Cell-mediated immune responses in cattle vaccinated with a vaccinia virus recombinant expressing the nucleocapsid protein of rinderpest virus

Assessment of the control measures of category A diseases of the Animal Health Law: Infection with rinderpest virus (Rinderpest)

EFSA received a mandate from the European Commission to assess the effectiveness of control measures against diseases included in the Category A list according to Regulation (EU) 2016/429 on transmissible animal diseases ('Animal Health Law'). This opinion belongs to a series of opinions where these control measures are assessed, with this opinion covering the assessment of control measures for rinderpest (RP), the only animal disease to have been globally eradicated. In this opinion, the AHAW Panel reviewed the effectiveness of: (i) clinical and laboratory sampling procedures, (ii) monitoring period and (iii) the minimum radius of the protection and surveillance zone, and the minimum length of time the measures should be applied in these zones. The general methodology used for this series of opinions has been published elsewhere. The transmission kernels used for the assessment of the minimum radius of the protection and surveillance zones are shown. Several scenarios for which control measures had to be assessed were agreed prior to the assessment. Considering that RP has been eradicated globally, a re-emergence that is not stopped in its early phases could have a devastating impact on animal health and the economy. The panel concludes that no suitable strategies are available to entirely mitigate the risk associated with granting derogations from killing of animals in an affected establishment or for animal movements. Therefore, the panel recommends to not grant any derogations. The monitoring period of 21 days was assessed as effective, except for the hypothetical first re-emergence of RP, when lack of awareness and diagnostic capability may extend the time to detection. It was concluded that the protection and the surveillance zones would contain 90% and > 99%, respectively, of the infections from an affected establishment. Enlarging the protection zone to 4 km would contain the disease spread with 95% probability.

Peste des Petits Ruminants Virus-Like Particles Induce a Potent Humoral and Cellular Immune Response in Goats

Peste des petits ruminants is a highly contagious acute or subacute disease of small ruminants caused by the peste des petits ruminants virus (PPRV), and it is responsible for significant economic losses in animal husbandry. Vaccination represents the most effective means of controlling this disease, with virus-like particle (VLP) vaccines offering promising vaccine candidates. In this study, a PPRV VLP-based vaccine was developed using a baculovirus expression system, allowing for the simultaneous expression of the PPRV matrix (M), hemagglutinin (H), fusion (F) and nucleocapsid (N) proteins in insect cells. Immunization of mice and goats with PPRV VLPs elicited a robust neutralization response and a potent cellular immune response. Mouse studies demonstrated that VLPs induced a more robust IFN-γ response in CD4⁺ and CD8⁺ T cells than PPRV Nigeria 75/1 and recruited and/or activated more B cells and dendritic cells in inguinal lymph nodes. In addition, PPRV VLPs induced a strong Th1 class response in mice, as indicated by a high IgG2a to IgG1 ratio. Goat studies demonstrated that PPRV VLPs can induce the production of antibodies specific for F and H proteins and can also stimulate the production of virus neutralizing antibodies to the same magnitude as the PPRV Nigeria 75/1 vaccine. Higher amounts of IFN-γ in VLP-immunized animal serum suggested that VLPs also elicited a cellular immune response in goats. These results demonstrated that VLPs elicit a potent immune response against PPRV infection in small ruminants, making PPRV VLPs a potential candidate for PPRV vaccine development.

Epidemiological and pathological study of feline morbillivirus infection in domestic cats in Japan

BACKGROUND

Feline morbillivirus (FmoPV) is a novel paramyxovirus found to infect domestic cats. FmoPV has been isolated in several countries in Asia and Europe and is considered to have genetic diversity. Also, it is suspected to be associated with feline renal diseases including tubulointerstitial nephritis (TIN), which affects domestic cats with a high incidence rate.

