Vaccines for invasive fungal infections

Immunoinformatic-guided designing and evaluating protein and mRNA-based vaccines against Cryptococcus neoformans for immunocompromised patients

BACKGROUND

Cryptococcus neoformans is a fungal pathogen that can cause serious meningoencephalitis in individuals with compromised immune systems due to HIV/AIDS (human immunodeficiency virus/acquired immunodeficiency syndrome), liver cirrhosis, and transplantation. Mannoproteins (MPs), glycoproteins in the C. neoformans capsule, crucially impact virulence by mediating adhesion to lung cells and modulating immune response via cytokine induction and phagocytosis influence. Therefore, creating a vaccine that can generate targeted antibodies to fight infection and prevent fungal illnesses is essential.

RESULTS

This research aims to create a unique, stable, and safe vaccine through bioinformatics methodologies, aiming at epitopes of T and B cells found in the MP of C. neoformans. Based on toxicity, immunogenicity, and antigenicity, this research predicted novel T cells (GNPVGGNVT, NPVGGNVTT, QTSYARLLS, TSVGNGIAS, WVMPGDYTN, AAATGSSSSGSTGSG, GSTGSGSGSAAAGST, SGSTGSGSGSAAAGS, SSGSTGSGSGSAAAG, and SSSGSTGSGSGSAAA) and B cell (ANGSTSTFQQRYTGTYTNGDGSLGTWTQGETVTPQTAYSTPATSNCKTYTSVGNGIASLALSNAGSNSTAAATNSSSGGASAAATGSSSSGSTGSGSGSAAAGSTAAASSSGDSSSSTSAAMSNGI, HGATGLGNPVGGNVTT, TMGPTNPSEPTLGTAI, GNPVGGNVTTNATGSD, and NSTAAATNSSSGGASA) epitopes for a multiple-epitope vaccine and constructed a vaccine subunit with potential immunogenic properties. The present study used four linkers (AAY, GPGPG, KK, and EAAAK linkers) to connect the epitopes and adjuvant. After constructing the vaccine, it was confronted with receptor docking and simulation analysis. Subsequently, the vaccine was cloned into the vector of Escherichia coli pET-28a ( +) by ligation process for the expression using the SnapGene tool, which confirmed a significant immune response. To assess the constructed vaccine's properties, multiple computational tools were employed. Based on the MP sequence, the tools evaluated the antigenicity, immunogenicity, cytokine-inducing capacity, allergenicity, toxicity, population coverage, and solubility.

CONCLUSION

Eventually, the results revealed a promising multi-epitope vaccine as a potential candidate for addressing global C. neoformans infection, particularly in immunocompromised patients. Yet, additional in vitro and in vivo investigations are necessary to validate its safety and effectiveness.

Simultaneous Determination of Posaconazole and Hemp Seed Oil in Nanomicelles through RP-HPLC via a Quality-by-Design Approach

The present study involves the development of a reverse-phase HPLC method employing the quality-by-design methodology for the estimation of posaconazole and hemp seed oil simultaneously in nanomicelles formulation. The successful separation of posaconazole and hemp seed oil was achieved together, and this is the first study to develop and quantify posaconazole and hemp seed oil nanomicelles with linoleic acid as the internal standard and developed a dual drug analytical method employing a quality-by-design approach. The study was performed on a Shimadzu Prominence-I LC-2030C 3D Plus HPLC system with a PDA detector and the Shim-pack Solar C8 column (250 mm × 4.6 mm × 5 μm) for analysis with a mobile phase ratio of methanol:water (80:20% v/v) maintaining the flow rate of 1.0 mL/min. The final wavelength was selected as 240 nm and the elution of hemp seed oil and posaconazole was obtained at 2.7 and 4.6 min, respectively, with a maximum run time of 8.0 min. Box Behnken design was employed to optimize the method, keeping the retention time, peak area, and theoretical plates as dependent variables, while the mobile phase composition, flow rate, and wavelengths were chosen as independent variables. Parameters such as specificity, accuracy, robustness, linearity, sensitivity, precision, ruggedness, and forced degradation study were performed to validate the method. The calibration curves of posaconazole and hemp seed oil were determined to be linear throughout the range for concentration. The suggested approach can be effectively utilized for estimating the content of drugs from their nanoformulation and proved suitable for both in vivo and in vitro research.

Invasive fungal infections

-

Harnessing the Immune Response to Fungal Pathogens for Vaccine Development

Invasive fungal infections are emerging diseases that kill over 1.5 million people per year worldwide. With the increase of immunocompromised populations, the incidence of invasive fungal infections is expected to continue to rise. Vaccines for viral and bacterial infectious diseases have had a transformative impact on human health worldwide. However, no fungal vaccines are currently in clinical use. Recently, interest in fungal vaccines has grown significantly. One Candida vaccine has completed phase 2 clinical trials, and research on vaccines against coccidioidomycosis continues to advance. Additionally, multiple groups have discovered various Cryptococcus mutant strains that promote protective responses to subsequent challenge in mouse models. There has also been progress in antibody-mediated fungal vaccines. In this review, we highlight recent fungal vaccine research progress, outline the wealth of data generated, and summarize current research for both fungal biology and immunology studies relevant to fungal vaccine development. We also review technological advancements in vaccine development and highlight the future prospects of a human vaccine against invasive fungal infections.

Antimicrobial immunotherapeutics: past, present and future

In this age of antimicrobial resistance (AMR) there is an urgent need for novel antimicrobials. One area of recent interest is in developing antimicrobial effector molecules, and even cell-based therapies, based on those of the immune system. In this review, some of the more interesting approaches will be discussed, including immune checkpoint inhibitors, Interferons (IFNs), Granulocyte-Macrophage Colony Stimulating Factor (GM-CSF), Chimeric Antigen Receptor (CAR) T cells, Antibodies, Vaccines and the potential role of trained immunity in protection from and/or treatment of infection.

