Expert review on poliovirus immunity and transmission.

Successfully managing risks to achieve wild polioviruses (WPVs) eradication and address the complexities of oral poliovirus vaccine (OPV) cessation to stop all cases of paralytic poliomyelitis depends strongly on our collective understanding of poliovirus immunity and transmission. With increased shifting from OPV to inactivated poliovirus vaccine (IPV), numerous risk management choices motivate the need to understand the tradeoffs and uncertainties and to develop models to help inform decisions. The U.S. Centers for Disease Control and Prevention hosted a meeting of international experts in April 2010 to review the available literature relevant to poliovirus immunity and transmission. This expert review evaluates 66 OPV challenge studies and other evidence to support the development of quantitative models of poliovirus transmission and potential outbreaks. This review focuses on characterization of immunity as a function of exposure history in terms of susceptibility to excretion, duration of excretion, and concentration of excreted virus. We also discuss the evidence of waning of host immunity to poliovirus transmission, the relationship between the concentration of poliovirus excreted and infectiousness, the importance of different transmission routes, and the differences in transmissibility between OPV and WPV. We discuss the limitations of the available evidence for use in polio risk models, and conclude that despite the relatively large number of studies on immunity, very limited data exist to directly support quantification of model inputs related to transmission. Given the limitations in the evidence, we identify the need for expert input to derive quantitative model inputs from the existing data.

Review and assessment of poliovirus immunity and transmission: synthesis of knowledge gaps and identification of research needs.

With the intensifying global efforts to eradicate wild polioviruses, policymakers face complex decisions related to achieving eradication and managing posteradication risks. These decisions and the expanding use of inactivated poliovirus vaccine (IPV) trigger renewed interest in poliovirus immunity, particularly the role of mucosal immunity in the transmission of polioviruses. Sustained high population immunity to poliovirus transmission represents a key prerequisite to eradication, but poliovirus immunity and transmission remain poorly understood despite decades of studies. In April 2010, the U.S. Centers for Disease Control and Prevention convened an international group of experts on poliovirus immunology and virology to review the literature relevant for modeling poliovirus transmission, develop a consensus about related uncertainties, and identify research needs. This article synthesizes the quantitative assessments and research needs identified during the process. Limitations in the evidence from oral poliovirus vaccine (OPV) challenge studies and other relevant data led to differences in expert assessments, indicating the need for additional data, particularly in several priority areas for research: (1) the ability of IPV-induced immunity to prevent or reduce excretion and affect transmission, (2) the impact of waning immunity on the probability and extent of poliovirus excretion, (3) the relationship between the concentration of poliovirus excreted and infectiousness to others in different settings, and (4) the relative role of fecal-oral versus oropharyngeal transmission. This assessment of current knowledge supports the immediate conduct of additional studies to address the gaps.

A human monoclonal antibody binds within the poliovirus receptor-binding site to neutralize all three serotypes.

Global eradication of poliovirus remains elusive, and it is critical to develop next generation vaccines and antivirals. In support of this goal, we map the epitope of human monoclonal antibody 9H2 which is able to neutralize the three serotypes of poliovirus. Using cryo-EM we solve the near-atomic structures of 9H2 fragments (Fab) bound to capsids of poliovirus serotypes 1, 2, and 3. The Fab-virus complexes show that Fab interacts with the same binding mode for each serotype and at the same angle of interaction relative to the capsid surface. For each of the Fab-virus complexes, we find that the binding site overlaps with the poliovirus receptor (PVR) binding site and maps across and into a depression in the capsid called the canyon. No conformational changes to the capsid are induced by Fab binding for any complex. Competition binding experiments between 9H2 and PVR reveal that 9H2 impedes receptor binding. Thus, 9H2 outcompetes the receptor to neutralize poliovirus. The ability to neutralize all three serotypes, coupled with the critical importance of the conserved receptor binding site make 9H2 an attractive antiviral candidate for future development.

Methods to Monitor Molecular Consistency of Oral Polio Vaccine.

Replication of viruses leads to emergence of mutations and their content in viral populations can increase by selection depending on growth conditions. Some of these mutations have deleterious effect on vaccine safety, such as neurovirulent reversions in the 5'-UTR of attenuated Sabin strains of poliovirus. Their content in vaccine batches must be tightly controlled during vaccine manufacture to ensure safety of the product. This chapter describes a quantitative molecular procedure called mutant analysis by PCR and restriction enzyme cleavage (MAPREC) that is used to monitor content of neurovirulent revertants in Oral Polio Vaccine (OPV). The method can be used for quantitative analysis of any other mutation in a viral population.

