Relevance of the Warburg Effect in Tuberculosis for Host-Directed Therapy

The spleen assumes a major role in blood glucose regulation in type 1 diabetes patients treated with BCG

The Bacillus Calmette-Guérin (BCG) vaccine, which has been used for > 100 years to prevent tuberculosis, is well-established for bladder cancer treatment, and under study for neurological and autoimmune diseases. In patients with type 1 diabetes (T1D), BCG vaccinations have been shown in randomized clinical trials to gradually lower blood sugar to near normal levels. This effect appears to be driven by a BCG-induced shift in lymphoid cells' glucose metabolism from oxidative phosphorylation to aerobic glycolysis. The latter is a state of high glucose utilization that draws more glucose from the blood. Apart from blood, it is unknown whether BCG establishes residence in any organs and alters their glucose metabolism. In this two-year-long clinical trial in type 1 diabetics, we use positron emission tomography (PET) and x-ray computed tomography (CT) to map organs that increase their uptake of the glucose analogue 18F-fluorodeoxyglucose (18F-FDG) before versus after BCG vaccinations. We also injected BALB/c mice with BCG to test for the presence of BCG in various organs. Results from both studies point to the spleen as the dominant site for glucose uptake and BCG residence. The human spleen is significant because its 47% increase in 18F-FDG uptake by a large population of lymphocytes and monocytes might help to explain BCG's systemic lowering of blood glucose to near normal levels. Findings suggest that the spleen, triggered by BCG, assumes a critical role in systemic glucose regulation in the absence of a functional pancreas.

The uncharted territory of host-pathogen interaction in tuberculosis

Mycobacterium tuberculosis (M.tb) effectively manipulates the host processes to establish the deadly respiratory disease, Tuberculosis (TB). M.tb has developed key mechanisms to disrupt the host cell health to combat immune responses and replicate efficaciously. M.tb antigens such as ESAT-6, 19kDa lipoprotein, Hip1, and Hsp70 destroy the integrity of cell organelles (Mitochondria, Endoplasmic Reticulum, Nucleus, Phagosomes) or delay innate/adaptive cell responses. This is followed by the induction of cellular stress responses in the host. Such cells can either undergo various cell death processes such as apoptosis or necrosis, or mount effective immune responses to clear the invading pathogen. Further, to combat the infection progression, the host secretes extracellular vesicles such as exosomes to initiate immune signaling. The exosomes can contain M.tb as well as host cell-derived peptides that can act as a double-edged sword in the immune signaling event. The host-symbiont microbiota produces various metabolites that are beneficial for maintaining healthy tissue microenvironment. In juxtaposition to the above-mentioned mechanisms, M.tb dysregulates the gut and respiratory microbiome to support its replication and dissemination process. The above-mentioned interconnected host cellular processes of Immunometabolism, Cellular stress, Host Microbiome, and Extracellular vesicles are less explored in the realm of exploration of novel Host-directed therapies for TB. Therefore, this review highlights the intertwined host cellular processes to control M.tb survival and showcases the important factors that can be targeted for designing efficacious therapy.

The multivalency game ruling the biology of immunity

Macrophages play a crucial role in our immune system, preserving tissue health and defending against harmful pathogens. This article examines the diversity of macrophages influenced by tissue-specific functions and developmental origins, both in normal and disease conditions. Understanding the spectrum of macrophage activation states, especially in pathological situations where they contribute significantly to disease progression, is essential to develop targeted therapies effectively. These states are characterized by unique receptor compositions and phenotypes, but they share commonalities. Traditional drugs that target individual entities are often insufficient. A promising approach involves using multivalent systems adorned with multiple ligands to selectively target specific macrophage populations based on their phenotype. Achieving this requires constructing supramolecular structures, typically at the nanoscale. This review explores the theoretical foundation of engineered multivalent nanosystems, dissecting the key parameters governing specific interactions. The goal is to design targeting systems based on distinct cell phenotypes, providing a pragmatic approach to navigating macrophage heterogeneity's complexities for more effective therapeutic interventions.

