Host Factors and Outcomes in Hospitalizations for Pneumocystis Jirovecii Pneumonia in the United States

Clinical performance of BALF droplet digital PCR for differential diagnosis of Pneumocystis jirovecii pneumonia and Pneumocystis jirovecii colonization

BACKGROUND

Accurate differentiation between Pneumocystis jirovecii (Pj) infection and colonization is crucial for effective treatment.

METHODS

From September 2016 to June 2022, 89 immunocompromised patients with unexplained lung infiltrates and clinical suspicion of Pj pneumonia were enrolled at Peking University People's Hospital. Bronchoalveolar lavage fluid (BALF) of these patients were detected by quantitative PCR (qPCR) and droplet digital PCR (ddPCR).

RESULTS

The performance of ddPCR was superior to qPCR in detecting Pj infection. Area under the curve was 0.97 (95 %CI: 0.94-1) for ddPCR of the BALF in all patients. The optimal threshold value for discriminating Pj infection from colonization by ddPCR was 13.98 copies/test, with a sensitivity of 97.96 %, specificity of 85.71 %. No obvious correlation between ddPCR copy number and disease severity was observed.

CONCLUSION

BALF ddPCR exhibits robust potential in detecting Pj and effectively discriminating colonization and infection.

Extracellular vesicles from Pneumocystis carinii-infected rats impair fungal viability but are dispensable for macrophage functions

Pneumocystis spp. are host obligate fungal pathogens that can cause severe pneumonia in mammals and rely heavily on their host for essential nutrients. The lack of a sustainable in vitro culture system poses challenges in understanding their metabolism, and the acquisition of essential nutrients from host lungs remains unexplored. Transmission electron micrographs show that extracellular vesicles (EVs) are found near Pneumocystis spp. within the lung. We hypothesized that EVs transport essential nutrients to the fungi during infection. To investigate this, EVs from P. carinii- and P. murina-infected rodents were biochemically and functionally characterized. These EVs contained host proteins involved in cellular, metabolic, and immune processes as well as proteins with homologs found in other fungal EV proteomes, indicating that Pneumocystis may release EVs. Notably, EV uptake by P. carinii indicated their potential involvement in nutrient acquisition and a possibility for using engineered EVs for efficient therapeutic delivery. However, EVs added to P. carinii in vitro did not show increased growth or viability, implying that additional nutrients or factors are necessary to support their metabolic requirements. Exposure of macrophages to EVs increased proinflammatory cytokine levels but did not affect macrophages' ability to kill or phagocytose P. carinii. These findings provide vital insights into P. carinii and host EV interactions, yet the mechanisms underlying P. carinii's survival in the lung remain uncertain. These studies are the first to isolate, characterize, and functionally assess EVs from Pneumocystis-infected rodents, promising to enhance our understanding of host-pathogen dynamics and therapeutic potential.IMPORTANCEPneumocystis spp. are fungal pathogens that can cause severe pneumonia in mammals, relying heavily on the host for essential nutrients. The absence of an in vitro culture system poses challenges in understanding their metabolism, and the acquisition of vital nutrients from host lungs remains unexplored. Extracellular vesicles (EVs) are found near Pneumocystis spp., and it is hypothesized that these vesicles transport nutrients to the pathogenic fungi. Pneumocystis proteins within the EVs showed homology to other fungal EV proteomes, suggesting that Pneumocystis spp. release EVs. While EVs did not significantly enhance P. carinii growth in vitro, P. carinii displayed active uptake of these vesicles. Moreover, EVs induced proinflammatory cytokine production in macrophages without compromising their ability to combat P. carinii. These findings provide valuable insights into EV dynamics during host-pathogen interactions in Pneumocystis pneumonia. However, the precise underlying mechanisms remain uncertain. This research also raises the potential for engineered EVs in therapeutic applications.

