A recombinant human parainfluenza virus type 3 (PIV3) in which the nucleocapsid N protein has been replaced by that of bovine PIV3 is at attenuated in primates

The shipping fever (SF) and Kansas (Ka) strains of bovine parainfluenza vir us type 3 (BPIV3) are restricted in their replication in rhesus monkeys 100 - to 1,000-fold compared to human parainfluenza virus type 3 (HPIV3), and t he Ba strain also was shown to be attenuated in humans. To initiate an inve stigation of the genetic basis of the attenuation of BPIV3 in primates, we produced viable chimeric HPIV3 recombinants containing the nucleoprotein (N ) open reading frame (ORF) from either BPIV3 Ka or SF in place of the HPIV3 N ORF. These chimeric recombinants mere designated cKa-N and cSF-N, respec tively. Remarkably, cKa-N and cSF-N grew to titers comparable to those of t heir HPIV3 and BPIV3 parents in LLC-MK2 monkey kidney and Madin-Darby bovin e kidney cells, Thus, the heterologous nature of the N protein did not impe de replication in vitro, However, cKa-N and cSF-N were each restricted in r eplication in rhesus monkeys to a similar extent as Iia and SF, respectivel y. This identified the BPIV3 N protein as a determinant of;the host range r estriction of BPIV3 in primates. These chimeras thus combine the antigenic determinants of BPIV3 with the host range restriction and attenuation pheno type of BPIV3, Despite their restricted replication in rhesus monkeys, the chimeric viruses induced a level of resistance to HPIV3 challenge in these animals which was indistinguishable from that conferred by immunization wit h HPIV3. The infectivity, attenuation, and immunogenicity of these BPIV3/HP IV3 chimeras suggest that the modified Jennerian approach described in the present report represents a novel method to design vaccines to protect agai nst HPIV3-induced disease in humans.