Risk of Invasive Fungal Infections in Patients With Chronic Lymphocytic Leukemia Treated With Bruton Tyrosine Kinase Inhibitors: A Case-Control Propensity Score-Matched Analysis

Background

Prior reports have suggested a possible increase in the frequency of invasive fungal infections (IFIs) with use of a Bruton tyrosine kinase inhibitor (BTKi) for treatment of chronic lymphoid malignancies such as chronic lymphocytic leukemia (CLL), but precise estimates are lacking. We aim to characterize the prevalence of IFIs among patients with CLL, for whom a BTKi is now the first-line recommended therapy.

Methods

We queried TriNetX, a global research network database, to identify adult patients with CLL using the International Classification of Diseases, Tenth Revision code (C91.1) and laboratory results. We performed a case-control propensity score-matched analysis to determine IFIs events by BTKi use. We adjusted for age, sex, ethnicity, and clinical risk factors associated with an increased risk of IFIs.

Results

Among 5358 matched patients with CLL, we found an incidence of 4.6% of IFIs in patients on a BTKi versus 3.5% among patients not on a BTKi at 5 years. Approximately 1% of patients with CLL developed an IFI while on a BTKi within this period. Our adjusted IFI event analysis found an elevated rate of Pneumocystis jirovecii pneumonia (PJP) (0.5% vs 0.3%, P = .02) and invasive candidiasis (3.5% vs 2.7%, P = .012) with the use of a BTKi. The number needed to harm for patients taking a BTKi was 120 and 358 for invasive candidiasis and PJP, respectively.

Conclusions

We found an adjusted elevated rate of PJP and invasive candidiasis with BTKi use. The rates are, however, low with a high number needed to harm. Additional studies stratifying other IFIs with specific BTKis are required to identify at-risk patients and preventive, cost-effective interventions.

Antifungal chemotherapies and immunotherapies for the future

Human fungal pathogens cause a broad plethora of infections, spanning cutaneous dermatophytoses to invasive infections in immunocompromised hosts. As eukaryotic pathogens are capable of morphotype switching, they present unique challenges both for drug development and the immunological response. Whilst current antifungal therapies are limited to the orally available triazoles, intravenous echonocandins and polyenes, and flucytosine and terbinafine, there has been recent significant progress in the antifungal armamentorium with ibrexafungerp, a novel orally available terpanoid that inhibits 1,3-beta-D-glucan-approved by Food and Drug Administration in 2021, and fosmanogepix, an orally available pro-drug of manogepix, which targets glycosylphosphatidylinositol-anchored protein maturation entering Phase 3 studies for candidaemia. A number of further candidates are in development. There has been significant use of existing immunotherapies such as recombinant interferon-γ and G-CSF for fungal disease in immunocompromised patients, and there are emerging opportunities for monoclonal antibodies targeting TH2 inflammation. Omalizumab, an anti-IgE monoclonal antibody in asthma, is now used routinely for the treatment of allergic bronchopulmonary aspergillosis, and further agents targeting IL-4 and IL-5 are being evaluated. In addition, T-cell CAR therapy is showing early promise for fungal disease. Thus, we are likely to see rapid advances to our approach to the management of fungal disease in the near future.

Tackling the emerging threat of antifungal resistance to human health

Invasive fungal infections pose an important threat to public health and are an under-recognized component of antimicrobial resistance, an emerging crisis worldwide. Across a period of profound global environmental change and expanding at-risk populations, human-infecting pathogenic fungi are evolving resistance to all licensed systemic antifungal drugs. In this Review, we highlight the main mechanisms of antifungal resistance and explore the similarities and differences between bacterial and fungal resistance to antimicrobial control. We discuss the research and innovation topics that are needed for risk reduction strategies aimed at minimizing the emergence of resistance in pathogenic fungi. These topics include links between the environment and One Health, surveillance, diagnostics, routes of transmission, novel therapeutics and methods to mitigate hotspots for fungal adaptation. We emphasize the global efforts required to steward our existing antifungal armamentarium, and to direct the research and development of future therapies and interventions.

