Vaccinations with recombinant variants of Aspergillus fumigatus allergen Asp f 3 protect mice against invasive aspergillosis

Fungal vaccines and adjuvants: a tool to reveal the interaction between host and fungi

Fungal infections are incurring high risks in a range from superficial mucosal discomforts (such as oropharyngeal candidiasis and vulvovaginal candidiasis) to disseminated life-threatening diseases (such as invasive pulmonary aspergillosis and cryptococcal meningitis) and becoming a global health problem in especially immunodeficient population. The major obstacle to conquer fungal harassment lies in the presence of increasing resistance to conventional antifungal agents used in newly clinically isolated strains. Although recombinant cytokines and mono-/poly-clonal antibodies are added into antifungal armamentarium, more effective antimycotic drugs are exceedingly demanded. It is comforting that the development of fungal vaccines and adjuvants opens up a window to brighten the prospective way in the diagnosis, prevention and treatment of fungal assaults. In this review, we focus on the progression of several major fungal vaccines devised for the control of Candida spp., Aspergillus spp., Cryptococcus spp., Coccidioides spp., Paracoccidioides spp., Blastomyces spp., Histoplasma spp., Pneumocystis spp. as well as the adjuvants adopted. We then expound the interaction between fungal vaccines/adjuvants and host innate (macrophages, dendritic cells, neutrophils), humoral (IgG, IgM and IgA) and cellular (Th1, Th2, Th17 and Tc17) immune responses which generally experience immune recognition of pattern recognition receptors, activation of immune cells, and clearance of invaded fungi. Furthermore, we anticipate an in-depth understanding of immunomodulatory properties of univalent and multivalent vaccines against diverse opportunistic fungi, providing helpful information in the design of novel fungal vaccines and adjuvants.

Humoral Immunity Against Aspergillus fumigatus

Aspergillus fumigatus is one the most ubiquitous airborne opportunistic human fungal pathogens. Understanding its interaction with host immune system, composed of cellular and humoral arm, is essential to explain the pathobiology of aspergillosis disease spectrum. While cellular immunity has been well studied, humoral immunity has been poorly acknowledge, although it plays a crucial role in bridging the fungus and immune cells. In this review, we have summarized available data on major players of humoral immunity against A. fumigatus and discussed how they may help to identify at-risk individuals, be used as diagnostic tools or promote alternative therapeutic strategies. Remaining challenges are highlighted and leads are given to guide future research to better grasp the complexity of humoral immune interaction with A. fumigatus.

Treatment of Invasive Aspergillosis: How It's Going, Where It's Heading

Despite improvements in treatment and diagnostics over the last two decades, invasive aspergillosis (IA) remains a devastating fungal disease. The number of immunocompromised patients and hence vulnerable hosts increases, which is paralleled by the emergence of a rise in IA cases. Increased frequencies of azole-resistant strains are reported from six continents, presenting a new challenge for the therapeutic management. Treatment options for IA currently consist of three classes of antifungals (azoles, polyenes, echinocandins) with distinctive advantages and shortcomings. Especially in settings of difficult to treat IA, comprising drug tolerance/resistance, limiting drug-drug interactions, and/or severe underlying organ dysfunction, novel approaches are urgently needed. Promising new drugs for the treatment of IA are in late-stage clinical development, including olorofim (a dihydroorotate dehydrogenase inhibitor), fosmanogepix (a Gwt1 enzyme inhibitor), ibrexafungerp (a triterpenoid), opelconazole (an azole optimized for inhalation) and rezafungin (an echinocandin with long half-life time). Further, new insights in the pathophysiology of IA yielding immunotherapy as a potential add-on therapy. Current investigations show encouraging results, so far mostly in preclinical settings. In this review we discuss current treatment strategies, give an outlook on possible new pharmaceutical therapeutic options, and, lastly, provide an overview of the ongoing research in immunotherapy for IA.

Application of anti-fungal vaccines as a tool against emerging anti-fungal resistance

After viruses and bacteria, fungal infections remain a serious threat to the survival and well-being of society. The continuous emergence of resistance against commonly used anti-fungal drugs is a serious concern. The eukaryotic nature of fungal cells makes the identification of novel anti-fungal agents slow and difficult. Increasing global temperature and a humid environment conducive to fungal growth may lead to a fungal endemic or a pandemic. The continuous increase in the population of immunocompromised individuals and falling immunity forced pharmaceutical companies to look for alternative strategies for better managing the global fungal burden. Prevention of infectious diseases by vaccines can be the right choice. Recent success and safe application of mRNA-based vaccines can play a crucial role in our quest to overcome anti-fungal resistance. Expressing fungal cell surface proteins in human subjects using mRNA technology may be sufficient to raise immune response to protect against future fungal infection. The success of mRNA-based anti-fungal vaccines will heavily depend on the identification of fungal surface proteins which are highly immunogenic and have no or least side effects in human subjects. The present review discusses why it is essential to look for anti-fungal vaccines and how vaccines, in general, and mRNA-based vaccines, in particular, can be the right choice in tackling the problem of rising anti-fungal resistance.

Fungal Vaccine Development: State of the Art and Perspectives Using Immunoinformatics

Fungal infections represent a serious global health problem, causing damage to health and the economy on the scale of millions. Although vaccines are the most effective therapeutic approach used to combat infectious agents, at the moment, no fungal vaccine has been approved for use in humans. However, the scientific community has been working hard to overcome this challenge. In this sense, we aim to describe here an update on the development of fungal vaccines and the progress of methodological and experimental immunotherapies against fungal infections. In addition, advances in immunoinformatic tools are described as an important aid by which to overcome the difficulty of achieving success in fungal vaccine development. In silico approaches are great options for the most important and difficult questions regarding the attainment of an efficient fungal vaccine. Here, we suggest how bioinformatic tools could contribute, considering the main challenges, to an effective fungal vaccine.

Antibodies to Combat Fungal Infections: Development Strategies and Progress

The finding that some mAbs are antifungal suggests that antibody immunity may play a key role in the defense of the host against mycotic infections. The discovery of antibodies that guard against fungi is a significant advancement because it gives rise to the possibility of developing vaccinations that trigger protective antibody immunity. These vaccines might work by inducing antibody opsonins that improve the function of non-specific (such as neutrophils, macrophages, and NK cells) and specific (such as lymphocyte) cell-mediated immunity and stop or aid in eradicating fungus infections. The ability of antibodies to defend against fungi has been demonstrated by using monoclonal antibody technology to reconsider the function of antibody immunity. The next step is to develop vaccines that induce protective antibody immunity and to comprehend the mechanisms through which antibodies mediate protective effects against fungus.

