[Caprine arthritis-encephalitis: trial of an adjuvant vaccine preparation. I. Clinical and virological study]

The Comparative Value of Feline Virology Research: Can Findings from the Feline Lentiviral Vaccine Be Translated to Humans?

Feline immunodeficiency virus (FIV) is a lentivirus of domestic cats that shares several similarities with its human counterpart, human immunodeficiency virus (HIV). Their analogies include genomic organization, lymphocyte tropism, viral persistence and induction of immunodeficiency. FIV is the only lentivirus for which a commercial vaccine is registered for prevention in either human or veterinary medicine. This provides a unique opportunity to investigate the mechanisms of protection induced by lentivirus vaccines at the population level and might contribute to the development of efficacious HIV vaccines. As well as having comparative value for vaccine studies, FIV research has shed some light on the relationship between lentiviral tropism and pathogenesis. Recent studies in our laboratory demonstrated that the interaction between FIV and its primary receptor changes as disease progresses, reminiscent of the receptor switch observed as disease progresses in HIV infected individuals. Here we summarise findings illustrating that, in addition to its veterinary significance, FIV has comparative value, providing a useful model to explore lentivirus–host interactions and to examine potential immune correlates of protection against HIV infection.

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.

Immunological parameters in goats experimentally infected with SRLV genotype E, strain Roccaverano

Genotype E of small ruminant lentivirus has been recently described in goats from different breeds in Italy. Genotype E infection may differ from known genotypes since deletions of dUTPase and VPR proteins have been confirmed in different independent areas and goat breed, and play a key role on virus replication and pathogenesis. In particular, genotype E Roccaverano strain has been described as low pathogenic since does not lead to clinical symptoms in goats. In contrast, classical CAEV infected goats of the same area and breed presented arthritis. In this study, we have used intratracheal and intra-bone marrow routes to establish genotype E persistent infections. Humoral and cellular immune responses elicited in the host against genotype E and genotype B derived antigens were evaluated until 200 days post-inoculation. Compared to genotype B antigen, seroconversion against genotype E GAG P16-25 antigen was detected at 2-3 weeks after inoculation, significantly earlier and at higher titres. Interestingly, antibody avidity did not increase in the course of the experiment neither against P16-25 nor against SU5, both derived from genotype E. T cell proliferation against P25-GST fusion protein antigens derived from genotype E was firstly detected at 15 days post-inoculation and was maintained throughout time until week 20 post-infection, while T cell proliferation against the genotype B P25 was not produced by the end of the experiment at 20 weeks post-inoculation. The strength of reaction was also higher when using P25 E as stimulator antigen. In contrast with antibody and T cell proliferation, cytotoxic-T-lymphocyte (CTL) activity in the circulating lymphocytes (effector cells) using blood-derived macrophages (BDM) as target cells, was not strain specific being surprisingly higher against genotype B infected antigen presenting cells (APCs). This is the first study reporting experimentally induced immunological changes in SRLV genotype E infection and indicates that CTL activity may be the adaptive immune response able to induce protection against heterologous infection.

Vaccination reduces the viral load and the risk of transmission of Jembrana disease virus in Bali cattle

The efficacy of a tissue-derived vaccine, which is currently used in Indonesia to control the spread of Jembrana disease in Bali cattle, was determined by quantifying the viral load in plasma following experimental infection with Jembrana disease virus. Virus transmission is most likely to occur during the acute phase of infection when viral titers are greater than 10(6) genomes/ml. Vaccinated cattle were found to have a 96% reduction in viral load above this threshold compared to control cattle. This would reduce the chance of virus transmission as the number of days above the threshold in the vaccinated cattle was reduced by 33%. Viral loads at the onset and resolution of fever were significantly lower in the vaccinated cattle and immune function was maintained with the development of antibody responses to Env proteins within 10-24 days post challenge. There was, however, no significant reduction in the duration of the febrile period in vaccinated animals. The duration and severity of clinical parameters were found to be variable within each group of cattle but the quantification of viral load revealed the benefits of vaccinating to reduce the risk of virus transmission as well as to ameliorate disease.

