Evidence for the denaturation of recombinant hepatitis B surface antigen on aluminium hydroxide gel

Biodegradable concanavalin A functionalized polycaprolactone nanoparticle: A promising avenue for cancer therapy

OBJECTIVE

Receptor-based tumor-selective delivery of therapeutic efficacy and therapeutic index of cytotoxic drugs that exhibit dose-limiting toxicity is observed. Concanavalin A (Con A) was selected as the ligand for the proposed system, which was appended to the polycaprolactone nanoparticles (NPs) carrying the drug to be a very efficient approach for the treatment of cancer.

METHODS

Preparation of plain polycaprolactone nanoparticles was carried out employing the emulsion diffusion evaporation technique. Con A was conjugated using carbodiimide chemistry by coupling -COOH group on the surface of nanoparticles. The paclitaxel-loaded Con A-conjugated nanoparticles were further subjected to the characterization of various parameters, that is, surface morphology, particle size, and polydispersity index. In vitro drug release study of both the formulations (plain & conjugated) was done using a dialysis tube up to 48 h in phosphate buffer (pH 7.4).

RESULTS

Studies done in xenograft models evidently propose a dose-dependent cytotoxicity response, that is, shrink in % cell growth with increase in the concentration of the drug. The fluorescence photomicrograph clearly revealed the access of the Con A-conjugated nanoparticles to the tumor. A noteworthy biodistribution difference of the paclitaxel from prepared systems was observed. At the same time, Con A-coupled nanoparticles increased the accumulation of paclitaxel in the tumor cells.

CONCLUSIONS

Hence, the Con A-conjugated nanoparticles formulation as compared to uncoupled solid lipid nanoparticles formulation and free drug solution showed nearly two times higher uptake because of the lectin receptors on the surface of tumors. Hence, it was envisaged to design polymeric nanoparticles which would be administered intravenously for better therapeutic efficacy.

Microcrystalline Tyrosine (MCT®): A Depot Adjuvant in Licensed Allergy Immunotherapy Offers New Opportunities in Malaria

Microcrystalline Tyrosine (MCT^®) is a widely used proprietary depot excipient in specific immunotherapy for allergy. In the current study we assessed the potential of MCT to serve as an adjuvant in the development of a vaccine against malaria. To this end, we formulated the circumsporozoite protein (CSP) of P. vivax in MCT and compared the induced immune responses to CSP formulated in PBS or Alum. Both MCT and Alum strongly increased immunogenicity of CSP compared to PBS in both C57BL/6 and BALB/c mice. Challenge studies in mice using a chimeric P. bergei expressing CSP of P. vivax demonstrated clinically improved symptoms of malaria with CSP formulated in both MCT and Alum; protection was, however, more pronounced if CSP was formulated in MCT. Hence, MCT may be an attractive biodegradable adjuvant useful for the development of novel prophylactic vaccines.

Mechanistic Analysis of the Effect of Deamidation on the Immunogenicity of Anthrax Protective Antigen

The spontaneous modification of proteins, such as deamidation of asparagine residues, can significantly affect the immunogenicity of protein-based vaccines. Using a "genetically deamidated" form of recombinant protective antigen (rPA), we have previously shown that deamidation can decrease the immunogenicity of rPA, the primary component of new-generation anthrax vaccines. In this study, we investigated the biochemical and immunological mechanisms by which deamidation of rPA might decrease the immunogenicity of the protein. We found that loss of the immunogenicity of rPA vaccine was independent of the presence of adjuvant. We assessed the effect of deamidation on the immunodominant neutralizing B-cell epitopes of rPA and found that these epitopes were not significantly affected by deamidation. In order to assess the effect of deamidation on T-cell help for antibody production elicited by rPA vaccine, we examined the ability of the wild-type and genetically deamidated forms of rPA to serve as hapten carriers. We found that when wild-type and genetically deamidated rPA were modified to similar extents with 2,4-dinitrophenyl hapten (DNP) and then used to immunize mice, higher levels of anti-DNP antibodies were elicited by wild-type DNP-rPA than those elicited by the genetically deamidated DNP-rPA, indicating that wild-type rPA elicits more T-cell help than the genetically deamidated form of the protein. These results suggest that a decrease in the ability of deamidated rPA to elicit T-cell help for antibody production is a possible contributor to its lower immunogenicity.

