Vaccine Approaches to Prevent Tuberculosis

Mycobacterium tuberculosis: immune response, biomarkers, and therapeutic intervention

Although tuberculosis (TB) is an infectious disease, the progression of the disease following Mycobacterium tuberculosis (MTB) infection is closely associated with the host's immune response. In this review, a comprehensive analysis of TB prevention, diagnosis, and treatment was conducted from an immunological perspective. First, we delved into the host's immune response mechanisms against MTB infection as well as the immune evasion mechanisms of the bacteria. Addressing the challenges currently faced in TB diagnosis and treatment, we also emphasized the importance of protein, genetic, and immunological biomarkers, aiming to provide new insights for early and personalized diagnosis and treatment of TB. Building upon this foundation, we further discussed intervention strategies involving chemical and immunological treatments for the increasingly critical issue of drug-resistant TB and other forms of TB. Finally, we summarized TB prevention, diagnosis, and treatment challenges and put forward future perspectives. Overall, these findings provide valuable insights into the immunological aspects of TB and offer new directions toward achieving the WHO's goal of eradicating TB by 2035.

[Morphological characteristics of inflammation in HIV-associated pulmonary tuberculosis with regard to the expression of myeloperoxidase]

OBJECTIVE

to characterize the morphological features of inflammation and the degree of myeloperoxidase expression in the lung of patients who died from HIV-associated tuberculosis (TB).

MATERIAL AND METHODS

Autopsy lung tissue specimens from 229 patients with HIV-associated TB were examined. A comparison group consisted of dead TB mono-infected patients (n = 30). Dead HIV/TB co-infected patients were divided into subgroups: 1) 50 patients with Stage 4A-4B and a CD4(+)-lymphocyte count of more than 200 cells/µl; 2) 54 with Stage 4B-4C and a CD4(+)-lymphocyte count of 100 to 200 cells/µl; 3) 125 with Stage 4C-5 and a CD4(+)-lymphocyte count of less than 100 cells/µl. Histological and immunohistochemical examinations of lung slices were performed using antibodies to myeloperoxidase (MPO).

RESULTS

The predominant types of an inflammatory response were revealed according to the level of CD4+ lymphocytes. The lungs in Subgroup 1 showed a predominant typical granulomatous response (82%). Subgroup 2 exhibited an exudative-productive inflammatory response (57.4%) while Subgroup 3 displayed an alterative necrotic type (92.8%). Subgroup 3 showed the most marked reduction in lymphocyte numbers in the areas of inflammation, which was accompanied by a significant increase in the relative density and other morphometric parameters of MPO-positive macrophages and granulocytes in the inflammatory infiltration zones and alveolar walls.

CONCLUSION

The identified changes in the lungs suggest that there is a decline in the magnitude of a delayed type hypersensitivity reaction, a progression of alterative necrotic processes as CD4(+) lymphocytes decrease in the systemic blood flow, and an increase in the proportion of functionally immature macrophages in the areas of inflammation, which reflects a substantially impaired local immune response to the persistence of M. tuberculosis in HIV infection.

Improving vaccines by incorporating immunological coadjuvants

While vaccination continues to be the most successful interventionist health policy to date, infectious disease remains a significant cause of death worldwide. A primary reason that vaccination is not able to generate effective immunity is a lack of appropriate adjuvants capable of initiating the desired immune response. Adjuvant combinations can potentially overcome this problem; however, the possible permutations to consider, which include the route and kinetics of vaccination, as well as combinations of adjuvants, are practically limitless. This review aims to summarize the current understanding of adjuvants and related immunological processes and how this knowledge can and has been applied to the strategic selection of adjuvant combinations as components of vaccines against human infectious disease.

Cytokines in response to proteins predicted in genomic regions of difference of Mycobacterium tuberculosis

Cellular immune responses are responsible for both protection and pathogenesis in tuberculosis, and are mediated/regulated by a complex network of pro-inflammatory, T helper (Th) type 1 and type 2 cytokines. In this study, the secretion of pro-inflammatory cytokines tumor necrosis factor-alpha (TNF-α), interleukin (IL)-6, IL-8 and IL-1β; Th1 cytokines interferon-gamma (IFN-γ), IL-2 and tumor necrosis factor-beta (TNF-β); and Th2 cytokines IL-4, IL-5 and IL-10 by the peripheral blood mononuclear cells (PBMCs) of pulmonary tuberculosis patients was studied. PBMCs were cultured in vitro in the absence and presence of complex mycobacterial antigens and peptides corresponding to 11 regions of difference (RD) of Mycobacterium tuberculosis that are deleted/absent in all vaccine strains of Mycobacterium bovis bacillus Calmette-Guérin (BCG). The culture supernatants were tested for secreted cytokines by FlowCytomix assay. PBMCs from the majority of patients (53-100%) spontaneously secreted detectable concentrations of all cytokines tested, except for IL2 (29%) and IL-10 (41%). The profiles of proinflammatory cytokines were largely similar for various complex antigens or RD peptides. However, with respect to Th1 and Th2 cytokines, the antigens could be divided into three groups; the first with Th1-bias (culture filtrate of M. tuberculosis, RD1, RD5, RD7, RD9 and RD10), the second with Th2-bias (whole cells and cell walls of M. tuberculosis, RD12, RD13 and RD15), and the third without Th1/Th2-bias (M. bovis BCG, RD4, RD6 and RD11). Complex mycobacterial antigens and RD proteins with Th1- and Th2-biases may have roles in protection and pathogenesis of tuberculosis, respectively.

