High-level expression and immunogenicity of a porcine circovirus type 2 capsid protein through codon optimization in Pichia pastoris

A novel strategy for an anti-idiotype vaccine: nanobody mimicking neutralization epitope of porcine circovirus type 2

Vaccination is the most effective method to protect humans and animals from diseases. Anti-idiotype vaccines are safer due to their absence of pathogens. However, the commercial production of traditional anti-idiotype vaccines using monoclonal and polyclonal antibodies (mAb and pAb) is complex and has a high failure rate. The present study designed a novel, simple, low-cost strategy for developing anti-idiotype vaccines with nanobody technology. We used porcine circovirus type 2 (PCV2) as a viral model, which can result in serious economic loss in the pig industry. The neutralizing mAb-1E7 (Ab1) against PCV2 capsid protein (PCV2-Cap) was immunized in the camel. And 12 nanobodies against mAb-1E7 were screened. Among them, Nb61 (Ab2) targeted the idiotype epitope of mAb-1E7 and blocked mAb-1E7's binding to PCV2-Cap. Additionally, a high-dose Nb61 vaccination can also protect mice and pigs from PCV2 infection. Epitope mapping showed that mAb-1E7 recognized the 75NINDFL80 of PCV2-Cap and 101NYNDFLG107 of Nb61. Subsequently, the mAb-3G4 (Ab3) against Nb61 was produced and can neutralize PCV2 infection in the PK-15 cells. Structure analysis showed that the amino acids of mAb-1E7 and mAb-3G4 respective binding to PCV2-Cap and Nb61 were also similar on the amino acids sequences and spatial conformation. Collectively, our study first provided a strategy for producing nanobody-based anti-idiotype vaccines and identified that anti-idiotype nanobodies could mimic the antigen on amino acids and structures. Importantly, as more and more neutralization mAbs against different pathogens are prepared, anti-idiotype nanobody vaccines can be easily produced against the disease with our strategy, especially for dangerous pathogens.IMPORTANCEAnti-idiotype vaccines utilize idiotype-anti-idiotype network theory, eliminating the need for external antigens as vaccine candidates. Especially for dangerous pathogens, they were safer because they did not contact the live pathogenic microorganisms. However, developing anti-idiotype vaccines with traditional monoclonal and polyclonal antibodies is complex and has a high failure rate. We present a novel, universal, simple, low-cost strategy for producing anti-idiotype vaccines with nanobody technology. Using a neutralization antibody against PCV2-Cap, a nanobody (Ab2) was successfully produced and could mimic the neutralizing epitope of PCV2-Cap. The nanobody can induce protective immune responses against PCV2 infection in mice and pigs. It highlighted that the anti-idiotype vaccine using nanobody has a very good application in the future, especially for dangerous pathogens.

Production of virus-like particles of porcine circovirus 2 in baculovirus expression system and its application for antibody detection

BACKGROUND

Porcine circovirus 2 (PCV-2) is one of the pathogens that leads to a growing and persistent threat in pigs. Thus, the development of serological detection methods for PCV-2 is of great necessity for clinical diagnosis as well as epidemiological investigations. This study aimed to establish an indirect enzyme-linked immunosorbent assay (ELISA) to examine antibodies against PCV-2 based on virus-like particles (VLPs).

RESULTS

Recombinant PCV-2 Cap protein was expressed in the baculovirus-insect cells system and PCV-2 VLPs were observed over transmission electron microscopy (TEM). The PCV-2 VLPs were shown to have good immunogenicity in mice and stimulated a high level of PCV-2 antibody titers. Using PCV-2 VLPs as coating antigen, the indirect ELISA can detect PCV-2 antibodies in animals with diagnostic sensitivity and specificity of 98.33% and 93.33% compared to immunofluorescence assay (IFA), respectively. The intra- and inter-assay coefficient variations (CVs) were < 10% in a batch, and < 15% in different batches, indicating good repeatability. There was no cross-reaction of this ELISA with antibodies against other porcine viruses. A total of 170 serum samples collected from different pig farms in China were tested for PCV-2 antibodies, and 151 (88.8%) samples were PCV-2 antibody positive.

CONCLUSION

Our findings suggest that this ELISA was rapid, specific, and reproducible and can be used for large-scale serological investigations of PCV-2 antibodies in pigs.

Recombinant vaccines in 2022: a perspective from the cell factory

The last big outbreaks of Ebola fever in Africa, the thousands of avian influenza outbreaks across Europe, Asia, North America and Africa, the emergence of monkeypox virus in Europe and specially the COVID-19 pandemics have globally stressed the need for efficient, cost-effective vaccines against infectious diseases. Ideally, they should be based on transversal technologies of wide applicability. In this context, and pushed by the above-mentioned epidemiological needs, new and highly sophisticated DNA-or RNA-based vaccination strategies have been recently developed and applied at large-scale. Being very promising and effective, they still need to be assessed regarding the level of conferred long-term protection. Despite these fast-developing approaches, subunit vaccines, based on recombinant proteins obtained by conventional genetic engineering, still show a wide spectrum of interesting potentialities and an important margin for further development. In the 80’s, the first vaccination attempts with recombinant vaccines consisted in single structural proteins from viral pathogens, administered as soluble plain versions. In contrast, more complex formulations of recombinant antigens with particular geometries are progressively generated and explored in an attempt to mimic the multifaceted set of stimuli offered to the immune system by replicating pathogens. The diversity of recombinant antimicrobial vaccines and vaccine prototypes is revised here considering the cell factory types, through relevant examples of prototypes under development as well as already approved products.

