Potent immune responses elicited by a bicistronic IBV DNA vaccine expressing S1 and IL-2 gene

Abstract:

Candidate IBV vaccines should elicit cellular responses as well as humoral responses. S1 gene of avian infectious bronchitis virus and interleukin-2 (IL-2) gene from chicken were inserted into the bicistronic pIRES-EGFP/DsRed plasmid. The pIRES-S1, pIRES-IL2 and pIRES-S1/IL-2 plasmid expressing or co-expressing S1 and IL-2 gene were constructed. Plasmids were transfected into the Vero cells by lipofectamine, and the expressed products were detected by RT-PCR and indirect immunofluorescence assay. The 7-day-old chickens were immunized intramuscularly with plasmids encapsulated by liposome and boosted three weeks later. Two weeks after boosting, chickens were challenged by virulent IBV strain. The results showed that coadministration of a plasmid expressing IL-2 with the S1 DNA vaccine led to only a marginal increase in humoral and T cell responses. However, immunization with the bicistronic plasmid pIRES-S1/IL-2 that co-expressing S1 and IL-2 under control of a single promoter led to a dramatic augmentation of humoral and T cell responses. The protective efficacy could be significantly enhanced after injection with plasmids pIRES-S1/IL-2 or pIRES-S1+pIRES-IL2. These results demonstrate that bicistronic DNA vaccine containing IL-2 elicit remarkably immune responses and suggest that optimal humoral and cellular responses priming requires the precise temporal and spatial codelivery of Ag and IL-2.