Proteomic Analysis Reveals Proteins Involved in the Mode of Action of β-Citronellol Identified From Citrus hystrix DC. Leaf Against Candida albicans

Candida albicans is a fungus that lives primarily on the mucosal surfaces of healthy humans, such as the oral cavity, vagina, and gastrointestinal tract. This commensal organism can be controlled by other microbiota, while certain conditions can increase the risk of C. albicans outgrowth and cause disease. Prevalence of the drug-resistant phenotype, as well as the severity of C. albicans infection in immunocompromised patients, presents a challenge for scientists to develop novel, effective treatment, and prevention strategies. β-Citronellol is an intriguing active compound of several plants that has been linked to antifungal activity, but data on the mechanism of action in terms of proteomic profiling are lacking. Here, β-citronellol identified from Citrus hystrix DC. leaf against C. albicans were evaluated. A proteomic approach was used to identify potential target proteins involved in the mode of action of β-citronellol. This study identified and discussed three protein groups based on the 126 major proteins that were altered in response to β-citronellol treatment, 46 of which were downregulated and 80 of which were upregulated. Significant protein groups include cell wall proteins (e.g., Als2p, Rbt1p, and Pga4p), cellular stress response enzymes (e.g., Sod1p, Gst2p, and Ddr48p), and ATP synthesis-associated proteins (e.g., Atp3p, Atp7p, Cox1p, and Cobp). Results demonstrated the complexities of protein interactions influenced by β-citronellol treatment and highlighted the potential of antifungal activity for future clinical and drug development research.

DectiSomes: Glycan Targeting of Liposomal Drugs Improves the Treatment of Disseminated Candidiasis

Candida albicans causes life-threatening disseminated candidiasis. Individuals at greatest risk have weakened immune systems. An outer cell wall, exopolysaccharide matrix, and biofilm rich in oligoglucans and oligomannans help Candida spp. evade host defenses. Even after antifungal treatment, the 1-year mortality rate exceeds 25%. Undoubtedly, there is room to improve drug performance. The mammalian C-type lectin pathogen receptors Dectin-1 and Dectin-2 bind to fungal oligoglucans and oligomannans, respectively. We previously coated amphotericin B-loaded liposomes, AmB-LLs, pegylated analogs of AmBisome, with the ligand binding domains of these two Dectins. DectiSomes, DEC1-AmB-LLs and DEC2-AmB-LLs, showed two distinct patterns of binding to the exopolysaccharide matrix surrounding C. albicans hyphae grown in vitro. Here we showed that DectiSomes were preferentially associated with fungal colonies in the kidneys. In a neutropenic mouse model of candidiasis, DEC1-AmB-LLs and DEC2-AmB-LLs delivering only one dose of 0.2 mg/kg AmB reduced the kidney fungal burden several fold relative to AmB-LLs. DEC1-AmB-LLs and DEC2-AmB-LLs increased the percent of surviving mice 2.5-fold and 8.3-fold, respectively, relative to AmB-LLs. Dectin-2 targeting of anidulafungin loaded liposomes, DEC2-AFG-LLs, and of commercial AmBisome, DEC2-AmBisome, reduced fungal burden in the kidneys several fold over their untargeted counterparts. The data herein suggest that targeting of a variety of antifungal drugs to fungal glycans may achieve lower safer effective doses and improve drug efficacy against a variety of invasive fungal infections.

Immunity to Invasive Fungal Diseases

Invasive fungal diseases are rare in individuals with intact immunity. This, together with the fact that there are only a few species that account for most mycotic diseases, implies a remarkable natural resistance to pathogenic fungi. Mammalian immunity to fungi rests on two pillars, powerful immune mechanisms and elevated temperatures that create a thermal restriction zone for most fungal species. Conditions associated with increased susceptibility generally reflect major disturbances of immune function involving both the cellular and humoral innate and adaptive arms, which implies considerable redundancy in host defense mechanisms against fungi. In general, tissue fungal invasion is controlled through either neutrophil or granulomatous inflammation, depending on the fungal species. Neutrophils are critical against Candida spp. and Aspergillus spp. while macrophages are essential for controlling mycoses due to Cryptococcus spp., Histoplasma spp., and other fungi. The increasing number of immunocompromised patients together with climate change could significantly increase the prevalence of fungal diseases.