NAD(H) homeostasis underlies host protection mediated by glycolytic myeloid cells in tuberculosis

Mycobacterium tuberculosis (Mtb) disrupts glycolytic flux in infected myeloid cells through an unclear mechanism. Flux through the glycolytic pathway in myeloid cells is inextricably linked to the availability of NAD+, which is maintained by NAD+ salvage and lactate metabolism. Using lung tissue from tuberculosis (TB) patients and myeloid deficient LDHA (LdhaLysM-/-) mice, we demonstrate that glycolysis in myeloid cells is essential for protective immunity in TB. Glycolytic myeloid cells are essential for the early recruitment of multiple classes of immune cells and IFNγ-mediated protection. We identify NAD+ depletion as central to the glycolytic inhibition caused by Mtb. Lastly, we show that the NAD+ precursor nicotinamide exerts a host-dependent, antimycobacterial effect, and that nicotinamide prophylaxis and treatment reduce Mtb lung burden in mice. These findings provide insight into how Mtb alters host metabolism through perturbation of NAD(H) homeostasis and reprogramming of glycolysis, highlighting this pathway as a potential therapeutic target.

Effects of n-butanol extract of Pulsatilla decoction on the NLRP3 inflammasome in macrophages infected with Candida albicans

ETHNOPHARMACOLOGICAL RELEVANCE

Pulsatilla decoction is a traditional Chinese medicine from Shang Han Lun that has been reported to have therapeutic efficacy in vulvovaginal candidiasis (VVC), and is a growth inhibitor of Candida albicans (C. albicans) in vitro, the causative agent of VVC.

AIM OF THE STUDY

In previous studies, Pulsatilla decoction has shown therapeutic benefits for VVC. With further chemical extraction of the decoction, the n-butanol extract (of Pulsatilla decoction; BEPD) was most effective against C. albicans and therapeutic for VVC. The mechanism, however, has not been elucidated. The regulation of NOD-like receptor protein 3 (NLRP3) inflammasome has recently been demonstrated as a critical component of the inflammasome complex that initiates the vaginal inflammatory response. Therefore, the effect of BEPD on NLRP3 associated with VVC was investigated.

MATERIALS AND METHODS

Ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was used for detecting the principal compounds of BEPD (Anemoside B4, Esculin, esculetin, Epiberberine, Berberine, Jatrorrhizine and Phellodendrine). BEPD-containing serum is prepared by intragastric administration of BEPD (4.6875 g/kg for seven days) in rats. PMA-induced THP-1 cells were challenged with C. albicans. The expression of CD68 to identify macrophages was examined by flow cytometry, the viability of THP-1 cells were assessed by CCK8 assay, the release of lactate dehydrogenase (LDH) was detected by LDH kit, and the secretion levels of IL-1β and IL-18 were evaluated through enzyme-linked immunosorbent assay (ELISA), the levels of NLRP3 were quantified by immunofluorescence, the levels of reactive oxygen species (ROS) were measured by ROS kit, and the expression of Dectin-1, Syk, TLR2, TLR4, MyD88, NF-κB, NLRP3, Caspase-1, and ASC proteins were detected by Western blot.

RESULTS

After administration of BEPD-containing serum, the levels of IL-1β, IL-18 and LDH released from macrophages were reduced in the BEPD-containing serum group compared to the model group. In addition, BEPD-containing serum inhibited the expression of ROS in macrophages, suppressed the expression of NLRP3 and inhibited the expression of TLRs/MyD88 and Dectin-1/Syk signaling pathway-related proteins.

CONCLUSIONS

BEPD suppressed the NLRP3 inflammasome and related signaling pathways in macrophages infected with C. albicans in vitro, thereby providing insight into the mechanism of BEPD action on VVC.

Inflammation-mediated tissue damage in pulmonary tuberculosis and host-directed therapeutic strategies

Treatment of tuberculosis (TB) involves the administration of anti-mycobacterial drugs for several months. The emergence of drug-resistant strains of Mycobacterium tuberculosis (Mtb, the causative agent) together with increased disease severity in people with co-morbidities such as diabetes mellitus and HIV have hampered efforts to reduce case fatality. In severe disease, TB pathology is largely attributable to over-exuberant host immune responses targeted at controlling bacterial replication. Non-resolving inflammation driven by host pro-inflammatory mediators in response to high bacterial load leads to pulmonary pathology including cavitation and fibrosis. The need to improve clinical outcomes and reduce treatment times has led to a two-pronged approach involving the development of novel antimicrobials as well as host-directed therapies (HDT) that favourably modulate immune responses to Mtb. HDT strategies incorporate aspects of immune modulation aimed at downregulating non-productive inflammatory responses and augmenting antimicrobial effector mechanisms to minimise pulmonary pathology and accelerate symptom resolution. HDT in combination with existing antimycobacterial agents offers a potentially promising strategy to improve the long-term outcome for TB patients. In this review, we describe components of the host immune response that contribute to inflammation and tissue damage in pulmonary TB, including cytokines, matrix metalloproteinases, lipid mediators, and neutrophil extracellular traps. We then proceed to review HDT directed at these pathways.

