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Mycobacterium tuberculosis (Mtb) infection induces pulmonary expression of the heme-degrading enzyme heme oxygenase-1 (HO-1). We have previously shown that pharmacological inhibition of HO-1 activity in experimental tuberculosis results in decreased bacterial loads and unexpectedly that this outcome depends on the presence of T lymphocytes. Here, we extend these findings by demonstrating that IFNγ production by T lymphocytes and NOS2 expression underlie this T-cell requirement and that HO-1 inhibition potentiates IFNγ-induced NOS2-dependent control of Mtb by macrophages in vitro. Among the products of heme degradation by HO-1 (biliverdin, carbon monoxide, and iron), only iron supplementation reverted the HO-1 inhibition-induced enhancement of bacterial control and this reversal was associated with decreased NOS2 expression and NO production. In addition, we found that HO-1 inhibition results in decreased labile iron levels in Mtb-infected macrophages in vitro and diminished iron accumulation in Mtb-infected lungs in vivo. Together these results suggest that the T-lymphocyte dependence of the therapeutic outcome of HO-1 inhibition on Mtb infection reflects the role of the enzyme in generating iron that suppresses T-cell-mediated IFNγ/NOS2-dependent bacterial control. In broader terms, our findings highlight the importance of the crosstalk between iron metabolism and adaptive immunity in determining the outcome of infection.

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb) remains a major public health problem worldwide due in part to the lack of an effective vaccine and to the lengthy course of antibiotic treatment required for successful cure. Combined immuno/chemotherapeutic intervention represents a major strategy for developing more effective therapies against this important pathogen. Because of the major role of CD4+ T cells in containing Mtb infection, augmentation of bacterial specific CD4+ T cell responses has been considered as an approach in achieving this aim. Here we present new data from our own research aimed at determining whether boosting CD4+ T cell responses can promote antibiotic clearance. In these studies, we first characterized the impact of antibiotic treatment of infected mice on Th1 responses to major Mtb antigens and then performed experiments aimed at sustaining CD4+ T cell responsiveness during antibiotic treatment. These included IL-12 infusion, immunization with ESAT-6 and Ag85B immunodominant peptides and adoptive transfer of Th1-polarized CD4+ T cells specific for ESAT-6 or Ag85B during the initial month of chemotherapy. These approaches failed to enhance antibiotic clearance of Mtb, indicating that boosting Th1 responses to immunogenic Mtb antigens highly expressed by actively dividing bacteria is not an effective strategy to be used in the initial phase of antibiotic treatment, perhaps because replicating organisms are the first to be eliminated by the drugs. These results are discussed in the context of previously published findings addressing this concept along with possible alternate approaches for harnessing Th1 immunity as an adjunct to chemotherapy.

Human primary monocytes are composed of a minor, more mature CD16+(CD14low/neg) population and a major CD16neg(CD14+) subset. The specific functions of CD16+ versus CD16neg monocytes in steady state or inflammation remain poorly understood. In previous work, we found that IL-12 is selectively produced by the CD16+ subset in response to the protozoan pathogen, Toxoplasma gondii. In this study, we demonstrated that this differential responsiveness correlates with the presence of an IFN-induced transcriptional signature in CD16+ monocytes already at baseline. Consistent with this observation, we found that in vitro IFN-γ priming overcomes the defect in the IL-12 response of the CD16neg subset. In contrast, pretreatment with IFN-γ had only a minor effect on IL-12p40 secretion by the CD16+ population. Moreover, inhibition of the mTOR pathway also selectively increased the IL-12 response in CD16neg but not in CD16+ monocytes. We further demonstrate that in contrast to IFN-γ, IFN-α fails to promote IL-12 production by the CD16neg subset and blocks the effect of IFN-γ priming. Based on these observations, we propose that the acquisition of IL-12 responsiveness by peripheral blood monocyte subsets depends on extrinsic signals experienced during their developmental progression in vivo. This process can be overridden during inflammation by the opposing regulatory effects of type I and II IFN as well as the mTOR inhibition.

