Protection against virulent Mycobacterium avium infection following DNA vaccination with the 35-kilodalton antigen is accompanied by induction of gamma interferon-secreting CD4(+) T cells

Subunit vaccine protects against a clinical isolate of Mycobacterium avium in wild type and immunocompromised mouse models

The nontuberculous mycobacteria (NTM) Mycobacterium avium is a clinically significant pathogen that can cause a wide range of maladies, including tuberculosis-like pulmonary disease. An immunocompromised host status, either genetically or acutely acquired, presents a large risk for progressive NTM infections. Due to this quietly emerging health threat, we evaluated the ability of a recombinant fusion protein ID91 combined with GLA-SE [glucopyranosyl lipid adjuvant, a toll like receptor 4 agonist formulated in an oil-in-water stable nano-emulsion] to confer protection in both C57BL/6 (wild type) and Beige (immunocompromised) mouse models. We optimized an aerosol challenge model using a clinical NTM isolate: M. avium 2-151 smt, observed bacterial growth kinetics, colony morphology, drug sensitivity and histopathology, characterized the influx of pulmonary immune cells, and confirmed the immunogenicity of ID91 in both mouse models. To determine prophylactic vaccine efficacy against this M. avium isolate, mice were immunized with either ID91 + GLA-SE or bacillus Calmette-Guérin (BCG). Immunocompromised Beige mice displayed a delayed influx of innate and adaptive immune cells resulting in a sustained and increased bacterial burden in the lungs and spleen compared to C57BL/6 mice. Importantly, both ID91 + GLA-SE and BCG vaccines significantly reduced pulmonary bacterial burden in both mouse strains. This work is a proof-of-concept study of subunit vaccine-induced protection against NTM.

Vaccine strategies against cystic fibrosis pathogens

A great number of cystic fibrosis (CF) pathogens such as Pseudomonas aeruginosa, the Burkholderia cepacia and the Mycobacterium abscessus complex raised difficult therapeutic problems due to their intrinsic multi-resistance to numerous antibiotics. Vaccine strategies represent one of the key weapons against these multi-resistant bacteria in a number of clinical settings like CF. Different strategies are considered in order to develop such vaccines, linked either to priming the host response, or by exploiting genomic data derived from the bacterium. Interestingly, virulence factors synthesized by various pathogens might serve as targets for vaccine development and have been, for example, evaluated in the context of CF.

Protective Immunity againstBordetella pertussisby a Recombinant DNA Vaccine and the Effect of Coinjection with a Granulocyte-Macrophage Colony Stimulating Factor Gene

A recombinant pertussis DNA vaccine was described here with its immunogenicity and the ability to induce protection against B. pertussis infection in mice. Three immunodominant antigen gene fragments of pertussis, pertussis toxin subunit 1 (pts1), fragments of pertactin (prn) and filamentous hemagglutinin (fha), were recombined as fragment pts1-prn-fha named ppf, and it was cloned to plasmid pVAX1 as pVAX1/ppf. Compared to those injected with pVAX1, the mice injected with pVAX1/ppf significantly elicited more antigen specific antibody anti-PTS1, anti-PRN, anti-FHA and cytokine IL-10, IFN-gamma. When pGM-CSF was coinjected with pVAX1/ppf, the mice showed significantly increases of the three antibodies and cytokine IL-10, IL-4, IFN-gamma and TNF-alpha compared to those injected with pVAX1 only. The mice in group pVAX1/ppf & pGM-CSF, in particular; induced much more anti-PTS1, IL-4 and TNF-alpha than those in group pVAX1/ppf. In the intracerebral mouse protection test, the mice immunized with pVAX1/ppf or pVAX1/ppf & pGM-CSF induced protection to a lethal dose of B. pertussis. The results indicate that recombinant DNA vaccine and pGM-CSF coinjection can induce protective immunity against B. pertussis, demonstrating a valuable method to prevent pertussis.