Evaluation of Methylotrophic Yeast Ogataea thermomethanolica TBRC 656 as a Heterologous Host for Production of an Animal Vaccine Candidate

Multiple yeast strains have been developed into versatile heterologous protein expression platforms. Earlier works showed that Ogataea thermomethanolica TBRC 656 (OT), a thermotolerant methylotrophic yeast, can efficiently produce several industrial enzymes. In this work, we demonstrated the potential of this platform for biopharmaceutical manufacturing. Using a swine vaccine candidate as a model, we showed that OT can be optimized to express and secrete the antigen based on porcine circovirus type 2d capsid protein at a respectable yield. Crucial steps for yield improvement include codon optimization and reduction of OT protease activities. The antigen produced in this system could be purified efficiently and induce robust antibody response in test animals. Improvements in this platform, especially more efficient secretion and reduced extracellular proteases, would extend its potential as a competitive platform for biopharmaceutical industries.

Expression of L-phosphinothricin synthesis enzymes in Pichia pastoris for synthesis of L-phosphinothricin

With the ban of highly toxic herbicides, such as paraquat and glyphosate, phosphinothricin (PPT) is becoming the most popular broad-spectrum and highly effective herbicide. The current PPT products in the market are usually a racemic mixture with two configurations, the D-type and L-type, of which only the L-PPT has the herbicidal activity. The racemic product is not atom economic, more toxic and may cause soil damage. Asymmetric synthesis of L-PPT has become a research focus in recent years, while biological synthesis methods are preferred for its character of environmental friendly and requiring less reaction steps when being compared to the chemical methods. We have developed a biological synthesis route to produce optically pure L-PPT from D,L-PPT in two steps using 2-carbonyl-4- (hydroxymethyl phosphonyl) butyric acid as the intermediate. In this study, we expressed the glutamate dehydrogenase and glucose dehydrogenase using Pichia pastoris as the first time. After a series of optimization, the total L-PPT yield reached 84%. The developed synthesis system showed a high potential for future industrial application. Compare to the previous plasmid-carrying-E. coli expression system, the established method may avoid antibiotic usage and provided an alternative way for industrial synthesis of optically pure L-PPT.

Bioprospecting Kluyveromyces marxianus as a Robust Host for Industrial Biotechnology

Kluyveromyces marxianus is an emerging non-conventional food-grade yeast that is generally isolated from diverse habitats, like kefir grain, fermented dairy products, sugar industry sewage, plants, and sisal leaves. A unique set of beneficial traits, such as fastest growth, thermotolerance, and broad substrate spectrum (i.e., hemi-cellulose hydrolysates, xylose, l-arabinose, d-mannose, galactose, maltose, sugar syrup molasses, cellobiose, and dairy industry) makes this yeast a particularly attractive host for applications in a variety of food and biotechnology industries. In contrast to Saccharomyces cerevisiae, most of the K. marxianus strains are apparently Crabtree-negative or having aerobic-respiring characteristics, and unlikely to endure aerobic alcoholic fermentation. This is a desirable phenotype for the large-scale biosynthesis of products associated with biomass formation because the formation of ethanol as an undesirable byproduct can be evaded under aerobic conditions. Herein, we discuss the current insight into the potential applications of K. marxianus as a robust yeast cell factory to produce various industrially pertinent enzymes, bioethanol, cell proteins, probiotic, fructose, and fructo-oligosaccharides, and vaccines, with excellent natural features. Moreover, the biotechnological improvement and development of new biotechnological tools, particularly CRISPR-Cas9-assisted precise genome editing in K. marxianus are delineated. Lastly, the ongoing challenges, concluding remarks, and future prospects for expanding the scope of K. marxianus utilization in modern biotechnology, food, feed, and pharmaceutical industries are also thoroughly vetted. In conclusion, it is critical to apprehend knowledge gaps around genes, metabolic pathways, key enzymes, and regulation for gaining a complete insight into the mechanism for producing relevant metabolites by K. marxianus.

Evaluation of a Virus-like Nanoparticle Porcine Circovirus Type-2 (PCV2) Capsid Protein Fused with the Pig Immunoglobulin Fc Fragment as a Novel Vaccine Candidate against PCV2 in Mice

Porcine circovirus Type 2 (PCV2) is a primary etiological pathogen of post-weaning multi-systemic wasting syndrome (PMWS). The capsid protein of PCV2 is the crucial immunogenic protein which can induce antibody generation and immune responses. However, there is still a lack of efficient PCV2 vaccines with high immunogenicity. In the current study, we developed a novel engineered PCV2 capsid (∆1-41aa)-pFc fusion protein (PCFP), which comprised a truncated capsid protein of PCV2 and a porcine IgG Fc fragment, fused to the capsid protein of PCV2 at the C-terminus. We found that this novel fusion protein could auto-assemble into virus-like nanoparticles with an estimated mean diameter of 22.6 nm, characterized by transmission electron microscopy. Immunization of BALB/c mice with this fusion protein significantly increased the production levels of anti-PCV2-capsid protein antibody in serum. Besides, the virus-like nanoparticles, PCFP was demonstrated to induce efficient cellular immune responses in mice, as evident by the high specific T cell reactivity to the PCFP fusion protein and the high production of the immune cytokines IFN-γ and IL-10 in an ex vivo re-stimulation system. Collectively, these findings demonstrate that the PCV2 truncated capsid subunit Fc-fusion protein can induce both cellular and humoral immune responses, and it displays great application potential.

