Packaged replicons of bovine viral diarrhea virus are capable of inducing a protective immune response.

Bovine viral diarrhea virus (BVDV) replicons with deletions within the capsid, E(RNS) or E1 encoding region were constructed and efficiently packaged with a helper cell line. High titres of packaged replicons were observed as early as 24 h after transfection, whereas no virus progeny could be detected after transfection of non-complementing cells. Infection of bovine cell cultures with rescued viruses resulted in one cycle of replication without release of infectious virus particles, and no genetic reversion of the generated viruses was detected. Packaged replicons with a deletion within the capsid-coding region were characterized in vivo in immunization and challenge trials. Following immunization of calves with the replication-deficient virus, neither virus shedding nor viremia was detected. After challenge infection with virulent BVDV, all vaccinates were completely protected from disease as measured by the absence of viremia and shedding of challenge virus, which indicated that a 'sterilizing immunity' could be induced with the generated replication-deficient packaged replicons.