Three-year duration of immunity in dogs vaccinated with a canarypox-vectored recombinant canine distemper virus vaccine

Two studies evaluated the duration of serologic response to the recombinant, canarypox-vectored canine distemper virus vaccine (Recombitek, Merial). Serologic duration of immunity was shown to be at least 36 months. Thus, Recombitek provides protection when administered less frequently than the manufacturer's label. After the initial vaccination protocol of two or more doses administered approximately 4 weeks apart, with the last dose given at 12 to 16 weeks of age or older, and re-vaccination at 1 year of age, Recombitek can confidently be readministered every 3 years with assurance of protection in immunocompetent dogs. This allows the vaccine to be administered in accordance with the recommendations of the American Animal Hospital Association Canine Vaccine Task Force and others.

Antigenic and Genetic Characterization of an Avian Poxvirus Isolated from an Endangered Hawaiian Goose (Branta sandvicensis)

An avian poxvirus from cutaneous lesions in a Hawaiian goose (Branta sandvicensis) was characterized in this study. The virus was isolated by inoculation onto the chorioallantoic membranes (CAMs) of developing chicken embryos. Cytoplasmic inclusion bodies were observed on histopathological examination of CAM lesions. Western blotting analysis using polyclonal antiserum against fowl poxvirus (FWPV) showed differences from FWPV, but a similar antigenic profile between Hawaiian goosepox (HGP) isolate and two previous Hawaiian poxvirus isolates were observed. Still three avian poxviruses from Hawaiian birds showed distinguishable reaction in approximately 27, 34, 35, and 81 kDa proteins when polyclonal antibodies against the Hawaiian poxvirus isolate (Alala/lanakila) were used. Restriction fragment length polymorphisms (RFLP) of DNA of this isolate also showed differences from those of FWPV and previous avianpox isolates from Hawaiian forest birds. While nucleotide sequences of a 5.3-kb PstI-HindIII fragment of the genome of HGP isolate revealed very high homology (99% identities) with Canary poxvirus (CNPV) ORF266-274, and like CNPV, homologs of three FWPV ORFs (199, 200, and 202) including any reticuloendotheliosis virus (REV) sequences are not present in the genome of HGP isolate.

Poxvirus-based vaccine candidates for HIV: two decades of experience with special emphasis on canarypox vectors

Poxvirus vectors have emerged as important vectors for licensed veterinary vaccines and candidate vaccines for humans. Vaccinia, highly-attenuated vaccinia strains and avipoxviruses have been assessed extensively in preclinical models, as well as in humans, to determine their immunogenicity and protective efficacy against HIV. The attenuated vaccinia strains and avipoxviruses have been shown to be safe and able to carry HIV genes and express their proteins to induce both antibodies and cellular immune responses. Preclinical studies show protection against HIV challenge. When using a live attenuated vector system, one must be cognizant of the potential for immune dampening because of vector-specific immunity. In this regard, avipoxviruses, such as canarypox, appear free of the inhibitory effects of vector immunity and repeated use. Unlike vaccinia-based vectors derived from classical vaccine strains, NYVAC and modified vaccinia Ankara may be less susceptible to this effect. In the coming 5 to 10 years, we will certainly know whether this class of vaccine candidates, either alone or in a prime-boost format with other vectors or proteins, will contribute to HIV disease management either from a preventive or therapeutic perspective. Additional Phase I and II studies, as well as human efficacy trials will provide new information. Furthermore, it is hoped that this body of data will contribute to a better understanding of the relevance of specific immunogenicity end points to protection and the predictive value of available animal models in HIV vaccine development.

Avipox-based simian immunodeficiency virus (SIV) vaccines elicit a high frequency of SIV-specific CD4+ and CD8+ T-cell responses in vaccinia-experienced SIVmac251-infected macaques

The ability of ALVAC- or fowlpox-based simian immunodeficiency virus (SIV) vaccines to boost SIV-specific CD4+ and CD8+ T-cell responses was tested in 10 vaccinia-experienced macaques infected with SIVmac251. The CD8+ T-cell response to the dominant Gag(181-189) CM9 was quantitated in seven Mamu-A*01-positive macaques by tetramer staining, by ex vivo cytotoxic T-lymphocyte (CTL) activity, and by intracellular cytokine staining (ICS) with the specific Gag(181-189) CM9 peptide. The overall CD8+ T-cell response to Gag was assessed using a peptide pool encompassing the entire Gag protein followed by measurement of TNF-alpha production in ICS assay. Similarly, virus-specific CD4+ T-cell responses were measured by ICS for TNF-alpha following stimulation with the Gag-overlapping peptide and by proliferative response following stimulation with purified p27 Gag. The two vaccine modalities effectively boosted both CD4+ and CD8+ SIV-specific T-cell response despite prior exposure to the vaccinia-derivative NYVAC vector, suggesting that sequential boosting with either avipox-based vector vaccine candidate is a realistic approach in immune therapy of human immunodeficiency virus type 1 (HIV-1)-infected individuals.

Use of restriction fragment length polymorphism, immunoblotting, and polymerase chain reaction in the differentiation of avian poxviruses

Restriction deoxyribonucleic acid (DNA) fragment profile analysis coupled with immunogenic protein profile analysis has provided useful information in determining the differences between vaccine strains and field isolates of fowlpox virus (FPV). The DNA of strains examined in this study clearly fell into 3 minor groups of restriction patterns similar but distinct from one another: restriction patterns exhibited by the vaccine strains except 1 vaccine strain, Vac-82; restriction profiles indicated by Vac-82 and field isolates FI-38 and FI-42; and restriction patterns indicated by field isolates FI-43, FI-51, FI-54, and FI-56. Furthermore, when the strains were analyzed and compared by immunoblotting analysis, they showed group differences similar to the differences in restriction profiles. Both techniques provided high sensitivity in verifying differences between vaccine strains and field isolates of FPV. The disparity found in restriction fragments or immunogenic protein profile between vaccine strains and field isolates does not exclude the appreciable high degree of DNA sequence conservation and homology. However, the minor disparity observed in these strains suggests a molecular basis for why vaccinated commercial flocks could have continually been infected by variant strains of FPV. A rapid and sensitive polymerase chain reaction method, which amplified a product from the 4b core protein gene of the FPV genome, was developed for identification and differentiation of members of the genus Avipoxvirus. Whereas total DNA from either vaccine strains or field isolates was used as template for amplifying a predicted product of 578 or 1409 bp, only cleavage of the amplified product (1409 bp) represented an additional detection technique for species differentiation. An attempt to distinguish between strains on the basis of amplification product was partially successful.

Development of a mixed antigen agar gel enzyme assay (AGEA) for the detection of antibodies to poxvirus in chicken and turkey sera

A mixed-antigen agar gel enzyme assay (AGEA) was developed to detect antibodies to poxviruses in chicken and turkey sera. The assay combines the principles of immunodiffusion and enzyme assay. For the detection of antibodies to fowl poxvirus (FP), pigeon poxvirus (PP) and turkey poxvirus (TP) in turkey serum samples, the three antigens were combined to form a mixed-antigen assay. To screen for antibodies to FP and PP in chicken serum samples, the two antigens were combined. When FP and PP viruses were combined as antigens, the sensitivity for chicken sera was 64% but the sensitivity of the agar gel precipitation test (AGPT) was 34% (P<0.001). When antibodies were detected in turkey sera using the mixed antigens, the AGEA had a sensitivity of 66.4% while that of AGPT was 25% (P<0.001).

