First-in-human phase 1 trial evaluating safety, pharmacokinetics, and pharmacodynamics of NLRP3 inflammasome inhibitor, GDC-2394, in healthy volunteers

Inappropriate and chronic activation of the cytosolic NOD-, LRR-, and pyrin domain-containing 3 (NLRP3) inflammasome, a key component of innate immunity, likely underlies several inflammatory diseases, including coronary artery disease. This first-in-human phase I trial evaluated safety, pharmacokinetics (PKs), and pharmacodynamics (PDs) of oral, single (150-1800 mg) and multiple (300 or 900 mg twice daily for 7 days) ascending doses (SADs and MADs) of GDC-2394, a small-molecule inhibitor of NLRP3, versus placebo in healthy volunteers. The study also assessed the food effect on GDC-2394 and its CYP3A4 induction potential in food-effect (FE) and drug-drug interaction (DDI) stages, respectively. Although GDC-2394 was adequately tolerated in the SAD, MAD, and FE cohorts, two participants in the DDI stage experienced grade 4 drug-induced liver injury (DILI) deemed related to treatment, but unrelated to a PK drug interaction, leading to halting of the trial. Both participants experiencing severe DILI recovered within 3 months. Oral GDC-2394 was rapidly absorbed; exposure increased in an approximately dose-proportional manner with low-to-moderate intersubject variability. The mean terminal half-life ranged from 4.1 to 8.6 h. Minimal accumulation was observed with multiple dosing. A high-fat meal led to delays in time to maximum concentration and minor decreases in total exposure and maximum plasma concentration. GDC-2394 had minimal CYP3A4 induction potential with the sensitive CYP3A4 substrate, midazolam. Exploratory ex vivo whole-blood stimulation assays showed rapid, reversible, and near-complete inhibition of the selected PD biomarkers, IL-1β and IL-18, across all tested doses. Despite favorable PK and target engagement PD, the GDC-2394 safety profile precludes its further development.

The IFN-inducible GTPase IRGB10 regulates viral replication and inflammasome activation during influenza A virus infection in mice

The upregulation of interferon (IFN)-inducible GTPases in response to pathogenic insults is vital to host defense against many bacterial, fungal, and viral pathogens. Several IFN-inducible GTPases play key roles in mediating inflammasome activation and providing host protection after bacterial or fungal infections, though their role in inflammasome activation after viral infection is less clear. Among the IFN-inducible GTPases, the expression of immunity-related GTPases (IRGs) varies widely across species for unknown reasons. Here, we report that IRGB10, but not IRGM1, IRGM2, or IRGM3, is required for NLRP3 inflammasome activation in response to influenza A virus (IAV) infection in mice. While IRGB10 functions to release inflammasome ligands in the context of bacterial and fungal infections, we found that IRGB10 facilitates endosomal maturation and nuclear translocation of IAV, thereby regulating viral replication. Corresponding with our in vitro results, we found that Irgb10^-/- mice were more resistant to IAV-induced mortality than WT mice. The results of our study demonstrate a detrimental role of IRGB10 in host immunity in response to IAV and a novel function of IRGB10, but not IRGMs, in promoting viral translocation into the nucleus.

IRF8 Regulates Transcription of Naips for NLRC4 Inflammasome Activation

Inflammasome activation is critical for host defenses against various microbial infections. Activation of the NLRC4 inflammasome requires detection of flagellin or type III secretion system (T3SS) components by NLR family apoptosis inhibitory proteins (NAIPs); yet how this pathway is regulated is unknown. Here, we found that interferon regulatory factor 8 (IRF8) is required for optimal activation of the NLRC4 inflammasome in bone-marrow-derived macrophages infected with Salmonella Typhimurium, Burkholderia thailandensis, or Pseudomonas aeruginosa but is dispensable for activation of the canonical and non-canonical NLRP3, AIM2, and Pyrin inflammasomes. IRF8 governs the transcription of Naips to allow detection of flagellin or T3SS proteins to mediate NLRC4 inflammasome activation. Furthermore, we found that IRF8 confers protection against bacterial infection in vivo, owing to its role in inflammasome-dependent cytokine production and pyroptosis. Altogether, our findings suggest that IRF8 is a critical regulator of NAIPs and NLRC4 inflammasome activation for defense against bacterial infection.

