Ibrexafungerp is efficacious in a neutropenic murine model of pulmonary mucormycosis as monotherapy and combined with liposomal amphotericin B.

Ibrexafungerp (formerly SCY-078) is the first member of the triterpenoid class that prevents the synthesis of the fungal cell wall polymer ß-(1,3)-D-glucan by inhibiting the enzyme glucan synthase. We evaluated the in vivo efficacy of ibrexafungerp against pulmonary mucormycosis using an established murine model. Neutropenic mice were intratracheally infected with either Rhizopus delemar or Mucor circinelloides. Treatment with placebo (diluent control), ibrexafungerp (30 mg/kg, PO BID), liposomal amphotericin B (LAMB 10 mg/kg IV QD), posaconazole (PSC 30 mg/kg PO QD), or a combination of ibrexafungerp plus LAMB or ibrexafungerp plus PSC began 16 h post-infection and continued for 7 days for ibrexafungerp or PSC and through day 4 for LAMB. Ibrexafungerp was as effective as LAMB or PSC in prolonging median survival (range: 15 days to >21 days) and enhancing overall survival (30%-65%) vs placebo (9 days and 0%; P < 0.001) in mice infected with R. delemar. Furthermore, median survival and overall percent survival resulting from the combination of ibrexafungerp plus LAMB were significantly greater compared to all monotherapies (P ≤ 0.03). Similar survival results were observed in mice infected with M. circinelloides. Monotherapies also reduce the lung and brain fungal burden by ~0.5-1.0log10 conidial equivalents (CE)/g of tissue vs placebo in mice infected with R. delemar (P < 0.05), while a combination of ibrexafungerp plus LAMB lowered the fungal burden by ~0.5-1.5log10 CE/g compared to placebo or any of the monotherapy groups (P < 0.03). These results are promising and warrant continued investigation of ibrexafungerp as a novel treatment option against mucormycosis.

Universal digital high-resolution melting for the detection of pulmonary mold infections.

Invasive mold infections (IMIs) are associated with high morbidity, particularly in immunocompromised patients, with mortality rates between 40% and 80%. Early initiation of appropriate antifungal therapy can substantially improve outcomes, yet early diagnosis remains difficult to establish and often requires multidisciplinary teams evaluating clinical and radiological findings plus supportive mycological findings. Universal digital high-resolution melting (U-dHRM) analysis may enable rapid and robust diagnoses of IMI. A universal fungal assay was developed for U-dHRM and used to generate a database of melt curve signatures for 19 clinically relevant fungal pathogens. A machine learning algorithm (ML) was trained to automatically classify these pathogen curves and detect novel melt curves. Performance was assessed on 73 clinical bronchoalveolar lavage samples from patients suspected of IMI. Novel curves were identified by micropipetting U-dHRM reactions and Sanger sequencing amplicons. U-dHRM achieved 97% overall fungal organism identification accuracy and a turnaround time of ~4 hrs. U-dHRM detected pathogenic molds (Aspergillus, Mucorales, Lomentospora, and Fusarium) in 73% of 30 samples classified as IMI, including mixed infections. Specificity was optimized by requiring the number of pathogenic mold curves detected in a sample to be >8 and a sample volume to be 1 mL, which resulted in 100% specificity in 21 at-risk patients without IMI. U-dHRM showed promise as a separate or combination diagnostic approach to standard mycological tests. U-dHRM's speed, ability to simultaneously identify and quantify clinically relevant mold pathogens in polymicrobial samples, and detect emerging opportunistic pathogens may aid treatment decisions, improving patient outcomes. IMPORTANCE: Improvements in diagnostics for invasive mold infections are urgently needed. This work presents a new molecular detection approach that addresses technical and workflow challenges to provide fast pathogen detection, identification, and quantification that could inform treatment to improve patient outcomes.

Performance of rapid on-site evaluation of touch imprints of bronchoscopic biopsies or lung tissue biopsies for the diagnosis of invasive pulmonary filamentous fungi infections in non-neutropenic patients.