Genetic and antigenic characterization of a poxvirus isolate from ostriches

Avian poxvirus was isolated from nodules on the heads and conjunctiva of two 3-to-4-wk-old ostrich chicks. The ostriches from which poxvirus was isolated had been placed on premises where turkeys that had shown evidence of poxvirus infection had been raised earlier. Microscopically, the nodules from the ostriches were composed of proliferating and hypertrophic epithelial cells that formed large fronds. Most of the hypertrophic epithelial cells contained large eosinophilic intracytoplasmic inclusion bodies characteristic of poxvirus. Characterization of the avian poxvirus isolated from the cutaneous lesions in ostriches was based on western blotting of virus antigen, restriction fragment length polymorphism of genomic DNA, pathogenesis, and cross-protection studies in chickens. Antigenic and genetic studies did not reveal any significant difference between the poxvirus isolated from ostriches (PVO) and fowl poxvirus (FPV). Further, susceptible chickens immunized with the PVO were protected when challenged with a virulent strain of FPV. Thus, the poxvirus isolated from ostriches had similar antigenic, genetic, and biological properties to FPV.

Canarypox vaccines induce antigen-specific human gammadelta T cells capable of interferon-gamma production

Induction of human gammadelta T cells was investigated in subjects who were vaccinated with live recombinant canarypox virus expressing human immunodeficiency virus (HIV) proteins or soluble MN rgp120. Both canarypox and rgp120 induced antigen-specific lymphoproliferative and interferon (IFN)-gamma responses. However, only canarypox vaccination induced increased gammadelta T cell responses detectable after secondary in vitro expansion (P<.02). These enhanced gammadelta T cell responses were specific for canarypox but not HIV antigens. Canarypox-specific gammadelta T cells were predominantly Vgamma9(+) and produced intracellular and secreted IFN-gamma. gammadelta T cell lines generated from canarypox vaccinees responded to canarypox antigens but not to mycobacterial antigens shown previously to induce bacille Calmette-Guérin-specific gammadelta T cells. Furthermore, canarypox vaccinations were associated with significantly higher NK cell expansions (P=.02). Increased IFN-gamma production by gammadelta T and NK cells could enhance the induction of protective type 1 memory immunity. Thus, stimulation of gammadelta T cells might be an important feature of live vaccines.

Multistage multiantigen heterologous prime boost vaccine for Plasmodium knowlesi malaria provides partial protection in rhesus macaques

A nonhuman primate model for malaria vaccine development allowing reliable, stringent sporozoite challenge and evaluation of both cellular and antibody responses is needed. We therefore constructed a multicomponent, multistage DNA vaccine for the simian malaria species Plasmodium knowlesi including two preerythrocytic-stage antigens, the circumsporozoite protein (PkCSP) and sporozoite surface protein 2 (PkSSP2), and two blood stage antigens, apical merozoite antigen 1 (PkAMA1) and merozoite surface protein 1 (PkMSP1p42), as well as recombinant canarypox viruses encoding the four antigens (ALVAC-4). The DNA vaccine plasmids expressed the corresponding antigens in vitro and induced antiparasite antibodies in mice. Groups of four rhesus monkeys received three doses of a mixture of the four DNA vaccine plasmids and a plasmid encoding rhesus granulocyte-monocyte colony-stimulating factor, followed by boosting with a single dose of ALVAC-4. Three groups received the priming DNA doses by different routes, either by intramuscular needle injection, by intramuscular injection with a needleless injection device, the Biojector, or by a combination of intramuscular and intradermal routes by Biojector. Animals immunized by any route developed antibody responses against sporozoites and infected erythrocytes and against a recombinant PkCSP protein, as well as gamma interferon-secreting T-cell responses against peptides from PkCSP. Following challenge with 100 P. knowlesi sporozoites, 1 of 12 experimental monkeys was completely protected and the mean parasitemia in the remaining monkeys was significantly lower than that in 4 control monkeys. This model will be important in preclinical vaccine development.

Cross-presentation by dendritic cells of tumor antigen expressed in apoptotic recombinant canarypox virus-infected dendritic cells

We have investigated the possible usefulness of recombinant canarypox virus (ALVAC) encoding the melanoma-associated Ag, Melan-A/MART-1 (MART-1), in cancer immunotherapy, using a dendritic cell (DC)-based approach. ALVAC MART-1-infected DC express, and are able to process and present, the Ag coded by the viral vector. One consistent feature of infection by ALVAC is that these viruses induce apoptosis, and we show cross-presentation of Ag when uninfected DC are cocultured with ALVAC MART-1-infected DC. Uptake of apoptotic virally infected DC by uninfected DC and subsequent expression of tumor Ag in the latter were verified by flow cytometry analysis, image cytometry, and confocal microscopy. Functional activity was monitored in vitro by the stimulation of a MART-1-specific cytotoxic T cell clone. Heightened efficiency in Ag presentation is evidenced in the 2- to 3-fold increase in IFN-gamma production by the T cell clone, as compared with the ALVAC-infected DC alone. Cocultures of ALVAC MART-1-infected and uninfected DC are able to induce MART-1-specific T cell immune responses, as assessed by HLA class I/peptide tetramer binding, IFN-gamma ELISPOT assays, and cytotoxicity tests. Overall, our data indicate that DC infected with recombinant canarypox viruses may represent an efficient presentation platform for tumor Ags, which can be exploited in clinical studies.

Modulation of the antibody response to the HIV envelope subunit by co-administration of infectious or heat-inactivated canarypoxvirus (ALVAC) preparations

Poxviruses are large DNA viruses capable of infecting a broad range of animal species. Infection is generally accompanied by an inflammatory response in the host, the extent of which varies considerably with the specific poxvirus and host species. Regarding ALVAC, a poxvirus derived from the canarypox vaccine strain, Kanapox, and which represents a promising immunization vehicle in humans, nothing is known about its inflammatory capacity. The present study was aimed at documenting this issue in rodents, including mice and guinea pigs. It was then attempted to evaluate how such properties could influence the immunogenicity of an antigen concomitantly administered with ALVAC preparations using the HIV envelope subunit, rgp160, as the model immunogen. The results revealed that ALVAC, either infectious or heat-inactivated, induced in both animal species an early inflammatory response, as evidenced by a rapid migration of neutrophils to the site of inoculation. In parallel, the canarypoxvirus was shown to strongly adjuvant the co-administered immunogen, resulting in a marked increase in Env-specific IgG, IgG1 and particularly IgG2(a) serum titers. Of further interest, the heat-inactivated preparation of ALVAC retained this immunostimulatory activity. Whether or not a link between the inflammatory and immunomodulatory properties of ALVAC exists remains to be established, but such features are clearly interesting with respect to the potential use of ALVAC as an immunization vehicle.

Safety and immunogenicity of a canarypox-vectored human immunodeficiency virus Type 1 vaccine with or without gp120: a phase 2 study in higher- and lower-risk volunteers

Live attenuated viral vectors that express human immunodeficiency virus (HIV) antigens are being developed as potential vaccines to prevent HIV infection. The first phase 2 trial with a canarypox vector (vCP205, which expresses gp120, p55, and protease) was conducted in 435 volunteers with and without gp120 boosting, to expand the safety database and to compare the immunogenicity of the vector in volunteers who were at higher risk with that in volunteers at lower risk for HIV infection. Neutralizing antibodies to the MN strain were stimulated in 94% of volunteers given vCP205 plus gp120 and in 56% of volunteers given vCP205 alone. CD8(+) cytotoxic T lymphocyte cells developed at some time point in 33% of volunteers given vCP205, with or without gp120. Phase 3 field trials with these or similar vaccines are needed, to determine whether efficacy in preventing HIV infection or in slowing disease progression among vaccinees who become infected is associated with the level and types of immune responses that were induced by the vaccines in this study.

