the development of suitable adjuvants for human use to enhance the efficacy of the upcoming vaccines for the prevention of life threatening infections. In the current study, we have tried to explore the immunogenic potential of nanoparticles (NPs) made of PLGA (poly lactic-co-glycolic acid), a biodegradable and biocompatible polymer approved by FDA for human use after entrapping rL7/L12 protein, an immunodominant antigen of Brucella. Adjuvant properties were exhibited by the formulation as it elicited high IgG antibody titers just after first immunization which increased significantly after the booster administration. A good elicitation of the Th1 cytokines especially IFN-γ was recorded. Amongst the IgG antibody subclasses, IgG1 remained the predominant subclass to be elicited in mice serum after immunization; however IgG1/2a ratio showed a mixed profile of Th1/Th2 response. Lymphocyte proliferation assay as a marker of amplification in cellular immunity demonstrated that the splenocytes of the immunized mice had a high proliferation index with reference to the control, revealing that L7/L12 entrapping PLGA nanoparticles are potent inducer of inflammatory cell response indispensable to combat Brucella infection. Enumeration of splenic CFU after 14 days of infection with Brucella abortus 544 showed a significant reduction in log CFU of splenic bacteria in the vaccinated mice as compared to the control group. Therefore it is evident that PLGA nano formulations delivering the entrapped vaccine candidate in mice elicit specific humoral as well as cellular responses specific to the entrapped Brucella antigen. So there is much promise in this approach and this work by highlighting the adjuvant properties of the PLGA nanospheres will accelerate the development of improved vaccines safe for human as well as veterinary use.

Encapsulated Brucella ovis Lacking a Putative ATP-Binding Cassette Transporter (ΔabcBA) Protects against Wild Type Brucella ovis in Rams

This study aimed to evaluate protection induced by the vaccine candidate B. ovis ΔabcBA against experimental challenge with wild type B. ovis in rams. Rams were subcutaneously immunized with B. ovis ΔabcBA encapsulated with sterile alginate or with the non encapsulated vaccine strain. Serum, urine, and semen samples were collected during two months after immunization. The rams were then challenged with wild type B. ovis (ATCC25840), and the results were compared to non immunized and experimentally challenged rams. Immunization, particularly with encapsulated B. ovis ΔabcBA, prevented infection, secretion of wild type B. ovis in the semen and urine, shedding of neutrophils in the semen, and the development of clinical changes, gross and microscopic lesions induced by the wild type B. ovis reference strain. Collectively, our data indicates that the B. ovis ΔabcBA strain is an exceptionally good vaccine strain for preventing brucellosis caused by B. ovis infection in rams.

Evaluation in mice of Brucella ovis attenuated mutants for use as live vaccines against B. ovis infection

Brucella ovis causes ram contagious epididymitis, a disease for which a specific vaccine is lacking. Attenuated Brucella melitensis Rev 1, used as vaccine against ovine and caprine brucellosis caused by B. melitensis, is also considered the best vaccine available for the prophylaxis of B. ovis infection, but its use for this purpose has serious drawbacks. In this work, two previously characterized B. ovis attenuated mutants (Δomp25d and Δomp22) were evaluated in mice, in comparison with B. melitensis Rev 1, as vaccines against B. ovis. Similarities, but also significant differences, were found regarding the immune response induced by the three vaccines. Mice vaccinated with the B. ovis mutants developed anti-B. ovis antibodies in serum of the IgG₁, IgG_2a and IgG_2b subclasses and their levels were higher than those observed in Rev 1-vaccinated mice. After an antigen stimulus with B. ovis cells, splenocytes obtained from all vaccinated mice secreted similar levels of TNF-α and IL12(p40) and remarkably high amounts of IFN-γ, a crucial cytokine in protective immunity against other Brucella species. By contrast, IL-1α -an enhancer of T cell responses to antigen- was present at higher levels in mice vaccinated with the B. ovis mutants, while IL-10, an anti-inflammatory cytokine, was significantly more abundant in Rev 1-vaccinated mice. Additionally, the B. ovis mutants showed appropriate persistence, limited splenomegaly and protective efficacy against B. ovis similar to that observed with B. melitensis Rev 1. These characteristics encourage their evaluation in the natural host as homologous vaccines for the specific prophylaxis of B. ovis infection.

