Species-specific but not genotype-specific primary and secondary isotype-specific NSP4 antibody responses in gnotobiotic calves and piglets infected with homologous host bovine (NSP4[A]) or porcine (NSP4[B]) rotavirus

Evolution of Animal South American RVA Told by the NSP4 Gene E12 Genotype

Rotavirus A (RVA) possesses a genome of 11 double-stranded (ds) RNA segments, and each segment encodes one protein, with the exception of segment 11. NSP4 is a non-structural multifunctional protein encoded by segment 10 that defines the E-genotype. From the 31 E-genotypes described, genotype E12 has been described in Argentina, Uruguay, Paraguay, and Brazil in RVA strains infecting different animal species and humans. In this work, we studied the evolutionary relationships of RVA strains carrying the E12 genotype in South America using phylogenetic and phylodynamic approaches. We found that the E12 genotype has a South American origin, with a guanaco (Lama guanicoe) strain as natural host. Interestingly, all the other reported RVA strains carrying the E12 genotype in equine, bovine, caprine, and human strains are related to RVA strains of camelid origin. The evolutionary path and genetic footprint of the E12 genotype were reconstructed starting with the introduction of non-native livestock species into the American continent with the Spanish conquest in the 16th century. The imported animal species were in close contact with South American camelids, and the offspring were exposed to the native RVA strains brought from Europe and the new RVA circulating in guanacos, resulting in the emergence of new RVA strains in the current lineages' strongly species-specific adaption. In conclusion, we proposed the NSP4 E12 genotype as a genetic geographic marker in the RVA strains circulating in different animal species in South America.

Probiotic as Adjuvant Significantly Improves Protection of the Lanzhou Trivalent Rotavirus Vaccine against Heterologous Challenge in a Gnotobiotic Pig Model of Human Rotavirus Infection and Disease

This preclinical study in the gnotobiotic (Gn) pig model of human rotavirus (HRV) infection and disease evaluates the effect of probiotic Lactobacillus rhamnosus GG (LGG) as a mucosal adjuvant on the immunogenicity and cross-protective efficacy of the Lanzhou live oral trivalent (G2, G3, G4) vaccine (TLV, aka LLR3). Gn pigs were immunized with three doses of TLV with or without concurrent administration of nine doses of LGG around the time of the first dose of the TLV vaccination, and were challenged orally with the virulent heterotypic Wa G1P[8] HRV. Three doses of TLV were highly immunogenic and conferred partial protection against the heterotypic HRV infection. LGG significantly enhanced the intestinal and systemic immune responses and improved the effectiveness of protection against the heterotypic HRV challenge-induced diarrhea and virus shedding. In conclusion, we demonstrated the immune-stimulating effects of probiotic LGG as a vaccine adjuvant and generated detailed knowledge regarding the cross-reactive and type-specific antibody and effector B and T cell immune responses induced by the TLV. Due to the low cost, ease of distribution and administration, and favorable safety profiles, LGG as an adjuvant has the potential to play a critical role in improving rotavirus vaccine efficacy and making the vaccines more cost-effective.

Impact of vaccination on the molecular epidemiology and evolution of group A rotaviruses in Latin America and factors affecting vaccine efficacy

Despite high rotavirus (RV) vaccine coverage (∼83%) and good effectiveness (∼77%) against RV-diarrhea hospitalization, RV is still contributing to the burden of diarrhea that persists in hospital settings in several Latin American countries, where RV vaccination is being implemented. Due to the extensive genomic and antigenic diversity, among co-circulating human RV, a major concern has been that the introduction of RV vaccination could exert selection pressure leading to higher prevalence of strains not included in the vaccines and/or emergence of new strains, thus, reducing the efficacy of vaccination. Here we review the molecular epidemiology of RV in Latin America and explore issues of RV evolution and selection in light of vaccination. We further explore etiologies behind the large burden of diarrhea remaining after vaccination in some countries and discuss plausible reasons for vaccine failures.