Epidemiology, Clinical Characteristics, and Diagnostic Testing Practices for Pneumocystis Pneumonia-Associated Hospitalizations, United States, 2019-2022

Among 9196 hospitalizations involving Pneumocystis pneumonia, those without HIV had higher in-hospital mortality (24.3% vs 10.5%, P < .001) when compared with those with HIV. These findings underscore the continued importance of Pneumocystis pneumonia clinical awareness and the need for comprehensive prophylaxis guidance, particularly for certain patients without HIV who are immunosuppressed.

The Clinical Value of Metagenomic Next-Generation Sequencing in Pneumocystis jirovecii Pneumonia

Background

The incidence of Pneumocystis jirovecii pneumonia (PJP) is increasing.

Methods

108 patients were analysed retrospectively at the Wuhan Union Hospital. The patients were classified into the PJP group or the P. jirovecii colonisation (PJC) group based on clinical diagnosis. Clinical data included demographics, laboratory examinations, treatment, and outcomes.

Results

A notable difference in the fungal load was seen between two groups, with median reads of 3215.79 vs. 5.61 in two groups, respectively (P<0.001). The optimal threshold value for discriminating P. jirovecii infection between colonisation for mNGS was six, and serum (1,3)-β-D-glucan (BDG) was 47.6 pg/mL. Besides, the positive detection rate of mNGS for co-pathogens in PJP patients was significantly higher than that of culture (88.16% vs. 22.37%, P<0.0001). Epstein-Barr virus and cytomegalovirus were the most common pathogens of co-infection in PJP patients. The antibiotic therapy in PJP patients was adjusted according to the mNGS results, of which seventeen (22.37%) were downgraded, 38 (50.0%) patients were upgraded, and 21 (27.63%) were unchanged. And almost all patients showed significant improvement in C-reactive protein.

Conclusion

mNGS is a promising and valuable technique with good performance for differentiating P. jirovecii infection and colonisation, the detection of pathogens, and antibiotic treatment.

Role of fungal burden in risk stratification of HIV-negative patients with Pneumocystis pneumonia: A 12-year, retrospective, observational, multicenter cohort

OBJECTIVES

This study aimed to explore the role of fungal burden in risk stratification of patients without HIV-negative patients with Pneumocystis pneumonia (PCP).

METHODS

This was a retrospective analysis of the characteristics associated with 30-day mortality in patients who were positive for P. jirovecii using polymerase chain reaction in bronchoalveolar lavage fluid between 2006 and 2017 in a multicenter cohort from Central Norway. The fungal burden was indicated by the cycle threshold (CT) values from semiquantitative real-time polymerase chain reaction targeting the β-tubulin gene.

RESULTS

We included 170 patients with proven or probable PCP. The all-cause 30-day mortality was 18.2%. After adjusting for host characteristics and premorbid corticosteroid use, a higher fungal burden was associated with a higher risk of dying: adjusted odds ratio 1.42 (95% confidence interval 0.48-4.25) for a CT value 31-36, increasing to odds ratio 5.43 (95% confidence interval 1.48-19.9) for a CT value ≤30 compared with patients with a CT value ≥37. The Charlson comorbidity index (CCI) improved the risk stratification: patients with a CT value ≥37 and CCI ≤2 had a 9% mortality risk compared with 70% among those with a CT value ≤30 and CCI ≥6. Comorbid cardiovascular disease, solid tumors, immunological disorders, premorbid corticosteroids, hypoxemia, abnormal leukocyte counts, low serum albumin, and C-reactive protein ≥100 were also independently associated with 30-day mortality. The sensitivity analyses did not suggest selection bias.

CONCLUSION

Fungal burden may improve the risk stratification of patients without HIV-negative patients with PCP.

Pneumocystis jirovecii pneumonia in intensive care units: a multicenter study by ESGCIP and EFISG

BACKGROUND

Pneumocystis jirovecii pneumonia (PJP) is an opportunistic, life-threatening disease commonly affecting immunocompromised patients. The distribution of predisposing diseases or conditions in critically ill patients admitted to intensive care unit (ICU) and subjected to diagnostic work-up for PJP has seldom been explored.

