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T Mark Doherty

Publications and source records attributed to T Mark Doherty.

At least 19 recordsLinked to original sources
PubMed2006

Mucosal administration of Ag85B-ESAT-6 protects against infection with Mycobacterium tuberculosis and boosts prior bacillus Calmette-Guerin immunity.

We have examined the intranasal administration of a vaccine against Mycobacterium tuberculosis (M.tb) consisting of the mucosal adjuvant LTK63 and the Ag Ag85B-ESAT-6. Vaccination with LTK63/Ag85B-ESAT-6 gave a strong and sustained Th1 response mediated by IFN-gamma-secreting CD4 cells, which led to long-lasting protection against tuberculosis, equivalent to that observed with bacillus Calmette-Guérin (BCG) or Ag85B-ESAT-6 in dimethyldioctadecylammonium bromide/monophosphoryl lipid A. Because a crucial element of novel vaccine strategies is the ability to boost BCG-derived immunity, we also tested whether LTK63/Ag85B-ESAT-6 could act as a BCG booster vaccine in BCG-vaccinated mice. We found that vaccinating with LTK63/Ag85B-ESAT-6 strongly boosted prior BCG-stimulated immunity. Compared with BCG-vaccinated nonboosted mice, we observed that infection with M.tb led to a significant increase in anti-M.tb-specific CD4 T cells in the lungs of LTK63/Ag85B-ESAT-6-boosted animals. This correlated with a significant increase in the protection against M.tb in LTK63/Ag85B-ESAT-6-boosted mice, compared with BCG-vaccinated animals. Thus, LTK63/Ag85B-ESAT-6 represents an efficient preventive vaccine against tuberculosis with a strong ability to boost prior BCG immunity.

Acyltransferases↗
PubMed2006

Alteration of epitope recognition pattern in Ag85B and ESAT-6 has a profound influence on vaccine-induced protection against Mycobacterium tuberculosis.

To analyze the effect of vaccine delivery systems on antigen recognition and vaccine efficacy, we compared immune responses in mice immunized either with an adenovirus vector expressing a fusion of Ag85B and ESAT-6 or with the recombinant fusion protein in a liposomal adjuvant. Both vaccines induced high levels of antigen-specific IFN-gamma production. The adjuvanted protein vaccine induced primarily a CD4 T cell response directed to the epitope Ag85B(241-255) and gave efficient protection against subsequent Mycobacterium tuberculosis infection. In contrast, the adenoviral construct induced a strong CD8 response predominantly targeted to the epitope ESAT-6(15-29) and no significant protection against infection. Vaccination with the protein vaccine resulted in highly accelerated recall of Ag85B(241-255)-specific T cells immediately post M. tuberculosis challenge whereas the ESAT-6(15-29) epitope was barely recognized during infection. Delivery of the viral construct in cationic liposomes switched the immune response to a protective one dominated by CD4 T cells targeted to the Ag85B(241-255) epitope. These data demonstrate that the nature of the T cell response to a vaccine antigen is more important than its magnitude with respect to protective efficacy and that vaccine-mediated changes in immunodominance can result in T cell responses of limited relevance during the natural infection.

Acyltransferases↗
PubMed2006

Recognition of stage-specific mycobacterial antigens differentiates between acute and latent infections with Mycobacterium tuberculosis.

Mycobacterium tuberculosis is estimated to infect 80 to 100 million people annually, the majority of whom do not develop clinical tuberculosis (TB) but instead maintain the infection in a latent state. These individuals generally become positive in response to a tuberculin skin test and may develop clinical TB at a later date, particularly if their immune systems are compromised. Latently infected individuals are interesting for two reasons. First, they are an important reservoir of M. tuberculosis, which needs to be considered for TB control. Second, if detected prior to recrudescence of the disease, they represent a human population that is making a protective immune response to M. tuberculosis, which is very important for defining correlates of protective immunity. In this study, we show that while responsiveness to early secretory antigenic target 6 is a good marker for M. tuberculosis infection, a strong response to the 16-kDa Rv2031c antigen (HspX or alpha-crystallin) is largely restricted to latently infected individuals, offering the possibility of differential immunodiagnosis of, or therapeutic vaccination against, TB.