A canarypox vector-expressing cytomegalovirus (CMV) phosphoprotein 65 induces long-lasting cytotoxic T cell responses in human CMV-seronegative subjects

The major matrix phosphoprotein 65 (pp65) of cytomegalovirus (CMV) is an important target of HLA-restricted cytotoxic T cells (CTL) after natural infection. A canarypox-CMV pp65 recombinant was studied for its ability to induce CMV pp65-specific CTL, helper T lymphocytes, and antibodies in a phase I clinical trial. Twenty-one CMV-seronegative adult volunteers were randomized to receive immunizations at months 0, 1, 3, and 6 with either canarypox-CMV pp65 or placebo. In canarypox-CMV pp65-immunized subjects, pp65-specific CTL were elicited after only 2 vaccinations and were present at months 12 and 26 in all subjects tested. Cell-depletion studies indicated that the CTL were phenotype CD8(+). Peripheral blood mononuclear cells proliferated in response to stimulation with purified pp65, and antibodies specific for pp65 also were detected. Canarypox-CMV pp65 is the first recombinant vaccine to elicit CMV-specific CTL responses, which suggests the potential usefulness of this approach in preventing disease caused by CMV.

Mature dendritic cells infected with canarypox virus elicit strong anti-human immunodeficiency virus CD8+ and CD4+ T-cell responses from chronically infected individuals

Recombinant canarypox virus vectors containing human immunodeficiency virus type 1 (HIV-1) sequences are promising vaccine candidates, as they replicate poorly in human cells. However, when delivered intramuscularly the vaccines have induced inconsistent and in some cases transient antigen-specific cytotoxic T-cell (CTL) responses in seronegative volunteers. An attractive way to enhance these responses would be to target canarypox virus to professional antigen-presenting cells such as dendritic cells (DCs). We studied (i) the interaction between canarypox virus and DCs and (ii) the T-cell responses induced by DCs infected with canarypox virus vectors containing HIV-1 genes. Mature and not immature DCs resisted the cytopathic effects of canarypox virus and elicited strong effector CD8+ T-cell responses from chronically infected HIV+ individuals, e.g., cytolysis, and secretion of gamma interferon (IFN-gamma) and beta-chemokines. Furthermore, canarypox virus-infected DCs were >30-fold more efficient than monocytes and induced responses that were comparable to those induced by vaccinia virus vectors or peptides. Addition of exogenous cytokines was not necessary to elicit CD8+ effector cells, although the presence of CD4+ T cells was required for their expansion and maintenance. Most strikingly, canarypox virus-infected DCs were directly able to stimulate HIV-specific, IFN-gamma-secreting CD4 helper responses from bulk as well as purified CD4+ T cells. Therefore, these results suggest that targeting canarypox virus vectors to mature DCs could potentially elicit both anti-HIV CD8+ and CD4+ helper responses in vivo.

DNA prime/canarypox boost-based immunotherapy of chronic hepatitis B virus infection in a chimpanzee

There are about 200 million chronic hepatitis B virus (HBV) carriers at high risk of development of cirrhosis and hepatocellular carcinoma. Termination of the carrier state may avert these risks. We have investigated immunotherapy for chronic HBV infection in a chimpanzee HBV carrier using recombinant DNA-based immunization followed by a recombinant canarypox booster. One week after the booster, HBV DNA declined greater than 400-fold and remained undetectable by the quantitative polymerase chain reaction (PCR) assay for 186 weeks. Plasma levels of hepatitis B surface antigen (HBsAg) declined for only a short time. The decline in HBV DNA correlated with a boost in gamma interferon production without a corresponding boost in cytotoxic T lymphocyte levels, and decline in the transcriptional template or covalently closed circular DNA level. Confirmation of these findings requires further studies in chimpanzees and/or in humans.

Phase I study in advanced cancer patients of a diversified prime-and-boost vaccination protocol using recombinant vaccinia virus and recombinant nonreplicating avipox virus to elicit anti-carcinoembryonic antigen immune responses

PURPOSE

This trial sought to determine, for the first time, the validity in human vaccinations of using two different recombinant vaccines in diversified prime-and-boost regimens to enhance T-cell responses to a tumor antigen.

PATIENTS AND METHODS

Eighteen patients with advanced tumors expressing carcinoembryonic antigen (CEA) were randomized to receive either recombinant vaccinia (rV)-CEA followed by three avipox-CEA vaccinations, or avipox-CEA (three times) followed by one rV-CEA vaccination. Subsequent vaccinations in both cohorts were with avipox-CEA. Immunologic monitoring was performed using a CEA peptide and the enzyme-linked immunospot assay for interferon gamma production.

RESULTS

rV-CEA followed by avipox-CEA was superior to the reverse order in the generation of CEA-specific T-cell responses. Further increases in CEA-specific T-cell precursors were seen when local granulocyte-macrophage colony-stimulating factor (GM-CSF) and low-dose interleukin (IL)-2 were given with subsequent vaccinations. The treatment was extremely well tolerated. Limited clinical activity was seen using vaccines alone in this patient population. Antibody production against CEA was also observed in some of the treated patients.

CONCLUSION

rV-CEA was more effective in its role as a primer of the immune system; avipox-CEA could be given up to eight times with continued increases in CEA T-cell precursors. Future trials should use rV-CEA first followed by avipox-CEA. Vaccines specific to CEA are able to generate CEA-specific T-cell responses in patients without significant toxicity. T-cell responses using vaccines alone may be inadequate to generate significant anticancer objective responses in patients with advanced disease. Cytokines such as GM-CSF and IL-2 may play a key role in generating such responses.

The use of a rapid ELISPOT assay to analyze peptide-specific immune responses in carcinoma patients to peptide vs. recombinant poxvirus vaccines

An enzyme-linked immunosorbent spot (ELISPOT) assay for interferon gamma production has been used to analyze specific T cell responses to a Flu 9-mer peptide, and a 9-mer peptide of carcinoembryonic antigen (CEA). Assays were performed on peripheral blood mononuclear cells (PBMC) of HLA-A2-positive patients with CEA-expressing carcinomas, both before and after vaccination with CEA-based vaccines, and from HLA-A2-positive healthy blood donors. The ELISPOT assay utilized aliquots of frozen PBMC, and assays were performed after 24 h in culture with peptide to rule out any artifacts due to long-term in vitro stimulation cycles. An internal standard was used for each assay to define reproducibility of the assay, and all samples from a given patient (pre- and post-vaccination, with both the Flu and CEA peptides) were analyzed simultaneously. The results indicated a trend towards healthy blood donors having higher levels of Flu-specific T cell precursors than do colon carcinoma patients, but these results were not statistically significant (P = 0.06). On the other hand, slightly higher CEA-specific T cell responses were observed in cancer patients with CEA-expressing carcinomas than in healthy blood donors. PBMC from two CEA-based vaccine clinical trials were analyzed for T cell responses to the same CEA peptide and to the Flu control peptide. The first trial consisted of three monthly vaccinations of CEA peptide (designated PPP) in adjuvant. The second trial consisted of cohorts receiving three monthly vaccinations of avipox-CEA recombinant (designated AAA) or cohorts receiving a primary vaccination with recombinant vaccinia-CEA followed by two monthly vaccinations with avipox-CEA (designated VAA). Few, if any, CEA-specific T cell responses were seen in the PPP vaccinations, while the majority of patients receiving the poxvirus CEA recombinants demonstrated increases in CEA-specific T cell responses and no increases in Flu-specific responses. CEA-specific IgG responses were also demonstrated in patients following recombinant CEA poxvirus vaccinations. Statistical analyses of the T cell responses to the same CEA peptide demonstrated a P value of 0.028 for the recombinant poxvirus vaccines, as compared with the peptide vaccine. There were no differences seen (P = 0.37) in Flu-specific responses after these two types of CEA vaccination. These results thus provide the first evidence that poxvirus recombinant-based vaccines are more potent in the initiation of tumor-antigen-specific T cell responses than vaccines employing peptide in adjuvant, when assays are conducted in an identical manner, and in defining responses to the same peptide. These results also demonstrate for the first time that an ELISPOT assay, performed over a 24-h period and without in vitro sensitization, can be successfully used to monitor immune responses to a tumor-associated antigen in cancer patients.

