HIV compromises Th17 and Th22 immunity in a humanized mouse model of Tuberculosis and HIV co-infection

Tuberculosis (TB) kills an estimated 1–2 million people per year and is the leading cause of death in people with HIV (PWH). The CD4+ T helper (Th) populations play significant roles in protective immunity to Mycobacterium tuberculosis (Mtb), and are also important host cells for HIV proliferation and persistence. Emerging evidence in PWH suggests that Th17 and Th22 cells may be preferentially depleted during HIV infection, an outcome that could pose a risk for Mtb containment during co-infection. We employed our humanized mouse model of co-infection to assess pulmonary and peripheral changes in Th17 and Th22 frequency and function due to infection with HIV, Mtb, or both. As determined with multi-plex ELISA, co-infection with HIV suppressed the cytokine response to Mtb including IL-17A, IL-22, IL-6, and IL-1β. Multi-parameter flow cytometric analysis revealed that Mtb and HIV/Mtb infection led to increased Th17+ cells in lung and decreased Th17+ cells in spleen. Following HIV or HIV/Mtb infection, Th22+ cells were significantly decreased in both lung and spleen. Importantly, HIV preferentially infected Th17 cells compared to Th22 and other Th subpopulations. Greater HIV viral load was also observed in the lung, but not spleen, of animals with Mtb/HIV co-infection compared to those with HIV mono-infection. Overall, these results suggest that HIV may compromise Th22 immunity, and exploit Th17+ cells to promote viral pathogenesis, in the setting of Mtb and HIV co-infection.

Y.B. Martinez-Martinez is supported by Conacyt-I2T2 in Mexico, Contex, and the James W. McLaughlin Fellowship Fund. Grant support was provided by NIH R01AI147948 award to J. Endsley

Effect of HIV status on Th17/IL-17 immune function in subjects undergoing tuberculosis treatment in Kenya

Mycobacterium tuberculosis and HIV remain top global public health concern. Complexities associated with Mtb/HIV coinfections, including in those virally suppressed with anti-retroviral therapy (ART), present significant challenges to efforts to reduce both infections. The pattern of cytokines produced by T helper (Th) lymphocytes plays a central role in susceptibility, relapse and reinfection to TB. To understand how HIV and ART status affects recovery of Th cell effector function, we conducted a prospective study of HIV+ or HIV- subjects from Nairobi, Kenya. Blood samples were taken at start of TB treatment and 5 months after. Cytokine bead array was used to assess human Th cell-derived cytokines isolated from plasma from Nil, TB1 and Mitogen QuantiFERON tubes, including; IL-4, IL-9, IL-10, IL-17A, IL-17F, IL-22, IFN-γ and TNF-α. Intracellular cytokine staining (ICS) of cryopreserved peripheral blood mononuclear cells was also performed to determine changes in baseline numbers of Th1, Th2, Th17, Th22, IL-10+ Th cells, as well as HIV+ Th cells, across treatment groups. Results show reduced plasma IL-9, IFNg and IL-22 activation by mitogen in TB+HIV+ subjects that is independent of ART status, while IL-17A is moderately reduced in TB+HIV+ART- subjects. Cytokine recall to TB1 antigen was observed to be similar across all treatment groups, with the exception that a moderate reduction of IFNg and IL-17A was observed in the TB-HIV+ group. In subjects compliant for ART, ISC analysis revealed greater numbers of HIV+ cells in TB+HIV+, compared to TB-HIV+, groups. These preliminary results identify defects in effector cytokines produced by Th cells that may persist after ART and contribute to poorer TB treatment outcomes in subjects with HIV.

