Mycobacterium tuberculosis-specific CD8+ T cells and their role in immunity

HIV-TB coinfection impairs CD8(+) T-cell differentiation and function while dehydroepiandrosterone improves cytotoxic antitubercular immune responses

Tuberculosis (TB) is the leading cause of death among HIV-positive patients. The decreasing frequencies of terminal effector (TTE ) CD8(+) T cells may increase reactivation risk in persons latently infected with Mycobacterium tuberculosis (Mtb). We have previously shown that dehydroepiandrosterone (DHEA) increases the protective antitubercular immune responses in HIV-TB patients. Here, we aimed to study Mtb-specific cytotoxicity, IFN-γ secretion, memory status of CD8(+) T cells, and their modulation by DHEA during HIV-TB coinfection. CD8(+) T cells from HIV-TB patients showed a more differentiated phenotype with diminished naïve and higher effector memory and TTE T-cell frequencies compared to healthy donors both in total and Mtb-specific CD8(+) T cells. Notably, CD8(+) T cells from HIV-TB patients displayed higher Terminal Effector (TTE ) CD45RA(dim) proportions with lower CD45RA expression levels, suggesting a not fully differentiated phenotype. Also, PD-1 expression levels on CD8(+) T cells from HIV-TB patients increased although restricted to the CD27(+) population. Interestingly, DHEA plasma levels positively correlated with TTE in CD8(+) T cells and in vitro DHEA treatment enhanced Mtb-specific cytotoxic responses and terminal differentiation in CD8(+) T cells from HIV-TB patients. Our data suggest that HIV-TB coinfection promotes a deficient CD8(+) T-cell differentiation, whereas DHEA may contribute to improving antitubercular immunity by enhancing CD8(+) T-cell functions during HIV-TB coinfection.

Protection against Mycobacterium tuberculosis infection offered by a new multistage subunit vaccine correlates with increased number of IFN-γ+ IL-2+ CD4+ and IFN-γ+ CD8+ T cells

Protein subunit vaccines present a compelling new area of research for control of tuberculosis (TB). Based on the interaction between Mycobacterium tuberculosis and its host, five stage-specific antigens of M. tuberculosis that participate in TB pathogenesis—Rv1813, Rv2660c, Ag85B, Rv2623, and HspX—were selected. These antigens were verified to be recognized by T cells from a total of 42 whole blood samples obtained from active TB patients, patients with latent TB infections (LTBIs), and healthy control donors. The multistage polyprotein A1D4 was developed using the selected five antigens as a potentially more effective novel subunit vaccine. The immunogenicity and protective efficacy of A1D4 emulsified in the adjuvant MTO [monophosphoryl lipid A (MPL), trehalose-6,6′-dibehenate (TDB), components of MF59] was compared with Bacillus Calmette-Guerin (BCG) in C57BL/6 mice. Our results demonstrated that A1D4/MTO could provide more significant protection against M. tuberculosis infection than the PBS control or MTO adjuvant alone judging from the A1D4-specific Th1-type immune response; however, its efficacy was inferior to BCG as demonstrated by the bacterial load in the lung and spleen, and by the pathological changes in the lung. Antigen-specific single IL-2-secreting cells and different combinations with IL-2-secreting CD4⁺ T cells were beneficial and correlated with BCG vaccine-induced protection against TB. Antigen-specific IFN-γ⁺IL-2⁺ CD4⁺ T cells were the only effective biomarker significantly induced by A1D4/MTO. Among all groups, A1D4/MTO immunization also conferred the highest number of antigen-specific single IFN-γ⁺ and IFN-γ⁺TNF-α⁺ CD4⁺ T cells, which might be related to the antigen load in vivo, and single IFN-γ⁺ CD8⁺ T cells by mimicking the immune patterns of LTBIs or curable TB patients. Our strategy seems promising for the development of a TB vaccine based on multistage antigens, and subunit antigen A1D4 suspended in MTO adjuvant warrants preclinical evaluation in animal models of latent infection and may boost BCG vaccination.

The safety and immunogenicity of an adenovirus type 35-vectored TB vaccine in HIV-infected, BCG-vaccinated adults with CD4(+) T cell counts >350 cells/mm(3)

BACKGROUND

The safety and immunogenicity of a replication deficient adenovirus serotype 35 tuberculosis (TB) vaccine containing gene inserts for Antigens (Ag) 85A, Ag85B and TB10.4 (AERAS-402/AD35.TB-S) was evaluated in previously BCG vaccinated, HIV-infected South African adults with baseline CD4 counts >350 cells/mm(3).

METHODS

Subjects were randomized (1:1) to receive two doses of either intramuscular AERAS-402/AD35.TB-S or placebo at month 0 and at month 1. Participants were monitored for adverse events 28 days after each vaccination and for serious adverse events over 12 months. CD4(+) and CD8(+) T-cell and antibody responses to vaccine antigens were evaluated post first and second vaccination.

RESULTS

26 subjects were randomly assigned to receive AERAS-402/AD35.TB-S (N=13) or placebo (N=13). The mean age was 29.0 years, all were Black-African, 88.5% were female, 46.2% were QuantiFERON Test (QFT) positive at baseline, and the median CD4 count was 559.5 cells/mm(3), all similar by treatment group. All subjects received their first vaccination and 24 subjects received their second vaccination. Injection site reactions and some systemic reactions were reported more commonly in the AERAS-402/AD35.TB-S versus placebo recipients. AERAS-402/AD35.TB-S did not appear to influence CD4 counts and HIV-1 viral load over the course of study follow-up. AERAS-402/AD35.TB-S induced a mixed CD4(+) T-cell and CD8(+) T-cell responses to Ag85B. The CD4(+) T-cell responses peaked to Ag85A and Ag85B 14 days after the second vaccination and had declined by Day 182. AERAS-402/AD35.TB-S predominantly induced CD4(+) T-cells expressing three (IFN-γ, TNF, IL-2) or two (IL-2 and TNF) cytokines, two weeks after the last vaccination, which did not differ by baseline Quantiferon test status. AERAS-402/AD35.TB-S induced strong Ag85A and Ag85B specific antibody responses, particularly after the second vaccination.

CONCLUSION

AERAS-402/AD35.TB-S was well tolerated, safe and induced predominantly polyfunctional CD4(+) and CD8(+) T-cell responses to vaccine.

Epitope-specific CD4+, but not CD8+, T-cell responses induced by recombinant influenza A viruses protect against Mycobacterium tuberculosis infection

Tuberculosis remains a global health problem, in part due to failure of the currently available vaccine, BCG, to protect adults against pulmonary forms of the disease. We explored the impact of pulmonary delivery of recombinant influenza A viruses (rIAVs) on the induction of Mycobacterium tuberculosis (M. tuberculosis)-specific CD4(+) and CD8(+) T-cell responses and the resultant protection against M. tuberculosis infection in C57BL/6 mice. Intranasal infection with rIAVs expressing a CD4(+) T-cell epitope from the Ag85B protein (PR8.p25) or CD8(+) T-cell epitope from the TB10.4 protein (PR8.TB10.4) generated strong T-cell responses to the M. tuberculosis-specific epitopes in the lung that persisted long after the rIAVs were cleared. Infection with PR8.p25 conferred protection against subsequent M. tuberculosis challenge in the lung, and this was associated with increased levels of poly-functional CD4(+) T cells at the time of challenge. By contrast, infection with PR8.TB10.4 did not induce protection despite the presence of IFN-γ-producing M. tuberculosis-specific CD8(+) T cells in the lung at the time of challenge and during infection. Therefore, the induction of pulmonary M. tuberculosis epitope-specific CD4(+), but not CD8(+) T cells, is essential for protection against acute M. tuberculosis infection in the lung.

