• Vaccine Name: Recombinant RNA replicons from attenuated VEE virus
• Target Pathogen: VEE Virus
• Target Disease: Venezuelan equine encephalitis
• Vaccine Ontology ID: VO_0004109
• Type: Recombinant vector vaccine
• Preparation: A plasmid encoding the VEE replicon vector was described previously (Davis et al., 1996; Pushko et al., 1997). The Ebola NP and GP genes from the Mayinga strain of Ebola virus were derived from pSP64- and pGEM3Zf(ÿ)-based plasmids (Sanchez et al., 1993; Sanchez et al., 1989). The fragments containing the NP and GP genes, respectively, were subcloned into a shuttle vector(Davis et al., 1996; Grieder et al., 1995). From the shuttle vector, NP or GP genes were transferred the replicon clone, resulting in plasmids encoding the NP or GP gene in place of the VEE structural protein genes.
  
  Transcripts of the replicon were pooled and cotransfected as described previously (Pushko et al., 1997). Transfected cells were incubated and harvested. Culture supernatants were clarified by centrifugation and VRP particles were concentrated and partially purified by centrifugation. VRP titers were determined as immunofluorescent foci after infection of BHK cells in eight-well chamber slides as previously described (Pushko et al., 1997; Pifat et al., 1988). Positive cells were counted, and the titers of the VRP preparations were calculated. Production and titration of Lassa N±VRP were described previously (Pushko et al., 1997). For expression assays, BHK cells were infected with NP- or GP±VRP, or cotransfected with replicon and helper RNAs. Cells were incubated before harvesting. Polypeptides were separated and Western blotting was carried out. VEE proteins in western blots were detected with sera from guinea pigs immunized with the live-attenuated TC-83 vaccine.
• Description: RNA replicons derived from an attenuated strain of Venezuelan equine encephalitis virus (VEE), an alphavirus, were configured as candidate vaccines for Ebola hemorrhagic fever. The Ebola nucleoprotein (NP) or glycoprotein (GP) genes were introduced into the VEE RNA downstream from the VEE 26S promoter in place of the VEE structural protein genes. The resulting recombinant replicons, expressing the NP or GP genes, were packaged into VEE replicon particles (NP–VRP and GP–VRP, respectively). The immunogenicity of NP–VRP and GP–VRP and their ability to protect against lethal Ebola infection were evaluated in BALB/c mice and in two strains of guinea pigs. The GP–VRP alone, or in combination with NP–VRP, protected both strains of guinea pigs and BALB/c mice, while immunization with NP–VRP alone protected BALB/c mice, but neither strain of guinea pig. Passive transfer of sera from VRP-immunized animals did not confer protection against lethal challenge. However, the complete protection achieved with active immunization with VRP, as well as the unique characteristics of the VEE replicon vector, warrant further testing of the safety and efficacy of NP–VRP and GP–VRP in primates as candidate vaccines against Ebola hemorrhagic fever.

Mouse Response

• Host Strain: BALB/c
• Vaccination Protocol: VRP were diluted and administered to BALB/c mice. Groups of mice were inoculated subcutaneously (s.c.).
• Side Effects: none
• Challenge Protocol: Challenge was carried out 4 weeks after final immunization with VRP. Mice were challeged i.p. with mouse-adapted Ebola virus. Animals wre observed daily for 60 days and morbidity and survival were recorded.
• Efficacy: The GP-VRP alone, or in combination with NP-VRP, protected BALB/c mice. Immunization with NP-VRP alone protected BALB/c mice. Passive transfer of sera from VRP-immunized animals did not confer protection against lethal challenge.

Guinea pig Response

• Host Strain: strain 2 or strain 13
• Vaccination Protocol: VRP were diluted and administered to BALB/c mice. Groups of guinea pigs were inoculated subcutaneously (s.c.).
• Side Effects: none
• Challenge Protocol: Challenge was carried out 4 weeks after final immunization with VRP. Guinea pigs were challeged s.c. with guinea pig-adapted Ebola virus. Animals wre observed daily for 60 days and morbidity and survival were recorded.
  
• Efficacy: The GP-VRP alone, or in combination with NP-VRP, protected both strains of guinea pigs. Immunization with NP-VRP alone protected neither strain of guinea pigs. Passive transfer of sera from VRP-immunized animals did not confer protection against lethal challenge.