Phase I clinical trial of a recombinant canarypoxvirus (ALVAC) vaccine expressing human carcinoembryonic antigen and the B7.1 co-stimulatory molecule

The generation of cytotoxic effector T cells requires delivery of two signals, one derived from a specific antigenic epitope and one from a costimulatory molecule. A phase I clinical trial was conducted with a non-replicating canarypoxvirus (ALVAC) constructed to express both human carcinoembryonic antigen (CEA) and the B7.1 costimulatory molecule. This was the first study in cancer patients to determine if the delivery of costimulation with a tumor vaccine was feasible and improved immune responses. Three cohorts of six patients, each with advanced CEA-expressing adenocarcinomas, were treated with increasing doses of an ALVAC-CEA-B7.1 vaccine (4.5 x 10(6), 4.5 x 10(7), and 4.5 x 10(8) plaque-forming units, PFU). Patients were vaccinated by intramuscular injection every 4 weeks for 3 months and monitored for side-effects, tumor growth and anti-CEA immune responses. ALVAC-CEA-B7.1 at doses up to 4.5 x 10(8) PFU was given without evidence of significant toxicity or autoimmune reactions. Three patients experienced clinically stable disease that correlated with increasing CEA-specific precursor T cells, as shown by in vitro interferon-gamma enzyme-linked immunoassay spot tests (ELISPOT). These three patients underwent repeated vaccination resulting in augmented CEA-specific T cell responses. This study represents the first use of costimulation to enhance antitumor vaccines in cancer patients. This approach resulted in CEA-specific immunity associated with stable diseases in three patients. This study also demonstrated that CEA-specific T cell responses could be sustained by repeated vaccinations. Although the number of patients was small, the addition of B7.1 to virus-based vaccines may improve immunological and stable diseases to vaccination against tumor-associated antigens with tolerable toxicity.

Poxvirus-induced immunostimulating effects on porcine leukocytes

The prophylactic application of inactivated parapox ovis viruses (Baypamun; Bayer AG, Leverkusen, Germany) has been shown to reduce efficiently the outbreak of stress-mediated diseases in different species. However, little is known about the basic mechanism behind this observed stimulatory property. We therefore tested eight inactivated poxvirus strains belonging to three different genera (Orthopoxvirus, Avipoxvirus, and Parapoxvirus) for their capacity to activate cells of the porcine innate and specific immune systems in vitro. The results indicated that poxviruses failed to induce increased phagocytosis, oxidative burst, or natural killer cell activity in swine. In contrast, enhanced release of interleukin-2, alpha interferon, and gamma interferon, as well as strong proliferation, could be measured. Flow cytometric analyses and cell sorting experiments identified T-helper cells as the main target responding to inactivated poxviruses: the activated cells had a CD4(high) CD25(+) major histocompatibility complex type II-positive phenotype and were the major source of secreted cytokines. Together, the results demonstrated that all tested poxviruses possessed immunostimulating capacity. These in vitro poxvirus-induced effects may be responsible at least in part for the in vivo immunostimulating capacity of inactivated poxviruses.

DNA prime-canarypox boost with polycistronic hepatitis C virus (HCV) genes generates potent immune responses to HCV structural and nonstructural proteins

DNA vaccination was employed to study immune responses to hepatitis C virus (HCV) proteins. As an immunizing strategy, we studied immune responses of BALB/c (H-2d) and C57BL/6 mice (H-2b) to HCV genes delivered intramuscularly as a polycistronic construct capsid/E1/E2/NS2/NS3 (pRC/C-NS3) encoding 5 structural and nonstructural proteins. We also evaluated canarypox virus containing the same HCV genes as a means for potentiating immune responses to naked DNA. Our results indicate that mice that received a polycistronic pRC/C-NS3 with canarypox booster had enhanced antibody and cellular responses to HCV proteins. Immunodominant CD8(+) T cell responses to several HCV structural and nonstructural proteins, characterized by cytotoxicity and interferon (IFN)-gamma production or IFN-gamma production without significant cytotoxicity, were observed in both strains of mice. The combination of naked DNA with a nonreplicating canarypox booster encoding HCV polycistronic pRC/C-NS3 genes appears to diversify and enhance T cell responses to HCV proteins.

Immunogenicity of whole-cell tumor preparations infected with the ALVAC viral vector

The immunogenicity of recombinant canarypox (ALVAC) viral vectors within murine whole-cell tumor vaccines was evaluated using the T cell thymic lymphoma STF10 and the B16 melanoma. Tumor cells were modified with the recombinant ALVAC vectors and injected into syngeneic mice. Control mice receiving cells alone all developed tumors, while mice injected with tumor variants bearing parental and recombinant vectors either completely rejected their tumors, or exhibited a significant delay in tumor formation. Rechallenge of mice receiving STF10-variant vaccines yielded a protective effect against parental tumor cells only when a modified regimen incorporating two vaccinations was utilized. Notably, the parental ALVAC virus was equivalent to all other recombinant ALVAC viruses in conferring antitumor immunity when using a prime-and-boost protocol. Tumorigenicity experiments in nude mice revealed that the effector mechanism mediating rejection of tumor cells bearing ALVAC vectors is multifactorial, in that the immunogenicity of STF10/ALVAC vaccines is reduced, but not completely abolished in these mice. Finally, in vitro experiments revealed that cytotoxic T cells specific for parental STF10 cells could be generated as a result of in vivo immunization with STF10/ALVAC vaccines.

Correlation between the immune response elicited in rabbits by env-recombinant avipox vaccines and the inhibition of HIV-1-specific functions

The fine immunoreactivity of the rabbit humoral response elicited by four env-recombinant avipoxviruses and their ability to stimulate a memory T-cell response and a protective immunity have been studied. The antibody specificity was compared with the serum neutralizing activity and virus-specific T-cell proliferative response. Resistance to challenge by cell-associated HIV-1 was monitored by PCR. Canarypox (CP) and fowlpox (FP) constructs, containing the complete env gene (IS(+)) from the HIV-1(SF2) strain, induced a higher profile of epitope recognition than their counterparts expressing the env gene deleted of the putative immunosuppressive region (IS(-)). Serum neutralizing activity was in agreement with fusion inhibition and lymphoproliferative response in rabbits immunized with CPIS(+), and only partially with FPIS(+). Rabbits failed to be infected, but anti- p55 gag-specific antibodies could be demonstrated by Western blot. This study confirms the ability of these non-replicative live recombinant viruses to elicit a complete immune response, capable of inhibiting specific HIV-1 functions.

