Generation of two bat influenza-vectored H5 vaccine candidates against HPAI H5N1 in chickens

Abstract

H5N1 highly pathogenic avian influenza (HPAI) represents a persistent global threat to both poultry and public health, necessitating the development of safe and effective vaccines. We utilized an established bat influenza vector to develop live attenuated vaccines, and demonstrated their safety and immunogenicity. In this study, we developed a bat influenza-vectored H5N1 vaccine (WT H17-H5N1) and its avian-adapted candidate (AA H17-H5N1) by introducing specific amino acid mutations (PB2 I382S, PB1 Q694H/I695K, and PA E141K) into the Bat09 polymerase complex to enhance avian adaptation and reduce safety concerns in potential mammalian use. To evaluate vaccine safety and immunogenicity, groups of specific pathogen free (SPF) chickens were intranasally primed and boosted with either 105 TCID50 of wild-type (WT) or avian-adapted prototype vaccine at 2 weeks interval, respectively. One group of chickens was mock-immunized as blank control. The birds were then monitored for clinical signs daily. Laryngotracheal and cloacal swabs were collected from each vaccinated bird at day 1, 3, 5 and 7 days post-immunization (dpi) to detect virus shedding. Three chickens in each group were euthanized at 3 and 5 dpi and tissue samples including brain, lung, heart, trachea, and intestine were collected for viral titration. Blood samples were collected from each bird at 2, 3 and 4 weeks post immunization to determine humoral immune responses through hemagglutination inhibition (HI) and neutralization assays. All chickens from mock-immunized and vaccine-immunized groups did not show clinical signs and grew normally. No virus was detected from swab and tissue samples collected from two groups of vaccinated chickens. HI and neutralization antibodies were detected from each bird of both vaccination groups. However, a higher HI and neutralization titer was found in avian-adapted prototype vaccine group than wild-type vaccine group. These results demonstrate safety and immunogenicity of bat influenza vectored H5 vaccine candidates and indicate that polymerase compatibility with the avian host can enhance the vaccine immunogenicity.