Non-Aspergillus mould lung infections

Non-Aspergillus filamentous fungi causing invasive mould infections have increased over the last years due to the widespread use of anti-Aspergillus prophylaxis and increased complexity and survival of immunosuppressed patients. In the few studies that have reported on invasive mould infection epidemiology, Mucorales are the most frequently isolated group, followed by either Fusarium spp. or Scedosporium spp. The overall incidence is low, but related mortality is exceedingly high. Patients with haematological malignancies and haematopoietic stem cell transplant recipients comprise the classical groups at risk of infection for non-Aspergillus moulds due to profound immunosuppression and the vast use of anti-Aspergillus prophylaxis. Solid organ transplant recipients also face a high risk, especially those receiving lung transplants, due to direct exposure of the graft to mould spores with altered mechanical and immunological elimination, and intense, associated immunosuppression. Diagnosing non-Aspergillus moulds is challenging due to unspecific symptoms and radiological findings, lack of specific biomarkers, and low sensitivity of cultures. However, the advent of molecular techniques may prove helpful. Mucormycosis, fusariosis and scedosporiosis hold some differences regarding clinical paradigmatic presentations and preferred antifungal therapy. Surgery might be an option, especially in mucormycosis. Finally, various promising strategies to restore or enhance the host immune response are under current evaluation.

Specific Focus on Antifungal Peptides against Azole Resistant Aspergillus fumigatus: Current Status, Challenges, and Future Perspectives

The prevalence of fungal infections is increasing worldwide, especially that of aspergillosis, which previously only affected people with immunosuppression. Aspergillus fumigatus can cause allergic bronchopulmonary aspergillosis and endangers public health due to resistance to azole-type antimycotics such as fluconazole. Antifungal peptides are viable alternatives that combat infection by forming pores in membranes through electrostatic interactions with the phospholipids as well as cell death to peptides that inhibit protein synthesis and inhibit cell replication. Engineering antifungal peptides with nanotechnology can enhance the efficacy of these therapeutics at lower doses and reduce immune responses. This manuscript explains how antifungal peptides combat antifungal-resistant aspergillosis and also how rational peptide design with nanotechnology and artificial intelligence can engineer peptides to be a feasible antifungal alternative.

Vaccination with Live or Heat-Killed Aspergillus fumigatus ΔsglA Conidia Fully Protects Immunocompromised Mice from Invasive Aspergillosis

Aspergillus fumigatus causes invasive aspergillosis (IA) in immunocompromised patients, resulting in high mortality rates. Currently, no vaccine formulations to promote immune protection in at-risk individuals have been developed. In this work, we deleted the sterylglucosidase-encoding gene, sglA, in Aspergillus fumigatus and investigated its role in fungal virulence and host vaccine protection. The ΔsglA mutant accumulated sterylglucosides (SGs), newly studied immunomodulatory glycolipids, and exhibited reduced hyphal growth and altered compositions of cell wall polysaccharides. Interestingly, the ΔsglA mutant was avirulent in two murine models of IA and was fully eliminated from the lungs. Both corticosteroid-induced immunosuppressed and cyclophosphamide-induced leukopenic mice vaccinated with live or heat-killed ΔsglA conidia were fully protected against a lethal wild-type A. fumigatus challenge. These results highlight the potential of SG-accumulating strains as safe and promising vaccine formulations against invasive fungal infections. IMPORTANCE Infections by Aspergillus fumigatus occur by the inhalation of environmental fungal spores called conidia. We found that live mutant conidia accumulating glycolipids named sterylglucosides are not able to cause disease when injected into the lung. Interestingly, these animals are now protected against a secondary challenge with live wild-type conidia. Remarkably, protection against a secondary challenge persists even with vaccination with heat-killed mutant conidia. These results will significantly advance the field of the research and development of a safe fungal vaccine for protection against the environmental fungus A. fumigatus.

Recombinant Aspergillus fumigatus antigens Asp f 3 and Asp f 9 in liposomal vaccine protect mice against invasive pulmonary aspergillosis

Invasive pulmonary aspergillosis caused by the ubiquitous mold Aspergillus fumigatus is a major threat to immunocompromised patients, causing unacceptably high mortality despite standard of care treatment, and costing an estimated $1.2 billion annually. Treatment for this disease has been complicated by the emergence of azole resistant strains of A. fumigatus, rendering first-line antifungal therapy ineffective. The difficulties in treating infected patients using currently available drugs make immunotherapeutic vaccination an attractive option. Here, we demonstrate the efficacy of VesiVax® adjuvant liposomes, consisting of a combination of two individual liposome preparations, to which two recombinant A. fumigatus surface antigens, Asp f 3 and Asp f 9 (VesiVax® Af3/9), have been chemically conjugated. Using a murine model, we demonstrate that VesiVax® Af3/9 is protective against infection by azole resistant strains of A. fumigatus in both steroid-suppressed and neutropenic mice as quantified by improved survival and reduced fungal burden in the lungs. This protection correlates with upregulation of IL-4 produced by splenocytes, and the presence of Asp f 3 and Asp f 9 specific IgG2a antibodies in the serum of mice given VesiVax® Af3/9. Furthermore, mice given VesiVax® Af3/9 with a subsequent course of liposomal amphotericin B (AmBisome®) had improved survival over those given either treatment alone, indicating a benefit to VesiVax® Af3/9 vaccination even in the case of infections that require follow-up antifungal treatment. These data demonstrate that prophylactic vaccination with VesiVax® Af3/9 is a promising method of protection against invasive pulmonary aspergillosis even as the changing face of the disease renders current therapies ineffective.

Pre-Exposure With Extracellular Vesicles From Aspergillus fumigatus Attenuates Inflammatory Response and Enhances Fungal Clearance in a Murine Model Pulmonary Aspergillosis

Aspergillus fumigatus is a ubiquitous and saprophytic filamentous fungus and the main etiologic agent of aspergillosis. Infections caused by A. fumigatus culminate in a strong inflammatory response that can evolve into respiratory failure and may be lethal in immunocompromised individuals. In the last decades, it has been demonstrated that extracellular vesicles (EVs) elicit a notable biological response in immune cells. EVs carry a variety of biomolecules, therefore are considered potential antigen delivery vehicles. The role of EVs as a strategy for modulating an effective response against infections caused by A. fumigatus remains unexplored. Here we investigate the use of EVs derived from A. fumigatus as an immunization tool to induce a more robust immune response to A. fumigatus pulmonary infection. In order to investigate that, male C57BL/6 mice were immunized with two doses of EVs and infected with A. fumigatus. Pre-exposure of mice to EVs was able to induce the production of specific IgG serum for fungal antigens. Besides that, the immunization with EVs reduced the neutrophilic infiltrate into the alveoli, as well as the extravasation of total proteins and the production of proinflammatory mediators IL-1β, IL-6, and CXCL-1. In addition, immunization prevented extensive lung tissue damage and also improved phagocytosis and fungus clearance. Noteworthy, immunization with EVs, associated with subclinical doses of Amphotericin B (AmB) treatment, rescued 50% of mice infected with A. fumigatus from lethal fungal pneumonia. Therefore, the present study shows a new role for A. fumigatus EVs as host inflammatory response modulators, suggesting their use as immunizing agents.

