Combined DNA vaccines formulated either in DDA or in saline protect cattle from Mycobacterium bovis infection

Towards Reverse Vaccinology for Bovine TB: High Throughput Expression of Full Length Recombinant Mycobacterium bovis Proteins

Bovine tuberculosis caused by Mycobacterium bovis, is a significant global pathogen causing economic loss in livestock and zoonotic TB in man. Several vaccine approaches are in development including reverse vaccinology which uses an unbiased approach to select open reading frames (ORF) of potential vaccine candidates, produce them as recombinant proteins and assesses their immunogenicity by direct immunization. To provide feasibility data for this approach we have cloned and expressed 123 ORFs from the M. bovis genome, using a mixture of E. coli and insect cell expression. We used a concatenated open reading frames design to reduce the number of clones required and single chain fusion proteins for protein pairs known to interact, such as the members of the PPE-PE family. Over 60% of clones showed soluble expression in one or the other host and most allowed rapid purification of the tagged bTB protein from the host cell background. The catalogue of recombinant proteins represents a resource that may be suitable for test immunisations in the development of an effective bTB vaccine.

Tuberculosis vaccine candidates based on mycobacterial cell envelope components

Even after decades searching for a new and more effective vaccine against tuberculosis, the scientific community is still pursuing this goal due to the complexity of its causative agent, Mycobacterium tuberculosis (Mtb). Mtb is a microorganism with a robust variety of survival mechanisms that allow it to remain in the host for years. The structure and nature of the Mtb envelope play a leading role in its resistance and survival. Mtb has a perfect machinery that allows it to modulate the immune response in its favor and to adapt to the host's environmental conditions in order to remain alive until the moment to reactivate its normal growing state. Mtb cell envelope protein, carbohydrate and lipid components have been the subject of interest for developing new vaccines because most of them are responsible for the pathogenicity and virulence of the bacteria. Many indirect evidences, mainly derived from the use of monoclonal antibodies, support the potential protective role of Mtb envelope components. Subunit and DNA vaccines, lipid extracts, liposomes and membrane vesicle formulations are some examples of technologies used, with encouraging results, to evaluate the potential of these antigens in the protective response against Mtb.

Experimental Infection Models of Tuberculosis in Domestic Livestock

In this article we present experimental Mycobacterium bovis infection models in domestic livestock species and how these models were applied to vaccine development, biomarker discovery, and the definition of specific antigens for the differential diagnosis of infected and vaccinated animals. In particular, we highlight synergies between human and bovine tuberculosis (TB) research approaches and data and propose that the application of bovine TB models could make a valuable contribution to human TB vaccine research and that close alignment of both research programs in a one health philosophy will lead to mutual and substantial benefits.

Trends and advances in the diagnosis and control of paratuberculosis in domestic livestock

Paratuberculosis (pTB) is a chronic granulomatous enteritis caused by Mycobacterium avium subsp. paratuberculosis (MAP) in a wide variety of domestic and wild animals. Control of pTB is difficult due to the lack of sensitive, efficacious and cost-effective diagnostics and marker vaccines. Microscopy, culture, and PCR have been used for the screening of MAP infection in animals for quite a long time. Besides, giving variable sensitivity and specificity, these tests have not been considered ideal for large-scale screening of domestic livestock. Serological tests like ELISA easily detects anti-MAP antibodies. However, it cannot differentiate between the vaccinated and infected animals. Nanotechnology-based diagnostic tests are underway to improve the sensitivity and specificity. Newer generation diagnostic tests based on recombinant MAP secretory proteins would open new paradigm for the differentiation between infected and vaccinated animals and for early detection of the infection. Due to higher seroreactivity of secretory proteins vis-à-vis cellular proteins, the secretory proteins may be used as marker vaccine, which may aid in the control of pTB infection in animals. Secretory proteins can be potentially used to develop future diagnostics, surveillance and monitoring of the disease progression in animals and the marker vaccine for the control and eradication of pTB.