Optimization of stability, encapsulation, release, and cross-priming of tumor antigen-containing PLGA nanoparticles

PURPOSE

In order to investigate Poly (lactic-co-glycolic acid) (PLGA) nanoparticles (NP) as potential vehicles for efficient tumor antigen (TA) delivery to dendritic cells (DC), this study aimed to optimize encapsulation/release kinetics before determining immunogenicity of antigen-containing NP.

METHODS

Various techniques were used to liberate TA from cell lines. Single (gp100) and multiple (B16-tumor lysate containing gp100) antigens were encapsulated within differing molecular weight PLGA co-polymers. Differences in morphology, encapsulation/release and biologic potency were studied. Findings were adopted to encapsulate fresh tumor lysate from patients with advanced tumors and compare stimulation of tumor infiltrating lymphocytes (TIL) against that achieved by soluble lysate.

RESULTS

Four cycles of freeze-thaw + 15 s sonication resulted in antigen-rich lysates without the need for toxic detergents or protease inhibitors. The 80 KDa polymer resulted in maximal release of payload and favorable production of immunostimulatory IL-2 and IFN-γ. NP-mediated antigen delivery led to increased IFN-γ and decreased immunoinhibitory IL-10 synthesis when compared to soluble lysate.

CONCLUSIONS

Four cycles of freeze-thaw followed by 15 s sonication is the ideal technique to obtain complex TA for encapsulation. The 80 KDa polymer has the most promising combination of release kinetics and biologic potency. Encapsulated antigens are immunogenic and evoke favorable TIL-mediated anti-tumor responses.

Acellular vaccines for ovine brucellosis: a safer alternative against a worldwide disease

Ovine brucellosis is a very contagious zoonotic disease distributed worldwide and constitutes a very important zoosanitary and economic problem. The control of the disease includes animal vaccination and slaughter of infected flocks. However, the commercially available vaccine in most countries is based on the attenuated strain Brucella melitensis Rev 1, which presents important safety drawbacks. This review is focused on the most recent and promising acellular vaccine proposals.

Polymer nanoparticles containing tumor lysates as antigen delivery vehicles for dendritic cell-based antitumor immunotherapy

Encapsulation of tumor-associated antigens in polymer nanoparticles (NP) is a promising approach to enhance efficiency of antigen delivery for anti-tumor vaccines. Head and neck squamous carcinoma (HNSCC) cell lines were initially used to generate tumor-associated antigens (TAA)-containing poly (lactic-co-glycolic acid) (PLGA) NP; encapsulation efficiency and release kinetics were profiled. Findings were adopted to entrap fresh tumor lysate from five patients with advanced HNSCC. To test the hypothesis that NP enhance antigen presentation, dendritic cell (DC) produced from patient blood monocyte precursors were loaded with either the un-encapsulated or NP-encapsulated versions of tumor lysates. These were used to stimulate freshly-isolated autologous CD8+ T cells. In four of five patients, anti-tumor CD8+ T cells showed significantly increased immunostimulatory IFN-γ (p=0.071) or decreased immmunoinhibitory IL-10 production (p=0.0004) associated with NP-mediated antigen delivery. The observations represent an enabling step in the production of clinically-translatable, inexpensive, highly-efficient, and personalized polymer-based immunotherapy for solid organ malignancies.

FROM THE CLINICAL EDITOR

Enhancing the antigen presentation may be a viable approach to increase the efficiency of tumor cell directed cytotoxicity via immune mechanisms. This study presents an example for this using head and neck cancer cell lines and nanotechnology-based encapsulated antigen presentation to dendritic cells. The observed CD8+ T-cell response was significantly enhanced. This method may pave the way to a highly efficient cancer cell elimination method with minimal to no toxicity.