Longitudinal multimodal imaging-compatible mouse model of triazole-sensitive and -resistant invasive pulmonary aspergillosis

Invasive pulmonary aspergillosis (IPA) caused by the mold Aspergillus fumigatus is one of the most important life-threatening infections in immunocompromised patients. The alarming increase of isolates resistant to the first-line recommended antifungal therapy urges more insights into triazole-resistant A. fumigatus infections. In this study, we systematically optimized a longitudinal multimodal imaging-compatible neutropenic mouse model of IPA. Reproducible rates of pulmonary infection were achieved through immunosuppression (sustained neutropenia) with 150 mg/kg cyclophosphamide at day −4, −1 and 2, and an orotracheal inoculation route in both sexes. Furthermore, increased sensitivity of in vivo bioluminescence imaging for fungal burden detection, as early as the day after infection, was achieved by optimizing luciferin dosing and through engineering isogenic red-shifted bioluminescent A. fumigatus strains, one wild type and two triazole-resistant mutants. We successfully tested appropriate and inappropriate antifungal treatment scenarios in vivo with our optimized multimodal imaging strategy, according to the in vitro susceptibility of our luminescent fungal strains. Therefore, we provide novel essential mouse models with sensitive imaging tools for investigating IPA development and therapy in triazole-susceptible and triazole-resistant scenarios.

Summary: A novel reproducible longitudinal multimodal imaging-compatible neutropenic mouse model of invasive pulmonary aspergillosis provides increased early fungal detection through novel red-shifted luciferase-expressing triazole-susceptible and -resistant Aspergillus fumigatus strains, and boosted bioluminescence.

Genetic Vaccination as a Flexible Tool to Overcome the Immunological Complexity of Invasive Fungal Infections

The COVID-19 pandemic has highlighted genetic vaccination as a powerful and cost-effective tool to counteract infectious diseases. Invasive fungal infections (IFI) remain a major challenge among immune compromised patients, particularly those undergoing allogeneic hematopoietic bone marrow transplantation (HSCT) or solid organ transplant (SOT) both presenting high morbidity and mortality rates. Candidiasis and Aspergillosis are the major fungal infections among these patients and the failure of current antifungal therapies call for new therapeutic aids. Vaccination represents a valid alternative, and proof of concept of the efficacy of this approach has been provided at clinical level. This review will analyze current understanding of antifungal immunology, with a particular focus on genetic vaccination as a suitable strategy to counteract these diseases.

Peroxiredoxin Asp f3 Is Essential for Aspergillus fumigatus To Overcome Iron Limitation during Infection

Aspergillus fumigatus is an important fungal pathogen that causes allergic reactions but also life-threatening infections. One of the most abundant A. fumigatus proteins is Asp f3. This peroxiredoxin is a major fungal allergen and known for its role as a virulence factor, vaccine candidate, and scavenger of reactive oxygen species. Based on the hypothesis that Asp f3 protects A. fumigatus against killing by immune cells, we investigated the susceptibility of a conditional aspf3 mutant by employing a novel assay. Surprisingly, Asp f3-depleted hyphae were killed as efficiently as the wild type by human granulocytes. However, we identified an unexpected growth defect of mutants that lack Asp f3 under low-iron conditions, which explains the avirulence of the Δaspf3 deletion mutant in a murine infection model. A. fumigatus encodes two Asp f3 homologues which we named Af3l (Asp f3-like) 1 and Af3l2. Inactivation of Af3l1, but not of Af3l2, exacerbated the growth defect of the conditional aspf3 mutant under iron limitation, which ultimately led to death of the double mutant. Inactivation of the iron acquisition repressor SreA partially compensated for loss of Asp f3 and Af3l1. However, Asp f3 was not required for maintaining iron homeostasis or siderophore biosynthesis. Instead, we show that it compensates for a loss of iron-dependent antioxidant enzymes. Iron supplementation restored the virulence of the Δaspf3 deletion mutant in a murine infection model. Our results unveil the crucial importance of Asp f3 to overcome nutritional immunity and reveal a new biological role of peroxiredoxins in adaptation to iron limitation.

Fungal vaccines

Invasive fungal disease continues to be a cause of significant life-threatening morbidity and mortality in humans, particularly in those with a diminished immune system, such as with haematological malignancies. The mainstay of treating such life-threatening fungal infection has been antifungal drugs, including azoles, echinocandins and macrocyclic polyenes. However, like antibiotic resistance, antifungal resistance is beginning to emerge, potentially jeopardizing the effectiveness of these molecules in the treatment of fungal disease. One strategy to avoid this is the development of fungal vaccines. However, the inability to provoke a sufficient immune response in the most vulnerable immunocompromised groups has hindered translation from bench to bedside. This review will assess the latest available data and will investigate potential Aspergillus antigens and feasible vaccine techniques, particularly for vaccination of high-risk groups, including immunocompromised and immunosuppressed populations.

Vaccine-Induced Protection in Two Murine Models of Invasive Pulmonary Aspergillosis

Life-threatening, invasive fungal infections (IFIs) cause over 1.5 million deaths worldwide and are a major public health concern with high mortality rates even with medical treatment. Infections with the opportunistic fungal pathogen, Aspergillus fumigatus are among the most common. Despite the growing clinical need, there are no licensed vaccines for IFIs. Here we evaluated the immunogenicity and protective efficacy of an A. fumigatus recombinant protein vaccine candidate, AF.KEX1, in experimental murine models of drug-induced immunosuppression. Immunization of healthy mice with AF.KEX1 and adjuvant induced a robust immune response. Following AF.KEX1 or sham immunization, mice were immunosuppressed by treatment with either cortisone acetate or hydrocortisone and the calcineurin inhibitor, tacrolimus. To test vaccine efficacy, immunosuppressed mice were intranasally challenged with A. fumigatus conidia (Af293) and weight and body temperature were monitored for 10 days. At study termination, organism burden in the lungs was evaluated by quantitative PCR and Gomori's methanamine silver staining. In both models of immunosuppression, AF.KEX1 vaccinated mice experienced decreased rates of mortality and significantly lower lung organism burden compared to non-vaccinated controls. The lung fungal burden was inversely correlated with the peak anti-AF.KEX1 IgG titer achieved following vaccination. These studies provide the basis for further evaluation of a novel vaccine strategy to protect individuals at risk of invasive aspergillosis due to immunosuppressive treatments.

