Deletion of African swine fever virus interferon inhibitors from the genome of a virulent isolate reduces virulence in domestic pigs and induces a protective response

Abstract

African swine fever virus (ASFV) encodes multiple copies of MGF360 and MGF530/505 gene families. These genes have been implicated in the modulation of the type I interferon (IFN) response. We investigated the effect of modulating the IFN response on virus attenuation and induction of protective immunity by deleting genes MGF360 (MGF360-10L, 11L, 12L, 13L, 14L) and MGF530/505 (MGF530/505-1R, 2R and 3R) and interrupting genes (MGF360-9L and MGF530/505-4R) in the genome of the virulent ASFV isolate Benin 97/1. Replication of this deletion mutant, BeninΔMGF, in porcine macrophages in vitro was similar to that of the parental virulent virus Benin 97/1 and the natural attenuated isolate OURT88/3, which has a similar deletion of MGF360 and 530/505 genes. Levels of IFN-β mRNA in macrophages infected with virulent Benin 97/1 isolate were barely detectable but high levels were detected in macrophages infected with OURT88/3 and intermediate levels in macrophages infected with BeninΔMGF. The data confirms that these MGF360 and MGF530/505 genes have roles in suppressing induction of type I IFN. Immunisation and boost of pigs with BeninΔMGF showed that the virus was attenuated and all pigs (5/5) were protected against challenge with a lethal dose of virulent Benin 97/1. A short transient fever was observed at day 5 or 6 post-immunisation but no other clinical signs. Following immunisation and boost with the OURT88/3 isolate 3 of 4 pigs were protected against challenge. Differences were observed in the cellular and antibody responses in pigs immunised with BeninΔMGF compared to OURT88/3. Deletion of IFN modulators is a promising route for construction of rationally attenuated ASFV candidate vaccine strains.

Current status and evolving approaches to African swine fever vaccine development

“…These MGFs have also been defined to determine viral replication and generalization of infection in ticks (Burrage, Lu, Neilan, Rock, & Zsak, ). Recently, Reis et al () reported that MGF‐deleted ASFV based on the virulent strain Benin 97/1 showed reduced virulence in domestic pigs and induced a protective response. Likewise, from in vitro experiments, it has been shown that the replication of Pr4 mutant lacking MGFs was significantly reduced in alveolar macrophages treated with IFN‐α (Golding et al, ).…”

“…Likewise, from in vitro experiments, it has been shown that the replication of Pr4 mutant lacking MGFs was significantly reduced in alveolar macrophages treated with IFN‐α (Golding et al, ). As a result, MGFs have been described to be IFN modulators and considered to be promising targets to rationally attenuate ASFV as a vaccine (Afonso et al, ; Golding et al, ; Reis et al, ). Another main host defence strategy against viral invasions is the elimination of infected cells through apoptosis (Gupta, ; Liang, Oh, & Jung, ; Nainu, Shiratsuchi, & Nakanishi, ).…”

“…Having noted the drawbacks of in vitro attenuated ASFVs, target gene‐deleted live attenuated and subunit vaccines become attractive options, and as a result, several gene‐deleted ASF vaccines have been attempted (Gallardo, Sánchez, et al, ; Monteagudo et al, ; O’Donnell et al, , ; Reis et al, ). By targeted deletion of virulence‐related genes, it has been shown that it would be possible to define the balance between attenuation and immunogenicity (Reis et al, ; Sánchez‐Cordón, Jabbar, et al, ). To date, several virulence‐associated ASFV genes such as 9GL, UK, CD2v, DP148R and MGFs have been deleted to generate attenuated ASF vaccines.…”

Different routes and doses influence protection in pigs immunised with the naturally attenuated African swine fever virus isolate OURT88/3

“…ASFV genotype I isolates have been historically described as the main circulating isolates in the African continent, being a major limiting factor for pig production in most of sub-Saharan countries of Western and Central African (Boshoff et al., 2007, EFSA AHAW Panel, 2015). Genetically modified attenuated viruses, for which genes for virulence factors have been deleted, may provide safe vaccines against ASF (Lewis et al., 2000, O'Donnell et al., 2015, Reis et al., 2016). Despite some safety problems, live attenuated vaccines have demonstrated a high effectiveness against experimental infections with homologous (Leitão et al., 2001, Boinas et al., 2004, Oura et al., 2005, King et al., 2011, Lacasta et al., 2015), and occasionally heterologous (King et al., 2011, Mur et al., 2013), virulent isolates of ASFV.…”

Unraveling the Armor of a Killer: Evasion of Host Defenses by African Swine Fever Virus

“…Experiments with deletion mutant viruses lacking multiple members of the multigene family 360 (MGF360) and MGF530 show that these genes inhibit the induction of IFN and may also have an impact on the STAT signaling cascade and/or components of the antiviral state (11)(12)(13). Importantly, recombinant viruses with similar deletions of MGF360 and MGF530 that were derived from three different genotypes are attenuated in pigs (11,13,14).…”