Dressing liposomal particles with chitosan and poly(vinylic alcohol) for oral vaccine delivery.

Liposomes have been used as adjuvants since 1974. One major limitation for the use of liposomes in oral vaccines is the lipid structure instability caused by enzyme activities. Our aim was to combine liposomes that could encapsulate antigens (i.e., Dtxd, diphtheria toxoid) with chitosan, which protects the particles and promotes mucoadhesibility. We employed physical techniques to understand the process by which liposomes (SPC: Cho, 3:1) can be sandwiched with chitosan (Chi) and stabilized by PVA (poly-vinylic alcohol), which are biodegradable, biocompatible polymers. Round, smooth-surfaced particles of REVs-Chi (reversed-phase vesicles sandwiched by Chi) stabilized by PVA were obtained. The REVs encapsulation efficiencies (Dtxd was used as the antigen) were directly dependent on the Chi and PVA present in the formulation. Chi adsorption on the REVs surface was accompanied by an increase of ζ-potential. In contrast, PVA adsorption on the REVs-Chi surface was accompanied by a decrease of ζ-potential. The presence of Dtxd increased the Chi surface-adsorption efficiency. The PVA affinity by mucine was 2,000 times higher than that observed with Chi alone and did not depend on the molecule being in solution or adsorbed on the liposomal surface. The liberation of encapsulated Dtxd was retarded by encapsulation within REVs-Chi-PVA. These results lead us to conclude that these new, stabilized particles were able to be adsorbed by intestinal surfaces, resisted degradation, and controlled antigen release. Therefore, REVs-Chi-PVA particles can be used as an oral delivery adjuvant.

Diphtheria toxoid conformation in the context of its nanoencapsulation within liposomal particles sandwiched by chitosan.

Chitosan (α-(1-4)-amino-2-deoxy-ß-D-glucan) is a deacetylated form of chitin, a polysaccharide from crustacean shells. Its unique characteristics, such as positive charge, biodegradability, biocompatibility, nontoxicity, and rigid structure, make this macromolecule ideal for an oral vaccine delivery system. We prepared reverse-phase evaporation vesicles (REVs) sandwiched by chitosan (Chi) and polyvinylic alcohol (PVA). However, in this method, there are still some problems to be circumvented related to protein stabilization. During the inverted micelle phase of protein nanoencapsulation, hydrophobic interfaces are expanded, leading to interfacial adsorption, followed by protein unfolding and aggregation. Here, spectroscopic and immunological techniques were used to ascertain the effects of the Hoffmeister series ions on diphtheria toxoid (Dtxd) stability during the inverted micelle phase. A correlation was established between the salts used in aqueous solutions and the changes in Dtxd solubility and conformation. Dtxd α-helical content was quite stable, which led us to conclude that encapsulation occurred without protein aggregation or without exposition of hydrophobic residues. Dtxd aggregation was 98% avoided by the kosmotropic, PO(2-)(4). This ion was used to prepare a stable Dtxd and immunologically recognized REV-Chi-PVA formulation in the presence of 50 mM of PO(2-)(4). Under these conditions, the Dtxd retained its immunological identity. Therefore, we could obtain the maximum Dtxd solubility and stability after contact with CH(3)CO(2)C(2)H(5) to begin its nanoencapsulation within ideal conditions. This was a technological breakthrough, because a simple solution, such as salt, addition avoided heterologous protein use.

Evaluation of a diphtheria and tetanus PLGA microencapsulated vaccine formulation without stabilizers.

Polymeric microspheres containing diphtheria and tetanus toxoids were prepared without protein stabilizers. A vaccine containing 2 Lf(tetanus) and 0.4 Lf(diphtheria) was injected either in BALB/c mice or in guinea-pigs. As control, a group received the alum-adsorbed unencapsulated toxoids. In mice, on day 44 one group and control received a booster and at day 111 the other group received the same booster dose. Before de booster, all groups had very low neutralizing antibodies, as determined by Toxin binding inhibition assay. One week after booster all groups had high antibody titers, especially those immunized with microencapsulated vaccine, which were at least 5 times higher than those immunized with alum vaccine for both antigens. Besides, guinea pigs receiving lower dose had antibodies titers as high as 60 UI/mL, and 30 times higher than those immunized with alum vaccine. Therefore by using an encapsulated vaccine without any kind of protein stabilizer we were able to induce in vivo protective responses irrespective of observed in vitro protein degradation by HPLC. Manipulating the vaccination schedule at the same time to the toxoids encapsulation does not only increase the antibody titers but also their specificity.

Lactic acid triggers, in vitro, thiomersal to degrade protein in the presence of PLGA microspheres.