The Peroxiredoxin Asp f3 Acts as Redox Sensor in Aspergillus fumigatus

The human pathogenic fungus Aspergillus fumigatus is readily eradicated by the innate immunity of immunocompetent human hosts, but can cause severe infections, such as invasive aspergillosis (IA), in immunocompromised individuals. During infection, the fungal redox homeostasis can be challenged by reactive oxygen species (ROS), either derived from the oxidative burst of innate immune cells or the action of antifungal drugs. The peroxiredoxin Asp f3 was found to be essential to cause IA in mice, but how Asp f3 integrates with fungal redox homeostasis remains unknown. Here, we show that in vivo, Asp f3 acts as a sensor for ROS. While global transcription in fungal hyphae under minimal growth conditions was fully independent of Asp f3, a robust induction of the oxidative stress response required the presence of the peroxiredoxin. Hyphae devoid of Asp f3 failed to activate several redox active genes, like members of the gliotoxin biosynthesis gene cluster and integral members of the Afyap1 regulon, the central activator of the ROS defense machinery in fungi. Upon deletion of the asp f3 gene Afyap1 displayed significantly reduced nuclear localization during ROS exposure, indicating that Asp f3 can act as an intracellular redox sensor for several target proteins.

Advances in Fungal Peptide Vaccines

Vaccination is one of the greatest public health achievements in the past century, protecting and improving the quality of life of the population worldwide. However, a safe and effective vaccine for therapeutic or prophylactic treatment of fungal infections is not yet available. The lack of a vaccine for fungi is a problem of increasing importance as the incidence of diverse species, including Paracoccidioides, Aspergillus, Candida, Sporothrix, and Coccidioides, has increased in recent decades and new drug-resistant pathogenic fungi are emerging. In fact, our antifungal armamentarium too frequently fails to effectively control or cure mycoses, leading to high rates of mortality and morbidity. With this in mind, many groups are working towards identifying effective and safe vaccines for fungal pathogens, with a particular focus of generating vaccines that will work in individuals with compromised immunity who bear the major burden of infections from these microbes. In this review, we detail advances in the development of vaccines for pathogenic fungi, and highlight new methodologies using immunoproteomic techniques and bioinformatic tools that have led to new vaccine formulations, like peptide-based vaccines.

Aspergillus fumigatus and Aspergillosis in 2019

Aspergillus fumigatus is a saprotrophic fungus; its primary habitat is the soil. In its ecological niche, the fungus has learned how to adapt and proliferate in hostile environments. This capacity has helped the fungus to resist and survive against human host defenses and, further, to be responsible for one of the most devastating lung infections in terms of morbidity and mortality. In this review, we will provide (i) a description of the biological cycle of A. fumigatus; (ii) a historical perspective of the spectrum of aspergillus disease and the current epidemiological status of these infections; (iii) an analysis of the modes of immune response against Aspergillus in immunocompetent and immunocompromised patients; (iv) an understanding of the pathways responsible for fungal virulence and their host molecular targets, with a specific focus on the cell wall; (v) the current status of the diagnosis of different clinical syndromes; and (vi) an overview of the available antifungal armamentarium and the therapeutic strategies in the clinical context. In addition, the emergence of new concepts, such as nutritional immunity and the integration and rewiring of multiple fungal metabolic activities occurring during lung invasion, has helped us to redefine the opportunistic pathogenesis of A. fumigatus.

Immunomodulation as a Therapy for Aspergillus Infection: Current Status and Future Perspectives

Invasive aspergillosis (IA) is the most serious life-threatening infectious complication of intensive remission induction chemotherapy and allogeneic stem cell transplantation in patients with a variety of hematological malignancies. Aspergillus fumigatus is the most commonly isolated species from cases of IA. Despite the various improvements that have been made with preventative strategies and the development of antifungal drugs, there is an urgent need for new therapeutic approaches that focus on strategies to boost the host’s immune response, since immunological recovery is recognized as being the major determinant of the outcome of IA. Here, we aim to summarize current knowledge about a broad variety of immunotherapeutic approaches against IA, including therapies based on the transfer of distinct immune cell populations, and the administration of cytokines and antibodies.

Fungal vaccines, mechanism of actions and immunology: A comprehensive review

Fungal infections include a wide range of opportunistic and invasive diseases. Two of four major fatal diseases in patients with human immunodeficiency virus (HIV) infection are related to the fungal infections, cryptococcosis, and pneumocystosis. Disseminated candidiasis and different clinical forms of aspergillosis annually impose expensive medical costs to governments and hospitalized patients and ultimately lead to high mortality rates. Therefore, urgent implementations are necessary to prevent the expansion of these diseases. Designing an effective vaccine is one of the most important approaches in this field. So far, numerous efforts have been carried out in developing an effective vaccine against fungal infections. Some of these challenges engaged in different stages of clinical trials but none of them could be approved by the United States Food and Drug Administration (FDA). Here, in addition to have a comprehensive overview on the data from studied vaccine programs, we will discuss the immunology response against fungal infections. Moreover, it will be attempted to clarify the underlying immune mechanisms of vaccines targeting different fungal infections that are crucial for designing an effective vaccination strategy.

Invasive Fungal Disease in Critically Ill Patients at High Risk: Usefulness of Lymphocyte Subtyping

OBJECTIVES

This study aimed to investigate the distinguishing ability of lymphocyte subtyping for diagnosis and prognosis of invasive fungal disease (IFD).

METHODS

We assessed lymphocyte subtyping and evaluated the quantitative changes in key immunological parameters at intensive care unit (ICU) admission in critically ill patients at high risk and their potential influence on diagnosis and outcome of IFD. The primary outcome was 28-day mortality.

RESULTS

Among the 124 critically ill patients with mean Candida score 3.89 (0.76), 19 (15.3%) were in the IFD group. CD28⁺CD8⁺ T-cell counts (area under the curve [AUC] 0.899, 95% confidence interval [CI], 0.834-0.964, P < .001) had better distinguishing ability than other immune parameters for IFD diagnosis. The cutoff value of CD28⁺CD8⁺ T-cell counts at ICU admission for IFD diagnosis was 59.5 cells/mm³, with 83.3% sensitivity and 86.4% specificity. Multivariate logistic regression analysis identified CD28⁺CD8⁺ T-cell count <59.5 cells/mm³ (odds ratio 59.7, 95% CI, 7.33-486.9, P < .001) as an independent predictor for IFD diagnosis. CD28⁺CD8⁺ T-cell counts could also predict 28-day mortality (AUC 0.656, 95% CI, 0.525-0.788, P = .045). Kaplan-Meier survival analysis provided evidence that natural killer cell count <76.0 cells/mm³ (log-rank test; P = .001), CD8⁺ T-cell count <321.5 cells/mm³ (log-rank test; P = .04), and CD28⁺CD8⁺ T-cell count <129.0 cells/mm³ (log-rank test; P = .02) at ICU admission were associated with lower survival probabilities.

CONCLUSION

CD28⁺CD8⁺ T-cell counts play an important role in early diagnosis of IFD. Low counts are associated with early mortality in critically ill patients at high risk of IFD. Our findings add evidence to the utility of lymphocyte subtyping in a diagnostic algorithm to better define IFD in critically ill patients at high risk.

