An adenovirus recombinant expressing the spike glycoprotein of porcine respiratory coronavirus is immunogenic in swine

The full-length spike (S) gene of porcine respiratory coronavirus (PRCV) was inserted into the genome of human adenovirus type 5 downstream of the early transcription region 3 promoter. The recombinant virus replicated in cultures of the swine testicle ST cell line and directed the synthesis of S antigen with a maximum yield of approximately 26 mu g per 10(6) cells. The antigen was cell-associated except in the late phase of the infection, when a small amount(3.5 mu g per 10(6) cells) was released. The cell-associated antigen consisted of polypeptides of molecular mass 160kDa and 175kDa, comigrating with the authentic precursor S' and the mature S protein of PRCV, respectively. The extracellular recombinant antigen corresponded to the 175kDa mature protein. Some recombinant S protein was exposed on the cell surface and was recognized by neutralization-mediating anti-S monoclonal antibodies. Piglets, inoculated oronasally with the recombinant adenovirus vector developed PRCV-neutralizing serum antibodies and were partially protected against PRCV challenge, demonstrating the potential of live adenovirus as vaccine vector.