MATERIALS AND METHODS

The primary objective of the study was to describe the characteristics of ICU patients subjected to diagnostic workup for PJP. The secondary objectives were: (i) to assess demographic and clinical variables associated with PJP; (ii) to assess the performance of Pneumocystis PCR on respiratory specimens and serum BDG for the diagnosis of PJP; (iii) to describe 30-day and 90-day mortality in the study population.

RESULTS

Overall, 600 patients were included in the study, of whom 115 had presumptive/proven PJP (19.2%). Only 8.8% of ICU patients subjected to diagnostic workup for PJP had HIV infection, whereas hematological malignancy, solid tumor, inflammatory diseases, and solid organ transplants were present in 23.2%, 16.2%, 15.5%, and 10.0% of tested patients, respectively. In multivariable analysis, AIDS (odds ratio [OR] 3.31; 95% confidence interval [CI] 1.13-9.64, p = 0.029), non-Hodgkin lymphoma (OR 3.71; 95% CI 1.23-11.18, p = 0.020), vasculitis (OR 5.95; 95% CI 1.07-33.22, p = 0.042), metastatic solid tumor (OR 4.31; 95% CI 1.76-10.53, p = 0.001), and bilateral ground glass on CT scan (OR 2.19; 95% CI 1.01-4.78, p = 0.048) were associated with PJP, whereas an inverse association was observed for increasing lymphocyte cell count (OR 0.64; 95% CI 0.42-1.00, p = 0.049). For the diagnosis of PJP, higher positive predictive value (PPV) was observed when both respiratory Pneumocystis PCR and serum BDG were positive compared to individual assay positivity (72% for the combination vs. 63% for PCR and 39% for BDG). Cumulative 30-day mortality and 90-day mortality in patients with presumptive/proven PJP were 52% and 67%, respectively.

CONCLUSION

PJP in critically ill patients admitted to ICU is nowadays most encountered in non-HIV patients. Serum BDG when used in combination with respiratory Pneumocystis PCR could help improve the certainty of PJP diagnosis.

How to diagnose and treat a non-HIV patient with Pneumocystis jirovecii pneumonia (PCP)?

BACKGROUND

Pneumocystis jirovecii Pneumonia (PCP) incidence is increasing in non-HIV infected patients. In contrast to PCP in patients infected with HIV, diagnosis is often delayed, and illness is associated with an increased mortality.

OBJECTIVE

To provide a comprehensive review of clinical presentation, risk factors, diagnostic strategies, and treatment options of PCP in non-HIV-infected patients.

SOURCES

Web-based literature review on PCP for trials, meta-analyses and systematic reviews using PubMed. Restriction to English language was applied.

CONTENT

Common underlying conditions in non-HIV-infected patients with PCP are haematological malignancies, autoimmune and inflammatory diseases, solid organ or haematopoietic stem cell transplant and prior exposure to corticosteroids. New risk groups include patients receiving monoclonal antibodies and immunomodulating therapies. Non-HIV-infected patients with PCP present with rapid onset and progression of pneumonia, increased duration of hospitalization and a significantly higher mortality rate than patients infected with HIV. PCP is diagnosed by a combination of clinical symptoms, radiological and mycological features. Immunofluorescence microscopy from bronchoalveolar lavage (BAL) or PCR testing CT imaging and evaluation of the clinical presentation are required. The established treatment regime consists of trimethoprim and sulfamethoxazole.

IMPLICATIONS

While the number of patients immunosuppressed for other causes than HIV is increasing, a simultaneous rise in PCP incidence is observed. In the group of non-HIV-infected patients, a rapid onset of symptoms, a more complex course, and a higher mortality rate are recorded. Therefore, time to diagnosis must be as short as possible to initiate effective therapy promptly. This review aims to raise awareness of PCP in an increasingly affected at-risk group and provide clinicians with a practical guide for efficient diagnosis and targeted therapy. Furthermore, it intends to display current inadequacies in research on the topic of PCP.

Case report: A HIV-negative hemodialysis patient positive for pANCA with severe pneumocystis pneumonia: A case report and review of literature

RATIONALE

Pneumocystis pneumonia (PCP) is an opportunistic fungal infection that occurs in people with impaired or suppressed immunity such as patients with human immunodeficiency virus or organ transplant. However, the incidence and characteristics of PCP in the population with long-term hemodialysis is poorly described in the literature.