Immune response to individual maedi-visna virus gag antigens

The lesions caused by maedi-visna virus (MVV) are known to be immune mediated with a presumed contribution by the response to viral antigens. However, very little is known about the T-cell response to individual viral proteins. We have therefore expressed the three individual gag antigens of MVV strain EV1 (p16, p25, and p14) in a bacterial expression system and used the purified recombinant proteins to analyze the antibody and CD4+ T-cell response to MVV. Plasma samples were taken from sheep after 1 year of infection with MVV. The titers for antibodies in these samples were determined by indirect enzyme-linked immunosorbent assays and were as follows: anti-p25 antibody, 1:400 to >1:3,200; anti-p16 antibody, 1:400 to 1:3,200; and anti-p14 antibody, 1:<100 to 1:3,200. When the induction of antibodies was followed over time postinfection (p.i.), samples positive for anti-p25 were seen by day 24 p.i., followed by anti-p16 by day 45 p.i., and lastly anti-p14 by day 100 p.i. T-cell proliferative responses to all three gag antigens were detected in persistently infected sheep peripheral blood lymphocytes. The antigens were therefore used to raise T-cell lines from persistently infected sheep. These T-cell lines were shown to be specific for the recombinant gag antigens and for viral antigen expressed on infected macrophages. The proliferative response was restricted to major histocompatibility complex class II HLA-DR and so was due to CD4+ T lymphocytes. All three gag antigens may therefore play a role in immune-mediated lesion formation in MVV disease by presentation on infected macrophages in lesions.

The roles of nonhuman primates in the preclinical evaluation of candidate AIDS vaccines

Preclinical studies in nonhuman primates (NHP) play key roles in AIDS vaccine development efforts. In addition to their traditional utilization to gauge vaccine safety and immunogenicity, NHP models are currently employed to an unprecedented extent and in unprecedented ways in contemporary basic and applied vaccine development efforts. Current studies employ NHP models to probe fundamental mechanisms of primate immune system regulation, to investigate pathogenic mechanisms of AIDS, and to optimize immunization strategies involving novel vaccine vectors. The use of experimental challenges of immunized NHPs with either simian immunodeficiency virus or chimeric simian/human immunodeficiency virus to generate preclinical vaccine efficacy data has emerged as an important criterion for facilitating entry of a given vaccine candidate into early phase clinical evaluation in humans. However, for studies of the biology of AIDS virus transmission, AIDS virus disease pathogenesis and AIDS virus vaccine efficacy that are predicated on experimental viral challenge to be most valuable, additional efforts need to be devoted to generating challenge models that more closely recapitulate HIV-1 infection in humans. Towards this end, improved communication between clinical and preclinical investigators, to promote a bidirectional flow of information focusing on individual research needs and shared goals should enable the NHP models to most effectively expedite progress toward the development of a safe and effective AIDS vaccine.

Requirement of diverse T-helper responses elicited by HIV vaccines: induction of highly targeted humoral and CTL responses

With the continued spread of the HIV/AIDS epidemic at alarming proportions there is a sense of urgency for an effective prophylactic HIV vaccine. However, in addition to the social, geopolitical and public health problems, the scientific challenges often seem insurmountable. Empirical approaches to develop an HIV/AIDS vaccine have been unsuccessful and this, coupled with the recent failure of the first Phase III clinical trials, calls for a strong rational approach based on a deeper scientific understanding of the correlates of immunity observed in both preclinical and clinical settings. While the field has been polarized between those who have been proponents of vaccines that induce strong cytotoxic T-cell responses, and those who advocate inducing neutralizing antibody responses, we have maintained middle ground. Based on our early preclinical observations in rigorous nonhuman primate vaccine efficacy studies, we have focused on vaccine strategies that induce potent T-helper immune responses capable of driving both cytotoxic, as well as broad highly effective neutralizing antibodies. The critical issue remains in the selection of the specific vaccine antigens. To date, our approach has been to utilize multiple structural as well as regulatory HIV antigens containing highly conserved epitopes. The current challenge faced is to design novel antigens based on mimicking envelope structures capable of inducing broad neutralizing antibodies. Our aim is to combine these with immunization strategies capable of eliciting potent cellular as well as humoral immune responses with the ultimate goal of providing mucosal barriers to HIV entry.