Microspheres of polymers like poly(lactic-co-glycolic acid) (PLGA) have been studied as a vehicle for controlled release vaccines. They require materials and processes that might change the protein antigenicity. Lactic acid is produced during microsphere degradation that occurs in tandem with protein liberation. In addition, most of the proteins that have been used in microencapsulation studies contain Thimerosal((R))(TM) and this can introduce another undesirable effect for their stability. We demonstrated in vitro that the thiosalycilic acid (TSA), produced after the reduction of TM by lactic acid, reduces the S-S bridge of the previously incubated diphtheric toxoid (Dtxd). This reduction is immediately followed by blocking the two -SH formed by the same TSA molecules. In the light of these conclusions it is necessary now, to reinterpret the in vitro protein degradation-stabilization data in the presence of PLGA microspheres, mainly for those proteins which contain S-S. We propose that all the PLGA microspheres microencapsulation studies and protein structural considerations should be done in the absence of TM as preservative.

Combination of pneumococcal surface protein A (PspA) with whole cell pertussis vaccine increases protection against pneumococcal challenge in mice.

Streptococcus pneumoniae is the leading cause of respiratory acute infections around the world. In Latin America, approximately 20,000 children under 5 years of age die of pneumococcal diseases annually. Pneumococcal surface protein A (PspA) is among the best-characterized pneumococcal antigens that confer protection in animal models of pneumococcal infections and, as such, is a good alternative for the currently available conjugated vaccines. Efficient immune responses directed to PspA in animal models have already been described. Nevertheless, few low cost adjuvants for a subunit pneumococcal vaccine have been proposed to date. Here, we have tested the adjuvant properties of the whole cell Bordetella pertussis vaccine (wP) that is currently part of the DTP (diphtheria-tetanus-pertussis) vaccine administrated to children in several countries, as an adjuvant to PspA. Nasal immunization of BALB/c mice with a combination of PspA5 and wP or wP(low)--a new generation vaccine that contains low levels of B. pertussis LPS--conferred protection against a respiratory lethal challenge with S. pneumoniae. Both PspA5-wP and PspA5-wP(low) vaccines induced high levels of systemic and mucosal antibodies against PspA5, with similar profile, indicating no essential requirement for B. pertussis LPS in the adjuvant properties of wP. Accordingly, nasal immunization of C3H/HeJ mice with PspA5-wP conferred protection against the pneumococcal challenge, thus ruling out a role for TLR4 responses in the adjuvant activity and the protection mechanisms triggered by the vaccines. The high levels of anti-PspA5 antibodies correlated with increased cross-reactivity against PspAs from different clades and also reflected in cross-protection. In addition, passive immunization experiments indicated that antibodies played an important role in protection in this model. Finally, subcutaneous immunization with a combination of PspA5 with DTP(low) protected mice against challenge with two different pneumococcal strains, opening the possibility for the development of a combined infant vaccine composed of DTP and PspA.

Bordetella pertussis monophosphoryl lipid A as adjuvant for inactivated split virion influenza vaccine in mice.

The world production capacity of influenza vaccines is a concern in face of the potential influenza pandemic. The use of adjuvants could increase several fold the current installed production capacity. Bordetella pertussis monophosphyl lipid A (MPLA) was produced by acid hydrolysis of LPS, obtained as a by-product of its removal from cellular pertussis vaccine, generating a product with 4 side chains. We have investigated different formulations including MPLA alone or combined with Al(OH)(3) as adjuvants for an inactivated split virion influenza vaccine. Our results demonstrate that MPLA at concentrations as low as 0.01 microg per dose of vaccine is effective, even with a 4-fold reduction of the regular vaccine dose, as measured by the induction of protective hemagglutination inhibition (HAI) titers. Al(OH)(3) can be combined with 0.01-10 microg MPLA, inducing even higher immune responses. Al(OH)(3) caused a drift of the immune response induced by the vaccine towards a Th2 profile, as evaluated by an increase in the IgG1:IgG2a ratio, while MPLA showed a more balanced response. Moreover, the use of MPLA and Al(OH)(3) combination led to the induction of the highest IgG levels together with the secretion of both IFN-gamma and IL-4. Although cell-mediated immune responses have not been usually taken into account for influenza vaccine formulations, they may be relevant for the induction of cross-protection as well as immunological memory for both inter-pandemic and pandemic influenza vaccines. Our results indicate that a more favorable profile of both humoral and cell-mediated immune responses may be obtained using the MPLA/Al(OH)(3) formulation.

LUVs recovered with Chitosan: a new preparation for vaccine delivery.