Stability of poly(epsilon-caprolactone) microparticles containing Brucella ovis antigens as a vaccine delivery system against brucellosis

In previous works, our research group has successfully proved the use of subcellular vaccines based on poly(epsilon-caprolactone) (PEC) microparticles containing an antigenic extract of Brucella ovis (HS) against experimental brucellosis in both mice and rams. However, the successful exploitation of pharmaceutical products, and therefore of this product as veterinary vaccine, requires preservation of both biological activity and native structure in all steps of development from purification to storage. In this context, we have carried out an accelerated stability study to evaluate the relative stability of HS when loading in PEC microparticles. For this purpose, freeze-dried microparticles were stored at 40 +/- 1 degrees C and 75% RH as a preliminary analysis of a stability testing. The results showed that both physico-chemical (size, morphology, antigen content, release profile) and biological (integrity and antigenicity of the HS) properties were preserved after 6 months of storage. On the contrary, after 1 year of storage, the HS release profile was dramatically affected probably due to a progressive loss of the polymer microstructure. In addition, the degradation and loss of the antigenicity of the HS components was also evident by SDS-PAGE and immunoblotting analysis. In fact, after 12 months of storage, only the integrity and antigenicity of two of the major protective proteins of the HS antigenic complex were preserved.

Streptococcus equi antigens adsorbed onto surface modified poly-epsilon-caprolactone microspheres induce humoral and cellular specific immune responses

Streptococcus equi subsp. equi is the causative agent of Strangles, which is one of the most costly and widespread infectious diseases, affecting the respiratory tract of Equidae. In this work, polyvinyl alcohol, alginate and chitosan were used in formulations of surface modified poly-epsilon-caprolactone microspheres which were evaluated after adsorption of S.equi enzymatic extract for physicochemical characteristics and in vivo immune responses in mice. After subcutaneous immunisation, the formulations induced higher lymphokines levels, in accordance with cellular and humoral immune responses, as compared to the free antigen, successfully activating the paths leading to Th1 and Th2 cells. The obtained results highlight the role of these microspheres as an adjuvant and their use to protect animals against strangles.

Optimization of the entrapment of bacterial cell envelope extracts into microparticles for vaccine delivery

The encapsulation of a Brucella ovis extract (HS) in microparticles has been proved effective against experimental infections in mice. This work describes different strategies to increase the HS loading and prepare large batches as necessary to test this vaccine in ovine. The mixture of HS with beta-cyclodextrin was optimized in order to increase the HS loading in microparticles. On the other hand, TROMS ('Total Recirculation One-Machine System') led microparticles with a more homogeneous size than the laboratory or standard procedure. Moreover, the initial burst release of HS from the standard microparticles was higher than for the TROMS ones. In fact, standard microparticles displayed a higher amount of adsorbed HS. On the contrary, both preparative methods were found effective to preserve the integrity and anti-genicity of the loaded HS. In summary, beta-CD can be used to increase the loading of large hydrophobic materials and TROMS is a valid large production of antigen-loaded microparticles.

Polymer Nanoparticles for Immunotherapy from Encapsulated Tumor-Associated Antigens and Whole Tumor Cells

Encapsulation of tumor-associated antigens (TAA) in polymer nanoparticles is a promising approach to increasing the efficiency of antigen (Ag) delivery for antitumor vaccines. We optimized a polymer preparation method to deliver both defined tumor-associated proteins and the complex mixtures of tumor Ags present in tumors. Tumor Ags were encapsulated in a biodegradable, 50:50 poly(D,L-lactide co-glycolide) copolymer (PLGA) by emulsification and solvent extraction. Two particular Ags were studied, gp100 (a melanoma-associated antigen) and ovalbumin (OVA), as well as mixtures of proteins and lysates of tumor cells. The efficiency of encapsulation was measured by protein assays of dissolved nanoparticles. Ag stability after release from nanoparticles was verified by SDS-acrylamide gel electrophoresis and Western blot analysis. Molecular weight and protein loading interact to define the encapsulation efficiency and release rate of nanoparticles formulated from 50:50 PLGA. A midrange molecular weight polymer had more desirable release properties at 100 mg/mL than at 50 mg/mL protein loading, indicating the need for optimization of nanoparticle formulation for preparations with different particle loadings. Mixtures of proteins derived from cell lysates were reliably encapsulated into nanoparticles, which released the spectrum of proteins contained in lysates. Antigenic proteins were co-encapsulated with cell lysate and released from nanoparticles; these Ags retained their antigenicity and functioned better than soluble Ags when tested in in vitro assays of T cell cytokine formation and in vivo tumor vaccination challenge.