Acute Disease↗
PubMed2006

The 6-kilodalton early secreted antigenic target-responsive, asymptomatic contacts of tuberculosis patients express elevated levels of interleukin-4 and reduced levels of gamma interferon.

It is well known that the majority of healthy individuals exposed to Mycobacterium tuberculosis do not become clinically ill. We have previously shown that in recently exposed healthy contacts of tuberculosis (TB) patients, a strong immune response to the M. tuberculosis 6-kDa early secreted antigenic target (ESAT-6) virulence factor correlated with a higher risk of subsequent disease, although the mechanism was unclear at that time. Inspired by recent reports that elevated expression of interleukin-4 (IL-4) in health care workers exposed to M. tuberculosis also correlated with a higher risk of their subsequently developing disease, we examined expression of IL-4, its competitive antagonist IL-4delta2, and gamma interferon (IFN-gamma) in healthy household contacts of TB patients from Ethiopia. We then compared cytokine expression to their recognition of ESAT-6 (which is largely restricted to members of the tuberculosis complex and which serves as a reliable marker of infection) or to Ag85A (an antigen that is conserved among the mycobacteria and serves as a nonspecific control). Our study shows that in these recently exposed individuals, there is a correlation between a strong response to ESAT-6 and elevated expression of IL-4. Further, elevated expression of IL-4 is associated with lower expression of its antagonistic splice variant IL-4delta2 and with the Th1 cytokine IFN-gamma, suggesting that in these at-risk individuals, immunity is skewed away from a protective Th1 response, even before the development of clinical symptoms.

Antigens, Bacterial↗
PubMed2005

Exchanging ESAT6 with TB10.4 in an Ag85B fusion molecule-based tuberculosis subunit vaccine: efficient protection and ESAT6-based sensitive monitoring of vaccine efficacy.

Previously we have shown that Ag85B-ESAT-6 is a highly efficient vaccine against tuberculosis. However, because the ESAT-6 Ag is also an extremely valuable diagnostic reagent, finding a vaccine as effective as Ag85B-ESAT-6 that does not contain ESAT-6 is a high priority. Recently, we identified a novel protein expressed by Mycobacterium tuberculosis designated TB10.4. In most infected humans, TB10.4 is strongly recognized, raising interest in TB10.4 as a potential vaccine candidate and substitute for ESAT-6. We have now examined the vaccine potential of this protein and found that vaccination with TB10.4 induced a significant protection against tuberculosis. Fusing Ag85B to TB10.4 produced an even more effective vaccine, which induced protection against tuberculosis comparable to bacillus Calmette-Guerin vaccination and superior to the individual Ag components. Thus, Ag85B-TB10 represents a new promising vaccine candidate against tuberculosis. Furthermore, having now exchanged ESAT-6 for TB10.4, we show that ESAT-6, apart from being an excellent diagnostic reagent, can also be used as a reagent for monitoring vaccine efficacy. This may open a new way for monitoring vaccine efficacy in clinical trials.

Acyltransferases↗
PubMed2005

Protection of macaques against Mycobacterium tuberculosis infection by a subunit vaccine based on a fusion protein of antigen 85B and ESAT-6.