Supported by NIH, NIAID, 1R01AI147948

Differential regulation of macrophage galactose-type lectin (MGL) orthologs by mycobacterial ligands

Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), is responsible for approximately 10 million new infections and 1.5 million deaths each year. Pattern recognition receptors (PRRs) expressed on the surface of macrophages play an important role in orchestrating the immune response to pathogens. Amongst these, the C-type lectin receptors (CLRs) are an important PRR system that is increasingly understood to mediate innate immunity to mycobacteria. We recently described a new anti-bacterial and anti-inflammatory role for the macrophage galactose-type lectin-1 (MGL-1) in a murine model of experimental TB. MGL is a type II CLR that is known to recognize galactose and N-acetylgalactosamine monosaccharides. We observed that exposure to Mtb activated expression of both murine MGL orthologues, MGL-1 and MGL-2. The specific pathogen-associated molecular patterns that activate MGL orthologue transcription, however, have yet to be determined. Here we demonstrate that expression of MGL-1 and MGL-2 are differentially regulated by cytokines, TLR agonists, and mycobacterial ligands. MGL-1 expression is activated by dexamethasone, IL-4, IL-10, and the mycobacterial cell wall glycolipid Trehalose 6,6′-dimycolate. In contrast, MGL-2 expression is activated by TLR2/6 and TLR2/1 agonists and total lipid extracts of mycobacteria. Use of a MyD88 inhibitor further showed that molecular regulation of MGL-1 and MGL-2 transcription, following exposure of macrophages to mycobacteria, is TLR pathway-dependent. These results identify overlapping and unique host immune pathways that differentially activate MGL orthologues following exposure to Mtb and could be targeted through immune modulation.

Coiled Coil Crosslinked Alginate Hydrogels Dampen Macrophage-Driven Inflammation

Alginate hydrogels are widely used for tissue engineering and regenerative medicine due to their excellent biocompatibility. A facile and commonly used strategy to crosslink alginate is the addition of Ca²⁺ that leads to hydrogelation. However, extracellular Ca²⁺ is a secondary messenger in activating inflammasome pathways following physical injury or pathogenic insult, which carries the risk of persistent inflammation and scaffold rejection. Here, we present graft copolymers of charge complementary heterodimeric coiled coil (CC) peptides and alginate that undergo supramolecular self-assembly to form Ca²⁺ free alginate hydrogels. The formation of heterodimeric CCs was confirmed using circular dichroism spectroscopy, and scanning electron microscopy revealed a significant difference in crosslink density and homogeneity between Ca²⁺ and CC crosslinked gels. The resulting hydrogels were self-supporting and display shear-thinning and shear-recovery properties. In response to lipopolysaccharide (LPS) stimulation, peritoneal macrophages and bone marrow-derived dendritic cells cultured in the CC crosslinked gels exhibited a 10-fold reduction in secretion of the proinflammatory cytokine IL-1β compared to Ca²⁺ crosslinked gels. A similar response was also observed in vivo upon peritoneal delivery of Ca²⁺ or CC crosslinked gels. Analysis of peritoneal lavage showed that macrophages in mice injected with Ca²⁺ crosslinked gels display a more inflammatory phenotype compared to macrophages from mice injected with CC crosslinked gels. These results suggest that CC peptides by virtue of their tunable sequence-structure-function relationship and mild gelation conditions are promising alternative crosslinkers for alginate and other biopolymer scaffolds used in tissue engineering.

Dual activity of niclosamide to suppress replication of integrated HIV-1 and Mycobacterium tuberculosis (Beijing)

The human immunodeficiency virus (HIV) pandemic is driving the re-emergence of tuberculosis (TB) as a global health threat, both by increasing the susceptibility of HIV-infected people to infection with Mycobacterium tuberculosis (Mtb), and increasing the rate of emergence of drug-resistant Mtb. There are several other clinical challenges for treatment of co-infected patients including: expense, pill burden, toxicity, and malabsorption that further necessitate the search for new drugs that may be effective against both pathogens simultaneously. The anti-helminthic niclosamide has been shown to have activity against a laboratory strain of Mtb in liquid culture while bacteriostatic activity against non-replicating M. abscessus was also recently described. Here we extend these findings to further demonstrate that niclosamide inhibits mycobacterial growth in infected human macrophages and mediates potent bacteriostatic activity against the virulent Mtb Beijing strain. Importantly, we provide the first evidence that niclosamide inhibits HIV replication in human macrophages and Jurkat T cells through post-integration effects on pro-virus transcription. The dual antiviral and anti-mycobacterial activity was further observed in an in vitro model of HIV and Mtb co-infection using human primary monocyte-derived macrophages. These results support further investigation of niclosamide and derivatives as anti-retroviral/anti-mycobacterial agents that may reduce clinical challenges associated with multi-drug regimens and drug resistance.