Necrotic cell death during Mycobacterium tuberculosis (Mtb) infection is considered host detrimental since it facilitates mycobacterial spread. Ferroptosis is a type of regulated necrosis induced by accumulation of free iron and toxic lipid peroxides. We observed that Mtb-induced macrophage necrosis is associated with reduced levels of glutathione and glutathione peroxidase-4 (Gpx4), along with increased free iron, mitochondrial superoxide, and lipid peroxidation, all of which are important hallmarks of ferroptosis. Moreover, necrotic cell death in Mtb-infected macrophage cultures was suppressed by ferrostatin-1 (Fer-1), a well-characterized ferroptosis inhibitor, as well as by iron chelation. Additional experiments in vivo revealed that pulmonary necrosis in acutely infected mice is associated with reduced Gpx4 expression as well as increased lipid peroxidation and is likewise suppressed by Fer-1 treatment. Importantly, Fer-1–treated infected animals also exhibited marked reductions in bacterial load. Together, these findings implicate ferroptosis as a major mechanism of necrosis in Mtb infection and as a target for host-directed therapy of tuberculosis.

As a major natural host for Toxoplasma gondii, the mouse is widely used for the study of the immune response to this medically important protozoan parasite. However, murine innate recognition of toxoplasma depends on the interaction of parasite profilin with TLR11 and TLR12, two receptors that are functionally absent in humans. This raises the question of how human cells detect and respond to T. gondii. In this study, we show that primary monocytes and dendritic cells from peripheral blood of healthy donors produce IL-12 and other proinflammatory cytokines when exposed to toxoplasma tachyzoites. Cell fractionation studies determined that IL-12 and TNF-α secretion is limited to CD16+ monocytes and the CD1c+ subset of dendritic cells. In direct contrast to their murine counterparts, human myeloid cells fail to respond to soluble tachyzoite extracts and instead require contact with live parasites. Importantly, we found that tachyzoite phagocytosis, but not host cell invasion, is required for cytokine induction. Together these findings identify CD16+ monocytes and CD1c+ dendritic cells as the major myeloid subsets in human blood-producing innate cytokines in response to T. gondii and demonstrate an unappreciated requirement for phagocytosis of live parasites in that process. This form of pathogen sensing is distinct from that used by mice, possibly reflecting a direct involvement of rodents and not humans in the parasite life cycle.

Background Effective treatment of Mycobacterium tuberculosis (Mtb) infection requires at least 6 months of daily therapy with multiple orally administered antibiotics. Although this drug regimen is administered annually to millions worldwide, the impact of such intensive antimicrobial treatment on the host microbiome has never been formally investigated. Here, we characterized the longitudinal outcome of conventional isoniazid-rifampin-pyrazinamide (HRZ) TB drug administration on the diversity and composition of the intestinal microbiota in Mtb-infected mice by means of 16S rRNA sequencing. We also investigated the effects of each of the individual antibiotics alone and in different combinations. Results While inducing only a transient decrease in microbial diversity, HRZ treatment triggered a marked, immediate and reproducible alteration in community structure that persisted for the entire course of therapy and for at least 3 months following its cessation. Members of order Clostridiales were among the taxa that decreased in relative frequencies during treatment and family Porphyromonadaceae significantly increased post treatment. Experiments comparing monotherapy and different combination therapies identified rifampin as the major driver of the observed alterations induced by the HRZ cocktail but also revealed unexpected effects of isoniazid and pyrazinamide in certain drug pairings. Conclusions This report provides the first detailed analysis of the longitudinal changes in the intestinal microbiota due to anti-tuberculosis therapy. Importantly, many of the affected taxa have been previously shown in other systems to be associated with modifications in immunologic function. Together, our findings reveal that the antibiotics used in conventional TB treatment induce a distinct and long lasting dysbiosis. In addition, they establish a murine model for studying the potential impact of this dysbiosis on host resistance and physiology. Electronic supplementary material The online version of this article (doi:10.1186/s40168-017-0286-2) contains supplementary material, which is available to authorized users.