Mycobacterium bovis Infection of Cattle and White-Tailed Deer: Translational Research of Relevance to Human Tuberculosis

Tuberculosis (TB) is a premier example of a disease complex with pathogens primarily affecting humans (i.e., Mycobacterium tuberculosis) or livestock and wildlife (i.e., Mycobacterium bovis) and with a long history of inclusive collaborations between physicians and veterinarians. Advances in the study of bovine TB have been applied to human TB, and vice versa. For instance, landmark discoveries on the use of Koch's tuberculin and interferon-γ release assays for diagnostic purposes, as well as Calmette and Guérin's attenuated M. bovis strain as a vaccine, were first evaluated in cattle for control of bovine TB prior to wide-scale use in humans. Likewise, recent discoveries on the role of effector/memory T cell subsets and polyfunctional T cells in the immune response to human TB, particularly as related to vaccine efficacy, have paved the way for similar studies in cattle. Over the past 15 years, substantial funding for development of human TB vaccines has led to the emergence of multiple promising candidates now in human clinical trials. Several of these vaccines are being tested for immunogenicity and efficacy in cattle. Also, the development of population-based vaccination strategies for control of M. bovis infection in wildlife reservoirs will undoubtedly have an impact on our understanding of herd immunity with relevance to the control of both bovine and human TB in regions of the world with high prevalence of TB. Thus, the one-health approach to research on TB is mutually beneficial for our understanding and control of TB in humans, livestock, and wildlife.

Overview of vaccination trials for control of tuberculosis in cattle, wildlife and humans

Vaccination is a key strategy for control of tuberculosis (TB), and considerable progress has been made in the past 5 years to develop improved vaccines for humans and animals, differentiate vaccinated animals from those infected with Mycobacterium bovis and deliver vaccines to wildlife. Studies have moved from testing vaccines in small animal models to clinical trials in humans and from experimental challenge studies in cattle and wildlife to evaluation of vaccines in the field. Candidate vaccines undergoing testing in humans include live mycobacterial vaccines to replace bacille Calmette Guérin (BCG), subunit vaccines (virus vector or protein) to boost BCG and therapeutic vaccines used as an adjunct to chemotherapy. In cattle, a number of diagnostic tests have been developed and successfully tested for differentiating infected from vaccinated animals, which will facilitate the use of BCG vaccine in cattle. Encouraging results have been obtained from recent field trials in cattle using BCG vaccine to protect against natural exposure to M. bovis. To date, no subunit TB vaccines have induced improved protection compared with that for BCG, but prime-boost combinations of BCG with DNA, protein or virus-vectored vaccines have induced better protection than BCG vaccine alone. Development of an oral bait BCG formulation has demonstrated the practicality of delivering TB vaccines to wildlife. Oral BCG preparations have induced protection against experimental challenge of M. bovis in possums, badgers, wild boar and white-tailed deer and against natural exposure to M. bovis in possums. Recent progress in TB vaccine development has provided much impetus for their future use.

Cationic liposomal vaccine adjuvants in animal challenge models: overview and current clinical status

Cationic liposome formulations can function as efficient vaccine adjuvants. However, due to the highly diverse nature of lipids, cationic liposomes have different physical-chemical characteristics that influence their adjuvant mechanisms and their relevance for use in different vaccines. These characteristics can be further manipulated by incorporation of additional lipids or stabilizers, and inclusion of carefully selected immunostimulators is a feasible strategy when tailoring cationic liposomal adjuvants for specific disease targets. Thus, cationic liposomes present a plasticity, which makes them promising adjuvants for future vaccines. This versatility has also led to a vast amount of literature on different experimental liposomal formulations in combination with a wide range of immunostimulators. Here, we have compiled information about the animal challenge models and administration routes that have been used to study vaccine adjuvants based on cationic liposomes and provide an overview of the applicability, progress and clinical status of cationic liposomal vaccine adjuvants.