Comparable quality attributes of hepatitis E vaccine antigen with and without adjuvant adsorption-dissolution treatment

Most vaccines require adjuvants for antigen stabilization and immune potentiation. Aluminum-based adjuvants are the most widely used adjuvants for human vaccines. Previous reports demonstrated the preservation of antigen conformation and other antigen characteristics after recovery from adjuvanted Hepatitis B and human papillomavirus vaccines. In this study, we used a combination of various physiochemical and immunochemical methods to analyze hepatitis E vaccine antigen quality attributes after recovery from adjuvants. All biochemical and biophysical methods showed similar characteristics of the p239 protein after recovery from adjuvanted vaccine formulation compared to the antigen in solution which never experienced adsorption/desorption process. Most importantly, we demonstrated full preservation of key antigen epitopes post-recovery from adjuvanted vaccine using a panel of murine monoclonal antibodies as exquisite probes. Antigenicity of p239 was probed with a panel of 9 mAbs using competition/blocking ELISA, surface plasmon resonance and sandwich ELISA methods. These multifaceted analyses demonstrated the preservation of antigen key epitopes and comparable protein thermal stability when adsorbed on adjuvants or of the recovered antigen post-dissolution treatment. A better understanding of the antigen conformation in adjuvanted vaccine will enhanced our knowledge of antigen-adjuvant interactions and facilitate an improved process control and development of stable vaccine formulation.

Freeze-thaw stress of Alhydrogel ® alone is sufficient to reduce the immunogenicity of a recombinant hepatitis B vaccine containing native antigen

Preventing losses in vaccine potency due to accidental freezing has recently become a topic of interest for improving vaccines. All vaccines with aluminum-containing adjuvants are susceptible to such potency losses. Recent studies have described excipients that protect the antigen from freeze-induced inactivation, prevent adjuvant agglomeration and retain potency. Although these strategies have demonstrated success, they do not provide a mechanistic understanding of freeze-thaw (FT) induced potency losses. In the current study, we investigated how adjuvant frozen in the absence of antigen affects vaccine immunogenicity and whether preventing damage to the freeze-sensitive recombinant hepatitis B surface antigen (rHBsAg) was sufficient for maintaining vaccine potency. The final vaccine formulation or Alhydrogel(®) alone was subjected to three FT-cycles. The vaccines were characterized for antigen adsorption, rHBsAg tertiary structure, particle size and charge, adjuvant elemental content and in-vivo potency. Particle agglomeration of either vaccine particles or adjuvant was observed following FT-stress. In vivo studies demonstrated no statistical differences in IgG responses between vaccines with FT-stressed adjuvant and no adjuvant. Adsorption of rHBsAg was achieved; regardless of adjuvant treatment, suggesting that the similar responses were not due to soluble antigen in the frozen adjuvant-containing formulations. All vaccines with adjuvant, including the non-frozen controls, yielded similar, blue-shifted fluorescence emission spectra. Immune response differences could not be traced to differences in the tertiary structure of the antigen in the formulations. Zeta potential measurements and elemental content analyses suggest that FT-stress resulted in a significant chemical alteration of the adjuvant surface. This data provides evidence that protecting a freeze-labile antigen from subzero exposure is insufficient to maintain vaccine potency. Future studies should focus on adjuvant protection. To our knowledge, this is the first study to systematically investigate how FT-stress to adjuvant alone affects immunogenicity. It provides definitive evidence that this damage is sufficient to reduce vaccine potency.