Expected final online publication date for the Annual Review of Immunology, Volume 40 is April 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Solid-State NMR Investigations of Extracellular Matrixes and Cell Walls of Algae, Bacteria, Fungi, and Plants

Extracellular matrixes (ECMs), such as the cell walls and biofilms, are important for supporting cell integrity and function and regulating intercellular communication. These biomaterials are also of significant interest to the production of biofuels and the development of antimicrobial treatment. Solid-state nuclear magnetic resonance (ssNMR) and magic-angle spinning-dynamic nuclear polarization (MAS-DNP) are uniquely powerful for understanding the conformational structure, dynamical characteristics, and supramolecular assemblies of carbohydrates and other biomolecules in ECMs. This review highlights the recent high-resolution investigations of intact ECMs and native cells in many organisms spanning across plants, bacteria, fungi, and algae. We spotlight the structural principles identified in ECMs, discuss the current technical limitation and underexplored biochemical topics, and point out the promising opportunities enabled by the recent advances of the rapidly evolving ssNMR technology.

Future Directions for Clinical Respiratory Fungal Research

There has been a growing appreciation of the importance of respiratory fungal diseases in recent years, with better understanding of their prevalence as well as their global distribution. In step with the greater awareness of these complex infections, we are currently poised to make major advances in the characterization and treatment of these fungal diseases, which in itself is largely a consequence of post-genomic technologies which have enabled rational drug development and a path towards personalized medicines. These advances are set against a backdrop of globalization and anthropogenic change, which have impacted the world-wide distribution of fungi and antifungal resistance, as well as our built environment. The current revolution in immunomodulatory therapies has led to a rapidly evolving population at-risk for respiratory fungal disease. Whilst challenges are considerable, perhaps the tools we now have to manage these infections are up to this challenge. There has been a welcome acceleration of the antifungal pipeline in recent years, with a number of new drug classes in clinical or pre-clinical development, as well as new focus on inhaled antifungal drug delivery. The "post-genomic" revolution has opened up metagenomic diagnostic approaches spanning host immunogenetics to the fungal mycobiome that have allowed better characterization of respiratory fungal disease endotypes. When these advances are considered together the key challenge is clear: to develop a personalized medicine framework to enable a rational therapeutic approach.

Lessons from an Educational Invasive Fungal Disease Conference on Hospital Antifungal Stewardship Practices across the UK and Ireland

Invasive fungal disease (IFD) is a growing health burden. High mortality rates, increasing numbers of at-risk hosts, and a limited availability of rapid diagnostics and therapeutic options mean that patients are increasingly exposed to unnecessary antifungals. High rates of prescriptions promote patient exposure to undue toxicity and drive the emergence of resistance. Antifungal stewardship (AFS) aims to guide antifungal usage and reduce unnecessary exposure and antifungal consumption whilst maintaining or improving outcomes. Here, we examine several AFS approaches from hospitals across the UK and Ireland to demonstrate the benefits of AFS practices and support the broader implementation of AFS as both a necessary and achievable strategy. Since the accuracy and turnaround times (TATs) of diagnostic tools can impact treatment decisions, several AFS strategies have included the development and implementation of diagnostic-driven care pathways. AFS informed treatment strategies can help stratify patients on a risk basis ensuring the right patients receive antifungals at the optimal time. Using a multidisciplinary approach is also key due to the complexity of managing and treating patients at risk of IFD. Through knowledge sharing, such as The Gilead Antifungal Information Network (GAIN), we hope to drive practices that improve patient management and support the preservation of antifungals for future use.

