Feline leukaemia vaccine protection against viral latency

Seventeen cats, which were previously vaccinated with a subunit, feline leukaemia vaccine (Leukocell) and subsequently challenged with virulent feline leukaemia virus (FeLV), were tested at 2 to 4 years postchallenge for reactivation of latent FeLV infections. Administration of weekly doses of methylprednisolone induced significant decreases in lymphocyte numbers, but did not reactivate virus in bone marrow cultures from 15 cats in vivo or in vitro. These cats were observed to be neither persistently or latently viraemic prior to corticosteroid administration. The results of this study indicate that the vaccine is effective in affording significant protection against latent FeLV infections, even after severe immunosuppression. This finding, coupled with previously published results indicating protection against persistent viraemia and tumour formation, makes this vaccine highly effective in protecting against FeLV infections and associated disease.     

Antibody induction after combined application of an adjuvanted recombinant FeLV vaccine and a multivalent modified live virus vaccine with a chlamydial component

The compatibility, safety and interaction on antibody induction of a combined vaccine application were assessed. Specific pathogen-free cats were vaccinated with either a modified live virus vaccine containing feline calici- (FCV), herpes- (FHV-1), parvovirus (FPV) and Chlamydophila felis (C. felis), an adjuvanted recombinant feline leukaemia virus (FeLV) vaccine or both vaccines in one syringe. After combined application, FeLV ELISA antibody titres were unaltered, However antibody production based on indirect immunofluorescence assay was remarkably enhanced for FCV and was at selected time points also enhanced for FHV-1 and C. felis but diminished for FPV. The use of these vaccines in combination was safe and will simplify vaccination schedules in veterinary practice.     

A vector expressing feline mature IL-18 fused to IL-1beta antagonist protein signal sequence is an effective adjuvant to a DNA vaccine for feline leukaemia virus

DNA vaccination using vectors expressing the gag/pol and env genes of feline leukaemia virus (FeLV) and plasmids encoding feline interleukin-12 (IL-12) and IL-18 completely protected cats from viraemia following challenge [Hanlon L, Argyle D, Bain D, Nicolson L, Dunham S, Golder MC, et al. Feline leukaemia virus DNA vaccine efficacy is enhanced by coadministration with interleukin-12 (IL-12) and IL-18 expression vectors. J Virol 2001;75:8424-33]. However, the relative contribution of each cytokine gene towards protection is unknown. This study aimed to resolve this issue. IL-12 and IL-18 constructs were modified to ensure effective expression, and bioactivity was demonstrated using specific assays. Kittens were immunised intramuscularly with FeLV DNA and various cytokine constructs. Together with control kittens, these were challenged oronasally with FeLV and monitored for 15 weeks. All six kittens given FeLV, IL-12 and IL-18 were protected from the establishment of persistent viraemia and four from latent infection. Of six kittens immunised with FeLV DNA and IL-18, all were protected from viraemia and five from latent infection. In contrast, three of five kittens given FeLV DNA and IL-12 became persistently viraemic. Therefore, the adjuvant effect on the FeLV DNA vaccine appears to reside in the expression of IL-18.     

Serological responses in cats vaccinated with FeLV ISCOM and an inactivated FeLV vaccine

Various approaches have been considered for generation of effective and safe vaccines against retroviruses, including HIV, with limited success. In the present vaccination study, encompassing 137 household cats, we have composed an experimental ISCOM subunit vaccine containing gp70 of feline leukaemia virus (FeLV)--the external glycosylated envelope protein, and the transmembrane protein p15E, with a commercial available inactivated FeLV vaccine (Leukocell). The two vaccines were estimated to contain approximately the same amount of gp70 antigen and the cats were immunized three times according to the recommendations of the commercial vaccine. A control preparation not containing gp70 or p15E was also included. During the observation period of 200 days all cats remained healthy and no virus was isolated during the isolation attempts. The serological responses were measured in ELISA, membrane immunofluorescence (MIF) and virus neutralization (VN) tests. In contrast to the cats in the other groups almost all ISCOM-vaccinated cats responded by seroconversion or increased titres in the three tests. The development of specific antibodies to gp70 and p15E were confirmed in Western blot. These results clearly illustrate the potential of the ISCOM structure for the development of safe and effective vaccines against retroviruses.     