Current trends to control fungal pathogens: exploiting our knowledge in the host-pathogen interaction

Human fungal infections remain a major challenge in medicine. Only a limited number of antifungal drugs are available, which are often related to severe adverse effects. In addition, there is an increased emergence related to resistant strains, which makes imperative to understand the host-pathogen interactions as well as to develop alternative treatments. Host innate and adaptive immunity play a crucial role controlling fungal infections; therefore, vaccines are a viable tool to prevent and treat fungal pathogens. Innate immunity is triggered by the interaction between the cell surface pattern recognition receptors (PRRs) and the pathogen-associated molecular patterns (PAMPs). Such an initial immunological response is yet little understood in fungal infections, in part due to the complexity and plasticity of the fungal cell walls. Described host cell-fungus interactions and antigenic molecules are addressed in this paper. Furthermore, antigens found in the cell wall and capsule, including peptides, glycoproteins, glycolipids, and glycans, have been used to trigger specific immune responses, and an increased production of antibodies has been observed when attached to immunogenic molecules. The recent biotechnological advances have allowed the development of vaccines against viral and bacterial pathogens with positive results; therefore, this technology has been applied to develop anti-fungal vaccines. Passive immunization has also emerged as an appealing alternative to treat disseminated mycosis, especially in immunocompromised patients. Those approaches have a long way to be seen in clinical cases. However, all studies discussed here open the possibility to have access to new therapies to be applied alone or in combination with current antifungal drugs. Herein, the state of the art of fungal vaccine developments is discussed in this review, highlighting new advances against Candida albicans, Aspergillus fumigatus, Cryptococcus neoformans, Paracoccidioides brasiliensis, and Sporothrix spp.

Methods of Controlling Invasive Fungal Infections Using CD8+ T Cells

Invasive fungal infections (IFIs) cause high rates of morbidity and mortality in immunocompromised patients. Pattern-recognition receptors present on the surfaces of innate immune cells recognize fungal pathogens and activate the first line of defense against fungal infection. The second line of defense is the adaptive immune system which involves mainly CD4+ T cells, while CD8+ T cells also play a role. CD8+ T cell-based vaccines designed to prevent IFIs are currently being investigated in clinical trials, their use could play an especially important role in acquired immune deficiency syndrome patients. So far, none of the vaccines used to treat IFI have been approved by the FDA. Here, we review current and future antifungal immunotherapy strategies involving CD8+ T cells. We highlight recent advances in the use of T cells engineered using a Sleeping Beauty vector to treat IFIs. Recent clinical trials using chimeric antigen receptor (CAR) T-cell therapy to treat patients with leukemia have shown very promising results. We hypothesized that CAR T cells could also be used to control IFI. Therefore, we designed a CAR that targets β-glucan, a sugar molecule found in most of the fungal cell walls, using the extracellular domain of Dectin-1, which binds to β-glucan. Mice treated with D-CAR+ T cells displayed reductions in hyphal growth of Aspergillus compared to the untreated group. Patients suffering from IFIs due to primary immunodeficiency, secondary immunodeficiency (e.g., HIV), or hematopoietic transplant patients may benefit from bioengineered CAR T cell therapy.

Targeting Glycans on Human Pathogens for Vaccine Design

Glycosylation is an important post-translational modification that is required for structural and stability purposes and functional roles such as signalling, attachment and shielding. Many human pathogens such as bacteria display an array of carbohydrates on their surface that are non-self to the host; others such as viruses highjack the host-cell machinery and present self-carbohydrates sometimes arranged in a non-self more immunogenic manner. In combination with carrier proteins, these glycan structures can be highly immunogenic. During natural infection, glycan-binding antibodies are often elicited that correlate with long-lasting protection. A great amount of research has been invested in carbohydrate vaccine design to elicit such an immune response, which has led to the development of vaccines against the bacterial pathogens Haemophilus influenzae type b, Streptococcus pneumonia and Neisseria meningitidis. Other vaccines, e.g. against HIV-1, are still in development, but promising progress has been made with the isolation of broadly neutralizing glycan-binding antibodies and the engineering of stable trimeric envelope glycoproteins. Carbohydrate vaccines against other pathogens such as viruses (Dengue, Hepatitis C), parasites (Plasmodium) and fungi (Candida) are at different stages of development. This chapter will discuss the challenges in inducing cross-reactive carbohydrate-targeting antibodies and progress towards carbohydrate vaccines.

The Fungal Cell Wall: Structure, Biosynthesis, and Function

The molecular composition of the cell wall is critical for the biology and ecology of each fungal species. Fungal walls are composed of matrix components that are embedded and linked to scaffolds of fibrous load-bearing polysaccharides. Most of the major cell wall components of fungal pathogens are not represented in humans, other mammals, or plants, and therefore the immune systems of animals and plants have evolved to recognize many of the conserved elements of fungal walls. For similar reasons the enzymes that assemble fungal cell wall components are excellent targets for antifungal chemotherapies and fungicides. However, for fungal pathogens, the cell wall is often disguised since key signature molecules for immune recognition are sometimes masked by immunologically inert molecules. Cell wall damage leads to the activation of sophisticated fail-safe mechanisms that shore up and repair walls to avoid catastrophic breaching of the integrity of the surface. The frontiers of research on fungal cell walls are moving from a descriptive phase defining the underlying genes and component parts of fungal walls to more dynamic analyses of how the various components are assembled, cross-linked, and modified in response to environmental signals. This review therefore discusses recent advances in research investigating the composition, synthesis, and regulation of cell walls and how the cell wall is targeted by immune recognition systems and the design of antifungal diagnostics and therapeutics.

Rodent Models of Invasive Aspergillosis due to Aspergillus fumigatus: Still a Long Path toward Standardization

Invasive aspergillosis has been studied in laboratory by the means of plethora of distinct animal models. They were developed to address pathophysiology, therapy, diagnosis, or miscellaneous other concerns associated. However, there are great discrepancies regarding all the experimental variables of animal models, and a thorough focus on them is needed. This systematic review completed a comprehensive bibliographic analysis specifically-based on the technical features of rodent models infected with Aspergillus fumigatus. Out the 800 articles reviewed, it was shown that mice remained the preferred model (85.8% of the referenced reports), above rats (10.8%), and guinea pigs (3.8%). Three quarters of the models involved immunocompromised status, mainly by steroids (44.4%) and/or alkylating drugs (42.9%), but only 27.7% were reported to receive antibiotic prophylaxis to prevent from bacterial infection. Injection of spores (30.0%) and inhalation/deposition into respiratory airways (66.9%) were the most used routes for experimental inoculation. Overall, more than 230 distinct A. fumigatus strains were used in models. Of all the published studies, 18.4% did not mention usage of any diagnostic tool, like histopathology or mycological culture, to control correct implementation of the disease and to measure outcome. In light of these findings, a consensus discussion should be engaged to establish a minimum standardization, although this may not be consistently suitable for addressing all the specific aspects of invasive aspergillosis.