Immunogenicity of inactivated polio vaccine with concurrent antiviral V-073 administration in mice.

Immunization of mice with inactivated polio vaccine (IPV) with concurrent dosing of poliovirus antiviral V-073 showed no detrimental impact on the elicitation of serum-neutralizing antibodies. A strategy involving coadministration of antiviral V-073 and IPV can be considered for the management of poliovirus incidents.

Immunological and pathogenic properties of poliovirus variants selected for resistance to antiviral drug V-073.

BACKGROUND: The National Research Council has recommended development of polio antiviral drugs to assist in management of outbreaks and to mitigate adverse consequences of vaccination. V-073 is a small molecule poliovirus capsid inhibitor that is being developed for these purposes. Antiviral use raises the potential of treatment-emergent resistance. Understanding virological consequences of resistance is important. METHODS: Six independent laboratory-derived V-073-resistant poliovirus variants were characterized for their ability to be neutralized by conventional vaccine-induced immune sera, to elicit serum neutralizing antibodies upon CD-1 mouse immunization, and to replicate in and to cause paralysis of TgPVR21 mice. RESULTS: V-073-resistant variants were effectively neutralized by oral poliovirus vaccine and inactivated poliovirus vaccine human immune sera. All variants elicited virus neutralizing antibody titres in CD-1 mice that were comparable to drug-susceptible parental and Sabin vaccine strain viruses. Infection efficiency of TgPVR21 mice by variants was comparable to (1 of 6 variants) or considerably lower than (5 of 6 variants) parental viruses. Drug-resistant variants replicated to levels comparable to (1 of 6 variants) or substantially less than (5 of 6 variants) their drug-susceptible parental viruses and were on average 1.4 log(10) (range 0.3 to >2.8 log10) less neurovirulent. CONCLUSIONS: Laboratory-derived V-073-resistant variants exhibit clear attenuation of pathogenic properties while maintaining immunological features of drug-susceptible viruses.

Universal oligonucleotide microarray for sub-typing of Influenza A virus.

A universal microchip was developed for genotyping Influenza A viruses. It contains two sets of oligonucleotide probes allowing viruses to be classified by the subtypes of hemagglutinin (H1-H13, H15, H16) and neuraminidase (N1-N9). Additional sets of probes are used to detect H1N1 swine influenza viruses. Selection of probes was done in two steps. Initially, amino acid sequences specific to each subtype were identified, and then the most specific and representative oligonucleotide probes were selected. Overall, between 19 and 24 probes were used to identify each subtype of hemagglutinin (HA) and neuraminidase (NA). Genotyping included preparation of fluorescently labeled PCR amplicons of influenza virus cDNA and their hybridization to microarrays of specific oligonucleotide probes. Out of 40 samples tested, 36 unambiguously identified HA and NA subtypes of Influenza A virus.

Cleavage of eukaryotic initiation factor eIF5B by enterovirus 3C proteases.

The enteroviruses poliovirus (PV), Coxsackie B virus (CVB) and rhinovirus (HRV) are members of Picornaviridae that inhibit host cell translation early in infection. Enterovirus translation soon predominates in infected cells, but eventually also shuts off. This complex pattern of modulation of translation suggests regulation by a multifactorial mechanism. We report here that eIF5B is proteolytically cleaved during PV and CVB infection of cultured cells, beginning at 3 hours post-infection and increasing thereafter. Recombinant PV, CVB and HRV 3Cpro cleaved purified native rabbit eukaryotic initiation factor (eIF) 5B in vitro at a single site (VVEQG, equivalent to VMEQG479 in human eIF5B) that is consistent with the cleavage specificity of enterovirus 3C proteases. Cleavage separates the N-terminal domain of eIF5B from its essential conserved central GTPase and C-terminal domains. 3Cpro-mediated cleavage of eIF5B may thus play an accessory role in the shutoff of translation that occurs in enterovirus-infected cells.

Quercetinase pirin makes poliovirus replication resistant to flavonoid quercetin.

