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Background. Correlates of immune protection in patients with human immunodeficiency virus (HIV)-associated cryptococcal meningitis are poorly defined. A clearer understanding of these immune responses is essential to inform rational development of immunotherapies. Methods. Cryptococcal-specific peripheral CD4 + T-cell responses were measured in 44 patients with HIV-associated cryptococcal meningitis at baseline and during follow-up. Responses were assessed following ex vivo cryptococcal mannoprotein stimulation, using 13-color flow-cytometry. The relationships between cryptococcal-specific CD4 + T-cell responses, clinical parameters at presentation, and outcome were investigated. Results. Cryptococcal-specific CD4 + T-cell responses were characterized by the production of macrophage inflammatory protein 1α, interferon γ (IFN-γ), and tumor necrosis factor α (TNF-α). Conversely, minimal interleukin 4 and interleukin 17 production was detected. Patients surviving to 2 weeks had significantly different functional CD4 + T-cell responses as compared to those who died. Patients with a response predominantly consisting of IFN-γ or TNF-α production had a 2-week mortality of 0% (0/20), compared with 25% (6/24) in those without this response (P=.025). Such patients also had lower fungal burdens (10 400 vs 390 000 colony-forming units/mL; P < .001), higher cerebrospinal fluid lymphocyte counts (122 vs 8 cells/μL; P < .001), and a trend toward faster rates of clearance of infection. Conclusions. The phenotype of the peripheral CD4 + T-cell response to Cryptococcus was associated with disease severity and outcome in HIV-associated cryptococcal meningitis. IFN-γ/TNF-α—predomiant responses were associated with survival.

The cryptococcal antigen (CRAG) lateral flow assay (LFA) had 100% sensitivity and specificity on cerebrospinal fluid samples. Pretreatment LFA titers correlated with quantitative cultures (R 2 = 0.7) and predicted 2- and 10-week mortality. The CRAG LFA is an accurate diagnostic assay for CSF and should be considered for point-of-care diagnosis of cryptococcal meningitis.

A common feature shared by systemic fungal pathogens of environmental origin, such as Cryptococcus neoformans , is their ability to adapt to mammalian core body temperature. In C. neoformans , this adaptation is accompanied by Ccr4-mediated decay of ribosomal protein mRNAs. Here we use the related, but thermo-intolerant species Cryptococcus amylolentus to demonstrate that this response contributes to host-temperature adaptation and pathogenicity of cryptococci. In a C. neoformans ccr4 Δ mutant, stabilized ribosomal protein mRNAs are retained in the translating pool, and stress-induced transcriptomic changes are reduced in comparison with the wild type strain, likely due to ineffective translation of transcription factors. In addition, the mutant displays increased exposure of cell wall glucans, and recognition by Dectin-1 results in increased phagocytosis by lung macrophages, linking mRNA decay to adaptation and immune evasion. The fungal pathogen Cryptococcus neoformans can adapt to mammalian core body temperature. Here, Bloom et al. show that Ccr4-mediated decay of ribosomal protein mRNAs is important for thermotolerance and immune evasion by promoting masking of cell wall glucans.

