Plant-made polio type 3 stabilized VLPs-a candidate synthetic polio vaccine

Poliovirus (PV) is the causative agent of poliomyelitis, a crippling human disease known since antiquity. PV occurs in two distinct antigenic forms, D and C, of which only the D form elicits a robust neutralizing response. Developing a synthetically produced stabilized virus-like particle (sVLP)-based vaccine with D antigenicity, without the drawbacks of current vaccines, will be a major step towards the final eradication of poliovirus. Such a sVLP would retain the native antigenic conformation and the repetitive structure of the original virus particle, but lack infectious genomic material. In this study, we report the production of synthetically stabilized PV VLPs in plants. Mice carrying the gene for the human PV receptor are protected from wild-type PV when immunized with the plant-made PV sVLPs. Structural analysis of the stabilized mutant at 3.6 Å resolution by cryo-electron microscopy and single-particle reconstruction reveals a structure almost indistinguishable from wild-type PV3.Despite the success of current vaccination against poliomyelitis, safe, cheap and effective vaccines remain sought for continuing eradication effort. Here the authors use plants to express stabilized virus-like particles of type 3 poliovirus that can induce a protective immune response in mice transgenic for the human poliovirus receptor.

[Complete Genome Characterization of Vaccine-derived Polioviruses Isolated in Yunnan,China]

To explore the genomic characterization of 4vaccine-derived poliovirus(VDPV)strains isolated from 2acute flaccid paralysis(AFP)cases in Yunnan Province in 2010 and 2012,respectively,the complete genome sequences of the 4strains were determined. Sequence analysis revealed that the complete genome length of the type Ⅱ and type Ⅰ VDPV was 7439nt and 7441 nt, respectively. Nucleotide and amino acid sequence similarities of type II VDPV were 95.4% and 97.7%,respectively,and type I VDPV were93.9% and 97.9%,respectively as compared with those of Sabin strains. Nucleotide substitutions were found at two important attenuation sites (nt 481 and nt in type Ⅱ VDPV, and three important attenuation sites(nt480,nt2795 and nt6203)in type I VDPV. Type 2 and type 1VDPV strains had 1.0% and2.3% divergence with Sabin strains, respectively. Similarity plot analysis showed multiple recombination events in the genome of the 4strains,which showed that the recombination was common and complex. Analysis of the characteristics of VDPVs on molecular level could provide valuable information on evolutionary dynamics and lay foundation for developing scientific and feasible strategy to control VDPV.

[Investigation of a Patient with Pre-vaccine-derived Poliovirus in Shandong Province, China]

To analyze the genetic characteristics of a polio-I highly variant vaccine recombinant virus in Shandong Province (China) in 2011 and to identify isolates from healthy contacts, two stool specimens from one patient with acute flaccid paralysis (AFP) and 40 stool specimens from his contacts were collected for virus isolation. The complete genome of poliovirus and VP1 coding region of the non-polio enterovirus were sequenced. Homologous comparison and phylogenetic analyses based on VP1 sequences were undertaken among coxsackievirus (CV) B1, CV-B3 isolates, and those in GenBank. One poliovirus (P1/11186), CV-A4 and CV-A8 were isolated from the AFP patient; one CV-A2, Echovirus 3 (E-3), E-12 and E-14, ten CV-B1, and five CV-B3 strains were isolated from his contacts. These results led us to believe that there may be a human enterovirus epidemic in this area, and that surveillance must be enhanced. P1/11186 was a type-1 vaccine-related poliovirus; it combined with type-2 and type-3 polioviruses in 2A and 3A regions, respectively. There were 25 nucleotide mutations with 9 amino-acid alterations in the entire genome. There were 8 nucleotide mutations with 5 amino-acid alterations in the VP1 region compared with the corresponding Sabin strains. Homology analyses suggested that the ten CV-B1 isolates had 97.0%-100% nucleotide and 98.9%-100% amino-acid identities with each other, as well as 92.6%-100% nucleotide and 99.2%-100% amino-acid identities among the five CV-B3 isolates. Phylogenetic analyses on the complete sequences of VP1 among CV-B1 and CV-B3 isolates showed that Shandong strains, together with strains from other provinces in China, had a close relationship and belonged to the same group.