Human immunodeficiency virus type 1 envelope-specific cytotoxic T lymphocytes response dynamics after prime-boost vaccine regimens with human immunodeficiency virus type 1 canarypox and pseudovirions

Virus-specific cytotoxic T lymphocytes (CTLs) may represent significant immune mechanisms in the control of human immunodeficiency virus (HIV) infection and, therefore, CTL induction may be a fundamental goal in the development of an efficacious acquired immunodeficiency syndrome (AIDS) vaccine. In the current study, prime-boost protocols were used to investigate the potential of noninfectious human immunodeficiency virus type 1 (HIV-1) pseudovirions (HIV PSV) in enhancing HIV-specific CTL responses in Balb/c mice primed with the recombinant canarypox vector, vCP205, encoding HIV-1 gp120 (MN strain) in addition to Gag/Protease (HIB strain). The prime-boost immunization regimens were administered intramuscularly and involved injections of vCP205 followed by boosts with HIV PSV. Previous vaccination strategies solely involving vCP205 had induced good cellular immune responses in uninfected human volunteers, despite some limitations. The use of genetically engineered HIV PSV was a logical step in the evaluation of whole noninfectious virus or inactivated virus vaccine strategies, particularly as a potential boosting agent for vCP205-primed recipients. Based on this current study, HIV PSV appeared to have the capability to effectively induce and boost cell-mediated HIV-1-specific responses. In order to observe the immune effects of HIV PSV in a prime-boost immunization strategy, both HIV vaccine immunogens required careful titration in vivo. This suggests that careful consideration should be given to the optimization of immunization protocols destined for human use.

Cytomegalovirus vaccine

Congenital cytomegalovirus disease is an unsolved public health problem, unlikely to be solved by means other than immune prophylaxis. Development of a vaccine has been hampered by low awareness of the problem, which is caused by the often delayed detection of abnormalities after birth. Nevertheless, cytomegalovirus vaccine development is active. An attenuated, live vaccine has been studied extensively, and an improved strain may result from genetic manipulation. An immunogenic viral glycoprotein (gB) vaccine is currently in clinical trial to determine if antibodies alone will be protective. The idea of a combined vaccine has been proposed, in which a canarypox recombinant containing several cytomegalovirus genes is used both to generate cellular immunity and to prime for augmented antibody responses to the viral glycoprotein. Finally, DNA plasmids containing cytomegalovirus genes are being investigated for their utility as vaccines.

Efficient human immunodeficiency virus ( HIV)-1 Gag-Env pseudovirion formation elicited from mammalian cells by a canarypox HIV vaccine candidate

Canarypox viruses undergo abortive replication in mammalian cells. Despite this restriction on replication in mammalian cells, significant immune responses have been shown in animals and in humans receiving recombinant canarypox vaccine vectors expressing heterologous immunogens. A recombinant canarypox vaccine candidate (vCP205), which expresses human immunodeficiency virus (HIV)-1 Gag, Env, and protease proteins, is presently under investigation in phase I and phase II human trials in the United States and elsewhere. In this study, the ability of vCP205 to elicit HIV Gag-Env pseudovirion formation in avian and mammalian cells was investigated. Gag-Env pseudovirions were produced from both avian and mammalian cell lines infected by this vaccine vector. A subset of mammalian cells was identified in which pseudovirion production and release was very efficient, surpassing the production from infected avian cells. The production of Gag-Env pseudovirions by canarypox HIV vaccine vectors may have important implications for future HIV vaccine design.

A canarypox vector expressing cytomegalovirus (CMV) glycoprotein B primes for antibody responses to a live attenuated CMV vaccine (Towne)

To develop a vaccine against cytomegalovirus (CMV), a canarypox virus (ALVAC) expressing CMV glycoprotein (gB) was evaluated alone or in combination with a live, attenuated CMV vaccine (Towne). Three doses of 106.5 TCID50 of ALVAC-CMV(gB) induced very low neutralizing or ELISA antibodies in most seronegative adults. However, to determine whether ALVAC-CMV(gB) could prime for antibody responses, 20 seronegative adults randomly received either 106.8 TCID50 of ALVAC-CMV(gB) or 106.8 TCID50 of ALVAC-RG, expressing the rabies glycoprotein, administered at 0 and 1 month, with all subjects receiving a dose of 103.5 pfu of the Towne vaccine at 90 days. For subjects primed with ALVAC-CMV(gB), neutralizing titers and ELISA antibodies to CMV(gB) developed sooner, were much higher, and persisted longer than for subjects primed with ALVAC-RG. All vaccines were well tolerated. These results demonstrate that ALVAC-CMV(gB) primes the immune system and suggest a combined-vaccine strategy to induce potentially protective levels of neutralizing antibodies.

Identification of five MAGE-A1 epitopes recognized by cytolytic T lymphocytes obtained by in vitro stimulation with dendritic cells transduced with MAGE-A1

MAGE genes are expressed by many human tumors of different histological types but not by normal cells, except for male germline cells. The Ags encoded by MAGE genes and recognized by T cells are therefore strictly tumor-specific. Clinical trials involving therapeutic vaccination of cancer patients with MAGE antigenic peptides or proteins are in progress. To increase the range of patients eligible for therapy with peptides, it is important to identify additional MAGE epitopes recognized by CTL. Candidate peptides known to bind to a given HLA have been used to stimulate T lymphocytes in vitro. In some instances, CTL clones directed against these synthetic peptides have been obtained, but these clones often failed to recognize tumor cells expressing the relevant gene. Therefore, we designed a method to identify CTL epitopes that selects naturally processed peptides. Monocyte-derived dendritic cells infected with a recombinant canarypoxvirus (ALVAC) containing the entire MAGE-A1 gene were used to stimulate CD8+ T lymphocytes from the blood of individuals without cancer. Responder cell microcultures that specifically lysed autologous cells expressing MAGE-A1 were cloned using autologous stimulator cells either transduced with a retrovirus coding for MAGE-A1 or infected with recombinant Yersinia-MAGE-A1 bacteria. The CTL clones were tested for their ability to lyse autologous cells loaded with each of a set of overlapping MAGE-A1 peptides. This strategy led to the identification of five new MAGE-A1 epitopes recognized by CTL clones on HLA-A3, -A28, -B53, -Cw2, and -Cw3 molecules. All of these CTL clones recognized target cells expressing gene MAGE-A1.

A canarypox vaccine expressing multiple human immunodeficiency virus type 1 genes given alone or with rgp120 elicits broad and durable CD8+ cytotoxic T lymphocyte responses in seronegative volunteers

Induction of CD8+ cytotoxic T cells is considered one of the important correlates for the protective efficacy of candidate human immunodeficiency virus type 1 (HIV-1) vaccines. To induce CD8+ cytotoxic T lymphocytes (CTLs) along with neutralizing antibody and CD4+ T cell help, a live canarypox virus construct expressing gp120, transmembrane gp41, the gag and protease genes, and sequences containing CTL epitopes in nef and pol was given simultaneously with, or followed by, rgp120 SF2. CD8+ CTLs were detected in 61% of volunteers at some time during the trial. Three to 6 months after the last immunization, the gene-specific responses were gag, 26/81; env, 17/77; nef, 12/77; and pol, 3/16. Simultaneous immunization with the canarypox vector and the subunit, beginning with the initial immunization, resulted in earlier antibody responses. In summary, a strategy of immunization with a canarypox vector expressing multiple genes of HIV-1 given with gp120 results in durable CD8+ CTL responses to a broad range of epitopes.