Invasive fungal infections kill more than 1.5 million people each year, with limited treatment options. There is no vaccine available in clinical use to prevent and control fungal infections. Our recent studies showed that a mutant of the F-box protein Fbp1, a subunit of the SCF(Fbp1) E3 ligase in Cryptococcus neoformans , elicited superior protective Th1 host immunity. Here, we demonstrate that the heat-killed fbp1 Δ cells (HK-fbp1) can be harnessed to confer protection against a challenge by the virulent parental strain, even in animals depleted of CD4 + T cells. This finding is particularly important in the context of HIV/AIDS-induced immune deficiency. Moreover, we observed that HK-fbp1 vaccination induces significant cross-protection against challenge with diverse invasive fungal pathogens. Thus, our data suggest that HK-fbp1 has the potential to be a broad-spectrum vaccine candidate against invasive fungal infections in both immunocompetent and immunocompromised populations. Cryptococcus neoformans is a fungal pathogen that infects the lungs and then often disseminates to the central nervous system, causing meningitis. How Cryptococcus is able to suppress host immunity and escape the antifungal activity of macrophages remains incompletely understood. We reported that the F-box protein Fbp1, a subunit of the SCF(Fbp1) E3 ligase, promotes Cryptococcus virulence by regulating host- Cryptococcus interactions. Our recent studies demonstrated that the fbp1 Δ mutant elicited superior protective Th1 host immunity in the lungs and that the enhanced immunogenicity of heat-killed fbp1 Δ yeast cells can be harnessed to confer protection against a subsequent infection with the virulent parental strain. We therefore examined the use of heat-killed fbp1 Δ cells in several vaccination strategies. Interestingly, the vaccine protection remains effective even in mice depleted of CD4 + T cells. This finding is particularly important in the context of HIV/AIDS-induced immune deficiency. Moreover, we observed that vaccinating mice with heat-killed fbp1 Δ induces significant cross-protection against challenge with diverse invasive fungal pathogens, including C. neoformans , C. gattii , and Aspergillus fumigatus , as well as partial protection against Candida albicans . Thus, our data suggest that the heat-killed fbp1Δ strain has the potential to be a suitable vaccine candidate against cryptococcosis and other invasive fungal infections in both immunocompetent and immunocompromised populations. IMPORTANCE Invasive fungal infections kill more than 1.5 million people each year, with limited treatment options. There is no vaccine available in clinical use to prevent and control fungal infections. Our recent studies showed that a mutant of the F-box protein Fbp1, a subunit of the SCF(Fbp1) E3 ligase in Cryptococcus neoformans , elicited superior protective Th1 host immunity. Here, we demonstrate that the heat-killed fbp1 Δ cells (HK-fbp1) can be harnessed to confer protection against a challenge by the virulent parental strain, even in animals depleted of CD4 + T cells. This finding is particularly important in the context of HIV/AIDS-induced immune deficiency. Moreover, we observed that HK-fbp1 vaccination induces significant cross-protection against challenge with diverse invasive fungal pathogens. Thus, our data suggest that HK-fbp1 has the potential to be a broad-spectrum vaccine candidate against invasive fungal infections in both immunocompetent and immunocompromised populations.

Development of a vaccine to protect against cryptococcosis is a priority given the enormous global burden of disease in at-risk individuals. Using glucan particles (GPs) as a delivery system, we previously demonstrated that mice vaccinated with crude Cryptococcus -derived alkaline extracts were protected against lethal challenge with Cryptococcus neoformans and Cryptococcus gattii . The goal of the present study was to identify protective protein antigens that could be used in a subunit vaccine. Using biased and unbiased approaches, six candidate antigens (Cda1, Cda2, Cda3, Fpd1, MP88, and Sod1) were selected, recombinantly expressed in Escherichia coli , purified, and loaded into GPs. Three mouse strains (C57BL/6, BALB/c, and DR4) were then vaccinated with the antigen-laden GPs, following which they received a pulmonary challenge with virulent C. neoformans and C. gattii strains. Four candidate vaccines (GP-Cda1, GP-Cda2, GP-Cda3, and GP-Sod1) afforded a significant survival advantage in at least one mouse model; some vaccine combinations provided added protection over that seen with either antigen alone. Vaccine-mediated protection against C. neoformans did not necessarily predict protection against C. gattii . Vaccinated mice developed pulmonary inflammatory responses that effectively contained the infection; many surviving mice developed sterilizing immunity. Predicted T helper cell epitopes differed between mouse strains and in the degree to which they matched epitopes predicted in humans. Thus, we have discovered cryptococcal proteins that make promising candidate vaccine antigens. Protection varied depending on the mouse strain and cryptococcal species, suggesting that a successful human subunit vaccine will need to contain multiple antigens, including ones that are species specific. IMPORTANCE The encapsulated fungi Cryptococcus neoformans and Cryptococcus gattii are responsible for nearly 200,000 deaths annually, mostly in immunocompromised individuals. An effective vaccine could substantially reduce the burden of cryptococcosis. However, a major gap in cryptococcal vaccine development has been the discovery of protective antigens to use in vaccines. Here, six cryptococcal proteins with potential as vaccine antigens were expressed recombinantly and purified. Mice were then vaccinated with glucan particle preparations containing each antigen. Of the six candidate vaccines, four protected mice from a lethal cryptococcal challenge. However, the degree of protection varied as a function of mouse strain and cryptococcal species. These preclinical studies identify cryptococcal proteins that could serve as candidate vaccine antigens and provide a proof of principle regarding the feasibility of protein antigen-based vaccines to protect against cryptococcosis. The encapsulated fungi Cryptococcus neoformans and Cryptococcus gattii are responsible for nearly 200,000 deaths annually, mostly in immunocompromised individuals. An effective vaccine could substantially reduce the burden of cryptococcosis. However, a major gap in cryptococcal vaccine development has been the discovery of protective antigens to use in vaccines. Here, six cryptococcal proteins with potential as vaccine antigens were expressed recombinantly and purified. Mice were then vaccinated with glucan particle preparations containing each antigen. Of the six candidate vaccines, four protected mice from a lethal cryptococcal challenge. However, the degree of protection varied as a function of mouse strain and cryptococcal species. These preclinical studies identify cryptococcal proteins that could serve as candidate vaccine antigens and provide a proof of principle regarding the feasibility of protein antigen-based vaccines to protect against cryptococcosis.