Medium optimization for high yield production of human serum albumin in Pichia pastoris and its efficient purification

OBJECTIVE

To improve the yield of recombinant human serum albumin (HSA) in Pichia pastoris by medium optimization and establish the related purification scheme.

RESULTS

A simplified version of the generally used buffered glycerol complex medium (BMGY), which contained yeast extract, glycerol and potassium salts, was found to be applicable. By decreasing the salt concentration of basal salt medium (BSM) to half of the original formula further, we achieved a high yield of 17.47 g/L HSA in the supernatant within a 192 h induction, which is the highest rHSA yield ever reported as far as we know. Accompanied with a three-step purification procedure which recovered two thirds of the desired protein at high purity, our work lays a solid foundation for large-scale industrial production of HSA.

CONCLUSION

Medium optimization plays a significant role in improving the yield of desired protein, lowering the production cost and helping to explore the producing strain's character.

Construction of polycistronic baculovirus surface display vectors to express the PCV2 Cap(d41) protein and analysis of its immunogenicity in mice and swine

To increase expression levels of the PCV2 Cap(d41) protein, novel baculovirus surface display vectors with multiple expression cassettes were constructed to create recombinant baculoviruses BacSC-Cap(d41), BacDD-2Cap(d41), BacDD-3Cap(d41), and BacDD-4Cap(d41). Our results reveal that the recombinant baculovirus BacDD-4Cap(d41) was able to express the highest levels of Cap(d41) protein. Optimum conditions for expressing the PCV2 Cap(d41) protein were determined, and our results show that 107 of Sf-9 infected with the recombinant baculovirus BacDD-4Cap(d41) at an MOI of 5 for 3 days showed the highest level of protein expression. Mice immunized with the 4Cap(d41) vaccine which was prepared from the recombinant baculovirus-infected cells (107) elicited higher ELISA titers compared to the Cap (d41) vaccine. The 4Cap(d41) vaccine could elicit anti-PCV2 neutralizing antibodies and IFN-γ in mice, as confirmed by virus neutralization test and IFN-γ ELISA. Moreover, the swine lymphocyte proliferative responses indicated that the 4Cap(d41) vaccine was able to induce a clear cellular immune response. Flow cytometry analysis showed that the percentage of CD4+ T cells and CD4+/CD8+ ratio was increased significantly in SPF pigs immunized with the 4Cap(d41) vaccine. Importantly, the 4Cap(d41) vaccine induced an IFN-γ response, further confirming that its effect is through cellular immunity in SPF pigs. An in vivo challenge study revealed that the 4Cap(d41) and the commercial vaccine groups significantly reduce the viral load of vaccinated pigs as compared with the CE negative control group. Taken together, we have successfully developed a 4Cap(d41) vaccine that may be a potential subunit vaccine for preventing the disease associated with PCV2 infections.

The Carboxyl Terminus of the Porcine Circovirus Type 2 Capsid Protein Is Critical to Virus-Like Particle Assembly, Cell Entry, and Propagation

The capsid protein (Cap) is the sole structural protein and the main antigen of porcine circovirus type 2 (PCV2). Structural loops of the Cap play crucial roles in viral genome packaging, capsid assembly, and virus-host interactions. Although the molecular mechanisms are yet unknown, the carboxyl terminus (CT) of the PCV2 Cap is known to play critical roles in the evolution, pathogenesis, and proliferation of this virus. In this study, we investigated functions of CT. Removal of this loop leads to abrogation of the in vitro Cap self-assembly into virus-like particles (VLPs). Likewise, the mutated virus resists rescue from PK15 cell culture. A conserved PXXP motif in the CT is dispensable for VLP assembly and subsequent cell entry. However, its removal leads to the subsequent failure of virus rescued from PK15 cells. Furthermore, substituting either the PCV1 counterpart or an AXXA for the PXXP motif still supports virus rescue from cell culture but results in a dramatic decrease in viral titers compared with wild type. In particular, a strictly conserved residue (²²⁷K) in the CT is essential for VLP entry into PK15 cells, and its mutation to alanine greatly attenuates cell entry of the VLPs, supporting a mechanism for the failure to rescue a mutated PCV2 infectious DNA clone (K227A) from PK15 cell culture. These results suggest the CT of the PCV2 Cap plays critical roles in virus assembly, viral-host cell interaction(s), and virus propagation in vitro IMPORTANCE The carboxyl terminus (CT) of porcine circovirus type 2 (PCV2) capsid protein (Cap) was previously reported to be associated with immunorecognition, alterations of viral titer in swine sera, and pathogenicity. However, the molecular mechanisms underlying these effects remain unknown. In this study, roles of the critical residues and motifs of the CT are investigated with respect to virus-like particle (VLP) assembly, cell entry, and viral proliferation. The results revealed that the positively charged ²²⁷K of the CT is essential for both cell entry of PCV2 VLPs and virus proliferation. Our findings, therefore, suggest that the CT should be considered one of the key epitopes, recognized by neutralizing antibodies, for vaccine design and a target for drug development to prevent PCV2-associated diseases (PCVADs). Furthermore, it is important to respect the function of ²²⁷K for its role in cell entry if using either PCV2 VLPs for nanoscale DNA/drug cell delivery or using PCV2 VLPs to display a variety of foreign epitopes for immunization.