Flavonoid quercetin and its derivative, methylquercetin, inhibit the replication of poliovirus in several cell lines. Here, we show that replication of poliovirus is inhibited by quercetin and that the extent of this inhibition depends on the intracellular content of pirin, a quercetinase. HeLa cells contain higher content of pirin protein than normal kidney human epithelial (NKE) or 293 cells do. Poliovirus replication in HeLa cells is significantly more resistant to quercetin than its replication in NKE and 293 cells. Overexpression of pirin reduced antiviral inhibitory effect of quercetin, while siRNA-induced suppression of pirin level made poliovirus replication more sensitive to the flavonoid. The results suggest that quercetinase activity of pirin determines the resistance of poliovirus infection to quercetin.

Different effect of proteasome inhibition on vesicular stomatitis virus and poliovirus replication.

Proteasome activity is an important part of viral replication. In this study, we examined the effect of proteasome inhibitors on the replication of vesicular stomatitis virus (VSV) and poliovirus. We found that the proteasome inhibitors significantly suppressed VSV protein synthesis, virus accumulation, and protected infected cells from toxic effect of VSV replication. In contrast, poliovirus replication was delayed, but not diminished in the presence of the proteasome inhibitors MG132 and Bortezomib. We also found that inhibition of proteasomes stimulated stress-related processes, such as accumulation of chaperone hsp70, phosphorylation of eIF2alpha, and overall inhibition of translation. VSV replication was sensitive to this stress with significant decline in replication process. Poliovirus growth was less sensitive with only delay in replication. Inhibition of proteasome activity suppressed cellular and VSV protein synthesis, but did not reduce poliovirus protein synthesis. Protein kinase GCN2 supported the ability of proteasome inhibitors to attenuate general translation and to suppress VSV replication. We propose that different mechanisms of translational initiation by VSV and poliovirus determine their sensitivity to stress induced by the inhibition of proteasomes. To our knowledge, this is the first study that connects the effect of stress induced by proteasome inhibition with the efficiency of viral infection.

1,25-dihydroxyvitamin d3 enhances systemic and mucosal immune responses to inactivated poliovirus vaccine in mice.

1,25-Dihydroxyvitamin D3 (DHVD3) coadministered with monovalent inactivated poliovirus vaccine (IPV) of all 3 serotypes significantly enhances antipoliovirus systemic and mucosal immunity in mice. Although serum immunoglobulin G antibodies are significantly higher in serotypes 2 and 3, and although salivary immunoglobulin A is significantly increased in serotypes 1 and 3, DHVD3 had the most dramatic effect on the level of neutralizing serum antibodies of all 3 IPV serotypes. These findings suggest a possible use of vitamin D3 as an adjuvant for currently used and proposed new Sabin IPVs.

Further development of a new transgenic mouse test for the evaluation of the immunogenicity and protective properties of inactivated poliovirus vaccine.

Recently, we developed and optimized a new method for the evaluation of the protective properties of serotype 2 inactivated poliovirus vaccines (IPV). The method is based on the immunization and subsequent challenge of transgenic (Tg) mice susceptible to poliovirus. We describe a similar method for the assessment of the protectiveness of serotype 1 IPV and demonstrate that experimental IPV produced from attenuated Sabin strain (sIPV) of serotype 1 poliovirus induced serum neutralizing antibodies, immunoglobulin (Ig) G, IgM, and salivary IgA at titers comparable to those induced by conventional IPV (cIPV) produced from the wild-type Mahoney strain. In contrast to our previous results with serotype 2 sIPV, serotype 1 sIPV provided even better protection of Tg mice than cIPV against challenge with wild-type Mahoney strain.

Antigenic evolution of vaccine-derived polioviruses: changes in individual epitopes and relative stability of the overall immunological properties.

The Sabin oral poliovirus vaccine (OPV) readily undergoes changes in antigenic sites upon replication in humans. Here, a set of antigenically altered descendants of the three OPV serotypes (76 isolates) was characterized to determine the driving forces behind these changes and their biological implications. The amino acid residues of OPV derivatives that lie within or close to the known antigenic sites exhibited a marked tendency to be replaced by residues characteristic of homotypic wild polioviruses, and these changes may occur very early in OPV evolution. The specific amino acid alterations nicely correlated with serotype-specific changes in the reactivity of certain individual antigenic sites, as revealed by the recently devised monoclonal antibody-based enzyme-linked immunosorbent assay. In comparison to the original vaccine, small changes, if any, in the neutralizing capacity of human or rabbit sera were observed in highly diverged vaccine polioviruses of three serotypes, in spite of strong alterations of certain epitopes. We propose that the common antigenic alterations in evolving OPV strains largely reflect attempts to eliminate fitness-decreasing mutations acquired either during the original selection of the vaccine or already present in the parental strains. Variability of individual epitopes does not appear to be primarily caused by, or lead to, a significant immune evasion, enhancing only slightly, if at all, the capacity of OPV derivatives to overcome immunity in human populations. This study reveals some important patterns of poliovirus evolution and has obvious implications for the rational design of live viral vaccines.