Correlates of protection against human rotavirus disease and the factors influencing protection in low-income settings

Rotaviruses (RV) are the leading cause of gastroenteritis in infants and children worldwide and are associated with high mortality predominately in low-income settings. The virus is classified into G and P serotypes and further into P genotypes based on differences in the surface-exposed proteins VP7 and VP4, respectively. Infection results in a variable level of protection from subsequent reinfection and disease. This protection is predominantly homotypic in some settings, whereas broader heterotypic protection is reported in other cohorts. Two antigenically distinct oral RV vaccines are licensed and are being rolled out widely, including in resource-poor setting, with funding provided by the GAVI alliance. First is a monovalent vaccine derived from a live-attenuated human RV strain, whereas the second is a pentavalent bovine-human reassortment vaccine. Both vaccines are highly efficacious in high-income settings, but greatly reduced levels of protection are reported in low-income countries. Here, the current challenges facing mucosal immunologists and vaccinologists aiming to define immunological correlates and to understand the variable levels of protection conferred by these vaccines in humans is considered. Such understanding is critical to maximize the public health impact of the current vaccines and also to the development of the next generation of RV vaccines, which are needed.

Inclusion of a universal tetanus toxoid CD4(+) T cell epitope P2 significantly enhanced the immunogenicity of recombinant rotavirus ΔVP8* subunit parenteral vaccines

Currently available live oral rotavirus vaccines, Rotarix(®) and RotaTeq(®), are highly efficacious in developed countries. However, the immunogenicity and efficacy of such vaccines in some developing countries are low. We reported previously that bacterially-expressed rotavirus ΔVP8* subunit vaccine candidates with P[8], P[4] or P[6] specificity elicited high-titer virus neutralizing antibodies in animals immunized intramuscularly. Of note was the finding that antibodies induced with the P[8]ΔVP8* vaccine neutralized both homotypic P[8] and heterotypic P[4] rotavirus strains to high titer. To further improve its vaccine potential, a tetanus toxoid universal CD4(+) T cell epitope P2 was introduced into P[8] or P[6]ΔVP8* construct. The resulting recombinant fusion proteins expressed in Escherichia coli were of high solubility and were produced with high yield. Two doses (10 or 20 μg/dose) of the P2-P[8]ΔVP8* vaccine or P2-P[6]ΔVP8* vaccine with aluminum phosphate adjuvant elicited significantly higher geometric mean homologous neutralizing antibody titers than the vaccines without P2 in intramuscularly immunized guinea pigs. Interestingly, high levels of neutralizing antibody responses induced in guinea pigs with 3 doses of the P2-P[8]ΔVP8* vaccine persisted for at least 6 months. Furthermore, in the gnotobiotic piglet challenge study, three intramuscular doses (50 μg/dose) of the P2-P[8]ΔVP8* vaccine with aluminum phosphate adjuvant significantly delayed the onset of diarrhea and significantly reduced the duration of diarrhea and the cumulative diarrhea score after oral challenge with virulent human rotavirus Wa (G1P[8]) strain. The P2-P[8]ΔVP8* vaccine induced serum virus neutralizing antibody and VP4-specific IgG antibody production prechallenge, and primed the pigs for higher antibody and intestinal and systemic virus-specific IFN-γ producing CD4(+) T cell responses postchallenge. These two subunit vaccines could be used at a minimum singly or preferably in bivalent formulation to provide antigenic coverage of most of the G types of global importance.

Virulence-associated genome mutations of murine rotavirus identified by alternating serial passages in mice and cell cultures

Although significant clinical efficacy and safety of rotavirus vaccines were recently revealed in many countries, the mechanism of their attenuation is not well understood. We passaged serially a cell culture-adapted murine rotavirus EB strain in mouse pups or in cell cultures alternately and repeatedly and fully sequenced all 11 genes of 21 virus samples passaged in mice or in cell cultures. Sequence analysis revealed that mouse-passaged viruses that regained virulence almost consistently acquired four kinds of amino acid (aa) substitutions in VP4 and substitution in aa 37 (Val to Ala) in NSP4. In addition, they gained and invariably conserved the 3' consensus sequence in NSP1. The molecular changes occurred along with the acquisition of virulence during passages in mice and then disappeared following passages in cell cultures. Intraperitoneal injection of recombinant NSP4 proteins confirmed the aa 37 site as important for its diarrheagenic activity in mice. These genome changes are likely to be correlated with rotavirus virulence.