BackgroundCryptococcosis is a life-threatening disease caused by Cryptococcus neoformans or C. gattii. Neutralizing autoantibodies (auto-Abs) against granulocyte-macrophage colony-stimulating factor (GM-CSF) in otherwise healthy adults with cryptococcal meningitis have been described since 2013. We searched for neutralizing auto-Abs in sera collected from Colombian patients with non-HIV-associated cryptococcosis in a retrospective national cohort from 1997 to 2016.MethodsWe reviewed clinical and laboratory records and assessed the presence of neutralizing auto-Abs against GM-CSF in 30 HIV negative adults with cryptococcosis (13 caused by C. gattii and 17 caused by C. neoformans).ResultsWe detected neutralizing auto-Abs against GM-CSF in the sera of 10 out of 13 (77%) patients infected with C. gattii and one out of 17 (6%) patients infected with C. neoformans.ConclusionsWe report eleven Colombian patients diagnosed with cryptococcosis who had auto-Abs that neutralize GM-CSF. Among these patients, ten were infected with C. gattii and only one with C. neoformans.Key Points• The importance of anticytokine autoantibodies in the pathogenesis of various infectious diseases, including opportunistic mycoses, is increasingly being reported.• Neutralizing auto-Abs against GM-CSF are present in Colombian patients with cryptococcosis caused by C. gattii or C. neoformans.

A vaccine capable of protecting at-risk persons against infections due to Cryptococcus neoformans and Cryptococcus gattii could reduce the substantial global burden of human cryptococcosis. Vaccine development has been hampered though, by lack of knowledge as to which antigens are immunoprotective and the need for an effective vaccine delivery system. We made alkaline extracts from mutant cryptococcal strains that lacked capsule or chitosan. The extracts were then packaged into glucan particles (GPs), which are purified Saccharomyces cerevisiae cell walls composed primarily of β-1,3-glucans. Subcutaneous vaccination with the GP-based vaccines provided significant protection against subsequent pulmonary infection with highly virulent strains of C. neoformans and C. gattii . The alkaline extract derived from the acapsular strain was analyzed by liquid chromatography tandem mass spectrometry (LC-MS/MS), and the most abundant proteins were identified. Separation of the alkaline extract by size exclusion chromatography revealed fractions that conferred protection when loaded in GP-based vaccines. Robust Th1- and Th17-biased CD4 + T cell recall responses were observed in the lungs of vaccinated and infected mice. Thus, our preclinical studies have indicated promising cryptococcal vaccine candidates in alkaline extracts delivered in GPs. Ongoing studies are directed at identifying the individual components of the extracts that confer protection and thus would be promising candidates for a human vaccine. IMPORTANCE The encapsulated yeast Cryptococcus neoformans and its closely related sister species, Cryptococcus gattii , are major causes of morbidity and mortality, particularly in immunocompromised persons. This study reports on the preclinical development of vaccines to protect at-risk populations from cryptococcosis. Antigens were extracted from Cryptococcus by treatment with an alkaline solution. The extracted antigens were then packaged into glucan particles, which are hollow yeast cell walls composed mainly of β-glucans. The glucan particle-based vaccines elicited robust T cell immune responses and protected mice from otherwise-lethal challenge with virulent strains of C. neoformans and C. gattii . The technology used for antigen extraction and subsequent loading into the glucan particle delivery system is relatively simple and can be applied to vaccine development against other pathogens. The encapsulated yeast Cryptococcus neoformans and its closely related sister species, Cryptococcus gattii , are major causes of morbidity and mortality, particularly in immunocompromised persons. This study reports on the preclinical development of vaccines to protect at-risk populations from cryptococcosis. Antigens were extracted from Cryptococcus by treatment with an alkaline solution. The extracted antigens were then packaged into glucan particles, which are hollow yeast cell walls composed mainly of β-glucans. The glucan particle-based vaccines elicited robust T cell immune responses and protected mice from otherwise-lethal challenge with virulent strains of C. neoformans and C. gattii . The technology used for antigen extraction and subsequent loading into the glucan particle delivery system is relatively simple and can be applied to vaccine development against other pathogens.