Heme oxygenase-1 (HO-1) is a stress response antioxidant enzyme which catalyzes the degradation of heme released during inflammation. HO-1 expression is upregulated in both experimental and human Mycobacterium tuberculosis infection, and in patients it is a biomarker of active disease. Whether the enzyme plays a protective versus pathogenic role in tuberculosis has been the subject of debate. To address this controversy, we administered tin protoporphyrin IX (SnPPIX), a well-characterized HO-1 enzymatic inhibitor, to mice during acute M. tuberculosis infection. These SnPPIX-treated animals displayed a substantial reduction in pulmonary bacterial loads comparable to that achieved following conventional antibiotic therapy. Moreover, when administered adjunctively with antimycobacterial drugs, the HO-1 inhibitor markedly enhanced and accelerated pathogen clearance. Interestingly, both the pulmonary induction of HO-1 expression and the efficacy of SnPPIX treatment in reducing bacterial burden were dependent on the presence of host T lymphocytes. Although M. tuberculosis expresses its own heme-degrading enzyme, SnPPIX failed to inhibit its enzymatic activity or significantly restrict bacterial growth in liquid culture. Together, the above findings reveal mammalian HO-1 as a potential target for host-directed monotherapy and adjunctive therapy of tuberculosis and identify the immune response as a critical regulator of this function., IMPORTANCE There is no reliable vaccine against tuberculosis (TB), and conventional antibiotic therapy is administered over at least 6 months. This prolonged treatment period can lead to noncompliance resulting in relapsed infection as well as the emergence of multidrug resistance. Thus, there is an urgent need for improved therapeutic regimens that can more rapidly and efficiently control M. tuberculosis in infected patients. Here, we describe a potential strategy for treating TB based on pharmacological inhibition of the host heme-degrading enzyme HO-1. This approach results in significantly reduced bacterial burdens in mice, and when administered in conjunction with conventional antibiotic therapy, leads to faster, more effective pathogen clearance without detectable direct effects on the mycobacteria themselves. Interestingly, the effects of HO-1 inhibition on M. tuberculosis infection in vivo are dependent on the presence of an intact host immune system. These observations establish mammalian HO-1 as a potential target for host-directed therapy of TB.

Infection with M. tuberculosis (Mtb) induces the upregulation of heme oxygenase-1 (HO-1), a powerful antioxidant enzyme that catalyzes the degradation of heme into iron, biliverdin and carbon monoxide. We observed that administration of tin protoporphyrin IX (SnPPIX), a well-characterized HO-1 activity inhibitor, to Mtb-infected mice resulted in pulmonary bacterial load reduction. Moreover, adjunct administration of SnPPIX to Mtb-infected mice receiving antibiotic treatment improved and accelerated pathogen clearance. Interestingly, both the induction of HO-1 expression in lungs of Mtb-infected mice and the efficacy of in vivo SnPPIX-mediated bacterial burden reduction were dependent on the presence of host TCR-α+ lymphocytes as well as IFN-γ suggesting a role for the immune response in the activity of the drug. Further investigation revealed that in the lungs of these immunodeficient mice the numbers of parenchymal CD11b+ myeloid cells staining positive for HO-1 were substantially reduced. SnPPIX treatment of Mtb-infected mouse bone marrow derived macrophages also resulted in diminished bacterial loads in vitro and this effect was reverted by iron supplementation and enhanced by iron chelation. Based on these observations we propose that HO-1 inhibition promotes control of Mtb by limiting the availability of nutrient iron and that the host Th1 response regulates this effect by controlling the recruitment to the lungs of a subset of myeloid cells that is both capable of HO-1 expression and permissive to bacterial infection. This work was supported by the intramural research program of the NIAID.

