A novel virus-like particle based on hepatitis B core antigen and substrate-binding domain of bacterial molecular chaperone DnaK

Expression, purification and refolding of pro-MMP-2 from inclusion bodies of E. coli

MMP-2 has been reported as the most validated target for cancer progression and deserves further investigation. However, due to the lack of methods for obtaining large amounts of highly purified and bioactive MMP-2, identifying specific substrates and developing specific inhibitors of MMP-2remains extremely difficult. In this study, the DNA fragment coding for pro-MMP-2 was inserted into plasmid pET28a in an oriented manner, and the resulting recombinant protein was effectively expressed and led to accumulation as inclusion bodies in E. coli. This protein was easy to purify to near homogeneity by the combination of common inclusion bodies purification procedure and cold ethanol fractionation. Then, our results of gelatin zymography and fluorometric assay revealed that pro-MMP-2 at least partially restored its natural structure and enzymatic activity after renaturation. We obtained approximately 11 mg refolded pro-MMP-2 protein from 1 L LB broth, which was higher than other strategies previously reported. In conclusion, a simple and cost-effective procedure for obtaining high amounts of functional MMP-2was developed, which would contribute to the progress of studies on the gamut of biological action of this important proteinase. Furthermore, our protocol should be appropriate for the expression, purification, and refolding of other bacterial toxic proteins.

Inhibition of RM-1 prostate carcinoma and eliciting robust immune responses in the mouse model by using VEGF-M2-GnRH3-hinge-MVP vaccine

GnRH and VEGF have been investigated as prostate carcinoma enhancers that support tumor spread and progression. Although both have documented roles in prostate carcinoma and many cancer types, the weak immunogenicity of these peptides has remained a major challenge for use in immunotherapy. Here, we describe a novel strategy to inhibit GnRH and VEGF production and assess the effect on the immune responses against these hormones using the RM-1 prostate cancer model. We designed a novel recombinant fusion protein which combined GnRH and VEGF as a vaccine against this tumor. The newly constructed fusion protein hVEGF121-M2-GnRH3-hinge-MVP contains the human vascular endothelial growth factor (hVEGF121) and three copies of GnRH in sequential linear alignment and T helper epitope MVP as an immunogenic vaccine. The effectiveness of the vaccine in eliciting an immune response and attenuating the prostate tumor growth was evaluated. Results showed that administration of a new vaccine effectively elicited humoral and cellular immune responses. We found that, a novel fusion protein, hVEGF121-M2-GnRH3-hinge-MVP, effectively inhibited growth of RM-1 prostate model and effectively promoted immune response. In conclusion, hVEGF121-M2-GnRH3-hinge-MVP is an effective dual mechanism tumor vaccine that limits RM-1 prostate growth. This vaccine may be a promising strategy for the treatment of hormone refractory prostate malignancies.

Chimeric virus-like particles containing a conserved region of the G protein in combination with a single peptide of the M2 protein confer protection against respiratory syncytial virus infection

To investigate the feasibility and efficacy of a virus-like particle (VLP) vaccine composed of the conserved antigenic epitopes of respiratory syncytial virus (RSV), the chimeric RSV VLPs HBcΔ-tG and HBcΔ-tG/M282-90 were generated based on the truncated hepatitis B virus core protein (HBcΔ). HBcΔ-tG consisted of HBcΔ, the conserved region (aa 144-204) of the RSV G protein. HBcΔ-tG was combined with a single peptide (aa 82-90) of the M2 protein to generate HBcΔ-tG/M282-90. Immunization of mice with the HBcΔ-tG or HBcΔ-tG/M282-90 VLPs elicited RSV-specific IgG and neutralizing antibody production and conferred protection against RSV infection. Compared with HBcΔ-tG, HBcΔ-tG/M282-90 induced decreased Th2 cytokine production (IL-4 and IL-5), increased Th1 cytokine response (IFN-γ, TNF-α, and IL-2), and increased ratios of IgG2a/IgG1 antibodies, thereby relieving pulmonary pathology upon subsequent RSV infection. Our results demonstrated that chimeric HBcΔ-tG/M282-90 VLPs represented an effective RSV subunit vaccine candidate.

Detection of antibodies against customized epitope: use of a coating antigen employing VEGF as fusion partner

Diagnosis of many infectious, autoimmune diseases and cancers depends on the detection of specific antibodies against peptide epitope by enzyme-linked immunosorbent assay (ELISA). However, small peptides are difficult to be coated on the plate surfaces. In this study, we selected GnRH as a model hapten to evaluate whether VEGF121 would be suitable as an irrelevant hapten-carrier to develop a universal platform for specific antibodies detection. Firstly, GnRH was fused to the C terminus of VEGF121 and the resultant fusion protein VEGF-GnRH expressed effectively as inclusion bodies in Escherichia coli. Thereafter, VEGF-GnRH was easily purified to near homogeneity with a yield of about 235 mg from 2.1 L induced culture. At last, VEGF-GnRH was used to perform ELISA and western blot, and our results suggested that VEGF-GnRH was capable of detecting anti-GnRH antibodies in sera both qualitatively and quantitatively. Indeed, previous studies of our laboratory had demonstrated that other fusion proteins such as VEGF-Aβ10, VEGF-GRP, VEGF-CETPC, and VEGF-βhCGCTP37 were able to detect their corresponding antibodies specifically. Therefore, VEGF121 may be a suitable irrelevant fusion partner of important diagnostic peptide markers. Our works would shed some light on the development of a universal platform for detection of specific antibodies.

