Intestinal trypsin can significantly modify antigenic properties of polioviruses: implications for the use of inactivated poliovirus vaccine.

It was recently reported that the intestinal protease trypsin cleaves in vitro the VP1 protein of type 3 poliovirus at antigenic site 1 (J. P. Icenogle, P. D. Minor, M. Ferguson, and J. M. Hogle, J. Virol. 60:297-301, 1986). We found that incubation of purified or crude type 3 poliovirus preparations with specimens of human intestinal fluid brings about a similar change in the virion structure. Sera from children immunized solely with the regular inactivated poliovirus vaccine (IPV) neutralized trypsin-cleaved Sabin 3 virus poorly, if at all, despite moderate levels of antibodies to the corresponding intact virus. Sera containing very high titers of the intact virus also neutralized the trypsin-cleaved virus but at a relatively weaker capacity. Most sera from older persons who may have been exposed to a natural poliovirus infection before the introduction of the poliovirus vaccines as well as sera from children infected with type 3 poliovirus during the recent outbreak in Finland were able to neutralize the trypsin-cleaved type 3 polioviruses. Serum specimens collected 1 month after a single dose of live poliovirus vaccine from children previously immunized with IPV were able to neutralize the trypsin-cleaved virus as well. During natural infection and after live poliovirus vaccine administration polioviruses are exposed to proteolytic enzymes in the gut. Our results may offer an alternative explanation for the relatively weak mucosal immunity obtained with IPV. Improvement of IPV preparations by incorporation of trypsin-treated type 3 polioviruses in the vaccine should be studied.     

Improved distribution of antigenic site specificity of poliovirus-neutralizing antibodies induced by a protease-cleaved immunogen in mice.

Previous studies showed that the distribution of antigenic site specificity of neutralizing antibodies to type 3 poliovirus obtained with the inactivated poliovirus vaccine can be deficient as compared with that obtained following poliovirus infection. This observation was shown by the relatively low capacity of sera from inactivated-poliovirus-vaccine-immunized persons to neutralize poliovirus cleaved at antigenic site 1. We investigated possibilities for improving the situation in a mouse model. Balb/c mice were immunized with intact or trypsin-cleaved type 3 poliovirus (Saukett strain). Sera from mice immunized with the intact virus readily neutralized the intact virus but neutralized the cleaved virus only rarely. In contrast, cleaved-virus-immunized mice produced antibodies that were able to neutralize the cleaved virus as well as the intact one. Mice immunized with a 100-fold-higher dose of the intact virus produced significant levels of antibodies to the cleaved virus, too. Somewhat surprisingly, mice immunized with high doses of the cleaved virus produced antibodies specific for the intact loop between beta sheets B and C of VP1 (virion protein 1), which should be cleaved in the immunogen. This was shown by a higher titer of antibodies to intact Saukett virus than to the corresponding cleaved virus, as well as to a type 1/type 3 hybrid poliovirus in which only the BC loop amino acids were derived from type 3 poliovirus. The cleavage-induced enhanced availability of antigenic determinants residing outside the BC loop was also shown by increased neutralization titers of monoclonal antibodies specific for some of these other determinants. These results indicate that by using a trypsin-cleaved type 3 poliovirus as a parenteral immunogen, it is possible to change the distribution of antigenic site specificities of neutralizing antibodies to resemble that following poliovirus infection.     

Modulation of humoral response to a 12-amino-acid site on the poliovirus virion.

Most monoclonal antibodies to poliovirus 3 but not poliovirus 1 require a single 12-amino-acid sequence in virion protein VP1 for neutralization (site 1). None of the available monoclonal antibodies requiring this site bound virions after tryptic cleavage of site 1. This result allowed the amount of site 1-specific antibodies to be determined in an antiserum by comparing its reactivity with virus and trypsin-cleaved virus. Antisera to poliovirus 3 Sabin strain (PS3) but not poliovirus 1 Sabin showed site 1 immunodominance, consistent with the frequency of isolation of site 1-specific monoclonal antibodies to these viruses. Cleavage of site 1 prior to immunization dramatically reduced the immunogenicity of this site in PS3. However, the antiserum against trypsin-cleaved PS3 still had a high neutralization titer, demonstrating that sites other than site 1 can elicit a neutralizing response to PS3. Other antisera to PS3 showed significant variability in the response to site 1, indicating that other factors, such as the genetic background of inbred mouse strains, the species immunized, and the immunization protocol, also affect immunodominance. In particular, a serum from a human infant recently immunized with oral trivalent vaccine had little response to site 1.     