Coexpression of PPE 34.9 Antigen of Mycobacterium avium subsp. Paratuberculosis with Murine Interferon Gamma in HeLa Cell Line and Study of Their Immunogenicity in Murine Model

Mycobacterium avium subsp. paratuberculosis (Map) is the causative agent of johne's disease whose immunopathology mainly depends on cell mediated immuneresponse. Genome sequencing revealed various PPE (Proline-Proline-Glutamic acid) protein family of Map which are immunologically importance candidate genes In present study we have developed a bicistrionic construct pIR PPE/IFN containing a 34.9 kDa PPE protein (PPE 34.9) of Map along with a cytokine gene encoding murine gamma Interferon gene (IFNγ) and a monocistrionic construct pIR PPE using a mammalian vector system pIRES 6.1. The construct were transfected in HeLa cell line and expression were studied by Western blot as well as Immunefluroscent assay using recombinant sera. Further we have compared the immunereactivity of these two constructs in murine model by means of DTH study, LTT, NO assay and ELISA. DTH response was higher in pIR PPE/IFN than pIR PPE group of mice, similar finding also observed in case of LTT and NO production assay . ELISA titer of the pIR PPE/IFN was less than that with PPE only. These preliminary finding can revealed a CMI response of this PPE protein of Map and IFNγ having synergistic effect on this PPE protein to elicit a T cell based immunity in mice.

Disseminated disease severity as a measure of virulence of Mycobacterium tuberculosis in the guinea pig model

Virulence is the measure of pathogenicity of a microorganism as determined by its ability to invade host tissues and to produce severe disease. In the low-dose aerosol guinea pig model the virulence of multiple strains of Mycobacterium tuberculosis was determined by measuring time of survival, bacterial loads in target organs, and the severity of pulmonary and extra-pulmonary lesions. Erdman K01, CSU93/CDC1551 and HN878 had shorter survival times compared to the common laboratory strain H37Rv. After 30 days of the infection bacilli had disseminated from the lungs resulting in microscopically visible lesions in peribronchial lymph nodes, peripancreatic lymph nodes, spleen, liver, pancreas, adrenal and heart. The extent of the lesion necrosis paralleled virulence when survival times were used as a measure as Erdman K01 and the two clinical isolates caused more necrosis and resulted in sooner death in infected animals than the H37Rv. The extent of extra-pulmonary lesion necrosis was a better predictor of virulence than the number of viable bacilli in the tissue. Overall, this study emphasizes the point that extra-pulmonary disease is a prominent feature of the guinea pig model and dissemination to organs not normally assayed such as the heart and adrenal glands should be taken into account in the assessment of the disease process.

Cellular immune responses to 35 kDa recombinant antigen of Mycobacterium avium paratuberculosis

Mycobacterium avium paratuberculosis is the causative agent of Johne disease, a chronic ulcerative intestinal condition in ruminant animals. Owing to the predominance of cellular response in subclinical forms of the infection, identification of M. a. paratuberculosis antigens eliciting host cell-mediated immune (CMI) reaction is crucial for early control of the disease. A 35 kDa protein of M. a. paratuberculosis was studied for its ability to elicit CMI responses using a mouse model. Lymphoproliferation and IFN-gamma response were used to measure the CMI response. Recombinant 35 kDa protein (P35) stimulated proliferation of mouse mononuclear splenocytes sensitized with M. a. paratuberculosis. The P35 elicited increased nitrite production from mononuclear splenocytes from M. a. paratuberculosis-sensitized mice. In addition, RT-PCR-based semiquantitative IFN-gamma measurement showed that stimulation with P35 is associated with significant expression of IFN-gamma mRNA in M. a. paratuberculosis-sensitized mouse splenocytes. The results indicate that the 35 kDa protein of M. a. paratuberculosis is associated with CMI response in the host.

DNA vaccines against mycobacterial diseases

Plasmid DNA vaccination is a very powerful and easy method for the induction of strong humoral and cell-mediated immune responses in mice. The technique has also been successfully applied for the definition of immunodominant, human T-cell epitopes using HLA-transgenic mice. By virtue of its strong capacity to induce CD4+-mediated Th1 and CD8+-mediated cytotoxic T-lymphocyte responses, this vaccine approach is particularly attractive for the prophylaxis of intracellular pathogens, such as Mycobacterium tuberculosis (TB) and other pathogenic mycobacteria. In small rodents, the potential of mycobacterial DNA vaccines is well established. In humans, DNA vaccines are clearly less immunogenic and, so far, TB-specific DNA vaccines have not been assessed in humans. However, a number of studies in cattle and sheep have demonstrated the potential of mycobacterial DNA vaccines in larger animals. Also, immunization protocols combining the potent priming capacity of plasmid DNA with subsequent boosting with recombinant protein, recombinant pox-viruses or with Mycobacterium bovis bacille Calmette-Guerin (BCG) vaccine are particularly promising for future applications. The potential of mycobacterial DNA vaccines for immunotherapy and post-exposure prophylaxis is still not clear.