PATIENT CONCERNS

We present a case of a 50-year-old female patient being transferred to our hospital in February 2022 with a 20-day history of cough and tight breath. She received amoxicillin and cephalosporin anti-infection treatment successively in local hospital but no significant improvement in symptoms. She had a 2-year history of hemodialysis and no relevant transplantation and human immunodeficiency virus infection. She was diagnosed as ANCA associated vasculitis (AAV) and given oral prednisone acetate (20 mg/day) and methotrexate (2.5 mg/week) half a year ago.

DIAGNOSES

Based on the patient's medical history, Lung computerized tomography image, the Next generation sequencing report, the patient was diagnosed with renal failure, anti-neutrophil cytoplasmic antibody associated vasculitis, and Pneumocystis pneumonia.

INTERVENTIONS

The dosage of immunosuppressant was reduced due to leucocyte dripping and fever, and antibiotic and antifungal treatment were also given. The patient's lung condition was getting worse and noninvasive ventilator was required to maintain blood oxygen. Blood filtration is used to remove toxins. Ganciclovir and trimethoprim-sulfamethoxazole was used based on the next generation sequencing report.

OUTCOMES

The patient died of respiratory failure.

LESSONS

The risk of PCP in hemodialysis patients may be higher than that in ordinary population, and the prognosis of patients with immunosuppression may be worse. Dynamic assessment of vasculitis activity is necessary for hemodialysis patients with AAV because infections may obscure lung symptoms of AAV. It is not recommended that hemodialysis patients with long-term immunosuppression should reduce or stop the dosage of immunosuppressive drugs during the treatment because it may aggravate the condition of PCP. There is still no clear conclusion on whether hemodialysis patients need preventive medicine, but the identification of risk factors and early diagnosis and treatment are important for the prognosis of PCP on hemodialysis population.

Clinical characteristics and risk factor analysis of Pneumocystis jirovecii pneumonia in patients with CKD: a machine learning-based approach

Patients with chronic kidney disease (CKD) who are being treated with immunosuppressive medications are at risk for developing Pneumocystis jirovecii pneumonia (PCP). We attempted to characterize the clinical aspects of PCP in CKD patients in order to alert high-risk patients with bad prognosis. A retrospective study of CKD patients was conducted from June 2018 to June 2022. Based on PCP diagnostic criteria, these patients were divided into PCP and non-PCP groups. Using univariate and multivariate logistic regression analysis, risk indicators were evaluated, and nomogram and decision tree were developed. Of the CKD patients screened for Pneumocystis carinii nucleic acid, 1512 were included. Two-hundred forty four (16.14%) were diagnosed with PCP. Of the PCP, 88.5% was receiving glucocorticoid (GC) therapy, of which 66.3% received more than 0.5 mg/kg GC. Multivariate analysis showed that membranous nephropathy (OR 2.35, 95% CI 1.45-3.80), immunosuppressive therapy (OR 1.94, 95% CI 1.06-3.69), and ground glass opacity of CT scanning (OR 1.71, 95% CI 1.10-2.65) were associated with increased risk of Pneumocystis carinii infection. The AUC of nomogram based on logistics regression was 0.78 (0.75-0.81). The mortality in patients with PCP was 32.40%. Univariate analysis and decision tree showed that pulmonary insufficiency (PO₂: OR 0.98, 95% CI 0.96-1.00), elevated APTT (OR 1.07, 95% CI 1.04-1.11), and reduced hemoglobin (OR 0.97, 95% CI 0.96-0.98) were associated with poor prognosis. PCP is not rare in CKD patients, particularly in those treated with immunosuppressive therapy. Considering the high mortality of the cases, further studies on the prevention and management of these patients are needed.