Pichia pastoris: A highly successful expression system for optimal synthesis of heterologous proteins

One of the most important branches of genetic engineering is the expression of recombinant proteins using biological expression systems. Nowadays, different expression systems are used for the production of recombinant proteins including bacteria, yeasts, molds, mammals, plants, and insects. Yeast expression systems such as Saccharomyces cerevisiae (S. cerevisiae) and Pichia pastoris (P. pastoris) are more popular. P. pastoris expression system is one of the most popular and standard tools for the production of recombinant protein in molecular biology. Overall, the benefits of protein production by P. pastoris system include appropriate folding (in the endoplasmic reticulum) and secretion (by Kex2 as signal peptidase) of recombinant proteins to the external environment of the cell. Moreover, in the P. pastoris expression system due to its limited production of endogenous secretory proteins, the purification of recombinant protein is easy. It is also considered a unique host for the expression of subunit vaccines which could significantly affect the growing market of medical biotechnology. Although P. pastoris expression systems are impressive and easy to use with well‐defined process protocols, some degree of process optimization is required to achieve maximum production of the target proteins. Methanol and sorbitol concentration, Mut forms, temperature and incubation time have to be adjusted to obtain optimal conditions, which might vary among different strains and externally expressed protein. Eventually, optimal conditions for the production of a recombinant protein in P. pastoris expression system differ according to the target protein.

Purification and characterization of immunogenic recombinant virus-like particles of porcine circovirus type 2 expressed in silkworm pupae

Porcine circovirus type 2 (PCV2) is a primary causative agent of postweaningmultisystemic wasting syndrome (PMWS), which has a significant economic impact on the swine industry. The capsid protein (Cap) encoded by ORF2 of the viral genome has been used effectively as a vaccine against PCV2 infection. The Cap protein can spontaneously assemble into virus-like particles (VLPs) that are safe and highly immunogenic for vaccine applications. Several expression systems, including bacteria, yeast and insect cells, have been utilized to produce PCV2 VLPs. However, in some cases, the recombinant Cap (rCap) proteins produced in bacteria and yeast do not assemble spontaneously. In this study, we expressed rCap protein using a silkworm-baculovirus expression vector system (silkworm-BEVS) for mass production of PCV2 VLPs and established a simple three-step protocol for its purification from pupae: extraction by detergent, ammonium sulfate precipitation and anion exchange column chromatography. Size-exclusion chromatography (SEC) analysis and transmission electron microscope (TEM) observation showed that purified rCap proteins formed VLPs with a similar morphology to that of the original virus. Furthermore, the VLPs produced in silkworms were capable of inducing neutralizing antibodies against PCV2 in mice. Our results demonstrated that the silkworm system is a powerful tool for the production of PCV2 VLPs and will be useful for the development of a reliable and cost-effective PCV2 vaccine.

Yeast-based vaccines: New perspective in vaccine development and application

In presently licensed vaccines, killed or attenuated organisms act as a source of immunogens except for peptide-based vaccines. These conventional vaccines required a mass culture of associated or related organisms and long incubation periods. Special requirements during storage and transportation further adds to the cost of vaccine preparations. Availability of complete genome sequence, well-established genetic, inherent natural adjuvant and non-pathogenic nature of yeast species viz. Saccharomyces cerevisiae, Pichia pastoris makes them an ideal model system for the development of vaccines both for public health and for on-farm consumption. In this review, we compile the work in this emerging field during last two decades with major emphases on S. cerevisiae and P. pastoris which are routinely used worldwide for expression of heterologous proteins with therapeutic value against infectious diseases along with possible use in cancer therapy. We also pointed towards the developments in use of whole recombinant yeast, yeast surface display and virus-like particles as a novel strategy in the fight against infectious diseases and cancer along with other aspects including suitability of yeast in vaccines preparations, yeast cell wall component as an immune stimulator or modulator and present status of yeast-based vaccines in clinical trials.

Efficient production of porcine circovirus virus-like particles using the nonconventional yeast Kluyveromyces marxianus

Porcine circovirus type 2 (PCV2) is a ubiquitous virus with high pathogenicity closely associated with the postweaning multisystemic wasting syndrome (PMWS) and porcine circovirus diseases (PCVDs), which caused significant economic losses in the swine industry worldwide every year. The PCV2 virus-like particles (VLPs) are a powerful subunit vaccine that can elicit high immune response due to its native PCV2 virus morphology. The baculovirus expression system is the widely used platform for producing commercial PCV2 VLP vaccines, but its yield and cost limited the development of low-cost vaccines for veterinary applications. Here, we applied a nonconventional yeast Kluyveromyces marxianus to enhance the production of PCV2 VLPs. After codon optimization, the PCV2 Cap protein was expressed in K. marxianus and assemble spontaneously into VLPs. Using a chemically defined medium, we achieved approximately 1.91 g/L of PCV2 VLP antigen in a 5-L bioreactor after high cell density fermentation for 72 h. That yield greatly exceeded to recently reported PCV2 VLPs obtained by baculovirus-insect cell, Escherichia coli and Pichia pastoris. By the means of two-step chromatography, 652.8 mg of PCV2 VLP antigen was obtained from 1 L of the recombinant K. marxianus cell culture. The PCV2 VLPs induced high level of anti-PCV2 IgG antibody in mice serums and decreased the virus titers in both livers and spleens of the challenged mice. These results illustrated that K. marxianus is a powerful yeast for cost-effective production of PCV2 VLP vaccines.

