Preliminary Evaluation of a Bunyavirus Vector for Cancer Immunotherapy.

Replicon particles of Rift Valley fever virus, referred to as nonspreading Rift Valley fever virus (NSR), are intrinsically safe and highly immunogenic. Here, we demonstrate that NSR-infected human dendritic cells can activate CD8(+) T cells in vitro and that prophylactic and therapeutic vaccinations of mice with NSR encoding a tumor-associated CD8 peptide can control the outgrowth of lymphoma cells in vivo. These results suggest that the NSR system holds promise for cancer immunotherapy.

Vertical transmission of Rift Valley fever virus without detectable maternal viremia.

Rift Valley fever virus (RVFV) is a zoonotic bunyavirus that causes abortions in domesticated ruminants. Sheep breeds exotic to endemic areas are reportedly the most susceptible to RVFV infection. Within the scope of a risk assessment program of The Netherlands, we investigated the susceptibility of a native breed of gestating sheep to RVFV infection. Ewes were infected experimentally during the first, second, or third trimester of gestation. Mortality was high among ewes that developed viremia. Four of 11 inoculated ewes, however, did not develop detectable viremia nor clinical signs and did not seroconvert for immunoglobulin G (IgG) or IgM antibodies. Surprisingly, these ewes were found to contain viral RNA in maternal and fetal organs, and the presence of live virus in fetal organs was demonstrated by virus isolation. We demonstrate that RVFV can be transmitted vertically in the absence of detectable maternal viremia.

Efficacy of three candidate Rift Valley fever vaccines in sheep.

Rift Valley fever virus (RVFV) is a mosquito-transmitted Bunyavirus that causes high morbidity and mortality among ruminants and humans. The virus is endemic to the African continent and the Arabian Peninsula and continues to spread into new areas. The explosive nature of RVF outbreaks requires that vaccines provide swift protection after a single vaccination. We recently developed several candidate vaccines and here report their efficacy in lambs within three weeks after a single vaccination. The first vaccine comprises the purified ectodomain of the Gn structural glycoprotein formulated in a water-in-oil adjuvant. The second vaccine is based on a Newcastle disease virus-based vector that produces both RVFV structural glycoproteins Gn and Gc. The third vaccine comprises a recently developed nonspreading RVFV. The latter two vaccines were administered without adjuvant. The inactivated whole virus-based vaccine produced by Onderstepoort Biological Products was used as a positive control. Five out of six mock-vaccinated lambs developed high viremia and fever and one lamb succumbed to the challenge infection. A single vaccination with each vaccine resulted in a neutralizing antibody response within three weeks after vaccination and protected lambs from viremia, pyrexia and mortality.

Protective efficacy of a Classical swine fever virus C-strain deletion mutant and ability to differentiate infected from vaccinated animals.

Classical swine fever (CSF) continues to be the most economically damaging pig disease in the world. The disease can be effectively controlled by vaccination with the live C-strain vaccine. This vaccine, however, does not enable the serological differentiation between infected and vaccinated animals (DIVA) and its use can therefore impose severe trade restrictions. CSF-specific diagnostic ELISAs detect antibodies directed against the conserved and immunodominant A domain of the E2 structural glycoprotein. We previously reported the production of a C-strain virus in which the immunodominant TAVSPTTLR epitope of the A domain is stably mutated with the aim to render the virus suitable as a DIVA vaccine. We here report that a single vaccination with this vaccine virus protected pigs from a lethal challenge dose of the highly virulent Brescia strain. Analysis of the sera, however, demonstrated that a commercially available E2 ELISA was unsuitable as an accompanying DIVA test.

Rift Valley fever virus immunity provided by a paramyxovirus vaccine vector.

Rift Valley fever virus (RVFV) causes recurrent large outbreaks among humans and livestock. Although the virus is currently confined to the African continent and the Arabian Peninsula, there is a growing concern for RVFV incursions into countries with immunologically naïve populations. The RVFV structural glycoproteins Gn and Gc are preferred targets in the development of subunit vaccines that can be used to control future outbreaks. We here report the production of Gn and Gc by a recombinant vaccine strain of the avian paramyxovirus Newcastle disease virus (NDV) and demonstrate that intramuscular vaccination with this experimental NDV-based vector vaccine provides complete protection in mice. We also demonstrate that a single intramuscular vaccination of lambs, the main target species of RVFV, is sufficient to elicit a neutralizing antibody response.

Intramuscular inoculation of calves with an experimental Newcastle disease virus-based vector vaccine elicits neutralizing antibodies against Rift Valley fever virus.

In the past decade, the use of Newcastle disease virus (NDV) as a vaccine vector for the prevention of economically important livestock diseases as well as for human diseases has been extensively explored. In this study, we have constructed a recombinant NDV vaccine virus, named NDFL-Gn, that produces the Rift Valley fever virus (RVFV) Gn glycoprotein. Calves were immunized via either the intranasal route or the intramuscular route. Delivery via the intranasal route elicited no detectable antibody responses, whereas delivery via the intramuscular route elicited antibodies against both NDV and the Gn protein. The RVFV-neutralizing activity of the antisera from intramuscularly vaccinated calves was demonstrated, suggesting that NDV is a promising vaccine vector for the prevention of RVF in calves.

Rational design of a classical swine fever C-strain vaccine virus that enables the differentiation between infected and vaccinated animals.

The C-strain of the classical swine fever virus (CSFV) is considered the gold standard vaccine for the control of CSF. This vaccine, however, does not enable the serological differentiation between infected and vaccinated animals (DIVA). Consequently, its use can impose severe trade restrictions. The immunodominant and evolutionarily conserved A-domain of the E2 structural glycoprotein is an important target in CSFV-specific ELISAs. With the ultimate aim to render the C-strain suitable as a DIVA vaccine, mutations were introduced that were expected to dampen the immunogenicity of the A-domain. In the first of two approaches, the feasibility of shielding the A-domain by N-linked glycans was evaluated, whereas in the second approach C-strain mutants were created with targeted deletions in the A-domain. Analysis of the antibody responses elicited in rabbits suggested that shielding of the A-domain by an N-linked glycan had a minor effect on the immune response against the A-domain, whereas a targeted deletion of only a single amino acid severely dampened this response. C-strain mutants with larger deletions were highly debilitated and incapable of sustained growth in vitro. By providing the viruses with the opportunity to increase their fitness by mutation, a mutant was rescued that found a way to compensate for the imposed fitness cost. Most of the identified mutations occurred in several independently evolved viruses, demonstrating parallel evolution. By virtue of this compensatory evolution, a well replicating and genetically stable C-strain mutant was produced that can be serologically differentiated from wildtype CSFV. The findings provide the molecular basis for the development of a novel, genetically stable, live attenuated CSF DIVA vaccine.