Stage-specific innate immune recognition of Aspergillus fumigatus and modulation by echinocandin drugs

CAR T cells targeting Aspergillus fumigatus are effective at treating invasive pulmonary aspergillosis in preclinical models

Aspergillus fumigatus is a ubiquitous mold that can cause severe infections in immunocompromised patients, typically manifesting as invasive pulmonary aspergillosis (IPA). Adaptive and innate immune cells that respond to A. fumigatus are present in the endogenous repertoire of patients with IPA but are infrequent and cannot be consistently isolated and expanded for adoptive immunotherapy. Therefore, we gene-engineered A. fumigatus-specific chimeric antigen receptor (Af-CAR) T cells and demonstrate their ability to confer antifungal reactivity in preclinical models in vitro and in vivo. We generated a CAR targeting domain AB90-E8 that recognizes a conserved protein antigen in the cell wall of A. fumigatus hyphae. T cells expressing the Af-CAR recognized A. fumigatus strains and clinical isolates and exerted a direct antifungal effect against A. fumigatus hyphae. In particular, CD8⁺ Af-CAR T cells released perforin and granzyme B and damaged A. fumigatus hyphae. CD8⁺ and CD4⁺ Af-CAR T cells produced cytokines that activated macrophages to potentiate the antifungal effect. In an in vivo model of IPA in immunodeficient mice, CD8⁺ Af-CAR T cells localized to the site of infection, engaged innate immune cells, and reduced fungal burden in the lung. Adoptive transfer of CD8⁺ Af-CAR T cells conferred greater antifungal efficacy compared to CD4⁺ Af-CAR T cells and an improvement in overall survival. Together, our study illustrates the potential of gene-engineered T cells to treat aggressive infectious diseases that are difficult to control with conventional antimicrobial therapy and support the clinical development of Af-CAR T cell therapy to treat IPA.

Analysis of the in vitro activity of human neutrophils against Aspergillus fumigatus in presence of antifungal and immunosuppressive agents

Neutrophils are essential in the first line defense against moulds. This in vitro study assessed different neutrophil effector mechanisms in the presence of clinically relevant antifungal and immunosuppressive agents. Therapeutic concentrations of liposomal amphotericin B led to reduced IL-8 and oxidative burst response to the synthetic stimulus PMA, whereas no major alterations of oxidative burst, phagocytosis, or cytokine response to germinated stages of Aspergillus fumigatus and no supra-additive effects of antifungal and immunosuppressive drugs were observed. Conventional and liposomal amphotericin B as well as voriconazole, however, led to reduced neutrophil extracellular trap formation in response to A. fumigatus germ tubes.

Precision medicine for hepatocelluar carcinoma using molecular pattern diagnostics: results from a preclinical pilot study

The aim of this study was to design a road map for personalizing cancer therapy in hepatocellular carcinoma (HCC) by using molecular pattern diagnostics. As an exploratory study, we investigated molecular patterns of tissues of two tumors from individual HCC patients, which in previous experiments had shown contrasting reactions to the phase 2 transforming growth factor beta receptor 1 inhibitor galunisertib. Cancer-driving molecular patterns encompass – inter alias – altered transcription profiles and somatic mutations in coding regions differentiating tumors from their respective peritumoral tissues and from each other. Massive analysis of cDNA ends and all-exome sequencing demonstrate a highly divergent transcriptional and mutational landscape, respectively, for the two tumors, that offers potential explanations for the tumors contrasting responses to galunisertib. Molecular pattern diagnostics (MPDs) suggest alternative, individual-tumor-specific therapies, which in both cases deviate from the standard sorafenib treatment and from each other. Suggested personalized therapies use kinase inhibitors and immune-focused drugs as well as low-toxicity natural compounds identified using an advanced bioinformatics routine included in the MPD protocol. The MPD pipeline we describe here for the prediction of suitable drugs for treatment of two contrasting HCCs may serve as a blueprint for the design of therapies for various types of cancer.

Deciphering chemokine properties by a hybrid agent-based model of Aspergillus fumigatus infection in human alveoli

The ubiquitous airborne fungal pathogen Aspergillus fumigatus is inhaled by humans every day. In the lung, it is able to quickly adapt to the humid environment and, if not removed within a time frame of 4–8 h, the pathogen may cause damage by germination and invasive growth. Applying a to-scale agent-based model of human alveoli to simulate early A. fumigatus infection under physiological conditions, we recently demonstrated that alveolar macrophages require chemotactic cues to accomplish the task of pathogen detection within the aforementioned time frame. The objective of this study is to specify our general prediction on the as yet unidentified chemokine by a quantitative analysis of its expected properties, such as the diffusion coefficient and the rates of secretion and degradation. To this end, the rule-based implementation of chemokine diffusion in the initial agent-based model is revised by numerically solving the spatio-temporal reaction-diffusion equation in the complex structure of the alveolus. In this hybrid agent-based model, alveolar macrophages are represented as migrating agents that are coupled to the interactive layer of diffusing molecule concentrations by the kinetics of chemokine receptor binding, internalization and re-expression. Performing simulations for more than a million virtual infection scenarios, we find that the ratio of secretion rate to the diffusion coefficient is the main indicator for the success of pathogen detection. Moreover, a subdivision of the parameter space into regimes of successful and unsuccessful parameter combination by this ratio is specific for values of the migration speed and the directional persistence time of alveolar macrophages, but depends only weakly on chemokine degradation rates.