High-level expression and immunogenicity of porcine circovirus type 2b capsid protein without nuclear localization signal expressed in Hansenula polymorpha

Currently, porcine circovirus type 2b (PCV2b) is the dominant PCV2 genotype causing postweaning multisystemic wasting disease (PMWS) in pigs worldwide. Efforts have been made to develop various recombinant capsid proteins of PCV2b used in vaccines against PCV2b. However, the nuclear localization signal (NLS) of PCV2b capsid protein (CP) was found to inhibit the expression of the whole length capsid protein in E.coli. Here, we expressed a NLS-deleted capsid protein (ΔCP) of PCV2b in Hansenula polymorpha based on the capsid protein of PCV2b strain Y-7 isolated in China. Comparatively, the ΔCP was expressed at a higher level than the CP. The purified ΔCP could self-assemble into virus like particles (VLPs) with similar morphology of the VLPs formed by CP. The purified ΔCP could be recognized by the anti-sera derived from the mice immunized by inactivated PCV2b particles. Furthermore, it induced higher levels of PCV2b specific antibodies than the purified CP in mice. These results showed that the ΔCP, a recombinant PCV2b capsid protein without nuclear localization signal sequence, could be efficiently expressed in Hansenula polymorpha, and used as a candidate antigen for the development of PCV2b vaccines.

Engineering strategies for enhanced production of protein and bio-products in Pichia pastoris: A review

Pichia pastoris has been recognized as one of the most industrially important hosts for heterologous protein production. Despite its high protein productivity, the optimization of P. pastoris cultivation is still imperative due to strain- and product-specific challenges such as promoter strength, methanol utilization type and oxygen demand. To address the issues, strategies involving genetic and process engineering have been employed. Optimization of codon usage and gene dosage, as well as engineering of promoters, protein secretion pathways and methanol metabolic pathways have proved beneficial to innate protein expression levels. Large-scale production of proteins via high cell density fermentation additionally relies on the optimization of process parameters including methanol feed rate, induction temperature and specific growth rate. Recent progress related to the enhanced production of proteins in P. pastoris via various genetic engineering and cultivation strategies are reviewed. Insight into the regulation of the P. pastoris alcohol oxidase 1 (AOX1) promoter and the development of methanol-free systems are highlighted. Novel cultivation strategies such as mixed substrate feeding are discussed. Recent advances regarding substrate and product monitoring techniques are also summarized. Application of P. pastoris to the production of biodiesel and other value-added products via metabolic engineering are also reviewed. P. pastoris is becoming an indispensable platform through the use of these combined engineering strategies.

Immunogenicity of adenovirus vaccines expressing the PCV2 capsid protein in pigs

Porcine circovirus type 2 (PCV2) is the main pathogen of porcine circovirus associated disease (PCVAD), causing great economic losses in pig industry. In previous study, we constructed adenovirus vector vaccines expressing PCV2 Cap either modified with Intron A and WPRE, or CD40L and GMCSF, and evaluated all of these vaccines in mice and in pigs. Although Ad-A-C-W and Ad-CD40L-Cap-GMCSF could induce stronger immune responses than Ad-Cap, neither of them was better than commercial inactivated vaccine PCV2 SH-strain. In this study, secretory recombinant adenoviruses (Ad-A-spCap-W and Ad-A-spCD40L-spCap-spGMCSF-W) and non-secretory recombinant adenovirus Ad-A-CD40L-Cap-GMCSF-W were constructed, and identified by western blot and confocal laser microscope observation. The results of ELISA and VN showed that humoral immune responses induced by Ad-A-spCap-W and Ad-A-CD40L-Cap-GMCSF-W were not significantly different from SH-strain, but Ad-A-spCD40L-spCap-spGMCSF-W could induce significantly higher humoral immune response than SH-strain. Lymphocytes proliferative and cytokines releasing levels of Ad-A-spCap-W and Ad-A-CD40L-Cap-GMCSF-W were not significantly different from SH-strain, but Ad-A-spCD40L-spCap-spGMCSF-W was significantly higher than SH-strain. PCV2-challenge experiment showed that virus loads were significantly reduced in Ad-A-spCD40L-spCap-spGMCSF-W vaccinated group, and no obviously clinical and microscopic lesions were observed in Ad-A-spCD40L-spCap-spGMCSF-W vaccinated group. Altogether, these results demonstrate that recombinant adenovirus vaccine Ad-A-spCD40L-spCap-spGMCSF-W induces stronger immune responses and provides better protection than commercial inactivated vaccine PCV2 SH-strain, and suggest that Ad-A-spCD40L-spCap-spGMCSF-W could be a potential vaccine candidate against PCVAD.

Immunogenicity Evaluation of Modified Adenovirus Vaccines Expressing Porcine Circovirus Type 2 Capsid Protein in Pigs