Tuberculosis vaccine research in China

It is now privately acknowledged that there may be little if any perceptible impact of the national Bacille Calmette-Guerin (BCG) vaccination program on disease prevalence, despite the extensive coverage of the newborn infant population and likely benefit in the early years of life. A better preventive vaccine than BCG is now being sought by Chinese researchers. Urgency has been added to the control problem by the emergence of multidrug-resistant tuberculosis (TB). Furthermore, expensive second-line drugs seem unlikely to be made available by the government to treat drug-resistant cases, so attention in addition has turned to the potential of immunotherapy as an adjunct to chemotherapy. Research trends are summarized here.

The secreted lipoprotein, MPT83, of Mycobacterium tuberculosis is recognized during human tuberculosis and stimulates protective immunity in mice

The long-term control of tuberculosis (TB) will require the development of more effective anti-TB vaccines, as the only licensed vaccine, Mycobacterium bovis bacille Calmette-Guérin (BCG), has limited protective efficacy against infectious pulmonary TB. Subunit vaccines have an improved safety profile over live, attenuated vaccines, such as BCG, and may be used in immuno-compromised individuals. MPT83 (Rv2873) is a secreted mycobacterial lipoprotein expressed on the surface of Mycobacterium tuberculosis. In this study, we examined whether recombinant MPT83 is recognized during human and murine M. tuberculosis infection. We assessed the immunogenicity and protective efficacy of MPT83 as a protein vaccine, with monophosphyl lipid A (MPLA) in dimethyl-dioctadecyl ammonium bromide (DDA) as adjuvant, or as a DNA vaccine in C57BL/6 mice and mapped the T cell epitopes with peptide scanning. We demonstrated that rMPT83 was recognised by strong proliferative and Interferon (IFN)-γ-secreting T cell responses in peripheral blood mononuclear cells (PBMC) from patients with active TB, but not from healthy, tuberculin skin test-negative control subjects. MPT83 also stimulated strong IFN-γ T cell responses during experimental murine M. tuberculosis infection. Immunization with either rMPT83 in MPLA/DDA or DNA-MPT83 stimulated antigen-specific T cell responses, and we identified MPT83_127–135 (PTNAAFDKL) as the dominant H-2^b-restricted CD8⁺ T cell epitope within MPT83. Further, immunization of C57BL/6 mice with rMPT83/MPLA/DDA or DNA-MPT83 stimulated significant levels of protection in the lungs and spleens against aerosol challenge with M. tuberculosis. Interestingly, immunization with rMPT83 in MPLA/DDA primed for stronger IFN-γ T cell responses to the whole protein following challenge, while DNA-MPT83 primed for stronger CD8⁺ T cell responses to MPT83_127–135. Therefore MPT83 is a protective T cell antigen commonly recognized during human M. tuberculosis infection and should be considered for inclusion in future TB subunit vaccines.

Comparative evaluation of MPT83 (Rv2873) for T helper-1 cell reactivity and identification of HLA-promiscuous peptides in Mycobacterium bovis BCG-vaccinated healthy subjects

MPT83 (Rv2873), a surface lipoprotein excreted in the culture of Mycobacterium tuberculosis, is immunoreactive in antibody assays in humans and animals and provides protection as a combined DNA vaccine in mice and cattle. This study was undertaken to determine the reactivity of MPT83 in T helper 1 (Th1)-cell assays, i.e., antigen-induced proliferation and gamma interferon (IFN-γ) secretion, using peripheral blood mononuclear cells (PBMCs) obtained from Mycobacterium bovis bacillus Calmette-Guérin (BCG)-vaccinated and/or M. tuberculosis-infected healthy subjects. PBMCs were tested with complex mycobacterial antigens and pools of synthetic peptides corresponding to MPT63, MPT83, MPB70, LppX, PPE68, CFP10, and ESAT-6. The results showed that MPT83 is among the strongest Th1 cell antigens of M. tuberculosis, and it was recognized equally strongly by BCG-vaccinated and by BCG-vaccinated and M. tuberculosis-infected healthy subjects. Furthermore, HLA heterogeneity of the responding donors suggested that MPT83 was presented to Th1 cells by several HLA-DR molecules. The analysis of the mature MPT83 sequence (amino acids [aa] 1 to 220) and its 14 overlapping synthetic peptides for binding prediction to HLA class II molecules and actual recognition of the peptides by PBMCs from HLA-DR-typed subjects in antigen-induced proliferation and IFN-γ assays suggested that Th1 cell epitopes were scattered throughout the sequence of MPT83. In addition, the HLA-promiscuous nature of at least three peptides, i.e., P11 (aa 151 to 175), P12 (aa 166 to 190), and P14 (aa 196 to 220), was suggested by HLA-DR binding predictions and recognition by HLA-DR heterogeneous donors in Th1 cell assays. These results support the inclusion of MPT83 in an antigen cocktail to develop a new antituberculosis vaccine.

