Development and evaluation of a bivalent vaccine based on recombinant newcastle disease virus expressing infectious bursal disease virus VP2L-CH3-CH4 in SPF chickens

Newcastle disease (ND) and infectious bursal disease (IBD) are two viral infectious diseases that are extremely damaging to the poultry industry and are widespread throughout the world. It is necessary to develop a safe and effective vaccine against IBD and ND because vaccination is an effective preventive measure. It has been discovered that recombinant proteins expressed by an expression system in which a fragment of mammalian Immunoglobulin G (IgG) Fragment crystallizable (Fc) is linked to a segment of a gene have antibody-like properties that increase the exogenous protein's serum half-life. Heavy chain constant region 3 and heavy chain constant region 4 (CH3-CH4) of Avian Immunoglobulin Y (IgY) is structurally very similar to mammalian Ig G Fc. In this study, a bivalent vaccine rClone30-VP2L-CH3-CH4-GMCSF was developed by using NDV rClone30-chGM-CSF vector to produce VP2L-CH3-CH4 fusion protein. The vaccine has been given to 14-day-old specific pathogen free (SPF) free chickens to test whether it has the potential to prevent IBD and ND. Anti-IBDV and anti-NDV antibody levels in serum were evaluated using ELISA and HI, respectively, and the contents of CD4⁺ T, CD8⁺ T, and B cells in leukocytes were determined via flow cytometry. The contents and mRNA transcription levels of four inflammatory factors, IL-1β, IL-4, IFN-γ and chGM-CSF, were detected by ELISA and real-time PCR respectively. The results showed that after vaccination with the rClone30-VP2L-CH3-CH4-GMCSF vaccine, the levels of anti NDV and anti IBDV antibodies in chickens were significantly higher than those of the rClone30 vaccine and commercial vaccines. Meanwhile, the contents and transcription levels of inflammatory factors in chickens inoculated with rClone30-VP2L-CH3-CH4-GMCSF were significantly increased, and the proliferation response of B cells, CD4⁺ and CD8⁺ T cells was also stronger. However, the rClone30-VP2L-CH3-CH4-GMCSF vaccine had no significant advantage over the rClone30-VP2L-GMCSF vaccine in any of the above-mentioned features. In summary, rClone30-VP2L-CH3-CH4-GMCSF can stimulate the body to produce a stronger immune response, showing its potential to be considered as vaccine against IBD and ND, but the addition of CH3-CH4 did not improve the vaccine's immune effect as expected. The research lays the foundation for developing vaccines for other infectious viral diseases and avoids a unrealistic vaccine optimization method.