Fungal cell wall dynamics and infection site microenvironments: signal integration and infection outcome

Upon entrance into the host, fungi encounter a myriad of host effector products and microenvironments that they sense and adapt to for survival. Alterations of the structure and composition of the cell wall is a major fungal adaptation mechanism to evade these environments. Here we discuss recent findings of host-microenvironmental induced fungal cell wall changes, including structure, composition, and protein content, and their effects on host immune responses. A take home message from these recent studies is an emerging understanding of how integration of multiple signals, of both fungal and host responses to dynamic infection site microenvironments, determines outcomes of infection. A challenge moving forward is to further understand these mechanisms and harness them for therapeutic benefit.

Eosinophils in fungus-associated allergic pulmonary disease

Asthma is frequently caused and/or exacerbated by sensitization to fungal allergens, which are ubiquitous in many indoor and outdoor environments. Severe asthma with fungal sensitization is characterized by airway hyperresponsiveness and bronchial constriction in response to an inhaled allergen that is worsened by environmental exposure to airborne fungi and which leads to a disease course that is often very difficult to treat with standard asthma therapies. As a result of complex interactions among inflammatory cells, structural cells, and the intercellular matrix of the allergic lung, patients with sensitization to fungal allergens may experience a greater degree of airway wall remodeling and progressive, accumulated pulmonary dysfunction as part of the disease sequela. From their development in the bone marrow to their recruitment to the lung via chemokine and cytokine networks, eosinophils form an important component of the inflammatory milieu that is associated with this syndrome. Eosinophils are recognized as complex multi-factorial leukocytes with diverse functions in the context of allergic fungal asthma. In this review, we will consider recent advances in our understanding of the molecular mechanisms that are associated with eosinophil development and migration to the allergic lung in response to fungal inhalation, along with the eosinophil’s function in the immune response to and the immunopathology attributed to fungus-associated allergic pulmonary disease.

Agent-based modeling approach of immune defense against spores of opportunistic human pathogenic fungi

Opportunistic human pathogenic fungi like the ubiquitous fungus Aspergillus fumigatus are a major threat to immunocompromised patients. An impaired immune system renders the body vulnerable to invasive mycoses that often lead to the death of the patient. While the number of immunocompromised patients is rising with medical progress, the process, and dynamics of defense against invaded and ready to germinate fungal conidia are still insufficiently understood. Besides macrophages, neutrophil granulocytes form an important line of defense in that they clear conidia. Live imaging shows the interaction of those phagocytes and conidia as a dynamic process of touching, dragging, and phagocytosis. To unravel strategies of phagocytes on the hunt for conidia an agent-based modeling approach is used, implemented in NetLogo. Different modes of movement of phagocytes are tested regarding their clearing efficiency: random walk, short-term persistence in their recent direction, chemotaxis of chemokines excreted by conidia, and communication between phagocytes. While the short-term persistence hunting strategy turned out to be superior to the simple random walk, following a gradient of chemokines released by conidial agents is even better. The advantage of communication between neutrophilic agents showed a strong dependency on the spatial scale of the focused area and the distribution of the pathogens.

Current perspectives on echinocandin class drugs

It has been nearly a decade since caspofungin was approved for clinical use as the first echinocandin class antifungal agent, followed by micafungin and anidulafungin. The echinocandin drugs target the fungal cell wall by inhibiting the synthesis of β-1,3-D-glucan, a critical cell wall component of many pathogenic fungi. They are fungicidal for Candida spp. and fungistatic for moulds, such as Aspergillus fumigatus, where they induce abnormal morphology and growth properties. The echinocandins have a limited antifungal spectrum but are highly active against most Candida spp., including azole-resistant strains and biofilms. As they target glucan synthase, an enzyme absent in mammalian cells, the echinocandins have a favorable safety profile. They show potent MIC and epidemiological cutoff values against susceptible Candida and Aspergillus isolates, and the frequency of resistance is low. When clinical breakthrough occurs, it is associated with high MIC values and mutations in Fks subunits of glucan synthase, which can reduce the sensitivity of the enzyme to the drug by several thousand-fold. Such strains were not adequately captured by an early clinical breakpoint for susceptibility prompting a revised lower value, which addresses the FKS resistance mechanism and new pharmacokinetic/pharmacodynamic studies. Elevated MIC values unlinked to therapeutic failure can occur and result from adaptive cell behavior, which is FKS-independent and involves the molecular chaperone Hsp90 and the calcineurin pathway. Mutations in FKS1 and/or FKS2 alter the kinetic properties of glucan synthase, which reduces the relative fitness of mutant strains causing them to be less pathogenic. The echinocandin drugs also modify the cell wall architecture exposing buried glucans, which in turn induce a variety of important host immune responses. Finally, the future for glucan synthase inhibitors looks bright with the development of new orally active compounds.

Innate antifungal immunity: the key role of phagocytes

Fungal diseases have emerged as significant causes of morbidity and mortality, particularly in immune-compromised individuals, prompting greater interest in understanding the mechanisms of host resistance to these pathogens. Consequently, the past few decades have seen a tremendous increase in our knowledge of the innate and adaptive components underlying the protective (and nonprotective) mechanisms of antifungal immunity. What has emerged from these studies is that phagocytic cells are essential for protection and that defects in these cells compromise the host's ability to resist fungal infection. This review covers the functions of phagocytes in innate antifungal immunity, along with selected examples of the strategies that are used by fungal pathogens to subvert these defenses.