Introduction Triple-negative breast cancer (TNBC) is an aggressive subtype of breast cancer that is diagnosed in approximately 15% of all human breast cancer (BrCa) patients. Currently, no targeted therapies exist for this subtype of BrCa and prognosis remains poor. Our laboratory has previously identified a proliferation/DNA repair/cell cycle gene signature (Tag signature) that is characteristic of human TNBC. We hypothesize that targeting the dysregulated biological networks in the Tag gene signature will lead to the identification of improved combination therapies for TNBC. Methods Cross-species genomic analysis was used to identify human breast cancer cell lines that express the Tag signature. Knock-down of the up-regulated genes in the Tag signature by siRNA identified several genes that are critical for TNBC cell growth. Small molecule inhibitors to two of these genes were analyzed, alone and in combination, for their effects on cell proliferation, cell cycle, and apoptosis in vitro and tumor growth in vivo. Synergy between the two drugs was analyzed by the Chou-Talalay method. Results A custom siRNA screen was used to identify targets within the Tag signature that are critical for growth of TNBC cells. Ribonucleotide reductase 1 and 2 (RRM1 and 2) and checkpoint kinase 1 (CHK1) were found to be critical targets for TNBC cell survival. Combination therapy, to simultaneously attenuate cell cycle checkpoint control through inhibition of CHK1 while inducing DNA damage with gemcitabine, improved therapeutic efficacy in vitro and in xenograft models of TNBC. Conclusions This combination therapy may have translational value for patients with TNBC and improve therapeutic response for this aggressive form of breast cancer.

Basal-like triple negative breast cancer (BTNBC) is characterized by the absence of estrogen receptor, progesterone receptor, and Her2 expression, and represents an estimated 15% of all human breast cancers. This subtype is highly prevalent in African American women (35%) and is associated with distant metastasis and poor prognosis. As there are currently no targeted therapies for this subtype of breast cancer, our research focuses on the development of improved therapies to increase patient survival. We have previously shown that primary mammary tumors from the C3(1)/SV40-TAg genetically engineered mouse (GEM) model express a critical proliferation/ DNA repair/ cell cycle gene signature (TAg signature) that is shared with human BTNBC. SV40-TAg functionally inactivates p53 and pRb, two critical tumor suppressor genes whose functions are lost in most human BTNBC. We hypothesize that targeting dysregulated genes and biological networks present in the TAg signature will lead to the identification of novel targets and potential combination therapies. To test this idea we developed a custom siRNA library screen to inhibit the expression of individual genes represented in the TAg signature using human MDA-MB-231 BTNBC cells. Additionally, we performed a synthetic lethal screen in which TAg signature genes were knocked down in MDA-MB-231 cells using pooled siRNAs in combination with either UCN-01 or gemcitabine, small molecule inhibitors of CHK1 and RRM1/2 respectively. It was found that the knockdown of BMI-1, EZH2, GeneA, GeneB, or GeneC significantly decreased cell proliferation with the addition of UCN-01 or gemcitabine. A second synthetic lethal screen was performed in which the above genes were knocked down using four deconvoluted siRNAs per gene with the addition of gemcitabine, UCN-01, or AZD7762 (a more specific CHK1 inhibitor). Synergistic activity was shown between the siRNA knockdown of these genes and UCN-01 and AZD7762 compared to siRNA alone. To determine whether the knockdown of these genes alters sensitivity to gemcitabine or CHK1 inhibitors, the EC50 values of these drugs are currently being evaluated in stable knockdown MDA-MB-231 cell lines expressing shRNA to the selected genes. Our results suggest that using GEM models to help identify new targets may be useful in the development of novel therapeutics for BTNBC in combination with available CHK1 inhibitors and/or gemcitabine. These studies will enhance our understanding of BTNBC and allow us to identify innovative combination therapies to treat this challenging form of breast cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr A198.