Vaccination against tuberculosis and leprosy

Heterogeneity in the granulomatous response to mycobacterial infection in patients with defined genetic mutations in the interleukin 12-dependent interferon-gamma production pathway

Patients with genetic lesions in the Type-1 cytokine/cytokine receptor pathway exhibit a selective susceptibility to severe infections with poorly pathogenic mycobacteria and non-typhi salmonella spp. These experiments of nature demonstrate that IL-12-dependent IFNgamma production is critical for granuloma formation and therefore host immunity against such pathogens. The essential role of granuloma formation for protective immunity to these organisms is emphasized by the differing granuloma forming capabilities and resultant clinical sequelae observed in these patients which seems to reflect their ability to produce or respond to IFNgamma (Fig. 9). At one pole of this spectrum, represented by the complete IFNgammaR1/2 deficient patients, there is a complete absence of mature granuloma formation, whereas with the less severe mutations (i.e. partial IFNgammaR1/2, complete IL-12p40 and complete IL-12Rbeta1 deficiency), granuloma formation is very heterogenous with wide variations in composition being observed. This suggests that in the latter individuals, who produce partial but suboptimal IFNgamma responses, other influences, including pathogen virulence and host genotype may also affect the type and scale of the cellular response elicited.

Secretory proteins of Mycobacterium habana induce a protective immune response against experimental tuberculosis

The capacity of proteins of Mycobacterium habana TMC 5135 secreted into culture medium during the mid-exponential growth phase (secretory proteins, SPs) to induce protective immunity against Mycobacterium tuberculosis H37Rv was studied in the mouse model. Mice immunized with SPs followed by a challenge with M. tuberculosis H37Rv showed lesser M. tuberculosis bacilli in their lung and spleen and survived longer than unimmunized controls. The findings suggest that SP antigens of M. habana are protective against tuberculosis infection.

Vaccination of the badger (Meles meles) against Mycobacterium bovis

This review summarizes current knowledge relating to the potential development of a vaccine against Mycobacterium bovis (M. bovis) for use in badgers. The serious economic loss incurred from bovine tuberculosis in Ireland is highlighted. The problems presented to national bovine tuberculosis eradication programmes by wildlife reservoirs of M bovis, in particular the badger and the brushtail possum, are outlined. Badger and possum ecology and the epidemiology of M. bovis infection in these species are compared in relation to control strategies. Current information regarding the immune responses of badgers and possums to M. bovis infection is presented. Vaccine types, carrier and adjuvant systems, available vaccines for human and animal tuberculosis and delivery to wildlife species are described. The feasibility of vaccinating badgers against M. bovis infection and the possible options for a vaccination strategy are discussed.

Serological distinction of integral plasma membrane proteins as a class of mycobacterial antigens and their relevance for human T cell activation

This study pertains to classification and antigenic analysis of mycobacterial plasma membrane proteins in relation to human T cell proliferative responses, using a 'fast grower' Mycobacterium fortuitum as model. Membrane vesicles, prepared by sonication and differential centrifugation, were subjected to biphasic Triton X-114 extraction for isolation of integral peripheral (aqueous phase) proteins. Neither protein pool showed any appreciable overlap serologically. SDS-PAGE showed five prominent bands in peripheral and three in the integral protein pool, whereas immunoblotting with rabbit antisera identified only two major antigens (60 and 67 kD) in the former and five (24, 34, 42, 51 and 54 kD) in the latter. ELISA with a panel of anti-mycobacterial MoAbs revealed that nine out of 12 previously known antigens were present in the peripheral protein pool. Only two of them (33 and 40 kD) were additionally detected amongst integral proteins. The membrane-associated immunosuppressive moiety lipoarabinomannan was semiquantitatively located in aqueous phase. In bulk T cell proliferation assays, seven out of 10 subjects belonging to a 'responder' background (BT-BB leprosy patients and healthy contacts) showed high responses for Myco. fortuitum antigens. Proliferative response with integral proteins was comparable to that with whole membrane, but it was significantly higher (P < 0.0005) than the response with peripheral proteins. The distinction and relevance of integral membrane proteins as a class of mycobacterial antigens make them worthy of consideration in a subunit vaccine design.