[Genetic Characteristics of Type 2 Vaccine-derived Poliovirus in Shanxi Province (China) in 2014]

The World Health Organization redefined the type 2 vaccine-derived poliovirus (VDPV) in 2010. To study the genetic characteristics and evolution of type 2 VDPV under this new definition, we conducted genome sequencing and analyses of type 2 VDPVs isolated from one patient with acute flaccid paralysis in Shanxi province (China) in 2014. Nucleotide sequencing revealed that the full-length of type 2 VDPV is 7439 bases encoding 2207 amino acids with no insertion or deletion of nucleotides compared with Sabin2. One nucleotide substitution identified as a key determinant of the attenuated phenotype of the Sabin 2 strain (A-G reversion at nucleotide nt 481 in the 5-end of the untranslated region) had reverted in the Shanxi type 2 VDPV. The other known key determinant of the attenuated phenotype of the Sabin 2 strain (U-->C reversion at nt2909 in the VP1 coding region that caused a Ile143Thr substitution in VP1) had not reverted in the Shanxi VDPV. The Shanxi type 2 VDPV was S2/S1 recombinant, the crossover site of which mapped to the 3-end of the 3D region (between nt 6247 and nt 6281). A phylogentic tree based on the VP1 coding region showed that evolution of the Shanxi type 2 VDPV was independent of other type 2 VDPVs detected worldwide. We estimated that the strain circulated for approximately = 11 months in the population according to the known evolution rate. The present study confirmed that the Chinese Polio Laboratory Network could discover the VDPV promptly and that it played an important part in maintenance of a polio-free China.

[Formation and identification of virus-like particles of poliovirus type I]

OBJECTIVE

To establish a method to produce virus-like particles (VLP) of poliovirus type I in Saccharomy cescerevisiae to develop potential novel recombinant vaccine against poliovirus type 1.

METHODS

The genes of P1 and 3CD of poliovirus type I were optimized, synthesized and inserted into expression vector, which was further transfected into Saccharomy cescerevisiae. The extracts of yeast cells were purified by CsCl density gradient centrifugation after induction and cell lysis.

RESULTS

Electrophoresis and sequencing analyses showed that the genes P1 and 3CD of poliovirus type I were successfully inserted into expression vector and encode a protein whose amino acid sequences were identical with wide-type genes of poliovirus type I. Electronic microscopy analysis showed that the VLPs of poliovirus type I could be efficiently formed in Saccharomy cescerevisiae.

CONCLUSION

The VLPs of poliovirus type I could be efficiently produced by co-expression of P1 and 3CD genes in Saccharomy cescerevisiae.

Multiple independent emergences of type 2 vaccine-derived polioviruses during a large outbreak in northern Nigeria

Since 2005, a large poliomyelitis outbreak associated with type 2 circulating vaccine-derived poliovirus (cVDPV2) has occurred in northern Nigeria, where immunization coverage with trivalent oral poliovirus vaccine (tOPV) has been low. Phylogenetic analysis of P1/capsid region sequences of isolates from each of the 403 cases reported in 2005 to 2011 resolved the outbreak into 23 independent type 2 vaccine-derived poliovirus (VDPV2) emergences, at least 7 of which established circulating lineage groups. Virus from one emergence (lineage group 2005-8; 361 isolates) was estimated to have circulated for over 6 years. The population of the major cVDPV2 lineage group expanded rapidly in early 2009, fell sharply after two tOPV rounds in mid-2009, and gradually expanded again through 2011. The two major determinants of attenuation of the Sabin 2 oral poliovirus vaccine strain (A481 in the 5'-untranslated region [5'-UTR] and VP1-Ile143) had been replaced in all VDPV2 isolates; most A481 5'-UTR replacements occurred by recombination with other enteroviruses. cVDPV2 isolates representing different lineage groups had biological properties indistinguishable from those of wild polioviruses, including efficient growth in neuron-derived HEK293 cells, the capacity to cause paralytic disease in both humans and PVR-Tg21 transgenic mice, loss of the temperature-sensitive phenotype, and the capacity for sustained person-to-person transmission. We estimate from the poliomyelitis case count and the paralytic case-to-infection ratio for type 2 wild poliovirus infections that ∼700,000 cVDPV2 infections have occurred during the outbreak. The detection of multiple concurrent cVDPV2 outbreaks in northern Nigeria highlights the risks of cVDPV emergence accompanying tOPV use at low rates of coverage in developing countries.

Highly divergent neurovirulent vaccine-derived polioviruses of all three serotypes are recurrently detected in Finnish sewage

In Finland, surveillance of potential re-emergence of poliovirus transmission is mainly based on environmental surveillance, i.e. search for infectious poliovirus in sewage samples. Since December 2008, 21 genetically highly divergent, neurovirulent vaccine-derived polioviruses (VDPV) have been isolated from sewage in Tampere, Finland. While the source of the VDPV is unknown, characteristics of the viruses resemble those of strains isolated from immunodeficient, persistently infected persons. No cases of suspected poliomyelitis have been reported in Finland since 1985.