Annexin1 regulates DC efferocytosis and cross-presentation during Mycobacterium tuberculosis infection

The phagocytosis of apoptotic cells and associated vesicles (efferocytosis) by DCs is an important mechanism for both self tolerance and host defense. Although some of the engulfment ligands involved in efferocytosis have been identified and studied in vitro, the contributions of these ligands in vivo remain ill defined. Here, we determined that during Mycobacterium tuberculosis (Mtb) infection, the engulfment ligand annexin1 is an important mediator in DC cross-presentation that increases efferocytosis in DCs and intrinsically enhances the capacity of the DC antigen-presenting machinery. Annexin1-deficient mice were highly susceptible to Mtb infection and showed an impaired Mtb antigen-specific CD8+ T cell response. Importantly, annexin1 expression was greatly downregulated in Mtb-infected human blood monocyte-derived DCs, indicating that reduction of annexin1 is a critical mechanism for immune evasion by Mtb. Collectively, these data indicate that annexin1 is essential in immunity to Mtb infection and mediates the power of DC efferocytosis and cross-presentation.

Understanding and overcoming the barriers to T cell-mediated immunity against tuberculosis

Despite the overwhelming success of immunization in reducing, and even eliminating, the global threats posed by a wide spectrum of infectious diseases, attempts to do the same for tuberculosis (TB) have failed to date. While most effective vaccines act by eliciting neutralizing antibodies, T cells are the primary mediators of adaptive immunity against TB. Unfortunately, the onset of the T cell response after aerosol infection with Mycobacterium tuberculosis (Mtb), the bacterium that causes TB, is exceedingly slow, and systemically administered vaccines only modestly accelerate the recruitment of effector T cells to the lungs. This delay seems to be orchestrated by Mtb itself to prolong the period of unrestricted bacterial replication in the lung that characterizes the innate phase of the response. When T cells finally arrive at the site of infection, multiple layers of regulation have been established that limit the ability of T cells to control or eradicate Mtb. From this understanding, emerges a strategy for achieving immunity. Lung resident memory T cells may recognize Mtb-infected cells shortly after infection and confer protection before regulatory networks are allowed to develop. Early studies using vaccines that elicit lung resident T cells by targeting the lung mucosa have been promising, but many questions remain. Due to the fundamental nature of these questions, and the need to understand and manipulate the early events in the lung after aerosol infection, only coordinated approaches that utilize tractable animal models to inform human TB vaccine trials will move the field toward its goal.

Cellular composition of granulomatous lesions in gut-associated lymphoid tissues of goats during the first year after experimental infection with Mycobacterium avium subsp. paratuberculosis

Mycobacterium avium subsp. paratuberculosis (MAP) causes lesions in naturally and experimentally infected ruminants which greatly differ in severity, cellular composition and number of mycobacteria. Morphologically distinct lesions are already found during the clinically inapparent phase of infection. The complex local host response and number of MAP were characterized at the initial sites of lesions, organized gut-associated lymphoid tissue, in experimentally infected goats. Tissues were collected at 3, 6, 9 and 12 month post-inoculation (mpi) from goat kids that had orally received 10 times 10mg of bacterial wet mass of MAP (JII-1961). The cellular composition of lesions in Peyer's patches in the jejunum and next to the ileocecal valve was evaluated in 21 MAP-inoculated goats, where lesions were compared with unaltered tissue of six control goats. CD68+, CD4+, CD8+, γδ T lymphocytes, B lymphocytes and plasma cells, MHC class II+ and CD25+ cells were demonstrated by immunohistochemistry in serial cryostat sections. At 3 mpi, extensive granulomatous infiltrates predominated, consisting of numerous epitheloid cells admixed with many CD4 and γδ T lymphocytes. Only single MAP were detected. This indicates a strong cellular immune reaction able to control MAP infection. γδ T lymphocytes were markedly increased in this type of lesion which may reflect their important role early in the pathogenesis of paratuberculosis. At 9 and 12 mpi, divergent lesions were observed which may reflect different outcomes of host-pathogen interactions. In five goats, minimal granulomatous lesions were surrounded by extensive lymphoplasmacytic infiltrates and no MAP were detected by immunohistochemistry. This was interpreted as effective host response that was able to eliminate MAP locally. In three goats, decreased numbers of lymphocytes, but extensive granulomatous infiltrates with numerous epitheloid cells containing increased numbers of mycobacteria were seen. This shift of the immune response resulted in uncontrolled mycobacterial multiplication. Focal and multifocal circumscribed granulomatous infiltrates of mainly epitheloid cells may represent sites of new infection, since they were observed in goats at all times after inoculation. Their presence in goats with minimal granulomatous lesions surrounded by extensive lymphoplasmacytic infiltrates may indicate that despite the local clearance, the infection may be perpetuated. The complex cellular immune reactions postulated for the pathogenesis of paratuberculosis were demonstrated at the local sites of infection. These early host-pathogen interactions are most likely essential for the eventual outcome of the MAP infection.

Combined use of Mycobacterium tuberculosis-specific CD4 and CD8 T-cell responses is a powerful diagnostic tool of active tuberculosis

Immune-based assays are promising tools to help to formulate diagnosis of active tuberculosis. A multiparameter flow cytometry assay assessing T-cell responses specific to Mycobacterium tuberculosis and the combination of both CD4 and CD8 T-cell responses accurately discriminated between active tuberculosis and latent infection.

The ESAT-6 protein of Mycobacterium tuberculosis interacts with beta-2-microglobulin (β2M) affecting antigen presentation function of macrophage

ESAT-6, an abundantly secreted protein of Mycobacterium tuberculosis (M. tuberculosis) is an important virulence factor, inactivation of which leads to reduced virulence of M. tuberculosis. ESAT-6 alone, or in complex with its chaperone CFP-10 (ESAT-6:CFP-10), is known to modulate host immune responses; however, the detailed mechanisms are not well understood. The structure of ESAT-6 or ESAT-6:CFP-10 complex does not suggest presence of enzymatic or DNA-binding activities. Therefore, we hypothesized that the crucial role played by ESAT-6 in the virulence of mycobacteria could be due to its interaction with some host cellular factors. Using a yeast two-hybrid screening, we identified that ESAT-6 interacts with the host protein beta-2-microglobulin (β2M), which was further confirmed by other assays, like GST pull down, co-immunoprecipitation and surface plasmon resonance. The C-terminal six amino acid residues (90-95) of ESAT-6 were found to be essential for this interaction. ESAT-6, in complex with CFP-10, also interacts with β2M. We found that ESAT-6/ESAT-6:CFP-10 can enter into the endoplasmic reticulum where it sequesters β2M to inhibit cell surface expression of MHC-I-β2M complexes, resulting in downregulation of class I-mediated antigen presentation. Interestingly, the ESAT-6:β2M complex could be detected in pleural biopsies of individuals suffering from pleural tuberculosis. Our data highlight a novel mechanism by which M. tuberculosis may undermine the host adaptive immune responses to establish a successful infection. Identification of such novel interactions may help us in designing small molecule inhibitors as well as effective vaccine design against tuberculosis.

