Response to a DNA vaccine against the H5N1 virus depending on the chicken line and number of doses

Protection conferred by an H5 DNA vaccine against highly pathogenic avian influenza in chickens: The effect of vaccination schedules

H5 highly pathogenic avian influenza (HPAI) viruses of the Asian lineage (A/goose/Guangdong/1/96) belonging to clade 2.3.4.4 have spread worldwide through wild bird migration in two major waves: in 2014/2015 (clade 2.3.4.4c), and since 2016 up to now (clade 2.3.4.4b). Due to the increasing risk of these H5 HPAI viruses to establish and persist in the wild bird population, implementing vaccination in certain sensitive areas could be a complementary measure to the disease control strategies already applied. In this study, the efficacy of a novel DNA vaccine, encoding a H5 gene (A/gyrfalcon/Washington/41088-6/2014 strain) of clade 2.3.4.4c was evaluated in specific pathogen-free (SPF) white leghorn chickens against a homologous and heterologous H5 HPAI viruses. A single vaccination at 2 weeks of age (1 dose), and a vaccination at 2 weeks of age, boosted at 4 weeks (2 doses), with or without adjuvant were characterized. The groups that received 1 dose with or without adjuvant as well as 2 doses with adjuvant demonstrated full clinical protection and a significant or complete reduction of viral shedding against homologous challenge at 6 and 25 weeks of age. The heterologous clade 2.3.4.4b challenge of 6-week-old chickens vaccinated with 2 doses with or without adjuvant showed similar results, indicating good cross-protection induced by the DNA vaccine. Long lasting humoral immunity was observed in vaccinated chickens up to 18 or 25 weeks of age, depending on the vaccination schedule. The analysis of viral transmission after homologous challenge showed that sentinels vaccinated with 2 doses with adjuvant were fully protected against mortality with no excretion detected. This study of H5 DNA vaccine efficacy confirmed the important role that this type of so-called third-generation vaccine could play in the fight against H5 HPAI viruses.

Manganese-based nanoadjuvants for enhancement of immune effect of DNA vaccines

As a highly pathogenic avian influenza virus, influenza A (H5N1) has been reported to infect humans, posing a major threat to both poultry industry and public health. It is an urgent need to develop a kind of effective vaccine to prevent death and reduce the incidence rate of H5N1 avian influenza. Compared with traditional inactivated or attenuated vaccines, deoxyribonucleic (DNA) vaccines have the advantages of continuously expressing plasmid-encoded antigens and inducing humoral and cellular immunity. However, the immune effect of DNA vaccines is limited to its poor immunogenicity. Using of nanoadjuvants with DNA vaccines holds a great promise to increase the transfection efficiency and immunogenicity of DNA vaccines. In this study, we developed a nano co-delivery system with a manganese-based liposome as adjuvant for delivery of a DNA vaccine. This system has been found to protect DNA vaccine, enhance phagocytosis as well as promote activation of antigen-presenting cells (APCs) and immune cells in draining lymph nodes. In addition, the effect of this nanovaccine has been evaluated in mouse models, where it induces highly potent hemagglutination inhibitory antibody (HI) and IgG antibodies, while activating both humoral and cellular immunity in the host. Overall, this strategy opens up a new prospect for manganese nanoadjuvants in increasing the immunogenicity of DNA vaccines.

High immune efficacy against different avian influenza H5N1 viruses due to oral administration of a Saccharomyces cerevisiae-based vaccine in chickens

A safe and effective vaccine is the best way to control large-scale highly pathogenic avian influenza virus (HPAI) A (H5N1) outbreaks. Saccharomyces cerevisiae (S. cerevisiae) is an ideal mucosal delivery vector for vaccine development, and we have previously shown that conventional administration of a S. cerevisiae-based vaccine (EBY100/pYD1-HA) via injection led to protection against the homologous H5N1 virus in a mouse model. Because the diameter of S. cerevisiae is approximately 10 μm, which results in a severe inflammation by injection route, therefore, oral administration is a more suitable approach for EBY100/pYD1-HA conferring protection in poultry. We extended our work by evaluating the immunogenicity and protective efficacy of oral vaccination with EBY100/pYD1-HA in the chicken model. Oral immunization with EBY100/pYD1-HA could induce robust serum IgG, mucosal IgA and cellular immune responses. Importantly, EBY100/pYD1-HA provided protection against challenges with a homologous and a heterologous H5N1 viruses. These findings suggest that EBY100/pYD1-HA, a promising H5N1 oral vaccine candidate, can avoid potential reassortment of other avian influenza viruses in oral administration of live virus vaccines and overcome the limitations of conventional injection routes. Importantly, this platform will be able to provide opportunities for broader applications in poultry during HPAI A (H5N1) outbreaks.