Structural and immunological analysis of anthrax recombinant protective antigen adsorbed to aluminum hydroxide adjuvant

New anthrax vaccines currently under development are based on recombinant protective antigen (rPA) and formulated with aluminum adjuvant. Because long-term stability is a desired characteristic of these vaccines, an understanding of the effects of adsorption to aluminum adjuvants on the structure of rPA is important. Using both biophysical and immunological techniques, we compared the structure and immunogenicity of freshly prepared rPA-Alhydrogel formulations to that of formulations stored for 3 weeks at either room temperature or 37°C in order to assess the changes in rPA structure that might occur upon long-term storage on aluminum adjuvant. Intrinsic fluorescence emission spectra of tryptophan residues indicated that some tertiary structure alterations of rPA occurred during storage on Alhydrogel. Using anti-PA monoclonal antibodies to probe specific regions of the adsorbed rPA molecule, we found that two monoclonal antibodies that recognize epitopes located in domain 1 of PA exhibited greater reactivity to the stored formulations than to freshly prepared formulations. Immunogenicity of rPA-Alhydrogel formulations in mice was assessed by measuring the induction of toxin-neutralizing antibodies, as well as antibodies reactive to 12-mer peptides spanning the length of PA. Mice immunized with freshly prepared formulations developed significantly higher toxin-neutralizing antibody titers than mice immunized with the stored preparations. In contrast, sera from mice immunized with stored preparations exhibited increased reactivity to nine 12-mer peptides corresponding to sequences located throughout the rPA molecule. These results demonstrate that storage of rPA-Alhydrogel formulations can lead to structural alteration of the protein and loss of the ability to elicit toxin-neutralizing antibodies.

The structure of HBsAg particles is not modified upon their adsorption on aluminium hydroxide gel

Current Hepatitis B vaccines are based on recombinant Hepatitis B surface antigen (HBsAg) virus-like particles adsorbed on aluminium (Al) gel. These particles exhibit a lipoprotein-like structure with about 70 protein S molecules in association with various types of lipids. To determine whether the adsorption on Al gel affects HBsAg structure, we investigated the effect of adsorption and mild desorption processes on the protein and lipid parts of the particles, using various techniques. Electron microscopy showed that the size and morphology of native and desorbed HBsAg particles were comparable. Moreover, infrared and Raman spectroscopy revealed that the secondary structure of the S proteins was not affected by the adsorption/desorption process. Affinity measurements with Surface Plasmon Resonance showed no difference between native and desorbed HBsAg for HBsAg-specific RF-1 monoclonal antibody. Steady-state and time-resolved fluorescence data of the intrinsic fluorescence of the S proteins further indicated that the adsorption/desorption of HBsAg particles on Al gel did not modify the environment of the most emitting Trp residues, confirming that the conformation of the S proteins remains intact. Moreover, using environment-sensitive 3-hydroxyflavone probes, no significant changes of the lipid core and lipid membrane surface of the HBsAg particles were observed during the adsorption/desorption process. Finally, the ratio between lipids and proteins in the particles was found to be similar before and after the adsorption/desorption process. Taken together, our data show that adsorption on Al gel does not affect the structure of the HBsAg particles.

Protein-excipient interactions: mechanisms and biophysical characterization applied to protein formulation development

The purpose of this review is to demonstrate the critical importance of understanding protein-excipient interactions as a key step in the rational design of formulations to stabilize and deliver protein-based therapeutic drugs and vaccines. Biophysical methods used to examine various molecular interactions between solutes and protein molecules are discussed with an emphasis on applications to pharmaceutical excipients in terms of their effects on protein stability. Key mechanisms of protein-excipient interactions such as electrostatic and cation-pi interactions, preferential hydration, dispersive forces, and hydrogen bonding are presented in the context of different physical states of the formulation such as frozen liquids, solutions, gels, freeze-dried solids and interfacial phenomenon. An overview of the different classes of pharmaceutical excipients used to formulate and stabilize protein therapeutic drugs is also presented along with the rationale for use in different dosage forms including practical pharmaceutical considerations. The utility of high throughput analytical methodologies to examine protein-excipient interactions is presented in terms of expanding formulation design space and accelerating experimental timelines.