Genotyping of measles virus in clinical specimens on the basis of oligonucleotide microarray hybridization patterns.

An oligonucleotide microarray hybridization method for identification of most known measles virus (MV) genotypes was developed. Like the conventional genotyping method, the microarray relied on detecting sequence differences in the 450-nucleotide region coding for the COOH-terminal 150 amino acids of the nucleoprotein (N). This region was amplified using PCR primers binding to all known MV genotypes. The microarray included 71 pairs of oligonucleotide probes (oligoprobes) immobilized on glass slides. Each pair consisted of a genotype-specific oligoprobe, which matched the sequence of only one target genotype, and a control oligoprobe, which contained mismatches at the nucleotide positions unique to this genotype. A pattern recognition algorithm based on cluster analysis of the ratios of hybridization signals from specific and control oligoprobes was used to identify the specific MV genotype. Following the initial validation, the method was used for rapid genotyping of two panels of coded samples. The results of this study showed good sensitivity (90.7%), specificity (100%), and genotype agreement (91.8%) for the new method compared to the results of genotyping conducted using phylogenetic analysis of viral sequences of the C terminus of the N gene. In addition, the microarray demonstrated the ability to identify potential new genotypes of MV based on the similarity of their hybridization patterns with those of known MV genotypes.

Proteolytic cleavage of the p65-RelA subunit of NF-kappaB during poliovirus infection.

Activation of NF-kappaB during viral infection is one of the critical elements in innate immune response. Several virus-specific factors, such as double-stranded RNA, can trigger host defense mechanisms by inducing NF-kappaB-mediated expression of cytokines and interferons. Early stages of poliovirus infection are also associated with degradation of IkappaB alpha and translocation of NF-kappaB into the nucleus. However, at later stages of poliovirus replication the p65-RelA component of the NF-kappaB complex undergoes a specific cleavage that coincides with the onset of intensive poliovirus protein synthesis and the appearance of the activity of poliovirus protease 3C. Indeed, the p65-RelA amino acid sequence contains the recognition site for 3C, and recombinant protein 3C was shown to be capable of proteolytic cleavage of p65-RelA, generating truncated product similar to that observed during poliovirus infection. Cleavage of p65-RelA occurs during replication of ECHO-1 and rhinovirus 14, suggesting that inactivation of NF-kappaB function by proteolytic cleavage of p65-RelA is the common mechanism by which picornaviruses suppress the innate immune response.

Stability of the prion protein-encoding (PRNP) gene in HeLa cells.

To assess the risk of the de novo emergence of the agent of transmissible spongiform encephalopathies in cultured cells, we examined the stability of the prion protein-encoding (PRNP) gene in HeLa cells and in cultures contaminated with HeLa cells that have been passaged extensively for over 50 years. Various sub-lineages of HeLa cells showed that some contained a mixture of a truncated PRNP gene (R3-R4 deletion) and a full-length PRNP gene, while others were homozygous for the R3-R4 deletion. That finding suggests that the progenitor of several popular sub-lineages of HeLa must have lost part or all of chromosome 20 early in the history of HeLa cells. No mutations were found in the PRNP genes. We conclude that the spontaneous appearance of mutations leading to expression of abnormal prion proteins in continuously passaged heteroploid cell lines is unlikely to pose a substantial risk for the safe production of biologicals in such cells.

Mapping of genomic segments of influenza B virus strains by an oligonucleotide microarray method.

Similar to other segmented RNA viruses, influenza viruses can exchange genome segments and form a wide variety of reassortant strains upon coreplication within a host cell. Therefore, the mapping of genome segments of influenza viruses is essential for understanding their phenotypes. In this work, we have developed an oligonucleotide microarray hybridization method for simultaneous genotyping of all genomic segments of two highly homologous strains of influenza B virus. A few strain-specific oligonucleotide probes matching each of the eight segments of the viral genomes of the B/Beijing/184/93 and B/Shangdong/7/97 strains were hybridized with PCR-amplified fluorescently labeled single-stranded DNA. Even though there were a few mismatches among the genomes of the studied virus strains, microarray hybridization showed highly significant and reproducible discrimination ability and allowed us to determine the origins of individual genomic segments in a series of reassortant strains prepared as vaccine candidates. Additionally, we were able to detect the presence of at least 5% of mixed genotypes in virus stocks even when conventional sequencing methods failed, for example, for the NS segment. Thus, the proposed microarray method can be used for (i) rapid and reliable genome mapping of highly homologous influenza B viruses and (ii) extensive monitoring of influenza B virus reassortants and the mixed genotypes. The array can be expanded by adding new oligoprobes and using more quantitative assays to determine the origin of individual genomic segments in series of reassortant strains prepared as vaccine candidates or in mixed virus populations.