Chitosan, alpha-(1-4)-amino-2-deoxy-beta-D-glucan, is a deacetylated form of chitin, an abundant natural polysaccharide present in crustacean shells. Its unique characteristics such as positive charge, biodegradability, biocompatibility, nontoxicity, and rigid linear molecular structure make this macromolecule ideal as drug carrier. The association between chitosan and liposomes was carefully described, where REVs (reverse phase evaporation vesicles) were sandwiched by chitosan. The usage of these particles in vaccine formulation is here proposed for the first time in the literature. The Chitosan-REVs now stabilized by polyvinilic alcohol were the vehicle for Diphtheria toxoid (Dtxd). Round chitosan-sandwiched REVs (REVs-Chi) particles of 373 +/- 17 nm containing 65% Dtxd were obtained. After 200 min of incubation in a simulated gastric fluid, 70% of the Dtxd was liberated from REVs-Chi in comparison to 100% of Dtxd liberated from pure REVs. In PBS, the Dtxd liberation from REVS-Chi was about 60%. Mice were immunized with Dtxd encapsulated within REVs-Chi and with other REVs/Dtxd formulations adsorbed onto Freund adjuvant or alumen [AIF and Al(OH)(3)]. The response patterns and the immune maturity were measured by IgG(1) and IgG(2a) titrations. REVs-Chi containing Dtxd elicited both antibodies production giving the animals higher immune response and selectivity. It was interesting that the memory of those mice immunized with REVs-Chi containing Dtxd enhanced, after booster, antibody production by 47% in contrast with 17 and 7% in mice immunized with the antigen vehiculated in REVs-AIF or REVs-Al(OH)(3), respectively.

Combination of Pneumococcal Surface Protein A (PspA)with Whole Cell Pertussis Vaccine Increases ProtectionAgainst Pneumococcal Challenge in Mice

Streptococcus pneumoniae is the leading cause of respiratory acute infections around the world. In Latin America, approximately 20,000 children under 5 years of age die of pneumococcal diseases annually. Pneumococcal surface protein PspA) is among the best-characterized pneumococcal antigens that confer protection in animal models of pneumococcal infections and, as such, is a good alternative for the currently available conjugated vaccines. Efficient immune responses directed to PspA in animal models have already been described. Nevertheless, few low cost adjuvants for a subunit pneumococcal vaccine have been proposed to date. Here, we have tested the adjuvant properties of the whole cell Bordetella pertussis vaccine (wP) that is currently part of the DTP (diphtheria-tetanus-pertussis) vaccine administrated to children in several countries, as an adjuvant to PspA. Nasal immunization of BALB/c mice with a combination of PspA5 and wP or wPlow – a new generation vaccine that contains low levels of B. pertussis LPS – conferred protection against a respiratory lethal challenge with S. pneumoniae. Both PspA5-wP and PspA5-wPlow vaccines induced high levels of systemic and mucosal antibodies against PspA5, with similar profile, indicating no essential requirement for B...

Ionic interfaces and diphtheria toxoid interactions.

We present here a systematic study on the purification of the diphtheria toxoid (Dtxd) produced at the Instituto Butantan, by adding only one step on the entire process of its production. Aliquots of 1.0 ml of Dtxd were added to an equal amount of Q-Sepharose previously equilibrated with 500 mM Tris, pH 5.0-9.0 (increments of 0.5 pH units). The best condition for the Dtxd monomer adsorption was achieved at pH 9.0. The best condition for desorption was obtained with 300 mM NaCl. After studying the gel binding capacity for Dtxd, a column (C20/20) equilibrated with 500 mM Tris, pH 9.0, was prepared. The purification factor for Dtxd was 1.5. The final recovery of Dtxd was 68.75%, with 90.31% purity. The process methodology presented here is a very realistic sequence of separation steps, which is perfectly compatible with the production requirements. Vaccination with "toxoid highly purified toxin" is known to confer a strong immunity on people in the absence of undesirable reactions, which led experts of European Pharmacopoeia to recommend its use both for children and adult vaccination.

Ionic interfaces and diphtheria toxoid interactions

We present here a systematic study on the purification of the diphtheria toxoid (Dtxd) produced at the Instituto Butantan, byadding only one step on the entire process of its production. Aliquots of 1.0 ml of Dtxd were added to an equal amount of QSepharosepreviously equilibrated with 500mM Tris, pH 5.0–9.0 (increments of 0.5 pH units). The best condition for the Dtxdmonomer adsorption was achieved at pH 9.0. The best condition for desorption was obtained with 300mM NaCl. After studyingthe gel binding capacity for Dtxd, a column (C20/20) equilibrated with 500mM Tris, pH 9.0, was prepared. The purification factorfor Dtxd was 1.5. The final recovery of Dtxd was 68.75%, with 90.31% purity. The process methodology presented here is a veryrealistic sequence of separation steps, which is perfectly compatible with the production requirements. Vaccination with ‘‘toxoidhighly purified toxin’’ is known to confer a strong immunity on people in the absence of undesirable reactions, which led experts ofEuropean Pharmacopoeia to recommend its use both for children and adult vaccination.