Rescue of IBV D-RNA by heterologous helper virus strains.

Coronavirus defective RNA (D-RNA) vectors could be developed to deliver selected genes for the production of recombinant coronavirus vaccines. An IBV D-RNA, CD-61, derived from a naturally occurring IBV Beaudette D-RNA, CD-91, is being developed as a D-RNA vector for IBV. In order to use CD-61 as a vector it will require rescue by heterologous strains in addition to Beaudette. Rescue will be determined by recognition of replication and packaging signals within the D-RNA by the helper virus. The 5' and 3' UTRs are believed to contain sequences involved in replication and transcription. The 5' and 3' UTRs of six strains of IBV have been sequenced and experiments performed using six strains of helper virus for rescue of CD-61 to determine whether rescue correlates with sequence conservation within the 5' and 3' UTRs. Results indicate that all strains of helper virus rescued the D-RNA to varying degrees. Sequence comparisons show a high degree of sequence identity in the UTRs, but enough strain differences exist to be used as markers. The 5' and 3' UTRs of the D-RNAs rescued by the heterologous strains were also sequenced and leader switching between the helper virus and the Beaudette leader on the D-RNAs was observed.