Prophylactic effect of low-dose trimethoprim-sulfamethoxazole for Pneumocystis jirovecii pneumonia in adult recipients of kidney transplantation: a real-world data study

OBJECTIVES

To evaluate the efficacy and safety of low-dose trimethoprim (TMP)-sulfamethoxazole (SMX) (TMP-SMX) as the primary prophylaxis for Pneumocystis jirovecii pneumonia (PJP) in adult recipients of kidney transplantation.

METHODS

Three kinds of prescriptions in kidney recipients were documented, including 20 mg TMP/100 mg SMX oral daily, 20 mg TMP/100 mg SMX oral every other day, and nonprophylaxis. The primary outcome was the incidence of PJP in the first 180 days of follow-up after kidney transplantation. The secondary outcomes were changes in renal and liver function.

RESULTS

Among the 1469 recipients, 1066 (72.56%) received 20 mg TMP/100 mg SMX daily, 127 (8.65%) received 20 mg TMP/100 mg SMX every other day, and 276 (18.79%) did not have prophylaxis prescription. The 276 recipients in the nonprophylaxis group had 124.92 person-years of follow-up, during which PJP occurred in 29 patients, for an incidence rate of 23.21 (95% confidence interval 15.76-32.72) per 100 person-years. The TMP-SMX daily group and the TMP-SMX every other day group had 524.89 and 62.07 person-years of follow-up, respectively, with no occurrence of PJP. There was no significant difference among the three groups in changes in renal and liver function (P >0.05, respectively). A total of 111 recipients in each group were enrolled in the propensity score matching analysis. It was revealed that the 111 nonprophylaxis recipients had 51.27 person-years of follow-up and 10 PJP cases. Prophylaxis was considered effective because there was a significant difference between the three groups (P <0.001).

CONCLUSION

Low-dose TMP-SMX prophylaxis significantly reduces the incidence of PJP within 6 months after kidney transplantation and has a favorable safety profile.

Development and Evaluation of Rapid and Accurate CRISPR/Cas13-Based RNA Diagnostics for Pneumocystis jirovecii Pneumonia

Background

Pneumocystis jirovecii can result in a serious pulmonary infection, Pneumocystis jirovecii pneumonia, in immunocompetent hosts. The diagnosis of Pneumocystis jirovecii pneumonia has long been a major clinical concern, and there are limitations with the currently utilized immunostaining and polymerase chain reaction diagnosis/detection technologies (e.g., insufficient sensitivity and accuracy). Hence, we sought to establish a rapid and RNA-specific transcription mediated amplification and CRISPR/Cas13a-based diagnostics targeted P. jirovecii-mitochondrial large subunit ribosomal RNA.

Methods

The procedure of the diagnostics included amplification of the extracted RNA samples by transcription mediated amplification, followed by CRISPR/Cas13 detection, and ultimately, the judgment of the results after 30 minutes of fluorescence signal. Later, the diagnostic performance of the CRISPR/Cas13-based diagnostics were tested on the 62 surplus clinical samples.

Results

This CRISPR/Cas13-based diagnostics achieved limits of detection of approximately 2 copies/µL transcribed RNA templates, with no cross reaction to other respiratory pathogens, including bacteria and fungi. Similar to in-house quantitative real-time polymerase chain reaction, CRISPR/Cas13-based diagnostics was still positive in 243-fold diluted bronchial alveolar lavage fluid. A preliminary evaluation of 62 surplus bronchial alveolar lavage fluid samples from patients suspected of Pneumocystis jirovecii pneumonia showed that CRISPR/Cas13-based diagnostics achieved a 78.9% sensitivity and a 97.7% specificity in the diagnosis of Pneumocystis jirovecii pneumonia.

Conclusion

Our study demonstrates that the CRISPR/Cas13-based diagnostics technique has good performance for the accurate and specific diagnosis of Pneumocystis jirovecii pneumonia.