Intradermal immunization with ovalbumin-loaded poly-?-caprolactone microparticles conferred protection in ovalbumin-sensitized allergic mice

BACKGROUND

Although immunotherapy has been reported as the only treatment able to revert the T-helper type 2 (Th2) response, its administration has some disadvantages such as the requirement of multiple doses, possible side-effects provoked by conventional adjuvants and the risk of suffering an anaphylactic shock. For these reasons, drug-delivery systems appear to be a promising strategy due to its ability to (i) transport the allergens, (ii) protect them from degradation, (iii) decrease the number of administrations and (iv) act as immuno-adjuvants.

OBJECTIVE

The aim of this work was to evaluate the properties of poly-epsilon-caprolactone (PCL) microparticles as adjuvants in immunotherapy using ovalbumin (OVA) as an allergen model. For this purpose, the protection capacity of these microparticles (OVA PCL) against OVA allergy was studied in a murine model.

METHODS

The humoral and cellular-induced immune response generated by OVA encapsulated into PCL microparticles was studied by immunizing BALB/c mice intradermically. Also, OVA-sensitized mice were treated with OVA PCL and OVA adsorbed to aluminium hydroxide (OVA-Alum). Fifteen days after therapy, animals were challenged with OVA and different signs of anaphylactic shock were evaluated.

RESULTS

One single shot by an intradermal route with OVA PCL resulted in a Th2-type immune response. In OVA-sensitized mice, treatment with OVA PCL elicited high OVA-specific IgG but low levels of IgE. Furthermore, OVA PCL mice group displayed lower levels of serum histamine and higher survival rate in comparison with the positive control group.

CONCLUSION

The anaphylactic shock suffered by OVA PCL-treated mice was weaker than the one induced in the OVA-Alum group. Hence, the intradermal immunization with OVA PCL microparticles induced hyposensitization in OVA-allergic mice.

Encapsulation of antigenic extracts of Salmonella enterica serovar

The properties of drug-vaccine delivery systems based on the use of biodegradable polymers, and its application in the control of experimental infection by Salmonella enterica serovar. Abortusovis (SAO), are described in this manuscript. Micelles of major membrane antigens from SAO (HSao extract) can be encapsulated in microparticles of poly(epsilon-caprolactone) or in nanoparticles of Gantrez polymer. The encapsulation process was optimized by the combined use of cyclodextrins. The resulting particles contained unaltered significant amounts of the antigenic complex. To establish the protective value of these subunit vaccines, particles were injected in one single dose (20 microg of HSao) subcutaneously in BALB/c mice in order to observe the protection conferred against experimental infection with the virulent strains S. Abortusovis 15/5. Control non-immunized animals resulted infected, as well as the group that received unloaded or HSao loaded into microparticles. In contrast, nanoparticles conferred a significant protection when compared to unvaccinated controls, similar to that induced by the attenuated commercial vaccine Rv6. In conclusion, protection against experimental infection in mice after one single shoot, and its potential for mucosal vaccination suggest that HSao-nanoparticles may represent a serious alternative to the conventional attenuated vaccines against S. Abortusovis.

Mucosal delivery of vaccines in domestic animals

Mucosal vaccination is proving to be one of the greatest challenges in modern vaccine development. Although highly beneficial for achieving protective immunity, the induction of mucosal immunity, especially in the gastro-intestinal tract, still remains a difficult task. As a result, only very few mucosal vaccines are commercially available for domestic animals. Here, we critically review various strategies for mucosal delivery of vaccines in domestic animals. This includes live bacterial and viral vectors, particulate delivery-systems such as polymers, alginate, polyphosphazenes, immune stimulating complex and liposomes, and receptor mediated-targeting strategies to the mucosal tissues. The most commonly used routes of immunization, strategies for delivering the antigen to the mucosal surfaces, and future prospects in the development of mucosal vaccines are discussed.