Proteomics as a Tool to Identify New Targets Against Aspergillus and Scedosporium in the Context of Cystic Fibrosis

Cystic fibrosis (CF) is a genetic disorder that increases the risk of suffering microbial, including fungal, infections. In this paper, proteomics-based information was collated relating to secreted and cell wall proteins with potential medical applications from the most common filamentous fungi in CF, i.e., Aspergillus and Scedosporium/Lomentospora species. Among the Aspergillus fumigatus secreted allergens, β-1,3-endoglucanase, the alkaline protease 1 (Alp1/oryzin), Asp f 2, Asp f 13/15, chitinase, chitosanase, dipeptidyl-peptidase V (DppV), the metalloprotease Asp f 5, mitogillin/Asp f 1, and thioredoxin reductase receive a special mention. In addition, the antigens β-glucosidase 1, catalase, glucan endo-1,3-β-glucosidase EglC, β-1,3-glucanosyltransferases Gel1 and Gel2, and glutaminase A were also identified in secretomes of other Aspergillus species associated with CF: Aspergillus flavus, Aspergillus niger, Aspergillus nidulans, and Aspergillus terreus. Regarding cell wall proteins, cytochrome P450 and eEF-3 were proposed as diagnostic targets, and alkaline protease 2 (Alp2), Asp f 3 (putative peroxiredoxin pmp20), probable glycosidases Asp f 9/Crf1 and Crf2, GPI-anchored protein Ecm33, β-1,3-glucanosyltransferase Gel4, conidial hydrophobin Hyp1/RodA, and secreted aspartyl protease Pep2 as protective vaccines in A. fumigatus. On the other hand, for Scedosporium/Lomentospora species, the heat shock protein Hsp70 stands out as a relevant secreted and cell wall antigen. Additionally, the secreted aspartyl proteinase and an ortholog of Asp f 13, as well as the cell wall endo-1,3-β-D-glucosidase and 1,3-β-glucanosyl transferase, were also found to be significant proteins. In conclusion, proteins mentioned in this review may be promising candidates for developing innovative diagnostic and therapeutic tools for fungal infections in CF patients.

The Fungal Cell Wall: Structure, Biosynthesis, and Function

The molecular composition of the cell wall is critical for the biology and ecology of each fungal species. Fungal walls are composed of matrix components that are embedded and linked to scaffolds of fibrous load-bearing polysaccharides. Most of the major cell wall components of fungal pathogens are not represented in humans, other mammals, or plants, and therefore the immune systems of animals and plants have evolved to recognize many of the conserved elements of fungal walls. For similar reasons the enzymes that assemble fungal cell wall components are excellent targets for antifungal chemotherapies and fungicides. However, for fungal pathogens, the cell wall is often disguised since key signature molecules for immune recognition are sometimes masked by immunologically inert molecules. Cell wall damage leads to the activation of sophisticated fail-safe mechanisms that shore up and repair walls to avoid catastrophic breaching of the integrity of the surface. The frontiers of research on fungal cell walls are moving from a descriptive phase defining the underlying genes and component parts of fungal walls to more dynamic analyses of how the various components are assembled, cross-linked, and modified in response to environmental signals. This review therefore discusses recent advances in research investigating the composition, synthesis, and regulation of cell walls and how the cell wall is targeted by immune recognition systems and the design of antifungal diagnostics and therapeutics.

In silico Identification of Potential Peptides or Allergen Shot Candidates Against Aspergillus fumigatus

Aspergillus fumigatus is capable of causing invasive aspergillosis or acute bronchopulmonary aspergillosis, and the current situation is alarming. There are no vaccine or allergen shots available for Aspergillus-induced allergies. Thus, a novel approach in designing of an effective vaccine or allergen shot candidate against A. fumigatus is needed. Using immunoinformatics approaches from the characterized A. fumigatus allergens, we have mapped epitopic regions to predict potential peptides that elicit both Aspergillus-specific T cells and B cell immune response. Experimentally derived immunodominant allergens were retrieved from www.allergen.org. A total of 23 allergenic proteins of A. fumigatus were retrieved. Out of 23 allergenic proteins, 13 of them showed high sequence similarity to both human and mouse counterparts and thus were eliminated from analysis due to possible cross-reactivity. Remaining allergens were subjected to T cell (major histocompatibility complex class I and II alleles) and B cell epitope prediction using immune epitope database analysis resource. Only five allergens have shown a common B and T cell epitopic region between human and mouse. They are Asp f1 {147-156 region (RVIYTYPNKV); Mitogillin}, Asp f2 {5-19 region (LRLAVLLPLAAPLVA); Hypothetical protein}, Asp f5 {305-322 region (LNNYRPSSSSLSFKY); Metalloprotease}, Asp f17 {98-106 region (AANAGGTVY); Hypothetical protein}, and Asp f34 {74-82 region (YIQDGSLYL); PhiA cell wall protein}. The epitopic region from these five allergenic proteins showed potential for development of single peptide- or multipeptide-based vaccine or allergen shots for experimental prioritization.

Aspergillus vaccines: Hardly worth studying or worthy of hard study?

Vaccines rank among the greatest advances in the history of public health. Yet, despite the need, there are no licensed vaccines to protect humans against fungal diseases, including aspergillosis. In this focused review, some of the major scientific and logistical challenges to developing vaccines to protect at-risk individuals against aspergillosis are discussed. Approaches that have shown promise in animal models include vaccines that protect against multiple fungal genera and those that are specifically directed to Aspergillus Advances in proteomics and glycomics have facilitated identification of candidate antigens for use in subunit vaccines. Novel adjuvants and delivery systems are becoming available that can skew vaccine responses toward those associated with protection. Immunotherapy consisting of adoptive transfer of Aspergillus-specific T cells to allogeneic hematopoietic transplant recipients has advanced to human testing but is technically difficult and of unproven benefit. While progress has been impressive, much work still needs to be done if vaccines against aspergillosis are to become a reality.

The Crystal Structure of Peroxiredoxin Asp f3 Provides Mechanistic Insight into Oxidative Stress Resistance and Virulence of Aspergillus fumigatus

Invasive aspergillosis and other fungal infections occur in immunocompromised individuals, including patients who received blood-building stem cell transplants, patients with chronic granulomatous disease (CGD), and others. Production of reactive oxygen species (ROS) by immune cells, which incidentally is defective in CGD patients, is considered to be a fundamental process in inflammation and antifungal immune response. Here we show that the peroxiredoxin Asp f3 of Aspergillus fumigatus inactivates ROS. We report the crystal structure and the catalytic mechanism of Asp f3, a two-cysteine type peroxiredoxin. The latter exhibits a thioredoxin fold and a homodimeric structure with two intermolecular disulfide bonds in its oxidized state. Replacement of the Asp f3 cysteines with serine residues retained its dimeric structure, but diminished Asp f3's peroxidase activity, and extended the alpha-helix with the former peroxidatic cysteine residue C61 by six residues. The asp f3 deletion mutant was sensitive to ROS, and this phenotype was rescued by ectopic expression of Asp f3. Furthermore, we showed that deletion of asp f3 rendered A. fumigatus avirulent in a mouse model of pulmonary aspergillosis. The conserved expression of Asp f3 homologs in medically relevant molds and yeasts prompts future evaluation of Asp f3 as a potential therapeutic target.