Update on vaccination of cattle and wildlife populations against tuberculosis

In this review, the status of vaccination strategies to reduce bovine tuberculosis of cattle and wildlife reservoirs of the disease is discussed, with a focus on recent developments. Recent work in vaccines to protect humans against tuberculosis has been followed by a similar surge of interest in developing vaccines against bovine tuberculosis. The human vaccine, bacille Calmette-Guérin (BCG) affords protection against tuberculosis in cattle, but this protection is variable. In addition, vaccination with BCG compromises control strategies based on skin testing animals. In general, no single vaccine approach has shown itself to be significantly superior to BCG alone, however, vaccine combinations of BCG and vaccinating moiety such as adjuvanted subunit, virus vectored or DNA vaccines have been shown to induce protection superior to that achieved by BCG alone. Vaccinating wildlife species against tuberculosis is also an area which has been subjected to scrutiny. Recent work has focused on vaccinating wildlife orally, via the use of BCG formulated in baits consumed by these species. Results from trials in a number of animal species indicate that oral BCG vaccination can reduce disease severity following experimental challenge with Mycobacterium bovis and in a recent field trial, oral BCG vaccination was shown to prevent infection of wild possums following natural exposure to M. bovis. In conclusion, recent studies in cattle and wildlife have demonstrated the practicality and effectiveness of vaccinating animals against tuberculosis and provide much impetus for future use of vaccines.

A combined DNA vaccine provides protective immunity against Mycobacterium bovis and Brucella abortus in cattle

We evaluated the immunogenicity and protective efficacy of a combined DNA vaccine containing six genes encoding immunodominant antigens from Mycobacterium bovis and Brucella abortus. The number of lymph node and spleen cultures positive for M. bovis and B. abortus from calves immunized with the combined DNA vaccine was significantly reduced (p < 0.01) compared with unvaccinated calves after challenge with virulent M. bovis and B. abortus 544. The combined DNA vaccine group displayed stronger antigen-specific interferon-gamma (IFN-gamma) responses and antigen-specific IFN-gamma ELISPOT activities 2 months after final immunization and after challenge. Antigen-specific CD4(+) and CD8(+) T cell responses in the combined DNA vaccine group were higher than either the Bacillus Calmette-Guerin (BCG)-positive or S19-positive control group. Likewise, more calves in the DNA vaccine group exhibited antigen-specific IgG titers and had higher IgG titers than those in the BCG- or S19-immunized groups 2 months after the final immunization. Moreover, two antigens in the combined DNA vaccine induced significant antigen-specific IFN-gamma responses 6 months after challenge (p < 0.05). Bacterial counts and pathological analyses of the challenged animals indicated that the combined DNA vaccine provided significantly better protection than the BCG vaccine against M. bovis, and the protection level induced by the combined DNA vaccine was comparable to S19 against B. abortus. This is the first report to demonstrate that a single combined DNA vaccine protects cattle against two infectious diseases.

