Genetic vaccination against tuberculosis

Immunotherapeutic Activities of a DNA Plasmid Carrying the Mycobacterial hsp65 Gene (DNAhsp65)

DNA vaccines have become relevant subject matter, and efforts for their development have been increasing due to their potential as technology platforms applicable for prophylactic and therapeutic approaches for infectious diseases and for cancer treatment, allergies, and autoimmune diseases. This review aimed to summarize current knowledge about the plasmid DNA vaccine carrying the mycobacterial hsp65 gene (DNAhsp65), which demonstrates immunomodulatory and immunoregulatory properties of both the innate and adaptive immune systems. The possible mechanisms associated with the modulation and regulatory role of DNAhsp65 in the control of various conditions is also discussed.

Modulation of angiogenic factor VEGF by DNA-hsp65 vaccination in a murine CNS tuberculosis model

Tuberculosis (TB) is a serious public health problem. Development of experimental models and vaccines are essential to elucidate physiopathological mechanisms and to control the disease. Vascular endothelial growth factor (VEGF) is a potent activator of vascular permeability and angiogenesis. VEGF seems to participate in breakdown of the blood brain-barrier (BBB) in tuberculous meningitis (TBM), contributing to worsening of disease. Therefore, the objective here was to extent the characterization of our previously described murine model of central nervous system TB (CNS-TB) by describing the VEGF participation in the CNS disease, and suggesting a vaccination plan in mice. Plasmid encoding DNA protein antigen DNA-hsp65 has been described as a protector against TB infection and was used here to test its effectiveness in the prevention of VEGF production and TB disease. Vaccinated mice and its controls were injected with Mycobacterium bovis bacillus Calmette-Guerin (BCG) in cerebellum. Four weeks after BCG injection, mice were perfused and brains were paraffin-embedded for VEGF expression analysis. We observed VEGF immunohistochemical expression in TBM and granulomas in non-vaccinated mice. The DNA-hsp65 treatment blocked the expression of VEGF in mice TBM. Therefore, our murine model indicated the VEGF participation in the physiopathology of CNS-TB and the potential prevention of the DNA-hsp65 in the disease progression.

Vaccine potential of influenza vectors expressing Mycobacterium tuberculosis ESAT-6 protein

We generated several attenuated recombinant influenza A vectors expressing the Mycobacterium tuberculosis early secretory antigenic target (ESAT-6) protein. The ESAT-6 protein was recently identified as one of the most promising protective antigens for cell-mediated immunity. The obtained vectors appeared to be capable of inducing ESAT-6 specific Th1 immune response in mice after intranasal immunization. We found that double immunization with two influenza vectors of different subtypes provided a significant level of protection in mice, when applied as prophylactic vaccine, as well as substantial therapeutic effect in mice with pre-established tuberculosis infection. Moreover, we found a strong synergistic effect when vaccination with Flu/ESAT-6 vectors was combined with isoniazid treatment, resulting in a dramatic reduction of bacterial load in the lungs of infected mice.

Development of new vaccines and diagnostic reagents against tuberculosis

Tuberculosis (TB) is a major infectious disease problem with one-third of the world population infected, 8 million people developing the active disease and 2 million dying of TB each year. The attenuated Mycobacterium bovis Bacillus Calmette Guerin (BCG) is the only available vaccine against TB. However, the trials conducted in different parts of the world have shown that this vaccine doe not provide consistent protection against TB. The purified protein derivative (PPD) of Mycobacterium tuberculosis is the commonly used reagent for the diagnosis of TB. However, PPD lacks specificity because of the presence of antigens crossreactive with M. bovis BCG and other mycobacteria. The studies to identify M. tuberculosis antigens and epitopes as candidates for new protective vaccines and specific diagnostic reagents against TB have led to the identification and characterization of several major antigens of M. tuberculosis including heat shock proteins (hsp) and secreted antigens present in the culture filtrate (CF) of M. tuberculosis. Some of these antigens have shown promise as new candidate vaccines (hsp60, Ag85 and ESAT-6, etc.) and specific diagnostic reagents (ESAT-6 and CFP10, etc.) for TB. Moreover, in the mouse model of TB, vaccination with DNA-hsp60 has immunotheraputic effects and helps in eradication of persisters. In addition, identification of proper adjuvant and delivery systems has shown the promise to overcome the problem of poor immunogenicity associated with subunit and peptide based vaccines. More recently, the comparison of the genome sequence of M. tuberculosis with M. bovis BCG and other mycobacteria has led to the identification of M. tuberculosis-specific genomic regions. Evaluation of these regions for encoding proteins with immunological reactivity can lead to the identification of additional antigens of M. tuberculosis useful as new vaccines and reagents for specific diagnosis of TB.