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.

Heterologous expression of a gene encoding a 35 kDa protein of Mycobacterium avium paratuberculosis in Escherichia coli

The full-length open reading frame coding for a potentially immunogenic 35 kDa protein of Mycobacterium avium paratuberculosis was generated using polymerase chain reaction technology. The gene was inserted in-frame into Escherichia coli expression plasmid pQE32. The resulting recombinant plasmid pPMP35 was transformed into E. coli M15. Analysis of the E. coli induced with isopropyl-beta-D-thiogalactopyranoside revealed that the protein accumulated into the cytoplasm as insoluble inclusion bodies. The level of expression of the recombinant 35 kDa protein (P35) was more than 30% of the total protein of E. coli cells. Expression of the recombinant protein was confirmed by immunoblotting. The P35 reacted with a rabbit antiserum raised against a sonicate of M. a. paratuberculosis. The protein was also recognized by serum from a goat with clinical paratuberculosis. Further, a polyclonal antiserum against P35 recognized a 35 kDa band in a membrane fraction of M. a. paratuberculosis. Also, the protein provoked a significant skin reaction in outbred guinea pigs sensitized with M. a. paratuberculosis, as well as in those sensitized with Mycobacterium avium. The results indicate that the 35 kDa protein of M. a. paratuberculosis is a membrane protein, having a role in the cellular immune response.

Vaccination with Plasmids Encoding the Leishmania Major GP63 Glycoprotein and CD40L Results in a Partial Suppression of the Inflammatory Reaction after Experimental Infection

The development of an effective vaccine against leishmaniasis is the aim of an intensive research effort, to bring relief to thousands of people worldwide. DNA vaccination is a promising approach in this direction, since it is able to generate a strong cellular immune response. We tested whether the co-administration of a plasmid encoding a truncated gp63 gene, that allows extracellular secretion of the encoded protein, and a plasmid encoding for CD40L could induce a protective response in genetically susceptible BALB/c mice and reduce the local inflammatory swelling after infection with Leishmania major. We document that vaccination with the combination of plasmids for gp63 and CD40L reduced inflammatory swelling, while vaccination with the truncated gp63-encoding plasmid resulted in an exacerbation of the local inflammatory reaction. These preliminary data indicate that the CD40L expression plasmid is consequently an efficient adjuvant for the induction of protective responses in the context of a DNA vaccination against leishmaniasis.

Gamma interferon responses induced by a panel of recombinant and purified mycobacterial antigens in healthy, non-mycobacterium bovis BCG-vaccinated Malawian young adults

We have previously shown that young adults living in a rural area of northern Malawi showed greater gamma interferon (IFN-gamma) responses to purified protein derivatives (PPD) prepared from environmental mycobacteria than to PPD from Mycobacterium tuberculosis. In order to define the mycobacterial species to which individuals living in a rural African population have been exposed and sensitized, we tested T-cell recognition of recombinant and purified antigens from M. tuberculosis (38 kDa, MPT64, and ESAT-6), M. bovis (MPB70), M. bovis BCG (Ag85), and M. leprae (65 kDa, 35 kDa, and 18 kDa) in >600 non-M. bovis BCG-vaccinated young adults in the Karonga District of northern Malawi. IFN-gamma was measured by enzyme-linked immunosorbent assay (ELISA) in day 6 supernatants of diluted whole-blood cultures. The recombinant M. leprae 35-kDa and 18-kDa and purified native M. bovis BCG Ag85 antigens induced the highest percentages of responders, though both leprosy and bovine tuberculosis are now rare in this population. The M. tuberculosis antigens ESAT-6 and MPT64 and the M. bovis antigen MPB70 induced the lowest percentages of responders. One of the subjects subsequently developed extrapulmonary tuberculosis; this individual had a 15-mm-diameter reaction to the Mantoux test and responded to M. tuberculosis PPD, Ag85, MPT64, and ESAT-6 but not to any of the leprosy antigens. We conclude that in this rural African population, exposure to M. tuberculosis or M. bovis is much less frequent than exposure to environmental mycobacteria such as M. avium, which have antigens homologous to the M. leprae 35-kDa and 18-kDa antigens. M. tuberculosis ESAT-6 showed the strongest association with the size of the Mantoux skin test induration, suggesting that among the three M. tuberculosis antigens tested it provided the best indication of exposure to, or infection with, M. tuberculosis.