Metabolic biological markers for diagnosing and monitoring the course of tuberculosis

The international biomedical community has been currently facing a need to find a simple and most accessible type of analysis that helps to diagnose tuberculosis (TB) with the maximum reliability even before the onset of clinical manifestations. Tuberculosis results in more deaths than any other pathogen, second only to pneumonia caused by the SARS-CoV-2 virus, but the majority of infected people remain asymptomatic. In addition, it is important to develop methods to distinguish various forms of tuberculosis infection course at early stages and to reliably stratify patients into appropriate groups (persons with a rapidly progressing infection, chronic course, latent infection carriers). Immunometabolism investigates a relationship between bioenergetic pathways and specific functions of immune cells that has recently become increasingly important in scientific research. The host anti-mycobacteria immune response in tuberculosis is regulated by a number of metabolic networks that can interact both cooperatively and antagonistically, influencing an outcome of the disease. The balance between inflammatory and immune reactions limits the spread of mycobacteria in vivo and protects from developing tuberculosis. Cytokines are essential for host defense, but if uncontrolled, some mediators may contribute to developing disease and pathology. Differences in plasma levels of metabolites between individuals with advanced infection, LTBI and healthy individuals can be detected long before the onset of the major related clinical signs. Changes in amino acid and cortisol level may be detected as early as 12 months before the onset of the disease and become more prominent at verifying clinical diagnosis. Assessing serum level of certain amino acids and their ratios may be used as additional diagnostic markers of active pulmonary TB. Metabolites, including serum fatty acids, amino acids and lipids may contribute to detecting active TB. Metabolic profiles indicate about increased indolamine 2.3-dioxygenase 1 (IDO1) activity, decreased phospholipase activity, increased adenosine metabolite level, and fibrous lesions in active vs. latent infection. TB treatment can be adjusted based on individual patient metabolism and biomarker profiles. Thus, exploring immunometabolism in tuberculosis is necessary for development of new therapeutic strategies.

On-Slide Heat Sterilization Enables Mass Spectrometry Imaging of Tissue Infected with High-Threat Pathogens Outside of Biocontainment: A Study Directed at Mycobacterium tuberculosis

Mass spectrometry imaging investigations of tissues infected with agents that require high-security biocontainment, such as Mycobacterium tuberculosis, have been limited due to incompatible sterilization techniques. Here we describe an on-slide heat sterilization method that enables mass spectrometry imaging investigations of pharmaceuticals, lipids, and metabolites in infected tissue samples outside of biocontainment. An evaluation of different temperatures and incubation times determined that 100 °C for 1 h was essential to sterilize 5 times the bacterial burden observed in tuberculosis (TB) cavity sections. Laser-capture microdissection combined with liquid chromatography with tandem mass spectrometry quantitation, in addition to mass spectrometry imaging, showed that no degradation was observed following the on-slide heat sterilization protocol for a variety of drug classes covering a range of physicochemical properties. Utilizing the tissue mimetic model, we demonstrated that the detection of lipid and metabolite ions was not impacted by heat sterilization and that, for several metabolites, the on-slide heat sterilization method improved the sensitivity when compared to control samples. An application of the on-slide heat sterilization to M. tuberculosis infected tissue enabled the first detection and spatial distribution of lipids indicative of a lysosomal storage disease phenotype within TB granuloma macrophages, in addition to the differential distribution of metabolites central to the fatty acid oxidation pathway. These initial investigations detected a pronounced heterogeneity within the cellular regions and necrotic cores of individual TB granulomas and across different evolving granulomas. This study provides the framework for mass spectrometry imaging investigations of high-threat pathogens outside of biocontainment.

