Influence of phthiocerol dimycocerosate on CD4(+) T cell priming and persistence during Mycobacterium tuberculosis infection.

The characterisation of mycobacterial factors that influence or modulate the host immune response may aid the development of more efficacious TB vaccines. We have previously reported that Mycobacterium tuberculosis deficient in export of Phthiocerol Dimycocerosates (DIM) (MT103(ΔdrrC)) is more attenuated than wild type M. tuberculosis and provides sustained protective immunity compared to the existing BCG vaccine. Here we sought to define the correlates of immunity associated with DIM deficiency by assessing the impact of MT103(ΔdrrC) delivery on antigen presenting cell (APC) function and the generation of CD4(+) T cell antigen-specific immunity. MT103(ΔdrrC) was a potent activator of bone marrow derived dendritic cells, inducing significantly greater expression of CD86 and IL-12p40 compared to BCG or the MT103 parental strain. This translated to an increased ability to initiate early in vivo priming of antigen-specific CD4(+) T cells compared to BCG with enhanced release of IFN-γ and TNF upon antigen-restimulation. The heightened immunity induced by MT103(ΔdrrC) correlated with greater persistence within the spleen compared to BCG, however both MT103(ΔdrrC) and BCG were undetectable in the lung at 70 days post-vaccination. In immunodeficient RAG (-/-) mice, MT103(ΔdrrC) was less virulent than the parental MT103 strain, yet MT103(ΔdrrC) infected mice succumbed more rapidly compared to BCG-infected animals. These results suggest that DIM translocation plays a role in APC stimulation and CD4(+) T cell activation during M. tuberculosis infection and highlights the potential of DIM-deficient strains as novel TB vaccine candidates.

Potent neutralizing anti-CD1d antibody reduces lung cytokine release in primate asthma model.

CD1d is a receptor on antigen-presenting cells involved in triggering cell populations, particularly natural killer T (NKT) cells, to release high levels of cytokines. NKT cells are implicated in asthma pathology and blockade of the CD1d/NKT cell pathway may have therapeutic potential. We developed a potent anti-human CD1d antibody (NIB.2) that possesses high affinity for human and cynomolgus macaque CD1d (KD ∼100 pM) and strong neutralizing activity in human primary cell-based assays (IC50 typically <100 pM). By epitope mapping experiments, we showed that NIB.2 binds to CD1d in close proximity to the interface of CD1d and the Type 1 NKT cell receptor ß-chain. Together with data showing that NIB.2 inhibited stimulation via CD1d loaded with different glycolipids, this supports a mechanism whereby NIB.2 inhibits NKT cell activation by inhibiting Type 1 NKT cell receptor ß-chain interactions with CD1d, independent of the lipid antigen in the CD1d antigen-binding cleft. The strong in vitro potency of NIB.2 was reflected in vivo in an Ascaris suum cynomolgus macaque asthma model. Compared with vehicle control, NIB.2 treatment significantly reduced bronchoalveolar lavage (BAL) levels of Ascaris-induced cytokines IL-5, IL-8 and IL-1 receptor antagonist, and significantly reduced baseline levels of GM-CSF, IL-6, IL-15, IL-12/23p40, MIP-1α, MIP-1ß, and VEGF. At a cellular population level NIB.2 also reduced numbers of BAL lymphocytes and macrophages, and blood eosinophils and basophils. We demonstrate that anti-CD1d antibody blockade of the CD1d/NKT pathway modulates inflammatory parameters in vivo in a primate inflammation model, with therapeutic potential for diseases where the local cytokine milieu is critical.

Protective immunity afforded by attenuated, PhoP-deficient Mycobacterium tuberculosis is associated with sustained generation of CD4+ T-cell memory.

Definition of protective immunity induced by effective vaccines is important for the design of new pathogen control strategies. Inactivation of the PhoP response-regulator in Mycobacterium tuberculosis results in a highly attenuated strain that demonstrates impressive protective efficacy in pre-clinical models of tuberculosis. In this report we demonstrate that the protection afforded by the M. tuberculosis phoP mutant strain is associated with the long-term maintenance of CD4(+) T-cell memory. Immunization of mice with SO2 resulted in enhanced expansion of M. tuberculosis-specific CD4(+) T cells compared with vaccination with the BCG vaccine, with an increased frequency of these cells persisting at extended time-points after vaccination. Strikingly, vaccination with SO2 resulted in sustained generation of CD4(+) T cells displaying a central memory phenotype, a property not shared by BCG. Further, SO2 vaccination markedly improved the generation of polyfunctional cytokine-secreting CD4(+) T cells compared with BCG vaccination. The improved generation of functionally competent memory T cells by SO2 correlated with augmented recall responses in SO2-vaccinated animals after challenge with virulent M. tuberculosis. This study defines a mechanism for the protective effect of the SO2 vaccine and suggests that deletion of defined virulence networks may provide vaccine strains with potent immuno-stimulatory properties.

