Development of in ovo-compatible NS1-truncated live attenuated influenza vaccines by modulation of hemagglutinin cleavage and polymerase acidic x frameshifting sites

Authors: GHORBANI, AMIR - The Ohio State University; NGUNJIRI, JOHN - The Ohio State University; ABUNDO, MICHAEL EDWARD - The Ohio State University; Pantin Jackwood, Mary; KENNEY, SCOTT - The Ohio State University; Lee, Chang

Submitted to: Vaccine
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/10/2023
Publication Date: 3/10/2023
Citation: Ghorbani, A., Ngunjiri, J.M., Abundo, M.C., Pantin Jackwood, M.J., Kenney, S.P., Lee, C.W. 2023. Development of in ovo-compatible NS1-truncated live attenuated influenza vaccines by modulation of hemagglutinin cleavage and polymerase acidic x frameshifting sites. Vaccine. 41(11):1848-1858. https://doi.org/10.1016/j.vaccine.2023.01.018.
DOI: https://doi.org/10.1016/j.vaccine.2023.01.018

Interpretive Summary: Avian influenza viruses continue to be serious threat for poultry production worldwide. Although humane killing of infected flocks is the preferred method to control highly pathogenic avian influenza in the U.S., there has been serious consideration for the use of vaccines as a component of integrated control programs. In poultry production, vaccination of chicken embryos inside eggs (in ovo) are cost-effective method and can protect chicks from disease early in their life. However, live vaccine candidates proven to be effective in older chickens are not safe enough to be used as in ovo vaccines. In this study, we incorporated couple of genetic modifications in the previously developed live vaccine candidate to further weaken the virus while maintaining its protective efficacy. We demonstrated that our approach can further attenuate and enhance the safety of embryo killing live vaccines which will be instrumental in developing future in ovo vaccines for poultry.

Technical Abstract: Emerging avian influenza viruses pose a high risk to poultry production, necessitating the need for more broadly protective vaccines. Live attenuated influenza vaccines offer excellent protective efficacies but their use in poultry farms is discouraged due to safety concerns related to emergence of reassortant viruses. Vaccination of chicken embryos inside eggs (in ovo) induces early immunity in young chicks while reduces the safety concerns related to the use of live vaccines on farms. However, in ovo vaccination using influenza viruses severely affects the egg hatchability. We previously engineered a high interferon-inducing live attenuated influenza vaccine candidate with an enhanced protective efficacy in chickens. Here, we asked whether we could further modify this high interferon-inducing vaccine candidate to develop an in ovo-compatible live attenuated influenza vaccine. We first showed that the enhanced interferon responses induced by the vaccine is not enough to attenuate the virus in ovo. To reduce the pathogenicity of the virus for chicken embryos, we replaced the hemagglutinin cleavage site of the H7 vaccine virus (PENPKTR/GL) with that of the H6-subtype viruses (PQIETR/GL) and disrupted the ribosomal frameshifting site responsible for viral polymerase acidic X protein expression. In ovo vaccination of chickens with up to 105 median egg infectious dose of the modified vaccine had minimal effects on hatchability while protecting the chickens against a heterologous challenge virus at two weeks of age. This study demonstrates that targeted genetic mutations can be applied to further attenuate and enhance the safety of live attenuated influenza vaccines to develop future in ovo vaccines for poultry.