Matthew B. Huante

A Humanized Mouse Model of Tuberculosis

Mycobacterium tuberculosis (M.tb) is the second leading infectious cause of death worldwide and the primary cause of death in people living with HIV/AIDS. There are several excellent animal models employed to study tuberculosis (TB), but many have limitations for reproducing human pathology and none are amenable to the direct study of HIV/M.tb co-infection. The humanized mouse has been increasingly employed to explore HIV infection and other pathogens where animal models are limiting. Our goal was to develop a small animal model of M.tb infection using the bone marrow, liver, thymus (BLT) humanized mouse. NOD-SCID/γc null mice were engrafted with human fetal liver and thymus tissue, and supplemented with CD34+ fetal liver cells. Excellent reconstitution, as measured by expression of the human CD45 pan leukocyte marker by peripheral blood populations, was observed at 12 weeks after engraftment. Human T cells (CD3, CD4, CD8), as well as natural killer cells and monocyte/macrophages were all observed within the human leukocyte (CD45+) population. Importantly, human T cells were functionally competent as determined by proliferative capacity and effector molecule (e.g. IFN-γ, granulysin, perforin) expression in response to positive stimuli. Animals infected intranasally with M.tb had progressive bacterial infection in the lung and dissemination to spleen and liver from 2–8 weeks post infection. Sites of infection in the lung were characterized by the formation of organized granulomatous lesions, caseous necrosis, bronchial obstruction, and crystallization of cholesterol deposits. Human T cells were distributed throughout the lung, liver, and spleen at sites of inflammation and bacterial growth and were organized to the periphery of granulomas. These preliminary results demonstrate the potential to use the humanized mouse as a model of experimental TB.

Characterization of an F1 Deletion Mutant of Yersinia pestis CO92, Pathogenic Role of F1 Antigen in Bubonic and Pneumonic Plague, and Evaluation of Sensitivity and Specificity of F1 Antigen Capture-Based Dipsticks

ABSTRACT We evaluated two commercial F1 antigen capture-based immunochromatographic dipsticks, Yersinia Pestis (F1) Smart II and Plague BioThreat Alert test strips, in detecting plague bacilli by using whole-blood samples from mice experimentally infected with Yersinia pestis CO92. To assess the specificities of these dipsticks, an in-frame F1-deficient mutant of CO92 (Δcaf) was generated by homologous recombination and used as a negative control. Based on genetic, antigenic/immunologic, and electron microscopic analyses, the Δcaf mutant was devoid of a capsule. The growth rate of the Δcaf mutant generally was similar to that of the wild-type (WT) bacterium at both 26 and 37°C, although the mutants growth dropped slightly during the late phase at 37°C. The Δcaf mutant was as virulent as WT CO92 in the pneumonic plague mouse model; however, it was attenuated in developing bubonic plague. Both dipsticks had similar sensitivities, requiring a minimum of 0.5 μg/ml of purified F1 antigen or 1 × 105 to 5 × 105 CFU/ml of WT CO92 for positive results, while the blood samples were negative for up to 1 × 108 CFU/ml of the Δcaf mutant. Our studies demonstrated the diagnostic potential of two plague dipsticks in detecting capsular-positive strains of Y. pestis in bubonic and pneumonic plague.

Antibacterial role for natural killer cells in host defense to Bacillus anthracis.

ABSTRACT Natural killer (NK) cells have innate antibacterial activity that could be targeted for clinical interventions for infectious disease caused by naturally occurring or weaponized bacterial pathogens. To determine a potential role for NK cells in immunity to Bacillus anthracis, we utilized primary human and murine NK cells, in vitro assays, and in vivo NK cell depletion in a murine model of inhalational anthrax. Our results demonstrate potent antibacterial activity by human NK cells against B. anthracis bacilli within infected autologous monocytes. Surprisingly, NK cells also mediate moderate antibacterial effects on extracellular vegetative bacilli but do not have activity against extracellular or intracellular spores. The immunosuppressive anthrax lethal toxin impairs NK gamma interferon (IFN-γ) expression, but neither lethal nor edema toxin significantly alters the viability or cytotoxic effector function of NK cells. Compared to human NK cells, murine NK cells have a similar, though less potent, activity against intracellular and extracellular B. anthracis. The in vivo depletion of murine NK cells does not alter animal survival following intranasal infection with B. anthracis spores in our studies but significantly increases the bacterial load in the blood of infected animals. Our studies demonstrate that NK cells participate in the innate immune response against B. anthracis and suggest that immune modulation to augment NK cell function in early stages of anthrax should be further explored in animal models as a clinical intervention strategy.

Pulmonary Tuberculosis in Humanized Mice Infected with HIV-1.