Poliovirus Sabin type 1 neutralization epitopes recognized by immunoglobulin A monoclonal antibodies.

Immunity to poliomyelitis is largely dependent on humoral neutralizing antibodies, both after natural (wild virus or vaccine) infection and after inactivated poliovirus vaccine inoculation. Although the production of local secretory immunoglobulin A (IgA) antibody in the gut mucosa may play a major role in protection, most of information about the antigenic determinants involved in neutralization of polioviruses derives from studies conducted with humoral monoclonal antibodies (MAbs) generated from parenterally immunized mice. To investigate the specificity of the mucosal immune response to the virus, we have produced a library of IgA MAbs directed at Sabin type 1 poliovirus by oral immunization of mice with live virus in combination with cholera toxin. The epitopes recognized by 13 neutralizing MAbs were characterized by generating neutralization-escape virus mutants. Cross-neutralization analysis of viral mutants with MAbs allowed these epitopes to be divided into four groups of reactivity. To determine the epitope specificity of MAbs, virus variants were sequenced and the mutations responsible for resistance to the antibodies were located. Eight neutralizing MAbs were found to be directed at neutralization site N-AgIII in capsid protein VP3; four more MAbs recognized site N-AgII in VP1 or VP2. One IgA MAb selected a virus variant which presented a unique mutation at amino acid 138 in VP2, not previously described. This site appears to be partially related with site N-AgII and is located in a loop region facing the VP2 N-Ag-II loop around residue 164. Only 2 of 13 MAbs proved able to neutralize the wild-type Mahoney strain of poliovirus. The IgA antibodies studied were found to be produced in the dimeric form needed for recognition by the polyimmunoglobulin receptor mediating secretory antibody transport at the mucosal level.     

Antigenic and biochemical characterization of poliovirus type 1 isolates

By the introduction of Sabin oral poliovirus vaccine, the circulation of wild type polioviruses has virtually disappeared in Japan. However, an outbreak of poliomyelitis associated with sporadic transmission of type 1 wild strain occurred in Nagano in 1980. Furthermore, we found that some type 1 wild strains were introduced into Japan from abroad in 1981. In recent surveys, the two poliovirus type 1 isolates which have non-vaccine-like antigenic character were detected in Aichi. Then, an investigation to trace the origin of these strains was performed, by using intratypic serodifferentiation and biochemical techniques. Electrophoretic migration patterns of their structural polypeptides were quite different from the vaccine virus. In the oligonucleotide mapping, however, one of them gave patterns very similar to those of the vaccine virus. We could conclude that one originated most probably from wild strains, and the other was an antigenic variant derived from the vaccine virus. It showed that oligonucleotide mapping was a very useful method for identification of antigenic modified Sabin type 1 derivatives.     

Long-term excretion of vaccine-derived poliovirus by a healthy child

A child was found to be excreting type 1 vaccine-derived poliovirus (VDPV) with a 1.1% sequence drift from Sabin type 1 vaccine strain in the VP1 coding region 6 months after he was immunized with oral live polio vaccine. Seventeen type 1 poliovirus isolates were recovered from stools taken from this child during the following 4 months. Contrary to expectation, the child was not deficient in humoral immunity and showed high levels of serum neutralization against poliovirus. Selected virus isolates were characterized in terms of their antigenic properties, virulence in transgenic mice, sensitivity for growth at high temperatures, and differences in nucleotide sequence from the Sabin type 1 strain. The VDPV isolates showed mutations at key nucleotide positions that correlated with the observed reversion to biological properties typical of wild polioviruses. A number of capsid mutations mapped at known antigenic sites leading to changes in the viral antigenic structure. Estimates of sequence evolution based on the accumulation of nucleotide changes in the VP1 coding region detected a "defective" molecular clock running at an apparent faster speed of 2.05% nucleotide changes per year versus 1% shown in previous studies. Remarkably, when compared to several type 1 VDPV strains of different origins, isolates from this child showed a much higher proportion of nonsynonymous versus synonymous nucleotide changes in the capsid coding region. This anomaly could explain the high VP1 sequence drift found and the ability of these virus strains to replicate in the gut for a longer period than expected.     

