Elsevier

Biologicals

Volume 43, Issue 6, November 2015, Pages 437-443
Biologicals

Comparative efficacy of virus like particle (VLP) vaccine of foot-and-mouth-disease virus (FMDV) type O adjuvanted with poly I:C or CpG in guinea pigs

https://doi.org/10.1016/j.biologicals.2015.09.004Get rights and content

Highlights

  • CpG adjuvanted FMDV-VLP vaccine induced significant cell mediated immune response in Guinea pigs.

  • FMDV-VLP vaccine with CpG showed 75% protection compared to 66% and 62% in ISA206 and poly IC based VLP vaccine.

  • CpG was more efficacious than ISA206 and Poly-IC adjuvants in providing protection against FMDV challenge in guinea pigs.

  • Protective efficacy of FMDV-VLP vaccine was enhanced by CpG adjuvant.

Abstract

Foot-and-mouth disease (FMD) is one of the most contagious and economically important diseases of cloven-hoofed livestock. Currently used inactivated FMD vaccines have short lived immunity besides risk of handling live virus. We studied recombinant FMD virus like particles (VLPs) encoded by FMDV type O/IND/R2/75 polyprotein genes expressed in Sf9 cells and adjuvanted with CpG or Poly I:C in inducing protective immune response in guinea pigs. Guinea pigs immunized with VLP + CpG vaccine had shown markedly higher cell mediated immunity (CMI) in comparison to the conventional vaccine group as evident from higher levels of IgG2 than IgG1. Although the humoral response was less in VLP + CpG compared to conventional vaccine, the lymphocyte stimulation index was more in VLP + CpG compared to conventional and VLP + Poly I:C vaccine groups. Finally the challenge experiments on 28 and 56 dpv had shown 75% protection in VLP + CpG immunized guinea pigs primary and boosted animals, while 50% and 62% protection in VLP + Poly I:C in primary and boosted animals, respectively. In conclusion, CpG adjuvant was found to be superior followed by ISA206 and Poly I:C in eliciting protection in VLP based FMD vaccines in guinea pigs.

Introduction

Foot-and-mouth disease (FMD) is a highly contagious viral disease of livestock that causes severe economic loss in susceptible cloven-hoofed animals, such as cattle, sheep, goats and pigs. FMD is a transboundary disease, caused by an RNA virus, Foot-and-Mouth Disease Virus (FMDV), a positive-sense single-stranded RNA virus belonging to genus Aphthovirus and family Picornaviridae [1]. The viral RNA is translated as a single open reading frame into a polyprotein, and cleaved predominantly by 3C viral protease to produce structural and non-structural proteins required for virus assembly and replication [2]. Among the seven known serotypes of FMDV, only three serotypes namely O, A and Asia1 are prevalent in India [3]. Use of inactivated FMD vaccine with oil adjuvant is the most effective way to control and eradicate FMD in endemic countries [4]. Although, the current FMD vaccine is chemically inactivated oil adjuvanted whole virus preparation that has been used to effectively control the disease in enzootic countries, its use may lead to new disease outbreaks due to a possible incomplete inactivation of the virus during manufacturing or inadvertent escape of virus [5]. To overcome these issues, new generation vaccines like virus-like particles (VLPs) are being developed as non-infectious, safe and marker vaccines. VLPs can mimic the epitopes present on the native virus, leading to stimulation of both B and T cells with increased cell mediated immunity (CMI) [6]. Baculovirus expression system (BVES) has been applied to developing veterinary vaccines based on VLPs produced in insect cells for blue tongue virus, bovine papillomavirus type1, chicken anemia virus, infectious bursal disease virus, porcine, mink and canine parvoviruses, and porcine encephalomyocarditis virus [6]. VLPs are also tested as vaccine candidates for FMDV type O [7] and type Asia1 viruses [8].

After translation of FMDV viral RNA, a 95 kDa polyprotein (P1) was produced inside host cell, which is cleaved by the viral 3C protease to yield VP0 (36 kDa), VP1 (32 kDa) and VP3 (27 kDa) to form the capsid. Auto-catalytic cleavage of VP0 into VP2 (28 kDa) and VP4 (8 kDa) occurs during encapsidation of the viral genome to produce the mature virus [9]. FMD virus capsids can be synthesized using recombinant techniques by expressing the P1 structural protein precursor and the 3C protease that cleaves it, since the capsid proteins spontaneously assemble to produce VLPs. The inherent problem is balancing the expression of P1 and 3C, the latter being toxic to insect cells, especially in the case of FMDV [9]. For FMD virus there are several report of VLPs produced for different serotypes [10], [11], including VLPs against FMDV Type O from our laboratory [7]. Earlier reports of generating VLPs of FMDV involved the use of wild type sequence of 3C [8], [10], [12]. However, considering the fact that 3C protease is toxic to cells [13], [14] and there is a need to reduce its toxicity, we introduced mutations in its critical amino acids. Amongst all serotypes, FMDV type O/IND/R2/75, the currently used Indian vaccine strain has huge potential as vaccine for use in Asian and Eurasian countries [15]. In this context, it is desirable to develop VLPs based vaccine for FMDV Type O/IND/R2/75.