Various new tuberculosis (TB) vaccine candidates in combination with new delivery systems, including subunit vaccines, are currently being evaluated by a number of laboratories. One vaccine candidate that has shown promising protective capacity in mice and guinea pigs is a fusion of Ag85B and ESAT-6. In this study, we have investigated the efficacy of this Ag85B-ESAT-6 fusion protein vaccine in a non-human primate model for TB. Vaccination of cynomolgus monkeys with the Ag85B-ESAT-6 fusion protein in two different adjuvant (DDA/MPL, AS02A) resulted in a reduction in bacterial number and/or lung pathology in animals challenged with Mycobacterium tuberculosis. Vaccination prevented an increase in C-reactive protein serum levels, general activation of CD4 and CD8 subsets and boosted development of humoral and cellular immune responses to a spectrum of mycobacterial antigens on exposure to M. tuberculosis infection. We show, in two independent experiments, that vaccination of primates with Ag85B-ESAT-6 induces protective immune responses, suggesting that Ag85B-ESAT-6 is a strong candidate for further clinical evaluation. As far as we are aware this is the first report of protection in primates with a subunit vaccine.

Acyltransferases↗
PubMed2005

TB subunit vaccines--putting the pieces together.

The search for a new and improved vaccine against tuberculosis (TB) is currently a very active field of research, which in the last 10 years has benefited tremendously from the completed Mycobacterium tuberculosis genome and the progress in molecular biology and computer science. In this review, we discuss how Genomics, Proteomics and Transcriptomics have accelerated the pace of antigen discovery and vaccine development and have changed this field completely, resulting in the identification of a large number of antigens with potential in TB vaccines. The next phase of this work has now started--putting the most relevant molecules back together as fusion molecules and cocktails. This requires carefully monitoring aspects as immunodominance, recognition in different populations as well as vaccine manufacturing.

Antigens, Bacterial↗
PubMed2005

Real world TB vaccines: clinical trials in TB-endemic regions.

The first 4 years of the 21st century have been an exciting time for tuberculosis (TB) research. After more than a half-century, the first new vaccines for TB are beginning to enter human clinical trials. Based on advances in proteomics and genomics, new vaccine candidates are filling the preclinical pipeline and our understanding of the natural history of M. tuberculosis infection is expanding rapidly. This review summarizes the developing consensus on the BCG vaccine and its limitations and discusses clinical trials of some of the new vaccines intended to supplement or replace it.

BCG Vaccine↗
PubMed2005

Evaluation of vaccines in the EU TB Vaccine Cluster using a guinea pig aerosol infection model of tuberculosis.

The TB Vaccine Cluster project funded by the EU Fifth Framework programme aims to provide novel vaccines against tuberculosis that are suitable for evaluation in humans. This paper describes the studies of the protective efficacy of vaccines in a guinea pig aerosol-infection model of primary tuberculosis. The objective was to conduct comparative evaluations of vaccines that had previously demonstrated efficacy in other animal models. Groups of 6 guinea pigs were immunized with vaccines provided by the relevant EU Vaccine Cluster partners. Survival over 17 or 26 weeks was used as the principal measure of vaccine efficacy following aerosol challenge with H37Rv. Counts of mycobacteria in lungs and spleens, and histopathological changes in the lungs, were also used to provide evidence of protection. A total of 24 vaccines were evaluated in 4 experiments each of a different design. A heterologous prime-boost strategy of DNA and MVA, each expressing Ag85A and a fusion protein of ESAT-6 and Ag85B in adjuvant, protected the guinea pigs to the same extent as BCG. Genetically modified BCG vaccines and boosted BCG strategies also protected guinea pigs to the same extent as BCG but not statistically significantly better. A relatively high aerosol-challenge dose and evaluation over a protracted time post-challenge allowed superior protection over BCG to be demonstrated by BCG boosted with MVA and fowl pox vectors expressing Ag85A.

Aerosols↗
PubMed2005

Effect of sample handling on analysis of cytokine responses to Mycobacterium tuberculosis in clinical samples using ELISA, ELISPOT and quantitative PCR.

Measuring cytokine responses to infection has proven to be invaluable for the understanding of immunity to tuberculosis in the laboratory. However, far less data are available from studies in humans and these have often produced conflicting results. Here we describe a comprehensive multi-center comparison of the most commonly used protocols for cytokine analysis: ELISA, ELISPOT and RT-PCR, in cohorts of TB patients, their household contacts and community controls. In particular, we have studied the effect on these protocols of conditions that commonly prevail in field studies, such as delays between sample collection and analysis, or different source material, such as whole blood or frozen PBMC. The results clearly show that while there is good correlation between the methods under optimal conditions, each method has strengths and weaknesses that render them more or less suitable for particular types of analyses. Researchers should carefully consider these factors when planning human field studies.