Influence of mouse strain and vaccine viability on T-cell responses induced by Mycobacterium bovis bacillus Calmette-Guérin

C57BL/6 and BALB/c mice were vaccinated with either live or heat-killed Mycobacterium bovis bacillus Calmette-Guérin (BCG) organisms, and splenic T cells were used to screen the stimulatory potential of fractionated somatic and secreted mycobacterial proteins by production of gamma interferon (IFN-gamma). Maximum responses were obtained with fractionated secreted proteins of Mycobacterium tuberculosis. There was no single dominant antigen, but five regions of mycobacterial proteins induced high concentrations of IFN-gamma. However, only two of the five regions stimulated T cells from both mouse strains: two were exclusively recognized by T cells from BALB/c mice, and one was exclusively recognized by T cells from C57BL/6 mice. T cells from mice vaccinated with heat-killed M. bovis BCG organisms failed to respond to fractionated secreted proteins but recognized several somatic antigen fractions. As late as 1 year after primary vaccination, memory T cells responded to similar protein regions, and IFN-gamma production was intensified by secondary infection. Our data confirm a central role for secreted proteins in immunity to mycobacteria. Moreover, we demonstrate that a major set of mycobacterium-reactive T cells is stimulated only by vaccination with live but not with heat-killed M. bovis BCG organisms. Because a major impact of genetic host factors on antigen recognition was observed, we favor the use of live carrier organisms which secrete mycobacterial proteins over subunit vaccines as an improved antituberculosis vaccine.

Triggering effects of BCG vaccine on antitumor and interleukin-1 secretory activity of T cell lymphokine-primed macrophages

By using an in vitro model, this work demonstrates that BCG (Bacillus Calmette-Guerin) vaccine is able to trigger activation of T cell lymphokine-primed murine macrophages (Mo) for both tumoricidal cytotoxicity and interleukin-1 (IL-1) secretion. The results presented support the view that BCG vaccine may essentially activate primed, but not intact Mo; and that macrophage-mediated both antitumor and immunostimulatory effects of BCG vaccine observed in the body may be largely defined by functional activity of T-lymphocytes responsible for antigen-induced production of macrophage-activating lymphokines.

The regulation of pulmonary immunity

No evidence has emerged which suggests that the principles of immunity derived from studies on cells from other body sites are contradicted in the lung and its associated lymphoid tissue. What is clear, however, is that the environment dictates the types of cells, their relationship to one another, and what perturbing events will set in motion either the development of an "active" immune response or tolerance. Investigating mechanisms for the development of lung immunity has increased our understanding of how human diseases develop and is continuing to suggest new ways to manipulate pulmonary immune responses. Demonstration that lung cells regulate both nonspecific inflammation and immunity through the expression of adhesion molecules and the secretion of cytokines offers hope for ways to design more effective vaccines, enhance microbial clearance in immunosuppressed hosts, and to suppress manifestations of immunologically mediated lung disease. Important lung diseases targeted for intensive research efforts in the immediate future are tuberculosis, asthma, and fibrotic lung disease. Perhaps even the common cold might be conquered. Considering the pace of current research on lung immunity, it may not be too ambitious to predict that these diseases may be conquered in the next decade.

Non-major histocompatibility complex-restricted cytotoxic activity of blood mononuclear cells stimulated with secreted mycobacterial proteins and other mycobacterial antigens