RESULTS

To clarify the state of FmoPV infection among domestic cats in Japan, an epidemiological survey was conducted. Twenty-one out of 100 cats were found to have serum antibodies (Ab) against FmoPV-N protein by indirect immunofluorescence assay (IF) using FmoPV-N protein-expressing HeLa cells. Twenty-two of the cats were positive for FmoPV RNA in the urine and/or renal tissues. In total, 29 cats were positive for Ab and/or viral RNA. These FmoPV-infected cats were classified into three different phases of infection: RNA+/Ab + (14 cats), RNA+/Ab- (8 cats) and RNA-/Ab + (7 cats). In immunohistochemistry (IHC), 19 out of 29 cats were positive for FmoPV-N protein in kidney tissues; however, the FmoPV-N protein was located in the inflammatory lesions with severe grade in only four out of the 19 cats. Since 15 out of 29 infected cats were positive for viral RNA and Ab, approximately half of the infected cats were persistently infected with FmoPV.

CONCLUSIONS

A statistically significant difference was observed between infection of FmoPV and the presence of inflammatory changes in renal lesions, indicating a relationship between FmoPV infection and feline renal diseases. However, we could not obtain histopathological evidence of a relationship between FmoPV infection and TIN.

Peste des petits ruminants virus infection of small ruminants: a comprehensive review

Peste des petits ruminants (PPR) is caused by a Morbillivirus that belongs to the family Paramyxoviridae. PPR is an acute, highly contagious and fatal disease primarily affecting goats and sheep, whereas cattle undergo sub-clinical infection. With morbidity and mortality rates that can be as high as 90%, PPR is classified as an OIE (Office International des Epizooties)-listed disease. Considering the importance of sheep and goats in the livelihood of the poor and marginal farmers in Africa and South Asia, PPR is an important concern for food security and poverty alleviation. PPR virus (PPRV) and rinderpest virus (RPV) are closely related Morbilliviruses. Rinderpest has been globally eradicated by mass vaccination. Though a live attenuated vaccine is available against PPR for immunoprophylaxis, due to its instability in subtropical climate (thermo-sensitivity), unavailability of required doses and insufficient coverage (herd immunity), the disease control program has not been a great success. Further, emerging evidence of poor cross neutralization between vaccine strain and PPRV strains currently circulating in the field has raised concerns about the protective efficacy of the existing PPR vaccines. This review summarizes the recent advancement in PPRV replication, its pathogenesis, immune response to vaccine and disease control. Attempts have also been made to highlight the current trends in understanding the host susceptibility and resistance to PPR.

Developing vaccines against foot-and-mouth disease and some other exotic viral diseases of livestock

Vaccines remain the main tool for the control of livestock viral diseases that pose a serious threat to animal and occasionally human health, reduce food security, distort trade in animals and their products, and undermine agricultural development in poor countries. Globalization and climate change increase the likelihood for new patterns of emergence and spread of livestock viruses. Conventionally attenuated and killed virus products have had spectacular success, and recent examples include the global eradication of rinderpest and the control of bluetongue in the UK and northern Europe. However, in many cases, livestock vaccines could benefit from improvement in some properties (e.g. stability, speed of onset and duration of immunity, and breadth of cross-protection to different serotypes or strains) and in some cases are not available at all. Compared with human vaccines, uptake of livestock products is highly cost-sensitive and their use may also need to be compatible with post-vaccination screening methods to determine whether or not animals continue to be infected. Requirements and prospects for new or improved vaccines are described for some priority viral diseases with potential for transboundary spread, particularly for foot-and-mouth disease.

Rescue of a chimeric rinderpest virus with the nucleocapsid protein derived from peste-des-petits-ruminants virus: use as a marker vaccine

The nucleocapsid (N) protein of all morbilliviruses has a highly conserved central region that is thought to interact with and encapsidate the viral RNA. The C-terminal third of the N protein is highly variable among morbilliviruses and is thought to be located on the outer surface and to be available to interact with other viral proteins such as the phosphoprotein, the polymerase protein and the matrix protein. Using reverse genetics, a chimeric rinderpest virus (RPV)/peste-des-petits-ruminants virus (PPRV) was rescued in which the RPV N gene open reading frame had been replaced with that of PPRV (RPV-PPRN). The chimeric virus maintained efficient replication in cell culture. Cattle vaccinated with this chimeric vaccine showed no adverse reaction and were protected from subsequent challenge with wild-type RPV, indicating it to be a safe and efficacious vaccine. The carboxyl-terminal variable region of the rinderpest N protein was cloned and expressed in Escherichia coli. The expressed protein was used to develop an indirect ELISA that could clearly differentiate between RPV- and PPRV-infected animals. The possibility of using this virus as a marker vaccine in association with a new diagnostic ELISA in the rinderpest eradication programme is discussed.

