Comparison of strategies for the production of FMDV empty capsids using the baculovirus vector system

Creation of poxvirus expressing foot-and-mouth and peste des petits ruminant disease virus proteins

OBJECTIVE

Foot-and-mouth disease (FMD) and Peste des petits ruminant disease (PPR) are acute and severe infectious diseases of sheep and are listed as animal diseases for compulsory immunization. However, there is no dual vaccine to prevent these two diseases. The Modified Vaccinia virus Ankara strain (MVA) has been widely used in the construction of recombinant live vector vaccine because of its large capacity of foreign gene, wide host range, high safety, and immunogenicity. In this study, MVA-GFP recombinant virus skeleton was used to construct dual live vector vaccines against FMD and PPR.

METHODS

The recombinant plasmid pUC57-FMDV P1-2A3CPPRV FH was synthesized and transfected into MVA-GFP infected CEF cells for homologous recombination.

RESULTS

The results showed that a recombinant virus without fluorescent labeling was obtained after multiple rounds of plaque screening. The recombinant virus successfully expressed the target proteins, and the empty capsid of FMDV could be observed by transmission electron microscope (TME), and the expression levels of foreign proteins (VP1 and VP3) detected by ELISA were like those detected in FMDV-infected cells. This study laid the foundation for the successful construction of a live vector vaccine against FMD and PPR.

KEY POINTS

• A recombinant MVA expressing FMDVP12A3C and PRRV HF proteins • Both the FMDV and PRRV proteins inserted into the virus were expressed • The proteins expressed by the recombinant poxvirus were assembled into VLPs.

Advanced Foot-And-Mouth Disease Vaccine Platform for Stimulation of Simultaneous Cellular and Humoral Immune Responses

Currently available commercial foot-and-mouth disease (FMD) vaccines have various limitations, such as the slow induction and short-term maintenance of antibody titers. Therefore, a novel FMD vaccine that can rapidly induce high neutralizing antibody titers to protect the host in early stages of an FMD virus infection, maintain high antibody titers for long periods after one vaccination dose, and confer full protection against clinical symptoms by simultaneously stimulating cellular and humoral immunity is needed. Here, we developed immunopotent FMD vaccine strains A-3A and A-HSP70, which elicit strong initial cellular immune response and induce humoral immune response, including long-lasting memory response. We purified the antigen (inactivated virus) derived from these immunopotent vaccine strains, and evaluated the immunogenicity and efficacy of the vaccines containing these antigens in mice and pigs. The immunopotent vaccine strains A-3A and A-HSP70 demonstrated superior immunogenicity compared with the A strain (backbone strain) in mice. The oil emulsion-free vaccine containing A-3A and A-HSP70 antigens effectively induced early, mid-term, and long-term immunity in mice and pigs by eliciting robust cellular and humoral immune responses through the activation of co-stimulatory molecules and the secretion of proinflammatory cytokines. We successfully derived an innovative FMD vaccine formulation to create more effective FMD vaccines.

Foot-and-Mouth Disease Virus: Immunobiology, Advances in Vaccines and Vaccination Strategies Addressing Vaccine Failures-An Indian Perspective

A mass vaccination campaign in India seeks to control and eventually eradicate foot-and-mouth disease (FMD). Biosanitary measures along with FMD monitoring are being conducted along with vaccination. The implementation of the FMD control program has drastically reduced the incidence of FMD. However, cases are still reported, even in regions where vaccination is carried out regularly. Control of FMD outbreaks is difficult when the virus remains in circulation in the vaccinated population. Various FMD risk factors have been identified that are responsible for FMD in vaccinated areas. The factors are discussed along with strategies to address these challenges. The current chemically inactivated trivalent vaccine formulation containing strains of serotype O, A, and Asia 1 has limitations including thermolability and induction of only short-term immunity. Advantages and disadvantages of several new-generation alternate vaccine formulations are discussed. It is unfeasible to study every incidence of FMD in vaccinated animals/areas in such a big country as India with its huge livestock population. However, at the same time, it is absolutely necessary to identify the precise reason for vaccination failure. Failure to vaccinate is one reason for the occurrence of FMD in vaccinated areas. FMD epidemiology, emerging and re-emerging virus strains, and serological status over the past 10 years are discussed to understand the impact of vaccination and incidences of vaccination failure in India. Other factors that are important in vaccination failure that we discuss include disrupted herd immunity, health status of animals, FMD carrier status, and FMD prevalence in other species. Recommendations to boost the search of alternate vaccine formulation, strengthen the veterinary infrastructure, bolster the real-time monitoring of FMD, as well as a detailed investigation and documentation of every case of vaccination failure are provided with the goal of refining the control program.