Understanding more about the host's immune response to different Cryptococcus spp. will provide additional insight into the pathogenesis of cryptocococcis. We hypothesized that the ability of C. gattii to cause disease in immunocompetent humans depends on a distinct innate cytokine response of the host to this emerging pathogen. In the current study we assessed the cytokine profile of human peripheral blood mononuclear cells (PBMCs) of healthy individuals, after in vitro stimulation with 40 different well-defined heat-killed isolates of C. gattii, C. neoformans and several hybrid strains. In addition, we investigated the involvement of TLR2, TLR4 and TLR9 in the pro-inflammatory cytokine response to C. gattii. Isolates of C. gattii induced higher concentrations of the pro-inflammatory cytokines IL-1β, TNF-α and IL-6 and the Th17/22 cytokine IL-17 and IL-22 compared to C. neoformans var neoformans and C. neoformans var grubii. In addition, clinical C. gattii isolates induced higher amounts of cytokines than environmental isolates. This difference was not observed in C. neoformans var. grubii isolates. Furthermore, we demonstrated a likely contribution of TLR4 and TLR9, but no role for TLR2, in the host's cytokine response to C. gattii. In conclusion, clinical heat-killed C. gattii isolates induced a more pronounced inflammatory response compared to other Cryptococcus species and non-clinical C. gattii. This is dependent on TLR4 and TLR9 as cellular receptors.

is a ubiquitous environmental yeast and a leading cause of invasive fungal infection in humans. The most recent estimate of global disease burden includes over 200,000 cases of cryptococcal meningitis each year. expresses several virulence factors that may have originally evolved to protect against environmental threats, and human infection may be an unintended consequence of these acquired defenses. Traditionally, has been viewed as a purely opportunistic pathogen that targets severely immune compromised hosts; however, during the past decade the spectrum of susceptible individuals has grown considerably. In addition, the closely related strain has recently emerged in North America and preferentially targets individuals with intact immunity. In parallel to the changing epidemiology of cryptococcosis, an increasing role for host immunity in the pathogenesis of severe disease has been elucidated. Initially, the HIV/AIDS epidemic revealed the capacity of to cause host damage in the absence of adaptive immunity. Subsequently, the development and clinical implementation of highly active antiretroviral treatment (HAART) led to recognition of an immune reconstitution inflammatory syndrome (IRIS) in a subset of HIV+ individuals, demonstrating the pathological role of host immunity in disease. A post-infectious inflammatory syndrome (PIIRS) characterized by abnormal T cell-macrophage activation has also been documented in HIV-negative individuals following antifungal therapy. These novel clinical conditions illustrate the highly complex host-pathogen relationship that underlies severe cryptococcal disease and the intricate balance between tolerance and resistance that is necessary for effective resolution. In this article, we will review current knowledge of the interactions between cryptococci and mammalian hosts that result in a tolerant phenotype. Future investigations in this area have potential for translation into improved therapies for affected individuals.

Key Points Cryptococcosis is a widespread opportunistic fungal infection of humans and other animals. Cryptococcus species that infect humans likely evolved as accidental pathogens in response to environmental selective pressure. Recent genomic analyses have highlighted the evolutionary history of Cryptococcus spp. and narrowed down the geographical origin of an unusual, hypervirulent outbreak. Despite being accidental pathogens, cryptococci display a remarkable ability to manipulate the human immune response to facilitate disease establishment and spread. Detailed in vivo and in vitro characterization of Cryptococcus spp. has started to elucidate the details of multiple mechanisms of pathogenesis that probably have important roles in disease severity. These include changes in fungal morphology, interactions with host phagocytes and mechanisms that allow Cryptococcus spp. to disseminate from the lung to the central nervous system. Renewed efforts to develop improved therapeutic approaches have highlighted potential new drugs and new uses for old drugs in the fight against cryptococcal disease. Recent studies have elucidated multiple virulence mechanisms used by Cryptococcus spp. to infect, disseminate within and ultimately kill their human host. In this Review, May et al . describe these recent developments in understanding host–fungal interactions, discuss how they affect disease severity and debate current and future therapeutic interventions against cryptococcosis. Cryptococcosis is a globally distributed invasive fungal infection that is caused by species within the genus Cryptococcus which presents substantial therapeutic challenges. Although natural human-to-human transmission has never been observed, recent work has identified multiple virulence mechanisms that enable cryptococci to infect, disseminate within and ultimately kill their human host. In this Review, we describe these recent discoveries that illustrate the intricacy of host–pathogen interactions and reveal new details about the host immune responses that either help to protect against disease or increase host susceptibility. In addition, we discuss how this improved understanding of both the host and the pathogen informs potential new avenues for therapeutic development.