The diagnosis of invasive pulmonary fungal disease depends on histopathology and mycological culture; there are few studies on touch imprints of bronchoscopic biopsies or lung tissue biopsies for the diagnosis of pulmonary filamentous fungi infections. The purpose of the present study was to explore the detection accuracy of rapid on-site evaluation of touch imprints of bronchoscopic biopsies or lung tissue biopsies for the filamentous fungi, and it aims to provide a basis for initiating antifungal therapy before obtaining microbiological evidence. We retrospectively analyzed the diagnosis and treatment of 44 non-neutropenic patients with invasive pulmonary filamentous fungi confirmed by glactomannan assay, histopathology, and culture from February 2017 to December 2023. The diagnostic positive rate and sensitivity of rapid on-site evaluation for these filamentous fungi identification, including diagnostic turnaround time, were calculated. Compared with the final diagnosis, the sensitivity of rapid on-site evaluation was 81.8%, and the sensitivity of histopathology, culture of bronchoalveolar lavage fluid, and glactomannan assay of bronchoalveolar lavage fluid was 86.4%, 52.3%, and 68.2%, respectively. The average turnaround time of detecting filamentous fungi by rapid on-site evaluation was 0.17 ± 0.03 hours, which was significantly faster than histopathology, glactomannan assay, and mycological culture. A total of 29 (76.3%) patients received earlier antifungal therapy based on ROSE diagnosis and demonstrated clinical improvement. Rapid on-site evaluation showed good sensitivity and accuracy that can be comparable to histopathology in identification of pulmonary filamentous fungi. Importantly, it contributed to the triage of biopsies for further microbial culture or molecular detection based on the preliminary diagnosis, and the decision on early antifungal therapy before microbiological evidence is available.

Organizing Pneumonia due to Secondary Invasive Pulmonary Mycosis and Cytomegalovirus Infection in a Patient with Lymphoma.

BACKGROUND: Reactivation of cytomegalovirus is more common in lymphoma patients undergoing hematopoietic stem cell transplantation, but reactivation of cytomegalovirus due to chemotherapy for lymphoma has rarely been reported. We report a case of a lymphoma patient with secondary pulmonary fungal infection and cytomegalovirus infection after chemotherapy, which ultimately led to organizing pneumonia. METHODS: Percutaneous lung biopsy, Next Generation Sequencing (NGS). RESULTS: NGS examination suggestive of cytomegalovirus infection, percutaneous lung biopsy suggests the presence of organizing pneumonia. The patient was discharged after a combination of antifungal and antiviral treatment with posaconazole, ganciclovir, and anti-inflammatory treatment with methylprednisolone. CONCLUSIONS: In patients with lymphoma, one should be alert for fungal and viral infections of the lungs when lung related clinical manifestations occur. Patients with persistent unrelieved symptoms after treatment should undergo lung biopsy or bronchoscopy to obtain pathologic tissue for definitive diagnosis.

Pulmonary dimorphic fungal infections among HIV/AIDS non-TB patients with chronic cough in Kampala, Uganda.

INTRODUCTION: Dimorphic fungi cause infection following the inhalation of spores into the pulmonary system. In the lower respiratory tract, the conidia transform into yeasts, which are engulfed by alveolar macrophages and may be destroyed without disease manifestation. However, in some immunocompromised individuals, they may persist and cause active fungal disease characterized by formation of granulomas in the infected tissues, which may mimic Mycobacterium tuberculosis (MTB). OBJECTIVE: To determine the prevalence of pulmonary dimorphic fungal infections among HIV/AIDS patients with non-TB chronic cough at Mulago National Referral and Teaching Hospital in Kampala, Uganda. METHODS: Sputum samples were collected from 175 consented HIV/AIDS patients attending the immuno-suppression syndrome (ISS) clinic at the hospital. Upon Xpert MTB/RIF sputum testing, 21 patients tested positive for MTB, and these were excluded from further analysis. The other 154 sputum negative samples were then subjected to PCR for dimorphic fungi at MBN Clinical Laboratories. Singleplex PCR was used to detect the target sequences in selected respective genes of each dimorphic fungal species of interest. DNA amplicons were detected based on gel electrophoresis. RESULTS: Dimorphic fungi were detected in 16.2% (25/154) of the studied population. Of these 9.1% (14/154) had Blastomyces dermatitidis and 7.1% (11/154) had Talaromyces marneffei. The remaining 84% of the studied participants had no dimorphic fungi. Histoplasma capsulatum, Coccidioides immitis and Paracoccidioides brasiliensis were not detected in any of the participants. CONCLUSION: Dimorphic fungi (B. dermatitidis and T. marneffei) were found in 16.2% of the HIV/AIDS patients with non-TB chronic cough in Kampala, Uganda. We recommend routine testing for these pathogens among HIV/AIDS patients with chronic cough.