Idiotypic T cells specific for Morbillivirus nucleocapsid protein process and present their TCR to cognate anti-idiotypic CD8+ T cells

CD8(+) T cells are activated by the presentation of antigenic peptide through MHC class I molecules. Newly synthesized proteins formed as defective ribosomal products (DRiPs) can act as a major source of antigenic peptides for MHC class I presentation pathway. Majority of these peptides are generated from the intracellular degradation of self antigens. In the present study, we have shown that newly synthesized T cell receptor (TCR) beta chains formed as DRiPs in T cells are ubiquitinated and degraded by the proteasomes. These TCR-DRiPs are processed and presented by activated T cells to cognate anti-idiotypic CD8(+) T cells. Presentation of TCR idiopeptide (peptide derived from the variable region of idiotypic TCR) by activated T cells leads to Bcl-2 expression and cytokine secretion by anti-idiotypic CD8(+) T cells. Presentation of intracellular antigen by T cells may have important implications in immunoregulation, control of lymphotropic virus infection and autoimmune diseases.

The Plowright vaccine strain of Rinderpest virus has attenuating mutations in most genes

The currently used vaccine strain of Rinderpest virus was derived by serial passage of the highly virulent Kabete ‘O’ strain (KO). A full-length cDNA copy of the KO strain was made from which a virus identical in pathogenicity to the wild-type virus was rescued. A series of chimeric viruses was prepared in which the coding sequences for the N, P, F, H or L proteins were replaced with the corresponding sequences from the vaccine strain. The KO-based virus with the vaccine strain H gene and that with the carboxy-terminal half of the L gene replaced with the corresponding sequence from the vaccine strain retained all or almost all of the virulence of the original KO virus. Animals infected with the KO-based virus containing the vaccine strain N, P or F gene, or the amino-terminal half of the L gene, developed high and prolonged pyrexia and leukopenia, but with reduced or absent lesions and other clinical signs; although partially attenuated, none was nearly as attenuated as the vaccine strain itself. These data indicate that the high attenuation and stability of the current vaccine are due to the accumulation of a number of separate mutations, none of which is itself so sufficiently debilitating that there is strong selective pressure in favour of the revertant.

Activated mouse T-cells synthesize MHC class II, process, and present morbillivirus nucleocapsid protein to primed T-cells

A pivotal step in the initiation of T-cell immunity is the presentation of antigenic peptides by major histocompatibility complex (MHC) expressed on antigen presenting cells. The expression of MHC class II molecules by mouse T-cells has not been shown unequivocally. In the present work, we demonstrate that activated mouse T-cells synthesize MHC class II molecules de novo and express them on their surface. Further, we have demonstrated that in vitro activated T-cells take up extra-cellular soluble nucleocapsid protein of a morbillivirus. The internalized antigen goes to antigen processing compartment as shown by co-localization of antigen and LAMP-1 using confocal microscopy. We show that activated T-cells express H2M, a chaperone molecule known to have a role in antigen presentation. Further, we demonstrate that activated T-cells process and present internalized extra-cellular antigen to primed T-cells as shown by IL-2 secretion and in vitro proliferation. The presentation of antigen by T-cells may have implications in immuno-regulation, control of infection by lymphotropic viruses and maintenance of immunological memory.