TCA cycle remodeling drives proinflammatory signaling in humans with pulmonary tuberculosis

The metabolic signaling pathways that drive pathologic tissue inflammation and damage in humans with pulmonary tuberculosis (TB) are not well understood. Using combined methods in plasma high-resolution metabolomics, lipidomics and cytokine profiling from a multicohort study of humans with pulmonary TB disease, we discovered that IL-1β-mediated inflammatory signaling was closely associated with TCA cycle remodeling, characterized by accumulation of the proinflammatory metabolite succinate and decreased concentrations of the anti-inflammatory metabolite itaconate. This inflammatory metabolic response was particularly active in persons with multidrug-resistant (MDR)-TB that received at least 2 months of ineffective treatment and was only reversed after 1 year of appropriate anti-TB chemotherapy. Both succinate and IL-1β were significantly associated with proinflammatory lipid signaling, including increases in the products of phospholipase A2, increased arachidonic acid formation, and metabolism of arachidonic acid to proinflammatory eicosanoids. Together, these results indicate that decreased itaconate and accumulation of succinate and other TCA cycle intermediates is associated with IL-1β-mediated proinflammatory eicosanoid signaling in pulmonary TB disease. These findings support host metabolic remodeling as a key driver of pathologic inflammation in human TB disease.

Pulmonary tuberculosis (TB) often results in pathologic lung inflammation that causes tissue damage and does not control bacterial replication. This impairs the host response to antibiotic treatment and can result in long term deficits in lung function. Currently, the role of host metabolism in regulating the inflammatory response in TB disease is not well understood. Here, we use detailed immunometabolic phenotyping to show that metabolic remodeling of the tricarboxylic acid (TCA) cycle is closely associated with pathologic inflammatory signaling in humans with TB disease. Accumulation of TCA cycle intermediates in plasma, including the proinflammatory metabolite succinate, as well as decreased concentrations of the anti-inflammatory metabolite itaconate, were associated with increases in IL-1β and upregulation of proinflammatory lipid signaling cascades. This inflammatory network was upregulated following delays in appropriate anti-TB treatment and was associated with prolonged time to sputum culture clearance of Mycobacterium tuberculosis. Our study provides new insights into the metabolic reprograming that leads to pathologic inflammation in humans with pulmonary TB.

Host Immune-Metabolic Adaptations Upon Mycobacterial Infections and Associated Co-Morbidities

Mycobacterial diseases are a major public health challenge. Their causative agents include, in order of impact, members of the Mycobacterium tuberculosis complex (causing tuberculosis), Mycobacterium leprae (causing leprosy), and non-tuberculous mycobacterial pathogens including Mycobacterium ulcerans. Macrophages are mycobacterial targets and they play an essential role in the host immune response to mycobacteria. This review aims to provide a comprehensive understanding of the immune-metabolic adaptations of the macrophage to mycobacterial infections. This metabolic rewiring involves changes in glycolysis and oxidative metabolism, as well as in the use of fatty acids and that of metals such as iron, zinc and copper. The macrophage metabolic adaptations result in changes in intracellular metabolites, which can post-translationally modify proteins including histones, with potential for shaping the epigenetic landscape. This review will also cover how critical tuberculosis co-morbidities such as smoking, diabetes and HIV infection shape host metabolic responses and impact disease outcome. Finally, we will explore how the immune-metabolic knowledge gained in the last decades can be harnessed towards the design of novel diagnostic and therapeutic tools, as well as vaccines.

Lactate cross-talk in host-pathogen interactions

Lactate is the main product generated at the end of anaerobic glycolysis or during the Warburg effect and its role as an active signalling molecule is increasingly recognised. Lactate can be released and used by host cells, by pathogens and commensal organisms, thus being essential for the homeostasis of host-microbe interactions. Infection can alter this intricate balance, and the presence of lactate transporters in most human cells including immune cells, as well as in a variety of pathogens (including bacteria, fungi and complex parasites) demonstrates the importance of this metabolite in regulating host-pathogen interactions. This review will cover lactate secretion and sensing in humans and microbes, and will discuss the existing evidence supporting a role for lactate in pathogen growth and persistence, together with lactate's ability to impact the orchestration of effective immune responses. The ubiquitous presence of lactate in the context of infection and the ability of both host cells and pathogens to sense and respond to it, makes manipulation of lactate a potential novel therapeutic strategy. Here, we will discuss the preliminary research that has been carried out in the context of cancer, autoimmunity and inflammation.