Co-infection with HIV increases the morbidity and mortality associated with tuberculosis due to multiple factors including a poorly understood microbial synergy. We developed a novel small animal model of co-infection in the humanized mouse to investigate how HIV infection disrupts pulmonary containment of Mtb. Following dual infection, HIV-infected cells were localized to sites of Mtb-driven inflammation and mycobacterial replication in the lung. Consistent with disease in human subjects, we observed increased mycobacterial burden, loss of granuloma structure, and increased progression of TB disease, due to HIV co-infection. Importantly, we observed an HIV-dependent pro-inflammatory cytokine signature (IL-1β, IL-6, TNFα, and IL-8), neutrophil accumulation, and greater lung pathology in the Mtb-co-infected lung. These results suggest that in the early stages of acute co-infection in the humanized mouse, infection with HIV exacerbates the pro-inflammatory response to pulmonary Mtb, leading to poorly formed granulomas, more severe lung pathology, and increased mycobacterial burden and dissemination.

N-Glycans on the Rift Valley Fever Virus Envelope Glycoproteins Gn and Gc Redundantly Support Viral Infection via DC-SIGN

Rift Valley fever is a mosquito-transmitted, zoonotic disease that infects humans and ruminants. Dendritic cell specific intercellular adhesion molecule 3 (ICAM-3) grabbing non-integrin (DC-SIGN) acts as a receptor for members of the phlebovirus genus. The Rift Valley fever virus (RVFV) glycoproteins (Gn/Gc) encode five putative N-glycan sequons (asparagine (N)–any amino acid (X)–serine (S)/threonine (T)) at positions: N438 (Gn), and N794, N829, N1035, and N1077 (Gc). The N-glycosylation profile and significance in viral infection via DC-SIGN have not been elucidated. Gc N-glycosylation was first evaluated by using Gc asparagine (N) to glutamine (Q) mutants. Subsequently, we generated a series of recombinant RVFV MP-12 strain mutants, which encode N-to-Q mutations, and the infectivity of each mutant in Jurkat cells stably expressing DC-SIGN was evaluated. Results showed that Gc N794, N1035, and N1077 were N-glycosylated but N829 was not. Gc N1077 was heterogeneously N-glycosylated. RVFV Gc made two distinct N-glycoforms: “Gc-large” and “Gc-small”, and N1077 was responsible for “Gc-large” band. RVFV showed increased infection of cells expressing DC-SIGN compared to cells lacking DC-SIGN. Infection via DC-SIGN was increased in the presence of either Gn N438 or Gc N1077. Our study showed that N-glycans on the Gc and Gn surface glycoproteins redundantly support RVFV infection via DC-SIGN.

Activation of NK cell granulysin by mycobacteria and IL-15 is differentially affected by HIV

NK cells play an important role in innate immunity to mycobacteria and are a significant source of the bactericidal effector molecule granulysin. Defects in NK cells have been described in HIV-infected patients, though mechanistic studies have focused on effector molecules relevant to anti-viral, and not anti-bacterial, function. Here we used primary NK cells from healthy human donors and an in vitro system to identify the phenotype of granulysin expressing NK cells, characterize activation stimuli that regulate granulysin, and to study the immediate effects of HIV on innate activation of NK cell granulysin expression. We observe that granulysin expression is co-associated with cytotoxicity receptors (NKp46, NKG2D) known to have important function in the cytotoxic response to M.tb-infected macrophages. Granulysin expression is significantly increased following exposure to IL-15 or Mycobacterium bovis BCG, but in contrast to our previous findings with CD8(+)T cells, expression is weakly activated by IL-21. Infection of PBMC with HIV-1 suppresses NK cell induction of granulysin by IL-15, but does not impair activation by BCG. These effects of HIV-1 are associated with reduced STAT5 phosphorylation in the IL-15 activated signaling cascade. These observations suggest that HIV may impair the anti-bacterial function of NK cells and have implications for clinical use of IL-15 to augment innate cell mediated immunity in HIV+ patients.

Mycobacterium tuberculosis-specific CD8+T cell recall in convalescing TB subjects with HIV co-infection

Memory T cell populations recover following phase I chemotherapy for tuberculosis (TB) and augment the effectiveness of antibiotics during the continuation phase of treatment. For those with human immunodeficiency virus (HIV), the CD8(+)T cells may have an especially important role in host defense to Mycobacterium tuberculosis (M.tb) as CD4(+)T cell function and/or numbers decline. Here we performed a preliminary study to investigate the impact of HIV infection status on CD8(+)T cell effector function during the convalescent TB period. Peripheral blood samples from convalescent HIV(+) and HIV(-) TB subjects were used to determine CD4(+)T cell count and monitor antigen-specific CD8(+) T cell activation of effector function (lymphoproliferation, IFN-γ, granulysin) in response to M.tb antigen. Our preliminary results suggest that HIV co-infection is associated with moderate suppression of the M.tb-specific memory CD8(+)T cell compartment in many subjects convalescent for TB. Interestingly, highly activated CD8(+)T cells were observed in recall experiments using peripheral blood from several HIV+ subjects that had low (<200 cells/mm(3)) CD4(+)T cell counts. Further investigation may provide important information for development of novel approaches to target M.tb-specific CD8(+)T cell memory to protect against TB in HIV-endemic regions.

