Development and characterization of MRC-5 and Vero cell-adapted enterovirus D68 strains for vaccine production.

Enterovirus D68 (EV-D68) is a pathogen that causes respiratory and neurological diseases. Currently, there are no licensed vaccines for EV-D68. Here, we adapted EV-D68 to MRC-5 and Vero cells, which are widely used in vaccine manufacturing, to develop EV-D68 strains applicable for vaccine production. We successfully isolated MRC-5 cell-adapted strains by serial passaging in MRC-5 cells. Although efforts to isolate Vero cell-adapted strains through serial passaging of EV-D68 in Vero cells were unsuccessful, we isolated Vero cell-adapted strains by serial passaging of MRC-5 cell-adapted strains in Vero cells. Inactivated whole-virion vaccines were prepared from vaccine-manufacturing cell-adapted strains and mice were immunized with these vaccines. We found that in some cases, the parental and cell-adapted strains induced similar levels of protective immunity against EV-D68, whereas in other cases, the cell-adapted strains were significantly less effective than the parental strains. These data provide valuable information for EV-D68 vaccine production.