Immunotherapy of Fungal Infections

Fungal organisms are ubiquitous in the environment. Pathogenic fungi, although relatively few in the whole gamut of microbial pathogens, are able to cause disease with varying degrees of severity in individuals with normal or impaired immunity. The disease state is an outcome of the fungal pathogen's interactions with the host immunity, and therefore, it stands to reason that deep/invasive fungal diseases be amenable to immunotherapy. Therefore, antifungal immunotherapy continues to be attractive as an adjunct to the currently available antifungal chemotherapy options for a number of reasons, including the fact that existing antifungal drugs, albeit largely effective, are not without limitations, and that morbidity and mortality associated with invasive mycoses are still unacceptably high. For several decades, intense basic research efforts have been directed at development of fungal immunotherapies. Nevertheless, this approach suffers from a severe bench-bedside disconnect owing to several reasons: the chemical and biological peculiarities of the fungal antigens, the complexities of host-pathogen interactions, an under-appreciation of the fungal disease landscape, the requirement of considerable financial investment to bring these therapies to clinical use, as well as practical problems associated with immunizations. In this general, non-exhaustive review, we summarize the features of ongoing research efforts directed towards devising safe and effective immunotherapeutic options for mycotic diseases, encompassing work on antifungal vaccines, adoptive cell transfers, cytokines, antimicrobial peptides (AMPs), monoclonal antibodies (mAbs), and other agents.

Immunoproteomics of Aspergillus for the development of biomarkers and immunotherapies

Filamentous fungi of the genus Aspergillus play significant roles as pathogens causing superficial and invasive infections as well as allergic reactions in humans. Particularly invasive mycoses caused by Aspergillus species are characterized by high mortality rates due to difficult diagnosis and insufficient antifungal therapy. The application of immunoproteomic approaches has a great potential to identify new targets for the diagnosis, therapy, and vaccine development of diseases caused by Aspergillus species. Serological proteome analyses (SERPA) that combine 2D electrophoresis with Western blotting are still one of the most popular techniques for the identification of antigenic proteins. However, recently a growing number of approaches have been developed to identify proteins, which either provoke an antibody response or which represent targets of T-cell immunity in patients with allergy or fungal infections. Here, we review advances in the studies of immune responses against pathogenic Aspergilli as well as the current status of diagnosis and immunotherapy of Aspergillus infections.

Immunotherapy for opportunistic infections: Current status and future perspectives

The outcome after allogeneic haematopoietic stem cell transplantation (allo-HSCT) has significantly improved during the last decades. However, opportunistic infections such as viral and mold infections are still a major obstacle for cure. Within this field, adoptive T cell therapy against pathogens is a promising treatment approach. Recently, the techniques to develop T cell products including pathogen-specific T cells have been sophisticated and are now available in accordance to good manufacturing practice (GMP). Here, we aim to summarize current knowledge about adoptive T cell therapy against viral and mold infections.

Genome-Wide Expression Profiling Reveals S100B as Biomarker for Invasive Aspergillosis

Invasive aspergillosis (IA) is a devastating opportunistic infection and its treatment constitutes a considerable burden for the health care system. Immunocompromised patients are at an increased risk for IA, which is mainly caused by the species Aspergillus fumigatus. An early and reliable diagnosis is required to initiate the appropriate antifungal therapy. However, diagnostic sensitivity and accuracy still needs to be improved, which can be achieved at least partly by the definition of new biomarkers. Besides the direct detection of the pathogen by the current diagnostic methods, the analysis of the host response is a promising strategy toward this aim. Following this approach, we sought to identify new biomarkers for IA. For this purpose, we analyzed gene expression profiles of hematological patients and compared profiles of patients suffering from IA with non-IA patients. Based on microarray data, we applied a comprehensive feature selection using a random forest classifier. We identified the transcript coding for the S100 calcium-binding protein B (S100B) as a potential new biomarker for the diagnosis of IA. Considering the expression of this gene, we were able to classify samples from patients with IA with 82.3% sensitivity and 74.6% specificity. Moreover, we validated the expression of S100B in a real-time reverse transcription polymerase chain reaction (RT-PCR) assay and we also found a down-regulation of S100B in A. fumigatus stimulated DCs. An influence on the IL1B and CXCL1 downstream levels was demonstrated by this S100B knockdown. In conclusion, this study covers an effective feature selection revealing a key regulator of the human immune response during IA. S100B may represent an additional diagnostic marker that in combination with the established techniques may improve the accuracy of IA diagnosis.

Proteomic Profiling of Serological Responses to Aspergillus fumigatus Antigens in Patients with Invasive Aspergillosis

Aspergillus fumigatus is the species that most commonly causes the opportunistic infection invasive aspergillosis (IA) in patients being treated for hematological malignancies. Little is known about the A. fumigatus proteins that trigger the production of Aspergillus-specific IgG antibodies during the course of IA. To characterize the serological response to A. fumigatus protein antigens, mycelial proteins were separated by 2-D gel electrophoresis. The gels were immunoblotted with sera from patients with probable and proven IA and control patients without IA. We identified 49 different fungal proteins, which gave a positive IgG antibody signal. Most of these antigens play a role in primary metabolism and stress responses. Overall, our analysis identified 18 novel protein antigens from A. fumigatus. To determine whether these antigens can be used as diagnostic or prognostic markers or exhibit a protective activity, we employed supervised machine learning with decision trees. We identified two candidates for further analysis, the protein antigens CpcB and Shm2. Heterologously produced Shm2 induced a strongly proinflammatory response in human peripheral blood mononuclear cells after in vitro stimulation. In contrast, CpcB did not activate the immune response of PBMCs. These findings could serve as the basis for the development of an immunotherapy of IA.