Adolescent↗
PubMed2005

The success and failure of BCG - implications for a novel tuberculosis vaccine.

Over the past 50 years, the Mycobacterium bovis bacille Calmette-Guérin (BCG) vaccine against tuberculosis (TB) has maintained its position as the world's most widely used vaccine, despite showing highly variable efficacy (0-80%) in different trials. The efficacy of BCG in adults is particularly poor in tropical and subtropical regions. Studies in animal models of TB, supported by data from clinical BCG trials in humans, indicate that this failure is related to pre-existing immune responses to antigens that are common to environmental mycobacteria and Mycobacterium tuberculosis. Here, we discuss the potential mechanisms behind the variation of BCG efficacy and their implications for an improved TB vaccination strategy.

Adolescent↗
PubMed2005

Vaccines for tuberculosis: novel concepts and recent progress.

Three-quarters of a century after the introduction of Mycobacterium bovis BCG, the first tuberculosis vaccine, new vaccines for tuberculosis are finally entering clinical trials. This breakthrough is based not only on advances in proteomics and genomics which have made the construction of new vaccines possible, but also on a greatly expanded knowledge of the immunology of tuberculosis. Here we review our current understanding of how Mycobacterium tuberculosis subverts or survives the host's immune response to cause disease and why the current vaccination strategy, which relies on BCG, is only partially successful in countering the pathogen. This provides a background for describing the new generation of vaccines designed to supplement or replace the current vaccine and the different approaches they take to stimulate immunity against M. tuberculosis.

Animals↗
PubMed2005

Assessing the serodiagnostic potential of 35 Mycobacterium tuberculosis proteins and identification of four novel serological antigens.

Improved diagnostic reagents are needed for the detection of Mycobacterium tuberculosis infections, and the development of a serodiagnostic test would complement presently available diagnostic methods. The aim of the present study was to identify novel serological targets for use for the future serodiagnosis of tuberculosis (TB). We cloned and expressed 35 M. tuberculosis proteins as recombinant proteins in Escherichia coli and analyzed their serodiagnostic potentials. By a two-step selection process, four superior seroantigens, TB9.7, TB15.3, TB16.3, and TB51, were identified, none of which has been described before. The four novel antigens were tested with panels of sera from smear-positive and smear-negative TB patients from areas both where TB is endemic and where TB is not endemic, with recognition frequencies ranging from 31 to 93% and with a specificity of at least 97%. The single most potent antigen was TB16.3, which had a sensitivity of 48 to 55% with samples from Danish resident TB patients and a sensitivity of 88 to 98% with samples from African TB patients. Importantly, the TB16.3 and the TB9.7 antigens were recognized by more than 85% of the samples from TB patients coinfected with human immunodeficiency virus, a patient group for which it is in general difficult to detect M. tuberculosis-specific antibodies.

Adult↗
PubMed2004

Comparative analysis of different vaccine constructs expressing defined antigens from Mycobacterium tuberculosis.

BACKGROUND: Studies of different vaccine constructs have demonstrated variable efficacy against Mycobacterium tuberculosis in animal models. Despite the fact that these vaccines have used one or another of a very small number of immunodominant antigens, a direct comparison of the relative efficacy of the antigens and delivery systems has been difficult, because the studies have used different parameters for assessment. METHODS: We compared the efficacies of the most commonly used vaccine constructs--adjuvanted protein, plasmid DNA, and live bacterial vectors--bearing the immunodominant secreted antigens early secreted antigen target-6 and antigen 85B, either alone or as a fusion protein. Mice were vaccinated with these constructs, and the effects of different delivery systems on protective efficacy (as assessed by survival studies and by monitoring bacterial load) and antigen-specific responses (including the contribution of CD4 and CD8 T cells to these responses) were assayed by various methods. RESULTS: The relative efficacy of different vaccines is dependent on the delivery system, the antigen, and the animal model. Likewise, the relative immunodominance of individual antigens in the fusion molecule is altered by the choice of delivery system. CONCLUSION: These results clearly demonstrate the importance of assessing vaccine function by use of multiple parameters and indicate which parameters are most reliable for assessing vaccine efficacy.

