Potency of a recombinant NDV-H5 vaccine against HPAI H5N1 virus challenge in presence or absence of maternal derived antibodies.

Abstract

Highly Pathogenic Avian Influenza (HPAI), especially the Asian H5N1 (AsH5N1), and velogenic Newcastle disease (NDV) virus infections are responsible for the two most contagious and economically devastating poultry diseases. Continuous outbreaks and spread of both diseases support the need for efficacious vaccine strategies. However, traditional inactivated vaccines present some well-known shortcomings and Avian Influenza virus (AIV) live vaccination is prohibited. To fight off both viruses at once, live bivalent NDV-vectored vaccines expressing the haemagglutinin of AIV (rNDV-HA) have been developed by reverse genetics. This thesis aimed investigating the vaccine potency of a recombinant NDV-H5 candidate vaccine administrated early in life in the absence or presence of passive immunity. An optimal vaccination schedule was developed by evaluating different vaccination strategies using the rNDV-H5 vaccine through animal challenge experiments during which clinical protection, viral shedding and immune responses were evaluated in specific pathogen free (SPF) chickens. First, different routes of vaccination and doses of vaccine were tested in order to determine the minimal protective dose against challenge with an antigenically close clade 1 AsH5N1 virus, the A/crested_eagle/Belgium/01/2004 strain. A clear dose dependency was observed after 1-day-old vaccination of SPF chickens with 105, 106 and 107 50 % embryo infectious dose (EID50) of vaccine followed by a challenge at 3 weeks of age. The 106 EID50-dose was shown as the minimal protective dose, allowing 90% clinical protection, significant reduced viral shedding and induction of significant NDV and H5 AIV serological responses. However, the H5 humoral response was weak and slow even after boost vaccinations despite good clinical protection and reduced viral excretion, suggesting a role of cellular and mucosal immunity in the induced protection. An ideal vaccine should be protective against a large panel of strains. In this context, the rNDV-H5 protective range was addressed by challenges with two antigenically divergent 15 clade 2.2.1 HPAI H5N1 Egyptian strains, one circulating in 2007 (A/chicken/Egypt/1709-1/2007, “Egypt 2007”) and the other in 2008 (A/chicken/Egypt/1709-6/2008, “Egypt 2008”). Vaccination of SPF chickens at 1-day-old and two weeks of age with 106 EID50 of rNDV-H5 vaccine was shown to be highly protective (90%) after challenge at 5 weeks of age with the “Egypt 2007” challenge strain but failed to protect against the “Egypt 2008” strain. One of the main shortcomings of early vaccination with live vaccines is the interference of maternal derived antibodies (MDA), often considered as one of the main reasons for vaccine failures. Since the rNDV-H5 vaccine candidate was shown as a good potential candidate for routine mass vaccination, there was a need to investigate the impact of specific H5- and NDV-MDA, alone or in combination, with the efficacy of the rNDV-H5 vaccine. To circumvent the logistical difficulty of obtaining a sufficient number of chicks with homogenous titres, an artificial model mimicking maternal passive immunity was developed. Different routes of injection and doses of H5N1 or NDV hyperimmunized polyclonal chicken serum were compared. The best results were obtained by combining egg yolk injection at embryonic day (ED) 14 with intraperitoneal (IP) injection at day-old, resulting in levels and duration of MDA approaching the natural decline of MDA. The interference of MDA on vaccination was compared in birds presenting either only NDV, both NDV and H5-MDA or no MDA. A strong interference of the NDV-H5-MDA was demonstrated resulting in reduced clinical protection and high viral shedding. Surprisingly, the NDV-MDA had a positive impact on the vaccine efficacy with full clinical protection and the absence of viral excretion after challenge with H5N1. To clarify the distinct impact of H5- and NDV-MDA, the artificial model was used to induce an H5 AIV or NDV specific artificial passive immunity in SPF birds. A strong interference of the H5-MDA with the rNDV-H5 vaccine efficacy was confirmed by a faster and complete mortality 16 compared with vaccinated SPF chickens. Moreover, the beneficial impact of the NDV-MDA was confirmed as well. In conclusion, in countries vaccinating against NDV and prohibiting AIV vaccination, the rNDV-H5 vaccine combined with a high prevalence of NDV-MDA in progeny could be a valuable vaccine candidate in case of emergency vaccination. However, in countries with high H5 seroprevalence, delivery at young age should be postponed until the decline of the H5-MDA

Date of Award	17 Mar 2014
Original language	French
Awarding Institution	University of Namur
Supervisor	JEAN-JACQUES LETESSON (Supervisor), Benoit Muylkens (Jury), Gwenaëlle DAUPHIN (Jury), Patrick Goubau (Jury), Eric Muraille (President), Thierry VAN DEN BERG (Supervisor), Giovanni CATTOLI (Jury) & B. Lambrecht (Jury)