A recombinant virus between the Sabin 1 and Sabin 3 vaccine strains of poliovirus as a possible candidate for a new type 3 poliovirus live vaccine strain.

Biological tests including the monkey neurovirulence test performed on recombinants between the virulent Mahoney and attenuated Sabin 1 strains of type 1 poliovirus indicated that the genome region encoding mainly the viral capsid proteins had little correlation with the neurovirulence or attenuation phenotype of the virus. The results suggested that new vaccine strains of type 2 and type 3 polioviruses may be constructed in vitro by replacing the sequence encoding the antigenic determinants in viral capsid proteins of the Sabin 1 genome by the corresponding sequences of the type 2 and type 3 genome, respectively. Accordingly, we constructed recombinants between the Sabin 1 and Sabin 3 strains of poliovirus in which genome sequences of the Sabin 1 strain encoding most or all capsid proteins were replaced by the corresponding genome sequences of the Sabin 3 strain. One of the recombinant viruses thus constructed was fully viable and showed antigenicity and immunogenicity identical to those of type 3 poliovirus. The monkey neurovirulence tests and in vitro phenotypic marker tests (temperature sensitivity of growth, sodium bicarbonate concentration dependency of growth under agar overlay, and size of plaque) were performed on the recombinant virus. The stability of the virus in regard to the temperature sensitivity phenotype was also tested. The results suggested that the recombinant virus is a possible candidate for a new type 3 poliovirus vaccine strain.     

Environmental Surveillance of Poliovirus in Sewage Water around the Introduction Period for Inactivated Polio Vaccine in Japan

Environmental virus surveillance was conducted at two independent sewage plants from urban and rural areas in the northern prefecture of the Kyushu district, Japan, to trace polioviruses (PVs) within communities. Consequently, 83 PVs were isolated over a 34-month period from April 2010 to January 2013. The frequency of PV isolation at the urban plant was 1.5 times higher than that at the rural plant. Molecular sequence analysis of the viral VP1 gene identified all three serotypes among the PV isolates, with the most prevalent serotype being type 2 (46%). Nearly all poliovirus isolates exhibited more than one nucleotide mutation from the Sabin vaccine strains. During this study, inactivated poliovirus vaccine (IPV) was introduced for routine immunization on 1 September 2012, replacing the live oral poliovirus vaccine (OPV). Interestingly, the frequency of PV isolation from sewage waters declined before OPV cessation at both sites. Our study highlights the importance of environmental surveillance for the detection of the excretion of PVs from an OPV-immunized population in a highly sensitive manner, during the OPV-to-IPV transition period.     

Chimpanzee-human monoclonal antibodies for treatment of chronic poliovirus excretors and emergency postexposure prophylaxis