Future of polio vaccines

Over the past half-century, global use of highly effective vaccines against poliomyelitis brought this disease to the brink of elimination. Mounting evidence supports the argument that a high level of population immunity must be maintained after wild poliovirus circulation is stopped to preserve a polio-free status worldwide. Shifting factors in the risk-benefit-cost equation favor the creation of new poliovirus vaccines for use in the foreseeable future. Genetically stable attenuated virus strains could be developed for an improved oral poliovirus vaccine, but proving their safety and efficacy would be impractical owing to the enormous size of the clinical trials required. Novel versions of inactivated poliovirus vaccine that could be used globally should be developed. An improved inactivated poliovirus vaccine must be efficacious, inexpensive, safe to manufacture and easy to administer. Combination products containing inactivated poliovirus vaccine and other protective antigens should become part of routine childhood immunizations around the world.

[Analysis on identification and genetic character of type I vaccine-derived poliovirus in Shanxi province in 2007]

OBJECTIVE

To describe the source of vaccine-derived poliovirus (VDPV) and the effect on local polio-free status, the VP1 coding region was sequenced and analyzed for type I VDPV in Shanxi province in 2007.

METHOD

The virus isolation was performed to double stool specimens from one case acute flaccid paralysis (AFP) patient. VP1 coding region of the isolated stain was sequenced and analyzed. The phylogenetic tree was constructed based on VP1 region sequence between Shanxi strains and other type I VDPVs.

RESULT

2 type I + II +III strains were isolated from double stool specimens from the AFP patient in Shanxi Province in 2007. VP1 sequencing of the two stains revealed > 1.0% divergence from the VP1 region of P I /Sabin vaccine strain. According to WHO criteria, the two stains were identified as type I vaccine-derived poliovirus (VDPV). Phylogenetic analysis based on VP1 coding sequence showed that the evolution distance of Shanxi type I VDPV was far away from other VDPVs detected in China. Moreover, no evidence supported the AFP patient as immunodeficiency patient. So Shanxi type I VDPVs were classified into ambiguous VDPV(aVDPV).

CONCLUSION

Considering the genetic character for Shanxi type I VDPV and the local OPV coverage, we highly suspected that an immunodeficiency patient in local area who long-term excreted VDPVs existed and resulted in the patient infection of VDPV in Shanxi in 2007. In the post era of polio eradication, the detection and management for the possible existing patient of long-term excretion VDPV should be strengthened.

Virus attenuation by genome-scale changes in codon pair bias

As a result of the redundancy of the genetic code, adjacent pairs of amino acids can be encoded by as many as 36 different pairs of synonymous codons. A species-specific "codon pair bias" provides that some synonymous codon pairs are used more or less frequently than statistically predicted. We synthesized de novo large DNA molecules using hundreds of over-or underrepresented synonymous codon pairs to encode the poliovirus capsid protein. Underrepresented codon pairs caused decreased rates of protein translation, and polioviruses containing such amino acid-independent changes were attenuated in mice. Polioviruses thus customized were used to immunize mice and provided protective immunity after challenge. This "death by a thousand cuts" strategy could be generally applicable to attenuating many kinds of viruses.

Oncolytic Treatment and Cure of Neuroblastoma by a Novel Attenuated Poliovirus in a Novel Poliovirus-Susceptible Animal Model

Neuroblastoma is one of the most common solid tumors in children. Treatment is of limited utility for high-risk neuroblastoma and prognosis is poor. Resistance of neuroblastoma to conventional therapies has prompted us to search for a novel therapeutic approach based on genetically modified polioviruses. Poliovirus targets motor neurons leading to irreversible paralysis. Neurovirulence can be attenuated by point mutations or by exchange of genetic elements between different picornaviruses. We have developed a novel and stable attenuated poliovirus, replicating in neuroblastoma cells, by engineering an indigenous replication element (cre), copied from a genome-internal site, into the 5'-nontranslated genomic region (mono-crePV). An additional host range mutation (A(133)G) conferred replication in mouse neuroblastoma cells (Neuro-2a(CD155)) expressing CD155, the poliovirus receptor. Crossing immunocompetent transgenic mice susceptible to poliovirus (CD155 tg mice) with A/J mice generated CD155 tgA/J mice, which we immunized against poliovirus. Neuro-2a(CD155) cells were then transplanted into these animals, leading to lethal tumors. Despite preexisting high titers of anti-poliovirus antibodies, established lethal s.c. Neuro-2a(CD155) tumors in CD155 tgA/J mice were eliminated by intratumoral administrations of A(133)Gmono-crePV. No signs of paralysis were observed. Interestingly, no tumor growth was observed in mice cured of neuroblastoma that were reinoculated s.c. with Neuro-2a(CD155). This result indicates that the destruction of neuroblastoma cells by A(133)Gmono-crePV may lead to a robust antitumor immune response. We suggest that our novel attenuated oncolytic poliovirus is a promising candidate for effective oncolytic treatment of human neuroblastoma or other cancer even in the presence of present or induced antipolio immunity.