[Differential diagnosis of coccidioidomycosis manifested by peripheral pulmonary lesion]. / Differentsial'naya diagnostika koktsidioidomikoza, manifestirovannogo perifericheskim obrazovaniem legkogo.

We present this clinical case as a demonstration of difficulties in differential diagnosis of pulmonary coccidioidomycosis. Differential diagnostics of peripheral pulmonary lesion performed using bronchoscopy with BAL and TBCB and video-assisted thoracic surgery (VATS) biopsy. Diagnostic specimens were tested using microbiological (luminescent microscopy, culture for M. tuberculosis (BACTEC MGIT960 and Lowenstein-Jensen Medium), RT-PCR, cytological and morphological (hematoxylin-eosin, Ziehl-Neelsen, PAS, Grocott methenamine silver (GMS) stainings) examinations. A diagnosis was verified correctly In Russia the country is not endemic for coccidioidomycosis and patient was treated accordingly. Diagnostics of peripheral pulmonary lesions requires of multidisciplinary approaches. Morphological examination, based on detection of only granulomatous inflammation in lung biopsy cannot be used for finally DS and requires microbiological confirmation for TB or other infections, and dynamic monitoring of the patient with concordance their anamnesis vitae and morbi.

Aspergillus niger pneumonia as superinfection in a patient with pulmonary tuberculosis.

We report a patient with severe cavitary pulmonary tuberculosis and Aspergillus niger superinfection, whose only comorbidity was untreated diabetes mellitus. A. niger pneumonia was proven by PCR, sequencing and culture of pleural and respiratory secretions. The patient was successfully treated with a four-drug antituberculous regimen, liposomal amphotericin B (up to 5 mg/kg/d) and pleuro-pneumonectomy. Histology of the resected lung revealed destroyed lung tissue with inflammatory cells and fungal conidia. There were large deposits of polarising material, which was found to be calcium oxalate. There was also nodular caseating necrosis bordered by epitheloid cells and connective tissue. Thus, all diagnostic criteria for invasive A. niger infection were met. Several local risk factors, such as extensive lung damage and tissue acidification, may have favoured superinfection by A. niger. This case highlights the diagnostic value of calcium oxalate crystals in lung tissue and the need for combined antimicrobial and surgical treatment in extensive invasive aspergillosis caused by A. niger.

[Susceptible mechanisms of pulmonary mucormycosis in diabetic patients].

Pulmonary mucormycosis is a rare pulmonary fungal infectious disease. Domestic and international studies have shown that diabetes is the most common underlying condition of this disease, especially with poor glycemic control and diabetic ketoacidosis. The susceptible mechanisms of pulmonary mucormycosis in diabetic patients are closely related to hyperglycemia and diabetic ketoacidosis-induced internal environment alterations. The detailed pathogenesis includes respiratory epithelial cell damage, vascular endothelial injury, immune cell dysfunction, coagulation abnormalities, iron-rich, and high keto-acid environment in diabetic patients. Pulmonary mucormycosis always presents atypical manifestations with rapid progress and poor prognosis in patients with diabetes. This article reviews the recent research progress in the susceptible mechanisms of pulmonary mucormycosis in patients with diabetes.

The lung microbiome in end-stage Lymphangioleiomyomatosis.

Lymphangioleiomyomatosis (LAM) is a progressive cystic lung disease with mortality driven primarily by respiratory failure. Patients with LAM frequently have respiratory infections, suggestive of a dysregulated microbiome. Here we demonstrate that end-stage LAM patients have a distinct microbiome signature compared to patients with end-stage chronic obstructive pulmonary disease.

