Analysis of neutralization-escape mutants selected from a mouse virulent type 1/type 2 chimeric poliovirus: identification of a type 1 poliovirus with antigenic site 1 deleted.

A chimeric type 1/type 2 poliovirus (v510), in which the antigenic site 1 (Ag1) of poliovirus type 1 (PV-1) Mahoney was replaced by the corresponding site of poliovirus type 2 (PV-2) Lansing, is known to be neurovirulent for mice and neutralized by both type 1 and type 2 monoclonal antibodies. Neutralization-escape mutants to monoclonal antibodies specifically recognizing the PV-2 sequence were obtained from v510. The nucleotide sequence and the mouse neurovirulence of mutants were determined. Amino acid substitutions obtained inside the replaced sequence, at positions 95 and 99, and outside this site, at positions 93 or 104, rendered the virus attenuated for mice. One of the escape mutants harboured a deletion of the entire substituted nonapeptide sequence in v510. This particular virus, which is a PV-1 Mahoney lacking the natural Ag1 loop, does not react with PV-2-specific monoclonal antibodies, has a ts phenotype, is heat-labile and is devoid of neurovirulence for mice.