Hepatitis B core-based virus-like particles to present heterologous epitopes

Since the first effort to recombinantly express the hepatitis B core protein (HBc) in bacteria, the remarkable virion-like structure has fuelled interest in unraveling the structural and antigenic properties of this protein. Initial studies proved HBc virus-like particles to possess strong immunogenic properties, which can be conveyed to linked antigens. More than 35 years later, numerous studies have been performed using HBc as a carrier protein for antigens derived from over a dozen different pathogens and diseases. In this review, the authors highlight the intriguing features of HBc as carrier and antigen, illustrated by some examples and experimental results that underscore the value of HBc as an antigen-presenting platform. Two of these HBc fusions, targeting influenza A and malaria, have even progressed into clinical testing. In the future, the HBc-based virus-like particles platform will probably continue to be used for the display of poorly immunogenic antigens, mainly because virus-like particle formation by HBc capsomers is compatible with nearly any available recombinant gene expression system.

Virus-like particles displaying envelope domain III of dengue virus type 2 induce virus-specific antibody response in mice

OBJECTIVE

Currently, dengue represents one of the most significant arboviral disease worldwide, for which a vaccine is not yet available. Persistent challenges in live viral dengue vaccines have sparked a keen interest in exploring non-replicating dengue vaccines. We have examined the feasibility of using the methylotrophic yeast Pichia pastoris to develop a chimeric vaccine candidate displaying the dengue virus type-2 (DENV-2) envelope domain III (EDIII), implicated in host receptor binding and in the induction of virus-neutralizing antibodies, on the surface of non-infectious virus-like particles (VLP)-based on the Hepatitis B virus core antigen (HBcAg).

METHODS

We designed a fusion antigen by inserting DENV-2 EDIII into c/e1 loop of HBcAg. A codon-optimized gene encoding this fusion antigen was integrated into the genome of P. pastoris, under the control of the Alcohol Oxidase 1 promoter. The antigen was expressed by methanol induction and purified to near homogeneity by Ni(2+) affinity chromatography. The purified antigen was characterized physically and functionally to evaluate its ability to assemble into VLPs, and elicit DENV-2-specific antibodies in mice.

RESULTS

This fusion antigen was expressed successfully to high yields and purified to near homogeneity. Electron microscopy and competitive ELISA analyses showed that it formed VLPs in which the EDIII moiety was accessible to different EDIII-specific antibodies. These VLPs were immunogenic in mice, stimulating the production of antibodies that could specifically recognize DENV-2 and neutralize its infectivity. However, virus-neutralizing antibody titers were modest.

CONCLUSIONS

Our data show: (i) insertion of EDIII into the c/e1 loop of HBcAg does not compromise particle assembly; and (ii) the chimeric VLPs elicit a specific humoral response against DENV-2. The strategy of displaying dengue virus EDIII using a VLP platform will need further optimization before it may be developed into a viable alternative option.

Chimeric Hepatitis B core antigen virus-like particles displaying the envelope domain III of dengue virus type 2

Background

Dengue is a global public health problem for which no drug or vaccine is available. Currently, there is increasing interest in developing non-replicating dengue vaccines based on a discrete antigenic domain of the major structural protein of dengue viruses (DENVs), known as envelope domain III (EDIII). The use of bio-nanoparticles consisting of recombinant viral structural polypeptides, better known as virus-like particles (VLPs), has emerged as a potential platform technology for vaccine development. This work explores the feasibility of developing nanoparticles based on E. coli-expressed recombinant Hepatitis B virus core antigen (HBcAg) designed to display EDIII moiety of DENV on the surface.

Findings

We designed a synthetic gene construct encoding HBcAg containing an EDIII insert in its c/e1 loop. The fusion antigen HBcAg-EDIII-2 was expressed in E. coli, purified to near homogeneity using Ni⁺² affinity chromatography and demonstrated to assemble into discrete 35–40 nm VLPs by electron microscopy. Competitive ELISA analyses showed that the EDIII-2 moieties of the VLPs are accessible to anti-EDIII-2-specific monoclonal and polyclonal antibodies, suggesting that they are surface-displayed. The VLPs were highly immunogenic eliciting high titer anti-EDIII-2 antibodies that were able to recognize, bind and neutralize infectious DENV based on ELISA, immunofluorescence and virus-neutralization assays.

Conclusion

This work demonstrates that HBcAg-derived nanoparticles can serve as a useful platform for the display of DENV EDIII. The EDIII-displaying nanoparticles may have potential applications in diagnostics/vaccines for dengue.

Immunization with a recombinant GnRH vaccine fused to heat shock protein 65 inhibits mammary tumor growth in vivo

Gonadotrophin-releasing hormone (GnRH) is the prime decapeptide hormone in the regulation of mammalian reproduction. Active immunization against GnRH has been a good treatment option to fight against hormone-dependent disease such as breast cancer. We designed and purified a novel protein vaccine Hsp65-GnRH(6) containing heat shock protein 65 (Hsp65) and six copies of GnRH in linear alignment. Immunization with Hsp65-GnRH(6) evoked strong humoral response in female mice. The generation of specific anti-GnRH antibodies was detected by ELISA and verified by western blot. In addition, anti-GnRH antibodies effectively neutralized endogenous GnRH activity in vivo, as demonstrated by the degeneration of the ovaries and uteri in the vaccinated mice. Moreover, the growth of EMT-6 mammary tumor allografts was inhibited by anti-GnRH antibodies. Histological examinations have shown that there was increased focal necrosis in tumors. Taken together, our results showed that immunization with Hsp65-GnRH(6) elicited high titer of specific anti-GnRH antibodies and further led to atrophy of reproductive organs. The specific antibodies could inhibit the growth of EMT-6 murine mammary tumor probably via an indirect mechanism that includes the depletion of estrogen. In view of these results, the protein vaccine Hsp65-GnRH(6) appears to be a promising candidate vaccine for hormone-dependent cancer therapy.