Development of a novel tool for Francisella tularensis immunology (MUC1P.915)

Tularemia, an acute infection caused by Francisella tularensis, can manifest in various forms. Pulmonary tularemia developed after an aerosol exposure to the bacterium has a high risk of mortality in unvaccinated individuals. Therefore, development of a vaccine is of critcal importance but is hampered by a relative lack of understanding of the protective adaptive immune response. Absence of immunological tools to study protective T cell responses has been one of the key hurdles in establishing the profile of immune responses to F. tularensis. We have developed a novel F. tularensis LVS, which constitutively expresses a vgrG-OVA fusion protein containing the epitopes OVA257-264 and OVA323-339. This will allow researchers to study antigen-specifc T cell responses during infecton by F. tularensis. Robust expression of this construct was confirmed by immunoblot from bacterial lysates. An additional chromosomally-integrated expression construct is also being generated for more stable expression throughout in vivo infections. This new tool will allow us to study the memory response to Francisella vaccinaton in ways previously difficult to do. Inital experiments are underway using OT-I and OT-II transgenic mice to study the pathogen-specifc response to Francisella following vaccinaton by the intradermal and intranasal routes in order to determine the ideal conditons for improving survival after pulmonary challenge, which remains a concern in a potental bioterror atack.

Caspase-1-independent interleukin-1β is required for clearance of bordetella pertussis infections and whole-cell vaccine-mediated immunity (INM6P.413)

Whooping cough remains a significant disease worldwide and its re-emergence in highly vaccinated populations has been attributed to a combination of imperfect vaccines and evolution of the pathogen. The focus of this study was to examine the role of IL-1α/β and the inflammasome in generation of the interleukin-1 (IL-1) response, which is required for the clearance of B. pertussis. We show that IL-1β but not IL-1α is required for mediating the clearance of B. pertussis from the lungs of mice. We further found that IL-1β and IL-1R deficient mice have normal but persistent levels of inflammation, characterized by immune cell infiltration, with significantly increased IFNγ and a normal IL-17A response during B. pertussis infection. Contrary to expectations, the cleavage of precursor IL-1β to its mature form did not require caspase-1 during primary infections within the lung despite being required by bone marrow-derived macrophages exposed to live bacteria. We also found that the caspase-1 inflammasome was not required for protective immunity against a B. pertussis challenge following vaccination with heat-killed whole cell B. pertussis, despite IL-1R signaling being required. These findings demonstrate that caspase-1-independent host factors are involved in the processing of protective IL-1β responses that are critical for bacterial clearance and vaccine-mediated immunity.

Toll-like receptor 4 limits transmission of Bordetella bronchiseptica

Transmission of pathogens has been notoriously difficult to study under laboratory conditions leaving knowledge gaps regarding how bacterial factors and host immune components affect the spread of infections between hosts. We describe the development of a mouse model of transmission of a natural pathogen, Bordetella bronchiseptica, and its use to assess the impact of host immune functions. Although B. bronchiseptica transmits poorly between wild-type mice and mice lacking other immune components, it transmits efficiently between mice deficient in Toll-Like Receptor 4 (TLR4). TLR4-mutant mice were more susceptible to initial colonization, and poorly controlled pathogen growth and shedding. Heavy neutrophil infiltration distinguished TLR4-deficient responses, and neutrophil depletion did not affect respiratory CFU load, but decreased bacterial shedding. The effect of TLR4 response on transmission may explain the extensive variation in TLR4 agonist potency observed among closely related subspecies of Bordetella. This transmission model will enable mechanistic studies of how pathogens spread from one host to another, the defining feature of infectious disease.

Endobronchial valve migration

Endobronchial valves are increasingly used as a treatment modality as a less invasive alternative to lung volume reduction surgery in patients with severe emphysema. Endobronchial valves have also been used to treat patients with persistent pulmonary air leaks and those with bronchopleural fistulae. We report a case of a 61-year-old male with severe bullous emphysema. Following video-assisted thoracoscopic surgery and giant bullectomy, he had a persistent air leak. We inserted two endobronchial valves (in the lingular lobe and the anterior segment of the upper lobe) and the air leak ceased immediately. However, over the subsequent 5 months following the insertion of the endobronchial valves, the patient suffered recurrent chest infections and the endobronchial valves were found to have migrated to the orifice of the basal segment of the left lower lobe and the orifice of the basal segments of the right lower lobe.

Refractory periodontitis: mixed infection with Bacteroides gingivalis and other unusual Bacteroides species. A case report

Host immune response and the predominant subgingival microflora were evaluated in a 47-year-old male exhibiting severe, recurrent periodontitis. The patient's neutrophils were chemotactically elevated but other functions were within normal limits. Significantly, Bacteroides gingivalis and Bacteroides zoogleoformans constituted 80% of the cultivable microflora and total cell count in subgingival plaque. The remainder of the cultivable microbiota was comprised of Fusobacterium nucleatum and Haemophillis aprophillis. The present study provides additional evidence for an association between B. gingivalis and severe, recurrent periodontal disease.