Contribution of Human Lung Parenchyma and Leukocyte Influx to Oxidative Stress and Immune System-Mediated Pathology following Nipah Virus Infection

ABSTRACT Nipah virus (NiV) is a zoonotic emerging paramyxovirus that can cause fatal respiratory illness or encephalitis in humans. Despite many efforts, the molecular mechanisms of NiV-induced acute lung injury (ALI) remain unclear. We previously showed that NiV replicates to high titers in human lung grafts in NOD-SCID/γ mice, resulting in a robust inflammatory response. Interestingly, these mice can undergo human immune system reconstitution by the bone marrow, liver, and thymus (BLT) reconstitution method, in addition to lung tissue engraftment, giving altogether a realistic model to study human respiratory viral infections. Here, we characterized NiV Bangladesh strain (NiV-B) infection of human lung grafts from human immune system-reconstituted mice in order to identify the overall effect of immune cells on NiV pathogenesis of the lung. We show that NiV-B replicated to high titers in human lung grafts and caused similar cytopathic effects irrespective of the presence of human leukocytes in mice. However, the human immune system interfered with virus spread across lung grafts, responded to infection by leukocyte migration to small airways and alveoli of the lung grafts, and accelerated oxidative stress in lung grafts. In addition, the presence of human leukocytes increased the expression of cytokines and chemokines that regulate inflammatory influx to sites of infection and tissue damage. These results advance our understanding of how the immune system limits NiV dissemination and contributes to ALI and inform efforts to identify therapeutic targets. IMPORTANCE Nipah virus (NiV) is an emerging paramyxovirus that can cause a lethal respiratory and neurological disease in humans. Only limited data are available on NiV pathogenesis in the human lung, and the relative contribution of the innate immune response and NiV to acute lung injury (ALI) is still unknown. Using human lung grafts in a human immune system-reconstituted mouse model, we showed that the NiV Bangladesh strain induced cytopathic lesions in lung grafts similar to those described in patients irrespective of the donor origin or the presence of leukocytes. However, the human immune system interfered with virus spread, responded to infection by leukocyte infiltration in the small airways and alveolar area, induced oxidative stress, and triggered the production of cytokines and chemokines that regulate inflammatory influx by leukocytes in response to infection. Understanding how leukocytes interact with NiV and cause ALI in human lung xenografts is crucial for identifying therapeutic targets.

Differential inflammasome activation signatures following intracellular infection of human macrophages with Mycobacterium bovis BCG or Trypanosoma cruzi

Pathogens frequently exploit or evade inflammasome activation in order to survive and proliferate. Alternatively, inadequate inflammasome activation by attenuated microorganisms or adjuvanted subunit vaccines may contribute to poor longevity of protection. To further understand these pathways, we determined the differential inflammasome transcriptome of human THP monocyte-derived macrophages in response to Mycobacterium bovis BCG, as compared to LPS or Trypanosoma cruzi. The results identify the highly specific innate recognition programs associated with inflammasome activation by human macrophages exposed to these microbial stimuli. BCG, T. cruzi, and LPS strongly induced expression of both unique and overlapping genes downstream of TLR signaling pathways including cytokines and chemokines that mediate inflammation and regulate cell death pathways. Compared to LPS, BCG failed to directly activate anti-apoptotic molecules and multiple NLR and inflammasome complex components including caspase-1, and actively repressed important signaling intermediates in AP-1 and NFκB transcription factor pathways. Both BCG and T. cruzi repressed expression of TXNIP, an anti-oxidant inhibitor that recruits caspase-1 to the NLRP3 inflammasome, while T. cruzi infection uniquely failed to activate TNF-α. These results identify unique pathogen specific strategies to activate inflammation and modulate cell death that may drive inflammatory outcomes and suggest avenues of investigation to optimize host immunity.

Nanoscale Peptide Self-assemblies Boost BCG-primed Cellular Immunity Against Mycobacterium tuberculosis

Bacillus Calmette-Guerin (BCG) is the only vaccine against TB and has limited protection efficacy, which wanes past adolescence. Multifunctional CD8+ T cells (IFN-γ+/TNF-α+/IL-2+) are associated with lower reactivation risk and enhanced control of active Mtb infection. Since boosting with BCG is contraindicated, booster vaccines that augment T cell immunity in the lungs of BCG-vaccinated individuals are urgently needed. We developed a vaccination strategy based on self-assembling peptide nanofibers presenting Mtb-specific CD8+ or CD4+ T cell epitopes that induce high frequency and antigen-specific effector memory T cells producing IFN-γ and IL-2. Intranasal immunization with peptide nanofibers was well tolerated in mice leading to increased antigen-specific CD8+ T cell population in the lungs. Co-assembled nanofibers of CD8+ T cell epitopes and toll-like receptor 2 (TLR2) agonists induced a 8-fold expansion in multifunctional CD8+ T cell populations in the lungs of vaccinated mice. Aerosol challenge with Mtb in BCG-primed and nanofiber-boosted mice provided an additional 0.5-log CFU reduction in lung bacterial load and indicating enhanced protection compared to BCG alone. Together, these data suggest that heterologous prime-boost with BCG and peptide nanofiber vaccines induces cell mediated immunity in the lung, reduces bacterial burden, and is a potentially safer alternative for boosting BCG-primed immunity.