Immunization with plasmid DNA expressing the caprine arthritis-encephalitis virus envelope gene: quantitative and qualitative aspects of antibody response to viral surface glycoprotein

Small ruminant lentivirus capsid protein (SRLV-p25) antigenic structural prediction and immunogenicity to recombinant SRLV-rp25-coupled to immunostimulatory complexes based on glycyrrhizinic acid

Small ruminant lentiviruses (SRLV) infect sheep and goats resulting in significant economic losses. This study evaluated for the first time the predicted conformational structure of the SRLV-capsid-protein 25 (SRLV-p25) and analyzed the antigenicity of recombinant protein (SRLV-rp25) in mice by coupling to an immunostimulatory complexes based on glycyrrhizinic acid liposomes (GAL) and tested plasma from goats and sheep naturally infected. Analysis in silico and conformational structure of SRLV-p25 (genotype B-FESC-752) showed similar characteristics to other lentiviral capsids. The efficient expression of SRLV-rp25 was confirmed by Western blot. The humoral immune responses in mice showed an increased level of antibodies from day 21 to 35 of the SRLV-rp25-GAL and SRLV-rp25-ISCOM® groups and the cellular immune response showed no significant difference in IL-10 levels (P >.05), however, a significant difference (P <.001) was observed when comparing SRLV-rp25-GAL with SRLV-rp25 groups. Immunoreactivity toward SRLV-rp25 revealed 61% of positive samples from naturally infected goats and sheep.

Small ruminant lentivirus capsid protein (SRLV-p25) antigenic structural prediction and immunogenicity to recombinant SRLV-rp25-coupled to immunostimulatory complexes based on glycyrrhizinic acid

Small ruminant lentiviruses (SRLV) infect sheep and goats resulting in significant economic losses. This study evaluated for the first time the predicted conformational structure of the SRLV-capsid-protein 25 (SRLV-p25) and analyzed the antigenicity of recombinant protein (SRLV-rp25) in mice by coupling to an immunostimulatory complexes based on glycyrrhizinic acid liposomes (GAL) and tested plasma from goats and sheep naturally infected. Analysis in silico and conformational structure of SRLV-p25 (genotype B-FESC-752) showed similar characteristics to other lentiviral capsids. The efficient expression of SRLV-rp25 was confirmed by Western blot. The humoral immune responses in mice showed an increased level of antibodies from day 21 to 35 of the SRLV-rp25-GAL and SRLV-rp25-ISCOM® groups and the cellular immune response showed no significant difference in IL-10 levels (P &gt;.05), however, a significant difference (P &lt;.001) was observed when comparing SRLV-rp25-GAL with SRLV-rp25 groups. Immunoreactivity toward SRLV-rp25 revealed 61% of positive samples from naturally infected goats and sheep.

Immunization against small ruminant lentiviruses

Multisystemic disease caused by Small Ruminant Lentiviruses (SRLV) in sheep and goats leads to production losses, to the detriment of animal health and welfare. This, together with the lack of treatments, has triggered interest in exploring different strategies of immunization to control the widely spread SRLV infection and, also, to provide a useful model for HIV vaccines. These strategies involve inactivated whole virus, subunit vaccines, DNA encoding viral proteins in the presence or absence of plasmids encoding immunological adjuvants and naturally or artificially attenuated viruses. In this review, we revisit, comprehensively, the immunization strategies against SRLV and analyze this double edged tool individually, as it may contribute to either controlling or enhancing virus replication and/or disease.

Small ruminant lentiviruses (SRLVs) break the species barrier to acquire new host range

Zoonotic events of simian immunodeficiency virus (SIV) from non-human primates to humans have generated the acquired immunodeficiency syndrome (AIDS), one of the most devastating infectious disease of the last century with more than 30 million people dead and about 40.3 million people currently infected worldwide. Human immunodeficiency virus (HIV-1 and HIV-2), the two major viruses that cause AIDS in humans are retroviruses of the lentivirus genus. The genus includes arthritis-encephalitis virus (CAEV) and Maedi-Visna virus (MVV), and a heterogeneous group of viruses known as small ruminant lentiviruses (SRLVs), affecting goat and sheep. Lentivirus genome integrates into the host DNA, causing persistent infection associated with a remarkable diversity during viral replication. Direct evidence of mixed infections with these two closely related SRLVs was found in both sheep and goats. The evidence of a genetic continuum with caprine and ovine field isolates demonstrates the absence of an efficient species barrier preventing cross-species transmission. In dual-infected animals, persistent infections with both CAEV and MVV have been described, and viral chimeras have been detected. This not only complicates animal trade between countries but favors the risk that highly pathogenic variants may emerge as has already been observed in the past in Iceland and, more recently, in outbreaks with virulent strains in Spain. SRLVs affecting wildlife have already been identified, demonstrating the existence of emergent viruses adapted to new hosts. Viruses adapted to wildlife ruminants may acquire novel biopathological properties which may endanger not only the new host species but also domestic ruminants and humans. SRLVs infecting sheep and goats follow a genomic evolution similar to that observed in HIV or in other lentiviruses. Lentivirus genetic diversity and host factors leading to the establishment of naturally occurring virulent versus avirulent infections, in addition to the emergence of new strains, challenge every aspect of SRLV control measures for providing efficient tools to prevent the transmission of diseases between wild ungulates and livestock.