Vaccines with aluminum-containing adjuvants: optimizing vaccine efficacy and thermal stability

Aluminum-containing adjuvants have been used to enhance the immune response against killed, inactivated, and subunit antigens for more than seven decades. Nevertheless, we are only beginning to gain important insight as to what may be some very fundamental parameters for optimizing their use. For example, there is evidence that the conventional approach of maximizing antigen binding (amount and/or strength) may not result in an optimal immune response. Adsorption of antigen onto the adjuvant has recently been suggested to decrease the thermal stability of some antigens; however, whether adsorption-induced alterations to the structure and/or stability of the antigen have consequences for the elicited immune response is unclear. Finally, the thermal stability of vaccines with aluminum-containing adjuvants is not robust. Optimizing the stability of these vaccines requires an understanding of the freeze sensitivity of the adjuvant, freeze and heat sensitivity of the antigen in the presence of the adjuvant, and perhaps most important, how (or whether) various approaches to formulation can be used to address these instabilities. This review attempts to summarize recent findings regarding issues that may dictate the success of vaccines with aluminum-containing adjuvants.

A recombinant capsid protein from Dengue-2 induces protection in mice against homologous virus

In the present work, we study the immunogenicity and protective capacity of a recombinant capsid protein from Dengue-2 virus. The capsid gene was cloned under the T5 phage promoter and expressed in Escherichia coli. The recombinant protein was obtained mainly associated to the soluble fraction upon cellular disruption and exhibited a pattern of high aggregation, determined by gel filtration chromatography. The semipurified preparation was inoculated in mice and after three doses, no antiviral antibodies were induced. On the other hand, mice intracranially challenged with homologous lethal virus, exhibited statistically significant protection with respect to the control group. These results describe, for the first time, the protective capacity of the capsid protein of Dengue virus indicating the existence of a protector mechanism, which is totally independent of the antibodies. This lack of induction of antiviral antibodies makes the capsid protein an attractive vaccine candidate against dengue since eliminates the potential risk of the induction of antibody dependent enhancement associated to the current vaccines under study.

Lipid microparticles for mucosal immunization against hepatitis B

Parenteral administration of vaccines often does not lead to optimal or long lasting protection against disease causing organisms particularly those that are inhaled, ingested or sexually transmitted. For optimal mucosal protection induction of immune response via mucosal routes is therefore highly desirable. Double emulsion-solvent evaporation (w/o/w) method best suited for water-soluble bioactives was selected for the preparation of hepatitis B surface antigen (HBsAg) loaded lipid microparticles. Intranasal route was considered for mucosal administration and hence to prepare the delivery system biocompatible and least irritable, soyalecithin (phospholipid) was taken instead of polymer because phosphatidylcholine is the major component of endogenous lung surfactant. The studies performed in present work included antigen characterization, development of lipid microparticles, stability studies of the prepared lipid microparticle formulations, percent mucoadhesion, ex vivo cellular uptake studies and in vivo studies. The general order obtained from in vivo studies for mucosal immune response (IgA) followed the sequence: LMST-HBsAg (IN)>LM-HBsAg (IN)>alum-HBsAg (IN)>LMST-HBsAg (IM)>alum-HBsAg (IM)>or=LM-HBsAg (IM)>plain HBsAg (IN)>plain HBsAg (IM).

Mechanism of adsorption of hepatitis B surface antigen by aluminum hydroxide adjuvant

Hepatitis B surface antigen (HBsAg) differs from many antigens because of its associated lipid bilayer that is largely composed of phospholipids. In general, phosphate groups adsorb strongly to hydroxylated mineral surfaces by ligand exchange. The purpose of this study was to investigate the mechanism of adsorption of hepatitis B surface antigen to aluminum hydroxide adjuvant with emphasis on the role of phospholipids in this adsorption. The adsorption of HBsAg by aluminum hydroxide adjuvant exhibits a high affinity adsorption isotherm. The Langmuir equation was used to calculate the adsorptive capacity (1.7 microg/microg Al), which is the amount of HBsAg adsorbed at monolayer coverage and the adsorptive coefficient (6.0 ml/microg), which is a measure of the strength of the adsorption force. The relatively high value of the adsorptive coefficient indicates that adsorption is due to a strong attractive force. Ligand exchange between a phosphate of the antigen and a surface hydroxyl of the adjuvant provides the strongest adsorption mechanism. The adsorption capacity of HBsAg was not affected by increased ionic strength indicating that electrostatic attraction is not the predominant adsorption force. Adsorption was also not affected by the addition of ethylene glycol indicating that hydrophobic interactions were not the predominant adsorption force. The strength of the adsorption force was indicated by the resistance of HBsAg to elution when exposed to interstitial fluid. Less than 5% of the HBsAg adsorbed to aluminum hydroxide adjuvant in a model vaccine was eluted during a 12 h in vitro exposure to interstitial fluid at 37 degrees C. Less than 1% of the adsorbed HBsAg in two commercial vaccines was eluted by in vitro exposure to interstitial fluid for 48 h at 37 degrees C. Thus, it was concluded that adsorption of HBsAg by aluminum hydroxide adjuvant is predominantly due to ligand exchange between the phospholipids in HBsAg and surface hydroxyls in aluminum hydroxide adjuvant.