Cytotoxic T cell epitope in cattle from the attachment glycoproteins of rinderpest and peste des petits ruminants viruses

The surface glycoproteins of rinderpest virus (RPV) confer protective immunity in cattle. We demonstrated that cattle immunized with a recombinant extracellular baculovirus expressing the hemagglutinin (H) protein of RPV (rECV-H) generate virus neutralizing antibody responses, bovine leukocyte antigen (BoLA) class II restricted helper T cell responses and BoLA class I restricted cytotoxic T cell (CTL) responses against RPV-H and hemagglutinin-neuraminidase (HN) glycoprotein of closely related Peste des petits ruminants virus (PPRV). In this study, employing autologous skin fibroblasts transiently expressing truncations of H and HN in a BoLA class I restricted lymphoproliferation assay, we have mapped a highly homologous domain (amino acids 400-423) on these proteins harboring a CTL epitope. Subsequently, based on sequence comparison with available BoLA class I binding motifs, we have identified a BoLA-A11 binding motif (amino acids 408-416) in the stimulatory domain. Autologous cells pulsed with a synthetic peptide corresponding to this sequence stimulated CTLs from rECV-H immunized as well as tissue culture attenuated RPV vaccinated cattle of different breeds and parentage. This is the first epitope identified in cattle on the attachment glycoproteins of RPV and PPRV.

Detection of equine arteritis virus (EAV)-specific cytotoxic CD8+ T lymphocyte precursors from EAV-infected ponies

Equine arteritis virus (EAV) causes a systemic infection in equids with variable outcome, ranging from subclinical infections to severe disease, and also has the capacity to induce abortion in pregnant mares and persistent infections in stallions. The serum virus-neutralizing antibody response that invariably develops in the infected animal lasts for many months or years and is believed to play an important role in virus clearance. However, very little is known about cellular immunity against EAV because of a lack of methods for evaluating these immune responses. In the present study, we describe methods for detecting cytotoxic T lymphocyte (CTL) precursors in the peripheral blood of EAV-convalescent ponies using a 51Cr release cytolysis assay. Primary equine dermal cells, used as CTL targets, were shown to express MHC I but not MHC II and to retain 51Cr efficiently and support EAV replication. Peripheral blood mononuclear cells (PBMC) collected from EAV-convalescent ponies that had been incubated with or without live EAV were used as effectors. EAV-induced PBMC cultures showed evidence of expansion and activation of lymphoblasts, with an increase in the CD8+/CD4+ ratio in comparison with mock-induced PBMC. The cytotoxicity induced by EAV-stimulated PBMC was virus specific, showed genetic restriction, was mediated by CD8+ T lymphocytes and could be detected for periods of 4 months to more than 1 year post-infection. These findings and methods will hopefully contribute to an understanding of virus–host interactions in horses, in particular the mechanisms of virus clearance occurring during EAV infection.

Cytotoxic T-lymphocyte activity specific for hemagglutinin (H) protein of canine distemper virus in dogs

Cytotoxic T-lymphocyte (CTL) responses to hemagglutinin (H) protein of canine distemper virus (CDV) were evaluated in dogs using the replication-deficient adenovirus protein expression system. Skin fibroblasts were isolated from two dogs and were infected with recombinant adenovirus bearing the CDV-H gene (Ade-CDVH). CTL assay was performed using fibroblasts expressing CDV-H protein as target cells and peripheral blood lymphocytes (PBL) collected from the same dogs one week after immunization of CDV as effector cells. Specific cytotoxic activity was observed against autologous but not heterologous fibroblasts expressing CDV-H protein. These results indicate that the CTL epitope(s) were localized in the H protein.

Recombinant hemagglutinin protein of rinderpest virus expressed in insect cells induces cytotoxic T-cell responses in cattle

Rinderpest virus (RPV), a member of the genus Morbillivirus within the Paramyxoviridae family, causes a highly contagious and often fatal disease known as rinderpest in wild and domestic ruminants. The envelope of the virus contains two surface glycoproteins, namely the hemagglutinin (H) and the fusion (F) proteins, both of which have been shown to confer protective immunity in animals. In this paper, we demonstrate that single administration of low doses of recombinant H protein of RPV expressed in insect cells in the form of extracellular virus induces long lasting bovine leukocyte antigen class I restricted cytotoxic T-cell (CTL) responses in cattle in the absence of adjuvant. This is the first report of CTL responses in cattle against one of the protective antigens of RPV.