Evaluation of immune responses and protective efficacy in a goat model following immunization with a coctail of recombinant antigens and a polyprotein of Mycobacterium avium subsp. paratuberculosis

The protective efficacy of four recombinant antigens (85A, 85B, superoxide dismutase [SOD], and a fusion polypeptide [Map74F]) of Mycobacterium avium subsp. paratuberculosis (MAP) along with the adjuvant dimethydioctadecyl ammonium bromide (DDA) was assessed in a goat challenge model. Animals were immunized with the four antigens with adjuvant DDA (Group I, eight goat kids) or without the adjuvant (Group II, eight goat kids) or adjuvant only (Group III, nine goat kids). Animals were boostered 3 weeks after the primary vaccination and challenged 3 weeks after the booster. Significant antigen-specific lymphoproliferation was observed in the immunized animals 3 weeks after the booster immunization. This response increased further at 4 weeks after the booster. Similarly, antigen-specific IFN-gamma responses increased in the immunized animals 3 weeks after the booster. The response was significantly higher for 85A and Map74F at 10 weeks after primary vaccination (APV) in Group I animals compared to the other two groups. CD4+ T-cell populations were higher in the vaccinated animals from 6 to 10 weeks APV than those of the control animals. A significant increase in recombinant antigen-specific IFN-gamma gene expression was detected in the vaccinated animals. At necropsy (38 weeks APV), our multicomponent subunit vaccine imparted a significant protection in terms of reduction of MAP burden in target organs as compared to sham-immunized goats. This study indicates that our multicomponent subunit vaccine induced a good Th1 response and conferred protection against MAP infection in a goat challenge model.

Immunization with a DNA vaccine cocktail induces a Th1 response and protects mice against Mycobacterium avium subsp. paratuberculosis challenge

Several antigens of Mycobacterium avium subsp. paratuberculosis have been studied as vaccine components and their immunogenicity has been evaluated. Previously, we reported that 85 antigen complex (85A, 85B, and 85C), superoxide dismutase (SOD), and 35kDa protein could induce significant lymphocyte proliferation as well as the elaboration of Th1-associated cytokines including interferon gamma (IFN-gamma), interleukin-2 (IL-2), IL-12 and tumor necrosis factor alpha (TNF-alpha). Based on these results, we cloned and expressed 85A, 85B, 85C, SOD, and 35kDa-protein genes into the eukaryotic expression plasmid pVR1020. C57BL/6 mice were immunized three times intramuscularly with the recombinant DNA cocktail and pVR1020 DNA alone as control. A significant reduction in the bacterial burden in the spleen and liver of mice immunized with the DNA cocktail as compared to the vector control group was found. Also, the relative severity of the liver and spleen histopathology paralleled the MAP culture results, more granulomas and acid-fast bacilli in the vector control animals. Moreover, mice immunized with the DNA cocktail developed both CD4(+) and CD8(+) T cell responses to the recombinant antigens and showed significant lymphocyte proliferation. The Th1 response related cytokine (IFN-gamma) levels increased in splenocytes obtained from immunized animals. These results indicate that the use of a recombinant DNA vaccine can provide protective immunity against mycobacterial infection by inducing a Th1 response.

Mutation of Arabidopsis BARD1 causes meristem defects by failing to confine WUSCHEL expression to the organizing center

Stem cell fate in the Arabidopsis thaliana shoot apical meristem (SAM) is controlled by WUSCHEL (WUS) and CLAVATA. Here, we examine BARD1 (for BRCA1-associated RING domain 1), which had previously been implicated in DNA repair functions; we find that it also regulates WUS expression. We observed severe SAM defects in the knockout mutant bard1-3. WUS transcripts accumulated >238-fold in bard1-3 compared with the wild type and were located mainly in the outermost cell layers instead of the usual organizing center. A specific WUS promoter region was recognized by nuclear protein extracts obtained from wild-type plants, and this protein-DNA complex was recognized by antibodies against BARD1. The double mutant (wus-1 bard1-3) showed prematurely terminated SAM structures identical to those of wus-1, indicating that BARD1 functions through regulation of WUS. BARD1 overexpression resulted in reduced WUS transcript levels, giving a wus-1-like phenotype. Either full-length BARD1 or a clone that encoded the C-terminal domain (BARD1:C-ter;bard1-3) was sufficient to complement the bard1-3 phenotype, indicating that BARD1 functions through its C-terminal domain. Our data suggest that BARD1 regulates SAM organization and maintenance by limiting WUS expression to the organizing center.