A caprine herpesvirus 1 vaccine adjuvanted with MF59™ protects against vaginal infection and interferes with the establishment of latency in goats

The immunogenicity and the efficacy of a beta-propiolactone-inactivated caprine herpesvirus 1 (CpHV-1) vaccine adjuvanted with MF59™ were tested in goats. Following two subcutaneous immunizations, goats developed high titers of CpHV-1-specific serum and vaginal IgG and high serum virus neutralization (VN) titers. Peripheral blood mononuclear cells (PBMC) stimulated in vitro with inactivated CpHV-1 produced high levels of soluble IFN-gamma and exhibited high frequencies of IFN-gamma producing cells while soluble IL-4 was undetectable. On the other hand, control goats receiving the inactivated CpHV-1 vaccine without adjuvant produced only low serum antibody responses. A vaginal challenge with virulent CpHV-1 was performed in all vaccinated goats and in naïve goats to assess the efficacy of the two vaccines. Vaginal disease was not detected in goats vaccinated with inactivated CpHV-1 plus MF59™ and these animals had undetectable levels of infectious challenge virus in their vaginal washes. Goats vaccinated with inactivated CpHV-1 in the absence of adjuvant exhibited a less severe disease when compared to naïve goats but shed titers of challenge virus that were similar to those of naïve goats. Detection and quantitation of latent CpHV-1 DNA in sacral ganglia in challenged goats revealed that the inactivated CpHV-1 plus MF59™ vaccine was able to significantly reduce the latent viral load when compared either to the naïve goats or to the goats vaccinated with inactivated CpHV-1 in the absence of adjuvant. Thus, a vaccine composed of inactivated CpHV-1 plus MF59™ as adjuvant was strongly immunogenic and induced effective immunity against vaginal CpHV-1 infection in goats.

Small ruminant lentiviruses: immunopathogenesis of visna-maedi and caprine arthritis and encephalitis virus

The small ruminant lentiviruses include the prototype for the genus, visna-maedi virus (VMV) as well as caprine arthritis encephalitis virus (CAEV). Infection of sheep or goats with these viruses causes slow, progressive, inflammatory pathology in many tissues, but the most common clinical signs result from pathology in the lung, mammary gland, central nervous system and joints. This review examines replication, immunity to and pathogenesis of these viruses and highlights major differences from and similarities to some of the other lentiviruses.

Mucosal immunization against ovine lentivirus using PEI-DNA complexes and modified vaccinia Ankara encoding the gag and/or env genes

Sheep were immunized against Visna/Maedi virus (VMV) gag and/or env genes via the nasopharynx-associated lymphoid tissue (NALT) and lung using polyethylenimine (PEI)-DNA complexes and modified vaccinia Ankara, and challenged with live virus via the lung. env immunization enhanced humoral responses prior to but not after VMV challenge. Systemic T cell proliferative and cytotoxic responses were generally low, with the responses following single gag gene immunization being significantly depressed after challenge. A transient reduction in provirus load in the blood early after challenge was observed following env immunization, whilst the gag gene either alone or in combination with env resulted in significantly elevated provirus loads in lung. However, despite this, a significant reduction in lesion score was observed in animals immunized with the single gag gene at post-mortem. Inclusion of IFN-gamma in the immunization mixture in general had no significant effects. The results thus showed that protective effects against VMV-induced lesions can be induced following respiratory immunization with the single gag gene, though this was accompanied by an increased pulmonary provirus load.

Expression of the gp150 maedi visna virus envelope precursor protein by mammalian expression vectors

There are very few previous reports of expression of native full-length maedi visna virus (MVV) Env gp150 protein in the literature. Therefore the use of different plasmid and viral expression vectors to obtain full-length gp150 was investigated. A mammalian expression plasmid, pN3-Env, was constructed containing the MVV env gene encoding the precursor protein gp150 Env. The functionality of the recombinant plasmid was tested for expression in HEK293 cells. A recombinant modified vaccinia Ankara virus, MVA-Env, with expression detected in avian cells was also made. The expression of the MVV gp150 Env precursor protein was shown for the first time upon transfection of the eukaryotic HEK293 cells by the pN3-Env plasmid DNA as demonstrated by Western blot analysis. These plasmid or viral expression vectors are of potential use in MVV vaccines.