Identification of a cytotoxic T-cell epitope on the recombinant nucleocapsid proteins of Rinderpest and Peste des petits ruminants viruses presented as assembled nucleocapsids

The nucleocapsid protein (N) of morbilliviruses is not only a major structural protein but also the most abundant protein made in infected cells. We overexpressed the N proteins of Rinderpest virus and Peste des petits ruminants virus in E. coli, which assemble into nucleocapsids in the absence of viral RNA that resemble nucleocapsids made in the virus-infected cells. Employing these assembled structures resembling subviral particles, we studied the induction of both the antibody response and the cytotoxic T-lymphocyte (CTL) response in a murine model (BALB/c). A single dose of the purified recombinant nucleocapsids of both viruses in the absence of an adjuvant induces a strong CTL response. The CTLs generated are antigen specific and cross-reactive with respect to each virus and, furthermore, this CTL response is MHC class I restricted. Based on the prediction for H-2(d)-restricted T-cell motifs we tested the lysis of transfected P815 (H-2(d)) cells expressing a nine amino acid potential CTL epitope, by splenic T cells in vitro restimulated with bacterially expressed RPV or PPRV N proteins. We extended our study to the bovine system both to analyze the immunogenicity of these recombinant proteins in the natural hosts and to show that PBMC from cattle vaccinated with Rinderpest vaccine proliferate in vitro, in response to restimulation with soluble nucleocapsid proteins. Furthermore, the murine CTL epitope functions in the bovine system as a cytotoxic T-cell epitope. This sequence, which is conserved in the N proteins of morbilliviruses, conforms well to the predicted algorithm for some of the most common BoLA CTL antigenic peptides.

Recovery and characterization of a chimeric rinderpest virus with the glycoproteins of peste-des-petits-ruminants virus: homologous F and H proteins are required for virus viability

Rinderpest (RP) and peste-des-petits-ruminants (PPR) are two important diseases of domestic ruminants. To improve on currently available vaccines against PPR, we have created cDNA copies of the RP virus genome in which either the fusion (F) or hemagglutinin (H) gene, or both, was replaced with the corresponding gene from PPR virus. It was necessary to develop a modified rescue system in which the T7 RNA polymerase was provided by a recombinant fowlpox virus and the entire rescue procedure took place in Vero cells before we could obtain live virus from these chimeric constructs. No virus was recovered when only one of the glycoprotein genes was changed, but a chimeric virus containing both F and H genes from PPR virus was reproducibly rescued from cDNA, indicating that a virus-specific functional interaction takes place between the F and H proteins. The rescued virus expressing the PPR glycoproteins grew more slowly in tissue culture than either parental virus and formed abnormally large syncytia. Goats infected with the chimera showed no adverse reaction, as assessed by clinical signs, temperature, leukocyte count, virus isolation, and serology, and were protected from subsequent challenge with wild-type PPR virus.

Vaccination of cattle with attenuated rinderpest virus stimulates CD4(+) T cell responses with broad viral antigen specificity

The immune responses of cattle inoculated with either a virulent or an attenuated vaccine strain of rinderpest virus (RPV) were examined by measuring the proliferation of peripheral blood mononuclear cells (PBMC) to whole RPV antigen preparations and to individual RPV major structural proteins expressed using recombinant adenoviruses. Responses to the T cell mitogen concanavalin A (ConA) were also measured as a control to monitor non-specific effects of infection with RPV on T cell responses. Infection with the vaccine strain of RPV was found to induce a strong CD4(+) T cell response. A specific response was detected to all RPV proteins tested, namely the haemagglutinin (H), fusion (F), nucleocapsid (N) and matrix (M) proteins, in animals vaccinated with the attenuated strain of the virus. No one protein was found to be dominant with respect to the induction of T cell proliferative responses. As expected, vaccination of cattle with an unrelated virus vaccine, a capripox vaccine, failed to produce a response to RPV antigens. While profound suppression of T cell responses was observed following infection with the virulent strain of RPV, no evidence of impairment of T cell responsiveness was observed following RPV vaccination, or on subsequent challenge of vaccinated animals with virulent virus.

