Novel Approach in DNA vaccine development against porcine circovirus type 2

Abstract

Porcine circovirus type 2 (PCV2) is an important viral pathogen in pig populations. However, commercial vaccines cannot provide complete protection with induced humoral immunity only against disease development. DNA vaccine is a candidate of great potential because it can induce both arms of the immune system, humoral and cellular immune responses. In this study, DNA vector pcDNA3.1 was inserted with a chimeric intron downstream of the CMV promoter followed by a Kozak sequence to enhance the expression of gene inserts. The C-terminal of the VP22 gene (VP22c), encoding one of the major tegument proteins of bovine herpesvirus-1, was fused to the N- or C- terminal of ORF2 gene encoding the most immunogenic capsid protein of PCV2. The expression of plasmids was confirmed in in vitro transfection of 293FT cells and the highest percentage of ORF2-positive cells was achieved from the plasmid with fusion of ORF2 to the C-terminal of VP22c (denoted as pVP22cORF2). Porcine GM-CSF gene was inserted into vector pSecTag2/Hygro for secreted expression (pGM-CSF). These two DNA plasmids were administered intramuscularly to pigs in combination. No detectable level of immunity was present in the vaccinated group before the virus challenge. However, the vaccinated group showed earlier and higher ORF2-specific antibody response and higher cellular immunity than the challenge control group after the virus challenge. Vaccinated pigs showed increased growth performance, reduced duration of clinical signs, as well as reduced viral load in serum, lung, and lymph nodes. Therefore, the developed DNA vaccine will be a potential candidate against PCV2 infection.

Keywords

• porcine circovirus type 2
• dna vaccine
• orf2
• protective immunity