The combination of plasmid interleukin-12 with a single DNA vaccine is more effective than Mycobacterium bovis (bacille Calmette-Guèrin) in protecting against systemic Mycobacterim avium infection

Sub-unit vaccines utilizing purified mycobacterial proteins or DNA vaccines induce partial protection against mycobacterial infections. For example, immunization with DNA vaccines expressing the gene for the immunodominant 35000 MW protein, common to Mycobacterium avium and Mycobacterium leprae but absent from the Mycobacterium tuberculosis complex, conferred significant protection against infection with either virulent M. avium or M. leprae in mice. However, the level of protection was equivalent to that obtained with the viable, attenuated vaccine, Mycobacterium bovis, bacille Calmette-Guèrin (BCG). The cytokine, interleukin (IL)-12, is essential for priming naïve CD4+ T lymphocytes to differentiate into interferon-gamma (IFN-gamma)-secreting T cells. We have used a novel self-splicing vector expressing both chains of murine IL-12 to determine if plasmid IL-12 would increase the efficacy of a vaccine expressing the M. avium 35000 MW protein (DNA-Av35). Co-immunization with p2AIL-12 and DNA-Av35 led to a significant increase in the number of antigen-specific IFN-gamma secreting cells and total amount of IFN-gamma released, but a concomitant fall in the antibody response to the 35000 MW protein. This pattern of response was associated with enhanced clearance of M. avium from the liver and spleen of coimmunized mice, and was significantly more effective than BCG or DNA-Av35. alone. Following M. avium challenge there was significant increase in the expansion of the 35000 MW antigen-reactive T cells in the coimmunized mice. Therefore, plasmid-delivered IL-12 acts as an effective adjuvant to increase the protective efficacy of a single DNA vaccine against M. avium infection above that achieved by BCG, and this strategy may improve the efficacy of subunit vaccines against M. leprae and M. tuberculosis.

Improving vaccines against tuberculosis

Tuberculosis remains a major cause of mortality and physical and economic deprivation worldwide. There have been significant recent advances in our understanding of the Mycobacterium tuberculosis genome, mycobacterial genetics and the host determinants of protective immunity. Nevertheless, the challenge is to harness this information to develop a more effective vaccine than BCG, the attenuated strain of Mycobacterium bovis derived by Calmette and Guérin nearly 90 years ago. Some of the limitations of BCG include the waning of the protective immunity with time, reduced effectiveness against pulmonary tuberculosis compared to disseminated disease, and the problems of a live vaccine in immuno-compromised subjects. Two broad approaches to vaccine development are being pursued. New live vaccines include either attenuated strains of Mycobacterium tuberculosis produced by random mutagenesis or targeted deletion of putative virulence factors, or by genetic manipulation of BCG to express new antigens or cytokines. The second approach utilizes non-viable subunit vaccines to deliver immunodominant mycobacterial antigens. Both protein and DNA vaccines induce partial protection against experimental tuberculosis infection in mice, however, their efficacy has generally been equivalent to or less than that of BCG. The comparative effects of cytokine adjuvants and vaccines targeting antigen presenting cells on enhancing protection will be discussed. Coimmunization with plasmid interleukin-12 and a DNA vaccine expressing Antigen 85B, a major secreted protein, was as protective as BCG. The combination of priming with DNA-85B and boosting with BCG was superior to BCG alone. Therefore it is possible to achieve a greater level of protection against tuberculosis than with BCG, and this highlights the potential for new tuberculosis vaccines in humans.