Identification of T-helper cell epitopes in the hypervariable region of the nucleocapsid (N) protein of rinderpest virus (RPV) in cattle

The proliferative responses to synthetic peptides by lymphocytes derived from rinderpest virus (RPV)-infected cattle, the natural host for RPV, were assayed by determining [3H]thymidine incorporation into the DNA. In eight out of twelve cattle tested, significant responses were detected to peptides representing amino acids 452-501 in the C-terminal hypervariable region of the virus nucleocapsid (N) protein. It appears that helper T-cell epitope(s) for cattle which can be broadly recognized within an MHC diverse population, exists in this region of the protein.

DNA vaccine encoding nucleocapsid and surface proteins of wild type canine distemper virus protects its natural host against distemper

Canine distemper virus (CDV), a member of the genus Morbillivirus induces a highly infectious, frequently lethal disease in dogs and other carnivores. Current vaccines against canine distemper consisting of attenuated viruses have been in use for many years and have greatly reduced the incidence of distemper in the dog population. However, certain strains may not guarantee adequate protection and others can induce post vaccinal encephalitis. We tested a DNA vaccine for its ability to protect dogs, the natural host of CDV, against distemper. We constructed plasmids containing the nucleocapsid, the fusion, and the attachment protein genes of a virulent canine distemper virus strain. Mice inoculated with these plasmids developed humoral and cellular immune responses against CDV antigens. Dogs immunized with the expression plasmids developed virus-neutralizing antibodies. Significantly, vaccinated dogs were protected against challenge with virulent CDV, whereas unvaccinated animals succumbed to distemper.

Long-term protective immunity to rinderpest in cattle following a single vaccination with a recombinant vaccinia virus expressing the virus haemagglutinin protein

A recombinant vaccine, produced by using a highly attenuated smallpox vaccine (LC16mO) as a vector and which expresses the rinderpest virus (RPV) haemagglutinin protein, has been developed. The properties of this vaccine, including its heat stability, efficacy in short-term trials, safety and genetic stability, have been confirmed in an earlier report. In the present study, the duration of the protective immunity generated by the vaccine in cattle was examined for up to 3 years following the administration of a single vaccination dose of 10(8) p.f.u. The vaccinated cattle were kept for 2 (group I) or 3 years (group II) and then challenged with a highly virulent strain of RPV. Four of five vaccinated cattle in group I and all six cattle in group II survived the challenge, some showing solid immunity without any clinical signs of rinderpest. Neutralizing antibodies were maintained at a significant level for up to 3 years and they increased rapidly following challenge. Lymphocyte proliferative responses to RPV were examined in group II cattle and were observed in four of the six vaccinated cattle in this group. The long-lasting protective immunity, in addition to the other properties confirmed previously, indicate the practical usefulness of this vaccine for field use.

DNA vaccination with both the haemagglutinin and fusion proteins but not the nucleocapsid protein protects against experimental measles virus infection

Plasmids that expressed the nucleocapsid, haemagglutinin and fusion proteins of measles virus (MV) were used to immunize cotton rats (Sigmodon hispidus) against intranasal MV infection. After immunization with all three plasmids, T cell responses and MV-specific antibodies were induced. A reduction in virus titre was observed in lung tissue from animals immunized with plasmids expressing the viral glycoproteins. Histologically, however, a moderate peribronchitis was observed after immunization with the plasmid expressing the fusion protein whereas, after immunization with plasmids expressing haemagglutinin or both glycoproteins, only mild or focal peribronchitis was seen. Immunization with the nucleocapsid did not reduce virus titres, probably because of the failure to induce neutralizing antibodies. A disadvantage of plasmid immunization was its inefficacy in the presence of MV-specific 'maternal' antibodies. This indicates that genetic immunization has to be improved to be a useful alternative vaccine against measles.