Brucella outer membrane complex-loaded microparticles as a vaccine against Brucella ovis in rams

Due to the important drawbacks of the Brucella melitensis Rev 1 vaccine, a safer vaccine based on an outer membrane complex from Brucella ovis encapsulated in poly-epsilon-caprolactone (PEC) microparticles (MP) was developed and tested in rams. Homogeneous batches of microparticles were prepared by a new double emulsion solvent evaporation method called "Total Recirculation One-Machine System" (TROMS). Such microparticles presented a mean diameter of 2 microm and displayed an antigen loading of about 13 microg HS per mg of microparticles. Subcutaneous vaccination of rams with 800 microg HS (hot saline antigenic extract of B. ovis) in PEC microparticles induced an adequate serological response against B. ovis antigens and conferred similar protection against challenge with B. ovis to that induced by the living attenuated B. melitensis Rev 1 reference vaccine. By contrast, lower doses (80 microg) of HS-PEC evoked reduced serological responses against B. ovis antigens and did not induce significant protection. The revaccination with 800 microg of HS-PEC increased the intensity and duration of the serological response against B. ovis antigens but did not improve the protection conferred by the single vaccination. Sample sera taken from any of the animals immunized with Rev 1 were seropositive in both Rose Bengal and the Complement Fixation tests (RBT, CFT) used for the diagnosis of smooth Brucella infections. By contrast, no positive reactors in both tests were recorded in the animals vaccinated with HS-PEC, being this a target objective of this study. HS-PEC microparticles can be used as a safe vaccine against brucellosis in rams, but further studies using higher doses of antigens are necessary to exploit their full potential for the prophylaxis of brucellosis in sheep.

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.

Microencapsulated subunit vaccine approach to enterotoxigenic Escherichia coli and other mucosal pathogens

Infections of the intestinal, urogenital, and respiratory tracts are serious health problems worldwide from both a morbidity and mortality perspective. Mucosal pathogens attach to surfaces of mucosa as a prerequisite for colonization and subsequent pathogenesis. By expressing various surface adhesins (colonization factors, CF) they are able to bind to specific mucosal receptors. Enterotoxigenic Escherichia coli (ETEC) can express numerous CF that allow them to attach to a variety of hosts. Mucosal immunity directed against pathogenic microorganisms is critical in host protection with secretory IgA being particularly important in preventing microoganisms from colonizing host cells. M cells likewise have an important immunological function in the small intestines by binding and transporting antigens to lymphocytes and macrophages thus enhancing the immune response. The use of subunit vaccines, such as antigen encapsulated microspheres, can act to effectively deliver specific antigens so as to optimize their immunological response. With the threat of bioterrorism becoming a reality in recent years, the miroencapsulation of antigens from potential bioterrorist agents may be an effective method of delivery so as to induce a level of protection in at risk individuals. The encapsulation of ETEC colonization factors in microspheres and their subsequent administration in small animals and humans has been conducted for many years. Evidence suggests that this type of delivery system for ETEC antigens may enhance their immunogenicity and provide protection against this microorganism.

Influence of the co-encapsulation of different excipients on the properties of polyester microparticle-based vaccine against brucellosis

This work evaluates the influence of different pharmaceutical auxiliaries (Pluronic F68, polyvinylpyrrolidone [PVP] or Tween 20), when mixed with an antigenic extract from Brucella ovis (hot saline; HS), on the characteristics of the resulting poly(epsilon-caprolactone) (PEC) and poly(lactide-co-glycolide) (PLGA) microparticles. In all cases, PEC microparticles were smaller than PLGA ones. Concerning the HS loading, PLGA microparticles were highly dependent on the type of the excipient used, whereas all the PEC formulations displayed similar encapsulation efficiencies. For both types of microparticles, the presence of PVP induced a burst release effect. On the contrary, the use of Tween 20 or Pluronic F68 dramatically modified this profile. For PLGA-Tween 20 and PEC-Pluronic F68 microparticles, the HS was released in a pulsatil way during the first 7 days followed by a continuous release for at least 3 weeks. The antigenicity of the HS components was kept in all cases. Phagocytosis by murine monocytes showed a clear difference based just on the hydrophobicity of the polymer, being PEC microparticles better engulfed. Cell activation quantified by the release of H2O2 did not showed major differences between batches, however, microparticles of PEC and Pluronic F68 induced the highest nitric oxide production. Together, these results confirm the advantageous qualities of the "HS-PEC-Pluronic F68 microparticles" as favorable candidate for vaccine purposes against brucellosis.