Porcine circovirus type 2 (PCV2) adenovirus vaccine has been reported, but strong immune responses induced by adenovirus vector can decrease vaccine efficacy. To reduce the immunogenicity of adenovirus proteins, in previous study, we constructed the PCV2 adenovirus vaccine either modified with human cytomegalovirus first intron (Intron A) and woodchuck hepatitis virus post-transcriptional regulatory element (WPRE) to increase the expression of Cap, or coexpressed porcine tumor necrosis factor-related activate protein (CD40L) and granulocyte macrophage colony-stimulating factor (GMCSF) to improve the immunogenicity of PCV2 Cap adenovirus vaccine. All these vaccines were evaluated in mice. In the present study, the protective immune responses of Intron A/WPRE-modified recombinant adenovirus Ad-A-C-W and CD40L/GMCSF-modified recombinant adenovirus Ad-CD40L-Cap-GMCSF were evaluated in pigs. Enzyme-linked immunosorbent assay and virus neutralization assay showed that both Ad-A-C-W and Ad-CD40L-Cap-GMCSF could induce a higher specific antibody and neutralizing antibody than Ad-Cap (p < 0.05). Lymphocyte proliferation assay and cytokine release assay showed that Ad-A-C-W and Ad-CD40L-Cap-GMCSF induced a stronger cellular immune response than Ad-Cap. The PCV2 challenge experiment showed that viral loads of Ad-A-C-W-vaccinated group and Ad-CD40L-Cap-GMCSF-vaccinated group were lower than Ad-Cap vaccinated group (p < 0.05) after pigs were oronasally challenged with 5 × 10⁵ TCID₅₀ PCV2. Autopsy and histopathological examination showed that no obvious clinical and microscopic lesions were observed in groups Ad-Cap, Ad-A-C-W, and Ad-CD40L-Cap-GMCSF. Taken together, the results demonstrated that two modified recombinant adenovirus vaccines (Ad-A-C-W and Ad-CD40L-Cap-GMCSF) induced stronger humoral and cellular immune responses and provided better protection than unmodified adenovirus Ad-Cap. Therefore, Ad-A-C-W and Ad-CD40L-Cap-GMCSF would be used as potential vaccines for prevention and control of PCV2 infection.

Extracellular expression and antiviral activity of a bovine interferon-alpha through codon optimization in Pichia pastoris

Interferons (IFNs) are the primary line of defense against infectious agents. In particular, IFN-α is an important antiviral cytokine and has a wide range of immune-modulating functions. Porcine and human IFN-α have been successfully prepared and play important roles in the prevention and therapy of viral diseases. To date, there has been limited applied research on bovine IFN-α. To achieve high-level expression of recombinant bovine IFN-α (bIFN-α) in Pichia pastoris for large-scale application, the bIFN-α gene was optimized and synthesized on the basis of codon bias of P. pastoris. Optimized bIFN-α (opti-bIFN-α) was successfully expressed in P. pastoris and directly secreted into the culture supernatant. The amount of extracellular soluble opti-bIFN-α was observed to be 200μg/mL in a shake flask. Expression efficiency of opti-bIFN-α was found to be about three times that of wild-type bIFN-α when the expression yield was compared at the same copies of the targeted gene. In addition, both the original cultural supernatant and purified opti-bIFN-α showed strong antiviral activity in MDBK cells (2×10(6)AU/mL and 1×10(7)AU/mg, respectively) and IBRS-2 cells (3×10(5)AU/mL and 1.5×10(6)AU/mg, respectively) against a recombinant vesicular stomatitis virus expressing the green fluorescence protein. In this study, we demonstrated high-level extracellular expression of opti-bIFN-α by P. pastoris. To the best of our knowledge, the opti-bIFN-α yield observed in this study is the highest to be reported to date. Our results demonstrated that the extracellular opti-bIFN-α with strong antiviral activity could be easily prepared and purified at a low cost and that it may be a potential biological therapeutic drug against bovine viral infections.

Secreted expression of truncated capsid protein from porcine circovirus type 2 in Pichia pastoris

OBJECTIVE

To achieve secreted expression of the truncated capsid protein from porcine circovirus type 2 (PCV2) in Pichia pastoris.

RESULTS

A truncated cap gene (tcap) with a deleted N-terminal nuclear localization signal was optimized and synthesized. Effective secreted expression was achieved in P. pastoris GS115. The high-productive recombinant strain for tCap was grown in a 5 l bioreactor and the productivity of tCap in supernatant reached 250 μg/ml. Furthermore, serum antibody test demonstrated that adjuvant-assisting tCap induced a significant increase of specific PCV2-Cap antibody over time in mice and a similar antibody level in pigs compared with a commercial Cap-based subunit vaccine.

CONCLUSION

This work establishes a secreted expression strategy in P. pastoris for the production of PCV2 Cap with superior bioactivity, and this strategy might provide potential uses in developing Cap-based subunit vaccine in the future.

Multi-omics data driven analysis establishes reference codon biases for synthetic gene design in microbial and mammalian cells

In this study, we analyzed multi-omics data and subsets thereof to establish reference codon usage biases for codon optimization in synthetic gene design. Specifically, publicly available genomic, transcriptomic, proteomic and translatomic data for microbial and mammalian expression hosts, Escherichia coli, Saccharomyces cerevisiae, Pichia pastoris and Chinese hamster ovary (CHO) cells, were compiled to derive their individual codon and codon pair frequencies. Then, host dependent and -omics specific codon biases were generated and compared by principal component analysis and hierarchical clustering. Interestingly, our results indicated the similar codon bias patterns of the highly expressed transcripts, highly abundant proteins, and efficiently translated mRNA in microbial cells, despite the general lack of correlation between mRNA and protein expression levels. However, for CHO cells, the codon bias patterns among various -omics subsets are not distinguishable, forming one cluster. Thus, we further investigated the effect of different input codon biases on codon optimized sequences using the codon context (CC) and individual codon usage (ICU) design parameters, via in silico case study on the expression of human IFNγ sequence in CHO cells. The results supported that CC is more robust design parameter than ICU for improved heterologous gene design.

