Induction of protective immunity in chickens immunised with plasmid DNA encoding infectious bursal disease virus antigens

Direct DNA inoculations were used to determine the efficacy of gene immunis ation of chickens to elicit protective immune responses against infectious bursal disease virus (IBDV). The vp2 gene of IBDV strains GP40 and D78, and the vp2-vp4-vp3 encoding segment of strain D78 were cloned in an expressio n vector which consisted of human cytomegalovirus (HCMV) immediate early en hancer and promoter, adenovirus tripartite leader sequences and SV40 polyad enylation signal. For purification of vaccine-quality plasmid DNA from E. c oli, an effective method was developed. Chickens were vaccinated by inocula tion of DNA by two routes (intramuscular and intraperitoneal). Two weeks la ter, chickens were boosted with DNA, and at 2 weeks post-boost, they were c hallenged with virulent IBDV strain. Low to undetectable levels of IBDV-spe cific antibodies and no protection were observed with DNA encoding VP2. How ever, plasmids encoding VP2-VP4-VP3 induced IBDW-specific antibodies and pr otection in the chickens. DNA immunisation opens a new approach to the deve lopment of gene vaccines for chickens against infectious diseases.