Effect of diethylcarbamazine on serum antibodies to feline infectious peritonitis in cats

In preceding studies by the author, use of the immunomodulator drug diethylcarbamazine resulted in the detection of antibodies to feline oncornavirus-associated cell membrane antigen in nine feline leukaemia virus infected cats that had previously given negative results to this antibody. In the present report, seven diethylcarbamazine-treated cats developed higher serum antibody titres to feline infectious peritonitis more frequently than did seven untreated controls. Since feline infectious peritonitis is caused by a coronavirus, these results suggest that diethylcarbamazine treatment could be exploited for vaccination and treatment strategies for non-retroviral in addition to retroviral infections.     

Protection against feline infectious peritonitis by intranasal inoculation of a temperature-sensitive FIPV vaccine

Cats vaccinated intranasally (i.n.) with a temperature sensitive feline infectious peritonitis virus (ts-FIPV) vaccine were protected against an FIP-inducing challenge. Seventeen of 20 vaccinated cats (85%) survived a rigorous virulent FIPV challenge that caused FIP in 12 of 12 non-vaccinated cats (100%), 10 (83%) of which died. Intranasal vaccination stimulated serum IgG and serum and salivary IgA antibody responses (measured by ELISA), FIPV-neutralizing antibody (VN), and a cell-mediated immune (CMI) response as measured by lymphocyte proliferation. The serum antibody response to vaccination was not associated with protection. In fact, the IgG, IgA and VN titres were much higher in control cats than in vaccinated cats following challenge suggesting an immune-mediated pathogenesis. In contrast, stimulation of a mucosal IgA response to vaccination was related to protection. The in vitro proliferation of peripheral blood lymphocytes in response to virulent FIPV was observed in vaccinated cats, in vaccinated and challenged cats but not in non-vaccinated challenged cats.     

Protection against oronasal challenge with virulent feline leukaemia virus lasts for at least 12 months following a primary course of immunisation with Leukocell 2 vaccine

The duration of immunity provided by a feline leukemia virus (FeLV) vaccine, Leukocell 2, was determined. Kittens were vaccinated when 9 and 12 weeks of age and were challenged 12 months later with FeLV-A/Glasgow-1. An oronasal challenge protocol without corticosteroid enhancement was developed in order to induce a persistent viraemia in a high proportion of adult cats. Fourteen of 18 (80%) of the vaccinated cats challenged in this way remained non-viraemic while 9/15 (60%) of age-matched controls became persistently infected, a preventable fraction of 63%. This difference was statistically significant (P=0.038). For comparison, 10 of 12 (83%) 15-17-week-old kittens challenged in the same way became persistently infected, confirming the relative resistance of adult animals to FeLV. Tests for virus neutralising and anti-feline oncornavirus-associated cell membrane antigen (FOCMA) antibodies suggested that the former were more important than the latter in protection. Thus, Leukocell 2 protected a significant proportion of cats from FeLV challenge 1 year after primary vaccination as kittens.     

Enzyme-linked immunosorbent assay (ELISA) for the detection of antibodies against foot-and-mouth disease virus. III. Evaluation of antibodies after infection and vaccination

Investigations using a liquid-phase blocking sandwich enzyme-linked immunosorbent assay (ELISA) for the measurement of antibodies against foot-and-mouth disease virus (FMDV) in sera from sheep and from cattle are reported, and results compared with those obtained by virus neutralization (VN) tests. Serum antibody titres in sheep after primary vaccination and in cattle challenged with a natural aerosol after vaccination were similar by ELISA and VN. However, the antibody levels detected in sera of cattle during early infection and of vaccinated cattle after intradermolingual challenge were clearly greater by ELISA than by VN. The ELISA titres in cattle sera following synthetic peptide vaccination indicated some relationship to protection and were clearly different from those recorded by VN. On the other hand, the antibody levels following conventional vaccination showed that ELISA and VN titres in cattle sera were related to protection. Although there was a good agreement between the ELISA antibody titre and protection for the four vaccines used, by VN the titre which afforded protection varied depending on the vaccine used. The ELISA was considered therefore to be more reliable than the VN and may prove useful for evaluating the immunological response of animals following infection and following vaccination.     

