Porcine circovirus type 2 protective epitope densely carried by chimeric papaya ringspot virus-like particles expressed in Escherichia coli as a cost-effective vaccine manufacture alternative.

Porcine circovirus type 2 (PCV2) still represents a major problem to the swine industry worldwide， causing high mortality rates in infected animals. Virus-like particles (VLPs) have gained attention for vaccine development， serving both as scaffolds for epitope expression and immune response enhancers. The commercial subunit vaccines against PCV2 consist of VLPs formed by the self-assembly of PCV2 capsid protein (CP) expressed in the baculovirus vector system. In this work， a PCV2 protective epitope was inserted into three different regions of papaya ringspot virus (PRSV) CP， namely， the N- and C-termini and a predicted antigenic region located near the N-terminus. Wild-type and chimeric CPs were modeled in silico， expressed in Escherichia coli， purified， and visualized by transmission electron microscopy. This is the first report that shows the formation of chimeric VLPs using PRSV as epitope-presentation scaffold. Moreover， it was found that PCV2 epitope localization strongly influences VLP length. Also， the estimated yields of the chimeric VLPs at a small-scale level ranged between 65 and 80 mg/L of culture medium. Finally， the three chimeric VLPs induced high levels of immunoglobulin G against the PCV2 epitope in immunized BALB/c mice， suggesting that these chimeric VLPs can be used for swine immunoprophylaxis against PCV2.