A combined DNA vaccine enhances protective immunity against Mycobacterium tuberculosis and Brucella abortus in the presence of an IL-12 expression vector

We examined the immunogenicity and protective efficacy of a combined DNA vaccine that included six genes encoding immunodominant antigens from Mycobacterium tuberculosis and Brucella abortus. The IL-12 adjuvant system was used for immunization in combination with the combined DNA vaccine (DNA-IL-12(+)). Mice immunized with DNA-IL-12(+) had significantly reduced CFU counts for M. tuberculosis and B. abortus in lung and spleen, respectively (P<0.001), and DNA-IL-12(+) elicited better protection than the combined DNA vaccine alone (DNA-IL-12(-)) or with the positive control groups after challenge with a virulent M. tuberculosis strain and B. abortus 2308 infection. The DNA-IL-12(+) group had stronger antigen-specific IFN-gamma ELISPOT activities and higher levels of antigen-specific CD4(+) and CD8(+) T cell responses than either the DNA-IL-12(-) or positive control groups. Likewise, antigen-specific IgG titers were also much higher than in other immunized groups. Moreover, DNA-IL-12(+) gave a stronger IgG2a-skewed response than did DNA-IL-12(-). In addition, its mean concentrations of IFN-gamma and IL-2 were about 2.5- to 4.5-fold higher than those observed in the DNA-IL-12(-)-treated mice, and were significantly higher than control groups (P<0.01 or P<0.001), whereas IL-4 and IL-10 secretion were lower. These results suggest that IL-12 acts as an adjuvant to enhance protective immunity against M. tuberculosis and B. abortus through the induction of stronger Th1-associated immune responses. This is the first report to show that a single combined DNA vaccine protects animals against two infectious diseases.

DNA vaccine using Mycobacterium bovis Ag85B antigen induces partial protection against experimental infection in BALB/c mice

Bovine tuberculosis is a major cause of economic loss in countries where it is endemic, and in some countries, it may be a significant zoonotic disease problem. Therefore, new strategies for vaccine development are required, and among them, genetic immunization has potential value. The main goal of this study was to test the Mycobacterium bovis Ag85B gene as a DNA vaccine following challenge with an M. bovis virulent strain (ATCC 19274). Groups of BALB/c mice (n = 10) were immunized four times intramuscularly with the pCI-Ag85B construct or the pCI vector alone as the control. High titers of total immunoglobulin G (IgG), IgG1, and IgG2a anti-Ag85B were measured in pCI-Ag85B immunized mice when compared to the pCI control group. Regarding cellular immunity, significant levels of gamma interferon (IFN-gamma) (1,100 +/- 157 pg/ml) and tumor necrosis factor alpha (650 +/- 42 pg/ml) but not interleukin-4 were detected in splenocyte culture supernatants of pCI-Ag85B-vaccinated mice following stimulation with recombinant Ag85B. Further, the main source of IFN-gamma is CD8(+) T cells, as demonstrated by intracellular cytokine staining. As far as protection, a significant reduction in bacterial load in spleens (P < 0.05) was detected in pCI-Ag85B-immunized mice compared to the pCI vector control group. The results obtained here suggest that use of the Ag85B DNA vaccine is a promising strategy to control M. bovis infection due to its ability to induce a Th1 type of immune response. However, protective efficacy needs to be improved, since partial protection was achieved in spleens but not in lungs of vaccinated mice.