Oral vaccination and protection of red foxes (Vulpes vulpes) against rabies using ONRAB,an adenovirus-rabies recombinant vaccine

Twenty-seven red foxes (Vulpes vulpes) were each offered a bait containing ONRAB^®, a recombinant oral rabies vaccine that uses a human adenovirus vector to express the immunogenic rabies virus glycoprotein; 10 controls received no vaccine baits. Serum samples collected from all foxes before treatment, and each week post-treatment for 16 weeks, were tested for the presence of rabies virus neutralizing antibody (RVNA). In the bait group, a fox was considered a responder to vaccination if serum samples from 3 or more consecutive weeks had RVNA ≥0.5 IU/ml. Using this criterion, 79% of adult foxes (11/14) and 46% of juveniles (6/13) responded to vaccination with ONRAB^®. Serum RVNA of adults first tested positive (≥0.5 IU/ml) between weeks 1 and 3, about 4 weeks earlier than in juveniles. Adults also responded with higher levels of RVNA and these levels were maintained longer. Serum samples from juveniles tested positive for 1–4 consecutive weeks; in adults the range was 2–15 weeks, with almost half of adults maintaining titres above 0.5 IU/ml for 9 or more consecutive weeks. Based on the kinetics of the antibody response to ONRAB^®, the best time to sample sera of wild adult foxes for evidence of vaccination is 7–11 weeks following bait distribution. Thirty-four foxes (25 ONRAB^®, 9 controls) were challenged with vulpine street virus 547 days post-vaccination. All controls developed rabies whereas eight of 13 adult vaccinates (62%) and four of 12 juvenile vaccinates (33%) survived. All foxes classed as non-responders to vaccination developed rabies. Of foxes considered responders to vaccination, 80% of adults (8/10) and 67% of juveniles (4/6) survived challenge. The duration of immunity conferred to foxes would appear adequate for bi-annual and annual bait distribution schedules as vaccinates were challenged 1.5 years post-vaccination.     

Antibody response after influenza vaccination in HIV-infected individuals: a consecutive 3-year study

In a consecutive 3-year study the antibody response after immunization with influenza vaccine of a cohort of HIV-infected adults was studied. The haemagglutination-inhibiting (HAI) antibody titres after vaccination correlated with the number of CD4(+) T lymphocytes (p<0.001), the prevaccination antibody titres (p<0.001), and the proliferative response to anti-CD3 (p<0.001). Severely impaired antibody responses were observed in HIV-infected individuals with CD4(+) T-lymphocyte counts < or =100x10(6)/l. Significantly higher prevaccination antibody titres were observed in healthy controls in the 2nd or 3rd year of vaccination, but not in HIV-infected individuals. Annually repeated vaccination of HIV-infected individuals did not lead to higher postvaccination antibody titres. Annual vaccination of HIV-infected individuals with CD4(+) T-lymphocyte counts exceeding 100x10(6)/l seems to be worthwhile, although it may not be expected to render the same level of protection against influenza as in non-infected individuals.     

