Involvement of the MGF 110-11L Gene in the African Swine Fever Replication and Virulence

Abstract

African swine fever (ASF) is a highly lethal hemorrhagic viral disease that causes extensive economic and animal welfare losses in the Eurasian pig (Sus scrofa) population. To date, no effective and safe vaccines have been marketed against ASF. A starting point for vaccine development is using naturally occurring attenuated strains as a vaccine base. Here, we aimed to remove the multigene family (MGF) 110 gene of unknown function from the Lv17/WB/Rie1 genome to improve the usability of the virus as a live-attenuated vaccine, reducing unwanted side effects. The MGF 110-11L gene was deleted using the CRISPR/Cas9 method, and the safety and efficacy of the virus were tested in pigs after isolation. The vaccine candidates administered at high doses showed reduced pathogenicity compared to the parental strain and induced immunity in vaccinated animals, although several mild clinical signs were observed. Although Lv17/WB/Rie1/d110-11L cannot be used as a vaccine in its current form, it was encouraging that the undesirable side effects of Lv17/WB/Rie1 at high doses can be reduced by additional mutations without a significant reduction in its protective capacity.

The Production of Recombinant African Swine Fever Virus Lv17/WB/Rie1 Strains and Their In Vitro and In Vivo Characterizations

“…Lv17/WB/Rie1-ΔGL and Lv17/WB/Rie1-ΔCD stocks were prepared according to Tamás et al (2023) [ 10 ]. PAMs were cultured as described above and infected with 3-3 MOI from Lv17/WB/Rie1-ΔGL and Lv17/WB/Rie1-ΔCD stocks.…”

“…To determine the specific infectivity (SI) of the different viral strains, PAM cells were infected with 0.01 MOI and sampled every 12 h for 108 h. SI was calculated as the ratio of the total viral genome copy to the number of infectious viruses, measured in FFUs (SI = genome copy/FFU). Viral titers and ASFV genome copies were determined as described by Tamás et al (2023) [ 10 ]. Briefly: p72-specific PCR was performed for quantification.…”

“…The pigs were observed for 7 days after the challenge infection, and clinical signs were recorded daily using a clinical score table developed earlier [ 10 , 26 ].…”

“…These experiments suggest that, after further targeted modifications, it could serve as a basis for an effective modified live virus (MLV) vaccine. Indeed, the deletion of the MGF 110–11L gene reduced the side effects of the virus, but not to the desired level [ 10 ].…”

Generation of High-Quality African Swine Fever Virus Complete Genome from Field Samples by Next-Generation Sequencing

“…The genomic surveillance of ASFV on the whole-genome level has also been used to monitor the ASFV variants on the rise in Germany [ 26 ]. In addition, the whole-genome sequencing of ASFV has contributed to vaccine candidate development [ 27 , 28 ].…”