D.M.A. Evans

Antigenic structure of polioviruses of serotypes 1, 2 and 3.

The antigenic sites recognized by monoclonal antibodies with neutralizing activity for the Sabin vaccine strains of poliovirus of serotypes 1, 2 and 3 have been studied by the isolation and characterization of mutants resistant to neutralization by antibody. Three distinct sites have been identified which are designated site 1, site 2 and site 3. Site 1 includes a region of 12 amino acids of VP1, from residues 89 to 100, and a corresponding region of VP1 has been identified as an antigenic site for poliovirus 2. This site was strongly immunodominant in type 2 and type 3 but was not detected for poliovirus 1. Site 2 is a complex site including residues 220 to 222 from VP1 (site 2a) with residues including 169 and 170 and others of VP2 (site 2b). Both site 2a and site 2b have been detected in type 1 poliovirus, while as yet only site 2b has been detected in type 3 poliovirus. Site 3 is a complex site including residues 286 to 290 from VP1 (site 3a) with residues including 58 and 59 and others of VP3 (site 3b). Both sites 3a and 3b have been detected in type 3 poliovirus, while as yet only site 3b has been detected in type 1 poliovirus.

The Temperature Sensitivity of the Sabin Type 3 Vaccine Strain of Poliovirus: Molecular and Structural Effects of a Mutation in the Capsid Protein VP3

The growth of the Sabin strain of type 3 poliovirus is reduced at high temperatures compared to that of its virulent precursor strain Leon. Recombinant viruses have been generated from infectious cDNA clones and demonstrate that the temperature-sensitive (ts) phenotype is mainly attributable to a difference in residue 91 of the virion protein VP3. Examination of non-ts mutants derived in vitro or in vivo reveals the existence of second site mutations some of which are clearly able to suppress the ts phenotype. The location of residue 91 of VP3, and of a number of candidate suppressor mutations, in the atomic structure of the virion suggests that the ts phenotype may result in destabilization of the particle and that the suppressors may function by stabilizing specific interfaces. It is not yet clear whether the ts phenotype is expressed at the level of the particle or in the form of defects in assembly or uncoating of the virion, or all three.

Principal and subsidiary antigenic sites of VP1 involved in the neutralization of poliovirus type 3

The characterization of over 300 mutants, derived from two strains of poliovirus type 3 and selected for resistance to neutralization by monoclonal antibodies, has led to the further definition of the major antigenic site involved in neutralization. The site encompasses amino acids 89 to 100 of VP1. A subsidiary antigenic site near the C-terminus of VP1 has been identified for the Sabin vaccine strain of poliovirus type 3. Of 59 monoclonal antibodies to poliovirus type 3 examined, 27 had virus-neutralizing activity and 25 of these were identified as directed against the major site on VP1 (designated site 1), indicating the immunodominant role of this site. One of the six monoclonal antibodies that recognized the subsidiary antigenic site on VP1 (designated site 2) possessed virus-neutralizing activity. The identification of the principal antigenic site of the virus provides a rational basis for attempts at the development of synthetic oligopeptide vaccines against poliovirus type 3.

Induction by synthetic peptides of broadly reactive, type-specific neutralizing antibody to poliovirus type 3.

A region of virus capsid protein VP1 located 89-100 amino acids from the N-terminus has been proposed to comprise a major antigenic site involved in the neutralization of poliovirus type 3. Synthetic peptides 10-18 amino acids in length, containing all or part of this sequence, were tested for their ability to induce antiviral antibodies. Rabbits, but not guinea pigs or mice, immunized with the most active peptide, developed hightitered, type-specific, neutralizing antibodies for a wide range of poliovirus type 3 strains. Consistent with the broad type specificity of the antibody response was the observation that amino acids 89-100 of VP1 are highly conserved among different poliovirus type 3 strains. This sequence thus appears to provide, at least in part, a molecular basis for serotype antigenic specificity. Individual amino acids from 93 to 98 within this sequence were shown to be important for the neutralization of virus by antipeptide sera by examination of the ability of the sera to neutralize laboratory-derived poliovirus type 3 mutants with known single amino acid substitutions in the proposed antigenic site.

Antigenic and molecular properties of type 3 poliovirus responsible for an outbreak of poliomyelitis in a vaccinated population

Virus isolated from an outbreak of poliomyelitis in Finland has been examined serologically and at the molecular level. The causative agent was an antigenically unusual strain of type 3 poliovirus, which was unrelated to the strains used to manufacture either live or killed poliovaccines. It is likely that the antigenic properties of the virus played a part in establishing a limited outbreak of poliomyelitis in a vaccinated population.

New poliovirus vaccines: a molecular approach☆

This article summarizes recent work on the determinants of antigenicity in poliovirus type 3 and reports on experiments in progress aimed at understanding the molecular basis of attenuation in Sabins type 3 vaccines. Ways in which this new information might be used to produce alternative, safe, inexpensive, multivalent vaccines against polio and other enteroviruses are discussed.

The construction and characterization of poliovirus antigen chimeras presenting defined regions of the human T lymphocyte marker CD4

Defined regions of the CDR2-like region of the T cell antigen CD4 that are implicated in the binding of the surface glycoprotein (gp120) of human immunodeficiency virus type 1 (HIV-1) to CD4+ T lymphocytes have been engineered in place of antigenic site 1 of Sabin type 1 poliovirus. The antigenic properties of the recovered chimeric virus particles were investigated using monoclonal antibodies (MAbs) and polyclonal serum to CD4. None of the MAbs tested neutralized the chimeras, presumably because they are directed against conformational determinants of the V1 domain of CD4. In contrast, the three antigen chimeras were neutralized by polyclonal serum to CD4, which suggested that the CD4-derived sequences were presented in a relevant conformation. A panel of six MAbs were raised against one of the chimeras, and the epitopes were mapped by the selection of neutralization-resistant mutants and cross-neutralization studies. Five of the six MAbs reacted with soluble CD4 (sCD4) in ELISA, and one (MAb 1686) bound to CD4 expressed at the surface of HeLa cells. The high affinity interaction between gp120 and sCD4 was not blocked by MAb 1686, and the poliovirus-CD4 chimeras did not interact with gp120. These results demonstrate that poliovirus can be used as an epitope expression vector for the presentation of sequences in an immunodominant location on the virus particle which adopt a native or near-native conformation, and supports the findings of previous studies involving the presentation of epitopes derived from pathogens.