Six poliovirus-neutralizing Fabs were recovered from a combinatorial Fab phage display library constructed from bone marrow-derived lymphocytes of immunized chimpanzees. The chimeric chimpanzee-human full-length IgGs (hereinafter called monoclonal antibodies [MAbs]) were generated by combining a chimpanzee IgG light chain and a variable domain of heavy chain with a human constant Fc region. The six MAbs neutralized vaccine strains and virulent strains of poliovirus. Five MAbs were serotype specific, while one MAb cross-neutralized serotypes 1 and 2. Epitope mapping performed by selecting and sequencing antibody-resistant viral variants indicated that the cross-neutralizing MAb bound between antigenic sites 1 and 2, thereby covering the canyon region containing the receptor-binding site. Another serotype 1-specific MAb recognized a region located between antigenic sites 2 and 3 that included parts of capsid proteins VP1 and VP3. Both serotype 2-specific antibodies recognized antigenic site 1. No escape mutants to serotype 3-specific MAbs could be generated. The administration of a serotype 1-specific MAb to transgenic mice susceptible to poliovirus at a dose of 5 μg/mouse completely protected them from paralysis after challenge with a lethal dose of wild-type poliovirus. Moreover, MAb injection 6 or 12 h after virus infection provided significant protection. The MAbs described here could be tested in clinical trials to determine whether they might be useful for treatment of immunocompromised chronic virus excretors and for emergency protection of contacts of a paralytic poliomyelitis case.     

Next Generation Inactivated Polio Vaccine Manufacturing to Support Post Polio-Eradication Biosafety Goals

Worldwide efforts to eradicate polio caused a tipping point in polio vaccination strategies. A switch from the oral polio vaccine, which can cause circulating and virulent vaccine derived polioviruses, to inactivated polio vaccines (IPV) is scheduled. Moreover, a manufacturing process, using attenuated virus strains instead of wild-type polioviruses, is demanded to enhance worldwide production of IPV, especially in low- and middle income countries. Therefore, development of an IPV from attenuated (Sabin) poliovirus strains (sIPV) was pursued. Starting from the current IPV production process based on wild type Salk strains, adaptations, such as lower virus cultivation temperature, were implemented. sIPV was produced at industrial scale followed by formulation of both plain and aluminium adjuvanted sIPV. The final products met the quality criteria, were immunogenic in rats, showed no toxicity in rabbits and could be released for testing in the clinic. Concluding, sIPV was developed to manufacturing scale. The technology can be transferred worldwide to support post polio-eradication biosafety goals.     

Characterization of a highly evolved vaccine-derived poliovirus type 3 isolated from sewage in Estonia

Two types of vaccine-derived polioviruses have been recently designated to emphasize the different origins of the evolved viruses: circulating vaccine-derived polioviruses (cVDPV) associated with outbreaks of paralytic disease and strains isolated from chronically infected immunodeficient individuals (iVDPV). We describe here a type 3 VDPV (PV3/EST/02/E252; later E252) isolated from sewage collected in Tallinn, Estonia, in October 2002. Due to aberrant properties in subtyping, the virus was subjected to detailed characterization. Partial genomic sequencing suggested that the closest relative was the oral vaccine strain PV3/Sabin, but the two virus strains shared only 86.7% of the 900 nucleotides (nt) coding for the capsid protein VP1. Phylogenetic analysis of the nearly complete genome [nt 19 to poly(A)] revealed multiple nucleotide substitutions throughout the genome and a possible Sabin 3/Sabin 1-recombination junction site in the 2C coding region. A calculation based on the estimated mutation frequency of the P1 region of polioviruses suggested that the E252 virus might have replicated in one or more individuals for approximately 10 years. No persons chronically excreting poliovirus are known in Estonia. Amino acid substitutions were seen in all known antigenic sites, which was consistent with the observed aberrant antigenic properties of the virus demonstrated by both monoclonal antibodies and human sera from vaccinated children. In spite of the apparent transmission potential, no evidence was obtained for circulation of the virus in the Estonian population.     

Shedding of Vaccine Viruses with Increased Antigenic and Genetic Divergence after Vaccination of Newborns with Monovalent Type 1 Oral Poliovirus Vaccine

