Evaluation of Newcastle disease virus LaSota strain attenuated by codon pair deoptimization of the HN and F genes for in ovo vaccination

Authors: ELDEMERY, FATMA - Oak Ridge Institute For Science And Education (ORISE); OU, CHANGBO - Guangxi University; Kim, Taejoong; Spatz, Stephen; Dunn, John; Silva, Robert; Yu, Qingzhong

Submitted to: Veterinary Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/4/2022
Publication Date: 12/6/2022
Citation: Eldemery, F., Ou, C., Kim, T.N., Spatz, S.J., Dunn, J.R., Silva, R.F., Yu, Q. 2022. Evaluation of Newcastle disease virus LaSota strain attenuated by codon pair deoptimization of the HN and F genes for in ovo vaccination. Veterinary Microbiology. 277:109625. https://doi.org/10.1016/j.vetmic.2022.109625.
DOI: https://doi.org/10.1016/j.vetmic.2022.109625

Interpretive Summary: In ovo vaccination is an attractive immunization approach, which can confer early protection against poultry infectious diseases and decrease vaccination costs for the poultry industry. However, commonly used Newcastle disease virus (NDV) vaccines cannot be administered in ovo because of the reduced hatchability and embryo mortality. During the past decade, a new genetic manipulation approach, codon pair deoptimization (CPD), has been used to efficiently and rapidly attenuate viruses by deoptimizing gene codes of the virulence genes. In this study, we aimed to attenuate the NDV LaSota (LS) vaccine strain for in ovo vaccination by CPD of its virulence genes, the fusion (F) and hemagglutinin-neuraminidase (HN) genes, with approximately 44% suboptimal codon substitutions. Three NDV LS recombinant viruses vectoring codon deoptimized F, HN, or both genes were generated using reverse genetics technology. Biological assays and in ovo vaccination experiments showed that the CPD of the virulence genes of the LS strain at the current level of suboptimal codon substitutions could not sufficiently attenuate the virus for in ovo vaccine. Codon deoptimizing a greater proportion of the F and HN genes or additional gene(s) may be required for sufficient attenuation of the LS strain.

Technical Abstract: In ovo vaccination is an attractive immunization approach for the poultry industry. However, commonly used Newcastle disease virus (NDV) vaccines cannot be administered in ovo because of the reduced hatchability and embryo mortality. The codon pair deoptimization (CPD) approach has been used to efficiently and rapidly attenuate viruses by targeting the virulence genes. In this study, we aimed to attenuate the NDV LaSota (LS) vaccine strain for in ovo vaccination by CPD of the fusion (F) or/and hemagglutinin-neuraminidase (HN) genes with approximately 44 % suboptimal codon substitutions. Three NDV LS recombinants expressing codon deoptimized F (rLS/F-d), HN (rLS/HN-d), or both genes (rLS/F+HN-d) were generated using reverse genetics technology. Biological assays showed that the CPD viruses retained similar hemagglutination activity and growth ability to the parental rLS virus. The CPD of the HN gene slightly attenuated the rLS/HN-d and rLS/F+HN-d viruses, whereas the CPD of the F gene marginally increased the rLS/F-d virus pathogenicity compared to rLS. Nevertheless, all three CPD rLS viruses were still lethal to 10-day-old specific-pathogen-free (SPF) chicken embryos. In ovo inoculation of 18-day-old SPF chicken embryos with the CPD viruses severely reduced chicken’s hatch and survival rates. These results suggested that the CPD of the surface glycoprotein genes of the LS strain at the current level of suboptimal codon substitutions could not sufficiently attenuate the virus for use as an in ovo vaccine, and codon deoptimizing a greater proportion of the F and HN genes or additional gene(s) may be required for sufficient attenuation of the LS strain.