Expression and Characterization of Yeast Derived Chikungunya Virus Like Particles (CHIK-VLPs) and Its Evaluation as a Potential Vaccine Candidate

Chikungunya virus (CHIKV) has emerged as a global health concern due to its recent spread in both old and new world. So far, no CHIKV specific drug or vaccine is licensed for human use. In this study, we report production of Chikungunya virus like particles (CHIK-VLPs) using novel yeast expression system (Pichia pastoris) and its evaluation as vaccine candidate. The gene encoding structural polyprotein of CHIKV from a recent epidemic strain was cloned into yeast expression system. The multicopy integrants were processed for expression of CHIK-VLPs. The VLPs were purified and confirmed through electron microscopic analysis for their morphological identity with CHIKV. The in vitro and in vivo evaluation of CHIK-VLPs as vaccine candidate was determined in Balb/c mice. Induction of both humoral and cellular immune response was observed with different doses of CHIK-VLPs. The humoral immune response was studied through different techniques like enzyme linked immunosorbent assay, IgG Isotyping and plaque reduction neutralization test. CHIK-VLPs were found to elicit high titer of antibodies that are able to recognize native CHIKV. Higher level of IgG2a and IgG1 subtypes was identified suggestive of balanced Th1/Th2 response. Both in vitro and in vivo neutralization activity of CHIK-VLPs antibodies was observed even with low concentration, which shows its high specificity and neutralizing activity against two different CHIKV strains. Neonatal mice receiving anti-CHIK-VLPs antibodies were protected from CHIKV challenge. Induction of cellular immune response was confirmed through higher level of TNF-α, IL-10 and substantial level of IL-2, IL-4 and IFN-γ indicating a balanced response. This is the first report, where CHIK-VLPs has been expressed by Pichia pastoris and evaluated for neutralizing activity against CHIKV. These promising results indicate the utility of CHIK-VLPs as a promising vaccine candidate against emerging CHIKV.

Chikungunya virus (CHIKV) has emerged in many parts of tropics in last decade. The absence of an approved vaccine or antiviral drug for CHIKV makes it one of the important public health challenges. Though attempt to develop a CHIKV vaccine was initiated in 1980s, however it has not succeeded so far. The Virus like particles (VLPs) are now explored as promising vaccine candidate against many viruses viz. HBV, HPV etc. In this study, we report the production of CHIK-VLPs using novel yeast expression system (Pichia pastoris) and its evaluation as vaccine candidate. These CHIK-VLPs share morphological identity to native CHIKV. The results indicate that CHIK-VLPs induced both cell mediated as well as humoral response in a balanced manner, which fulfils its criteria as a potent immunogen. Further, antibodies generated against CHIK-VLPs demonstrated efficient in vitro and in vivo neutralization activity, as evaluated through plaque reduction in Vero cells and protection in CHIKV infected neonatal mice respectively using two different CHIKV strains, which makes it a promising vaccine candidate. The yeast expressed CHIK-VLPs has high potential for development of an effective vaccine candidate against CHIKV during epidemic situations.

Protective efficacy of Bluetongue virus-like and subvirus-like particles in sheep: presence of the serotype-specific VP2, independent of its geographic lineage, is essential for protection

There have been multiple separate outbreaks of Bluetongue (BT) disease of ruminants in Europe since 1998, often entering via the Mediterranean countries of Italy, Spain and Greece. BT is caused by an orbivirus, Bluetongue virus (BTV), a member of the family Reoviridae. BTV is a non-enveloped double-capsid virus, which encodes 7 structural proteins (VP1-VP7) and several non-structural proteins (NS1, NS2, NS3/3a and NS4) from ten double-stranded RNA segments of the genome. In this report, we have prepared BTV virus-like particles (VLPs, composed of VP2, VP3, VP5 and VP7) and sub-viral, inner core-like particles (CLPs, VP3 and VP7) using a recombinant baculovirus expression system. We compared the protective efficacy of VLPs and CLPs in sheep and investigated the importance of geographical lineages of BTV in the development of vaccines. The Greek crossbred Karagouniko sheep, which display mild to sub-clinical BT, were vaccinated with VLPs or CLPs of BTV-1, derived from western lineage and were challenged with virulent BTV-1 from an eastern lineage. All VLP-vaccinated animals developed a neutralising antibody response to BTV-1 from both lineages prior to challenge. Moreover, post-challenged animals had no clinical manifestation or viraemia and the challenged virus replication was completely inhibited. In contrast, CLP-vaccinated animals did not induce any neutralising antibody response but developed the group specific VP7 antibodies. CLPs also failed to prevent the clinical manifestation and virus replication, but in comparison to controls, the severity of disease manifestation and viraemia was mitigated. The data demonstrated that the outer capsid was essential for complete protection, while the geographical origin of the BTV was not critical for development of a serotype specific vaccine.