Prevalence of coccidioidomycosis in cystic fibrosis patients residing in Southern Arizona.

Sparse data exists about patients with cystic fibrosis (CF) and their risk of contracting coccidioidiomycosis or Valley Fever, which is highly endemic in southern Arizona. A retrospective review of medical records of 79 adult CF patients residing in Arizona was performed. Two cases only of coccidioidomycosis were documented between in the 790 patient years. However, false-positive serologies were found in 15 patients. This 10-year retrospective review of 79 adult CF patients found that there was a lower prevalence of coccidioidomycosis in CF patients compared to that of the general population of the area. LAY SUMMARY: Patients with cystic fibrosis (CF) suffer from chronic lung infection. Little is known about CF and fungal infection. Coccidioidomycosis is a fungal infection common in Arizona and this study shows a lower infection rate from Coccidioidomycosis in CF patients compared to the general population.

State-of-the-art review of secondary pulmonary infections in patients with COVID-19 pneumonia.

BACKGROUND: The incidence of secondary pulmonary infections is not well described in hospitalized COVID-19 patients. Understanding the incidence of secondary pulmonary infections and the associated bacterial and fungal microorganisms identified can improve patient outcomes. OBJECTIVE: This narrative review aims to determine the incidence of secondary bacterial and fungal pulmonary infections in hospitalized COVID-19 patients, and describe the bacterial and fungal microorganisms identified. METHOD: We perform a literature search and select articles with confirmed diagnoses of secondary bacterial and fungal pulmonary infections that occur 48 h after admission, using respiratory tract cultures in hospitalized adult COVID-19 patients. We exclude articles involving co-infections defined as infections diagnosed at the time of admission by non-SARS-CoV-2 viruses, bacteria, and fungal microorganisms. RESULTS: The incidence of secondary pulmonary infections is low at 16% (4.8-42.8%) for bacterial infections and lower for fungal infections at 6.3% (0.9-33.3%) in hospitalized COVID-19 patients. Secondary pulmonary infections are predominantly seen in critically ill hospitalized COVID-19 patients. The most common bacterial microorganisms identified in the respiratory tract cultures are Pseudomonas aeruginosa, Klebsiella species, Staphylococcus aureus, Escherichia coli, and Stenotrophomonas maltophilia. Aspergillus fumigatus is the most common microorganism identified to cause secondary fungal pulmonary infections. Other rare opportunistic infection reported such as PJP is mostly confined to small case series and case reports. The overall time to diagnose secondary bacterial and fungal pulmonary infections is 10 days (2-21 days) from initial hospitalization and 9 days (4-18 days) after ICU admission. The use of antibiotics is high at 60-100% involving the studies included in our review. CONCLUSION: The widespread use of empirical antibiotics during the current pandemic may contribute to the development of multidrug-resistant microorganisms, and antimicrobial stewardship programs are required for minimizing and de-escalating antibiotics. Due to the variation in definition across most studies, a large, well-designed study is required to determine the incidence, risk factors, and outcomes of secondary pulmonary infections in hospitalized COVID-19 patients.

Detection of glucosamine as a marker for Aspergillus niger: a potential screening method for fungal infections.

Several species of fungus from the genus Aspergillus are implicated in pulmonary infections in immunocompromised patients. Broad screening methods for fungal infections are desirable, as cultures require a considerable amount of time to provide results. Herein, we developed degradation and detection methods to produce and detect D-glucosamine (GlcN) from Aspergillus niger, a species of filamentous fungus. Ultimately, these techniques hold the potential to contribute to the diagnosis of pulmonary fungal infections in immunocompromised patients. In the following studies, we produced GlcN from fungal-derived chitin to serve as a marker for Aspergillus niger. To accomplish this, A. niger cells were lysed and subjected to a hydrochloric acid degradation protocol. Products were isolated, reconstituted in aqueous solutions, and analyzed using hydrophilic interaction liquid chromatography (HILIC) in tandem with electrospray ionization time-of-flight mass spectrometry. Our results indicated that GlcN was produced from A. niger. To validate these results, products obtained via fungal degradation were compared to products obtained from the degradation of two chitin polymers. The observed retention times and mass spectral extractions provided a two-step validation confirming that GlcN was produced from fungal-derived chitin. Our studies qualitatively illustrate that GlcN can be produced from A. niger; applying these methods to a more diverse range of fungi offers the potential to render a broad screening method for fungal detection pertinent to diagnosis of fungal infections.

