Characterization of an attenuated Japanese encephalitis virus adapted to African green monkey kidney cells, Vero

Live attenuated Japanese encephalitis (JE) virus SA14-14-2 produced in primary dog kidney cells (PDR) was adapted to African green monkey kidney cells, Vero. In an effort to gain insight into the molecular basis of the biological characteristics of the isolated SA14-14-2 (Vero) strain, the 1,500 nucleotide sequence encoding the envelope (E) gene which possesses major neutralizing epitopes was determined and compared with the sequences of two other attenuated JE virus strains, SA14-14-2 (PHK) and SA14-14-2 (PDK). The amino acid sequence of the C-terminal region (a.a. 280-500) of the SA14-14-2 (Vero) E gene was found to be identical to those of strains SA14-14-2 (PHK) and SA14-14-2 (PDK), while the N-terminal region (a.a. 1-279) showed sequence variation. The distribution of mutations in the N-terminal region was nearly the same among the three attenuated strains, suggesting that the N-terminal sequences might be related with virus-host cell specificity. However, it was found that Lys and Val (a.a.138 and 176, respectively), known to be responsible for attenuation, are still conserved in SA14-14-2 (Vero). Animal testing showed that SA14-14-2 (Vero) has a neurovirulence phenotype similar tp that of the parent SA14-14-2 (PDK) strain in suckling mice. The SA14-14-2 (Vero) grew very efficiently in Vero cells enough to support vaccine production. The growth characteristics of SA14-14-2 (Vero) in Vero cell and conservation of attenuation determinant of neurovirulence support that SA14-14-2 (Vero) could be developed as a new vaccine strain for human use.