Confirming the absence of parental African swine fever virus as a potential contaminant of recombinant live attenuated ASF vaccines

Authors: Velazquez, Lauro; Ramirez-Medina, Elizabeth; RAI, AYUSHI - Oak Ridge Institute For Science And Education (ORISE); Pruitt, Sarah; VUONO, ELIZABETH - Mississippi State University; Espinoza, Nallely; Gay, Cyril; Witte, Steven; Gladue, Douglas; Borca, Manuel

Submitted to: Biologicals
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/21/2023
Publication Date: 6/3/2023
Citation: Velazquez Salinas, L., Ramirez Medina, E., Rai, A., Pruitt, S.E., Vuono, E., Espinoza, N.N., Gay, C.G., Witte, S.B., Gladue, D.P., Borca, M.V. 2023. Confirming the absence of parental African swine fever virus as a potential contaminant of recombinant live attenuated ASF vaccines. Biologicals. 3;83:101685. https://doi.org/10.1016/j.biologicals.2023.101685.
DOI: https://doi.org/10.1016/j.biologicals.2023.101685

Interpretive Summary: Currently, there is not a specific protocol to safety test vaccine candidates for African Swine Fever virus produced by recombination. For this reason, using our three vaccine candidates (ASFV-G-DeltaMGF, ASFV-G-Delta9 GLDeltaUK and ASFV-G-DeltaI177L), we developed a model protocol to ensure that master seed virus stock used for vaccine production does not contain residual highly virulent parental virus (Georgia field isolate). This protocol describes experimental infections in pigs as well as the evaluation of clinical samples by qPCRs that discriminate between vaccine virus from field isolates.

Technical Abstract: African Swine Fever (ASF) is a devastating disease that is currently producing a panzootic significantly impacting the swine industry worldwide. One of the major challenges for advancing the development of ASF vaccines has been the absence of international standards for ASF vaccine purity, potency, safety, and efficacy. To date, the most effective experimental vaccines have been live attenuated strains of viruses. Most of these promising vaccine candidates have been developed by deleting virus genes involved in the process of viral pathogenesis and disease production. This approach requires genomic modification of a parental virus field strain through a process of homologous recombination followed by purification of the recombinant attenuated virus. In this scenario, it is critical to confirm the absence of any parental virulent virus in the final virus stock used for vaccine production. We present here a protocol to establish the purity of virus stock using the live attenuated vaccine candidates ASFV-G-DeltaMGF, ASFV-G-Delta9 GLDeltaUK and ASFV-G-DeltaI177L. Procedures described here includes inoculation in susceptible pigs followed by the assessment of the obtained material by differential qPCRs that allows the identification of vaccine virus from ASFV field isolates. This protocol is proposed as a model to ensure that master seed virus stock used for vaccine production does not contain residual parental virulent virus. Procedures described here includes a passage in susceptible pigs followed by the assessment of the obtained material by differential qPCRs that allows the identification of vaccine virus from ASFV field isolates.