Neutralising antibody response in domestic cats immunised with a commercial feline immunodeficiency virus (FIV) vaccine

Across human and veterinary medicine, vaccines against only two retroviral infections have been brought to market successfully, the vaccines against feline leukaemia virus (FeLV) and feline immunodeficiency virus (FIV). FeLV vaccines have been a global success story, reducing virus prevalence in countries where uptake is high. In contrast, the more recent FIV vaccine was introduced in 2002 and the degree of protection afforded in the field remains to be established. However, given the similarities between FIV and HIV, field studies of FIV vaccine efficacy are likely to advise and inform the development of future approaches to HIV vaccination.Here we assessed the neutralising antibody response induced by FIV vaccination against a panel of FIV isolates, by testing blood samples collected from client-owned vaccinated Australian cats. We examined the molecular and phenotypic properties of 24 envs isolated from one vaccinated cat that we speculated might have become infected following natural exposure to FIV. Cats vaccinated against FIV did not display broadly neutralising antibodies, suggesting that protection may not extend to some virulent recombinant strains of FIV circulating in Australia.     

No benefit of therapeutic vaccination in clinically healthy cats persistently infected with feline leukemia virus

Therapeutic vaccinations have a potential application in infections where no curative treatment is available. In contrast to HIV, efficacious vaccines for a cat retrovirus, feline leukemia virus (FeLV), are commercially available. However, the infection is still prevalent, and no effective treatment of the infection is known. By vaccinating persistently FeLV-infected cats and presenting FeLV antigens to the immune system of the host, e.g., in the form of recombinant and/or adjuvanted antigens, we intended to shift the balance toward an advantage of the host so that persistent infection could be overcome by the infected cat. Two commercially available FeLV vaccines efficacious in protecting naïve cats from FeLV infection were tested in six experimentally and persistently FeLV-infected cats: first, a canarypox-vectored vaccine, and second, an adjuvanted, recombinant envelope vaccine was repeatedly administered with the aim to stimulate the immune system. No beneficial effects on p27 antigen and plasma viral RNA loads, anti-FeLV antibodies, or life expectancy of the cats were detected. The cats were unable to overcome or decrease viremia. Some cats developed antibodies to FeLV antigens although not protective. Thus, we cannot recommend vaccinating persistently FeLV-infected cats as a means of improving their FeLV status, quality of life or life expectancy. We suggest testing of all cats for FeLV infection prior to FeLV vaccination.     

Efficacy of an inactivated FeLV vaccine compared to a recombinant FeLV vaccine in minimum age cats following virulent FeLV challenge

The aim of the study was to determine the efficacy of an inactivated feline leukemia virus (FeLV) vaccine (Versifel^® FeLV, Zoetis.) compared to a recombinant FeLV vaccine (Purevax^® FeLV, Merial Animal Health) in young cats, exposed under laboratory conditions to a highly virulent challenge model. The study was designed to be consistent with the general immunogenicity requirements of the European Pharmacopoeia 6.0 Monograph 01/2008:1321—Feline Leukaemia Vaccine (Inactivated) with the exception that commercial-strength vaccines were assessed. Fifty seronegative cats (8–9 weeks old) were vaccinated subcutaneously on two occasions, three weeks apart, with either placebo (treatment group T01), Versifel FeLV Vaccine (treatment group T02), or Purevax FeLV Vaccine (treatment group T03) according to the manufacturer's directions. Cats were challenged three weeks after the second vaccination with a virulent FeLV isolate (61E strain). Persistent FeLV antigenemia was determined from 3 to 15 weeks postchallenge. Bone marrow samples were tested for the presence of FeLV proviral DNA to determine FeLV latent infection. At week 15 after challenge with the virulent FeLV 61E strain, the Versifel FeLV Vaccine conferred 89.5% protection against FeLV persistent antigenemia and 94.7% protection against FeLV proviral DNA integration in bone marrow cells. In comparison, the Purevax FeLV Vaccine conferred 20% protection against FeLV persistent antigenemia and 35% protection against FeLV proviral DNA integration in bone marrow cells following challenge. The data from this study show that the Versifel FeLV Vaccine was efficacious in preventing both FeLV persistent p27 antigenemia and FeLV proviral DNA integration in bone marrow cells of cats challenged with this particular challenge model under laboratory conditions and provided better protection than Purevax FeLV in this experimental challenge model with highly virulent FeLV.     