A combined DNA vaccine-prime, BCG-boost strategy results in better protection against Mycobacterium bovis challenge

In this study, we demonstrated that calves vaccinated with a combined DNA vaccine encoding Ag85B, MPT- 64, and MPT-83 antigens from the Mycobacterium tuberculosis for the priming and subsequently boosting with BCG prior to experimental challenge with virulent Mycobacterium bovis (M. bovis) resulted in improved immune responses over immunizing. Vaccination with the combined DNA/BCG induced higher levels of antigen- specific gamma interferon (IFN-gamma) in whole-blood cultures 4 weeks after final vaccination and the level of antigen-specific IFN-gamma in response to Ag85, MPT-64, and MPT-83 were still higher 4 weeks after challenge when compared to the combined DNA group. There was a significant bias toward induction of CD4+ T cells rather than CD8+ T cells responses, and the mean percentage of CD4+ T cells was increased about 2.6-fold in peripheral blood mononuclear cells (PBMC) cultures in DNA prime-BCG boost vaccination when compared to the nonvaccinated group. In addition, DNA prime-BCG boost vaccination resulted in stronger humoral immune responses, and the levels of the specific antibodies to three antigens were increased two- to 32- fold when compared to the combined DNA group. Vaccination with the combined DNA/BCG induced a high level of protection against an intratracheal challenge with virulent M. bovis, based on a significant enhancement of six pathological and microbiological parameters of protection compared to the nonvaccinated group. Finally, the combined DNA/BCG increased the protective efficacy by more than 10-100-fold as measured by reduced CFU counts in the lungs from calves challenged with M. bovis compared to the combined DNA and BCG groups. These results suggest that use of the prime-boost strategy offers better protection against bovine tuberculosis than does the combined DNA vaccines and BCG.

Development of cattle TB vaccines in the UK

In 1996, an independent scientific committee chaired by Professor John Krebs, tasked to review the problem of bovine tuberculosis (TB) in GB, concluded that vaccination of cattle offered the best long-term solution for controlling the disease in the National Herd. This view has been re-affirmed recently in the House of Commons Environment, Food and Rural Affairs Committee's report on Bovine TB (2004) and by the findings of the Independent Scientific Group Vaccine Scoping Sub-committee. Significant progress in developing TB vaccines for cattle has been made over the last 5 years. Specifically: (i) DNA or protein subunit vaccines used in combination with BCG have been shown to give superior protection against experimental challenge in cattle than BCG (heterologous prime-boost); (ii) prototype reagents that allow discrimination between vaccinated and infected animals have been developed; and (iii) and correlates of disease severity have been identified that can predict the success or failure of vaccination. These significant advances are detailed in this review with a summary of future directions that TB vaccine development for cattle is likely to take.

Immunization with DNA vaccines encoding different mycobacterial antigens elicits a Th1 type immune response in lambs and protects against Mycobacterium avium subspecies paratuberculosis infection

Paratuberculosis, or Johne's disease, is a disease of domestic and wild ruminants that culminate with a chronic enteritis caused by Mycobacterium avium subsp. paratuberculosis. The aim of this work was to evaluate the type of immune response, Th1 or Th2, induced by DNA vaccinations in lambs of Sarda breed. Twenty-five lambs, serum negative for M. paratuberculosis, were selected at birth from equally serum negative mothers. The lambs were inoculated at 5 months of age with three different mycobacterial antigens cloned into a mammalian expression vector as fusion protein with the enhanced green fluorescent protein (pEGFP-N1). The animals were divided in five groups containing each five lambs. Each group was vaccinated as following (A: physiological solution; B: Gudair; C: p-85A-Mav; D: p-85A-BCG; E: p-Hsp65). Immune response was evaluated by measuring the expression of INF-gamma (Th1 type response) and IL-10 (Th2 type response) by real-time PCR. Gene expression was estimated by comparing the results with that of beta-actin. INF-gamma expression level was increased in lambs vaccinated with plasmids codifying mycobacterial antigens, in particular with p-Hsp65, in comparison with the controls suggesting stimulation of a Th1 immune response similar to that supported by natural infection of M. paratuberculosis. Moreover, animals were infected orally with live M. paratuberculosis. Three months after vaccination and again INF-gamma and IL-10 expression was evaluated in order to verify in vivo the protection level of the vaccines. Plasmids p-85A-BCG and p-Hsp65 seem to elicit a stronger protective immune response against M. paratuberculosis by evaluating the expression level of INF-gamma and evaluating the presence of M. paratuberculosis and animal cell organ damage post-mortem.