Analysis of antigenic profiles of inactivated poliovirus vaccine and vaccine-derived polioviruses by block-ELISA method

A new block-ELISA test for quantitative evaluation of relative reactivity of antigenic sites was developed and used to reveal the detailed epitope structure of inactivated poliovirus vaccines (IPV) and live poliovirus strains. Poliovirus was captured on ELISA plates coated with rabbit anti-poliovirus IgG and blocked by monoclonal antibodies (Mabs) specific to individual epitopes before the remaining reactive antigenic sites were quantified by polyclonal anti-poliovirus IgG conjugate. The decrease of conjugate binding by the pre-treatment with a Mab reflects its contribution to the overall reactivity of poliovirus antigen. The level of block activity of Mabs for a given antigen can be expressed as a percent of reduction of antigenic reactivity as determined by ELISA test. It can be normalized by expressing this value as a ratio to the block activity of a reference sample. The data on the blocking-activity of a panel of monoclonal antibodies specific to different antigenic sites represents the epitope composition (antigenic profile) of a sample. Quantitative differences in epitope composition were determined for nine samples of inactivated poliovirus vaccine (IPV) and compared with the International Reference Reagent. This method could be used for monitoring consistency of IPV production, comparison of vaccines made by different manufacturers, and for the analysis of antigenically modified strains of attenuated poliovirus. Antigenic structures of two isolates of type 1 vaccine-derived poliovirus (VDPV) were compared with the structures of parental Sabin 1 and wild-type Mahoney strains using 17 monoclonal antibodies and revealed significant differences, suggesting that the method can be used for screening of field isolates and rapid identification of antigenically divergent VDPV strains.