8-Hydroxyquinolines are bactericidal against Mycobacterium tuberculosis

There is an urgent need for new treatments effective against Mycobacterium tuberculosis, the causative agent of tuberculosis. The 8-hydroxyquinoline series is a privileged scaffold with anticancer, antifungal, and antibacterial activities. We conducted a structure-activity relationship study of the series regarding its antitubercular activity using 26 analogs. The 8-hydroxyquinolines showed good activity against M. tuberculosis, with minimum inhibitory concentrations (MIC90) of <5 μM for some analogs. Small substitutions at C5 resulted in the most potent activity. Substitutions at C2 generally decreased potency, although a sub-family of 2-styryl-substituted analogs retained activity. Representative compounds demonstrated bactericidal activity against replicating M. tuberculosis with >4 log kill at 10× MIC over 14 days. The majority of the compounds demonstrated cytotoxicity (IC₅₀ of <100 μM). Further development of this series as antitubercular agents should address the cytotoxicity liability. However, the 8-hydroxyquinoline series represents a useful tool for chemical genomics to identify novel targets in M. tuberculosis.

A potent Lassa virus antiviral targets an arenavirus virulence determinant

Arenaviruses are a significant cause of hemorrhagic fever, an often-fatal disease for which there is no approved antiviral therapy. Lassa fever in particular generates high morbidity and mortality in West Africa, where the disease is endemic, and a recent outbreak in Nigeria was larger and more geographically diverse than usual. We are developing LHF-535, a small-molecule viral entry inhibitor that targets the arenavirus envelope glycoprotein, as a therapeutic candidate for Lassa fever and other hemorrhagic fevers of arenavirus origin. Using a lentiviral pseudotype infectivity assay, we determined that LHF-535 had sub-nanomolar potency against the viral envelope glycoproteins from all Lassa virus lineages, with the exception of the glycoprotein from the LP strain from lineage I, which was 100-fold less sensitive than that of other strains. This reduced sensitivity was mediated by a unique amino acid substitution, V434I, in the transmembrane domain of the envelope glycoprotein GP2 subunit. This position corresponds to the attenuation determinant of Candid#1, a live-attenuated Junín virus vaccine strain used to prevent Argentine hemorrhagic fever. Using a virus-yield reduction assay, we determined that LHF-535 potently inhibited Junín virus, but not Candid#1, and the Candid#1 attenuation determinant, F427I, regulated this difference in sensitivity. We also demonstrated that a daily oral dose of LHF-535 at 10 mg/kg protected mice from a lethal dose of Tacaribe virus. Serial passage of Tacaribe virus in LHF-535-treated Vero cells yielded viruses that were resistant to LHF-535, and the majority of drug-resistant viruses exhibited attenuated pathogenesis. These findings provide a framework for the clinical development of LHF-535 as a broad-spectrum inhibitor of arenavirus entry and provide an important context for monitoring the emergence of drug-resistant viruses.

