Molecular characterization of human rotavirus vaccine strain CDC-9 during sequential passages in Vero cells

We have developed several candidate human rotavirus vaccine strains with common serotypes via adaptation in Vero cells, adhering to the Good Laboratory Practice (GLP) guidelines. We sequenced the entire genome of a G1P[8] strain CDC-9 in original stool and passaged materials from Vero cells and examined its genetic relatedness to the prototype human rotavirus KU and other strains. With the exception of VP3 gene which was closely related to that of strain DS-1, the culture-adapted CDC-9 strain shared moderate to high nt (range 83.4%-95.1%) and deduced aa (range 81.3%-97.9%) sequence identities with the KU and other G1P[8] strains. Alignments of the deduced aa sequences of 11 gene segments of the wild-type and culture-adapted CDC-9 showed complete sequence identity in genes encoding NSP2, NSP3, NSP4, VP1, VP2, VP3 and VP7, a single aa change in genes coding for NSP1, NSP5 and VP6 and several scattered aa changes in the VP4 gene during the passage in Vero cells. Two of the VP4 aa substitutions (385 and 388) are within sites associated with neutralization resistant mutants selected by cross-reactive monoclonal antibodies. Although some sequence changes were evident, we do not know if these changes contribute to the possible attenuation of this strain. Further testing of this vaccine strain in clinical trials is justified.