Generation in yeast of recombinant virus-like particles of porcine circovirus type 2 capsid protein and their use for a serologic assay and development of monoclonal antibodies

Background

Porcine circovirus type 2 (PCV2) is considered to be an important emerging pathogen associated with a number of different syndromes and diseases in pigs known as PCV2-associated diseases. It has been responsible for significant mortality among pigs and remains a serious economic problem to the swine industry worldwide leading to significant negative impacts on profitability of pork production.

Results

In this study we have demonstrated that PCV2 capsid (Cap) protein based virus-like particles (VLPs) were efficiently produced in yeast S. cerevisiae and induced production of monoclonal antibodies (MAbs) reactive with virus-infected cells. Moreover, PCV2 Cap VLPs served as a highly specific recombinant antigen for the development of an indirect IgG PCV2 Cap VLP-based ELISA for the detection of virus-specific IgG antibodies in swine sera. Four hundred-nine serum samples collected from pigs in Lithuania were tested for PCV2-specific IgG to determine the sensitivity and specificity of the newly developed ELISA in parallel using a commercial SERELISA test as a gold standard. From 409 tested serum samples, 297 samples were positive by both assays. Thirty-nine sera from 112 serum samples were determined as negative by SERELISA but were found to be positive both in the newly developed indirect IgG PCV2 Cap VLP-based ELISA and the PCR test.

Conclusions

We have demonstrated that S. cerevisiae expression system is an alternative to insect/baculovirus expression system for production of homogenous in size and shape PCV2 Cap protein-based VLPs similar to native virions. Yeast expression system tolerated native virus genes encoding PCV2 Cap protein variants as well as the codon-optimized gene. Moreover, yeast-derived PCV2 Cap VLPs were capable to induce the generation of PCV2-specific MAbs that did not show any cross-reactivity with PCV1-infected cells. The high sensitivity and specificity of the indirect IgG PCV2 Cap VLP-based ELISA clearly suggested that this assay is potentially useful diagnostic tool for screening PCV2–suspected samples.

Secreted production of assembled Norovirus virus-like particles from Pichia pastoris

BACKGROUND

Norovirus virus-like particles (NoV VLPs) have recently been explored as potential vaccine platforms due to their ability to produce an effective immune response. Expression of the main structural protein, VP1, leads to formation of self-assembled particles with similar characteristics to the original virus. These NoV VLPs have been expressed in Escherichia coli, yeast and insect cells. Expression in E. coli and insect cells share downstream processing issues due to the presence of inclusion bodies or the need for numerous purification steps. NoV VLPs have also been produced in the yeast P. pastoris; however the protein was only expressed intracellularly.

RESULTS

We have successfully expressed and secreted the VP1 protein in the novel P. pastoris strain, Bg11, using the methanol inducible pJ912 expression vector, containing the cDNA of NoV VP1. Expression of the VP1 protein in Bg11 was carried out in a 1.5 L bioreactor resulting in a total yield of NoV VLPs greater than 0.6 g/L. NoV VLPs obtained from the culture supernatant were purified via ion-exchange chromatography, resulting in particles with a purity over 90%. The average size of the particles after purification was 40 nm. Transmission electron microscopy was used to visualize the morphology of the particles and saliva-binding assay confirmed that the NoV VLPs bind to Histo-Blood Group Antigens (HBGA).

CONCLUSIONS

In this study we describe the expression and characterization of fully assembled Norovirus virus-like particles obtained from P. pastoris. The particles are similar in size, morphology and binding capacity, as previously described, for the original NoV. Our results detail the successful expression and secretion of VLPs in P. pastoris, improving their candidacy as a vaccine platform.

High yield production of pigeon circovirus capsid protein in the E. coli by evaluating the key parameters needed for protein expression

Background

Pigeon circovirus (PiCV) is considered to be a viral agent central to the development of young pigeon disease syndrome (YPDS). The Cap protein, a structural protein encoded by the cap (or C1) gene of PiCV, has been shown to be responsible for not only capsid assembly, but also has been used as antigen for detecting antibody when the host is infected with PiCV. The antigenic characteristics of the Cap protein potentially may allow the development of a detection kit that could be applied to control PiCV infection. However, poor expression and poor protein solubility have hampered the production of recombinant Cap protein in the bacteria. This study was undertaken to develop the optimal expression of recombinant full-length Cap protein of PiCV using an E. coli expression system.

Results

The PiCV cap gene was cloned and fused with different fusion partners including a His-tag, a GST-tag (glutathioine-S-transferase tag) and a Trx-His-tag (thioredoxin-His tag). The resulting constructs were then expressed after transformation into a number of different E. coli strains; these then had their protein expression evaluated. The expression of the recombinant Cap protein in E. coli was significantly increased when Cap protein was fused with either a GST-tag or a Trx-His tag rather than a His-tag. After various rare amino acid codons presented in the Cap protein were optimized to give the sequence rCap_opt, the expression level of the GST-rCap_opt in E. coli BL21(DE3) was further increased to a significant degree. The highest protein expression level of GST-rCap_opt obtained was 394.27 ± 26.1 mg/L per liter using the E. coli strain BL21(DE3)-pLysS. Moreover, approximately 74.5% of the expressed GST-rCap_opt was in soluble form, which is higher than the soluble Trx-His-rCap_opt expressed using the BL21(DE3)-pLysS strain. After purification using a GST affinity column combined with ion-exchange chromatography, the purified recombinant GST-rCap_opt protein was found to have good antigenic activity when tested against PiCV-infected pigeon sera.

