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

Authors: Gladue, Douglas; O'DONNELL, VIVIAN - Animal And Plant Health Inspection Service (APHIS); RAMIEREZ-MEDINA, ELIZABETH - University Of Connecticut; RAI, AYUSHI - Oak Ridge Institute For Science And Education (ORISE); Pruitt, Sarah; VUONO, ELIZABETH - University Of Mississippi; SILVA, EDIANE - University Of Kansas; VELAZQUEZ-SALINAS, LAURO - University Of Kansas; Borca, Manuel

Submitted to: Viruses
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/16/2020
Publication Date: 10/20/2020
Citation: Gladue, D.P., O'Donnell, V., Ramierez-Medina, E., Rai, A., Pruitt, S.E., Vuono, E., Silva, E., Velazquez-Salinas, L., Borca, M.V. 2020. 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. Viruses. https://doi.org/10.3390/v12101185.
DOI: https://doi.org/10.3390/v12101185

Interpretive Summary: African swine fever virus (ASFV) causes a devastating disease in swine, called African swine fever (ASF), that is currently spreading across Europe and Asia. Commercial vaccines are not available, but vaccine candidates have been developed by deleting specific genes in ASFV. One candidate, with a single mutation, was able to protect animals against ASF but was not fully attenuated causing some ASF clinical signs, therefore, two additional deletions were added to this ASFV. The additional deletions decreased the ability for the virus to replicate in cell culture. When tested for vaccine efficacy in pigs, the virus with additional deletions was no longer protective. This study constitutes an example of the unpredictability of genetic manipulation involving simultaneous deletion of multiple genes from the ASFV genome.

Technical 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 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 attenuation of different ASFV strains, although the degree of attenuation varies across isolates. Here, we investigate the possibility of increased safety of the experimental vaccine strain ASFV-G-'9GL 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-'9GL/'CD2v and ASFV-G-'9GL/'CD2v/'EP153R, harboring two and three gene deletions, respectively. ASFV-G-'9GL/'CD2v/'EP153R, but not ASFV-G-'9GL/'CD2v, had a decreased ability to replicate in vitro in swine macrophage cultures when compared with parental ASFV-G-'9GL. Importantly, ASFV-G-'9GL/'CD2v and ASFV-G-'9GL/'CD2v/'EP153R 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-'9GL offered robust protection during challenge. Therefore, deletion of CD2-like and C-type lectin-like genes significantly decreased the protective potential of ASFV-G-'9GL as a vaccine candidate. This study constitutes an example of the unpredictability of genetic manipulation involving simultaneous deletion of multiple genes from the ASFV genome.