Characterization of a vero cell-adapted virulent strain of enterovirus 71 suitable for use as a vaccine candidate

Enterovirus 71 (EV71) is a neurotrophic virus that causes seasonal morbidity and mortality in children throughout the world with increasing frequency in recent years. Because of the lack of an effective antiviral agent, primary prevention, including the development of effective vaccines, is a top priority in terms of control strategies. Poliovirus vaccine technology, both live attenuated and inactivated, killed virus vaccines, can be adopted for use with EV71 because of their relatedness. In this study, we have characterized a laboratory-adapted EV71 strain, YN3-4a, which exhibits different characteristics from those of its parent isolate, neu, in having a rapid growth rate in Vero cells, a larger plaque size, and a lower LD₅₀ in newborn mice. The YN3-4a can be produced at a high viral titer of up to 10¹⁰ tissue culture infective dose (TCID₅₀) when grown in Vero cells, an approved substrate for virus vaccine production. Mouse antiserum raised against YN3-4a can neutralize a broad range of strains of EV71 isolated at different times from a variety of geographic regions. On passage in Vero cells, YN3-4a remained genetically and phenotypically stable. Many of the above-described features, such as high viral yield, strong immunogenicity, broad-based antigenic coverage, and passage stability, are desirable features in a prototype virus for the development of an inactivated viral vaccine.