For the final stages in the eradication of poliovirus type 1 (P1), the World Health Organization advocates the selective use of monovalent type 1 oral poliovirus vaccine (mOPV1). To compare the immunogenicity of mOPV1 with that of trivalent OPV (tOPV) in infants, a study was performed in Egypt in 2005. Newborns were vaccinated with mOPV1 or tOPV immediately after birth and were challenged with mOPV1 after 1 month. Vaccination with mOPV1 at birth resulted in significantly higher seroconversion against P1 viruses and lower excretion of P1 viruses than vaccination with tOPV. Intratypic differentiation of the viruses shed by the newborns revealed the presence of remarkably high numbers of antigenically divergent (AD) P1 isolates, especially in the mOPV1 study group. The majority of these AD P1 isolates (71%) were mOPV1 challenge derived and were shed by newborns who did not seroconvert to P1 after the birth dose. Genetic characterization of the viruses revealed that amino acid 60 of the VP3 region was mutated in all AD P1 isolates. Isolates with substitution of residue 99 of the VP1 region had significantly higher numbers of nonsynonymous mutations in the VP1 region than isolates without this substitution and were preferentially shed in the mOPV1 study group. The widespread use of mOPV1 has proven to be a powerful tool for fighting poliovirus circulation in the remaining areas of endemicity. This study provides another justification for the need to achieve high vaccination coverage in order to prevent the circulation of AD strains.Polioviruses are the causative agents of human poliomyelitis and belong to the genus Enterovirus in the family Picornaviridae. The virus is transmitted primarily by the fecal-oral route and replicates in the human intestinal tract. The virus may also be transmitted through respiratory droplets and may replicate for a short period in the upper respiratory tract and tonsillar tissue. From either site of primary replication, the virus may invade the central nervous system and cause paralysis following infection and destruction of motor neurons. Three serologically different types of poliovirus can be distinguished (poliovirus type 1 [P1], P2, and P3), and only limited cross-protection exists between serotypes (35).In 1988, the World Health Assembly passed a resolution to eradicate wild poliovirus globally. A worldwide vaccination campaign with the trivalent oral poliovirus vaccine (tOPV) was launched by the World Health Organization (WHO). This vaccine contains the three attenuated poliovirus vaccine strains developed by Albert Sabin in the proportion of 10:1:6 for P1, P2, and P3, respectively. These OPV strains have been selected to replicate successfully in the human intestinal tract but not in the cells of the central nervous system. In addition to a strong humoral response, these strains generate strong intestinal immunity (12). Sabin type 1 is considered to be the most stable of the three attenuated poliovirus serotypes (19). This strain has 54 mutations compared to the parental Mahoney strain, of which 6 are primarily responsible for attenuation. Sabin type 2 has two major determinants of attenuation, and Sabin type 3 has three determinants of attenuation (11, 32). Upon replication in the human intestinal tract, the sites of attenuation can mutate, which results in reversion of the Sabin strains toward a parental neurovirulent phenotype. Also as a consequence of replication in the host, antibodies are produced that recognize the antigenic sites of the Sabin strains (42). This immunogenic pressure could favor the selection of antigenically divergent (AD) viruses with substituted residues in parts of these antigenic sites. AD Sabin viruses might circulate among a population for a long period and evolve into vaccine-derived polioviruses (VDPVs; with differences of >1% from the prototype Sabin viruses in the VP1 region) capable of causing outbreaks. These viruses might escape current diagnostic screening methods, and the risk for generation of these viruses should be reduced as much as possible (1, 9, 16).The tOPV vaccination campaigns have been very successful, since the number of countries with endemic wild poliovirus circulation decreased from >125 in 1988 to 4 in 2006, and wild type 2 poliovirus has likely been eradicated since 1999 (5). The tOPV vaccine, however, is known to be less immunogenic against type 1 and 3 polioviruses. After tOPV administration, the superior replicative capacity of the P2 vaccine strain interferes with effective replication of the other two serotype viruses in the human intestine (30). To eradicate wild P1 as well, vaccination with monovalent type 1 oral poliovirus vaccine (mOPV1) was introduced in the remaining countries where poliovirus is endemic, since this vaccine is more immunogenic for type 1 than the tOPV (4, 20).In 2005/2006, a clinical study was conducted in Egypt to compare the immunogenicity of mOPV1 with that of the tOPV in newborns (15). Newborns were vaccinated with mOPV1 or tOPV as soon as possible after birth and were challenged with mOPV1 4 weeks later. Vaccination with mOPV1 at birth resulted in a higher humoral and mucosal protection against P1 at day 28 than vaccination with tOPV at birth.In line with the recommendations of the WHO Polio Laboratory Network, we determined the antigenic characters of all the viruses shed by the newborns of the Egyptian study by using an intratypic differentiation (ITD) enzyme-linked immunosorbent assay (ELISA). The outcome of this analysis, an unexpectedly high percentage of AD isolates, prompted further investigation. To determine the possible presence of VDPVs and to gain insight into the genetic and antigenic evolution of the mOPV1 and tOPV isolates shed by the newborns in this study, we determined the sequences of the capsid regions of these isolates. We looked for correlates with antigenic change and rates of mutagenesis in the viruses and compared the evolution rates of the viruses shed by vaccinees of both study groups. We also linked the serological data collected during the study to the excretion of Sabin 1 isolates.     