Immuno-stimulating molecules such as polyriboinosinic:polyribocytidylic acid (Poly I:C) and CpG Oligo deoxy nucleotides (CpG ODN) are used to improve the potency and efficacy of vaccines [16], [17], [18]. The advantages of Poly I:C in vaccine formulations are increased humoral and/or cell mediated immune responses as they are potent inducers of IL-12 and type-I interferon secretion by the activation of innate immunity via the TLR3 receptor [19]. Cao et al. [20] reported that the Poly I:C mixed with multi-epitope peptide vaccine induced improved neutralizing antibody titre against FMDV in mice and suggested a dose of 100 μg of Poly I:C with antigen for mouse inoculation.

Recently, several studies have shown that synthetic ODN containing unmethylated CpG dinucleotide (CpG ODN) is a potent adjuvant due to its capability of activating B cells, inhibiting apoptosis of B cells and inducing the maturation [21]. Further it was suggested that CpG ODN could boost the immune response elicited by vaccines by improving protein immunogenicity [22], inducing both humoral and cellular responses as well as shift in the isotype of IgG antibodies elicited by immunization, increase the magnitude of vaccine induced responses [23], accelerate the development of vaccine induced responses [24], [25], upregulate immunoglobulin gene expression [26] and inhibit Rous Sarcoma Virus induced allergy in guinea pigs [27]. Increased potency of vaccines with addition of CpG ODN as adjuvants targeting infectious diseases [29] are of BiothraxR anthrax vaccine [17], foot-and-mouth-disease inactivated virus vaccine [16], combination of CpG ODN and montanide ISA206 adjuvant combined with recombinant FMDV vaccine in cattle [24].

In this report, we tested the efficacy of ISA206, Poly I:C, and CpG adjuvanted FMDV VLP type O vaccine in two different vaccination regimens (primary and booster) in conferring protection against challenge in guinea pigs.

Section snippets

CpG ODN and poly(I:C)

CpG Oligodeoxynucleotides (or CpG ODN) are short single-stranded synthetic DNA molecules that contain a cytosine “C” followed by a guanine “G”. The “p” refers to the phosphodiester backbone of DNA, however some ODN have a modified phosphorothioate backbone. The CpG available from commercial source (CpG ODN 10109) were procured from M/S Integrated DNA Technology, Bangalore, India and the sequence of CpG used is 5′-TCGTcgTTTTAcgGCGCcgTGCCG-3′. The CpG was synthesized on phosphorothioate backbone

Screening for expression of capsid proteins of FMDV in insect cells by S-ELISA

The baculovirus expressed FMDV type O VLPs were tested in S-ELISA using anti-146s FMDV Type O polyclonal sera raised in rabbits and guinea pigs. The mean S-ELISA reactivity (A492 nm) of lysates and supernatants (n = 6) of six batches of VLPs produced in Sf9 cells were 2.288 for lysate and 0.591 for supernatant respectively, while the positive control (BHK21 cell grown inactivated 146S of FMDV Type O) showed A492 nm of 2.382 indicating the ability of the VLPs expressed in Sf9 could react with

Discussion

Foot- and- mouth disease (FMD) is the most devastating viral disease of cloven footed animals causing huge economic loss and disrupting the food security in developing countries. Though vaccination with the conventional vaccine remains the key factor in controlling spread of the virus, short duration of immunity, escape from production plant [5], requirement of booster dose weaken the immunogenic property of the current vaccine. Moreover the conventional vaccine preparation could contain

Conflict of interest statement

The authors do not have any conflict of interest to declare.

Acknowledgments

The authors thank Director, IVRI, Izatnagar and Joint Director, IVRI Campus, Hebbal, Bangalore for providing the necessary facilities to carry out the research work. Authors are also grateful to the assistance provided by laboratory staff of FMD Vaccine Production Laboratory and Isolation unit of Yelahanka, IVRI Campus, Bangalore, India. The financial assistance granted to the first author, M. Terhuja, in the form of Institute Fellowship for Master degree from IVRI is gratefully acknowledged.

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