Massive Cavitation by Pneumocystis jirovecii in an Immunocompromised Patient

Since the development of antiretroviral therapy (ART) and antibiotic prophylaxis, the incidence of opportunistic infections in human immunodeficiency virus-acquired immunodeficiency syndrome (HIV-AIDS) has been drastically reduced. However, third-world countries remain a fertile ground for medication nonadherence and inappropriate patient follow-up. Here, we present the case of a 42-year-old male with a history of HIV who presented with worsening shortness of breath and atypical chest pain. A chest X-ray and chest computed tomography scan revealed a left parahilar cavitation measuring 86 mm in diameter. A percutaneous lung biopsy revealed Pneumocystis jirovecii. Appropriate antibiotics were started, and the patient’s clinical status significantly improved. This case illustrates the devastating consequences of uncontrolled HIV-AIDS. ART and prophylactic antibiotics remain the cornerstone of treatment to ameliorate progressive lung damage in patients.

Evolving epidemiology of pneumocystis pneumonia: Findings from a longitudinal population-based study and a retrospective multi-center study in Germany

Background

Pneumocystis pneumonia (PCP) is a life-threatening opportunistic infectious disease of immunocompromised patients. Its incidence has decreased worldwide in the past, but data concerning its recent epidemiology are lacking.

Methods

We retrospectively analyzed all German inpatient cases from January 1, 2014 to December 31, 2019, to describe the recent epidemiology, incidence, clinical course, mortality and underlying diseases of PCP. Simultaneously, we conducted a retrospective multi-center study at two German university hospitals, and analyzed PCP cases treated there to gain deeper insights on the basis of primary patient data.

Findings

The incidence of PCP significantly increased from 2·3 to 2·6 per 100,000 population from 2014 to 2019 (1,857 to 2,172 cases, +17·0%, p < 0·0001), as well as PCP-related deaths (516 to 615 cases, +19·2%, p = 0·011). The spectrum of underlying diseases changed: Risk groups with established chemoprophylaxis for PCP based on international guidelines (HIV, hematologic malignancies, and transplantation) showed a significant decrease in PCP cases and deaths. Others, especially those with solid malignancies, and autoimmune and pulmonary diseases showed a significant increase in case numbers and deaths. Data from the retrospective multi-center study added information regarding prophylaxis and diagnostics of PCP.

Interpretation

The incidence of PCP has reversed its trend, showing a significant increase in mortality on population level. Patients who were not previously considered in prophylactic measures are increasingly affected by PCP. This development deserves further investigation, and additional comprehensive guidelines for the use of chemoprophylaxis in new risk groups are needed.

Funding

Department of Nephrology and Hypertension, University Hospital Schleswig-Holstein, Kiel.

Proteomic Profiling and Functional Analysis of B Cell-Derived Exosomes upon Pneumocystis Infection

Pneumocystis is a life-threatening fungal pathogen that frequently causes fatal pneumonia (PCP) in immunocompromised individuals. Recently, B cells have been reported to play a crucial role in the pathogenesis of PCP through producing antibodies and activating CD4+ T cell response. Exosomes are nanoscale small extracellular vesicles abundant with protein cargo and can mediate immune response during infectious disease. In this study, using tandem mass tag-based quantitative proteomics coupled with bioinformatic analysis, we attempted to characterize exosomes derived from B lymphocytes in response to PCP. Several proteins were verified by parallel reaction monitoring (PRM) analysis. Also, the effects of B cell exosomes on CD4+ T cell response and phagocytic function of macrophages were clarified. Briefly, 1701 proteins were identified from B cell exosomes, and the majority of them were reported in Vesiclepedia. A total of 51 differentially expressed proteins of B cell exosomes were found in response to PCP. They were mainly associated with immune response and transcription regulation. PRM analysis confirmed the significantly changed levels of histone H1.3, vimentin, and tyrosine-protein phosphatase nonreceptor type 6 (PTPN6). Moreover, a functional study revealed the proinflammatory profile of B cell exosomes on CD4+ T cell response in PCP. Taken together, our results suggest the involvement of exosomes derived from B cells in cell-to-cell communication, providing new information on the function of B cells in response to PCP.