Vaccination with the T cell antigen Mtb 8.4 protects against challenge with Mycobacterium tuberculosis

The development of an effective vaccine against Mycobacterium tuberculosis is a research area of intense interest. Mounting evidence suggests that protective immunity to M. tuberculosis relies on both MHC class II-restricted CD4(+) T cells and MHC class I-restricted CD8(+) T cells. By purifying polypeptides present in the culture filtrate of M. tuberculosis and evaluating these molecules for their ability to stimulate PBMC from purified protein derivative-positive healthy individuals, we previously identified a low-m.w. immunoreactive T cell Ag, Mtb 8.4, which elicited strong Th1 T cell responses in healthy purified protein derivative-positive human PBMC and in mice immunized with recombinant Mtb 8.4. Herein we report that Mtb 8.4-specific T cells can be detected in mice immunized with the current live attenuated vaccine, Mycobacterium bovis-bacillus Calmette-Guérin as well as in mice infected i.v. with M. tuberculosis. More importantly, immunization of mice with either plasmid DNA encoding Mtb 8.4 or Mtb 8.4 recombinant protein formulated with IFA elicited strong CD4(+) T cell and CD8(+) CTL responses and induced protection on challenge with virulent M. tuberculosis. Thus, these results suggest that Mtb 8.4 is a potential candidate for inclusion in a subunit vaccine against TB.

Intracellular bacteria as targets and carriers for vaccination

In this review we discuss intracellular bacteria as targets and carriers for vaccines. For clarity and ease of comprehension, we focus on three microbes, Mycobacterium tuberculosis, Listeria monocytogenes and Salmonella, with an emphasis on tuberculosis, one of the leading causes of death from infectious disease. Novel vaccination strategies against these pathogens are currently being considered. One approach favors the use of live attenuated vaccines and vaccine carrier strains thereof, either for heterologous antigen presentation or DNA vaccine delivery. This strategy includes both the improvement of attenuated vaccine strains as well as the 'de novo' generation of attenuated variants of virulent pathogens. An alternative strategy relies on the application of subunit immunizations, either as nucleic acid vaccines or protein antigens of the pathogen. Finally, we present a short summary of the vaccination strategies against tuberculosis.

Characterization of the memory/activated T cells that mediate the long-lived host response against tuberculosis after bacillus Calmette-Guérin or DNA vaccination

The memory/activated T cells, which mediate the long-lived host response against tuberculosis, in mice immunized with either bacillus Calmette-Guérin (BCG) or mycobacterium heat-shock protein 65 (hsp 65) antigen expressed from plasmid DNA (DNA-hsp 65), were characterized. Protection against Mycobacterium tuberculosis challenge by DNA-hsp 65 vaccination was associated with the presence of lymph node T-cell populations in which CD8+/CD44hi interferon-gamma (IFN-gamma)-producing/cytotoxic cells were prominent even after 8 or 15 months of plasmid DNA-mediated immunizations, whereas after BCG vaccination the majority were CD4+/CD44lo IFN-gamma-producing T cells. When the cells were separated into CD4+CD8- and CD8+CD4- and then into CD44hi and CD44lo types, CD44lo cells were essentially unable to transfer protection in adoptive transfer experiments, the most protective CD44hi cells were CD8+CD4- and those from DNA-vaccinated mice were much more protective than those from BCG-immunized mice. The frequency of protective T cells and the level of protection were increased up to 8 months and decreased after 15 months following DNA or BCG immunizations.

The potential use of heat-shock proteins to vaccinate against mycobacterial infections

Over the last few years, some of our experiments in which mycobacterial heat-shock protein (HSP) antigens were presented to the immune system as if they were viral antigens have had a significant impact on our understanding of protective immunity against tuberculosis. They have also markedly enhanced the prospects for new vaccines. We now know that the mycobacterial HSP65 antigen can confer protection equal to that from live BCG vaccine in mice.

DNA encoding individual mycobacterial antigens protects mice against tuberculosis

Over the last few years, some of our experiments in which mycobacterial antigens were presented to the immune system as if they were viral antigens have had a significant impact on our understanding of protective immunity against tuberculosis. They have also markedly enhanced the prospects for new vaccines. We now know that individual mycobacterial protein antigens can confer protection equal to that from live BCG vaccine in mice. A critical determinant of the outcome of immunization appears to be the degree to which antigen-specific cytotoxic T cells are generated by the immune response. Our most recent studies indicate that DNA vaccination is an effective way to establish long-lasting cytotoxic T cell memory and protection against tuberculosis.

Heat shock proteins in immune reactions

The review concerns heat shock proteins and their significance in immune reactions. It focuses on problems of physiological and pathological interactions in etiology and duration of autoimmune diseases and infection processes, especially fungal infections. New trends are described in exploitation of heat shock proteins for preparation of specific protective vaccines.

Control of immune responses by gene immunization

The use of plasmid DNA to elicit immune responses has greatly increased our ability to skew the desired immune response to a particular antigen. DNA immunization elicits potent cell-mediated responses including humoral immunity as well as cytolytic T-lymphocyte immunity. This review will first discuss the overall immune response induced by naked DNA vaccination and will then summarize recent advances in basic research on DNA immunization, which have furthered our understanding of the role of DNA as an adjuvant as well as a carrier of genetic material. Subsequently, we will consider the possible mechanisms by which DNA immunization is able to induce such immune responses and how DNA immunization may be useful in both basic science research and also in future vaccine development in various disease processes. Finally, we will examine the advantages and disadvantages of DNA vaccines as well as safety issues. In conclusion, DNA vaccination shows promise in a number of areas including infectious diseases, allergy and cancer immunotherapies.