TNF regulates chemokine induction essential for cell recruitment, granuloma formation, and clearance of mycobacterial infection

Host immunity to mycobacterial infection is dependent on the activation of T lymphocytes and their recruitment with monocytes to form granulomas. These discrete foci of activated macrophages and lymphocytes provide a microenvironment for containing the infection. The cytokine, TNF, is essential for the formation and maintenance of granulomas, but the mechanisms by which TNF regulates these processes are unclear. We have compared the responses of TNF-deficient (TNF(-/-)) and wild-type C57BL/6 mice to infection with Mycobacterium smegmatis, a potent inducer of TNF, and virulent Mycobacterium tuberculosis to delineate the TNF-dependent and -independent components of the process. The initial clearance of M. smegmatis was TNF independent, but TNF was required for the early expression of mRNA encoding C-C and C-X-C chemokines and the initial recruitment of CD11b(+) macrophages and CD4(+) T cells to the liver during the second week of infection. Late chemokine expression and cell recruitment developed in TNF(-/-) mice associated with enhanced Th1-like T cell responses and mycobacterial clearance, but recruited leukocytes did not form tight granulomas. Infection of TNF(-/-) mice with M. tuberculosis also resulted in an initial delay in chemokine induction and cellular recruitment to the liver. Subsequently, increased mRNA expression was evident in TNF(-/-) mice, but the loosely associated lymphocytes and macrophages failed to form granulomas and prevent progressive infection. Therefore, TNF orchestrates early induction of chemokines and initial leukocyte recruitment, but has an additional role in the aggregation of leukocytes into functional granulomas capable of controlling virulent mycobacterial infection.

Determinants of vaccine-induced resistance in animal models of pulmonary tuberculosis

A more effective vaccine will be essential if the global tuberculosis (TB) pandemic is ever to be controlled. A large number of new tuberculosis vaccines have been developed, representing the whole range of modern strategies for vaccine formulation and delivery. There is currently no alternative to testing these new vaccines in experimental animals challenged with virulent Mycobacteriurn tuberculosis in order to assess their protective efficacy. Although such testing is being carried out in several animal species (mice, guinea pigs, rabbits), all rational models include pulmonary challenge with a low dose of virulent mycobacteria. The quantitative measures for TB vaccines include increased survival, amelioration of clinical signs and symptoms (e.g. prevention of weight loss), decreased lesion size, reduction in bacillary loads in the lungs, and prevention of extrapulmonary dissemination and hematogenous reseeding of the lung. Although the ultimate objective of vaccination in humans is to prevent transmission to susceptible contacts, no such measurement is being used in animal studies of new vaccines. The validation of an immunological "correlate of protection" is urgently needed. Candidates for such a correlate include antigen-specific interferon-gamma production by T cells of the memory phenotype (CD45RB(high) or mycobacterial killing by macrophages co-cultured with immune T cells. Additional animal models must be developed for vaccines designed to prevent endogenous reactivation or exogenous reinfection, or to be used as a adjunct to chemotherapy.

Comparative protective effects of recombinant DNA and Mycobacterium bovis bacille Calmette-Guérin vaccines against M. avium infection

A range of strategies are being explored to develop more effective vaccines against mycobacterial infection, including immunization with DNA plasmids encoding single mycobacterial bacterial genes and the use of recombinant live vectors based on the current vaccine, Mycobacterium bovis bacille Calmette-Guérin (BCG). We have compared these two approaches using a model of virulent M. avium infection, and the gene for the immunodominant 35 kDa protein which is shared by M. avium and M. leprae, but absent from BCG. Recombinant BCG over-expressing the M. avium 35 kDa protein (BCG-35) induced strong antigen-specific proliferative and interferon-gamma (IFN-gamma)-secreting T cell responses. These were comparable to those induced by a single immunization with a plasmid expressing the same antigen (DNA-35); however, repeat DNA-35 immunization evoked the strongest IFN-gamma release. Immunization with BCG-35 significantly reduced the growth of virulent M. avium, although this effect was similar to that induced by wild-type BCG. Immunization with DNA-35 resulted in significantly greater (2 x log(10)) reduction in the growth of M. avium. Prime-boost strategies combining DNA-35 and BCG-35 increased the protective effect above that achieved by BCG-35, but they were not more protective than DNA-35 alone. Therefore, recombinant BCG-35 and BCG induced similar levels of protection in this model, and maximal protection against M. avium infection was attained by immunization with DNA encoding the 35 kDa protein.