Genetic Susceptibility to Fungal Infections and Links to Human Ancestry

Over the ages, fungi have associated with different parts of the human body and established symbiotic associations with their host. They are mostly commensal unless there are certain not so well-defined factors that trigger the conversion to a pathogenic state. Some of the factors that induce such transition can be dependent on the fungal species, environment, immunological status of the individual, and most importantly host genetics. In this review, we discuss the different aspects of how host genetics play a role in fungal infection since mutations in several genes make hosts susceptible to such infections. We evaluate how mutations modulate the key recognition between the pathogen associated molecular patterns (PAMP) and the host pattern recognition receptor (PRR) molecules. We discuss the polymorphisms in the genes of the immune system, the way it contributes toward some common fungal infections, and highlight how the immunological status of the host determines fungal recognition and cross-reactivity of some fungal antigens against human proteins that mimic them. We highlight the importance of single nucleotide polymorphisms (SNPs) that are associated with several of the receptor coding genes and discuss how it affects the signaling cascade post-infection, immune evasion, and autoimmune disorders. As part of personalized medicine, we need the application of next-generation techniques as a feasible option to incorporate an individual’s susceptibility toward invasive fungal infections based on predisposing factors. Finally, we discuss the importance of studying genomic ancestry and reveal how genetic differences between the human race are linked to variation in fungal disease susceptibility.

fuPCR as diagnostic method for the detection of rare fungal pathogens, such as Trichosporon, Cryptococcus and Fusarium

Fungal respiratory tract colonisation is a common finding in patients with hematologic neoplasms due to immunosuppression inherent in the diseases and exacerbated by therapy. This greatly increases the risk of fungal infections of the lungs, which is associated with significant mortality. Therefore, reliable diagnostic methods with rapidly available results are needed to administer adequate antifungal therapy.We have established an improved method for fungal DNA extraction and amplification that allows simultaneous detection of fungal families based on a set of multiplexed real time PCR reactions (fuPCR). We analysed respiratory rinses and blood of 94 patients with haematological systemic diseases by fuPCR and compared it with the results of culture and serological diagnostic methods. 40 healthy subjects served as controls.Regarding Candida species, the highest prevalence resulted from microbiological culture of respiratory rinses and from detection of antibodies in blood serum in patients (61% and 47%, respectively) and in the control group (29% and 51%, respectively). Detection of other pathogenic yeasts, such as Cryptococcus and Trichosporon, and moulds, such as Fusarium, was only possible in patients by fuPCR from both respiratory rinses and whole blood and serum. These fungal species were found statistically significantly more frequent in respiratory rinses collected from patients after myeloablative therapy for stem cell transplantation compared to samples collected before treatment (p<<0.05i>).The results show that fuPCR is a valuable complement to culturing and its inclusion in routine mycological diagnostics might be helpful for early detection of pathophysiologically relevant respiratory colonisation for patients with hematologic neoplasms.

LAY ABSTRACT

We validated a set of PCR reactions (fuPCR) for use in routine diagnostic. In contrast to culture and serological methods, only by fuPCR pathogenic yeasts (Cryptococcus and Trichosporon) and moulds (Aspergillus and Fusarium) were detected in respiratory rinses and blood of haematological patients.

Challenges and Opportunities in Understanding Genetics of Fungal Diseases: Towards a Functional Genomics Approach

Infectious diseases are a leading cause of morbidity and mortality worldwide, and human pathogens have long been recognized as one of the main sources of evolutionary pressure, resulting in a high variable genetic background in immune-related genes. The study of the genetic contribution to infectious diseases has undergone tremendous advances over the last decades. Here, focusing on genetic predisposition to fungal diseases, we provide an overview of the available approaches for studying human genetic susceptibility to infections, reviewing current methodological and practical limitations. We describe how the classical methods available, such as family-based studies and candidate gene studies, have contributed to the discovery of crucial susceptibility factors for fungal infections. We will also discuss the contribution of novel unbiased approaches to the field, highlighting their success but also their limitations for the fungal immunology field. Finally, we show how a systems genomics approach can overcome those limitations and can lead to efficient prioritization and identification of genes and pathways with a critical role in susceptibility to fungal diseases. This knowledge will help to stratify at-risk patient groups and, subsequently, develop early appropriate prophylactic and treatment strategies.