Targeted induction of antigen expression within dendritic cells modulates antigen-specific immunity afforded by recombinant BCG.

The targeted modulation of antigen expression by recombinant vaccine vehicles would significantly aid development of effective immunotherapeutic strategies. In this report we demonstrate that the Mycobacterium tuberculosis hspX promoter can be used to regulate in vivo induction of antigens expressed by recombinant Bacille Calmette Guérin (rBCG). HspX promoter induction occurred rapidly upon entry of rBCG into cultured dendritic cells (DCs), as evidenced by GFP levels in DCs when infected with BCG:P(hspX)-GFP, in which P(hspX) controlled GFP expression. Vaccination of mice with BCG:P(hspX)-GFP led to rapid in vivo induction of GFP associated with an influx of GFP(+) DCs at the infection site. P(hspX)-driven antigen expression resulted in an improved capacity of DCs to prime antigen-specific T cells, as infection of DCs with BCG:P(hspX)-85B, where the hspX promoter controls expression of M. tuberculosis Ag85B, led to enhanced proliferation of Ag85B-reactive CD4(+) T cells compared to BCG overexpressing Ag85B using the strong Mycobacterium bovis hsp60 promoter. This enhancement of rBCG-induced immunity was also evident in vivo; mice vaccinated with BCG:P(hspX)-85B displayed markedly improved generation of Ag85B-reactive IFN-γ-secreting T cells compared to control BCG-vaccinated mice, which was most pronounced at extended times points post-vaccination. These data reveal a novel strategy to enhance the development and maintenance of vaccine-specific T cell responses.

Modulation of pulmonary DC function by vaccine-encoded GM-CSF enhances protective immunity against Mycobacterium tuberculosis infection.

The rational design of new vaccines engineered to target key components of the host immune response is crucial to aid control of important infectious diseases such as tuberculosis. In this report, we determined whether modifying the function of pulmonary APC could improve protection against infection with Mycobacterium tuberculosis. Targeted delivery to the lung of the cytokine GM-CSF, expressed by the Mycobacterium bovis BCG vaccine strain, increased pulmonary DC numbers and secretion of the immunoregulatory cytokine IL-12, compared with parental BCG immunization. This impact on APC number by BCG:GM-CSF resulted in accelerated priming of antigen-specific CD4+ T cells in the mediastinal lymph nodes and increased migration of activated CD4+ T cells into the lung. i.n. administration of BCG:GM-CSF resulted in significantly increased protection against M. tuberculosis infection compared with mice vaccinated with BCG alone. BCG:GM-CSF exhibited an improved safety profile, as immunodeficient RAG1-/- mice vaccinated i.n. with BCG:GM-CSF survived significantly longer than control BCG-vaccinated mice. These data demonstrate that manipulating immune cells in the lung by BCG-based delivery of GM-CSF can assist the development of protective mucosal immunity against pulmonary bacterial infection.

Antigen load governs the differential priming of CD8 T cells in response to the bacille Calmette Guerin vaccine or Mycobacterium tuberculosis infection.

One reason proposed for the failure of Mycobacterium bovis bacille Calmette Guérin (BCG) vaccination to adequately control the spread of tuberculosis is a limited ability of the vaccine to induce effective CD8 T cell responses. However, the relative capacity of the BCG vaccine and virulent Mycobacterium tuberculosis to induce activation of CD8 T cells, and the factors that govern the initial priming of these cells after mycobacterial infection, are poorly characterized. Using a TCR transgenic CD8 T cell transfer model, we demonstrate significant activation of Ag-specific CD8 T cells by BCG, but responses were delayed and of reduced magnitude compared with those following infection with M. tuberculosis. The degree of CD8 T cell activation was critically dependent on the level of antigenic stimulation, as modifying the infectious dose to achieve comparable numbers of BCG or M. tuberculosis in draining lymph nodes led to the same pattern of CD8 T cell responses to both strains. Factors specific to M. tuberculosis infection did not influence the priming of CD8 T cells, as codelivery of M. tuberculosis with BCG did not alter the magnitude of BCG-induced T cell activation. Following transfer to RAG-1(-/-) recipients, BCG and M. tuberculosis-induced CD8 T cells conferred equivalent levels of protection against M. tuberculosis infection. These findings demonstrate that BCG is able to prime functional CD8 T cells, and suggest that effective delivery of Ag to sites of T cell activation by vaccines may be a key requirement for optimal CD8 T cell responses to control mycobacterial infection.