Development and evaluation of a virus like particle based vaccine candidate against Indian Isolate of porcine circovirus 2d in pig.

Porcine circovirus type 2d (PCV2d) is the predominant genotype etiological agent of porcine circovirus-associated disease (PCVAD), causes substantial economic losses to the swine industry worldwide, including in India. Since currently available vaccines are mainly based on the PCV2a genotype, which is unable to offer cross protective immunity against emerging PCV2d strains, development of PCV2d specific vaccine is necessary. In this study, an indigenous virus-like particle (VLP)-based vaccine candidate was developed using the capsid coding gene (orf2) of an Indian PCV2d isolate expressed in a baculovirus-insect cell system. Recombinant capsid protein expression and self-assembly into VLPs were confirmed by Western blotting and transmission electron microscopy. The purified VLPs showed favourable thermostability as well as pH stability and elicited strong humoral and cellular immune responses in in vivo porcine model. A delayed booster immunization strategy resulted in prolonged antibody persistence. In further, in vivo challenge study with virulent homologous PCV2d virus vaccinated animals were protected against PCV2 clinical signs. Further, absence of detectable viral DNA in swab and tissue samples, and markedly alleviated histopathological lesions compared with unvaccinated controls animals. Overall, these findings suggest that the indigenous PCV2d VLP vaccine candidate is highly immunogenic and provides protective immunity against homologous PCV2d challenge, highlighting its potential indigenous vaccine candidate for controlling PCVAD against PCV2d.