Editorial: Basic and Applied Research Toward the Development of Vaccines Against African Swine Fever Virus

Daniel Pérez Núñez^1,2*Sandra Blome³Linda Kathleen Dixon⁴

• ¹Centre for Molecular Biology Severo Ochoa, Spanish National Research Council (CSIC), Madrid, Spain
• ²Centro de Biologia Molecular Severo Ochoa, Madrid, Spain
• ³Friedrich-Loeffler-Institut Bundesforschungsinstitut fur Tiergesundheit, Greifswald, Germany
• ⁴Pirbright Institute, Pirbright, United Kingdom

The ASFV genome contains up to ~190 open reading frames (ORFs) based on DNA sequence analysis. These are transcribed into mRNAs in the cytoplasm by the virus encoded RNA polymerase and stage specific transcription factors (Cackett et al., 2020). Cackett et al. (Cackett et al., 2024), present the first accurate map of the transcripts across the ASFV genome. This was achieved by determining full length sequences of viral mRNAs at early and late stages of infection in combination with the identification of transcript 5' start and 3' termination sites. The study also identified consensus early and late ASFV promoter motifs and termination sequences. Transcript read through to downstream ORFs was identified particularly late during infection. This information is critical to confirm which ORFs are transcribed and to accurately predict the sequences of proteins encoded and the timing of their expression. The information also aids the design of genome deletions and modifications used in construction of LAVs.To improve vaccine development better understanding of factors that regulate the immune responses leading to protection against virulent virus challenge is required. Radulovic et al., extend their previous study which compared responses of specific pathogen free (SPF) pigs with those of farm pigs following inoculation with a moderately virulent ASFV strain (Radulovic et al., 2022). The SPF and farm pigs differed in their gut microbiome and their basal immune activation status. Less severe disease was observed in SPF pigs than in conventional farm pigs. In this article response to challenge, after 4 months, with virulent virus were compared. The SPF pigs were fully protected and showed little or no viremia. In contrast, farm pigs developed high viremia, proinflammatory cytokine responses and severe clinical signs. Forty percent of the farm pigs reached the humane endpoint. These striking results indicate that limited prior immune exposure to other pathogens and/or the microbiome composition of SPF pigs promotes resilience to infection with a moderately virulent strain and the development of strong protective immunity against virulent ASFV challenge (Radulovic et al., 2025).The limited availability of ASFV susceptible, continuously growing cell lines representing the natural target cells, monocytes/macrophages, has hindered research and vaccine development. Takenouchi et al. (Takenouchi et al., 2024), describe an immortalized macrophage cell line from red river hogs (Potamochoerus porcus) African natural hosts which tolerate ASFV infection. The RRH cell line was confirmed to have a macrophage like phenotype by analysis of cell surface markers, activation of pro-inflammatory cytokine and IFN- production and phagocytic activity. Interestingly the replication kinetics of ASFV in the RRH cell line were more variable and reached lower titres compared with the IPKM porcine macrophage derived cell line. These cells provide an excellent new tool to investigate ASFV replication and elucidate the innate immune responses in naturally tolerant host species. In addition, these cells would enable large-scale vaccine production and standardized viral growth assays, eliminating the need for primary pig cells. This tool is critical for current and future vaccine platforms such as LAVs.The development of ASFV subunit vaccines is hindered by lack of knowledge of protective antigens and an effective delivery system. Gao et al. (Gao et al., 2024), investigate recombinant Saccaromyces cerevisiae (SC), which has been certified by the US Food and Drug Administration as safe for use in the food industry, as a novel method to deliver ASFV antigens. In this proof of concept study sequences, which code for the antigenic regions from 8 ASFV proteins fused to a Dendritic Cell targeting peptide, were inserted into yeast chromosomes. The ASFV proteins were stably expressed on the surface of recombinant SC strains. Oral immunization of mice induced strong humoral, mucosal and cellular Th1 and Th2 immune responses. Future testing in swine, including challenge studies, will determine the vaccine potential of this novel approach for ASFV.The safety evaluation of live attenuated vaccines requires sensitive methods to detect replication of the vaccine virus. Assays that can differentiate between vaccinated and naturally infected animals (DIVA assays) facilitate this process. Luan et al., describe a sensitive and rapid visual assay to detect the ASFV KP177R gene. Recombinase polymerase amplification is used as a first step. Subsequently guide RNAs direct Cas12a resulting in non-specific single-strand DNA cleavage which can be detected by colorimetric assays. The KP177R gene can be deleted without affecting virus replication or virulence and therefore could be used as a potential marker for DIVA diagnostics. This assay has potential for use in the field.