The ESAT-6 protein of Mycobacterium tuberculosis interacts with beta-2-microglobulin (β2M) affecting antigen presentation function of macrophage

ESAT-6, an abundantly secreted protein of Mycobacterium tuberculosis (M. tuberculosis) is an important virulence factor, inactivation of which leads to reduced virulence of M. tuberculosis. ESAT-6 alone, or in complex with its chaperone CFP-10 (ESAT-6:CFP-10), is known to modulate host immune responses; however, the detailed mechanisms are not well understood. The structure of ESAT-6 or ESAT-6:CFP-10 complex does not suggest presence of enzymatic or DNA-binding activities. Therefore, we hypothesized that the crucial role played by ESAT-6 in the virulence of mycobacteria could be due to its interaction with some host cellular factors. Using a yeast two-hybrid screening, we identified that ESAT-6 interacts with the host protein beta-2-microglobulin (β2M), which was further confirmed by other assays, like GST pull down, co-immunoprecipitation and surface plasmon resonance. The C-terminal six amino acid residues (90–95) of ESAT-6 were found to be essential for this interaction. ESAT-6, in complex with CFP-10, also interacts with β2M. We found that ESAT-6/ESAT-6:CFP-10 can enter into the endoplasmic reticulum where it sequesters β2M to inhibit cell surface expression of MHC-I-β2M complexes, resulting in downregulation of class I-mediated antigen presentation. Interestingly, the ESAT-6:β2M complex could be detected in pleural biopsies of individuals suffering from pleural tuberculosis. Our data highlight a novel mechanism by which M. tuberculosis may undermine the host adaptive immune responses to establish a successful infection. Identification of such novel interactions may help us in designing small molecule inhibitors as well as effective vaccine design against tuberculosis.

M. tuberculosis is a dangerous and highly successful pathogen that has evolved several mechanisms to manipulate the host immune regulatory network. Proteins secreted by M. tuberculosis play important roles in virulence. One such protein is ESAT-6, which is secreted along with its chaperone CFP-10. Despite a host of studies highlighting modulation of immune responses by ESAT-6, there have not been many that identified host proteins interacting with ESAT-6. We have now found that the host protein β2M interacts very specifically with ESAT-6 at its C-terminal region. The soluble ESAT-6:CFP-10 complex was found to be trafficked into the endoplasmic reticulum, and treatment with recombinant ESAT-6:CFP-10 or the over-expression of ESAT-6 reduced cell surface expression of β2M and molecules which remain associated with it like HLA-I. Recombinant ESAT-6:CFP-10 was also found to reduce classical and cross presentation of peptide antigens by MHC-I molecules. In summary, our data indicate that interaction between ESAT-6 and β2M can reduce the levels of available free β2M that associate with HLA/MHC-I molecules. This could be an interesting mechanism by which M. tuberculosis inhibits classical and cross presentation of peptide antigens in order to prevent or delay the onset of anti-mycobacterial adaptive immune responses.

The present and future of tuberculosis vaccinations

The clinical, social, and economic burden of tuberculosis (TB) remains high worldwide, thereby highlighting the importance of TB prevention. The bacilli Calmette-Guérin (BCG) vaccine that is currently available can protect younger children but is less effective in adults, the major source of TB transmission. In addition, the emergence of drug-resistant Mycobacterium tuberculosis (Mtb) strains and the high prevalence of HIV infection have significantly complicated TB prognosis and treatment. Together, these data highlight the need for new and more effective vaccines. Recently, several vaccines containing multiple antigens, including some of those specific for dormant Mtb strains, have been developed. These vaccines appear to be the best approach for satisfactory Mtb prevention. However, until a new vaccine is proven more effective and safe than BCG, BCG should remain part of the immunization schedules for neonates and children at risk for TB as a fundamental prophylactic measure.

Orchestration of pulmonary T cell immunity during Mycobacterium tuberculosis infection: immunity interruptus

Despite the introduction almost a century ago of Mycobacterium bovis BCG (BCG), an attenuated form of M. bovis that is used as a vaccine against Mycobacterium tuberculosis, tuberculosis remains a global health threat and kills more than 1.5 million people each year. This is mostly because BCG fails to prevent pulmonary disease--the contagious form of tuberculosis. Although there have been significant advances in understanding how the immune system responds to infection, the qualities that define protective immunity against M. tuberculosis remain poorly characterized. The ability to predict who will maintain control over the infection and who will succumb to clinical disease would revolutionize our approach to surveillance, control, and treatment. Here we review the current understanding of pulmonary T cell responses following M. tuberculosis infection. While infection elicits a strong immune response that contains infection, M. tuberculosis evades eradication. Traditionally, its intracellular lifestyle and alteration of macrophage function are viewed as the dominant mechanisms of evasion. Now we appreciate that chronic inflammation leads to T cell dysfunction. While this may arise as the host balances the goals of bacterial sterilization and avoidance of tissue damage, it is becoming clear that T cell dysfunction impairs host resistance. Defining the mechanisms that lead to T cell dysfunction is crucial as memory T cell responses are likely to be subject to the same subject to the same pressures. Thus, success of T cell based vaccines is predicated on memory T cells avoiding exhaustion while at the same time not promoting overt tissue damage.

DNA immunization of Mycobacterium tuberculosis resuscitation-promoting factor B elicits polyfunctional CD8(+) T cell responses

Purpose

T cell-mediated immune responses, and particularly activation of polyfunctional T cells that simultaneously produce multiple cytokines, are necessary for the control of Mycobacterium tuberculosis. In the present study, we examined if DNA immunization of Mycobacterium tuberculosis resuscitation-promoting factor B (RpfB) elicits polyfunctional T cell responses in mice.

Materials and Methods

C57BL/6 mice were immunized intramuscularly three times, at 3-week intervals, with RpfB-expressing plasmid DNA. For comparison, protein immunization was performed with recombinant RpfB in control mice. After immunization, RpfB-specific T cell responses were assessed by interferon-γ (IFN-γ) enzyme-linked immunosorbent spot assay and intracellular cytokine staining (ICS), and T cell polyfunctionality was assessed from the ICS data.

Results

RpfB DNA immunization induced not only humoral immune responses, but also CD8⁺ and CD4⁺ T cell responses. Immunodominant T-cell epitopes were identified within RpfB by assays with overlapping peptides. RpfB DNA immunization elicited a polyfunctional CD8⁺ T cell response that was dominated by a functional phenotype of IFN-γ⁺/TNF-α⁺/IL-2^-/CD107a⁺.

Conclusion

RpfB DNA immunization elicits polyfunctional CD8⁺ T cell responses, suggesting that RpfB DNA immunization might induce protective immunity against tuberculosis.

Novel vaccination strategies against tuberculosis

The tuberculosis (TB) pandemic continues to rampage despite widespread use of the BCG (Bacillus Calmette-Guérin) vaccine. Novel vaccination strategies are urgently needed to arrest global transmission and prevent the uncontrolled development of multidrug-resistant forms of Mycobacterium tuberculosis. Over the last two decades, considerable progress has been made in the field of vaccine development with numerous innovative preclinical candidates and more than a dozen vaccines in clinical trials. These vaccines are developed either as boosters of the current BCG vaccine or as novel prime vaccines to replace BCG. Given the enormous prevalence of latent TB infection, vaccines that are protective on top of an already established infection remain a high priority and a significant scientific challenge. Here we discuss the current state of TB vaccine research and development, our understanding of the underlying immunology, and the requirements for an efficient TB vaccine.

