RECOVERY OF A FULLY VIABLE CHIMERIC HUMAN PARAINFLUENZA VIRUS (PIV) TYPE-3 IN WHICH THE HEMAGGLUTININ-NEURAMINIDASE AND FUSION GLYCOPROTEINS HAVE BEEN REPLACED BY THOSE OF PIV TYPE-1

The recent recovery of human parainfluenza virus type 3 (PIV3) from cD NA, together with the availability of a promising, highly characterize d live attenuated PIV3 vaccine virus, suggested a novel strategy for t he rapid development of comparable recombinant vaccine viruses for hum an PIV1 and PIV2. The strategy, illustrated here for PIV1, is to creat e chimeric viruses in which the two protective antigens, the hemagglut inin-neuraminidase (HN) and fusion (F) envelope glycoproteins, of an a ttenuated PIV3 variant are replaced by those of PIV1 or PIV2. As a fir st step, this has been achieved by using recombinant wild-type (wt) PI V3 as the recipient for PIV1 HN and F, engineered so that each PIV1 op en reading frame is flanked by the existing PIV3 nontranslated regions and transcription signals. This yielded a viable chimeric recombinant virus, designated rPIV3-1, that encodes the PIV1 HN and F glycoprotei ns in the background of the wt PIV3 internal proteins. There were thre e noteworthy findings. First, in contrast to recently reported glycopr otein replacement chimeras of vesicular somatitis virus or measles vir us, the PIV3-1 chimera replicates in LLC-MK2 cells and in the respirat ory tract of hamsters as efficiently as its PIV1 and PIV3 parents. Thi s is remarkable because the HN and F glycoproteins share only 43 and 4 7%, respectively, overall amino acid sequence identity between serotyp es. In particular, the cytoplasmic tails share only 9 to 11% identity, suggesting that their presumed role in virion morphogenesis does not involve sequence-specific contacts. Second, rPIV3-1 was found to posse ss biological properties derived from each of its parent viruses. Spec ifically, it requires trypsin for efficient plaque formation in tissue culture, like its PIV1 parent but unlike PIV3. On the other hand, it causes an extensive cytopathic effect (CPE) in LLC-MK2 cultures which resembles that of its PIV3 parent but differs from that of its noncyto pathic PIV1 parent. This latter Ending indicates that the genetic basi s for the CPE of PIV3 in tissue culture lies outside regions encoding the HN or F glycoprotein. Third, it should now be possible to rapidly develop a live attenuated PIV1 vaccine by the staged introduction of k nown, characterized attenuating mutations present in a live attenuated PIV3 vaccine candidate into the PIV3-1 cDNA followed by recovery of a ttenuated derivatives of rPIV3-1.