Safety and immunogenicity of a live recombinant canarypox virus expressing HIV type 1 gp120 MN MN tm/gag/protease LAI (ALVAC-HIV, vCP205) followed by a p24E-V3 MN synthetic peptide (CLTB-36) administered in healthy volunteers at low risk for HIV infection. AGIS Group and L'Agence Nationale de Recherches sur Le Sida

A live recombinant canarypox vector expressing HIV-1 gpl20 MN tm/gag/protease LAI (ALVAC-HIV, vCP205) alone or boosted by a p24E-V3 MN synthetic peptide (CLTB-36) was tested in healthy volunteers at low risk for HIV infection for their safety and immunogenicity. Both antigens were well tolerated. ALVAC-HIV (vCP205) induced low levels of neutralizing antibodies against HIV-1 MN in 33% of the volunteers. None of them had detectable neutralizing antibodies against a nonsyncytium-inducing HIV-1 clade B primary isolate (Bx08). After the fourth injection of vCP205, CTL activity was detected in 33% of the volunteers and was directed against Env, Gag, and Pol. This activity was mediated by both CD4+ and CD8+ lymphocytes. On the other hand, the CLTB-36 peptide was poorly immunogenic and induced no neutralizing antibodies or CTLs. Although the ALVAC-HIV (vCP205) and CLTB-36 prime-boost regimen was not optimal, further studies with ALVAC-HIV (vCP205) are warranted because of its clear induction of a cellular immune response and utility as a priming agent for other subunit antigens such as envelope glycoproteins, pseudoparticles, or new peptides.

Mucosal vaccination with recombinant poxvirus vaccines protects ferrets against symptomatic CDV infection

Canine distemper virus (CDV) infection of ferrets causes a disease characterized by fever, erythema, conjunctivitis and leukocytopenia, similar clinically to measles except for the fatal neurologic sequelae of CDV. We vaccinated juvenile ferrets twice at 4-week intervals by the intranasal or intraduodenal route with attenuated vaccinia (NYVAC) or canarypox virus (ALVAC) constructs containing the CDV hemagglutinin and fusion genes. Controls were vaccinated with the same vectors expressing rabies glycoprotein. Animals were challenged intranasally 4 weeks after the second vaccination with virulent CDV. Body weights, white blood cell (WBC) counts and temperatures were monitored and ferrets were observed daily for clinical signs of infection. WBCs were assayed for the presence of viral RNA by RT-PCR. Intranasally vaccinated animals survived challenge with no virologic or clinical evidence of infection. Vaccination by the intraduodenal route did not provide complete protection. All control animals developed typical distemper. Ferrets can be effectively protected against distemper by mucosal vaccination with poxvirus vaccines.

Induction of immune responses to HIV-1 by canarypox virus (ALVAC) HIV-1 and gp120 SF-2 recombinant vaccines in uninfected volunteers. NIAID AIDS Vaccine Evaluation Group

OBJECTIVE

To determine the ability of live attenuated canarypox virus expressing HIV antigens to induce CD8+ cytotoxic T-cell responses and to prime for neutralizing antibody responses to boosting with purified recombinant gp120 subunit vaccine.

DESIGN

A prospective, double-blind, randomized, immunogenicity and safety study was conducted in healthy adults at low risk for acquiring HIV infection and who were seronegative for HIV.

METHODS

CD8+ cytotoxic T-cells directed against Env or Gag expressing target cells were measured after live recombinant canarypox-HIV-1 vaccine priming (vaccine given at days 0, 7, 14 and 21). Neutralizing antibodies were measured after subunit boosting (vaccine given at days 28 and 84).

RESULTS

CD8+ CTL were induced in 64% of volunteers by the live recombinant canarypox-HIV-1 vaccine. All volunteers who received two doses of subunit vaccine after live recombinant canarypox priming developed neutralizing antibodies directed against laboratory strains of HIV-1 and seven out of eight volunteers tested developed neutralizing antibodies to the primary isolate, BZ167, but to none of eight other primary isolates. Unprimed controls had low or absent neutralizing antibodies after two doses of subunit vaccine.

CONCLUSIONS

The live canarypox vector was safe, stimulated cytotoxic T-cells and primed for a vigorous neutralizing antibody response upon boosting with subunit gp120 vaccine. This vaccine combination should be evaluated further for inducing protection against HIV infection.

Primary Th1 cell immunization against HIVgp160 in SCID-hu mice coengrafted with peripheral blood lymphocytes and skin

SCID-hu mouse models are of interest in the pathologic investigation of HIV infection, but obtaining a T cell response in SCID-hu-PBL mice is still controversial. We have developed a SCID model by engrafting human skin and autologous PBLs from HIV-seronegative individuals. The study describes the ability of this human-mouse chimera to generate in vivo a primary T lymphocyte response against HIV Ag. The injection of human autologous PBLs was performed 4 to 5 wk after the skin engraftment. Two weeks after injection of PBLs, chimeric mice were immunized with recombinant canary pox virus expressing HIV-1 LAIgp160 (vCP-LAIgp160) and supplemented or not with rIL-2. Intradermal vCP-LAIgp160 injection induced an intradermal perivascular human lymphocytic infiltrate and an epidermic network of CD1a+, CD80+, and CD86+ cells. We derived CD4+ T cell lines (STLs) from the human skin graft of immunized mice, showing that STLs mediated an MHC class II-restricted cytolytic activity directed against HIV-LAIgp160 Ags. Cytokine gene expression in both human skin cells and in STLs showed a predominance of IL-2, IFN-gamma, and IL-12 transcripts. Finally, the T cell repertoire analysis using the immunoscope technique showed a very limited CDR3 length polymorphism in the skin infiltrating lymphocytes suggesting an Ag-specific repertoire. The ability to induce a primary Th1 cell response in vivo affords a useful preclinical model for testing vaccine strategies.

Replication-defective canarypox (ALVAC) vectors effectively activate anti-human immunodeficiency virus-1 cytotoxic T lymphocytes present in infected patients: implications for antigen-specific immunotherapy

In the attempt to develop immunotherapeutic strategies for acquired immunodeficiency syndrome capable of activating effector cells in an antigen-specific manner while maintaining the broadest possible T-cell repertoire, we evaluated two canarypox (ALVAC)-based vectors for their capacity to induce ex vivo activation/expansion of human immunodeficiency virus (HIV)-specific CD8+ cytotoxic lymphocyte precursors (CTLp) obtained from HIV-1-infected donors. These two vectors, vCP205 encoding HIV-1 gp120 + TM (28 amino acid transmembrane anchor sequence) in addition to Gag/protease and vCP300 encoding gp120 + Gag/protease as well as Nef and Pol CTL determinants, are pancytotropic but replication incompetent in mammalian cells. Bulk peripheral blood mononuclear cells (PBMCs) or enriched CD8+ T cells were stimulated for 10 days with autologous ALVAC-infected PBMCs in the presence of different cytokine combinations (interleukin-2 [IL-2], IL-4, IL-7, and IL-12). Activation by ALVAC constructs was highly antigen-specific, because vCP205 elicited only Env and Gag CTL, whereas vCP300 elicited broader reactivities against Env, Gag, Pol, and Nef determinants. The ALVAC activation of CTLp was IL-2 dependent and enhanced by the addition of IL-7, whereas IL-4 and IL-12 failed to augment cytotoxic reactivities elicited by these constructs. The expansion of enriched CD8+ T cells after activation with vCP300 was higher in patients with CD4 counts greater than 400 cells/microL. Two rounds of in vitro stimulation (IVS) with vCP300 resulted in nearly an eightfold expansion of CD8+ lymphocytes over a 25-day period. After the second IVS, an average 3.2-fold increase among the different antigen-specific CTL frequencies was achieved. These studies clearly show that HIV-recombinant ALVAC vectors represent powerful polyvalent antigenic stimuli for activation and expansion of the CD8 lymphocyte response that occurs as a result of HIV infection.

