An alternative approach for a genetic vaccine HSV-1 amplicon vector encoded heterologous virus-like particles

Abstract

The overall goal of this thesis was to evaluate if herpes simplex virus type-1 (HSV-1) amplicon vectors are possible candidate vectors to establish a new vaccine vector platform against rotavirus (RV) infections and Foot-and-mouth disease virus (FMDV). RV infections lead to severe gastroenteritis in young children, killing more than half a million infants worldwide per year. Almost all children both in developing and developed countries are infected with RV during their first years of life and even advanced levels of sanitation and hygiene appear unable to control the spread of RV infections, which highlights the urgent need for the development of an effective prophylactic anti-RV vaccine. FMDV is one of the most devastating viruses affecting cloven-hoofed animals, like cattle, sheep, goats and pigs. Foot-and mouth disease (FMD) represents one of the most important epidemics of farm animals and continues to be of major economic importance across the world. FMDV spreads rapidly in a susceptible population and presently, the disease is controlled by slaughter of infected or in-contact animals, and quarantine and decontamination for the whole region. An effective and safe vaccine against FMD would be most desirable. Virus-like particles (VLPs) are most promising candidates for the development of vaccines, as they are very similar to the equivalent virus, but safer than attenuated virus vaccines, since they do not contain genetic material. VLPs mimic the overall structure of virus particles and are therefore readily recognized by the immune system as they represent viral antigens in a more authentic conformation. In the present work, HSV-1 amplicon vectors have been developed that co-express the structural genes required for capsid assembly, of the two RNA viruses, FMDV and RV. The designed amplicon vectors provide a high safety level as they can be produced by using a helper virus-free packaging system leading to the absence of expression of any HSV-1 gene. The high transgene capacity (150 kbp) allows the insertion of several genes, and the simultaneous expression of the different structural genes of FMDV and RV was achieved by introducing internal ribosome entry site (IRES) sequences. Expression of the individual genes alone or in combination was demonstrated by Western and immune fluorescence analyses. The capability of the vectors to support the production of RV and FMDV VLPs in the vector-transduced cells was demonstrated by electron microscopy. Inoculation of mice with these vectors resulted in the expression of viral antigens, followed by induction of immune responses and a variable level of protection against challenge with a high dose of wild type virus. Moreover, the results obtained by vaccinating mice with inactivated vectors showed that induction of immune responses required de novo synthesis of proteins from the vectors and the contamination of vector stocks with preformed proteins is not contributing to the immune responses, as demonstrated with inactivated amplicon vectors that do not support protein synthesis. In the case of FMDV amplicon vectors, induction of immune responses and protection against challenge were higher with amplicon vectors than with adenovirus vectors expressing the same FMDV proteins and required no adjuvants. Taken together, the results presented in this work suggest that HSV-1 amplicon vectors are attractive candidates for the development of complex but safe genetic vaccines against viral infections.