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

The Brucella abortus S19 DeltavjbR live vaccine candidate is safer than S19 and confers protection against wild-type challenge in BALB/c mice when delivered in a sustained-release vehicle

Brucellosis is an important zoonotic disease of nearly worldwide distribution. Despite the availability of live vaccine strains for bovine (S19, RB51) and small ruminants (Rev-1), these vaccines have several drawbacks, including residual virulence for animals and humans. Safe and efficacious immunization systems are therefore needed to overcome these disadvantages. A vjbR knockout was generated in the S19 vaccine and investigated for its potential use as an improved vaccine candidate. Vaccination with a sustained-release vehicle to enhance vaccination efficacy was evaluated utilizing the live S19 DeltavjbR::Kan in encapsulated alginate microspheres containing a nonimmunogenic eggshell precursor protein of the parasite Fasciola hepatica (vitelline protein B). BALB/c mice were immunized intraperitoneally with either encapsulated or nonencapsulated S19 DeltavjbR::Kan at a dose of 1 x 10(5) CFU per animal to evaluate immunogenicity, safety, and protective efficacy. Humoral responses postvaccination indicate that the vaccine candidate was able to elicit an anti-Brucella-specific immunoglobulin G response even when the vaccine was administered in an encapsulated format. The safety was revealed by the absence of splenomegaly in mice that were inoculated with the mutant. Finally, a single dose with the encapsulated mutant conferred higher levels of protection compared to the nonencapsulated vaccine. These results suggest that S19 DeltavjbR::Kan is safer than S19, induces protection in mice, and should be considered as a vaccine candidate when administered in a sustained-release manner.

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.

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.

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.