Anti-HBs after hepatitis B immunization with plasma-derived and recombinant DNA-derived vaccines: binding to mutant HBsAg

The G145R mutant of the small S-protein is a major escape mutant of hepatitis B virus observed in natural infection, after immunization and HBIG therapy. In a previous study we found that plasma-derived and recombinant DNA-derived vaccine HBsAg reacted differently with monoclonal antibodies sensitive for the G145R change. In the present study we investigated the binding of polyclonal anti-HBs obtained after immunization with plasma vaccine and recombinant DNA vaccine to synthetic peptides (adw(2), adr) and rHBsAg (HepG2) (ayw(3); wild type and a 145R mutant). Anti-HBs binding to synthetic peptids (25-mers, 7aa overlap) from the "a"-loop was significantly reduced by the G145R substitution and by changing the amino acid sequence from adw(2) into adr. With mutant G145R rHBsAg the inhibitory activity of vaccine anti-HBs was decreased compared to rHBsAg wild type. In general only minor differences were observed between plasma vaccine and recombinant DNA vaccine related antibody responses. However, the individual heterogeneity in epitope specific reactivity with its possible consequences for protection (against escape mutants) is not reflected in an anti-HBs titer by standard anti-HBs assays. The presented differentiation in anti-HBs response after immunization may deliver new tools for evaluation of future vaccines.

Aggregation of recombinant hepatitis B surface antigen induced in vitro by oxidative stress

In order to examine whether oxygen radicals could be responsible for aggregation of recombinant hepatitis B surface antigen (HBsAg) during its assembly in yeast, purified HBsAg was oxidized with ammonium peroxodisulphate (AP) and analyzed by non-denaturing and denaturing size exclusion chromatography, immunoassay and immunoelectron microscopy. As a result, peroxodisulphate radicals induced a reproducible aggregation of HBsAg. At 44 mM AP, the aggregation process took a few hours and the resulting structures were large, branched and non-antigenic. During more gentle oxidation with 9 mM AP and 20-80 microM Cu2+, a continuous structural modification to HBsAg delaying for tens of hours preceded the aggregation event. During this pre-aggregation period, peroxidation of HBsAg lipids and covalent cross-linking of S protein chains occurred that led a complete loss of antigenicity of oxidized particles. In contrast, yeast-derived HBsAg aggregate is decomposed to S monomers under reducing conditions and recognized by anti-HBsAg polyclonal and monoclonal antibodies, suggesting that is has been assembled in vivo from antigenic and reversibly cross-linked particles. Based on these observations, we conclude that oxidation, at least with respect to the specific molecular sites oxidized by AP, is not a primary event in HBsAg aggregate formation in vivo. Since oxidized HBsAg was shown to be irreversibly cross-linked and non-antigenic, there are no suitable techniques for detection HBsAg oxidation in biological samples. Hence, at present, the magnitude of the in-vivo oxidative damage to HBsAg cannot be evaluated and thus, whether the plasma-derived HBsAg undergoes radical-induced oxidation in the course of viral hepatitis remains to be established. If this occurs, this process is expected to contribute to low HBsAg levels in chronic hepatitis B carriers, failure of the currently available immunoassays to identify HBsAg-positive blood donors and inconsistency in the results provided by HBsAg- and anti-HBsAg-based tests in several recent reports.