The Dominant-Negative Inhibition of Double-Stranded RNA-Dependent Protein Kinase PKR Increases the Efficacy of Rift Valley Fever Virus MP-12 Vaccine

Abstract

f Rift Valley fever virus (RVFV), belonging to the genus Phlebovirus, family Bunyaviridae, is endemic to sub-Saharan Africa and causes a high rate of abortion in ruminants and hemorrhagic fever, encephalitis, or blindness in humans. MP-12 is the only RVFV strain excluded from the select-agent rule and handled at a biosafety level 2 (BSL2) laboratory. MP-12 encodes a functional major virulence factor, the NSs protein, which contributes to its residual virulence in pregnant ewes. We found that 100% of mice subcutaneously vaccinated with recombinant MP-12 (rMP12)-murine PKRN167 (mPKRN167), which encodes a dominant-negative form of mouse double-stranded RNA (dsRNA)-dependent protein kinase (PKR) in place of NSs, were protected from wild-type (wt) RVFV challenge, while 72% of mice vaccinated with MP-12 were protected after challenge. rMP12-mPKRN167 induced alpha interferon (IFN-␣) in sera, accumulated RVFV antigens in dendritic cells at the local draining lymph nodes, and developed high levels of neutralizing antibodies, while parental MP-12 induced neither IFN-␣ nor viral-antigen accumulation at the draining lymph node yet induced a high level of neutralizing antibodies. The present study suggests that the expression of a dominant-negative PKR increases the immunogenicity and efficacy of live-attenuated RVFV vaccine, which will lead to rational design of safe and highly immunogenic RVFV vaccines for livestock and humans.

Rift Valley fever virus MP-12 vaccine encoding Toscana virus NSs retains neuroinvasiveness in mice

“…Therefore, we aim to develop second-generation MP-12 vaccines that encode DIVA markers while retaining strong immunogenicity. MP-12 NSs is fully functional (Billecocq et al, 2008;Ikegami et al, 2006Ikegami et al, , 2009Kalveram et al, 2011a) and is dispensable for vaccine efficacy in mice (Lihoradova et al, 2012). Potential disadvantages of MP-12 lacking NSs is a slightly lower level of neutralizing antibody in vaccinated ruminants (Morrill et al, 2013) and inefficient replication in MRC-5 cells, which have been used for MP-12 amplification for vaccine manufacturing (Ikegami et al, 2006;Lokugamage et al, 2012).…”

The two faces of Rift Valley fever virus virulence factor NSs: The development of a vaccine and the elucidation of pathogenesis

“…23 Moreover, it was found that 80% of rMP-12-DNSs 16/198-vaccinated mice are protected from challenge with wild-type RVFV. 23 Although these results demonstrate the ability to generate effective DIVA vaccines with increased safety, it was also shown that the immunogenicity of rMP-12-DNSs 16/198 is not as high as the MP-12 vaccine in sheep. 26 A likely explanation for this result is that complete disruption of NSs obviates the virus's ability to counteract the host IFN response and reduces viral replication in vivo.…”

“…23 Conversely, MP-12 vaccination induces viremia in 30% of mice without any detectable induction of IFN-a. 23 Moreover, it was found that 80% of rMP-12-DNSs 16/198-vaccinated mice are protected from challenge with wild-type RVFV. 23 Although these results demonstrate the ability to generate effective DIVA vaccines with increased safety, it was also shown that the immunogenicity of rMP-12-DNSs 16/198 is not as high as the MP-12 vaccine in sheep.…”

“…21,22 The research group led by Tetsuro Ikegami has had a longtime interest in developing an effective RVF vaccine with a DIVA marker by genetically manipulating the NSs gene. [23][24][25] They have previously generated a recombinant MP-12 lacking a functional NSs by the deletion of amino acid residues 16 to 198 [rMP-12-DNSs 16/198 (also referred as rMP-12-C13type)] and used the mouse model to demonstrate that rMP-12-DNSs 16/198 vaccination fails to produce detectable viremia but does induce detectable IFN-a in the sera. 23 Conversely, MP-12 vaccination induces viremia in 30% of mice without any detectable induction of IFN-a.…”

“…[23][24][25] They have previously generated a recombinant MP-12 lacking a functional NSs by the deletion of amino acid residues 16 to 198 [rMP-12-DNSs 16/198 (also referred as rMP-12-C13type)] and used the mouse model to demonstrate that rMP-12-DNSs 16/198 vaccination fails to produce detectable viremia but does induce detectable IFN-a in the sera. 23 Conversely, MP-12 vaccination induces viremia in 30% of mice without any detectable induction of IFN-a. 23 Moreover, it was found that 80% of rMP-12-DNSs 16/198-vaccinated mice are protected from challenge with wild-type RVFV.…”