Effect of dietary fatty acids on humoral immune response of turkeys

1. This study examined the effect of increasing amounts of dietary polyunsaturated fatty acids on the fatty acid composition in serum and antibody production following a standard vaccination programme in growing turkeys. Turkey poults were fed on 5 diets containing 75g/kg added fat made up of different proportions of palm and soyabean oils, and were vaccinated against Newcastle disease, infectious bronchitis and necrotic enteritis according to a standard vaccination programme. Blood samples were taken before and one week after each vaccination. 2. Fatty acid composition in serum reflected the composition of the diets although arachidonic acid concentration was not changed by dietary fatty acid content. Growth, erythrocyte and leukocyte parameters were not affected by the respective diets. 3. Specific antibody production was related quadratically to serum linoleic and total n-6 polyunsaturated fatty acid concentrations. No correlation was found with linolenic or arachidonic acids. 4. It is concluded that dietary fatty acid composition can augment the specific anti-vaccine immune response in turkey poults.

Protection of dogs against canine distemper by vaccination with a canarypox virus recombinant expressing canine distemper virus fusion and hemagglutinin glycoproteins

OBJECTIVES

To evaluate the safety and efficacy of a live canarypox virus recombinant-canine distemper virus (CDV) combination vaccine against virulent CDV challenge exposure, and to document lack of interference among the other modified-live virus (MLV) components.

ANIMALS

33 specific-pathogen-free (SPF) Beagle pups (7 to 10 weeks old).

PROCEDURE

A canarypox virus recombinant-CDV combination vaccine was tested for safety and efficacy along with MLV components (canine adenovirus type 2, canine coronavirus, canine parainfluenza virus, and canine parvovirus) in 26 SPF Beagle pups. The combination vaccine was rehydrated with either Leptospira canicola-L icterohaemorrhagiae combination bacterin (vaccine 1) or sterile diluent (vaccine 2). An additional group of 7 seronegative SPF pups received the control MLV components devoid of the combination vaccine (vaccine 3). Two vaccinations were administered 21 days apart, either IM or SC. The dose of the combination vaccine used to inoculate these pups was 40 times lower than the recommended commercial dose. At 21 days after the booster vaccination, all pups were challenge exposed with a virulent CDV strain, then were observed for 21 days to record morbidity and mortality.

RESULTS

Adverse local or generalized reactions were not induced by vaccinations. All vaccinates seroconverted to CDV. Serum antibody titers to MLV components were not different, with or without inclusion of the combination vaccine. After challenge exposure, morbidity and mortality in vaccinates were 0% (0/26); in control dogs, values were 100% morbidity and 86% mortality (6/7). Brain impression smear slides made from all dogs that did not survive challenge exposure were CDV positive by use of a direct fluorescein isothiocyanate method.

CONCLUSIONS

The canarypox virus-CDV combination vaccine, administered SC or IM, is a safe product that elicits CDV seroconversion, does not interfere with other vaccine components, and protects vaccinated pups against virulent CDV challenge exposure.

Comparison of field and vaccine strains of Australian fowlpox viruses

The mild fowlpox vaccine, FPV M, widely used in Australia is composed of two predominant genotypes based upon differences identifiable in restriction enzyme analyses of plaque purified derivatives of this vaccine. The differences, where identifiable, were in the end fragments of the genomes. Five field isolates of FPV from chickens in New South Wales showed restriction enzyme profiles closely related to the more virulent (standard) vaccine strain, FPV S. The FPV S strain differs from FPV M in both terminal genome fragments and in the presence of a PstI fragment of approximately 10kb (this fragment was also present in PstI digests of all of the field isolates). Plaque purified derivatives of FPV M showed similar lesion development upon inoculation into the wing web of chickens. The field isolates showed significantly higher virulence in day-old and three-week-old chickens in comparison with FPV M. One field isolate was similar to the FPV S vaccine. Two isolates had slowly developing wing web lesions, caused significant secondary lesions in three-week-old chickens and generalised poxvirus infection when inoculated into day-old chickens. For two isolates, the primary wing web lesion took even longer to develop and resolve although these isolates did not cause generalised poxvirus infection. It was possible to identify four virulence/pathogenicity types amongst these vaccine and field isolates of FPV. These strains may allow the characterisation of FPV encoded virulence factors. The field strains with higher virulence may be suitable as parent strains for the construction of FPV recombinants with enhanced immune responses to co-expressed vaccine antigens when compared with current FPV M strain based recombinants.

Evaluation of a commercial quail pox vaccine (Bio-Pox Q) for the control of "variant" fowl poxvirus infections

Groups of 3-week-old specific pathogen-free chickens immunized with a commercial live-virus quail pox vaccine (Bio-Pox Q) were not protected against challenge with "variant" poxviruses isolated from chickens that were previously vaccinated with commercial fowl pox vaccine. The percentages of vaccinated chickens resistant to challenge with each of the five variant field isolates were 0%, 20%, 0%, 20%, and 10%, respectively. However, when immunity engendered by the variant field isolates was challenged with the commercial quail pox vaccine virus, 80%, 70%, 80%, 50%, and 60% of the vaccinates, respectively, were protected. Results from cross-immunity studies indicate that the commercial quail pox vaccine does share some immunologic relationship with these variant poxvirus field isolates, but not enough to be used in the control of some outbreaks of pox caused by variant poxviruses.

Cross-protection test of an avian poxvirus isolated from houbara bustards

An avian poxvirus was isolated previously from the houbara bustard (Chlamydotis undulata). We carried out a cross-protection test on 66 captive-bred canaries. Thirty-five canaries were vaccinated with a commercial canary poxvirus (CP) vaccine. Three weeks later all 66 birds were assigned randomly to six different groups: group Ia (n = 14) was vaccinated and challenged with houbara bustard poxvirus (HP) strain; group Ib (n = 13) was vaccinated and challenged with a CP strain; group Ic (n = 7) was vaccinated and not inoculated; group IIa (n = 14) was nonvaccinated and challenged with HP strain; group IIb (n = 11) was nonvaccinated and challenged with a CP strain; and group IIc (n = 7) was not vaccinated and not challenged. Vaccinated groups (Ia, Ib, Ic) had no losses and remained healthy. All of the birds (100%) in group IIb died within 10 days, and 10 birds (71.4%) of group IIa died within 20 days. The nonvaccinated control group (IIc) remained healthy. Poxvirus was isolated from the liver, digestive tract, lungs, and inoculation lesions of nonvaccinated dead CP- and HP-challenged birds. Secondary bacterial infections were higher among nonvaccinated HP-challenged birds (85.7%) than in nonvaccinated CP-challenged birds (25%). The results of this experiment reveal a degree of immunogenic relatedness between CP and HP strain and support the recommendation that houbara bustards be vaccinated with a CP vaccine.

p53 as a target for cancer vaccines: recombinant canarypox virus vectors expressing p53 protect mice against lethal tumor cell challenge

The p53 protein is an attractive target for immunotherapy, because mutations in the p53 gene are the most common genetic alterations found in human tumors. These mutations result in high levels of p53 protein in the tumor cell, whereas the expression level of wild-type p53 in nonmalignant tissue is usually much lower. Several canarypox virus recombinants expressing human or murine p53 in wild-type or mutant form were constructed. Immunization with these viruses protected BALB/c mice from a challenge with an isogenic and highly tumorigenic mouse fibroblast tumor cell line expressing high levels of mutant p53. The tumor protection was equally effective regardless of whether wild-type or mutant p53 was used for the immunization, indicating that the immunologic response was not dependent on any particular p53 mutation and that immunization with this live virus vaccine works effectively against mutant p53 protein expressed in a tumor cell. In tumors escaping immunologic rejection, the expression of the p53 protein was commonly down-regulated.