Mitochondrial fusion mediated by mitofusin 1 regulates macrophage mycobactericidal activity by enhancing autophagy

Mitochondria as a highly dynamic organelle continuously changes morphology and position during its life cycle. Mitochondrial dynamics including fission and fusion play a critical role in maintaining functional mitochondria for ATP production, which is directly linked to host defense against Mtb infection. However, how macrophages regulate mitochondrial dynamics during Mycobacterium tuberculosis (Mtb) infection remains elusive. In this study, we found that Mtb infection induced mitochondrial fusion through enhancing the expression of mitofusin 1 (MFN1), which resulted in increased ATP production. Silencing MFN1 inhibited mitochondrial fusion and subsequently reduced ATP production, which, in turn, severely impaired macrophages mycobactericidal activity by inhibiting autophagy. Impairment of mycobactericidal activity and autophagy was replicated using oligomycin, an inhibitor of ATP synthase. In summary, our study revealed MFN1-mediated mitochondrial fusion is essential for macrophages mycobactericidal activity through the regulation of ATP dependent autophagy. MFN1-mediated metabolism pathway might be targets for development of host direct therapy (HDT) strategy against TB.

Type I interferon decreases macrophage energy metabolism during mycobacterial infection

Metabolic reprogramming powers and polarizes macrophage functions, but the nature and regulation of this response during infection with pathogens remain controversial. In this study, we characterize the metabolic and transcriptional responses of murine macrophages to Mycobacterium tuberculosis (Mtb) in order to disentangle the underlying mechanisms. We find that type I interferon (IFN) signaling correlates with the decreased glycolysis and mitochondrial damage that is induced by live, but not killed, Mtb. Macrophages lacking the type I IFN receptor (IFNAR) maintain glycolytic flux and mitochondrial function during Mtb infection in vitro and in vivo. IFNβ itself restrains the glycolytic shift of inflammatory macrophages and initiates mitochondrial stress. We confirm that type I IFN acts upstream of mitochondrial damage using macrophages lacking the protein STING. We suggest that a type I IFN-mitochondrial feedback loop controls macrophage responses to mycobacteria and that this could contribute to pathogenesis across a range of diseases.

Dot/Icm-Dependent Restriction of Legionella pneumophila within Neutrophils

The Dot/Icm type IV secretion system (T4SS) of Legionella pneumophila is essential for lysosomal evasion and permissiveness of macrophages for intracellular proliferation of the pathogen. In contrast, we show that polymorphonuclear cells (PMNs) respond to a functional Dot/Icm system through rapid restriction of L. pneumophila. Specifically, we show that the L. pneumophila T4SS-injected amylase (LamA) effector catalyzes rapid glycogen degradation in the PMNs cytosol, leading to cytosolic hyperglucose. Neutrophils respond through immunometabolic reprogramming that includes upregulated aerobic glycolysis. The PMNs become activated with spatial generation of intracellular reactive oxygen species within the Legionella-containing phagosome (LCP) and fusion of specific and azurophilic granules to the LCP, leading to rapid restriction of L. pneumophila. We conclude that in contrast to macrophages, PMNs respond to a functional Dot/Icm system, and specifically to the effect of the injected amylase effector, through rapid engagement of major microbicidal processes and rapid restriction of the pathogen. IMPORTANCE Legionella pneumophila is commonly found in aquatic environments and resides within a wide variety of amoebal hosts. Upon aerosol transmission to humans, L. pneumophila invades and replicates with alveolar macrophages, causing pneumonia designated Legionnaires' disease. In addition to alveolar macrophages, neutrophils infiltrate into the lungs of infected patients. Unlike alveolar macrophages, neutrophils restrict and kill L. pneumophila, but the mechanisms were previously unclear. Here, we show that the pathogen secretes an amylase (LamA) enzyme that rapidly breakdowns glycogen stores within neutrophils, and this triggers increased glycolysis. Subsequently, the two major killing mechanisms of neutrophils, granule fusion and production of reactive oxygen species, are activated, resulting in rapid killing of L. pneumophila.

