Deletion of CD2-Like (CD2v) and C-Type Lectin-Like (EP153R) Genes from African Swine Fever Virus Georgia-∆9GL Abrogates Its Effectiveness as an Experimental Vaccine

Abstract

African swine fever virus (ASFV) is currently the most dreaded infectious disease affecting the global swine production industry. There is no commercial vaccine available, making the culling of infected animals the current solution to control outbreaks. Effective experimental vaccines have been developed by deleting virus genes associated with virulence. Deletion of the ASFV 9GL gene (∆9GL) has resulted in the attenuation of different ASFV strains, although the degree of attenuation varies across isolates. Here, we investigated the possibility of the increased safety of the experimental vaccine strain ASFV-G-Δ9GL by deleting two additional virus genes involved in pathogenesis, CD2v, a CD2 like viral encoded gene from the EP402R open reading frame (ORF), and C-type lectin-like viral gene, encoded from the EP153R ORF. Two new recombinant viruses were developed, ASFV-G-Δ9GL/ΔCD2v and ASFV-G-Δ9GL/ΔCD2v/ΔEP153R, harboring two and three gene deletions, respectively. ASFV-G-Δ9GL/ΔCD2v/ΔEP153R, but not ASFV-G-Δ9GL/ΔCD2v, had a decreased ability to replicate in vitro in swine macrophage cultures when compared with parental ASFV-G-Δ9GL. Importantly, ASFV-G-Δ9GL/ΔCD2v and ASFV-G-Δ9GL/ΔCD2v/ΔEP153R induced almost undetectable viremia levels when inoculated into domestic pigs and failed to protect them against challenge with parental virulent ASFV-Georgia, while ASFV-G-Δ9GL offered robust protection during challenge. Therefore, the deletion of CD2-like and C-type lectin-like genes significantly decreased the protective potential of ASFV-G-Δ9GL as a vaccine candidate. This study constitutes an example of the unpredictability of genetic manipulation involving the simultaneous deletion of multiple genes from the ASFV genome.

Role of African swine fever virus (ASFV) proteins EP153R and EP402R in reducing viral persistence and virulence from attenuated BeninΔDP148R

“…However, the role of these gene interruptions in virus virulence is unclear since OURT88/3 and NH/P68 viruses also have large deletion of multiple genes belonging to MGF 360 and MGF 505 from close to the left genome end (26,40). Both the single deletion of EP402R and the simultaneous deletion of EP402R and EP153R from an attenuated Georgia/07 strain (ASFV-G-Δ9GL) decreased the ability to protect against challenge (41). Serum antibodies against both CD2v and EP153R were shown to mediate haemadsorption inhibition and to be involved in serotype-specific protective immunity, representing good targets for ASFV serotype classification and evolution (42,43).…”

African Swine Fever Virus as a Difficult Opponent in the Fight for a Vaccine—Current Data

“…Previous studies showed that the deletion of another IFN inhibitor (A276R) from the NH/P68 isolate resulted in a complete loss of protection against Arm07 challenge, as opposed to the complete protection provided by vaccination with wild-type NH/P68 [ 67 ]. The next example of the unpredictability of genetic manipulation involving simultaneous deletion of multiple genes from the ASFV genome is the study conducted by Gladue et al [ 68 ]. The authors showed that the deletion of CD2-like and C-type lectin-like genes significantly decreased the protective potential of the experimental vaccine strain attenuated following the deletion of 9GL from the Georgia 2010 isolate (ASFV-G-∆9GL).…”

“…After these gene manipulations, viremia levels induced by ASFV-G-Δ9GL/ΔCD2v and ASFV-G-Δ9GL/ΔCD2v/ΔEP153R were almost undetectable when inoculated in domestic pigs and did not protect animals against challenge with the parental virulent strain ASFV-Georgia, in contrast to ASFV-G-Δ9GL, which provided robust protection during challenge. ASFV-G-Δ9GL/ΔCD2v/ΔEP153R also had a decreased ability to replicate in vitro in swine macrophage cultures when compared with parental ASFV-G-Δ9GL [ 68 ].…”

“…These studies confirm that the results of ASFV genetic modifications may be unpredictable and experimental validation of new strains is essential in any case. Moreover, the results suggest that the rational development of new ASFV vaccines requires great caution and avoidance of the direct transfer of results obtained by specific gene deletions in a given virus strain to a new field of isolates [ 68 ].…”

Proteome Analysis in PAM Cells Reveals That African Swine Fever Virus Can Regulate the Level of Intracellular Polyamines to Facilitate Its Own Replication through ARG1

“…The expression of the A224L can activate NF-κB, which may inhibit apoptosis by activating the transcription of some anti-apoptotic genes [ 11 , 12 ]. The EP153R is a C-type lectin protein, which can downregulate the expression of MHC-I, inhibits cell apoptosis, and participates in the process of adsorbing blood cells [ 13 ]. It was also reported that no phosphorylation of eIF2 α or increased induction of CHOP was detected in ASFV E70 isolates-infected cells with the deletion of the DP71L gene [ 14 ], indicating that ASFV may encode other inhibitors of this pathway.…”