Yeast expressed recombinant Hemagglutinin protein of novel H1N1 elicits neutralising antibodies in rabbits and mice

Currently available vaccines for the pandemic Influenza A (H1N1) 2009 produced in chicken eggs have serious impediments viz limited availability, risk of allergic reactions and the possible selection of sub-populations differing from the naturally occurring virus, whereas the cell culture derived vaccines are time consuming and may not meet the demands of rapid global vaccination required to combat the present/future pandemic. Hemagglutinin (HA) based subunit vaccine for H1N1 requires the HA protein in glycosylated form, which is impossible with the commonly used bacterial expression platform. Additionally, bacterial derived protein requires extensive purification and refolding steps for vaccine applications. For these reasons an alternative heterologous system for rapid, easy and economical production of Hemagglutinin protein in its glycosylated form is required. The HA gene of novel H1N1 A/California/04/2009 was engineered for expression in Pichia pastoris as a soluble secreted protein. The full length HA- synthetic gene having α-secretory tag was integrated into P. pastoris genome through homologous recombination. The resultant Pichia clones having multiple copy integrants of the transgene expressed full length HA protein in the culture supernatant. The Recombinant yeast derived H1N1 HA protein elicited neutralising antibodies both in mice and rabbits. The sera from immunised animals also exhibited Hemagglutination Inhibition (HI) activity. Considering the safety, reliability and also economic potential of Pichia expression platform, our preliminary data indicates the feasibility of using this system as an alternative for large-scale production of recombinant influenza HA protein in the face of influenza pandemic threat.

Immunogenicity of recombinant VP2 proteins of all nine serotypes of African horse sickness virus

African horse sickness (AHS) is an equine disease with a mortality of up to 90% for susceptible horses. The causative agent AHS virus (AHSV) is transmitted by species of Culicoides. AHSV serogroup within the genus Orbivirus of the Reoviridae family consists of nine serotypes that show no or very limited cross-neutralization. Of the seven structural proteins (VP1-VP7) of AHSV, VP2 is the serotype specific protein, and the major target for neutralizing antibodies. In this report, recombinant VP2 proteins of all nine serotypes were expressed individually by the baculovirus expression system and the immunogenicity of each was studied by immunization of guinea pigs with single VP2 as well as with cocktails of VP2 proteins. Homologous neutralizing antibodies measured by 50% plaque reduction assay showed varying degrees (from 37 to 1365) of titers for different VP2 proteins. A low cross-neutralizing antibody titer was found for genetically related AHSV serotypes. Immunization with VP2 cocktails containing equal amounts of each of the VP2 proteins also triggered neutralizing antibodies albeit to lower titers (4-117) to each of the serotypes in the cocktail. This study is a first step to develop a VP2 subunit vaccine for AHS and our results indicate that VP2 subunit vaccines are feasible individually or in a multi-serotype cocktail.