Early life DNA vaccination with the H gene of Canine distemper virus induces robust protection against distemper

Young mink kits (n = 8) were vaccinated with DNA plasmids encoding the viral haemagglutinin protein (H) of a vaccine strain of Canine distemper virus (CDV). Virus neutralising (VN) antibodies were induced after 2 immunisations and after the third immunisation all kits had high VN antibody titres. The VN antibody titres remained high for more than 4 months and the mink were protected against viraemia, lymphopenia, clinical disease and changes in the percentage of IFN-γ producing peripheral blood leucocytes after challenge inoculation with a recent wild type strain of CDV. Essentially, these results demonstrate that early life DNA vaccination with the H gene of a CDV vaccine strain induced robust protective immunity against a recent wild type CDV.     

Oral rabies vaccination of arctic foxes (Alopex lagopus) with an attenuated vaccine.

Arctic foxes were immunized with the SAG1 oral rabies vaccine. The effectiveness was determined by the serological response and by the survival to a challenge dose of rabies virus from an Alaskan fox. Vaccine virus was isolated from saliva 1 h after the liquid vaccine was placed directly into the mouth but not subsequently (tested up to 1 week postvaccination). Two weeks after vaccination, protective antibody levels were present in all foxes and all vaccinated foxes survived challenge at 9 weeks postvaccination. At 26 weeks postvaccination (17 weeks postchallenge) all but one fox had detectable antibody levels. Neural tissue harvested from surviving foxes was negative for rabies virus by direct immunofluorescent testing. One of the foxes vaccinated with SAG1 seroconverted and survived challenge even though the titre of the vaccine used was almost 4 logs less than that used to vaccinate the other foxes. These results suggest that the avirulent SAG1 oral rabies vaccine is very effective in protecting arctic foxes.     

Effect of diethylcarbamazine on cats given feline leukaemia virus vaccine

Leukocell (Norden Laboratories, Lincoln, NE, USA), a commercially available retroviral vaccine, is given to protect susceptible cats against feline leukaemia virus. Oral diethylcarbamazine, an immunomodulator used in the treatment of filariasis, when given with 1 ml i.m. Leukocell, increased titres and duration of serum antibodies to feline oncornavirus-associated cell membrane antigen and transient average monocyte counts in treated/vaccinated cats as compared to cats that received vaccine without diethylcarbamazine. These results may have implications for the development of more effective retroviral vaccination techniques for humans as well as for cats.     

Genetically-engineered subunit vaccine against feline leukaemia virus: protective immune response in cats.

A recombinant retroviral subunit vaccine has been developed that successfully protects cats from infectious feline leukaemia virus (FeLV) challenge. The antigen used is a non-glycosylated protein derived from the envelope glycoprotein of FeLV subgroup A, expressed in Escherichia coli. This recombinant protein, rgp70D, includes the entire exterior envelope protein gp70, plus the first 34 amino acids from the transmembrane protein p15E. The vaccine consists of purified rgp70D absorbed on to aluminium hydroxide and used in conjunction with a novel saponin adjuvant. Cats immunized with this formulation developed a strong humoral immune response, including neutralizing and feline oncornavirus-associated cell membrane antigen antibodies. Vaccinated animals showed an anamnestic response upon intraperitoneal challenge with FeLV-A, and were protected from viral infection. In contrast, the control animals developed viraemia shortly after the challenge, which in most cases became chronic. Formulation of the same antigen with other widely used adjuvants elicited poor protective immune responses in cats.     