Conclusions

These findings shows that the E. coli-expressed full-length PiCV Cap protein has great potential in terms of large-scaled production and this should allow in the future the development of a serodiagnostic kit that is able to clinically detect PiCV infection in pigeons.

Expression, purification and antibody preparation using different constructs of PCV2 capsid protein

Capsid protein (Cap) of porcine circovirus 2 (PCV2) contained critical epitopes for inducing a protective immune response. Here, different fragments of PCV2 Cap protein were cloned, expressed, purified and used to raise polyclonal antibodies. The result showed the recombinant plasmids expressed efficiently in the prokaryotic system. Western blot and ELISA showed the recombinant protein had antigenicity and immunogenicity. Furthermore, efficiency of different constructs to produce antibody against PCV2 was compared. Reactivity and specificity of the polyclonal antibody were characterized by Western blot and indirect immunofluorescent assays. The results indicated that polyclonal antiserum prepared from protein ΔCap17-233 had better reactivity and specificity against PCV2 in comparison to that of protein ΔCap51-233 and the inactivated vaccine. These results will contribute to further studies focusing on the gene and vaccine development against PCV2.

Gene and protein sequence optimization for high-level production of fully active and aglycosylated lysostaphin in Pichia pastoris

Lysostaphin represents a promising therapeutic agent for the treatment of staphylococcal infections, in particular those of methicillin-resistant Staphylococcus aureus (MRSA). However, conventional expression systems for the enzyme suffer from various limitations, and there remains a need for an efficient and cost-effective production process to facilitate clinical translation and the development of nonmedical applications. While Pichia pastoris is widely used for high-level production of recombinant proteins, there are two major barriers to the production of lysostaphin in this industrially relevant host: lack of expression from the wild-type lysostaphin gene and aberrant glycosylation of the wild-type protein sequence. The first barrier can be overcome with a synthetic gene incorporating improved codon usage and balanced A+T/G+C content, and the second barrier can be overcome by disrupting an N-linked glycosylation sequon using a broadened choice of mutations that yield aglyscosylated and fully active lysostaphin. The optimized lysostaphin variants could be produced at approximately 500 mg/liter in a small-scale bioreactor, and 50% of that material could be recovered at high purity with a simple 2-step purification. It is anticipated that this novel high-level expression system will bring down one of the major barriers to future development of biomedical, veterinary, and research applications of lysostaphin and its engineered variants.

Optimizing plant transporter expression in Xenopus oocytes

BACKGROUND

Rapid improvements in DNA synthesis technology are revolutionizing gene cloning and the characterization of their encoded proteins. Xenopus laevis oocytes are a commonly used heterologous system for the expression and functional characterization of membrane proteins. For many plant proteins, particularly transporters, low levels of expression can limit functional activity in these cells making it difficult to characterize the protein. Improvements in synthetic DNA technology now make it quick, easy and relatively cheap to optimize the codon usage of plant cDNAs for Xenopus. We have tested if this optimization process can improve the functional activity of a two-component plant nitrate transporter assayed in oocytes.

RESULTS

We used the generally available software (http://www.kazusa.or.jp/codon/; http://genomes.urv.es/OPTIMIZER/) to predict a DNA sequence for the plant gene that is better suited for Xenopus laevis. Rice OsNAR2.1 and OsNRT2.3a DNA optimized sequences were commercially synthesized for Xenopus expression. The template DNA was used to synthesize cRNA using a commercially available kit. Oocytes were injected with cRNA mixture of optimized and original OsNAR2.1 and OsNRT2.3a. Oocytes injected with cRNA obtained from using the optimized DNA template could accumulate significantly more NO3- than the original genes after 16 h incubation in 0.5 mM Na15NO3. Two-electrode voltage clamp analysis of the oocytes confirmed that the codon optimized template resulted in significantly larger currents when compared with the original rice cDNA.

CONCLUSION

The functional activity of a rice high affinity nitrate transporter in oocytes was improved by DNA codon optimization of the genes. This methodology offers the prospect for improved expression and better subsequent functional characterization of plant proteins in the Xenopus oocyte system.

Expression, purification, and immunogenic characterization of Epstein-Barr virus recombinant EBNA1 protein in Pichia pastoris

Epstein-Barr virus (EBV) is a ubiquitous human herpesvirus associated with the development of both lymphoid and epithelial tumors. EBNA1 is the only viral protein expressed in all EBV-associated malignancies and plays important roles in EBV latency. Thus, EBNA1 is thought to be a promising antigen for immunotherapy of all EBV-associated malignancies. This study was undertaken to produce recombinant EBNA1 protein in Pichia pastoris and evaluate its immunogenicity. The truncated EBNA1 (E1ΔGA, codons 390-641) was expressed as a secretory protein with an N-terminal histidine tag in the methylotrophic yeast P. pastoris and purified by Ni-NTA affinity chromatography. The purified proteins were then used as antigens to immunize BALB/c mice for production of polyclonal antibodies. Western blot analysis showed that the polyclonal antibodies specifically recognized the EBNA1 protein in B95-8 cell lysates. The recombinant E1ΔGA also induced strong lymphoproliferative and Th1 cytokine responses in mice. Furthermore, mice immunized with E1ΔGA developed CD4+ and CD8+ T cell responses. These findings showed that the yeast-expressed E1ΔGA retained good immunogenicity and might be a promising vaccine candidate against EBV-associated malignancies.