DNA vaccination with VP2 gene fragment confers protection against Infectious Bursal Disease Virus in Chickens

Infectious Bursal Disease Virus (IBDV) causes immunosuppression in young chickens by destruction of antibody producing B cells in the Bursa of Fabricius and poses a potential threat to the poultry industry. We have examined the protective efficacy of a subunit DNA vaccine against IBDV infection in chickens in this study. An immunodominant VP2 gene fragment (VP252–417) was cloned into CMV promoter based DNA vaccine vector pVAX1 and in vitro expression of the DNA encoded antigens was confirmed by transfection of CHO cells with vaccine constructs followed by RT-PCR and western blot analysis using IBDV-antiserum. Two weeks old chickens were immunized intramuscularly with pVAXVP252–417 and the in vivo transcription of the plasmid DNA was confirmed by RT-PCR analysis of DNA injected muscle tissue at different intervals of post immunization. Tissue distribution analysis revealed that the plasmid DNA was extensively distributed in muscle, spleen, kidney, liver, and bursa tissues. Chickens immunized with pVAXVP252–417 developed high titer (1:12,000) of anti-VP252–417 antibodies. Further, chicken splenocytes from pVAXVP252–417 immunized group showed a significantly high proliferation to the whole viral and recombinant antigen (P < 0.01) compared to control groups, which implies that pVAXVP252–417 codes for immunogenic fragment which has epitopes capable of eliciting both B and T cell responses. This is evident by the fact that, pVAXVP252–417 immunized chicken conferred 75% protection against virulent IBDV (vIBDV) challenge compared to the control group. Thus, the present study confirms that the immunodominant VP2 fragment can be used as a potential DNA vaccine against IBDV infection in chickens.