Induction of specific CD8+ memory T cells and long lasting protection following immunization with Salmonella typhimurium expressing a lymphocytic choriomeningitis MHC class I-restricted epitope

Numerous studies have shown the potential of Salmonella typhimurium as a vector for delivery of heterologous proteins for vaccination against other pathogens. Earlier studies showed that the inefficient elicitation of MHC class I-restricted responses could limit the use of S. typhimurium as a heterologous antigen delivery vector for vaccination. We recently developed an approach to overcome this limitation by using a bacterial-encoded specialized protein secretion system, termed type III, to deliver proteins into the class I antigen presenting pathways. Thus, peptides of interest fused to proteins bearing the type III secretion signal, which can elicit protective CTL responses. Because protective immunity is usually assessed a few weeks after vaccination, there is a paucity of information regarding duration of protective immunity induced by this system. We show here that mice immunized orally with S. typhimurium vectors expressing a MHC class I-restricted epitope of the lymphocytic choriomeningitis virus (LCMV) nucleoprotein developed specific antiviral CTL responses. CD8+ T cells were found to be necessary for this CTL activity against targets presenting the LCMV epitope. The survival of mice challenged with lethal doses of LCMV 60 or 135 days after vaccination was as complete as the survival of mice challenged 2 weeks after immunization with the same vectors. By demonstrating their ability to induce prolonged protective immunity after oral delivery, S. typhimurium vectors have met an essential requirement in support of their development as vectors for heterologous vaccination.

Tuberculosis DNA vaccines

DNA vaccines have been the subject of intense investigation for the past 10 y, during which time several tuberculosis (TB) DNA vaccines have been shown to confer protective immunity in animal models. So far, proof of principle for priming of immune responses by a naked DNA vaccine (malaria) has been demonstrated in humans, but potency remains a significant limitation. However, new DNA vaccine formulations and delivery systems are being developed with markedly improved potency in animal models. Therefore, there is a clear path to the human clinical testing of TB DNA vaccines.

Endogenous inhibition of antimycobacterial immunity by IL-10 varies between mycobacterial species

Interleukin (IL)-10 is an immunoregulatory cytokine that inhibits both Th1-like T cell responses and macrophage activation. Deficiency of IL-10 has been associated with increased Th1-like CD4+ T-cell responses and increased clearance of some intracellular pathogens, however, its role in mycobacterial infections is controversial. In order to examine the effects of mycobacterial virulence on the outcome of infection we compared infection with Mycobacterium avium and virulent Mycobacterium tuberculosis in C57Bl/6 IL-10-/- mice. M. avium infection in IL-10-/- mice resulted in sustained increases in interferon (IFN)-gamma-secreting T-cell responses and was associated with the increased clearance of M. avium from the liver and lung. By contrast, M. tuberculosis infection in IL-10-/- mice led to a transient increase in IFN-gamma T-cell responses at 4 weeks postinfection, with reduced bacterial burden in the lungs. This was not sustained so that by 8 weeks there was no difference to wild-type (WT) mice. In vitro infection of IL-10-/- macrophages with M. avium, but not M. tuberculosis, led to an increased IL-12 production. Therefore, endogenous IL-10 exerts a significant inhibition on specific IFN-gamma T-cell responses to M. avium infection, however, this effect is short lived during the M. tuberculosis infection, and fails to influence the long-term course of infection.

DNA encoding a single mycobacterial antigen protects against leprosy infection

The continuing incidence of leprosy infection around the world and the inability of Mycobacterium bovis bacille Calmette-Guérin (BCG) to protect certain populations clearly indicates that an improved vaccine against leprosy is needed. The immuno dominant 35 kDa protein, shared by Mycobacterium leprae and Mycobacterium avium, but not Mycobacterium tuberculosis or BCG, is recognised by >90% of leprosy patients, making it an ideal candidate antigen for a subunit vaccine. Immunization of outbred Swiss Albino mice with a DNA-35 vaccine stimulated specific T cell activation and IFN-gamma production. DNA-35 immunization induced significant levels of protection against M. leprae footpad infection, comparable to that produced by BCG. Therefore, DNA immunization with the 35 kDa antigen is effective against M. leprae infection and genetic immunization with a combination of antigens holds the potential for an improved vaccine against leprosy.