Synergistic immunosuppressive effect of anti-TNF combined with methotrexate on antibody responses to the 23 valent pneumococcal polysaccharide vaccine

INTRODUCTION: The efficacy of the immune response upon vaccination in patients treated with anti-tumor necrosis factor-alpha (anti-TNF) with or without methotrexate is the subject of debate. We studied the effect of immunosuppressive treatment, including anti-TNF and methotrexate, on the response to pneumococcal polysaccharide (PPS) vaccine. METHODS: Fifty-two patients treated with immunosuppressives including anti-TNF (anti-TNF group), 41 patients given a similar immunosuppressive regimen without anti-TNF (no anti-TNF group), and 18 healthy controls were vaccinated with a 23 valent PPS vaccine. The percentage of patients treated with methotrexate in the anti-TNF and no anti-TNF group was 65% and 76%, respectively. Antibodies against four of the vaccine antigens (PPS 6B, 9V, 19F and 23F) were measured before and 4 weeks after vaccination. The primary outcome was the response rate, defined as the percentage with a postvaccination titer 0.35 microg/ml in combination with at least a twofold increase in antibody titer. The protection rate was defined as a postvaccination titer > or = 0.35 microg/ml. RESULTS: The use of methotrexate was the strongest predictor of impaired vaccination outcome. Anti-TNF caused an additional immunosuppressive effect in the presence of methotrexate, leading to the lowest response percentages in patients using the combination of these two drugs. The underlying disease, other immunosuppressives such as prednisone or type of anti-TNF agent used did not influence vaccination outcome. CONCLUSIONS: Patients who were treated with the combination of methotrexate and anti-TNF demonstrated a significantly impaired immune response following pneumococcal polysaccharide vaccination as compared to patients treated with either methotrexate or anti-TNF only or immunosuppressives excluding these two compounds.     

Comparison of neutralising antibody assays for detection of antibody to influenza A/H3N2 viruses: an international collaborative study

A study was performed to investigate the reproducibility of haemagglutinin-inhibition (HI) and virus neutralising (VN) assays for detection of anti-influenza antibody. Participants in 11 laboratories from eight countries measured antibody to egg-grown A/Japan/434/2003, cell-grown A/Japan/434/2003 and A/Panama/2007/99 (H3N2) viruses in 18 human and two post-infection ferret sera. There was significant intra-laboratory assay variability for VN compared to HI. For replicate assays within laboratories, 14/410 (3%) and 130/631 (21%) titres differed by >2-fold (p<0.0001), and 0/410 (0%) and 35/631 (6%) titres differed by >5-fold (p<0.0001) by HI and VN, respectively. Although both assays showed inter-laboratory variation, VN assays were significantly more variable than HI. Median geometric coefficients of variation (GCV) for VN assays with each virus were 256%, 323% and 359% compared to 138%, 155% and 261% with HI. A serum standard improved inter-laboratory agreement and reduced median GCVs. This study raises concern about comparability of serology results from H5N1 vaccine trials and it is proposed that an International Standard for influenza H5N1 antibody is developed.     

Differences of humoral and cellular immune response to an acellular pertussis booster in adolescents with a whole cell or acellular primary vaccination

To study the pertussis-specific immune response of adolescents with different prevaccination schedules, we measured the humoral and cell-mediated immunity (CMI) to pertussis antigens before and after a five-component Tdap booster vaccination in 78 adolescents, who had previously received either five doses of a two-component acellular pertussis vaccine (aP; last dose age 4-6 years), four doses of aP (last dose age 18-24 months), or four doses of whole cell pertussis vaccine (wcP; last dose age 18-24 months). The proportion of participants with a twofold rise in titre was 79% against pertussis toxin (PT), 94% against filamentous hemagglutinin (FHA), and 99% against pertactin (PRN) without significant differences between the three groups. However, participants with primary wcP vaccination showed higher postvaccination titres to pertussis toxin (geometric mean titre, GMT 50.3EU/ml) than those with either four (GMT 17.1EU/ml) or five (GMT 16.4EU/ml) previous aP doses. CMI indices to PT, FHA, PRN and fimbriae (FIM) increased after vaccination and were similar between groups. The current adolescent Tdap booster immunization induced good humoral and cellular immune response to pertussis. The higher antibody titres to pertussis toxin may indicate a more effective priming of B cell memory after primary whole-cell vaccination.