Tuberculosis as part of the natural history of HIV infection in developing countries

An enhanced, refocused research agenda is critical to reducing the burden of tuberculosis (TB) in the human immunodeficiency virus (HIV) epidemic in developing countries. TB threatens HIV-infected patients before and after initiation of antiretroviral therapy, is difficult to diagnose, is rapidly fatal when it is drug resistant, and is being spread in clinics and hospitals. Research priorities include improved and point-of-care TB diagnostics; TB treatment and prevention during HIV infection, drug-resistant TB, and childhood TB; and optimization of TB and HIV program integration. With new TB diagnostics and drugs reaching approval, research must focus on effectively deploying these advancements. Research must include evaluations of individual, household, health care, and community approaches. Studies must apply implementation science to determine how to increase and adapt effective interventions to reduce TB burden in the context of HIV infection. Investment in this research will improve the lives of persons infected with HIV and contribute to efforts to reduce the global TB burden.

Cutinase-like protein-6 of Mycobacterium tuberculosis is recognised in tuberculosis patients and protects mice against pulmonary infection as a single and fusion protein vaccine

Infection with Mycobacterium tuberculosis continues to be a leading cause of death in many regions of the world, and control of this disease is hampered by the lack of a safe and effective vaccine. Secreted proteins of M. tuberculosis are an important group of antigens for subunit vaccines which target this infection. We have tested three secreted members of the cutinase-like protein (CULP) family of M. tuberculosis for their potential as protein vaccine antigens. Culp6 elicited a strong T lymphocyte response in M. tuberculosis infected mice, and importantly, in tuberculosis (TB) patients tested. Culp1, Culp2 and Culp6 when delivered as protein vaccines to mice, induced potent IFN-gamma responses which in turn translated into a significant level of protection against aerosol M. tuberculosis infection. A Culp1-6 fusion protein provided an increased level of protection against infection compared to Culp1 or Culp6 alone. The data presented here may indicate that the cell wall-associated, putatively essential protein Culp6, shown here for the first time to be recognised in TB patients, is an attractive candidate for inclusion in future subunit vaccines.

Immune responses and protective efficacy of the gene vaccine expressing Ag85B and ESAT6 fusion protein from Mycobacterium tuberculosis

Genetic immunity is a new promising approach for the development of novel tuberculosis vaccines. In this study, it is shown that DNA vaccines expressing the fusion protein of antigen 85B (Ag85B) and early secreted antigenic target 6-kDa antigen (ESAT6) can induce high levels of specific IgG2a antibody subtype in the mice. With the prolongation of postimmunization time, the levels of IgG2a antibody decrease gradually. Although a high-level specific IgG2a antibody subtype is also elicited by classical BCG, the ratio of antibody subtypes IgG2a to IgG1 changes 4 weeks after immunization, and IgG1 is gradually shifted to the main antibody subtype. DNA vaccines also elicit cellular immunity as shown by specific spleen lymphocytes proliferation to Ag85B or ESAT6 protein and the production of high levels of IFN-gamma and IL-2, which is similar to that elicited by BCG. Vaccination of mice with DNA vaccines expressing the fusion protein Ag85B-ESAT6 results in a significant level of protection against the subsequent high-dose challenge with virulent Mycobacterium tuberculosis (MTB) H37Rv. Dramatic reduction in the number of MTB colony-forming units in the spleens and lungs is observed. Pathological examination showed that recombinant plasmid and BCG groups have only minor damage and organizational structures that are kept relatively complete, while in the control group, spleens and lungs are damaged seriously. Therefore, although the reducing degree of mycobacterial loads in the organ of mice immunized with recombinant plasmid is not more than that of BCG, through the analysis of pathological changes, we may conclude that the protective effect provided by DNA vaccine expressing the Ag85B-ESAT6 fusion protein is equivalent to that afforded by the classical BCG.

Immunological diversity within a family of cutinase-like proteins of Mycobacterium tuberculosis

Secreted proteins of Mycobacterium tuberculosis play key roles in the assembly of the mycobacterial cell wall, with many being major targets of the host immune response. To date, meaningful characterization of a significant proportion of this important group of proteins is lacking. Among the group of putatively secreted proteins of M. tuberculosis are 7 cutinase-like proteins (CLP), not previously characterized in terms of their immunogenicity or vaccine protective efficacy. Although the CLP vary in the degree of homology with one another, they all share a similar active catalytic triad, closely homologous to that of the cutinase of Fusarium solani. By construction of DNA vaccines of all 7 CLP, and expression and purification of soluble, recombinant CLP, this study addresses the immunological responses to these proteins. Clp1, 2, 3 and 6 were found to elicit significant IFN-gamma secretion in DNA immunized mice, with the antigens also demonstrating specificity in terms of CLP-generated T cell IFN-gamma release, with minimal cross reactivity of humoral responses. Finally, following delivery of DNA vaccines, Clp1, 2 and 6, conferred a moderate yet reproducible and significant level of protection in a murine aerosol model of M. tuberculosis infection.

Co-infection with human immunodeficiency virus and tuberculosis in Asia

Asia has the highest numbers of tuberculosis cases (60% of the global total) and has experienced a marked rise in HIV seroprevalence (22% of the global total) in key subpopulations of these highly populous nations. Thus, co-infected patients are a challenge for practitioners and public health workers alike. The U.S.-Japan Cooperative Medical Science Program is spearheading interdisciplinary collaborations in Asia to address the many outstanding research priorities for HIV-tuberculosis co-infection. There is an urgency to this agenda for many reasons, including the frequency with which tuberculosis accounts for the death of HIV-infected persons in Asia, and the continued rise of multiple drug-resistant Mycobacterium tuberculosis. We review briefly the public health situation in Asia, highlighting research questions from US-Japan-Asian partner joint meetings, and cite salient studies to indicate trends and challenges.