IMPORTANCE

Serial passage of a virulent wild-type virus in vitro often results in loss of virulence of the virus in an original animal host, while serial passage of a cell culture-adapted avirulent virus in vivo often gains virulence in an animal host. Actually, live attenuated virus vaccines were originally produced by serial passage in cell cultures. Although clinical efficacy and safety of rotavirus vaccines were recently revealed, the mechanism of their attenuation is not well understood. We passaged serially a murine rotavirus by alternating switch of host (mice or cell cultures) repeatedly and sequenced the eleven genes of the passaged viruses to identify mutations associated with the emergence or disappearance of virulence. Sequence analysis revealed that changes in three genes (VP4, NSP1, and NSP4) were associated with virulence in mice. Intraperitoneal injection of recombinant NSP4 proteins confirmed its diarrheagenic activity in mice. These genome changes are likely to be correlated with rotavirus virulence.

Resistance to rotavirus infection in adult volunteers challenged with a virulent G1P1A[8] virus correlated with serum immunoglobulin G antibodies to homotypic viral proteins 7 and 4

BACKGROUND

In a study performed in 1983, 18 adult volunteers received oral challenge with the virulent human rotavirus strain D (G1P1A[8],NSP4[B]). To identify correlates of resistance to rotavirus infection, we analyzed levels of serum immunoglobulin (Ig) A and IgG antibodies to various rotaviral antigens in 16 of the 18 volunteers.

METHODS

We used immunocytochemical assays that involved a total of 16 different recombinant baculoviruses, with each baculovirus expressing one of the following major serotype/genotype rotavirus proteins for the serologic assays: (1) viral protein (VP) 4 with P1A[8], P1B[4], P2A[6], P3[9], or P4[10] specificity; (2) VP7 with G1-G4 or G9 specificity; and (3) nonstructural viral protein (NSP) 4 with genotype A, B, C, or D specificity.

RESULTS

The prechallenge titers of IgG antibody to VP7 types G1, G3, G4, and G9; VP4 types P1A[8], P1B[4], P2A[6], and P4[10]; and NSP4 type [A] in the group of noninfected volunteers (n = 11) were significantly higher than those in the group of infected volunteers (n = 5; of these 5 volunteers, 4 were symptomatically infected). Moreover, logistic regression analysis showed that resistance to rotavirus infection most closely correlated with higher prechallenge titers of IgG antibody to homotypic VP7 (G1) and VP4 (P1A[8]).

CONCLUSIONS

These results suggest that protection against rotavirus infection and disease is primarily VP7/VP4 homotypic and, to a lesser degree, heterotypic.

A longitudinal cohort study in calves evaluated for rotavirus infections from 1 to 12 months of age by sequential serological assays

Using an immunocytochemical staining assay involving six different recombinant baculoviruses with each expressing one of the major bovine rotavirus VP7 (G6, G8 and G10) and VP4 (P6[1], P7[5] and P8[11]) serotypes, we analyzed IgG antibody responses to individual proteins in archival serum samples collected from 31 calves monthly from 1 to 12 months of age during 1974-1975 in Higley, Arizona. Seroresponses to VP7 and VP4, as determined by a fourfold or greater antibody response, were not always elicited concurrently following infection: in some calves, (1) seroresponses to VP7 were detected earlier than to VP4 or vice versa; and (2) a subsequent second seroresponse was detected for VP7 or VP4 only. In addition, a second infection was more likely to be caused by different G and/or P types. Analyses of serum samples showed that the most frequent G-P combination was G8P6[1], followed by G8P7[5], G8P8[11] and G6P6[1].