Influence of copy number on the expression levels of pandemic influenza hemagglutinin recombinant protein in methylotrophic yeast Pichia pastoris

The hemagglutinin (HA) gene of novel Swine Origin Influenza A/California/04/2009 (H1N1) was engineered for expression in Pichia pastoris as a soluble secreted protein. The full length HA-synthetic gene having α secretory tag under the control of AOX1 promoter was integrated into P. pastoris genome through homologous recombination. The resultant Pichia clones having single and multiple copy integrants of the expression cassettes were screened for the expression of full length HA protein in the culture supernatant. In order to completely exploit the expression potential of the P. pastoris expression system, a systematic investigation on the influence of gene copy number on the expression of the recombinant protein was made. A panel of Pichia clones carrying increasing copies of the heterologous gene was selected based on Geneticin resistance and SYBR green-based quantitative real-time PCR approach. Using these strategies, recombinant Pichia transformants carrying up to a maximum of four to six copies of the transgene were identified. After optimising the expression conditions for shaker flask culture, the resultant clones demonstrated that the increase in copy number results in a proportional elevation in the expression level of H1N1HA recombinant protein. Our findings clearly suggest that the gene dosage effect play a vital role in high level expression of the pandemic Influenza HA protein in yeast system.

Integration and expression of Bluetongue VP2 gene in somatic embryos of peanut through particle bombardment method

After pre-culture and treatment of osmosis, zygotic embryos of peanut (Arachis hypogaea L.) were transformed via particle bombardment with a plasmid containing a Bluetongue VP2 gene (BTVP2) comprising neutralizing epitopes. Selection for Kanamycin resistant calluses and somatic embryos was initiated at 12th day post-bombardment on medium containing 25 mg/L Kanamycin. Under continuous selection, 12.38% Kanamycin resistant plantlets were regenerated from bombarded somatic embryos. The presence and integration of BTVP2 DNA in regenerated Kanamycin resistant plants were confirmed by southern hybridization assay using non-radioactive Digoxiginin BTVP2 probe. Beta-glucuronidase (GUS) enzyme activity was detected in transgenic somatic embryos but not from control, non-transformed embryos. The expression of the BTVP2 protein was confirmed through RT-PCR (reverse transcription polymerase chain reaction) using the RNA isolated from the transgenic callus employing BTVP2-specific primers. The production of transgenic peanut was mainly focused on evaluating a newly improved somatic embryogenesis regeneration system as well as the gene transfer method and to produce the Bluetongue outer coat protein that comprises the neutralizing epitopes.

Antibody-quantum dot conjugates exhibit enhanced antibacterial effect vs. unconjugated quantum dots

The effect of a 20-min exposure to antibody-quantum dot (Ab-QD) conjugates on colony counts of Escherichia coli was assessed by the spread-plate method and compared with exposure to unconjugated QDs having only amine or carboxyl groups on their surfaces. Under these conditions, Ab-QD conjugates generally exhibited >90% reduction in colony-forming units as compared to untreated E. coli and E. coli treated with unconjugated QDs after incubation for as long as 41 h. The antibacterial effect of Ab-QD conjugates vs. unconjugated QDs on Salmonella enterica subsp. enterica serovar Typhimurium was also assessed by means of a disk-diffusion technique which demonstrated greater growth inhibition (approximately 3 mm greater) by Ab-QD conjugate-impregnated disks than by unconjugated-QD-only-impregnated disks at a 10-microg disk load. At a 25-microg disk load, both treatment groups exhibited nearly equal growth inhibition.

A simple Pichia pastoris fermentation and downstream processing strategy for making recombinant pandemic Swine Origin Influenza a virus Hemagglutinin protein

The present Influenza vaccine manufacturing process has posed a clear impediment to initiation of rapid mass vaccination against spreading pandemic influenza. New vaccine strategies are therefore needed that can accelerate the vaccine production. Pichia offers several advantages for rapid and economical bulk production of recombinant proteins and, hence, can be attractive alternative for producing an effective influenza HA based subunit vaccine. The recombinant Pichia harboring the transgene was subjected to fed-batch fermentation at 10 L scale. A simple fermentation and downstream processing strategy is developed for high-yield secretory expression of the recombinant Hemagglutinin protein of pandemic Swine Origin Influenza A virus using Pichia pastoris via fed-batch fermentation. Expression and purification were optimized and the expressed recombinant Hemagglutinin protein was verified by sodium dodecyl sulfate polyacrylamide gel electrophoresis, Western blot and MALDI-TOF analysis. In this paper, we describe a fed-batch fermentation protocol for the secreted production of Swine Influenza A Hemagglutinin protein in the P. pastoris GS115 strain. We have shown that there is a clear relationship between product yield and specific growth rate. The fed-batch fermentation and downstream processing methods optimized in the present study have immense practical application for high-level production of the recombinant H1N1 HA protein in a cost effective way using P. pastoris.