On the Treatment of Pneumocystis jirovecii Pneumonia: Current Practice Based on Outdated Evidence

Pneumocystis jirovecii pneumonia (PCP) is a common opportunistic infection causing more than 400000 cases annually worldwide. Although antiretroviral therapy has reduced the burden of PCP in persons with human immunodeficiency virus (HIV), an increasing proportion of cases occur in other immunocompromised populations. In this review, we synthesize the available randomized controlled trial (RCT) evidence base for PCP treatment. We identified 14 RCTs that were conducted 25-35 years ago, principally in 40-year-old men with HIV. Trimethoprim-sulfamethoxazole, at a dose of 15-20 mg/kg per day, is the treatment of choice based on historical practice rather than on quality comparative, dose-finding studies. Treatment duration is similarly based on historical practice and is not evidence based. Corticosteroids have a demonstrated role in hypoxemic patients with HIV but have yet to be studied in RCTs as an adjunctive therapy in non-HIV populations. The echinocandins are potential synergistic treatments in need of further investigation.

The Long-Acting Echinocandin, Rezafungin, Prevents Pneumocystis Pneumonia and Eliminates Pneumocystis from the Lungs in Prophylaxis and Murine Treatment Models

Rezafungin is a novel echinocandin in Phase 3 development for prevention of invasive fungal disease caused by Candida spp., Aspergillus spp. and Pneumocystis jirovecii in blood and marrow transplantation patients. For such patients, standard antifungal prophylaxis currently comprises an azole for Candida and Aspergillus plus trimethoprim-sulfamethoxazole (TMP-SMX) for Pneumocystis pneumonia (PCP) despite drug-drug-interactions and intolerability that may limit their use, thus, alternatives are desirable. Rezafungin demonstrates a favorable safety profile and pharmacokinetic properties that allow for once-weekly dosing in addition, to antifungal activity against these predominant pathogens. Herein, the in vivo effects of rezafungin against Pneumocystis murina pneumonia were evaluated in immunosuppressed mouse models of prophylaxis and treatment using microscopy and qPCR assessments. In the prophylaxis model, immunosuppressed mice inoculated with P. murina were administered TMP-SMX (50/250 mg/kg 1×/week or 3×/week), caspofungin (5 mg/kg 3×/week), rezafungin (20 mg/kg, 1×/week or 3×/week; 5 mg/kg, 3×/week) intraperitoneally for 2, 4, 6 and 8 weeks, then immunosuppressed for an additional 6 weeks. Rezafungin administered for 4 weeks prevented P. murina from developing infection after rezafungin was discontinued. In the treatment model, immunosuppressed mice with P. murina pneumonia were treated with rezafungin 20 mg/kg 3×/week intraperitoneally for 2, 4, 6 and 8 weeks. Treatment with rezafungin for 8 weeks resulted in elimination of P. murina. Collectively, these studies showed that rezafungin could both prevent infection and eliminate P. murina from the lungs of mice. These findings support the obligate role of sexual reproduction for survival and growth of Pneumocystis spp. and warrant further investigation for treatment of P. jirovecii pneumonia in humans.

The Persistent Challenge of Pneumocystis Growth Outside the Mammalian Lung: Past and Future Approaches

The pathogenic fungi in the genus, Pneumocystis, have eluded attempts to continuously grow them in an ex vivo cultivation system. New data from transcriptomic and genomic sequencing studies have identified a myriad of absent metabolic pathways, helping to define their host obligate nature. These nutrients, factors, and co-factors are acquired from their mammalian host and provide clues to further supplementation of existing media formulations. Likewise, a new appreciation of the pivotal role for the sexual cycle in the survival and dissemination of the infection suggests that Pneumocystis species are obligated to undergo mating and sexual reproduction in their life cycle with a questionable role for an asexual cycle. The lack of ascus formation in any previous cultivation attempts may explain the failure to identify a sustainable system. Many characteristics of these ascomycetes suggest a biotrophic existence within the lungs of the mammalian hosts. In the present review, previous attempts at growing these fungi ex vivo are summarized. The significance of their life cycle is considered, and a list of potential supplements based on the genomic and transcriptomic studies is presented. State of the art technologies such as metabolomics, organoids, lung-on-a chip, and air lift cultures are discussed as potential growth systems.