Evolution of the Sabin strain of type 3 poliovirus in an immunodeficient patient during the entire 637-day period of virus excretion

A 20-year-old female hypogammaglobulinemic patient received monotypic Sabin 3 vaccine in 1962. The patient excreted type 3 poliovirus for a period of 637 days without developing any symptoms of poliomyelitis, after which excretion appeared to have ceased spontaneously. The evolution of Sabin 3 throughout the entire period of virus excretion was studied by characterization of seven sequential isolates from the patient. The isolates were analyzed in terms of their antigenic properties, virulence, sensitivity for growth at high temperatures, and differences in nucleotide sequence from the Sabin type 3 vaccine. The isolates followed a main lineage of evolution with a rate of nucleotide substitution that was very similar to that estimated for wild-type poliovirus during person-to-person transmission. There was a delay in the appearance of antigenic variants compared to sequential type 3 isolates from healthy vaccines, which could be one of the possible explanations for the long-term excretion of virus from the patient. The distribution of mutations in the isolates identified regions of the virus possibly involved in adaptation for growth in the human gut and virus persistence. None of the isolates showed a full reversion of the attenuated and temperature-sensitive phenotypes of Sabin 3. Information of this sort will help in the assessment of the risk of spread of virulent polioviruses from long-term excretors and in the design of therapies to stop long-term excretion. This will make an important contribution to the decision-making process on when to stop vaccination once wild poliovirus has been eradicated.     

Neurovirulence of type 1 polioviruses isolated from sewage in Japan.

Sixteen type 1 poliovirus strains were isolated from a sewage disposal plant located downstream of the Oyabe River in Japan between October 1993 and September 1995. The isolates were intratypically differentiated as vaccine-derived strains. Neutralizing antigenicity analysis with monoclonal antibodies and estimation of neurovirulence by mutant analysis by PCR and restriction enzyme cleavage (MAPREC) were performed for 13 type 1 strains of these isolates. The isolates were classified into three groups. Group I (five strains) had a variant type of antigenicity and neurovirulent phenotype. Group II (four strains) had the vaccine type of antigenicity and neurovirulent phenotype. Group III (four strains) had the vaccine type of antigenicity and an attenuated phenotype. Furthermore, it was demonstrated that the virulent isolates were neutralized by human sera obtained after oral poliomyelitis vaccine (OPV) administration, and the sera of rats immunized with inactivated poliovirus vaccine. Although vaccination was effective against virulent polioviruses, virulent viruses will continue to exist in the environment as long as OPV is in use.     

The antibody response of seronegative infants to inactivated poliovirus vaccine of enhanced potency

The immunogenic efficacy of inactivated poliovirus vaccine of enhanced potency (IPV-E), containing 40, 8 and 32 D-antigen units of types 1, 2 and 3, respectively, was evaluated in tritypic seronegative infants. Eighty infants aged six to 45 weeks, with no antibody detectable at a 1 : 4 dilution, were given two doses of a quadruple vaccine containing diphtheria-pertussis-tetanus (DPT) vaccine and IPV-E at intervals of four weeks (37 infants, group 1) or eight weeks (43 infants, group 2) between doses. All infants of group 2 responded with antibody to the three types of polioviruses. In group 1, all responded to types 1 and 3 antigens but only 36 responded to type 2. Antibody titres were higher in infants immunized at eight week than at four week intervals. Thus, two doses of IPV-E, especially when given eight weeks apart, are sufficient for primary immunization against poliomyelitis. If DPT vaccine of enhanced potency is combined with IPV-E, two doses of such a quadruple vaccine may be sufficient for primary immunization against four diseases; this possibility deserves evaluation.     

