African swine fever vaccine candidate ASFV-G-deltaI177L produced in the swine macrophage-derived cell line IPKM remains genetically stable and protective against homologous virulent challenge

Authors: Ramirez-Medina, Elizabeth; RAI, AYUSHI - Oak Ridge Institute For Science And Education (ORISE); Espinoza, Nallely; Spinard Iii, Edward; MEYERS, AMANDA - Oak Ridge Institute For Science And Education (ORISE); VALLADARES, ALYSSA - Oak Ridge Institute For Science And Education (ORISE); Velazquez, Lauro; Gay, Cyril; Gladue, Douglas; Borca, Manuel; Silva, Ediane; Burton, Leeanna; Clark, Jason

Submitted to: Pathogens
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/1/2023
Publication Date: 10/8/2023
Citation: Ramirez Medina, E., Rai, A., Espinoza, N.N., Spinard III, E.J., Meyers, A., Valladares, A., Velazquez Salinas, L., Gay, C.G., Gladue, D.P., Borca, M.V., Silva, E.B., Burton, L.J., Clark, J.A. 2023. African swine fever vaccine candidate ASFV-G-deltaI177L produced in the swine macrophage-derived cell line IPKM remains genetically stable and protective against homologous virulent challenge. Pathogens. 15(10). Article 2064. https://doi.org/10.3390/v15102064.
DOI: https://doi.org/10.3390/v15102064

Interpretive Summary: A main limitation in the control of African swine fever, is large-scale production of live attenuated vaccines licensed for commercial use in animals. Currently, licensed vaccines are being produced in a less than ideal process that requires primary cells derived from large amounts of pig blood each time a vaccine is produced. This study focused on the adaptation of a previously described and patented live attenuated vaccine (ASFV-G-delta9GL/deltaUK) in IPKM, an immortalized pig cell line that can grow continually in the laboratory. Our results demonstrated that this cell line supported the replication of the vaccine virus in high titers, without introducing undesirable genetic changes and more importantly, maintaining the original phenotype of this vaccine in pigs, the natural host of ASFV. These results provide valuable data toward large-scale manufacturing of licensed vaccine candidates against ASFV.

Technical Abstract: We have previously reported that the recombinant African Swine Fever (ASF) vaccine candidate ASFV-G-delta9GL/deltaUK efficiently induces protection in domestic pigs challenged with the virulent field isolate Georgia 2010 (ASFV-G). As reported, ASFV-G-delta9GL/deltaUK induced protection, when intramuscularly (IM) administered at doses of 104 HAD50 or higher, prevents ASF clinical disease in pigs challenged with the parental ASFV-G strain. Like other recombinant vaccine candidates obtained from ASFV field isolates, ASFV-G-delta9GL/deltaUK stocks need to be produced in primary cultures of swine macrophages, which constitutes an important limitation in the production of large virus stocks at the industrial level. Here, we report the production of ASFV-G-delat9GL/deltaUK stocks using IPKM cells, a cell line derived from swine macro-phages. We show that ten successive passages of ASFV-G-delta9GL/deltaUK in IPKM cells induced small changes in the virus genome when compared with the original virus stock. The produced virus, ASFV-G-delta9GL/deltaUKp10, showed similar growth kinetics in primary swine macrophages cultures as the original parental virus ASFV-G-delta9GL/deltaUK (ASFV-G-delta9GL/deltaUKp0). The protective efficacy of ASFV-G-delta9GL/deltaUKp10 was evaluated in pigs that were IM inoculated with either 104 or 106 HAD50 of ASFV-G-delta9GL/deltaUKp10. While animals inoculated with 104 HAD50 present a partial protection against the challenge with the virulent parental virus ASFV-G, those inoculated with 106 HAD50 developed a strong virus-specific antibody response and were completely protected. Therefore, as was just recently reported for another ASF vaccine candidate, ASFV-G-deltaI177L, IPKM cells are an effective alternative to develop stocks for those vaccine candidates which exclusively grow in swine macrophages.