Recent advances towards tuberculosis control: vaccines and biomarkers

Of all infectious diseases, tuberculosis (TB) remains one of the most important causes of morbidity and mortality. Recent advances in understanding the biology of Mycobacterium tuberculosis (Mtb) infection and the immune response of the infected host have led to the development of several new vaccines, a number of which are already undergoing clinical trials. These include pre-exposure prime vaccines, which could replace bacille Calmette-Guérin (BCG), and pre-exposure booster vaccines given in addition to BCG. Infants are the target population of these two types of vaccines. In addition, several postexposure vaccines given during adolescence or adult life, in addition to BCG as a priming vaccine during infancy, are undergoing clinical testing. Therapeutic vaccines are currently being assessed for their potential to cure active TB as an adjunct to chemotherapy. BCG replacement vaccines are viable recombinant BCG or double-deletion mutants of Mtb. All booster vaccines are composed of one or several antigens, either expressed by viral vectors or formulated with adjuvants. Therapeutic vaccines are killed mycobacterial preparations. Finally, multivariate biomarkers and biosignatures are being generated from high-throughput data with the aim of providing better diagnostic tools to specifically determine TB progression. Here, we provide a technical overview of these recent developments as well of the relevant computational approaches and highlight the obstacles that still need to be overcome.

High-frequency vaccine-induced CD8⁺ T cells specific for an epitope naturally processed during infection with Mycobacterium tuberculosis do not confer protection

Relatively few MHC class I epitopes have been identified from Mycobacterium tuberculosis, but during the late stage of infection, CD8(+) T-cell responses to these epitopes are often primed at an extraordinary high frequency. Although clearly available for recognition during infection, their role in resistance to mycobacterial infections still remain unclear. As an alternative to DNA and viral vaccination platforms, we have exploited a novel CD8(+) T-cell-inducing adjuvant, cationic adjuvant formulation 05 (dimethyldioctadecylammonium/trehalose dibehenate/poly (inositic:cytidylic) acid), to prime high-frequency CD8 responses to the immunodominant H2-K(b) -restricted IMYNYPAM epitope contained in the vaccine Ag tuberculosis (TB)10.4/Rv0288/ESX-H (where ESX is mycobacterial type VII secretion system). We report that the amino acid C-terminal to this minimal epitope plays a decisive role in proteasomal cleavage and epitope priming. The primary structure of TB10.4 is suboptimal for proteasomal processing of the epitope and amino acid substitutions in the flanking region markedly increased epitope-specific CD8(+) T-cell responses. One of the optimized sequences was contained in the closely related TB10.3/Rv3019c/ESX-R Ag and when recombinantly expressed and administered in the cationic adjuvant formulation 05 adjuvant, this Ag promoted very high CD8(+) T-cell responses. This abundant T-cell response was functionally active but provided no protection against challenge, suggesting that CD8(+) T cells play a limited role in protection against M. tuberculosis in the mouse model.

Progress in tuberculosis vaccine development and host-directed therapies--a state of the art review

Tuberculosis continues to kill 1·4 million people annually. During the past 5 years, an alarming increase in the number of patients with multidrug-resistant tuberculosis and extensively drug-resistant tuberculosis has been noted, particularly in eastern Europe, Asia, and southern Africa. Treatment outcomes with available treatment regimens for drug-resistant tuberculosis are poor. Although substantial progress in drug development for tuberculosis has been made, scientific progress towards development of interventions for prevention and improvement of drug treatment outcomes have lagged behind. Innovative interventions are therefore needed to combat the growing pandemic of multidrug-resistant and extensively drug-resistant tuberculosis. Novel adjunct treatments are needed to accomplish improved cure rates for multidrug-resistant and extensively drug-resistant tuberculosis. A novel, safe, widely applicable, and more effective vaccine against tuberculosis is also desperately sought to achieve disease control. The quest to develop a universally protective vaccine for tuberculosis continues. So far, research and development of tuberculosis vaccines has resulted in almost 20 candidates at different stages of the clinical trial pipeline. Host-directed therapies are now being developed to refocus the anti-Mycobacterium tuberculosis-directed immune responses towards the host; a strategy that could be especially beneficial for patients with multidrug-resistant tuberculosis or extensively drug-resistant tuberculosis. As we are running short of canonical tuberculosis drugs, more attention should be given to host-directed preventive and therapeutic intervention measures.

In search of a new paradigm for protective immunity to TB

Clinical trials of vaccines against Mycobacterium tuberculosis are well under way and results are starting to come in. Some of these results are not so encouraging, as exemplified by the latest Aeras-422 and MVA85A trials. Other than empirically determining whether a vaccine reduces the number of cases of active tuberculosis, which is a daunting prospect given the chronic nature of the disease, we have no way of assessing vaccine efficacy. Therefore, investigators seek to identify biomarkers that predict vaccine efficacy. Historically, focus has been on the production of interferon-γ by CD4(+) T cells, but this has not been a useful correlate of vaccine-induced protection. In this Opinion article, we discuss recent advances in our understanding of the immune control of M. tuberculosis and how this knowledge could be used for vaccine design and evaluation.

Classification of human leukocyte antigen (HLA) supertypes

Identification of new antigenic peptides, derived from infectious agents or cancer cells, which bind to human leukocyte antigen (HLA) class I and II molecules, is of importance for the development of new effective vaccines capable of activating the cellular arm of the immune response. However, the barrier to the development of peptide-based vaccines with maximum population coverage is that the restricting HLA genes are extremely polymorphic resulting in a vast diversity of peptide-binding HLA specificities and a low population coverage for any given peptide-HLA specificity. One way to reduce this complexity is to group thousands of different HLA molecules into several so-called HLA supertypes: a classification that refers to a group of HLA alleles with largely overlapping peptide binding specificities. In this chapter, we focus on the state-of-the-art classification of HLA supertypes including HLA-I supertypes and HLA-II supertypes and their application in development of peptide-based vaccines.

Mycobacterium tuberculosis-specific CD8+ T cells are functionally and phenotypically different between latent infection and active disease

Protective immunity to Mycobacterium tuberculosis (Mtb) remains poorly understood and the role of Mtb-specific CD8(+) T cells is controversial. Here we performed a broad phenotypic and functional characterization of Mtb-specific CD8(+) T cells in 326 subjects with latent Mtb infection (LTBI) or active TB disease (TB). Mtb-specific CD8(+) T cells were detected in most (60%) TB patients and few (15%) LTBI subjects but were of similar magnitude. Mtb-specific CD8(+) T cells in LTBI subjects were mostly T EMRA cells (CD45RA(+) CCR7(-)), coexpressing 2B4 and CD160, and in TB patients were mostly TEM cells (CD45RA(-) CCR7(-)), expressing 2B4 but lacking PD-1 and CD160. The cytokine profile was not significantly different in both groups. Furthermore, Mtb-specific CD8(+) T cells expressed low levels of perforin and granulysin but contained granzymes A and B. However, in vitro-expanded Mtb-specific CD8(+) T cells expressed perforin and granulysin. Finally, Mtb-specific CD8(+) T-cell responses were less frequently detected in extrapulmonary TB compared with pulmonary TB patients. Mtb-specific CD8(+) T-cell proliferation was also greater in patients with extrapulmonary compared with pulmonary TB. Thus, the activity of Mtb infection and clinical presentation are associated with distinct profiles of Mtb-specific CD8(+) T-cell responses. These results provide new insights in the interaction between Mtb and the host immune response.

Evaluation of immunological parameters in purified protein derivative positive tuberculin workers

OBJECTIVE(S)

According to the occupationally risk of infection in staff workers who have direct contact with mycobacterium species, we investigated their immunological parameters and compared with healthy purified protein derivative (PPD) negative volunteers. Materials and Methods : We investigated 20 PPD positive volunteers working at Tuberculin Unit of Razi Vaccine and Serum Research Institute and PPD negative healthy controls with no exposure or history of active tuberculosis. The percentages of circulating lymphocyte subpopulations were detected by flowcytometry. IL-4 and IFN-γ production levels were measured by ELISA in supernatants of PPD-stimulated peripheral blood mononuclear cells (PBMCs) culture. Results : Tuberculin workers showed an increase in IFN-γ level and significant decrease of CD4+ T cells percentage and CD4/CD8 ratio compared to PPD negative normal individuals. However the IL-4 production and percentage of other lymphocyte population has been unchanged.

