• Vaccine Name: YFV17D/LAS-GPC
• Target Pathogen: Lassa Fever Virus
• Target Disease: Lassa fever
• Vaccine Ontology ID: VO_0004088
• Type: Live Attenuated
• Preparation: The YFV17D/LASV-GPC plasmid is constructed in the background of the full-length YFV17D cDNA clone by fusion PCR mutagenesis. The LASV-GPC gene of the AV strain is amplified by RT/PCR and cloned into pcDNA. The nucleotide sequences of PCR-derived DNA fragments and gene fusions are confirmed by sequencing. The recombinant YFV17D/LASV-GPC plasmid is linearized by XhoI and used for in vitro RNA transcription (Bredenbeek et al., 2006).
• Virulence:
• Description: YFV17D/LAS-GPC is a Yellow Fever Vaccine 17D (YFV17D) that has been used as a vector for the Lassa virus glycoprotein precursor (LASV-GPC) resulting in construction of YFV17D/LASV-GPC recombinant virus. The virus is replication-competent and processes the LASV-GPC in cell cultures (Bredenbeek et al., 2006).

Guinea pig Response

• Host Strain: 13
• Vaccination Protocol: Sixteen outbred guinea pigs were subcutaneously inoculated with 1 × 10^5 PFU/0.5 ml of the recombinant YFV17D/LASV-GPC virus and two animals were sacrificed at days 0, 4, 7, 10 and 14 to track the virus distribution in blood and tissues. At day 14, six animals were boosted with the same dose of the recombinant virus and plasma samples were collected on days 8, 15 and 24 after to measure antibody responses against YFV17D and LASV-GPC in IgG ELISA. Antigens were prepared from serum-free virus stocks of YFV17D and MOP/LAS (Lukashevich et al., 2005) by ultracentrifugation on sucrose cushion. Concentrated viruses were suspended in carbonate–bicarbonate buffer, briefly sonicated and used to cover wells of microtitration plates overnight at 4 °C. After blocking, 1:100 dilutions of guinea pig sera were added and incubated for 2 h at room temperature. Challenge experiments were preformed (Bredenbeek et al., 2006).
• Persistence: None noted
• Side Effects: None noted
• Efficacy: 80% of animals were protected against the fatal challenge. This study demonstrates the potential to develop an YFV17D-based bivalent vaccine against Lassa Virus (Bredenbeek et al., 2006).
• Description: 80% of animals were protected against the fatal challenge. Incomplete protection could be explained by differences in vaccine formulation (GPC + NP vs. GPC) and by GPC sequence differences between AV and Josiah strains of LASV. Blood and tissue samples were collected from vaccinated animals at different time points for hematology, blood chemistry, RNA extraction, plaque assay, virus isolation and ELISA. As expected, the inoculated animals had no clinical manifestations and all standard measurable blood and chemistry parameters were in normal ranges. In plasma, the recombinant virus was not detectable by plaque assay or by biological amplification. Recombinant viral RNA was not detectable by RT/PCR in 140 μl of plasma extracted on days 4, 10, and 21. However, when RNA samples were prepared from 0.5 ml of total blood, an RT/PCR assay gave a strong positive signal on day 4 after YFV17D/ LAS-GPC inoculation. Still, blood samples collected on day 10 and 21 were PCR negative. Viral RNA sequences were only transiently detectable on days 7–14 in spleen and liver. Nucleotide sequence analysis of PCR products confirmed their derivation from YFV17D/LAS-GPC. Taken together, these data confirm that recombinant YF17D/LAS-GPC replicated poorly in tissues of vaccinated guinea pigs. Interestingly, in clinical trials in individuals vaccinated with chimeric YFV17D-based vaccines, viremia levels were even lower than the levels of YFV17D determined to be safe. This suggests that insertion of a foreign gene can affect in vivo viral replication and make recombinant YFV17D-based vaccines even safer than the parental vaccine, YFV17D (Bredenbeek et al., 2006).