African swine fever virus vaccine candidate ASFV‐G‐ Δ I177L efficiently protects European and native pig breeds against circulating Vietnamese field strain

Abstract

The recent spread of African swine fever (ASF) in the People's Republic of China and neighbouring countries in Asia has had significant economic consequences with an estimated direct cost of $55-$130 billion. This pandemic, originally detected in Republic of Georgia in 2007, has devastated the swine industry in large geographical areas of Southeast Asia with 14 countries reporting ASF outbreaks since the first documented case was confirmed in the city of Shenyang, Liaoning Province, China, on 3 August 2018. In the absence of any available vaccines, the control of ASF relies on the detection and culling of infected animals. The United States Department of Agriculture recently developed a recombinant experimental vaccine candidate, ASFV-G-ΔI177L, by deleting the I177L gene from the genome of the highly virulent pandemic ASFV strain Georgia, which efficaciouly protects pigs from the parental virus. Here, the initial studies were extended demonstrating that ASFV-G-ΔI177L is able to protect pigs against the virulent ASFV isolate currently circulating and producing disease in Vietnam with similar efficacy as reported against the Georgia strain. Comparative studies performed using a large number of pigs of European and Vietnamese origin demonstrated that a minimum protective dose of 10 2 HAD 50 of ASFV-G-ΔI177L equally protects animals of both breeds. In concurrence with those results, the onset of immunity in these animal breed showed appearance of protection in approximately one-third of the animals by the second week post vaccination, with full protection achieved by the fourth week post vaccination. Therefore, results presented here demonstrated that ASFV-G-ΔI177L is able to induce protection against virulent Vietnameese ASFV field strains and is effective in protecting local breeds of pigs as efficiently as previously shown for European cross-bred pigs. To our knowledge, this is the first report showing the efficacy of a Georgia 2007 based vaccine candidate in Asian breed of pigs or challenged with an Asian ASFV strain.

Deletion of African Swine Fever Virus Histone-like Protein, A104R from the Georgia Isolate Drastically Reduces Virus Virulence in Domestic Pigs

“…The attenuation of ASFV virulence by deletion of a single gene is not a very common feature. Actually, only nine individual genes have been reported to produce attenuation of ASFV virulence: I177L [ 10 , 38 ], 9Gl [ 12 , 16 ], CD2 [ 14 , 15 ], A137 [ 11 ], I226R [ 39 ], I267L [ 40 ], NL [ 41 ], UK [ 42 ], and DP148R [ 43 ], and only five of these genes in the ASFV-G isolate or its derivative viruses: I177L [ 10 , 38 ], 9Gl [ 12 ], A137 [ 11 ], I226R [ 39 ], and I267L [ 40 ]. Although the deletion of the A104R gene does not completely attenuate ASFV-G, it could potentially be used to increase the safety of already attenuated strains.…”

Evaluation of the Safety Profile of the ASFV Vaccine Candidate ASFV-G-ΔI177L

“…Peripheral blood mononuclear cells (PBMCs) were prepared from fresh defibrinated swine blood as previously described [ 15 ]. Briefly, ethylenediaminetetraacetic acid (EDTA)-treated swine blood was mixed with red blood cell (RBC) lysis buffer (155 mM NH 4 Cl, 10 mMKHCO 3 , 0.1 mM EDTA) at room temperature for 15 min and centrifuged at 2000 rpm for 10 min to remove the lysis buffer.…”

“…DNA extraction was performed using a Patho Gene-spin DNA/RNA Extraction Kit (Intron Biotechnology, Gyeonggi, Korea) for nasal swab samples or a QIAamp DNA Blood Mini Kit (Qiagen, Hilden, Germany) for blood samples. Detection of ASFV, using B646L (encoding for p72) as the target gene, was carried out using the VetMAX African Swine Fever Virus Detection Kit (Thermo Fisher Scientific, Waltham, MA, USA) as previously described [ 15 ]. Samples with Ct values < 45 were considered positive.…”

“…Experimental live attenuated vaccine viruses, generated by deleting virus genes associated with virulence, have been shown to be effective [ 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 ]. One of these vaccines, ASFV-G-ΔI177L [ 7 ], induces effective protection against its parental virulent virus strain, Georgia 2007, as well as a virulent Vietnamese field strain isolated in 2019 [ 15 ]. This vaccine has been selected for further development and commercialization, which includes a thorough assessment of its safety characteristics.…”

Antigenic and immunogenic properties of recombinant proteins consisting of two immunodominant African swine fever virus proteins fused with bacterial lipoprotein OprI

“…Due to advances in molecular biology and an in-depth knowledge of ASFV, much progress has been made in live attenuated vaccines generated by targeted gene deletion [19]. Numerous genedeleted ASFVs have shown good efficacy and improved safety profile [20][21][22], and accompanying genetic tests to discriminate between infected and vaccinated animals were established [23]. Although live attenuated vaccines against ASF displayed good potential, some of them still suffered from severe adverse side effects and safety issues [4,24].…”