Human Circulating Antibody-Producing B Cell as a Predictive Measure of Mucosal Immunity to Poliovirus

Background

The “gold standard” for assessing mucosal immunity after vaccination with poliovirus vaccines consists in measuring virus excretion in stool after challenge with oral poliovirus vaccine (OPV). This testing is time and resource intensive, and development of alternative methods is a priority for accelerating polio eradication. We therefore evaluated circulating antibody-secreting cells (ASCs) as a potential means to evaluate mucosal immunity to poliovirus vaccine.

Methods

199 subjects, aged 10 years, and previously immunized repeatedly with OPV, were selected. Subjects were assigned to receive either a booster dose of inactivated poliovirus vaccine (IPV), bivalent OPV (bOPV), or no vaccine. Using a micro-modified whole blood-based ELISPOT assay designed for field setting, circulating poliovirus type-specific IgA- and IgG-ASCs, including gut homing α4β7+ ASCs, were enumerated on days 0 and 7 after booster immunization. In addition, serum samples collected on days 0, 28 and 56 were tested for neutralizing antibody titers against poliovirus types 1, 2, and 3. Stool specimens were collected on day 28 (day of bOPV challenge), and on days 31, 35 and 42 and processed for poliovirus isolation.

Results

An IPV dose elicited blood IgA- and IgG-ASC responses in 84.8 to 94.9% of subjects, respectively. In comparison, a bOPV dose evoked corresponding blood ASC responses in 20.0 to 48.6% of subjects. A significant association was found between IgA- and IgG-ASC responses and serum neutralizing antibody titers for poliovirus type 1, 2, 3 (p<0.001). In the IPV group, α4β7⁺ ASCs accounted for a substantial proportion of IgA-ASCs and the proportion of subjects with a positive α4β7⁺ IgA-ASC response to poliovirus types 1, 2 and 3 was 62.7%, 89.8% and 45.8%, respectively. A significant association was observed between virus excretion and α4β7⁺ IgA^- and/or IgG-ASC responses to poliovirus type 3 among immunized children; however, only a weak association was found for type 1 poliovirus.

Discussion

Our results suggest that virus-specific blood ASCs, especially for type 3 poliovirus, can serve as surrogate of mucosal immunity after vaccination. Further studies are needed to evaluate the duration of such memory responses and to assess the programmatic utility of this whole blood-based mucosal ASC testing for the polio eradication program.     

中国婴儿中脊灰母传抗体水平对两种疫苗免疫效果的影响

为了了解2月龄婴儿中针对脊髓灰质炎病毒的中和抗体水平,并探讨母传抗体对脊髓灰质炎减毒活疫苗(OPV)和灭活疫苗(IPV)免疫效果的影响。对416名2月龄婴儿分别接种OPV和IPV,采集免疫前后血清,用微量中和法检测血清中Ⅰ、Ⅱ、Ⅲ型脊髓灰质炎病毒中和抗体滴度,评价抗体GMT水平及4倍增长情况。检测结果显示,2月龄婴儿母传抗体Ⅰ、Ⅱ、Ⅲ型阳性率分别为45%、38.2%和17.5%,抗体GMT水平为9.0、8.1和5.2。经接种两组疫苗后,母传抗体阳性者与阴性者免后抗体GMT水平相比,OPV组无明显差异,IPV组阳性者略低于阴性者。在免前抗体滴度<1∶32人群中,OPV组免后抗体滴度4倍增长率及几何滴度增长倍数分别为:Ⅰ型93.6%、71.2;Ⅱ型98.2%、43.7;Ⅲ型91.7%、47.9;IPV组免后抗体滴度4倍增长率及几何滴度增长倍数分别为:Ⅰ型82%、9.4;Ⅱ型62.8%、5.1;Ⅲ型95.6%、11.7;在免前抗体滴度1∶32～1∶128人群中,OPV组Ⅰ型92.3%、23;Ⅱ型86.4%、13.9;Ⅲ型55.6%、4.1;IPV组Ⅰ型48%、2.5;Ⅱ型15%、0.9;Ⅲ型55.6%、2.7。目前中国2月龄婴儿免前脊灰抗体阳性率较高,尤其是Ⅰ、Ⅱ型。脊灰母传抗体对两种疫苗免疫效果有一定干扰,对IPV疫苗的影响较为明显。     