DISCUSSION

These observations suggest that the immunological parameters of tuberculin workers with PPD positive reaction, who are occupationally exposed to mycobacterium antigens, could be changed. Future studies will be directed towards cytokine networking and regulatory lymphocytes, which will help us validate the significant data presented in this study.

An unbiased peptide-wide discovery approach to select Mycobacterium tuberculosis antigens that target CD8+ T cell response during infection

Accruing data strongly support the possible role of CD8+ T cells in immunity against tuberculosis (TB). Multivalent vaccines against Mycobacterium tuberculosis (Mtb) that incorporate CD8+ T cell antigens with those that elicit CD4+ T cells are therefore highly desirable. To screen for potential CD8+ T cell antigens that are produced by Mtb during infection, we isolated pathogen-derived peptides that bound to MHC Class I molecules expressed in adherent splenocytes obtained from Mtb-infected mice. Mass spectroscopy analysis revealed the following four nonamer peptides that had 100% homology with Mtb proteins: DGYVGAPAH (MT_0401), TTMPLFAD (MT_1164), RSGAATPVR (MT_2160.1) and LAAVVGVVL (MT_0078). The gene MT_0401 codes the protein 5'-phosphoribosylglycinamide transformylase 2 and the other three genes code for hypothetical proteins with unknown function. The NCBI/Blast analysis showed that among the four peptides DGYVGAPAH had the highest maximum alignment score and lowest E value (number of alignments expected by chance). Therefore, we assessed whether MT_0401 expressed in two genetic vaccine formulations was capable of stimulating CD8+ T cell response that is specific to DGYVGAPAH peptide. When mice were immunized with a recombinant plasmid DNA and an E1/E3-deleted Adenovirus 5 expressing MT0401 protein, using both homologous and heterologous prime-boost protocols, they developed strong DGYVGAPAH-specific CD8+ T cell response as well as antibody and CD4+ specific T cell response to the full length MT0401 protein. Equally important was the observation that mice infected with Mtb developed DGYVGAPAH-specific CD8+ T cell responses in both spleen and lungs. These results demonstrate that Mtb antigens that are processed and presented via MHC Class I machinery can be readily identified by the described approach and may be useful candidate antigens to stimulate specific CD8+ T cell responses in vaccine development programs.

Modulation of NKG2D expression in human CD8(+) T cells corresponding with tuberculosis drug cure

Background

Biomarkers predicting tuberculosis treatment response and cure would facilitate drug development. This study investigated expression patterns of the co-stimulation molecule NKG2D in human tuberculosis and treatment to determine its potential usefulness as a host biomarker of tuberculosis drug efficacy.

Methods

Tuberculosis patients (n = 26) were recruited in Lahore, Pakistan, at diagnosis and followed up during treatment. Household contacts (n = 24) were also recruited. NKG2D expression was measured by qRT-PCR in RNA samples both ex vivo and following overnight mycobacterial stimulation in vitro. Protein expression of NKG2D and granzyme B was measured by flow cytometry.

Results

NKG2D expression in newly diagnosed tuberculosis patients was similar to household contacts in ex vivo RNA, but was higher following in vitro stimulation. The NKG2D expression was dramatically reduced by intensive phase chemotherapy, in both ex vivo blood RNA and CD8⁺ T cell protein expression, but then reverted to higher levels after the continuation phase in successfully treated patients.

Conclusion

The changes in NKG2D expression through successful treatment reflect modulation of the peripheral cytotoxic T cell response. This likely reflects firstly in vivo stimulation by live Mycobacterium tuberculosis, followed by the response to dead bacilli, antigen-release and finally immunopathology resolution. Such changes in host peripheral gene expression, alongside clinical and microbiological indices, could be developed into a biosignature of tuberculosis drug-induced cure to be used in future clinical trials.

T cell-mediated host immune defenses in the lung

Evidence has increasingly shown that the lungs are a major site of immune regulation. A robust and highly regulated immune response in the lung protects the host from pathogen infection, whereas an inefficient or deleterious response can lead to various pulmonary diseases. Many cell types, such as epithelial cells, dendritic cells, macrophages, neutrophils, eosinophils, and B and T lymphocytes, contribute to lung immunity. This review focuses on the recent advances in understanding how T lymphocytes mediate pulmonary host defenses against bacterial, viral, and fungal pathogens.

Chronic pulmonary cavitary tuberculosis in rabbits: a failed host immune response

The molecular determinants of the immune response to Mycobacterium tuberculosis HN878 infection in a rabbit model of pulmonary cavitary tuberculosis were studied. Aerosol infection of rabbits resulted in a highly differentially expressed global transcriptome in the lungs at 2 weeks, which dropped at 4 weeks and then gradually increased. While IFNγ was progressively upregulated throughout the infection, several other genes in the IFNγ network were not. T-cell activation network genes were gradually upregulated and maximally induced at 12 weeks. Similarly, the IL4 and B-cell activation networks were progressively upregulated, many reaching high levels between 12 and 16 weeks. Delayed peak expression of genes associated with macrophage activation and Th1 type immunity was noted. Although spleen CD4(+) and CD8(+) T cells showed maximal tuberculosis antigen-specific activation by 8 weeks, macrophage activation in lungs, lymph nodes and spleen did not peak until 12 weeks. In the lungs, infecting bacilli grew exponentially up to 4 weeks, followed by a steady-state high bacillary load to 12 weeks that moderately increased during cavitation at 16 weeks. Thus, the outcome of HN878 infection of rabbits was determined early during infection by a suboptimal activation of innate immunity and delayed T-cell activation.

Human Mycobacterium tuberculosis CD8 T Cell Antigens/Epitopes Identified by a Proteomic Peptide Library

Identification of CD8⁺ T cell antigens/epitopes expressed by human pathogens with large genomes is especially challenging, yet necessary for vaccine development. Immunity to tuberculosis, a leading cause of mortality worldwide, requires CD8⁺ T cell immunity, yet the repertoire of CD8 antigens/epitopes remains undefined. We used integrated computational and proteomic approaches to screen 10% of the Mycobacterium tuberculosis (Mtb) proteome for CD8 Mtb antigens. We designed a weighting schema based upon a Multiple Attribute Decision Making:framework to select 10% of the Mtb proteome with a high probability of containing CD8⁺ T cell epitopes. We created a synthetic peptide library consisting of 15-mers overlapping by 11 aa. Using the interferon-γ ELISPOT assay and Mtb-infected dendritic cells as antigen presenting cells, we screened Mtb-specific CD8⁺ T cell clones restricted by classical MHC class I molecules (MHC class Ia molecules), that were isolated from Mtb-infected humans, against this library. Three novel CD8 antigens were unambiguously identified: the EsxJ family (Rv1038c, Rv1197, Rv3620c, Rv2347c, Rv1792), PE9 (Rv1088), and PE_PGRS42 (Rv2487c). The epitopes are B5701-restricted EsxJ_24–34, B3905-restricted PE9_53–67, and B3514-restricted PE_PGRS42_48–56, respectively. The utility of peptide libraries in identifying unknown epitopes recognized by classically restricted CD8⁺ T cells was confirmed, which can be applied to other intracellular pathogens with large size genomes. In addition, we identified three novel Mtb epitopes/antigens that may be evaluated for inclusion in vaccines and/or diagnostics for tuberculosis.