Lassa fever is a viral hemorrhagic fever disease that is transmitted to humans primarily through contact with the urine or feces of infected rodents. The disease is endemic in West Africa, and an unusually large outbreak occurred in Nigeria in early 2018. The case fatality rate was 25% among confirmed cases, underscoring the need for an effective antiviral therapy. Here, we evaluated the small-molecule drug LHF-535, which targets the arenavirus envelope glycoprotein, for broad-spectrum activity against Lassa viruses of different lineages and related arenaviruses that cause hemorrhagic fever diseases in South America. We also selected for LHF-535-resistant viruses and characterized their genotype and phenotype. Using a combination of surrogate systems and wild-type viruses, we determined that all tested Lassa virus strains and New World hemorrhagic fever arenaviruses were sensitive to LHF-535. Sensitivity to the drug was modulated by specific amino acid changes in the viral envelope glycoprotein, and the majority of emerging drug-resistant viruses were attenuated for virulence. Similarly, the live-attenuated vaccine strain for Argentine hemorrhagic fever was also resistant to LHF-535. These findings indicate that LHF-535 targets a viral virulence determinant, the mutation of which may result in the emergence of drug-resistant viruses, but with reduced capacity for virulence.

Construction of an overexpression library for Mycobacterium tuberculosis

There is a pressing need to develop novel anti-tubercular drugs. High-throughput phenotypic screening yields chemical series that inhibit bacterial growth. Target identification for such series is challenging, but necessary for optimization of target engagement and the development of series into clinical drugs. We constructed a library of recombinant Mycobacterium tuberculosis strains each expressing a single protein from an inducible promoter as a tool for target identification. The library of 1733 clones was arrayed in 96-well plates for rapid screening and monitoring growth. The library contains the majority of the annotated essential genes as well as genes involved in cell wall and fatty acid biosynthesis, virulence factors, regulatory proteins, efflux, and respiration pathways. We evaluated the growth kinetics and plasmid stability over three passages for each clone in the library. We determined expression levels (mRNA and/or protein) in 396 selected clones. We screened the entire library and identified the Alr-expressing clone as the only recombinant strain, which grew in the presence of d-cycloserine (DCS). We confirmed that the Alr-expressing clone was resistant to DCS (7-fold shift in minimum inhibitory concentration). The library represents a new tool that can be used to screen for compound resistance and other phenotypes.

In Vitro Evaluation of Novel Nitazoxanide Derivatives against Mycobacterium tuberculosis

Nitazoxanide has antiparasitic and antibiotic activities including activity against Mycobacterium tuberculosis. We prepared and evaluated a set of its analogues to determine the structure-activity relationship, and identified several amide- and urea-based analogues with low micromolar activity against M. tuberculosis in vitro. Pharmacokinetics in the rat suggested a path forward to obtain bioavailable compounds. The series had a good microbiological profile with bactericidal activity in vitro against replicating and nonreplicating M. tuberculosis. Analogues had limited activity against other Gram-positive bacteria but no activity against Gram-negative bacteria. Our studies identified the key liability in this series as cytotoxicity. Future work concentrating on identifying the target(s) could assist in removing activity against eukaryotic cells.

A Target-Based Whole Cell Screen Approach To Identify Potential Inhibitors of Mycobacterium tuberculosis Signal Peptidase

The general secretion (Sec) pathway is a conserved essential pathway in bacteria and is the primary route of protein export across the cytoplasmic membrane. During protein export, the signal peptidase LepB catalyzes the cleavage of the signal peptide and subsequent release of mature proteins into the extracellular space. We developed a target-based whole cell assay to screen for potential inhibitors of LepB, the sole signal peptidase in Mycobacterium tuberculosis, using a strain engineered to underexpress LepB (LepB-UE). We screened 72,000 compounds against both the Lep-UE and wild-type (wt) strains. We identified the phenylhydrazone (PHY) series as having higher activity against the LepB-UE strain. We conducted a limited structure-activity relationship determination around a representative PHY compound with differential activity (MICs of 3.0 μM against the LepB-UE strain and 18 μM against the wt); several analogues were less potent against the LepB overexpressing strain. A number of chemical modifications around the hydrazone moiety resulted in improved potency. Inhibition of LepB activity was observed for a number of compounds in a biochemical assay using cell membrane fraction derived from M. tuberculosis. Compounds did not increase cell permeability, dissipate membrane potential, or inhibit an unrelated mycobacterial enzyme, suggesting a specific mode of action related to the LepB secretory mechanism.