A prolonged immune response to antigen delivered in poly (epsilon-caprolactone) microparticles

A single dose vaccine formulation which induces both humoral and cell-mediated immune responses over a prolonged period would provide a potent weapon against infectious disease. We have used a water-in-oil-in-oil, solvent evaporation method for generating poly epsilon-caprolactone microparticles and tested their ability to induce an immune response against the model antigen ovalbumin. We hypothesized that the initial release of antigen from the surface of the poly epsilon-caprolactone microparticles would act as the priming dose and that the delayed release over the following months, due to diffusion from or break-down of the microparticles, would act as a boost to the immune response. Ovalbumin encapsulated in the poly epsilon-caprolactone microparticles was able to induce both antibody and cell-mediated immune responses. However our results suggest that the spontaneous release had little effect on the immune response. Despite this the response was maintained for at least 8 months following a single immunization. Both humoral and cell-mediated immune responses were induced in mice. This simple method of vaccine formulation offers a cost-efficient way to deliver antigen in a single dose to the immune system.

The recombinant Omp31 from Brucella melitensis alone or associated with rough lipopolysaccharide induces protection against Brucella ovis infection in BALB/c mice

Immunogenicity and protective activity against Brucella ovis of detergent-extracted recombinant Omp31 (rOmp31 extract) from Brucella melitensis produced in Escherichia coli, purified rough lipopolysaccharide from B. ovis (R-LPS) and a mixture of rOmp31 extract and R-LPS (rOmp31 extract + R-LPS) were assessed in BALB/c mice. The experimental vaccines were compared with a hot saline extract (HS extract) from B. ovis mainly composed of outer membrane proteins (OMPs) and R-LPS, and known to be protective in mice against a B. ovis infection. Serum antibodies to Omp31 and R-LPS were detected in the corresponding mice using Western blotting with B. ovis whole-cell lysates and ELISA with purified antigens. Protection was evaluated by comparing the levels of infection in the spleens of vaccinated mice challenged with B. ovis. A significantly lower number of B. ovis colony-forming units in spleens relative to unimmunized (saline injected) controls were considered as protection. Mice immunized with rOmp31 extract or rOmp31 extract mixed with R-LPS developed antibodies that bound to the B. ovis surface with similar titers. Vaccination with rOmp31 extract plus R-LPS provided the best protection level, which was comparable with that given by HS extract. Similar protection was also obtained with rOmp31 extract alone and, to a lesser degree, with R-LPS. Comparisons between groups showed that an extract from E. coli-pUC19 (devoid of Omp31) provided no protection relative to either HS extract, rOmp31 extract or rOmp31 extract mixed with R-LPS. In conclusion, the recombinant Omp31 associated or not with B. ovis R-LPS, could be an interesting candidate for a subcellular vaccine against B. ovis infection.

Development of microparticles prepared by spray-drying as a vaccine delivery system against brucellosis

The antigenic extract Hot Saline from Brucella ovis was microencapsulated by the spray-drying technique with different polyesters (poly-lactide-co-glycolide RG502H [PLGA], and blends with poly- epsilon -caprolactone [PEC]) in order to obtain microparticles smaller than 5 microm. Microparticles were tested for encapsulation efficiency, release studies, acidification of the in vitro release medium, and in vitro J744-macrophage experiments (phagocytosis and toxicity of the preparations) to determine the optimal formulation for vaccination purposes. Formulation containing no PCL showed the highest encapsulation efficiency, although the differences were not significant. The in vitro release kinetics were characterized by a high burst effect after 1 h of incubation, followed by a slow and continuous release. For the formulation based on PLGA, the pH of the medium during release dropped from 7.4 to 3.5 while the presence of PEC attenuated the pH drop. All formulations showed light toxicity by the MTT assay, but differences were observed in terms of phagocytosis, as particles prepared with PEC showed the higher uptake by J744-macrophages and cell respiratory burst, determined by oxygen peroxide release. All these characteristics suggest that the microparticulated antigenic formulation containing the higher ratio of PEC is susceptible to be used in animal vaccination studies.