Pulmonary Blastomycosis: A Rare Cause of Acute Chest Syndrome and Prolonged Fevers in a Pediatric Patient With Sickle Cell Disease.

Blastomyces is a fungus found in the soil of regions of North America including the Mississippi and Ohio River Valleys. It can be inhaled into the lungs and cause pneumonia and disseminated disease. Although blastomycosis is not widely reported in the sickle cell literature, sickle cell patients may be at increased risk of complications from blastomycosis pneumonia due to their immune compromise and risk of developing acute chest syndrome. We describe the case of a 13-year-old female with homozygous sickle cell disease who presented with pneumonia and acute chest syndrome and was found to have pulmonary blastomycosis.

[The spectrum of pathogens in 187 cases of pulmonary fungal disease diagnosed by histopathology-a retrospective analysis].

Objective: To investigate the spectrum of pathogens causing lung fungal disease diagnosed by histopathology through histochemical special staining, compared to the fungal culture results, and to further evaluate the diagnostic value of histochemical special staining in pulmonary fungal disease. Methods: We performed a retrospective analysis of 187 cases of pulmonary fungal disease diagnosed by histopathology in Peking Union Medical College Hospital from 2001 to 2015 (including 92 cases with pulmonary resection or open lung biopsy, 33 with percutaneous lung biopsy and 62 ones with fiberoptic bronchoscopic lung biopsy). All cases were treated with hexamine silver, PAS, mucus carmine and acid-fast staining in addition to conventional HE staining. The clinical records and the fungal culture results were reviewed. Results: There were 103 male and 84 female patients, aged from 12 to 70 years [average (48±14) years]. There were 85 cases(45.5%) of pulmonary aspergillosis(including 60 cases of invasive infection and 25 cases of aspergilloma), 51 cases(27.3%) of pulmonary cryptococosis, 6 cases (3.2%)of pulmonary mucormycosis, 3 cases(1.6%) of pulmonary histoplasmosis, 3 cases (1.6%)of pulmonary candidiasis, and 2 cases (1.1%) of pneumocystosis, while in the remaining 37 cases (19.8%) the pathogens could not be clearly classified by microscopy due to limited tissue or degeneration. Among the 88 patients with pulmonary fungal disease diagnosed by histopathology from 2011 to 2015, 35 ones (39.9%) were detected by fungal culture (including lung biopsy, intraoperative swab, blood, bronchoalveolar lavage fluid and sputum, etc.). The diagnostic results of 18 cases were completely consistent between histopathological examination and fungal culture (18/35, 51.4%), while 13 cases (13/35, 37.1%) were diagnosed by histopathology but no fungi were cultured, and in 3 cases (3/35,8.6%) the culture was positive for fungi which could not be classified clearly by histopathology. In another case the pathogen was found to be Cryptococcus histopathologically but the lavage culture grew"candida", but the patient's blood cryptococcal antigen was positive. Conclusions: Among patients with histopathological diagnosis of pulmonary fungal disease, pulmonary aspergillosis was the most common, followed by pulmonary cryptococcosis, pulmonary mucormycosis, pulmonary histoplasmosis, pulmonary candidiasis and pneumocystosis. A small number of cases could not be classified by histopathology through histochemical special staining. There was a high consistency in discovering fungal pathogens between pathological histochemical special staining and culture method, but 37% pulmonary fungal disease diagnosed by histopathology were culture negative. In practice, the role of histochemical special staining in diagnosing pulmonary fungal disease should be paid more attention.

Inhalation of Stachybotrys chartarum Fragments Induces Pulmonary Arterial Remodeling.