Heterologous expression of Bluetongue VP2 viral protein fragment in Pichia pastoris

The partial VP2-encoding gene of Bluetongue virus serotype 23 (BTV-23) was amplified using reverse transcription polymerase chain reaction (RT-PCR) and inserted into pPICK9K vector. Recombinant plasmid DNA was integrated into the genome of Pichia pastoris by electroporation and expressed protein was identified by SDS-PAGE. High-level secreted expression was achieved after selecting the Mut ( + ) phenotype with multi-copy integrant in the recombinant yeast. The partial fragment of Bluetongue VP2 protein (BTV VP2) of approximately 45 KDa was secreted into the culture supernatant by the recombinant yeast when induced with methanol. Western and immuno dot-blotting methods confirmed the expressed BTV VP2 protein. The expressed protein has been demonstrated to be immunogenic in rabbits. A standardized method has been evolved for optimal expression and high-level production of the recombinant protein (284 mg/L). This is the first report demonstrating the possibility of mass production of BTV VP2 protein using P. pastoris.

Optimization of Dengue-3 recombinant NS1 protein expression in E. coli and in vitro refolding for diagnostic applications

Dengue non-structural protein (NS1) is known to be protective antigen and also has immense application for serodiagnosis. Several serodiagnostic assays available for dengue viral infection are dependent on tissue culture-grown viral proteins. This task is unsafe, laborious, more expensive that makes it unsuitable for routine large-scale production. Although bacterial expression is relatively simple and easy for recombinant protein expression, it is more challenging to make NS1 protein with native structural and immunological features using bacterial expression system. We have successfully developed a method leading to the purification and refolding of recombinant dengue virus type 3 (DENV3) NS1. The gene encoding NS1 was amplified and cloned in pET28a (+) vector. In order to increase the purity of the recombinant NS1, the transgene was engineered to carry 6× Histidine tags at both N and C-terminal ends. The recombinant construct (pETNS1) was transformed into E. coli Rosetta-gami cells and the expression conditions viz IPTG concentration, media type, temperature, and harvest time were optimized. The size of the expressed protein was found to be ~45 kDa and the authenticity of the expressed protein was confirmed using anti-His and anti-NS1 monoclonal antibodies. The NS1 protein was purified under denaturing conditions, to attain the native conformation, NS1 protein was in vitro refolded and dialyzed. The refolded NS1 protein was detected by commercial Immuno chromatographic strip and NS1 specific monoclonal antibodies. IgM antibody capture ELISA was performed using refolded recombinant NS1 protein which recognized the IgM antibodies in dengue-positive samples of acute phase of infection. Our result suggests that rNS1 protein has immense diagnostic potential and can be used in developing point of care diagnostic assays.

Fed batch fermentation and purification strategy for high yield production of Brucella melitensis recombinant Omp 28 kDa protein and its application in disease diagnosis

Brucellosis is a disease caused by bacteria belonging to the genus Brucella. It affects cattle, goat, sheep, dog and humans. The serodiagnosis of brucellosis involves detection of antibodies generated against the LPS or whole cell bacterial extracts, however these tests lack sensitivity and specificity. The present study was performed to optimize the culture condition for the production of recombinant Brucella melitensis outer membrane protein 28 kDa protein in E.coli via fed batch fermentation. Expression was induced with 1.5mM isopropyl β thiogalactoside and the expressed recombinant protein was purified using Ni-NTA affinity chromatography. After fed-batch fermentation the dry cell weight of 17.81 g/L and a purified protein yield of 210.10 mg/L was obtained. The purified Brucella melitensis recombinant Omp 28 kDa protein was analyzed through SDS- poly acrylamide gel electrophoresis and western blotting. The obtained recombinant protein was evaluated for its diagnostic application through Indirect ELISA using brucellosis suspected human sera samples. Our results clearly indicate that recombinant Omp28 produced via fed batch fermentation has immense potential as a diagnostic reagent that could be employed in sero monitoring of brucellosis.