In-depth 2-DE reference map of Aspergillus fumigatus and its proteomic profiling on exposure to itraconazole

Aspergillus fumigatus (A. fumigatus) is a medically important opportunistic fungus that may lead to invasive aspergillosis in humans with weak immune system. Proteomic profiling of this fungus on exposure to itraconazole (ITC), an azole antifungal drug, may lead to identification of its molecular targets and better understanding on the development of drug resistance against ITC in A. fumigatus. Here, proteome analysis was performed using 2-DE followed by mass spectrometric analysis which resulted in identification of a total of 259 unique proteins. Further, proteome profiling of A. fumigatus was carried out on exposure to ITC, 0.154 μg/ml, the minimum inhibitory concentration (MIC50). Image analysis showed altered levels of 175 proteins (66 upregulated and 109 downregulated) of A. fumigatus treated with ITC as compared to the untreated control. Peptide mass fingerprinting led to the identification of 54 proteins (12 up-regulated and 42 down-regulated). The differentially expressed proteins include proteins related to cell stress, carbohydrate metabolism and amino acid metabolism. We also observed four proteins, including nucleotide phosphate kinase (NDK), that are reported to interact with calcineurin, a protein involved in regulation of cell morphology and fungal virulence. Comparison of differentially expressed proteins on exposure to ITC with artemisinin (ART), an antimalarial drug with antifungal activity(1), revealed a total of 26 proteins to be common among them suggesting that common proteins and pathways are targeted by these two antifungal agents. The proteins targeted by ITC may serve as important leads for development of new antifungal drugs.

Proteomic Analysis of Pathogenic Fungi Reveals Highly Expressed Conserved Cell Wall Proteins

We are presenting a quantitative proteomics tally of the most commonly expressed conserved fungal proteins of the cytosol, the cell wall, and the secretome. It was our goal to identify fungi-typical proteins that do not share significant homology with human proteins. Such fungal proteins are of interest to the development of vaccines or drug targets. Protein samples were derived from 13 fungal species, cultured in rich or in minimal media; these included clinical isolates of Aspergillus, Candida, Mucor, Cryptococcus, and Coccidioides species. Proteomes were analyzed by quantitative MS^E (Mass Spectrometry-Elevated Collision Energy). Several thousand proteins were identified and quantified in total across all fractions and culture conditions. The 42 most abundant proteins identified in fungal cell walls or supernatants shared no to very little homology with human proteins. In contrast, all but five of the 50 most abundant cytosolic proteins had human homologs with sequence identity averaging 59%. Proteomic comparisons of the secreted or surface localized fungal proteins highlighted conserved homologs of the Aspergillus fumigatus proteins 1,3-β-glucanosyltransferases (Bgt1, Gel1-4), Crf1, Ecm33, EglC, and others. The fact that Crf1 and Gel1 were previously shown to be promising vaccine candidates, underlines the value of the proteomics data presented here.

Optimizing Outcomes in Immunocompromised Hosts: Understanding the Role of Immunotherapy in Invasive Fungal Diseases

A major global concern is the emergence and spread of systemic life-threatening fungal infections in critically ill patients. The increase in invasive fungal infections, caused most commonly by Candida and Aspergillus species, occurs in patients with impaired defenses due to a number of reasons such as underlying disease, the use of chemotherapeutic and immunosuppressive agents, broad-spectrum antibiotics, prosthetic devices and grafts, burns, neutropenia and HIV infection. The high morbidity and mortality associated with these infections is compounded by the limited therapeutic options and the emergence of drug resistant fungi. Hence, creative approaches to bridge the significant gap in antifungal drug development needs to be explored. Here, we review the potential anti-fungal targets for patient-centered therapies and immune-enhancing strategies for the prevention and treatment of invasive fungal diseases.

Adoptive transfer of Aspergillus-specific T cells as a novel anti-fungal therapy for hematopoietic stem cell transplant recipients: Progress and challenges

Although newer antifungal drugs have substantially altered the natural history of invasive aspergillosis, the disease still accounts for significant morbidity and mortality in hematopoietic stem cell transplant recipients. Both the evidence supporting a protective role of T cells against this fungal pathogen and the documented efficacy of adoptive transfer of antigen-specific T cells for prophylaxis and treatment of viral infections post-transplant have stimulated much interest towards development of Aspergillus-specific T cells (Asp-STs) for adoptive immunotherapy in the allogeneic transplant setting. In contrast to the remarkable progress with virus-specific T cells, clinical development of fungus-specific T cells is still in its infancy. Several groups have characterized Asp-STs in healthy individuals and patients with malignant hematological diseases, while others sought to develop GMP-compliant methods of expanding or bioengineering Asp-STs ex vivo as immunotherapy. This review highlights the recent advances in this field, and discusses critical issues involved in development and protocol design of Asp-ST immunotherapy.

Whole glucan particles as a vaccine against murine aspergillosis

Vaccination with heat-killed Saccharomyces cerevisiae (HKY) protects against experimental infection by pathogenic fungi of five genera. Here we tested whether purified Saccharomyces cell wall β-glucan could induce protection against systemic aspergillosis. CD-1 mice were given three weekly vaccine doses subcutaneously prior to intravenous infection with Aspergillus fumigatus. Mice received PBS, 2.5 mg HKY, whole glucan particles (WGP), WGP conjugated to BSA (0.06 to 12 mg per dose), a soluble medium molecular mass (MMW) β-glucan alone or MMW-BSA (≤24 mg per dose). Survival and c.f.u. were determined, and cytokine induction and anti-β-glucan antibodies were assessed in vaccinated mice. Neither soluble MMW glucan, nor MMW-BSA was effective. HKY protected in two studies (survival and c.f.u. were reduced in brain and kidney organs, P<0.004). Six or 12 mg WGP or WGP-BSA prolonged survival (P≤0.004) and reduced c.f.u. in each organ (P≤0.015) in both experiments; 0.6 mg WGP or WGP-BSA prolonged survival (P≤0.015) and reduced c.f.u. (P≤0.015) in one experiment. Cytokine profiles in serum and bronchoalveolar lavage from uninfected vaccinated mice showed an innate and adaptive immune profile (i.e. upregulation of colony stimulating factors, interferons, TNF-α, chemokines such as MCP-1, MIP-1α, RANTES and KC, and Th17-activating cytokines such as IL-6, IL-1β, IL-17). No anti-β-glucan antibodies were in the sera, suggesting an adaptive T cell-mediated, not a B cell-mediated, protective response. Vaccination with WGP or WGP-BSA proved protective against systemic aspergillosis, equivalent to that of HKY, supporting the potential of particulate β-glucans, alone or conjugated, as vaccines against aspergillosis.

Immune modulators as adjuncts for the prevention and treatment of invasive fungal infections

Invasive fungal diseases are increasingly important opportunistic infections that are intimately linked to immune-suppression in the context of cytotoxic treatment of neoplastic diseases, stem cell and solid-organ transplantation, and primary immune deficiencies. Mortality rates remain high despite the availability of novel antifungals that are both safe and highly active in vitro, suggesting that clinical outcomes may be improved through modulation of host immunity. Ongoing advances in our knowledge of fungal-host interactions facilitate rational design of novel immunotherapeutics. Thus, antifungal immunotherapy now includes age-old interventions such as granulocyte and immunoglobulin transfusions, as well as promising experimental techniques such as antifungal vaccines and adoptive immunotherapy. To realize the potential of these rapidly evolving technologies, transition from the bench to clinical-phase studies must occur at a more rapid pace.