Plant-produced SVPs of IBDV, a potential vaccine candidate for chickens

LUCERO, MARÍA SOLEDAD; RICHETTA, MATÍAS; CHIMENO ZOTH, SILVINA; GRAVISACO, MARÍA JOSÉ; PINTO, SILVINA; BERINSTEIN, ANALÍA; GOMEZ, EVANGELINA

Albufeira

Conferencia; Plant-Based Vaccines, Antibodies & Biologics; 2017

Introduction-Infectious bursaldisease virus (IBDV) is the etiological agent of animmunosuppressive and highly contagious disease that affects young birdscausing important economic losses in the poultry industry. The structural proteinVP2 contains the major neutralizing epitopes and is capable of forming subviralparticles (SVPs) when expressed in heterologous systems such as E. coli, yeast and insect cells. Forthese reasons, VP2 has been widely used for the development of subunit vaccinesin order to meet the needs of new generation vaccines as effective as thetraditional virus based ones. We have previously demonstrated that crudeextract of VP2 transiently expressed in Nicotiana benthamiana is able toelicit a protective immune response against IBDV challenge when administeredintramuscularly (im.) in a prime/boost scheme. However, these results were notobserved when the same immunogen was given by oral or intranasalroutes. Taking into account that SVPs are immunogenic because they mimic virusstructure and retain the wild type epitopes, and that expression of complexmolecules is feasible in plants, we decided to investigate if SVPs were beingassembled in N. benthamiana and ifthey were able to elicit a protective immune response by parenteral and mucosalroutes.Objectives-The objectives of the present work were to obtain SVPs using a transient expression system together with aneasy and rapid purification method, and to evaluate their immunogenicity byintramuscular or oral administration in the viral natural host.  Materials and Methods-Transient expression was performed by the agroinfiltrationof N. benthamiana plants with asuspension of recombinant bacteria harboring the VP2 gene. SVPs were purifiedby ultracentrifugation in a discontinuous sucrose gradient and their presenceconfirmed by electron microscopy and Western Blot. Six animals in each groupwere inoculated with the SVPs with different prime/boost schemes (im./im.;oral/oral or im./oral) at 0 and 14 dpi. Control chickens were inoculated with GFPas a non-related antigen. Animals were bled by the wing vein every 10 days andthree weeks after boost, chickens were challenged by oral inoculationwith 4,35x109 pfu of intermediate IBDV strain. Five days later,animals were euthanized and bursae were removed for lymphocyte isolation andflow cytometry analysis, histopathological observation and virus isolation. Serum samples were evaluated for the presence ofspecific antibodies against IBDV with a commercial ELISA and for virusneutralizing activity using chicken embryo fibroblasts (CEFs).Results- Efficiently assembled IBD subviral particles were easilyrecovered from leave material. Animals which received at least one im.injection of the antigen developed high titres of specific antibodies, with virusneutralizing activity. Also, their bursae presented few infiltrating Tcells, low viral charge and normal morphology compared to animals in thecontrol groups. However, results obtained from the group vaccinated only by theoral route were heterogeneous leading to partial protection of few chickensafter challenge.Conclusionand Discussion- These results demonstrate for the first timethat plants are capable of producing efficiently assembled IBD subviralparticles which are easily recovered from leave material and are able to elicitan immune response in chickens. Thus, we think this technology has a greatpotential as a platform to produce a nanovaccine against Infectious bursal disease.