Abstract
BackgroundHuman rotaviruses are the main cause of severe gastroenteritis in children and are responsible for over 500 000 deaths annually. There are two live rotavirus vaccines currently available, one based on human rotavirus serotype G1P[8], and the other a G1-G4 P[8] pentavalent vaccine. However, the recent emergence of the G9 and other novel rotavirus serotypes in Africa and Asia has prompted fears that current vaccines might not be fully effective against these new varieties.ResultsWe report an effort to develop an affordable candidate rotavirus vaccine against the new emerging G9P[6] (RVA/Human-wt/ZAF/GR10924/1999/G9P[6]) strain. The vaccine is based on virus-like particles which are both highly immunogenic and safe. The vaccine candidate was produced in Nicotiana benthamiana by transient expression, as plants allow rapid production of antigens at lower costs, without the risk of contamination by animal pathogens. Western blot analysis of plant extracts confirmed the successful expression of two rotavirus capsid proteins, VP2 and VP6. These proteins assembled into VLPs resembling native rotavirus particles when analysed by transmission electron microscopy (TEM). Expression of the rotavirus glycoprotein VP7 and the spike protein VP4 was also tried. However, VP7 expression caused plant wilting during the course of the time trial and expression could never be detected for either protein. We therefore created three fusion proteins adding the antigenic part of VP4 (VP8*) to VP6 in an attempt to produce more appropriately immunogenic particles. Fusion protein expression in tobacco plants was detected by western blot using anti-VP6 and anti-VP4 antibodies, but no regular particles were observed by TEM, even when co-expressed with VP2.ConclusionOur results suggest that the rotavirus proteins produced in N. benthamiana are candidates for a subunit vaccine specifically for the G9P[6] rotavirus strain. This could be more effective in developing countries, thereby possibly providing a higher overall efficacy for the existing vaccines. The production of rotavirus proteins in plants would probably result in lower manufacturing costs, making it more affordable for developing countries. Further investigation is required to evaluate the immunogenic potential of the VLPs and fusion proteins created in this study.Electronic supplementary materialThe online version of this article (doi:10.1186/s12985-015-0436-8) contains supplementary material, which is available to authorized users.
Highlights
Human rotaviruses are the main cause of severe gastroenteritis in children and are responsible for over 500 000 deaths annually
Expression of Rotavirus recombinant proteins in tobacco plants All rotavirus proteins used for this study derive from the G9 P[6] strain which is predominant in South Africa and other sub-Saharan regions [21, 22]
NSs is a RNA silencing suppressor protein which inhibits the onset of post-transcriptional gene silencing (PTGS) [36]
Summary
Human rotaviruses are the main cause of severe gastroenteritis in children and are responsible for over 500 000 deaths annually. Rotavirus (RV) infection has probably been a problem as long as humankind has existed, but the connection between RV as the leading cause of severe diarrhoeal disease and dehydration in children under the age of five worldwide was only made in the 1970s [1]. Virions are triple-layered and contain a viral genome that consists of 11 segments of double-stranded RNA (dsRNA). These dsRNAs encode six structural proteins (VPs) and six non-structural proteins (NSPs). VP4 forms 60 spikes on the outer surface of the virus (Fig. 1). The neutralizing epitope of VP8* was produced in tobacco plants and has shown to confer protection against bovine rotavirus infection in a mouse model [9]
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