Stachybotrys chartarum is a fungal contaminant within the built environment and a respiratory health concern in the United States. The objective of this study was to characterize the mechanisms influencing pulmonary immune responses to repeatedly inhaled S. chartarum. Groups of B6C3F1/N mice repeatedly inhaled viable trichothecene-producing S. chartarum conidia (strain A or strain B), heat-inactivated conidia, or high-efficiency particulate absolute-filtered air twice per week for 4 and 13 weeks. Strain A was found to produce higher amounts of respirable fragments than strain B. Lung tissue, serum, and BAL fluid were collected at 24 and 48 hours after final exposure and processed for histology, flow cytometry, and RNA and proteomic analyses. At 4 weeks after exposure, a T-helper cell type 2-mediated response was observed. After 13 weeks, a mixed T-cell response was observed after exposure to strain A compared with a T-helper cell type 2-mediated response after strain B exposure. After exposure, both strains induced pulmonary arterial remodeling at 13 weeks; however, strain A-exposed mice progressed more quickly than strain B-exposed mice. BAL fluid was composed primarily of eosinophils, neutrophils, and macrophages. Both the immune response and the observed pulmonary arterial remodeling were supported by specific cellular, molecular, and proteomic profiles. The immunopathological responses occurred earlier in mice exposed to high fragment-producing strain A. The rather striking induction of pulmonary remodeling by S. chartarum appears to be related to the presence of fungal fragments during exposure.

Cryptococcus neoformans Evades Pulmonary Immunity by Modulating Xylose Precursor Transport.

Cryptococcus neoformans is a fungal pathogen that kills almost 200,000 people each year and is distinguished by abundant and unique surface glycan structures that are rich in xylose. A mutant strain of C. neoformans that cannot transport xylose precursors into the secretory compartment is severely attenuated in virulence in mice yet surprisingly is not cleared. We found that this strain failed to induce the nonprotective T helper cell type 2 (Th2) responses characteristic of wild-type infection, instead promoting sustained interleukin 12p40 (IL-12p40) induction and increased IL-17A (IL-17) production. It also stimulated dendritic cells to release high levels of proinflammatory cytokines, a behavior we linked to xylose expression. We further discovered that inducible bronchus-associated lymphoid tissue (iBALT) forms in response to infection with either wild-type cryptococci or the mutant strain with reduced surface xylose; although iBALT formation is slowed in the latter case, the tissue is better organized. Finally, our temporal studies suggest that lymphoid structures in the lung restrict the spread of mutant fungi for at least 18 weeks after infection, which is in contrast to ineffective control of the pathogen after infection with wild-type cells. These studies demonstrate the role of xylose in modulation of host response to a fungal pathogen and show that cryptococcal infection triggers iBALT formation.

CD200R1 regulates eosinophilia during pulmonary fungal infection in mice.

CD200 receptor 1(CD200R1) signalling limits myeloid cell responses and reduces autoimmunity, alloimmunity and viral-mediated immunopathology, but has never been examined in the context of eosinophilic inflammation. Susceptibility to lung fungal infection is associated with T-helper 2 (Th2) cytokine dominated responses and strong eosinophilic pathology. Blockade of CD200R1 enhances type I cytokine responses in many infectious and non-infectious settings and so may promote a more protective response to fungal infection. By contrast, we demonstrate that, rather than promoting type I cytokine responses, CD200R1 blockade enhanced eosinophilia in a mouse model of Cryptococcus neoformans infection, whereas CD200R1 agonism reduced lung eosinophilia - with neither strategy completely altering fungal burden. Thus, we reveal a surprising disconnect between pulmonary eosinophilia and cryptococcal burden and dissemination. This research has 2 important implications. Firstly, a lack of CD200R1 signalling enhances immune responses regardless of cytokine polarisation, and secondly reducing eosinophils does not allow protective immunity to develop in susceptible fungal system. Therefore, agonists of CD200R1 may be beneficial for eosinophilic pathologies.

Titan cells formation in Cryptococcus neoformans is finely tuned by environmental conditions and modulated by positive and negative genetic regulators.