Immune vulnerability of infants to tuberculosis

One of the challenges faced by the infant immune system is learning to distinguish the myriad of foreign but nonthreatening antigens encountered from those expressed by true pathogens. This balance is reflected in the diminished production of proinflammatory cytokines by both innate and adaptive immune cells in the infant. A downside of this bias is that several factors critical for controlling Mycobacterium tuberculosis infection are significantly restricted in infants, including TNF, IL-1, and IL-12. Furthermore, infant T cells are inherently less capable of differentiating into IFN- γ -producing T cells. As a result, infected infants are 5-10 times more likely than adults to develop active tuberculosis (TB) and have higher rates of severe disseminated disease, including miliary TB and meningitis. Infant TB is a fundamentally different disease than TB in immune competent adults. Immunotherapeutics, therefore, should be specifically evaluated in infants before they are routinely employed to treat TB in this age group. Modalities aimed at reducing inflammation, which may be beneficial for adjunctive therapy of some forms of TB in older children and adults, may be of no benefit or even harmful in infants who manifest much less inflammatory disease.

Involvement of CD244 in regulating CD4+ T cell immunity in patients with active tuberculosis

CD244 (2B4) is a member of the signaling lymphocyte activation molecule (SLAM) family of immune cell receptors and it plays an important role in modulating NK cell and CD8⁺ T cell immunity. In this study, we investigated the expression and function of CD244/2B4 on CD4⁺ T cells from active TB patients and latent infection individuals. Active TB patients had significantly elevated CD244/2B4 expression on M. tuberculosis antigen-specific CD4⁺ T cells compared with latent infection individuals. The frequencies of CD244/2B4-expressing antigen-specific CD4⁺ T cells were significantly higher in retreatment active TB patients than in new active TB patients. Compared with CD244/2B4-dull and -middle CD4⁺ T cells, CD244/2B4-bright CD4⁺ T cell subset had significantly reduced expression of IFN-γ, suggesting that CD244/2B4 expression may modulate IFN-γ production in M. tuberculosis antigen-responsive CD4⁺ T cells. Activation of CD244/2B4 signaling by cross-linking led to significantly decreased production of IFN-γ. Blockage of CD244/2B4 signaling pathway of T cells from patients with active TB resulted in significantly increased production of IFN-γ, compared with isotype antibody control. In conclusion, CD244/2B4 signaling pathway has an inhibitory role on M. tuberculosis antigen-specific CD4⁺ T cell function.

Discovering naturally processed antigenic determinants that confer protective T cell immunity

CD8+ T cells (TCD8) confer protective immunity against many infectious diseases, suggesting that microbial TCD8 determinants are promising vaccine targets. Nevertheless, current T cell antigen identification approaches do not discern which epitopes drive protective immunity during active infection - information that is critical for the rational design of TCD8-targeted vaccines. We employed a proteomics-based approach for large-scale discovery of naturally processed determinants derived from a complex pathogen, vaccinia virus (VACV), that are presented by the most frequent representatives of four major HLA class I supertypes. Immunologic characterization revealed that many previously unidentified VACV determinants were recognized by smallpox-vaccinated human peripheral blood cells in a variegated manner. Many such determinants were recognized by HLA class I-transgenic mouse immune TCD8 too and elicited protective TCD8 immunity against lethal intranasal VACV infection. Notably, efficient processing and stable presentation of immune determinants as well as the availability of naive TCD8 precursors were sufficient to drive a multifunctional, protective TCD8 response. Our approach uses fundamental insights into T cell epitope processing and presentation to define targets of protective TCD8 immunity within human pathogens that have complex proteomes, suggesting that this approach has general applicability in vaccine sciences.

Shortening the 'short-course' therapy- insights into host immunity may contribute to new treatment strategies for tuberculosis

Achieving global control of tuberculosis (TB) is a great challenge considering the current increase in multidrug resistance and mortality rate. Considerable efforts are therefore being made to develop new effective vaccines, more effective and rapid diagnostic tools as well as new drugs. Shortening the duration of TB treatment with revised regimens and modes of delivery of existing drugs, as well as development of new antimicrobial agents and optimization of the host response with adjuvant immunotherapy could have a profound impact on TB cure rates. Recent data show that chronic worm infection and deficiencies in micronutrients such as vitamin D and arginine are potential areas of intervention to optimize host immunity. Nutritional supplementation to enhance nitric oxide production and vitamin D-mediated effector functions as well as the treatment of worm infection to reduce immunosuppressive effects of regulatory T (Treg) lymphocytes may be more suitable and accessible strategies for highly endemic areas than adjuvant cytokine therapy. In this review, we focus mainly on immune control of human TB, and discuss how current treatment strategies, including immunotherapy and nutritional supplementation, could be optimized to enhance the host response leading to more effective treatment.

T cells home to the thymus and control infection

The thymus is a target of multiple pathogens. How the immune system responds to thymic infection is largely unknown. Despite being considered an immune-privileged organ, we detect a mycobacteria-specific T cell response in the thymus following dissemination of Mycobacterium avium or Mycobacterium tuberculosis. This response includes proinflammatory cytokine production by mycobacteria-specific CD4(+) and CD8(+) T cells, which stimulates infected cells and controls bacterial growth in the thymus. Importantly, the responding T cells are mature peripheral T cells that recirculate back to the thymus. The recruitment of these cells is associated with an increased expression of Th1 chemokines and an enrichment of CXCR3(+) mycobacteria-specific T cells in the thymus. Finally, we demonstrate it is the mature T cells that home to the thymus that most efficiently control mycobacterial infection. Although the presence of mature T cells in the thymus has been recognized for some time, to our knowledge, these data are the first to show that T cell recirculation from the periphery to the thymus is a mechanism that allows the immune system to respond to thymic infection. Maintaining a functional thymic environment is essential to maintain T cell differentiation and prevent the emergence of central tolerance to the invading pathogens.

Antigen-specific CD8(+) T cells and protective immunity to tuberculosis

The continuing HIV/AIDS epidemic and the spread of multi-drug resistant Mycobacterium tuberculosis has led to the perpetuation of the worldwide tuberculosis epidemic. While M. bovis BCG is widely used as a vaccine, it lacks efficacy in preventing pulmonary tuberculosis in adults [1]. To combat this ongoing scourge, vaccine development for tuberculosis is a global priority. Most infected individuals develop long-lived protective immunity, which controls and contains M. tuberculosis in a T cell-dependent manner. An effective T cells response determines whether the infection resolves or develops into clinically evident disease. Consequently, there is great interest in determining which T cells subsets mediate anti-mycobacterial immunity, delineating their effector functions, and evaluating whether vaccination can elicit these T cells subsets and induce protective immunity. CD4(+) T cells are critical for resistance to M. tuberculosis in both humans and rodent models. CD4(+) T cells are required to control the initial infection as well as to prevent recrudescence in both humans and mice [2]. While it is generally accepted that class II MHC-restricted CD4(+) T cells are essential for immunity to tuberculosis, M. tuberculosis infection elicits CD8(+) T cells responses in both people and in experimental animals. CD8(+) T cells are also recruited to the lung during M. tuberculosis infection and are found in the granulomas of infected people. Thus, how CD8(+) T cells contribute to overall immunity to tuberculosis and whether antigens recognized by CD8(+) T cells would enhance the efficacy of vaccine strategies continue to be important questions.

