Immune protection duration and efficacy stability of DNA vaccine encoding Eimeria tenella TA4 and chicken IL-2 against coccidiosis

- Our data demonstrated 25μg was really the optimal dose of DNA vaccine pVAX1.0-TA4-IL-2;
- The immune protection duration of the DNA vaccination was at least 9 weeks post last immunization;
- The efficacies of three batches DNA vaccine of pVAX1.0-TA4-IL-2 were effective and stable.

In our previous study, an effective DNA vaccine encoding Eimeria tenella TA4 and chicken IL-2 was constructed. In the present study, the immunization dose of the DNA vaccine pVAX1.0-TA4-IL-2 was further optimized. With the optimized dose, the dynamics of antibodies induced by the DNA vaccine was determined using indirect ELISA. To evaluate the immune protection duration of the DNA vaccine, two-week-old chickens were intramuscularly immunized twice and the induced efficacy was evaluated by challenging with E. tenella at 5, 9, 13, 17 and 21 weeks post the last immunization (PLI) separately. To evaluate the efficacy stability of the DNA vaccine, two-week-old chickens were immunized with 3 batches of the DNA vaccine, and the induced efficacy was evaluated by challenging with E. tenella. The results showed that the optimal dose was 25 μg. The induced antibody level persisted until 10 weeks PPI. For the challenge time of 5 and 9 weeks PLI, the immunization resulted in ACIs of 182.28 and 162.23 beyond 160, showing effective protection. However, for the challenge time of 13, 17 and 21 weeks PLI, the immunization resulted in ACIs below 160 which means poor protection. Therefore, the immune protection duration of the DNA vaccination was at least 9 weeks PLI. DNA immunization with three batches DNA vaccine resulted in ACIs of 187.52, 191.57 and 185.22, which demonstrated that efficacies of the three batches DNA vaccine were effective and stable. Overall, our results indicate that DNA vaccine pVAX1.0-TA4-IL-2 has the potential to be developed as effective vaccine against coccidiosis.