Vaccination of sheep with Maedi-visna virus gag gene and protein, beneficial or harmful?

In spite of intense efforts no vaccine is yet available that protects against lentiviral infections. Sheep were immunised eight times over a period of 2.5 years with the maedi-visna (MVV) gag gene on two different vectors, 2 sheep with VR1012-gag-CTE and 2 sheep with pcDNA3.1-gag-CTE. All sheep responded to some of the mature MVV Gag proteins in Western blot (WB). Three of them responded to the virus in lymphocyte proliferation test. The sheep received a boost with recombinant Gag protein resulting in elevated antibody response. However, when they were challenged intratracheally with MVV they all became immediately infected as judged by a strong rise in antibody titer and virus isolation from blood. It is therefore clear that the vaccination gave no protection. It is even possible that it facilitated infectivity since virus was isolated earlier from all the vaccinated sheep than from any of the unvaccinated sheep infected in the same way with the same dose.

Mucosal immunization of sheep with a Maedi-Visna virus (MVV) env DNA vaccine protects against early MVV productive infection

Gene gun mucosal DNA immunization of sheep with a plasmid expressing the env gene of Maedi-Visna virus (MVV) was used to examine the protection against MVV infection in sheep from a naturally infected flock. For immunization, sheep were primed with a pcDNA plasmid (pcDNA-env) encoding the Env glycoproteins of MVV and boosted with combined pcDNA-env and pCR3.1-IFN-gamma plasmid inoculations. The pcDNA plasmid used in the control group contained the lacZ coding sequences instead of the env gene. Within a month post-challenge, the viral load in the vaccinated group was lower (p < or = 0.05) and virus was only detected transiently compared with the control group. Furthermore, 2 months later, neutralizing antibodies (NtAb) were detected in all the control animals and none of the vaccinated animals (p < or = 0.01). These results demonstrated a significant early protective effect of this immunization strategy against MVV infection that restricts the virus replication following challenge in the absence of NtAb production. This vaccine protective effect against MVV infection disappeared after two years post-challenge, when active replication of MVV challenge strain was observed. Protection conferred by the vaccine could not be explained by OLA DRB1 allele or genotype differences. Most of the individuals were DRB1 heterozygous and none was totally resistant to infection.

Antibody response to the surface envelope of caprine arthritis-encephalitis lentivirus: disease status is predicted by SU antibody isotype

This study evaluated the hypothesis that the disease status of Saanen goats infected with caprine arthritis-encephalitis lentivirus (CAEV) is associated with the focus of immune responses to viral antigens, particularly the surface envelope glycoprotein (SU). Specifically, we have proposed that Th2 responses promote progressive immune-mediated arthritis, whereas Th1 responses restrict virus replication and development of clinical disease. The present study determined the isotype of SU antibodies associated with progressor and long-term nonprogressor (LTNP) status. We show that chronically infected goats that develop clinical arthritis have predominantly IgG1 antibodies to SU during both preclinical and clinical stages of disease, whereas SU antibodies of LTNP goats are relatively biased toward IgG2. Additional studies determined the isotype of SU antibodies induced initially by CAEV infection. These experiments show that initial IgG1-dominated responses to SU are associated with subsequent development of preclinical inflammatory joint lesions, whereas lack of joint pathology is associated with an IgG2 bias of initial responses to SU. Our results using the CAEV model suggest that isotype bias of SU antibodies is a reliable indicator of clinical disease caused by lentiviruses. Isotype analysis may be a useful method to screen candidate lentiviral vaccines intended to prevent disease progression.

Predominant cell-mediated immunity in the oral mucosa: gene gun-based vaccination against infectious diseases

BACKGROUND

Direct immunization via epithelial surfaces has been considered for many vaccine approaches, including DNA vaccines. It remains to be determined, however, which body site is suitable for genetic vaccination.

OBJECTIVE

To characterize the effects of the oral mucosa-mediated genetic vaccination, we compared antigen-specific immune responses of the oral mucosal DNA vaccine to the flank skin vaccination against influenza virus and malaria parasite.

METHODS

DNA vaccines against the influenza A/WSN/33 (H1N1) hemagglutinin and the malaria Plasmodium berghei circumsporozoite protein were administered respectively three times at 3-week intervals into the oral mucosa, skin, or liver of hamsters. The effects of their vaccine were evaluated by antigen-specific antibody production and cell-mediated killing activity. Furthermore, the in vivo malaria challenge test was also performed after the vaccination.

