An infectious clone of human parainfluenza virus type 3.

A full-length clone of the human parainfluenza virus type 3 (HPIV-3) genome (called pHPIV-3) was constructed, and recombinant, infectious HPIV-3 was generated by transfecting pHPIV-3 and support plasmids encoding the HPIV-3 NP, P, and L proteins into HeLa cells infected with a vaccinia virus recombinant which expresses T7 RNA polymerase. T7 RNA polymerase promoters on the transfected plasmids direct the synthesis of transcripts encoding the NP, P, and L proteins and a full-length, positive-sense copy of the HPIV-3 genome. Generation of virus was dependent on transfection of pHPIV-3 and the HPIV-3 P- and L-encoding plasmids. However, a plasmid encoding the NP protein was not required since NP was expressed from pHPIV-3. Recovered virus was neutralized by anti-HPIV-3 antisera and shown to contain specific base substitutions characteristic of pHPIV-3. Recombination was shown to occur during recovery, as viruses with two distinct genotypes and phenotypes were isolated. The ability to produce infectious HPIV-3 engineered to contain specific alterations within the HPIV-3 genes and cis-acting elements expedites the study of all aspects of the virus replication cycle. Additionally, analysis of mutations may lead to the identification of attenuating genotypes, a key step in the development of a live virus vaccine.