Long-term circulation of vaccine-derived poliovirus that causes paralytic disease.

Successful implementation of the global poliomyelitis eradication program raises the problem of vaccination against poliomyelitis in the posteradication era. One of the options under consideration envisions completely stopping worldwide the use of the Sabin vaccine. This strategy is based on the assumption that the natural circulation of attenuated strains and their derivatives is strictly limited. Here, we report the characterization of a highly evolved derivative of the Sabin vaccine strain isolated in a case of paralytic poliomyelitis from a 7-month-old immunocompetent baby in an apparently adequately immunized population. Analysis of the genome of this isolate showed that it is a double (type 1-type 2-type 1) vaccine-derived recombinant. The number of mutations accumulated in both the type 1-derived and type 2-derived portions of the recombinant genome suggests that both had diverged from their vaccine predecessors approximately 2 years before the onset of the illness. This fact, along with other recent observations, points to the possibility of long-term circulation of Sabin vaccine strain derivatives associated with an increase in their neurovirulence. Comparison of genomic sequences of this and other evolved vaccine-derived isolates reveals some general features of natural poliovirus evolution. They include a very high preponderance and nonrandom distribution of synonymous substitutions, conservation of secondary structures of important cis-acting elements of the genome, and an apparently adaptive character of most of the amino acid mutations, with only a few of them occurring in the antigenic determinants. Another interesting feature is a frequent occurrence of tripartite intertypic recombinants with either type 1 or type 3 homotypic genomic ends.

Retrospective analysis of a local cessation of vaccination against poliomyelitis: a possible scenario for the future.

The global eradication of poliomyelitis will require substantial changes in immunization practices. One of the proposed scenarios includes cessation of vaccination with live oral poliovirus vaccine (OPV) and the creation of an OPV stockpile for emergency response in case of the reintroduction of poliovirus into circulation. We describe here a retrospective analysis of the cessation of OPV usage in a region of the Byelorussian Republic of the former Soviet Union in 1963 to 1966. During this period, a widespread circulation and evolution of independent lineages of vaccine-derived polioviruses took place in the region. Some of these lineages appeared to originate from OPV given to 40 children in the community during this period of essentially no vaccinations. The data demonstrate very high risks associated with both the local cessation of OPV vaccination and the proposed use of OPV to control a possible reemergence of poliovirus in the postvaccination period. The high transmissibility of OPV-derived viruses in nonimmune population, documented here, and the known existence of long-term OPV excretors should be also considered in assessing risks of the synchronized global cessation of OPV usage.

Evaluation of immunogenicity and protective properties of inactivated poliovirus vaccines: a new surrogate method for predicting vaccine efficacy.

An assay for the evaluation of protective properties of inactivated poliovirus vaccines (IPVs) in transgenic (Tg) mice susceptible to poliovirus has been developed and optimized for type 2 IPV. This method was used to compare the immunogenicity and protective properties of experimental IPV produced from the attenuated Sabin strain (sIPV) with those of conventional IPV (cIPV) produced from the wild-type (wt) poliovirus MEF-1 strain. Modified enzyme-linked immunosorbent assays (ELISAs) were used to measure immune response in serum and saliva samples from test mice. Tg mice were vaccinated and were challenged either with wt poliovirus or virulent poliovirus derived from the vaccine strain. Compared with cIPV, sIPV induced lower levels of antibodies and did not completely protect mice against challenge with wt virus but did protect mice against challenge with the virulent vaccine-derived strain. This may be due to an 18% nucleotide difference between the MEF-1 and Sabin 2 strains, resulting in 72 amino acid substitutions and leading to antigenic dissimilarity. Immunological properties of both strains, revealed by cross-neutralization tests and ELISAs, confirmed that MEF-1 possesses broader immunogenicity than does Sabin 2. This animal model may be used for the assessment of new IPVs and of combination vaccines containing an IPV component.