Enhanced SIV replication and accelerated progression to AIDS in macaques primed to mount a CD4 T cell response to the SIV envelope protein

Given the dual role of CD4 T cells as both immune effectors and targets for HIV infection, the balance of CD4 versus CD8 T cell-mediated responses induced by candidate AIDS vaccines may be critical in determining postvaccination infection outcomes. An attenuated recombinant varicella-zoster virus vaccine expressing the simian immunodeficiency virus (SIV) envelope (Env) elicited nonneutralizing Env-binding antibodies and little if any cytotoxic T lymphocyte responses in rhesus macaques (Macaca mulatta). After challenge with SIV, Env vaccinees manifested increased levels of SIV replication, more rapid CD4 depletion, and accelerated progression to AIDS compared with controls. Enhanced SIV replication correlated with increased CD4 T cell proliferation soon after SIV challenge, apparently the result of an anamnestic response to SIV antigens. Thus activation of virus-specific CD4 T cells at the time of exposure to a CD4 T cell-tropic lentivirus, in the absence of an effective CD8 response, may enhance virus replication and disease. These data suggest suggest that candidate AIDS vaccines may not simply be either efficacious or neutral; they may also have the potential to be harmful.

The induction of a protective immunity against Jembrana disease in cattle by vaccination with inactivated tissue-derived virus antigens

The ability to induce a protective immunity against Jembrana disease, an acute lentivirus disease of Bali cattle (Bos javanicus) present in Indonesia, was investigated. A protective immune response was induced in cattle by vaccination with virus-containing plasma and spleen tissue derived from acutely affected cattle. The virus was inactivated with Triton X-100 and emulsified in either incomplete Freund's adjuvant or a mineral oil adjuvant (MOA). The vaccination procedure suppressed the duration and severity of the disease but did not completely prevent the development of disease in animals challenged with 100 infectious doses of virus.

Antibody reactivity to the transmembrane protein of the caprine arthritis encephalitis virus correlates with severity of arthritis: no evidence for the involvement of epitope mimicry

Serum and synovial antibody reactivities of caprine arthritis encephalitis virus (CAEV) infected goats were assessed by Western blotting against purified CAEV antigen and the greatest intensity of reactivity in the serum of arthritic goats was to the gp45 transmembrane protein (TM). The extracytoplasmic domain of the TM gene was cloned into a pGEX vector and expressed in Escherichia coli as a glutathione S transferase fusion protein (GST-TM). This clone was found to be 90.5 and 89.2% homologous to published sequences of CAEV TM gene. Serum of 16 goats naturally infected with CAEV were examined by Western blotting for reactivity to the fusion protein. Antibody reactivity to the GST-TM correlated with clinically detectable arthritis (R = 0.642, P < or = 0.007). The hypothesis that the immune response to the envelope proteins of the CAEV contributes to the severity of arthritis in goats naturally infected with CAEV via epitope mimicry was tested. Antibodies from 5 CAEV infected goats were affinity purified against the GST-TM fusion protein and tested for cross-reactivity with a series of goat synovial extracts and proteogylcans. No serum antibody response or cross-reactivity of affinity purified antibodies could be detected. Peptides of the CAEV SU that were predicted to be linear epitopes and a similar heat shock protein 83 (HSP) peptide identified by database searching, were synthesized and tested for reactivity in CAEV goats using ELISA, in vitro lymphocyte proliferation and delayed type hypersensitivity (DTH) assays. Peripheral blood lymphocytes from 10 of 17 goats with long term natural CAEV infections proliferated in vitro in response to CAEV and in vivo 3 of 7 CAEV infected goats had a DTH reaction to CAEV antigen. However, none of the peptides elicited significant cell mediated immune responses from CAEV infected goats. No antibody reactivity to the SU peptides or HSP peptide was found. We observed that the antibody reactivity to the CAEV TM protein associated with severity of arthritis however epitope mimicry by the envelope proteins of CAEV is unlikely to be involved.

[Caprine arthritis-encephalitis: trial of an adjuvant vaccine preparation. II. Study of the antibody response]

In an experiment of vaccination against caprine arthritis encephalitis virus (CAEV), the antibody response in three groups of young goats was followed by AGIDT, ELISA, seroneutralization, western blot. Goats of group I, inoculated with inactivated virus mixed with adjuvant, showed a few weeks after vaccination a high antibody response, clearly enhanced after infectious intraarticular challenge. These antibodies did not protect against arthritis, which appeared more severe in this group. In the other groups (group II, control adjuvant, with the weakest clinical expression, group III, control tissue culture medium), the levels of circulating antibodies appeared much lower. No neutralizing antibodies could be detected during the whole experiment. A western blot analysis revealed mainly in group I a high antibody response against gp 135 antigen. The important immune reaction might be involved in enhancement of viral infectivity in this group.