The effect of varying dietary concentrations of vitamin A on immune response in the turkey

1. The effect of dietary vitamin A on antibody production and T-cell proliferative response was determined in poults from 21 to 41 d old. Poults were fed on soyabean meal-sorghum-based diets with concentrations of supplemented vitamin A from 0 to 13.2 micrograms/g retinol equivalents from hatching and were immunised with Newcastle disease virus (NDV) and turkey pox vaccines. T-cell proliferation response to concanavlin A was determined in vitro at 31 d old. Antibodies to NDV and turkey pox in serum were determined at 10 and 20 d after inoculation. 2. Poults receiving the diet with no added dietary vitamin A died by 22 d and had very low concentrations of plasma and liver vitamin A. 3. Increasing dietary concentrations of vitamin A enhanced the proliferative response until the diet contained 6.0 micrograms/g, above which the response began to decrease. The antibody titres to NDV and turkey pox increased as dietary vitamin A increased, with maximal values found 10 d after inoculation with 6.0 micrograms/g. At 20 d after inoculation low antibody titres were found with low vitamin A intake. 4. These data suggest that maximal immune responses in the poult may be achieved at dietary intakes of vitamin A at or higher than those recommended by NRC (1984, 1994).

Biological and immunogenic properties of a canarypox-rabies recombinant, ALVAC-RG (vCP65) in non-avian species

A canarypox-based (ALVAC) recombinant expressing the rabies G glycoprotein has been utilized to assess in vitro and in vivo biological properties of the canarypox virus vector system. In vitro studies have shown that no replication of the virus can be detected on six human-derived cell lines, nor can the virus be readily adapted to replicate on non-avian cells. Expression of the rabies G can be detected on all cell lines analyzed in the absence of productive viral replication. Analysis of viral-specific DNA accumulation indicated that the block in the replication cycle in the human cell lines analyzed occurred prior to DNA replication. The exact nature of the block, however, remains unknown. The concept of using a non-replicating immunization vehicle has been demonstrated through extensive in vivo studies in a range of species including non-human primates and humans. The results of such in vivo studies have exemplified the safety and immunogenicity of the ALVAC vaccine vector.

A prime-boost approach to HIV preventive vaccine using a recombinant canarypox virus expressing glycoprotein 160 (MN) followed by a recombinant glycoprotein 160 (MN/LAI). The AGIS Group, and l'Agence Nationale de Recherche sur le SIDA

The safety and the immunogenicity of a recombinant canarypox live vector expressing the human immunodeficiency virus type 1 (HIV-1) gp160 gene from the MN isolate, ALVAC-HIV (vCP125), followed by booster injections of a soluble recombinant hybrid envelope glycoprotein MN/LAI (rgp160), were evaluated in vaccinia-immune, healthy adults at low risk for acquiring HIV-1 infection. Volunteers (n = 20) received vCP125 (10(6) TCID50) at 0 and 1 month, followed randomly by rgp160 formulated in alum or in Freund's incomplete adjuvant (FIA) at 3 and 6 months. Local and systemic reactions were mild or moderate and resolved within the first 72 hr after immunization. No significant biological changes in routine tests were observed in any volunteer. Two injections of vCP125 did not elicit antibodies. Neutralizing antibodies (NA) against the HIV-1 MN isolate were detected in 65 and 90% of the subjects after the first and the second rgp 160 booster injections, respectively. Six months after the last boost, only 55% were still positive. Seven of 14 sera with the highest NA titers against MN weakly cross-neutralized the HIV-1 SF2 isolate; none had NA against the HIV-1 LAI or against a North American primary isolate. Specific lymphocyte T cell proliferation to rgp 160 was detected in 25% of the subjects after vCP125 and in all subjects after the first booster injection and 12 months after the first injection. An envelope-specific cytotoxic lymphocyte activity was found in 39% of the volunteers and characterized for some of them as CD3+, CD8+, MHC class I restricted. The adjuvant formulation did not influence significantly the immune responses.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of HIV-1 envelope gene by recombinant avipox viruses

Recombinant canarypox (CP) and fowlpox (FP) viruses that contained two forms of the HIV-1 (SF2 strain) env gene were engineered and their expression analysed in chick, simian and human cells. These vectors can efficiently replicate in avian but not in mammalian cells, in which infection is abortive. The two forms, consisting of the entire env open reading frame (IS+) or of the same gene lacking the putative immunosuppressive (IS-) region (amino acids 583-599), were individually inserted into the two virus vector backgrounds. In order to avoid premature transcription termination of the foreign gene and to improve protein expression, a mutagenesis was also performed within the T5NT motif without altering the amino acid sequence. By immunoprecipitation analyses, cells infected with CP and FP recombinants expressed HIV-1 env polypeptides of the appropriate molecular weight. We observed that the gp160 precursor was proteolytically cleaved except in MRC-5 cells infected with the IS- recombinants and that these polypeptides were glycosylated. Further analysis of these recombinant viruses by indirect immunofluorescence and syncytia inhibition assays indicated that the gp120 gp41 complex was present on the surface of infected cells, the number of syncytia being significantly lower when cells were infected by the CPIS- or FPIS- recombinants. Moreover, sera of immunized rabbits revealed the presence of specific antibodies in animals inoculated either with CP or with FP recombinants. These new constructs, which are unable to support a productive infection in human cells, might therefore also be a good anti-HIV-1 candidate vaccine in seropositive hosts.

Avipox virus-vectored Japanese encephalitis virus vaccines: use as vaccine candidates in combination with purified subunit immunogens

An avipox virus, canarypox (ALVAC), which is naturally host-range restricted, was used to construct recombinants encoding the Japanese encephalitis virus (JEV) prM, E and NS1 genes (vCP107) and prM and E genes (vCP140). Mice immunized with these recombinant viruses produced JEV neutralizing antibodies and were protected from lethal JEV challenge. Protection was also observed in mice immunized with a subunit vaccine candidate, consisting of extracellular particles (EPs; RNA-free subviral membrane vesicles containing prM/M and E proteins) derived from HeLa cell cultures infected with a JEV-vaccinia recombinant. Mice primed with vCP107 and boosted with EPs had higher antibody levels than mice immunized twice with EPs alone, although the levels were comparable to that obtained in mice immunized twice with the recombinant virus. Mice immunized with a mixture of recombinant virus (vCP107) plus EPs had neutralizing antibody titres higher than mice immunized with the recombinant virus or EPs alone.

Safe and effective poxvirus vectors--NYVAC and ALVAC

This paper describes the development and in vitro/in vivo characterization of two highly attenuated recombinant poxvirus vectors. The vectors, NYVAC and ALVAC, exhibit a restricted host range and a greatly enhanced degree of attenuation following inoculation into a range of animal species by a variety of routes. The safety profile of these vectors, together with their demonstrated ability to induce both humoral and cell-mediated immune responses to extrinsic antigens, makes them ideal candidates for use as vaccines in both human and veterinary disease situations.