Joint deletion of multifunctional MGF505-7R and H240R genes generates a safe and effective African swine fever virus attenuated live vaccine candidate

African swine fever(ASF)caused by the ASF virus(ASFV)is a highly contagious disease of pigs and wild boars.Currently,there are no safe,effective commercial vaccines available.The genome of ASFV HLJ/18 contains more than 180 genes,including a few virulence-related genes.Identifying these key virulence genes through individual deletion and subsequent pathogenicity testing in pigs is a laborious process.In addition,some ASFV genes are indispensable for viral replication and cannot be deleted.Over the past 30 years,scientists have confirmed that certain ASFV genes particularly those host antiviral innate immune responses,are associated with the virulence of ASFV strains.Although knockout of these genes does not impact viral replication,it does attenuate the virulence of ASFV in pigs.Pigs immunized with these live attenuated vaccine candidates can provide partial or complete protection.Based on these findings,we propose a new concept that ASFV immunomodulatory genes involved in type I interferon(IFN)production,IFN-JAK-STAT signaling,inflammatory responses,cell death(involved in apoptosis,necrosis,and pyroptosis),and autophagy may be related to the pathogenicity of ASFV.An unbiased screening may identify more ASFV immunomodulatory or multifunctional genes,simplifying the confirmation of ASFV virulence-related genes.In line with these theories,we have identified MGF505-7R and H240R as key virulence genes determining the pathogenicity of the ASFV HLJ/18 strain.Deletion of MGF505-7R,H240R alone or both attenuate the virulence of ASFV HLJ/18 in pigs,providing a paradigm for developing attenuated live vaccines from basic research results.