Immunoprophylaxis of poliomyelitis in Ukraine with the use of inactivated vaccine

In connection with the cessation of the circulation of "wild" poliovirus on the territory of the European region, including Ukraine, the strategy of the vaccinal prophylaxis of poliomyelitis is reviewed. Its main aims are the creation of a high level of the specific protection of the population, the prophylaxis of vaccine-associated paralytic poliomyelitis and a decrease in the intensity of the circulation vaccine polioviruses. These aims may be achieved only by the inclusion of vaccinations with inactivated poliomyelitis vaccine (IPV) into the immunization schedule. IPV "Imovax Polio" produced by the firm "Aventis Pasteur" (France) has been shown to have low reactogenicity and high effectiveness, especially with respect to type 3 poliovirus, under the conditions of Ukraine. On the basis of our studies all children, starting from the age of 3 months, are recommended to be vaccinated first with two injections of IPV, followed by further immunization with oral vaccine.     

Analysis of the human T-cell response to picornaviruses: identification of T-cell epitopes close to B-cell epitopes in poliovirus.

Little is known about the nature and specificity of T-cell-mediated responses to picornaviruses in humans. In this study, the nature of the T-cell response to seven picornaviruses, including polioviruses, coxsackieviruses B3 and B4, human rhinovirus 14, and encephalomyocarditis virus, was determined. Twenty-nine individuals responded to poliovirus type 3, coxsackievirus B3, and encephalomyocarditis virus by proliferation of T cells, and from such cultures, 130 virus-specific T-cell lines were established. T-cell lines generated in response to encephalomyocarditis virus were exclusively strain specific. However, the majority of T-cell lines established in response to viruses, other than encephalomyocarditis virus, were cross-reactive to each other. Their cross-reactivity was confirmed in 2 of the 30 picornavirus-specific clonally derived T-cell lines from two subjects, but the majority of these lines were serotype specific. T-cell epitopes adjacent to each of the B-cell antigenic sites in VP1 of poliovirus type 3 were identified. The response to the region adjacent to B-cell antigenic site 1 (residues 97 to 114) was dominant between individuals. The localization of this major CD4 T-cell epitope may permit the construction of chimeric viruses utilizing the natural picornavirus T-cell response to augment production of antibody specific for inserted sequences.     

Engineering a poliovirus type 2 antigenic site on a type 1 capsid results in a chimaeric virus which is neurovirulent for mice.

Poliovirus type 2 (PV-2) Lansing strain produces a fatal paralytic disease in mice after intracerebral injection, whereas poliovirus type 1 (PV-1) Mahoney strain causes disease only in primates. Atomic models derived from the three-dimensional crystal structure of the PV-1 Mahoney strain have been used to locate three antigenic sites on the surface of the virion. We report here the construction of type 1-type 2 chimaeric polioviruses in which antigenic site 1 from the PV-1 Mahoney strain was substituted by that of the PV-2 Lansing strain by nucleotide cassette exchange in a cloned PV-1 cDNA molecule. These chimaeras proved to have mosaic capsids with composite type 1 and type 2 antigenicity, and induced a neutralizing response against both PV-1 and PV-2 when injected into rabbits. Moreover, a six-amino-acid change in PV-1 antigenic site 1 was shown to be responsible for a remarkable host-range mutation in so far as one of the two type 1-type 2 chimaera was highly neurovirulent for mice.