Rational design of genetically stable, live-attenuated poliovirus vaccines of all three serotypes: relevance to poliomyelitis eradication

The global eradication of poliomyelitis caused by wild-type virus is likely to be completed within the next few years, despite immense logistic and political difficulties, and may ultimately be followed by the cessation of vaccination. However, the existing live-attenuated vaccines have the potential to revert to virulence, causing occasional disease, and viruses can be shed by immunocompromised individuals for prolonged periods of time. Moreover, several outbreaks of poliomyelitis have been shown to be caused by viruses derived from the Sabin vaccine strains. The appearance of such strains depends on the prevailing circumstances but poses a severe obstacle to strategies for stopping vaccination. Vaccine strains that are incapable of reversion at a measurable rate would provide a possible solution. Here, we describe the constructions of strains of type 3 poliovirus that are stabilized by the introduction of four mutations in the 5' noncoding region compared to the present vaccine. The strains are genetically and phenotypically stable under conditions where the present vaccine loses the attenuating mutation in the 5' noncoding region completely. Type 1 and type 2 strains in which the entire 5' noncoding regions of Sabin 1 and Sabin 2 were replaced exactly with that of one of the type 3 strains were also constructed. The genetic stability of 5' noncoding regions of these viruses matched that of the type 3 strains, but significant phenotypic reversion occurred, illustrating the potential limitations of a rational approach to the genetic stabilization of live RNA virus vaccines.

Retrospective study on poliomyelitis cases in northern Greece

Here we report the results of a retrospective study on the epidemiological characteristics and genetic relationships of the virus isolates responsible for the last poliomyelitis cases in Greece. The last wild poliomyelitis case in Greece was detected in 1996, and the last vaccine-related strain was isolated in 1998. The whole of Europe, including Greece, is now considered to be polio-free.

Negative selection on neutralization epitopes of poliovirus surface proteins: implications for prediction of candidate epitopes for immunization

For development of effective vaccines against viruses, it is of importance to choose appropriate epitopes as the target for immunization. These epitopes should eventually be determined experimentally, but it would be helpful if we could predict candidate epitopes computationally because it accelerates the entire process. To predict candidate epitopes for immunization, it is of great interest to characterize the target epitopes of poliovirus vaccine, which has empirically proven to be the most effective among all vaccines available. Here I show that almost all amino acid sites of poliovirus surface proteins VP1, VP2, and VP3 including neutralization epitopes are negatively selected and no site is under positive selection. These results, together with those obtained in previous studies, indicate that vaccines directed against epitopes, which consist of negatively selected sites protect vaccinees more effectively than those directed against epitopes which contain positively selected sites. These observations suggest that candidate epitopes for immunization are predicted by the molecular evolutionary analysis of viral protein (and its coding nucleotide) sequences, as the epitopes which consist exclusively of negatively selected amino acid sites.

Isolation and characterization of circulating type 1 vaccine-derived poliovirus from sewage and stream waters in Hispaniola

Twenty-one cases of acute flaccid paralysis (AFP) were reported on the island of Hispaniola in 2000. Laboratory analysis confirmed the presence of circulating vaccine-derived poliovirus (cVDPV) type 1 in stool samples obtained from patients. As a complement to the active search for cases of AFP, environmental sampling was conducted during November and December 2000, to test for cVDPV in sewage, streams, canals, and public latrines. Fifty-five environmental samples were obtained and analyzed for the presence of polioviruses by use of cell culture followed by neutralization and reverse-transcription polymerase chain reaction. Of the 23 positive samples, 10 tested positive for poliovirus type 1, 7 tested positive for poliovirus type 2, 5 tested positive for poliovirus type 3, and 1 tested positive for both poliovirus type 2 and type 3. By sequence analysis of the complete viral capsid gene 1 (VP1), a 2.1%-3.7% genetic sequence difference between 7 type 1 strains and Sabin type 1 vaccine strain was found. Phylogenetic analysis showed that these viruses are highly related to cVDPV isolated from clinical cases and form distinct subclusters related to geographic region. Our findings demonstrate a useful role for environmental surveillance of neurovirulent polioviruses in the overall polio eradication program.

