A recombinant attenuated PRRSV vaccine expressing the PCV2 capsid protein confers protective immunity in pigs

Porcine reproductive and respiratory syndrome virus (PRRSV) and porcine circovirus type 2 (PCV2) are major swine pathogens that cause severe disease and frequently occur as coinfections in pig herds. Current vaccination strategies against PRRSV and PCV2 commonly rely on separate vaccines, which may increase the complexity of immunization programs and require repeated animal handling. Therefore, a bivalent vaccine platform capable of inducing immune responses against both pathogens would be valuable for simplifying vaccination strategies. In this study, the attenuated PRRSV strain HuN4-F112 was used as a live viral vector to express the PCV2d capsid (Cap) protein. The recombinant virus rHuN4-F112-Cap was successfully rescued using a reverse-genetics system. rHuN4-F112-Cap showed growth characteristics comparable to those of the parental HuN4-F112 strain in MARC-145 cells, and expression of the inserted PCV2 Cap gene was confirmed. A single intramuscular immunization with rHuN4-F112-Cap induced PRRSV and PCV2 specific antibody responses in piglets, as well as PCV2-neutralizing antibodies before challenge. In separate challenge models, vaccinated piglets showed reduced PCV2 DNA loads and milder lymphoid lesions after PCV2 challenge, and reduced clinical signs, lower PRRSV RNA loads, milder pulmonary lesions, and improved survival after highly pathogenic PRRSV challenge compared with DMEM-inoculated controls. These findings indicate that rHuN4-F112-Cap has potential as a bivalent live-vector vaccine candidate against PRRSV and PCV2.