Rotavirus genotypes in Slovenia: Unexpected detection of G8P[8] and G12P[8] genotypes

A rotavirus surveillance study was undertaken in Slovenia from December 2005 to March 2006. Stool samples from 114 children hospitalized with acute viral gastroenteritis were collected from two main Slovenian hospitals. These confirmed rotavirus-positive samples were selected for a rotavirus G and P genotype prevalence study. Six untypable strains of genotype G were further analyzed with sequencing of the VP7, VP8*, and NSP4 genes. The findings of the study were that the G1 genotype was the most prevalent, found in 72 samples (63.2%), followed by G9 in 26 samples (22.8%), G4 in 10 samples (8.8%), and G3 in 2 samples (1.7%). All G genotypes were combined with the P[8] genotype specificity. After sequence analysis, one G8 and two G12 genotypes were also characterized. In a VP7-based phylogenetic analysis, the G8P[8] strain (SI-885/06) was more closely related to the Cody I801 bovine strain than to other human strains. Both G12 strains (SI-264/06 and SI-403/06) were shown to belong to the Se585 G12 cluster. In the VP8* phylogenetic tree, all analyzed strains except one, belonged to the P[8] lineage II and shared high identity in amino acid sequence. All characterized strains were clustered into the NSP4 genotype B. The molecular characterization of this G8 strain supports the theory of interspecies transmission of rotaviruses and animal-human genome reassortment. This is the first report on rotavirus G12 detection in Slovenia.

Evaluation of serum antibody responses against the rotavirus nonstructural protein NSP4 in children after rhesus rotavirus tetravalent vaccination or natural infection

The immune response elicited by the rotavirus nonstructural protein NSP4 and its potential role in protection against rotavirus disease are not well understood. We investigated the serological response to NSP4 and its correlation with disease protection in sera from 110 children suffering acute diarrhea, associated or not with rotavirus, and from 26 children who were recipients of the rhesus rotavirus tetravalent (RRV-TV) vaccine. We used, as antigens in an enzyme-linked immunosorbent assay (ELISA), affinity-purified recombinant NSP4 (residues 85 to 175) from strains SA11, Wa, and RRV (genotypes A, B, and C, respectively) fused to glutathione S-transferase. Seroconversion to NSP4 was observed in 54% (42/78) of the children who suffered from natural rotavirus infection and in 8% (2/26) of the RRV-TV vaccine recipients. Our findings indicate that NSP4 evokes significantly (P < 0.05) higher seroconversion rates after natural infection than after RRV-TV vaccination. The serum antibody levels to NSP4 were modest (titers of < or = 200) in most of the infected and vaccinated children. A heterotypic NSP4 response was detected in 48% of the naturally rotavirus-infected children with a detectable response to NSP4. Following natural infection or RRV-TV vaccination, NSP4 was significantly less immunogenic than the VP6 protein when these responses were independently measured by ELISA. A significant (P < 0.05) proportion of children who did not develop diarrhea associated with rotavirus had antibodies to NSP4 in acute-phase serum, suggesting that serum antibodies against NSP4 might correlate with protection from rotavirus diarrhea. In addition, previous exposures to rotavirus did not affect the NSP4 seroconversion rate.

Mucosal immunization with a ricin toxin B subunit-rotavirus NSP4 fusion protein stimulates a Th1 lymphocyte response

The castor-oil plant Ricinus communis A-B dimeric toxin B subunit (RTB) was genetically linked at its N-terminus with a 90 amino acid peptide from simian rotavirus SA-11 non-structural protein NSP4(90) and produced in Escherichia coli BL21 cells. Biologically active recombinant NSP4(90)-RTB fusion protein was shown to bind glycoprotein asialofetuin receptor molecules in an in vitro enzyme-linked immunosorbent assay (ELISA). Oral inoculation of the purified NSP4(90)-RTB ligand-antigen fusion protein delivered the chimeric protein to intestinal epidermal cells for mucosal immunization against rotavirus infection. Mice fed the NSP4(90)-RTB fusion protein generated higher humoral and intestinal antibody titers than mice inoculated with NSP4(90) alone. Titers of serum IgG2a antibodies were significantly higher than IgG1 titers suggesting a dominant Th1 lymphocyte immune response. ELISA measurement of cytokines secreted from splenocyte isolated from immunized mice confirmed NSP4(90)-RTB fusion protein stimulates a strong Th1 cell-mediated immune response. The experimental results demonstrate that the ricin toxin B subunit N-terminus can be used as a site for delivery of virus antigens to the gut associated lymphoid tissues for RTB-mediated immune stimulation of antiviral mucosal immune responses.