Effects of Vaccine Strain Mutations in Domain V of the Internal Ribosome Entry Segment Compared in the Wild Type Poliovirus Type 1 Context

Initiation of poliovirus (PV) protein synthesis is governed by an internal ribosome entry segment structured into several domains including domain V, which is accepted to be important in PV neurovirulence because it harbors an attenuating mutation in each of the vaccine strains developed by A. Sabin. To better understand how these single point mutations exert their effects, we placed each of them into the same genomic context, that of PV type 1. Only the mutation equivalent to the Sabin type 3 strain mutation resulted in significantly reduced viral growth both in HeLa and neuroblastoma cells. This correlated with poor translation efficiency in vitro and could be explained by a structural perturbation of the domain V of the internal ribosome entry segment, as evidenced by RNA melting experiments. We demonstrated that reduced cell death observed during infection by this mutant is due to the absence of inhibition of host cell translation. We confirmed that this shut-off is correlated principally with cleavage of eIF4GII and not eIF4GI and that this cleavage is significantly impaired in the case of the defective mutant. These data support the previously reported conclusion that the 2A protease has markedly different affinities for the two eIF4G isoforms.

[Antigen differences of genetic variants Abent+ and Abent- poliovirus vaccine strain of III type]

Hybridomes--producers of monoclonal antibodies (MAB) were obtained able to differentiate the variants Abent+ and Abent- poliovirus vaccine strain in the virus neutralizing reaction. Using the obtained panel the changes of the epitope structure of capsid proteins of poliovirus variants (dissociants) were found which appeared during reproduction in cell culture. It proves the fact that there exist essential antigenic differences of superficial virion's proteins, which appear during the process of dissociation.

Characterization of CHAT and Cox type 1 live-attenuated poliovirus vaccine strains

CHAT and Cox type 1 live-attenuated poliovirus strains were developed in the 1950s to be used as vaccines for humans. This paper describes their characterization with respect to virulence, sensitivity for growth at high temperatures, and complete nucleotide and amino acid sequences. The results are compared to those for their common parental wild virus, the Mahoney strain, and to those for two other poliovirus strains derived from Mahoney, the Sabin 1 vaccine strain and the mouse-adapted LS-a virus. Analysis of four isolates from cases of vaccine-associated paralytic poliomyelitis related to the CHAT vaccine revealed genetic and phenotypic properties of the CHAT strain following replication in the human gut. CHAT-VAPP strain 134 contained a genome highly evolved from that of CHAT (1.1% nucleotide differences), suggesting long-term circulation of a vaccine-derived strain in the human population. The molecular mechanisms of attenuation and evolution of poliovirus in humans are discussed in the context of the global polio eradication initiative.

[Mutation and recombination variability of vaccine polioviruses isolated in Belarus (1960-1999)]

One hundred and eight vaccine-derived strains of types 1, 2, and 3 poliovirus (25 PV1, 34 PV2, and 48 PV3) isolated in Belarus in 1960-1999 were analyzed by double restriction fragment length polymorphism assay (RFLP-1, -3D1). Forty-four (40.7%) of strains were genetically modified. Eight (7.4%) PV were modified by mutation, 16 (14.8%) by recombination, and 20 (18.5%) by both mutation and recombination. The genomes of 16 PV were analyzed by multiple RFLP technique covering VP1-, VP1/VP2A-, P2-, 3AC-, and 3D1-coding regions. The majority of recombinants were "simple" (with one crossing over site). One strain was "double" recombinant (two crossings over sites) and one more "multiple" recombinant (three crossing over sites). Partial nucleotide sequencing of some recombinant strains showed that the degree of these strains' divergence was less than 1% in comparison with the original vaccine viruses.

The vaccine origin of the 1968 epidemic of type 3 poliomyelitis in Poland

A clear association was demonstrated between the use of USOL-D-bac type 3 poliovirus live-attenuated vaccine and the 1968 poliomyelitis epidemic in Poland. The epidemic followed small-scale trials with Sabin and USOL-D-bac type 3 vaccine strains carried out in seven countries including Poland. Factors that might have contributed to the genesis and development of the epidemic were the pattern of virus excretion from vaccinees, mutations found in viruses from the epidemic, and the particular vaccination policies in Poland during the previous years. These findings may provide essential insights into the strategies for stopping polio immunisation once wild poliovirus has been eradicated.