Design, synthesis and biological evaluation of novel diazaspirodecanone derivatives containing piperidine-4-carboxamide as chitin synthase inhibitors and antifungal agents

A series of novel 2-oxo-(1-oxo-2,8-diazaspiro[4.5]decane-8-yl)ethylpiperidine carboxamide derivatives were designed, synthesized and characterized by ¹H NMR, ¹³C NMR and HRMS spectroscopy. All eighteen newly prepared compounds were evaluated for their inhibition against chitin synthase (CHS) and antifungal activities in vitro. The enzyme assay revealed that compound 5h showed excellent inhibitory activity against CHS with IC₅₀ value of 0.10 mM, and the compounds 5b, 5d and 5q showed good inhibition against chitin synthase with IC₅₀ values of 0.13 mM, 0.18 mM and 0.15 mM, respectively, while IC₅₀ value of ployoxin B was 0.08 mM. Meanwhile, the others of these compounds exhibited moderate inhibition potency against chitin synthase. The antifungal assay showed compound 5h had excellent antifungal activity compared with the control drugs fluconazole and polyoxin B against these tested strains including C. albicans, A. fumigatus, C. neoformans and A. flavus. Its excellent antifungal activity was consistent with its excellent chitin synthase inhibition. Compound 5k and 5l against C. albicans were comparable with fluconazole, and they showed strong antifungal potency against A. flavus with MIC values of 0.07 mmol/L and 0.13 mmol/L respectively. Compound 5m had similar MIC value against A. fumigatus to fluconazole. The phenomenon that compounds 5b, 5d and 5q that showed good enzymatic inhibition didn't exert good antifungal activity, while compounds 5k, 5l and 5m that showed moderate chitin synthase inhibition exhibited excellent antifungal activity was discussed. Furthermore, the trial of drug combination showed that compounds had synergistic effects or additive effects with fluconazole against tested fungi which also verified that these designed compounds targeted different targets from that of fluconazole. Additionally, the antibacterial trial showed that all synthesized compounds had little potency against tested bacteria strains. These results indicated that the designed compounds were potential chitin synthase inhibitors and had selectively antifungal activities.

Preclinical safety evaluation of amphotericin A21: A novel antifungal

Safety studies are essential in drug development. This study evaluates the safety of Amphotericin A21 (AmB-A21), a derivative of amphotericin B with antifungal therapeutic potential. We performed a chronic toxicity study, a targeted organ study and a dermal irritation test. To evaluate chronic toxicity, 18 male adult rats were treated orally with AmB-21 (2 mg/kg) for 26 weeks. The effects on body-weight and animal health were measured, and haematological, clinical chemistry and histopathological tests were conducted on various organs. In the target organ toxicity study, male adult rats received a daily oral dose of AmB-21 (2 mg/kg) for 6 and 17 weeks; testicle histology and testosterone levels were then evaluated. For the dermal irritation study, AmB-21 (200 and 1000 mg/kg) was placed on the skin of adult male rabbits; macroscopic and microscopic studies, as well as haematological and clinical chemistry tests were then conducted. The chronic toxicity study revealed that AmB-21 caused testicle damage, and the testicle-targeted study showed structural alterations and changes in testosterone levels at 17 weeks. However, these alterations were no longer observed 8 weeks after discontinuation of treatment, and the testes showed very similar characteristics to those in the control group. The dermal irritation study showed skin thickening and reddening in rabbits treated with 2000 mg of AmB-A21 after 14 days of exposure. This same group also showed changes in liver enzymes, renal parameters and platelet levels. Based on our results, we consider AmB-21 to be a potential candidate for safe, long-term antifungal treatment given its reduced side effects.

Atypical Presentation of Severe Fungal Necrotizing Fasciitis in a Patient with X-Linked Agammaglobulinemia

X-linked agammaglobulinemia is a rare primary immunodeficiency due to a BTK mutation. The patients are characteristically deficient in peripheral B cells and serum immunoglobulins. While they are susceptible to infections caused by bacteria, enteroviruses, and parasites, fungal infections are uncommon in XLA patients. Here, we report a boy of Malay ethnicity who suffered from recurrent upper respiratory tract infections and severe progressive necrotizing fasciitis caused by Saksenaea erythrospora. Immunological tests showed a B cell deficiency and hypogammaglobulinemia. Whole-exome sequencing identified a dinucleotide deletion (c.1580_1581del) in BTK, confirmed by Sanger sequencing and predicted to be disease causing by in silico functional prediction tools (Varsome and MutationTaster2) but was absent in the gnomAD database. This mutation resulted in a frameshift and premature termination (p.C527fs), which disrupted the protein structure. The mother was heterozygous at the mutation site, confirming her carrier status. Flow cytometric analysis of monocyte BTK expression showed it to be absent in the patient and bimodal in the mother. This study describes a novel BTK mutation in a defined hotspot and an atypical fungal phenotype in XLA. Further studies are required to understand the pathogenesis of fungal infection in XLA.