Generation of acid resistant virus like particles of vaccine strains of foot-and-mouth disease virus (FMDV)

Foot-and-mouth disease (FMD) is a contagious viral disease affecting cloven hoofed livestock. Insect cell expressed virus like particles (VLPs) are potential alternative to overcome the limitations of inactivated vaccine. However, at pH < 6.5, virus particles disassociate into pentameric structure resulting in loss of antigenicity. Accordingly, we generated seven mutant VLPs containing mutations in the structural genes of FMDV vaccine strains (N17D and/or H145Y for serotypes O/IND/R2/75 and Asia1/IND/63/72; and H142D for serotype A/IND/40/00) by PCR based site directed mutagenesis. Acid resistant VLPs produced by baculovirus expression system were tested for acid stability at pH 7.5, 6.5, 6.0 and 5.5 followed by reactivity in sandwich-ELISA (s-ELISA), which revealed mutant-1 (N17D) of serotype O and Asia1 retained the antigenicity in s-ELISA even at pH 5.5 as compared to other VLPs and wild-types. Further, the 75S empty capsids obtained in sucrose density gradient, when tested in liquid phase blocking ELISA (LPBE) in comparison to cell culture antigen indicated that the VLPs were stable at acidic pH. Transmission electron microscopy of OM-1 confirmed the intact morphology of the empty VLPs. It is concluded that acid resistant VLPs could be useful for developing new generation vaccine or diagnostic for FMDV.

In vivo production of recombinant proteins using occluded recombinant AcMNPV-derived baculovirus vectors

Trichoplusia ni insect larvae infected with vectors derived from the Autographa californica multiple nucleopolyhedrovirus (AcMNPV), are an excellent alternative to insect cells cultured in conventional bioreactors to produce recombinant proteins because productivity and cost-efficiency reasons. However, there is still a lot of work to do to reduce the manual procedures commonly required in this production platform that limit its scalability. To increase the scalability of this platform technology, a current bottleneck to be circumvented in the future is the need of injection for the inoculation of larvae with polyhedrin negative baculovirus vectors (Polh-) because of the lack of oral infectivity of these viruses, which are commonly used for production in insect cell cultures. In this work we have developed a straightforward alternative to obtain orally infective vectors derived from AcMNPV and expressing recombinant proteins that can be administered to the insect larvae (Trichoplusia ni) by feeding, formulated in the insect diet. The approach developed was based on the use of a recombinant polyhedrin protein expressed by a recombinant vector (Polh+), able to co-occlude any recombinant Polh- baculovirus vector expressing a recombinant protein. A second alternative was developed by the generation of a dual vector co-expressing the recombinant polyhedrin protein and the foreign gene of interest to obtain the occluded viruses. Additionally, by the incorporation of a reporter gene into the helper Polh+ vector, it was possible the follow-up visualization of the co-occluded viruses infection in insect larvae and will help to homogenize infection conditions. By using these methodologies, the production of recombinant proteins in per os infected larvae, without manual infection procedures, was very similar in yield to that obtained by manual injection of recombinant Polh- AcMNPV-based vectors expressing the same proteins. However, further analyses will be required for a detailed comparison of production yields reached by injection vs oral infections for different recombinant proteins. In conclusion, these results open the possibility of future industrial scaling-up production of recombinant proteins in insect larvae by reducing manual operations.

Foot-and-mouth disease vaccines

Foot-and-mouth disease (FMD) is a highly contagious disease of cloven-hoofed animals. The disease affects many areas of the world, often causing extensive epizootics in livestock, mostly farmed cattle and swine, although sheep, goats and many wild species are also susceptible. In countries where food and farm animals are essential for subsistence agriculture, outbreaks of FMD seriously impact food security and development. In highly industrialized developed nations, FMD endemics cause economic and social devastation mainly due to observance of health measures adopted from the World Organization for Animal Health (OIE). High morbidity, complex host-range and broad genetic diversity make FMD prevention and control exceptionally challenging. In this article we review multiple vaccine approaches developed over the years ultimately aimed to successfully control and eradicate this feared disease.

IRES mediated expression of viral 3C protease for enhancing the yield of FMDV empty capsids using baculovirus system

For expression of FMDV empty capsids, high protease activity associated with 3C co-expressed with P1 polyprotein has been reported to adversely affect the yields of capsids. Limiting the levels of 3Cpro relative to P1-2A polypeptide is thus critical to enhance the yields. In this study, FMDV internal ribosome entry site (IRES) sequence which serves as an alternative to the CAP-dependent translation initiation mechanism, was used for controlled translation of 3C protease. Baculovirus expressing bicistronic cDNA cassette containing two open reading frames-FMDV capsid gene (P1-2A) and 3Cpro intervened by IRES was prepared. Analysis of the expression in insect cells infected with baculovirus showed increased accumulation of processed capsids. Recombinant capsids showed higher immunoreactivity similar to the whole virus antigen, when reacted with polyclonal antibodies against the purified whole virus 146S particles. Thus, inclusion of the IRES upstream of 3Cpro facilitated reduced expression of the protease in baculovirus expression system, without causing significant proteolysis, thereby contributing to improved yields of the processed capsid antigens.