The study of novel DNA vaccines against tuberculosis: induction of pathogen-specific CTL in the mouse and monkey models of tuberculosis

RESULTS

HSP65 + IL-12 DNA vaccine showed higher protective efficacy compared with BCG in both mouse and monkey models of TB. It induced the TB-specific CTL in the mouse model of TB, while little level of activity was observed after the injection of BCG. It also showed strong therapeutic efficacy against MDR-TB. In the monkey model, the vaccine augmented the production of IFN-γ and IL-2 from PBL and the therapeutic effect was correlated with the level of IL-2. We next evaluated the potential of DNA vaccine encoding a granulysin, which is an important defensive molecule expressed by human T cells. We found that granulysin-encoding vaccine induced the differentiation of the CTL in vitro and in vivo. It also showed therapeutic efficacy against TB in the monkey as well as the mouse model. The DNA vaccine encoding a Ksp37 also induced the TB-specific CTL in vitro and in vivo in the mouse model. It augmented the production of IL-2, IFN-γ and IL-6 from T cells and spleen cells. A synergistic effect on the activation of the TB-specific CTL was observed by the combination of Ksp37 DNA vaccine with granulysin DNA vaccine.

PURPOSE AND METHODS

Emergence of the multi-drug resistant (MDR) Mycobacterium tuberculosis (TB) is a big problem in the world. We have developed novel TB vaccines [DNA vaccines encoding HSP65 + IL-12, granulysin or killer-specific secretory protein of 37kDa (Ksp37)] using Hemagglutinating virus of Japan -envelope (HVJ-E). It is suggested that the activity of the TB-specific CTL is one of the most important factor for the resistance to TB and immunity for TB in chronic human TB disease. Therefore, we examined the level of activation of the TB-specific CTL after the administration of these vaccines.

CONCLUSION

These data indicate that our novel vaccines (HSP65 + IL-12 DNA, granulysin and Ksp37) have a capability to activate the TB-specific CTL and will be very strong protective and therapeutic vaccines against TB.

Immunotherapy for TB

Mycobacterium tuberculosis was one of the first human pathogens to be identified as the cause of a specific disease – TB. TB was also one of the first specific diseases for which immunotherapy was attempted. In more than a century since, multiple different immunotherapies have been attempted, alongside vaccination and antibiotic treatment, with varying degrees of success. Despite this, TB remains a major worldwide health problem that causes nearly 2 million deaths annually and has infected an estimated 2 billion people. A major reason for this is that M. tuberculosis is an ancient human pathogen that has evolved complex strategies for persistence in the human host. It has thus been long understood that, to effectively control TB, we will need to address the ability of the pathogen to establish a persistent, latent infection in most infected individuals. This review discusses what is presently known about the interaction of M. tuberculosis with the immune system, and how this knowledge has been used to design immunotherapeutic strategies.

Mycobacterium tuberculosis inhibits neutrophil apoptosis, leading to delayed activation of naive CD4 T cells

Mycobacterium tuberculosis promotes its replication by inhibiting the apoptosis of infected macrophages. A proapoptotic M. tuberculosis mutant lacking nuoG, a subunit of the type I NADH dehydrogenase complex, exhibits attenuated growth in vivo, indicating that this virulence mechanism is essential. We show that M. tuberculosis also suppresses neutrophil apoptosis. Compared to wild-type, the nuoG mutant spread to a larger number of lung phagocytic cells. Consistent with the shorter lifespan of infected neutrophils, infection with the nuoG mutant resulted in fewer bacteria per infected neutrophil, accelerated bacterial acquisition by dendritic cells, earlier trafficking of these dendritic cells to lymph nodes, and faster CD4 T cell priming. Neutrophil depletion abrogated accelerated CD4 T cell priming by the nuoG mutant, suggesting that inhibiting neutrophil apoptosis delays adaptive immunity in tuberculosis. Thus, pathogen modulation of apoptosis is beneficial at multiple levels, and enhancing phagocyte apoptosis promotes CD4 as well as CD8 T cell responses.

Inside or outside the phagosome? The controversy of the intracellular localization of Mycobacterium tuberculosis

The localization of Mycobacterium tuberculosis (Mtb) inside the macrophage has been a matter of debate in recent years. Upon inhalation, the bacterium is taken up into macrophage phagosomes, which are manipulated by the bacterium. Subsequent translocation of the bacilli into the cytosol has been observed by several groups, while others fail to observe this phenomenon. Here, we review the available literature in favour of and against this idea, and scrutinize the existing data on how human macrophages control Mtb infection, relating this to the robustness of the host cell. We conclude that both phagosomal maturation inhibition and escape from the phagosome are part of the greater infection strategy of Mtb. The balance between the host cell and the infecting bacterium is an important factor in determining the outcome of infection as well as whether phagosomal escape occurs and can be captured.

Lung neutrophils facilitate activation of naive antigen-specific CD4+ T cells during Mycobacterium tuberculosis infection

Initiation of the adaptive immune response to Mycobacterium tuberculosis occurs in the lung-draining mediastinal lymph node and requires transport of M. tuberculosis by migratory dendritic cells (DCs) to the local lymph node. The previously published observations that 1) neutrophils are a transiently prominent population of M. tuberculosis-infected cells in the lungs early in infection and 2) that the peak of infected neutrophils immediately precedes the peak of infected DCs in the lungs prompted us to characterize the role of neutrophils in the initiation of adaptive immune responses to M. tuberculosis. We found that, although depletion of neutrophils in vivo increased the frequency of M. tuberculosis-infected DCs in the lungs, it decreased trafficking of DCs to the mediastinal lymph node. This resulted in delayed activation (CD69 expression) and proliferation of naive M. tuberculosis Ag85B-specific CD4 T cells in the mediastinal lymph node. To further characterize the role of neutrophils in DC migration, we used a Transwell chemotaxis system and found that DCs that were directly infected by M. tuberculosis migrated poorly in response to CCL19, an agonist for the chemokine receptor CCR7. In contrast, DCs that had acquired M. tuberculosis through uptake of infected neutrophils exhibited unimpaired migration. These results revealed a mechanism wherein neutrophils promote adaptive immune responses to M. tuberculosis by delivering M. tuberculosis to DCs in a form that makes DCs more effective initiators of naive CD4 T cell activation. These observations provide insight into a mechanism for neutrophils to facilitate initiation of adaptive immune responses in tuberculosis.

Lipids, apoptosis, and cross-presentation: links in the chain of host defense against Mycobacterium tuberculosis

Eicosanoids regulate whether human and murine macrophages infected with Mycobacterium tuberculosis die by apoptosis or necrosis. The death modality is important since apoptosis is associated with diminished pathogen viability and should be viewed as a form of innate immunity. Apoptotic vesicles derived from infected macrophages are also an important source of bacterial antigens that can be acquired by dendritic cells to prime antigen-specific T cells. This review integrates in vitro and in vivo data on how apoptosis of infected macrophages is linked to development of T cell immunity against M. tuberculosis.

Modulation of cell death by M. tuberculosis as a strategy for pathogen survival

It has been clearly demonstrated that in vitro, virulent M. tuberculosis can favor necrosis over apoptosis in infected macrophages, and this has been suggested as a mechanism for evading the host immune response. We recently reported that an effect consistent with this hypothesis could be observed in cells from the blood of TB patients, and in this paper, we review what is known about evasion strategies employed by M. tuberculosis and in particular consider the possible interaction of the apoptosis-inhibiting effects of M. tuberculosis infection with another factor (IL-4) whose expression is thought to play a role in the failure to control M. tuberculosis infection. It has been noted that IL-4 may exacerbate TNF-α-induced pathology, though the mechanism remains unexplained. Since pathology in TB typically involves inflammatory aggregates around infected cells, where TNF-α plays an important role, we predicted that IL-4 would inhibit the ability of cells to remove M. tuberculosis by apoptosis of infected cells, through the extrinsic pathway, which is activated by TNF-α. Infection of human monocytic cells with mycobacteria in vitro, in the presence of IL-4, appears to promote necrosis over apoptosis in infected cells—a finding consistent with its suggested role as a factor in pathology during M. tuberculosis infection.