Optimization and Evaluation of 5-Styryl-Oxathiazol-2-one Mycobacterium tuberculosis Proteasome Inhibitors as Potential Antitubercular Agents

This is the first report of 5-styryl-oxathiazol-2-ones as inhibitors of the Mycobacterium tuberculosis (Mtb) proteasome. As part of the study, the structure-activity relationship of oxathiazolones as Mtb proteasome inhibitors has been investigated. Furthermore, the prepared compounds displayed a good selectivity profile for Mtb compared to the human proteasome. The 5-styryl-oxathiazol-2-one inhibitors identified showed little activity against replicating Mtb, but were rapidly bactericidal against nonreplicating bacteria. (E)-5-(4-Chlorostyryl)-1,3,4-oxathiazol-2-one) was most effective, reducing the colony-forming units (CFU)/mL below the detection limit in only seven days at all concentrations tested. The results suggest that this new class of Mtb proteasome inhibitors has the potential to be further developed into novel antitubercular agents for synergistic combination therapies with existing drugs.

Synthesis and anti-tubercular activity of 3-substituted benzo[b]thiophene-1,1-dioxides

We demonstrated that the 3-substituted benzothiophene-1,1-dioxide class of compounds are effective inhibitors of Mycobacterium tuberculosis growth under aerobic conditions. We examined substitution at the C-3 position of the benzothiophene-1,1-dioxide series systematically to delineate structure–activity relationships influencing potency and cytotoxicity. Compounds were tested for inhibitory activity against virulent M. tuberculosis and eukaryotic cells. The tetrazole substituent was most potent, with a minimum inhibitory concentration (MIC) of 2.6 µM. However, cytotoxicity was noted with even more potency (Vero cell TC50 = 0.1 µM). Oxadiazoles had good anti-tubercular activity (MICs of 3–8 µM), but imidazoles, thiadiazoles and thiazoles had little activity. Cytotoxicity did not track with anti-tubercular activity, suggesting different targets or mode of action between bacterial and eukaryotic cells. However, we were unable to derive analogs without cytotoxicity; all compounds synthesized were cytotoxic (TC50 of 0.1–5 µM). We conclude that cytotoxicity is a liability in this series precluding it from further development. However, the series has potent anti-tubercular activity and future efforts towards identifying the mode of action could result in the identification of novel drug targets.

Identification of the translational start site of codon-optimized mCherry in Mycobacterium tuberculosis

BACKGROUND

Fluorescent proteins are used widely as reporter genes in many organisms. We previously codon-optimized mCherry for Mycobacterium tuberculosis and generated expression constructs with high level expression in mycobacteria with multiple uses in vitro and in vivo. However, little is known about the expression of fluorescent proteins in mycobacteria and the translational start codon for mCherry has not been experimentally determined.

RESULTS

We determined the translational start site for functional (fluorescent) mCherry in mycobacteria. Several potential translational start codons were identified; introduction of downstream stop codons by mutagenesis was used to determine which start codon was utilized in the bacterial cells. Fluorescent protein was expressed from a construct which would allow translation of a protein of 226 amino acids or a protein of 235 amino acids. No fluorescence was seen when a construct which could give rise to a protein of 219 amino acids was used. Similar results were obtained in mycobacteria and in Escherichia coli. Western blotting confirmed that mCherry was expressed from the constructs encoding 235 or 226 amino acids, but not from the plasmid encoding 219 amino acids. N-terminal sequencing and mass determination confirmed that the mature protein was 226 amino acids and commenced with the amino acid sequence AIIKE.

CONCLUSION

We conclude that mCherry is expressed in M. tuberculosis as a smaller protein than expected lacking the GFP-derived N-terminal sequence designed to allow efficient fusions.