• Vaccine Name: Live attenuated vaccine TC-83
• Target Pathogen: VEE Virus
• Target Disease: Venezuelan equine encephalitis
• Vaccine Ontology ID: VO_0004105
• Type: Live, attenuated vaccine
• Antigen: Stocks of TC-83 were prepared by propagation from a vial of vaccine for human use (National Drug Company, Philadelphia PA, Lot 4, run 2). Virulent VEEV strains were prepared as suckling mouse brain suspensions by standard methods.
• Preparation: Stocks of TC-83 were prepared by propagation from a vial of vaccine for human use (National Drug Company, Philadelphia PA, Lot 4, run 2). Virulent VEEV strains were prepared as suckling mouse brain suspensions by standard methods. In vitro virus propagation and plaque assays were performed in BHK21 cells, grown in Glasgow minimal essential medium. A hyperimmune rabbit antiserum raised against TC-83 virus was kindly provided by T. Webber, DET, at CBD, Porton Down.
• Virulence: none
• Description: TC-83 has proven safe and effective for immunisation of horses (Eddy et al., 1972; Walton et al., 1972)and has US Food and Drug Administration Investigational New Drug status for use in Humans (IND No. 142). Vaccination with TC-83 virus produced solid protection against subcutaneous challenge with Venezuelan equine encephalitis (VEEV) viruses from homologous and heterologous serogroups, but breakthrough infection and disease occurred after airborne challenge.

Mouse Response

• Host Strain: outbred Porton TO
• Vaccination Protocol: Subcutaneous (s.c.) inoculations of TC-83 virus in L15 MM, L15 MM alone, or virulent VEEV in L15 MM were delivered into the scruff of the neck in a volume of 100 μl. The number of s.c. LD50/ml was determined by titration using five mice per dilution.
• Challenge Protocol: Infection by the airborne route was achieved using a specially constructed small animal exposure box(Phillpotts et al., 1997). Briefly, mice were exposed loose in a box of 80 l capacity, vented through a HEPA filter, to a virus-containing aerosol produced using a Collison nebuliser (8 l/min). The virus suspending fluid was L15 MM with 2% trehalose and the exposure time was 20 min. The air in the box was sampled with a glass impinger running at 1 l/min and the quantity of virus present in the Collison spray reservoir at the end of each run was determined by back-titration. A titration experiment was performed for each virus (five mice per dilution) in order to calculate the number of LD50 delivered by a given dilution of virus in the spray. As there was a linear relationship between the quantity of virus in the Collison reservoir and the impinger, in subsequent experiments the dose of virus delivered was calculated from titration of the impinger contents. Data for each virus at each time point were from a single exposure.
• Efficacy: Vaccination with TC-83 virus produced solid protection against subcutaneous challenge with Venezuelan equine encephalitis (VEEV) viruses from homologous and heterologous serogroups, but breakthrough infection and disease occurred after airborne challenge.
• Description: Infection by the airborne route was achieved using a specially constructed small animal exposure box(Phillpotts et al., 1997).