Perspectives on clinical and preclinical testing of new tuberculosis vaccines

This review hopes to improve the selection of new tuberculosis (TB) vaccines by providing several perspectives on the immunization of humans, mice, guinea pigs, rabbits, and monkeys which have not usually been considered. (i) In human TB vaccine trials, the low rate of healing of Mycobacterium bovis BCG lesions (used as the control group) would distinguish individuals who might be helped by vaccination from the 95% who do not need it and would make these trials more conclusive. (ii) The rabbit immune response to Mycobacterium tuberculosis is much more effective in arresting tuberculosis than those of other laboratory animals, so pulmonary tubercle counting in rabbits should be included in all preclinical TB vaccine testing. (iii) Both delayed-type hypersensitivity (DTH) and cell-mediated immunity (CMI) are necessary to control the growth of M. tuberculosis. The testing of new TB vaccines in mice or in guinea pigs may not detect important antigens needed for human immunization. Mice respond poorly to tuberculin-like antigens that cause DTH. Guinea pigs respond poorly to antigens that cause CMI. Rabbits and humans respond well to both DTH and CMI antigens. Since monkeys are very susceptible to M. tuberculosis, they may not be as useful as rabbits for preclinical vaccine evaluation. (iv) Critical antigens (possibly ESAT-6 or CFP-10) might increase the immunity of the host to a greater extent than that produced by a natural M. tuberculosis infection and therefore would be useful in both prophylaxis and immunotherapy. Such critical antigens would increase the host's ability to neutralize key components of M. tuberculosis that enable it to survive in both laboratory animals and humans.

Respiratory mucosal immunization with adenovirus gene transfer vector induces helper CD4 T cell-independent protective immunity

BACKGROUND

Virus-vectored vaccine is a powerful activator of CD8 T cell-mediated immunity and is especially amenable to respiratory mucosal immunization, offering hopes for use in humans with diminished helper CD4 T cell function. However, whether virus-mediated mucosal immunization can produce immune protective CD8 T cells without the CD4 T cell help remains to be investigated.

METHODS

We used a replication-deficient adenovirus vector expressing an Mycobacterium tuberculosis antigen Ag85A for intranasal vaccination and evaluated its effect on CD8 T cell activation and protection in mice depleted of CD4 T cells.

RESULTS

Intranasal vaccination of CD4 T cell-depleted mice led to suboptimal generation of Ag-specific tetramer(+) or interferon (IFN)-gamma-producing CD8 T cells in the lung and spleen but this was observed mainly at the early time after vaccination. Reduced CD8 T cell priming was also accompanied by decreased CD8 T cell responses (CTL). Nevertheless, the ratio of Ag-specific CD8 T cells to IFN-gamma-producing CD8 T cells in CD4 T cell-depleted hosts remained comparable to that in CD4 T cell-competent hosts. Furthermore, the 'unhelped' CD8 T cells also displayed a similar immune phenotype as the 'helped' counterparts. The animals with 'unhelped' CD8 T cells were as well-protected from pulmonary M. tuberculosis challenge as those with 'helped' CD8 T cells in the absence of CD4 T cells.

CONCLUSIONS

The data obtained in the present study suggest that the fully immune protective CD8 T cells can still be generated by respiratory mucosal viral-mediated immunization without CD4 T cells and that CD8 T cells, 'helped' or 'unhelped', can confer significant protection against pulmonary tuberculosis independent of CD4 T cells.

Mycobacterium tuberculosis directs immunofocusing of CD8+ T cell responses despite vaccination

Vaccines that elicit T cell responses try to mimic protective memory T cell immunity after infection by increasing the frequency of Ag-specific T cells in the immune repertoire. However, the factors that determine immunodominance during infection and after vaccination and the relation between immunodominance and protection are incompletely understood. We previously identified TB10.4(20-28) as an immunodominant epitope recognized by H2-K(d)-restricted CD8(+) T cells after M. tuberculosis infection. Here we report a second epitope, EspA(150-158), that is recognized by a substantial number of pulmonary CD8(+) T cells. The relative abundance of these T cells in the naive repertoire only partially predicts their relative frequency after M. tuberculosis infection. Furthermore, although vaccination with recombinant vaccinia virus expressing these epitopes changes their relative immunodominance in the preinfection T cell repertoire, this change is transient after challenge with M. tuberculosis. We speculate that factors intrinsic to the chronic nature of M. tuberculosis infection establishes the hierarchy of immunodominance and may explain the failure of some vaccines to provide protection.

Decreased expression of T-cell costimulatory molecule CD28 on CD4 and CD8 T cells of mexican patients with pulmonary tuberculosis

Patients with tuberculosis frequently develop anergy, a state of T-cell hyporesponsiveness in which defective T-cell costimulation could be a factor. To know if the expression of T-cell costimulatory molecules was altered in tuberculosis, we analyzed the peripheral blood T-cell phenotype of 23 Mexican patients with pulmonary tuberculosis. There was severe CD4 (P < .001) and CD8 (P < .01) lymphopenia and upregulation of costimulatory molecule CD30 on CD4 and CD8 T cells (P < .05); this increase was higher in relapsing tuberculosis. The main finding was severe downregulation of the major costimulatory molecule CD28 on both CD8 and CD4 T cells (P < .001). Depletion of the CD4/CD28 subset, a hitherto undescribed finding, is relevant because CD4 T cells constitute the main arm of the cell-mediated antimycobacterial immune response.

Concomitant activation and antigen uptake via human dectin-1 results in potent antigen-specific CD8+ T cell responses

Dectin-1, a C-type lectin recognizing fungal and mycobacterial pathogens, can deliver intracellular signals that activate dendritic cells (DCs), resulting in initiation of immune responses and expansion of Th17 CD4(+) T cell responses. In this paper, we studied the roles of human Dectin-1 (hDectin-1) expressed on DCs in the induction and activation of Ag-specific CD8(+) T cell responses. We first generated an agonistic anti-hDectin-1 mAb, which recognizes the hDectin-1 Glu(143)-Ile(162) region. It bound to in vitro monocyte-derived DCs and to in vivo CD1c(+)CD1a(+) dermal DCs but not to epidermal Langerhans cells. Anti-hDectin-1-mediated DC activation resulted in upregulation of costimulatory molecules and secretion of multiple cytokines and chemokines in a Syk-dependent manner. DCs activated with the anti-hDectin-1 mAb could significantly enhance both neo and foreign Ag-specific CD8(+) T cell responses by promoting both the expansion of CD8(+) T cells and their functional activities. We further demonstrated that delivering Ags to DCs via hDectin-1 using anti-hDectin-1-Ag conjugates resulted in potent Ag-specific CD8(+) T cell responses. Thus, hDectin-1 expressed on DCs can contribute to the induction and activation of cellular immunity against intracellular pathogens, such as mycobacteria, that are recognized by DCs via Dectin-1. Vaccines based on delivering Ags to DCs with an agonistic anti-hDectin-1 mAb could elicit CD8(+) T cell-mediated immunity.