Immunogenicity and Pathogenicity of Chimeric Infectious DNA Clones of Pathogenic Porcine Circovirus Type 2 (PCV2) and Nonpathogenic PCV1 in Weanling Pigs

Abstract

Porcine circovirus type 2 (PCV2) is the primary causative agent of postweaning multisystemic wasting syndrome (PMWS), whereas the ubiquitous porcine circovirus type 1 (PCV1) is nonpathogenic for pigs. We report here the construction and characterization of two chimeric infectious DNA clones of PCV1 and PCV2. The chimeric PCV1-2 clone contains the PCV2 capsid gene cloned in the backbone of the nonpathogenic PCV1 genome. A reciprocal chimeric PCV2-1 DNA clone was also constructed by replacing the PCV2 capsid gene with that of PCV1 in the backbone of the PCV2 genome. The PCV1, PCV2, and chimeric PCV1-2 and PCV2-1 DNA clones were all shown to be infectious in PK-15 cells, and their growth characteristics in vitro were determined and compared. To evaluate the immunogenicity and pathogenicity of the chimeric infectious DNA clones, 40 specific-pathogen-free (SPF) pigs were randomly assigned into five groups of eight pigs each. Group 1 pigs received phosphate-buffered saline as the negative control. Group 2 pigs were each injected in the superficial inguinal lymph nodes with 200 g of the PCV1 infectious DNA clone. Group 3 pigs were each similarly injected with 200 g of the PCV2 infectious DNA clone, group 4 pigs were each injected with 200 g of the chimeric PCV1-2 infectious DNA clone, and group 5 pigs were each injected with 200 g of the reciprocal chimeric PCV2-1 infectious DNA clone. As expected, seroconversion to antibodies to the PCV2 capsid antigen was detected in group 3 and group 4 pigs. Group 2 and 5 pigs all seroconverted to PCV1 antibody. Gross and microscopic lesions in various tissues of animals inoculated with the PCV2 infectious DNA clone were significantly more severe than those found in pigs inoculated with PCV1, chimeric PCV1-2, and reciprocal chimeric PCV2-1 infectious DNA clones. These data indicated that the chimeric PCV1-2 virus with the immunogenic ORF2 capsid gene of pathogenic PCV2 cloned into the nonpathogenic PCV1 genomic backbone induces a specific antibody response to the pathogenic PCV2 capsid antigen but is attenuated in pigs. Future studies are warranted to evaluate the usefulness of the chimeric PCV1-2 infectious DNA clone as a genetically engineered live-attenuated vaccine against PCV2 infection and PMWS.

Protective immunity against porcine circovirus 2 by vaccination with ORF2-based DNA and subunit vaccines in mice

“…Thus, the target cells for PCV2 replication have not been clearly identified thus far. With regard to PCV2 immunization, no data regarding lymphocyte subsets in cellular immune responses have been recorded recently, although ORF2-based vaccines against PCV2 have been reported previously (Blanchard et al, 2003;Fan et al, 2008;Fenaux et al, 2003; A load value of 0 is equal to ,10 3 copies ml 21 (the threshold of sensitivity of the quantitative PCR).…”

“…Kamstrup et al (2004) subsequently investigated the potential of a DNA vaccine encoding the PCV2 Cap protein in mice and demonstrated the production of antibody. On the other hand, Fenaux et al (2003Fenaux et al ( , 2004 focused on a chimeric PCV1-PCV2, which was shown to induce specific antibody responses and protection against PCV2 in pigs. Recent studies on live virus vectors have shown that a recombinant pseudorabies virus (Ju et al, 2005;Song et al, 2007) and adenovirus (Wang et al, 2006(Wang et al, , 2007 expressing Cap protein can elicit specific humoral and/or lymphocyte proliferation responses in mice and/or pigs, encouraging further studies of PCV2 vaccines.…”

Experimental Reproduction of Postweaning Multisystemic Wasting Syndrome in Pigs by Dual Infection with Mycoplasma hyopneumoniae and Porcine Circovirus Type 2

“…Experimental PCV2 vaccines have been shown to protect PCV2-infected pigs from developing the characteristic PCV2-associated lymphoid lesions. 15,16 M. hyopneumoniae vaccines are well established in the field and have been shown to be economically beneficial in reducing losses associated with respiratory disease. 35 However, recent field studies have indicated that M. hyopneumoniae vaccination in PMWS-affected herds actually increased the incidence of PMWS.…”

Reproduction of PMWS in immunostimulated SPF piglets transfected with infectious cloned genomic DNA of type 2 porcine circovirus

“…With this aim, Fenaux et al [14,15] investigated the infection ability of a PCV2 molecular DNA clone when injected directly into the liver and inguinal lymph nodes. Only mild pathological lesions were observed in four-weekold SPF piglets despite widespread distribution of the virus in their organs.…”