Understanding Metabolic Regulation Between Host and Pathogens: New Opportunities for the Development of Improved Therapeutic Strategies Against Mycobacterium tuberculosis Infection

Mycobacterium tuberculosis (Mtb) causes chronic granulomatous lung disease in humans. Recently, novel strategies such as host-directed therapeutics and adjunctive therapies that enhance the effect of existing antibiotics have emerged to better control Mtb infection. Recent advances in understanding the metabolic interplay between host immune cells and pathogens have provided new insights into how their interactions ultimately influence disease outcomes and antibiotic-treatment efficacy. In this review, we describe how metabolic cascades in immune environments and relevant metabolites produced from immune cells during Mtb infection play critical roles in the progression of diseases and induction of anti-Mtb protective immunity. In addition, we introduce how metabolic alterations in Mtb itself can lead to the development of persister cells that are resistant to host immunity and can eventually evade antibiotic attacks. Further understanding of the metabolic link between host cells and Mtb may contribute to not only the prevention of Mtb persister development but also the optimization of host anti-Mtb immunity together with enhanced efficacy of existing antibiotics. Overall, this review highlights novel approaches to improve and develop host-mediated therapeutic strategies against Mtb infection by restoring and switching pathogen-favoring metabolic conditions with host-favoring conditions.

Mycobacterium tuberculosis RipA Dampens TLR4-Mediated Host Protective Response Using a Multi-Pronged Approach Involving Autophagy, Apoptosis, Metabolic Repurposing, and Immune Modulation

Reductive evolution has endowed Mycobacterium tuberculosis (M. tb) with moonlighting in protein functions. We demonstrate that RipA (Rv1477), a peptidoglycan hydrolase, activates the NFκB signaling pathway and elicits the production of pro-inflammatory cytokines, TNF-α, IL-6, and IL-12, through the activation of an innate immune-receptor, toll-like receptor (TLR)4. RipA also induces an enhanced expression of macrophage activation markers MHC-II, CD80, and CD86, suggestive of M1 polarization. RipA harbors LC3 (Microtubule-associated protein 1A/1B-light chain 3) motifs known to be involved in autophagy regulation and indeed alters the levels of autophagy markers LC3BII and P62/SQSTM1 (Sequestosome-1), along with an increase in the ratio of P62/Beclin1, a hallmark of autophagy inhibition. The use of pharmacological agents, rapamycin and bafilomycin A1, reveals that RipA activates PI3K-AKT-mTORC1 signaling cascade that ultimately culminates in the inhibition of autophagy initiating kinase ULK1 (Unc-51 like autophagy activating kinase). This inhibition of autophagy translates into efficient intracellular survival, within macrophages, of recombinant Mycobacterium smegmatis expressing M. tb RipA. RipA, which also localizes into mitochondria, inhibits the production of oxidative phosphorylation enzymes to promote a Warburg-like phenotype in macrophages that favors bacterial replication. Furthermore, RipA also inhibited caspase-dependent programed cell death in macrophages, thus hindering an efficient innate antibacterial response. Collectively, our results highlight the role of an endopeptidase to create a permissive replication niche in host cells by inducing the repression of autophagy and apoptosis, along with metabolic reprogramming, and pointing to the role of RipA in disease pathogenesis.

Lactate Metabolism and Signaling in Tuberculosis and Cancer: A Comparative Review

Infection with Mycobacterium tuberculosis (Mtb) leading to tuberculosis (TB) disease continues to be a major global health challenge. Critical barriers, including but not limited to the development of multi-drug resistance, lack of diagnostic assays that detect patients with latent TB, an effective vaccine that prevents Mtb infection, and infectious and non-infectious comorbidities that complicate active TB, continue to hinder progress toward a TB cure. To complement the ongoing development of new antimicrobial drugs, investigators in the field are exploring the value of host-directed therapies (HDTs). This therapeutic strategy targets the host, rather than Mtb, and is intended to augment host responses to infection such that the host is better equipped to prevent or clear infection and resolve chronic inflammation. Metabolic pathways of immune cells have been identified as promising HDT targets as more metabolites and metabolic pathways have shown to play a role in TB pathogenesis and disease progression. Specifically, this review highlights the potential role of lactate as both an immunomodulatory metabolite and a potentially important signaling molecule during the host response to Mtb infection. While long thought to be an inert end product of primarily glucose metabolism, the cancer research field has discovered the importance of lactate in carcinogenesis and resistance to chemotherapeutic drug treatment. Herein, we discuss similarities between the TB granuloma and tumor microenvironments in the context of lactate metabolism and identify key metabolic and signaling pathways that have been shown to play a role in tumor progression but have yet to be explored within the context of TB. Ultimately, lactate metabolism and signaling could be viable HDT targets for TB; however, critical additional research is needed to better understand the role of lactate at the host-pathogen interface during Mtb infection before adopting this HDT strategy.