RESULTS

Significant specific antibody production was not observed in each case, but interferon-gamma production and cell-mediated killing activity were strongly induced in splenic lymphocytes from hamsters with the oral vaccination. The in vivo malaria challenge after the oral mucosal vaccination significantly delayed the blood-appearance day of the parasites in comparison with other immunization sites (P<0.05).

CONCLUSION

These results suggest that gene immunization via the oral mucosa may induce cell-mediated immunity more efficiently than via the skin or liver, and that the oral mucosa may be one of the most suitable tissues for gene gun-based DNA vaccination against infectious diseases.

Prime-boost vaccination with plasmid DNA encoding caprine-arthritis encephalitis lentivirus env and viral SU suppresses challenge virus and development of arthritis

This study evaluated the efficacy of prime-boost vaccination for immune control of caprine arthritis-encephalitis virus (CAEV), a macrophage tropic lentivirus that causes progressive arthritis in the natural host. Vaccination of Saanen goats with pUC-based plasmid DNA expressing CAEV env induces T helper type 1 (Th1) biased immune responses to vector-encoded surface envelope (SU), and the plasmid-primed Th1 response is expanded following boost with purified SU in Freund's incomplete adjuvant (SU-FIA) (J. C. Beyer et al., 2001, Vaccine 19, 1643-1651). Four goats vaccinated with env expression plasmids and boosted with SU-FIA were challenged intravenously with 1 x 10(4) TCID(50) of CAEV at 428 days after SU-FIA boost and evaluated by immunological, virological, and disease criteria. Controls included two goats primed with pUC18 and eight unvaccinated goats. Goats receiving prime-boost vaccination with CAEV env plasmids and SU-FIA became infected but suppressed postchallenge virus replication, provirus loads in lymph node, and development of arthritis for at least 84 weeks.

Host range of small-ruminant lentivirus cytopathic variants determined with a selectable caprine arthritis- encephalitis virus pseudotype system

The small-ruminant lentiviruses ovine maedi-visna virus (MVV) and caprine arthritis-encephalitis virus (CAEV) cause encephalitis, progressive pneumonia, arthritis, and mastitis in sheep and goats. Icelandic MVV strains, which are lytic in tissue culture, have a wide species distribution of functional receptors, which includes human cells. In contrast, functional receptors for the nonlytic CAEV CO are absent from human cells. To determine if the wide species distribution of functional receptors is a common property of MVV strains or related to cytopathic phenotype, we tested the infectivity of viruses pseudotyped with the envelope glycoproteins of MVV K1514, CAEV CO, and lytic and nonlytic North American MVV strains to cells of different species. Replication-defective CAEV proviral constructs lacking the env, tat, and vif genes and carrying the neomycin phosphotransferase gene in the vif-tat region were developed for the infectivity assays. Cotransfection of human 293T cells with these proviral constructs and plasmids expressing CAEV, MVV, or vesicular stomatitis virus envelope glycoproteins produced infectious pseudotyped virus which induced resistance of infected cells to G418. Using these pseudotypes, we confirmed the wide species distribution of Icelandic MVV receptors and the narrow host range of CAEV. However, functional receptors for the two North American MVV strains tested, unlike the Icelandic MVV and similar to CAEV, were limited to cells of ruminant species, regardless of cytopathic phenotype. The results indicate a differential receptor recognition by MVV strains which is unrelated to cytopathic phenotype.

Plasmid DNA encoding caprine interferon gamma inhibits antibody response to caprine arthritis-encephalitis virus (CAEV) surface protein encoded by a co-administered plasmid expressing CAEV env and tat genes

This study characterized immune responses of Saanen goats co-immunized with pUC18 based plasmids expressing caprine arthritis-encephalitis virus (CAEV) rev-env (pENV) or tat-rev-env (pTAT-ENV) and a second plasmid encoding caprine interferon gamma (IFNgamma). A previous study reported that immunization with pENV or pTAT-ENV induces IgG2 biased antibody responses to plasmid encoded CAEV surface envelope protein (SU). We show here that regional lymph nodes (LN) of pENV and pTAT-ENV immunized goats contain a dominant subset of SU activated IFNgamma+ Th1 lymphocytes. Co-immunization with pENV or pTAT-ENV and a caprine IFNgamma cDNA expression plasmid (pcIFNgamma) did not potentiate activation of SU responsive Th1 lymphocytes. However, the antibody response to SU encoded by pTAT-ENV was inhibited by co-immunization with pcIFNgamma. Results indicate that synergistic effects of CAEV Tat and IFNgamma suppress the primary adaptive B cell response to plasmid encoded SU.