Comparative host transcriptome in response to pathogenic fungi identifies common and species-specific transcriptional antifungal host response pathways

Candidiasis, aspergillosis, and mucormycosis cause the majority of nosocomial fungal infections in immunocompromised patients. Using an unbiased transcriptional profiling in PBMCs exposed to the fungal species causing these infections, we found a core host response in healthy individuals that may govern effective fungal clearance: it consists of 156 transcripts, involving canonical and non-canonical immune pathways. Systematic investigation of key steps in antifungal host defense revealed fungal-specific signatures. As previously demonstrated, Candida albicans induced type I and Type II interferon-related pathways. In contrast, central pattern recognition receptor, reactive oxygen species production, and host glycolytic pathways were down-regulated in response to Rhizopus oryzae, which was associated with an ER-stress response. TLR5 was identified to be uniquely regulated by Aspergillus fumigatus and to control cytokine release in response to this fungus. In conclusion, our data reveals the transcriptional profiles induced by C. albicans, A. fumigatus, and R. oryzae, and describes both the common and specific antifungal host responses that could be exploited for novel therapeutic strategies.

Innate Inspiration: Antifungal Peptides and Other Immunotherapeutics From the Host Immune Response

The purpose of this review is to describe antifungal therapeutic candidates in preclinical and clinical development derived from, or directly influenced by, the immune system, with a specific focus on antimicrobial peptides (AMP). Although the focus of this review is AMP with direct antimicrobial effects on fungi, we will also discuss compounds with direct antifungal activity, including monoclonal antibodies (mAb), as well as immunomodulatory molecules that can enhance the immune response to fungal infection, including immunomodulatory AMP, vaccines, checkpoint inhibitors, interferon and colony stimulating factors as well as immune cell therapies. The focus of this manuscript will be a non-exhaustive review of antifungal compounds in preclinical and clinical development that are based on the principles of immunology and the authors acknowledge the incredible amount of in vitro and in vivo work that has been conducted to develop such therapeutic candidates.

Breakthrough invasive fungal infections: Who is at risk?

The epidemiology of invasive fungal infections (IFIs) in immunocompromised individuals has changed over the last few decades, partially due to the increased use of antifungal agents to prevent IFIs. Although this strategy has resulted in an overall reduction in IFIs, a subset of patients develop breakthrough IFIs with substantial morbidity and mortality in this population. Here, we review the most significant risk factors for breakthrough IFIs in haematology patients, solid organ transplant recipients, and patients in the intensive care unit, focusing particularly on host factors, and highlight areas that require future investigation.

Immunotherapy as an Antifungal Strategy in Immune Compromised Hosts

Purpose of Review

IFIs cause high morbidity and mortality in the immunocompromised host worldwide. Although highly effective, conventional antifungal chemotherapy faces new challenges due to late diagnosis and increasing numbers of drug-resistant fungal strains. Thus, antifungal immunotherapy represents a viable treatment option, and recent advances in the field are summarized in this review.

Recent Findings

Antifungal immunotherapies include application of immune cells as well as the administration of cytokines, growth factors, and antibodies. Novel strategies to treat IFIs in the immunocompromised host target intracellular signaling pathways using SMTs such as checkpoint inhibitors.

Summary

Studies using cytokines or chemokines exerted a potential adjuvant role to conventional antifungal therapy, but issues on toxicity for some agents have to be resolved. Cell-based immunotherapies are very labor-intense and costly, but NK cell transfer and CAR T cell therapy provide exciting strategies to combat IFIs. Antibody-mediated protection and checkpoint inhibition are additional novel immunotherapeutic approaches.