Several observations indicate that non-major histocompatibility complex (MHC)-restricted cytotoxicity, mediated for example by natural killer cells and lymphokine-activated killer cells, may serve as an important antimicrobial defense mechanism. The purpose of the present study was to investigate the influences of different mycobacterial antigens on non-MHC-restricted cytotoxicity and further to investigate the ways by which various lymphocyte subpopulations contribute to the development of this cytotoxicity. Non-MHC-restricted cytotoxicity was induced following stimulation of mononuclear cells with tuberculin purified protein derivative, Mycobacterium bovis bacillus Calmette-Guérin (BCG), short- and long-term culture filtrates of virulent Mycobacterium tuberculosis H37Rv, and 30-31-kDa secreted mycobacterial protein. These antigens also induced proliferation and production of gamma interferon. The CD4+ cells proliferated and expressed interleukin-2 receptors following stimulation with mycobacterial antigens. Depletion studies after antigen stimulation showed that the cytotoxic effector cells were CD16+ CD56+ and CD4-; the CD4+ cells alone did not mediate non-MHC-restricted cytotoxicity. To evaluate the influence of CD4+ cells on the development of non-MHC-restricted cytotoxicity, blood mononuclear cells were depleted of CD4+ cells before antigen stimulation. When mononuclear cells were incubated with purified protein derivative or short-term culture filtrate in the absence of CD4+ cells, cytotoxic activity was reduced. This reduction was abolished by interleukin-2 but not by gamma interferon. We conclude that several mycobacterial antigens are able to induce non-MHC-restricted cytotoxicity. This study indicates that non-MHC-restricted cytotoxicity following stimulation with mycobacterial antigens is induced by cytokines released by antigen-specific activated CD4+ cells.

Immunology of leprosy

The host immune response to Mycobacterium leprae is critical for control of the infection but also responsible for the immunopathological damage to skin and nerves. The complex and varied immune responses to the organism are the basis for the clinical spectrum of disease ranging from tuberculoid to lepromatous leprosy. The cellular interactions underlying this spectrum are discussed and the antigenic components of the bacillus briefly reviewed. M. leprae has evolved a variety of mechanisms to avoid macrophage bactericidal mechanisms. These result in the persistence of bacilli and the release of cytokines leading to chronic granulomatous inflammation. The immune response to M. leprae is dynamic and spontaneous variations in cellular reactivity occur with time leading to type I and II leprosy reactions. The factors which preset the host immune response to a tuberculoid or lepromatous pattern and which precipitate reactional episodes remain to be elucidated.

In vivo depletion of CD4 and CD8 T lymphocytes impairs Mycobacterium w vaccine-induced protection against M. tuberculosis in mice

In the present study we sought to determine the relative role of CD4 and CD8 T cells in Mycobacterium w-induced protective immunity against tuberculosis of mice by in vivo depletion with specific monoclonal antibodies (mAb). Mice were immunized first with M.w, 4 weeks later treated with anti-CD4, anti-CD8 or a combination of both mAb and subsequently infected with M. tuberculosis H37Rv i.v. Numbers of colony-forming units in animals depleted of CD4 T cells, CD8 T cells or both T cell populations were significantly higher than those in control mice receiving irrelevant mAb or no mAb. Cytokine production by T cell subsets was also determined by culturing the cells remaining after in vivo depletion in the presence or absence of mycobacterial antigens. CD8 (CD4 depleted) T cells produced lower levels of interferon-gamma than CD4 (CD8 depleted) T cells. These data suggest that both CD4 and CD8 T cells participate in resistance against tuberculosis induced by vaccination with M.w.

Tuberculosis and leprosy: attempts to identify T-cell antigens of potential value for vaccine design

Tuberculosis and leprosy are chronic bacterial infectious diseases which represent major health problems worldwide. It is generally accepted that, on the one hand, effective vaccination strategies are required for satisfactory control of these diseases and, on the other hand, that currently available vaccination measures are insufficient for this purpose. Ideally, a subunit vaccine should be designed which is composed of one or a few protective antigens. In this brief treatise our approach towards the identification of antigens with potential value for vaccine design is described. It comprises high resolution fractionation by two-dimensional gel electrophoresis, transfer of separated fractions by electroelution and testing of separated fractions with viable T cells and accessory cells. Using this approach we find: (1) multiple antigens are recognized by T cells from leprosy and tuberculosis patients as well as healthy contacts; (2) apparently, suppressive antigens exist in leprosy; (3) an antigen cluster which is apparently indicative for immunity against M. tuberculosis is present among secreted proteins. We hope that further improvement of this methodology will help in the rational design of subunit vaccines against tuberculosis and leprosy.