The pathogenic fungus Cryptococcus neoformans exhibits morphological changes in cell size during lung infection, producing both typical size 5 to 7 µm cells and large titan cells (> 10 µm and up to 100 µm). We found and optimized in vitro conditions that produce titan cells in order to identify the ancestry of titan cells, the environmental determinants, and the key gene regulators of titan cell formation. Titan cells generated in vitro harbor the main characteristics of titan cells produced in vivo including their large cell size (>10 µm), polyploidy with a single nucleus, large vacuole, dense capsule, and thick cell wall. Here we show titan cells derived from the enlargement of progenitor cells in the population independent of yeast growth rate. Change in the incubation medium, hypoxia, nutrient starvation and low pH were the main factors that trigger titan cell formation, while quorum sensing factors like the initial inoculum concentration, pantothenic acid, and the quorum sensing peptide Qsp1p also impacted titan cell formation. Inhibition of ergosterol, protein and nucleic acid biosynthesis altered titan cell formation, as did serum, phospholipids and anti-capsular antibodies in our settings. We explored genetic factors important for titan cell formation using three approaches. Using H99-derivative strains with natural genetic differences, we showed that titan cell formation was dependent on LMP1 and SGF29 genes. By screening a gene deletion collection, we also confirmed that GPR4/5-RIM101, and CAC1 genes were required to generate titan cells and that the PKR1, TSP2, USV101 genes negatively regulated titan cell formation. Furthermore, analysis of spontaneous Pkr1 loss-of-function clinical isolates confirmed the important role of the Pkr1 protein as a negative regulator of titan cell formation. Through development of a standardized and robust in vitro assay, our results provide new insights into titan cell biogenesis with the identification of multiple important factors/pathways.

IFN-γ immune priming of macrophages in vivo induces prolonged STAT1 binding and protection against Cryptococcus neoformans.

Development of vaccines against opportunistic infections is difficult as patients most at risk of developing disease are deficient in aspects of the adaptive immune system. Here, we utilized an experimental immunization strategy to induce innate memory in macrophages in vivo. Unlike current trained immunity models, we present an innate memory-like phenotype in macrophages that is maintained for at least 70 days post-immunization and results in complete protection against secondary challenge in the absence of adaptive immune cells. RNA-seq analysis of in vivo IFN-γ primed macrophages revealed a rapid up-regulation of IFN-γ and STAT1 signaling pathways following secondary challenge. The enhanced cytokine recall responses appeared to be pathogen-specific, dependent on changes in histone methylation and acetylation, and correlated with increased STAT1 binding to promoter regions of genes associated with protective anti-fungal immunity. Thus, we demonstrate an alternative mechanism to induce macrophage innate memory in vivo that facilitates pathogen-specific vaccine-mediated immune responses.

The Cryptococcus neoformans Titan cell is an inducible and regulated morphotype underlying pathogenesis.

Fungal cells change shape in response to environmental stimuli, and these morphogenic transitions drive pathogenesis and niche adaptation. For example, dimorphic fungi switch between yeast and hyphae in response to changing temperature. The basidiomycete Cryptococcus neoformans undergoes an unusual morphogenetic transition in the host lung from haploid yeast to large, highly polyploid cells termed Titan cells. Titan cells influence fungal interaction with host cells, including through increased drug resistance, altered cell size, and altered Pathogen Associated Molecular Pattern exposure. Despite the important role these cells play in pathogenesis, understanding the environmental stimuli that drive the morphological transition, and the molecular mechanisms underlying their unique biology, has been hampered by the lack of a reproducible in vitro induction system. Here we demonstrate reproducible in vitro Titan cell induction in response to environmental stimuli consistent with the host lung. In vitro Titan cells exhibit all the properties of in vivo generated Titan cells, the current gold standard, including altered capsule, cell wall, size, high mother cell ploidy, and aneuploid progeny. We identify the bacterial peptidoglycan subunit Muramyl Dipeptide as a serum compound associated with shift in cell size and ploidy, and demonstrate the capacity of bronchial lavage fluid and bacterial co-culture to induce Titanisation. Additionally, we demonstrate the capacity of our assay to identify established (cAMP/PKA) and previously undescribed (USV101) regulators of Titanisation in vitro. Finally, we investigate the Titanisation capacity of clinical isolates and their impact on disease outcome. Together, these findings provide new insight into the environmental stimuli and molecular mechanisms underlying the yeast-to-Titan transition and establish an essential in vitro model for the future characterization of this important morphotype.