Acyltransferases↗
PubMed2004

Healthy individuals that control a latent infection with Mycobacterium tuberculosis express high levels of Th1 cytokines and the IL-4 antagonist IL-4delta2.

The majority of healthy individuals exposed to Mycobacterium tuberculosis will not develop disease and identifying what constitutes "protective immunity" is one of the holy grails of M. tuberculosis immunology. It is known that IFN-gamma is essential for protection, but it is also apparent that IFN-gamma levels alone do not explain the immunity/susceptibility dichotomy. The controversy regarding correlates of immunity persists because identifying infected but healthy individuals (those who are immune) has been problematic. We have therefore used recognition of the M. tuberculosis virulence factor early secretory antigenic target 6 to identify healthy, but infected individuals from tuberculosis (TB)-endemic and nonendemic regions (Ethiopia and Denmark) and have compared signals for cytokines expressed directly ex vivo with the pattern found in TB patients. We find that TB patients are characterized by decreased levels of Th1 cytokines and increased levels of IL-10 compared with the healthy infected and noninfected community controls. Interestingly, the healthy infected subjects exhibited a selective increase of message for the IL-4 antagonist, IL-4delta2, compared with both TB patients or noninfected individuals. These data suggest that long-term control of M. tuberculosis infection is associated not just with elevated Th1 responses but also with inhibition of the Th2 response.

Adult↗
PubMed2004

Increased expression of mRNA encoding interleukin (IL)-4 and its splice variant IL-4delta2 in cells from contacts of Mycobacterium tuberculosis, in the absence of in vitro stimulation.

Expression of interleukin (IL)-4 is increased in tuberculosis and thought to be detrimental. We show here that in healthy contacts there is increased expression of its naturally occurring antagonist, IL-4delta2 (IL-4delta2). We identified contacts by showing that their peripheral blood mononuclear cells (PBMC) released interferon (IFN)-gamma in response to the Mycobacterium tuberculosis-specific antigen 6 kDa early secretory antigenic target (ESAT-6). Fresh unstimulated PBMC from these contacts contained higher levels of mRNA encoding IL-4delta2 (P=0.002) than did cells from ESAT-6 negative donors (noncontacts). These data indicate that contact with M. tuberculosis induces unusual, previously unrecognized, immunological events. We tentatively hypothesize that progression to active disease might depend upon the underlying ratio of IL-4 to IL-4delta2.

Adolescent↗
PubMed2004

New vaccines against tuberculosis.

In September 2000, recognizing the effect of communicable diseases as obstacles to development in poorer countries, the European Commission assembled a special round table on 'accelerated action targeted at major communicable diseases within the context of poverty reduction'. The three major communicable diseases discussed were tuberculosis (TB), malaria and HIV. One outcome of this discussion was a workshop examining issues related to the fight against TB in Africa, which took place in Gorée, Sénégal, in May 2001. The timing was propitious, as new vaccines for TB (recombinant MVA and BCG, and adjuvanated recombinant fusion proteins or peptide constructs), are just beginning to enter human clinical trials. All but the last of these have shown promise in animal models, up to and including non-human primates, and all are strongly immunogenic and apparently safe. Humans trials for safety and efficacy are thus the logical next step. This review summarizes recent advances in tuberculosis vaccine development, with a special emphasis on issues raised at the Gorée meeting about testing and deploying new generation vaccines in TB-endemic areas such as Africa.

Animals↗