The COX- inhibitor indomethacin reduces Th1 effector and T regulatory cells in vitro in Mycobacterium tuberculosis infection.

BACKGROUND: Tuberculosis (TB) causes a major burden on global health with long and cumbersome TB treatment regimens. Host-directed immune modulating therapies have been suggested as adjunctive treatment to TB antibiotics. Upregulated cyclooxygenase-2 (COX-2)-prostaglandin E2 (PGE2) signaling pathway may cause a dysfunctional immune response that favors survival and replication of Mycobacterium tuberculosis (Mtb). METHODS: Blood samples were obtained from patients with latent TB (n = 9) and active TB (n = 33) before initiation of anti-TB chemotherapy. COX-2 expression in monocytes and ESAT-6 and Ag85 specific T cell cytokine responses (TNF-α, IFN-γ, IL-2), proliferation (carboxyfluorescein succinimidyl ester staining) and regulation (FOXP3+ T regulatory cells) were analysed by flow cytometry and the in vitro effects of the COX-1/2 inhibitor indomethacin were measured. RESULTS: We demonstrate that indomethacin significantly down-regulates the fraction of Mtb specific FOXP3+ T regulatory cells (ESAT-6; p = 0.004 and Ag85; p < 0.001) with a concomitant reduction of Mtb specific cytokine responses and T cell proliferation in active TB. Although active TB tend to have higher levels, there are no significant differences in COX-2 expression between unstimulated monocytes from patients with active TB compared to latent infection. Monocytes in both TB groups respond with a significant upregulation of COX-2 after in vitro stimulation. CONCLUSIONS: Taken together, our in vitro data indicate a modulation of the Th1 effector and T regulatory cells in Mtb infection in response to the COX-1/2 inhibitor indomethacin. The potential role as adjunctive host-directed therapy in TB disease should be further evaluated in both animal studies and in human clinical trials.

Human regulatory T cells control TCR signaling and susceptibility to suppression in CD4+ T cells.

Human CD4(+)CD25(hi)FOXP3(+) regulatory T cells maintain immunologic tolerance and prevent autoimmune and inflammatory immune responses. Regulatory T cells undergo a similar activation cycle as conventional CD4(+) T cells upon antigen stimulation. Here, we demonstrate that T cell receptors and costimulation are required to activate the regulatory T cell suppressive function. Regulatory T cells suppressed the T cell receptor signaling in effector T cells in a time-dependent manner that corresponded with inhibition of cytokine production and proliferation. Modulation of the activation level and thereby the suppressive capacity of regulatory T cells imposed distinct T cell receptor signaling signatures and hyporesponsiveness in suppressed and proliferating effector T cells and established a threshold for effector T cell proliferation. The immune suppression of effector T cells was completely reversible upon removal of regulatory T cells. However, the strength of prior immune suppression by regulatory T cells and corresponding T cell receptor signaling in effector T cells determined the susceptibility to suppression upon later reexposure to regulatory T cells. These findings demonstrate how the strength of the regulatory T cell suppressive function determines intracellular signaling, immune responsiveness, and the later susceptibility of effector T cells to immune suppression and contribute to unveiling the complex interactions between regulatory T cells and effector T cells.

Targeting Tuberculosis and HIV Infection-Specific Regulatory T Cells with MEK/ERK Signaling Pathway Inhibitors.

Human regulatory T cells (Tregs) are essential in maintaining immunological tolerance and suppress effector T cells. Tregs are commonly up-regulated in chronic infectious diseases such as tuberculosis (TB) and human immunodeficiency virus (HIV) infection and thereby hamper disease-specific immune responses and eradication of pathogens. The MEK/ERK signaling pathway is involved in regulation of the FoxP3 transcription factor, which directs a lineage-specific transcriptional program to define Tregs and control their suppressive function. Here, we aimed to target activation of disease-specific Tregs by inhibition of the MEK/ERK signaling pathway based on the hypothesis that this would improve anti-HIV and anti-TB immunity. Stimulation of T cells from untreated TB (n = 12) and HIV (n = 8) patients with disease-specific antigens in vitro in the presence of the MEK inhibitor (MEKI) trametinib (GSK1120212) resulted in significant down-regulation of both FoxP3 levels (MFI) and fractions of resting (CD45RA+FoxP3+) and activated (CD45RA-FoxP3++) Tregs. MEKI also reduced the levels of specific T effector cells expressing the pro-inflammatory cytokines (IFN-γ, TNF-α and IL-2) in both HIV and TB patients. In conclusion, MEKIs modulate disease antigen-specific Treg activation and may have potential application in new treatment strategies in chronic infectious diseases where reduction of Treg activity would be favorable. Whether MEKIs can be used in current HIV or TB therapy regimens needs to be further investigated.