Prophylaxis and Therapeutic Ability of Inactivated Dermatophytic Vaccine Against Dermatophytosis in the Rabbits as an Animal Model

Objectives

Dermatophytosis is a group of cutaneous diseases widely distributed in human and animals. It causes serious infection in some human cases and economic losses in farm animals. The primary aim of this study is to conduct an investigation of prophylaxis and a potential therapeutic vaccine against dermatophytosis.

Materials and Methods

The rabbit was chosen as an animal model of dermatophytosis for a case control study conducted in two parts. Inactivated cells of Trichophyton mentagrophytes were prepared for use as a vaccine. The prophylaxis part included vaccination of rabbits with the prepared vaccine either alone or with Freund's adjuvant, followed by infection with the same fungus. The second part included treatment of infected rabbits with an inactivated vaccine.

Results

The prepared vaccine showed prophylactic ability against infection with T. mentagrophytes for more than 6 months without requiringan adjuvant and also revealed at herapeutic ability in infected animals after a short time (16 days), compared with the control group.

Conclusion

Inactivated vaccine gives animals durable protection and shortens the treatmenttime for infection with dermatophytosis.

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 Immunological Memory in Invasive Fungal Infections - A Dream so Close yet so Far

The invasive fungal infections (IFIs) are a major cause of mortality due to infectious disease worldwide. Majority of the IFIs are caused by opportunistic fungi including Candida, Aspergillus and Cryptococcus species. Lack of approved antifungal vaccines and the emergence of antifungal drug-resistant strains pose major constraints in controlling IFIs. A comprehensive understanding of the host immune response is required to develop novel fungal vaccines to prevent death from IFIs. In this review, we have discussed the challenges associated with the development of antifungal vaccines. We mentioned how host-pathogen interactions shape immunological memory and development of long-term protective immunity to IFIs. Furthermore, we underscored the contribution of long-lived innate and adaptive memory cells in protection against IFIs and summarized the current vaccine strategies.

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

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

Therapies and Vaccines Based on Nanoparticles for the Treatment of Systemic Fungal Infections

Treatment modalities for systemic mycoses are still limited. Currently, the main antifungal therapeutics include polyenes, azoles, and echinocandins. However, even in the setting of appropriate administration of antifungals, mortality rates remain unacceptably high. Moreover, antifungal therapy is expensive, treatment periods can range from weeks to years, and toxicity is also a serious concern. In recent years, the increased number of immunocompromised individuals has contributed to the high global incidence of systemic fungal infections. Given the high morbidity and mortality rates, the complexity of treatment strategies, drug toxicity, and the worldwide burden of disease, there is a need for new and efficient therapeutic means to combat invasive mycoses. One promising avenue that is actively being pursued is nanotechnology, to develop new antifungal therapies and efficient vaccines, since it allows for a targeted delivery of drugs and antigens, which can reduce toxicity and treatment costs. The goal of this review is to discuss studies using nanoparticles to develop new therapeutic options, including vaccination methods, to combat systemic mycoses caused by Candida sp., Cryptococcus sp., Paracoccidioides sp., Histoplasma sp., Coccidioides sp., and Aspergillus sp., in addition to providing important information on the use of different types of nanoparticles, nanocarriers and their corresponding mechanisms of action.

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.

Effects of immune suppression in murine models of disseminated Candida glabrata and Candida tropicalis infection and utility of a synthetic peptide vaccine

Candida species are the second most frequent cause of fungal infections worldwide. Current knowledge of immunity to Candida has been gleaned almost exclusively from studies on Candida albicans, the most common disease-causing species. Knowledge of immunity to non-albicans Candida (NAC) species is still at an early stage due to the lack of tractable animal models with which to study these important pathogens. This is partly because many NAC species are not usually pathogenic in mouse models of candidiasis. In this study, we established an immunosuppressed mouse model of disseminated candidiasis by the two clinically important NAC species, C. glabrata and C. tropicalis. The inbred mouse strains, A/J and BALB/c, show distinct susceptibilities to disseminated Candida infection. A/J mice, deficient for complement C5, are more susceptible to disseminated infection with both C. glabrata and C. tropicalis compared to BALB/c mice, the latter having functional C5. Here we show that peptide-pulsed dendritic cell (DC) vaccination with a peptide derived from a C. tropicalis cell surface protein, significantly improved survival and reduced the fungal burdens of disseminated candidiasis in these immunocompromised mice. Importantly, this study is the first report of protective efficacy conferred by a peptide vaccine against medically important NAC species in immunosuppressed hosts. Establishing this experimental mouse model provides an important tool to further understand pathogenesis and host resistance in Candida infection. Significantly, our findings also demonstrate how this model can be used to evaluate new control strategies against candidiasis, such as vaccines.

Immunotherapy against Systemic Fungal Infections Based on Monoclonal Antibodies

The increasing incidence in systemic fungal infections in humans has increased focus for the development of fungal vaccines and use of monoclonal antibodies. Invasive mycoses are generally difficult to treat, as most occur in vulnerable individuals, with compromised innate and adaptive immune responses. Mortality rates in the setting of our current antifungal drugs remain excessively high. Moreover, systemic mycoses require prolonged durations of antifungal treatment and side effects frequently occur, particularly drug-induced liver and/or kidney injury. The use of monoclonal antibodies with or without concomitant administration of antifungal drugs emerges as a potentially efficient treatment modality to improve outcomes and reduce chemotherapy toxicities. In this review, we focus on the use of monoclonal antibodies with experimental evidence on the reduction of fungal burden and prolongation of survival in in vivo disease models. Presently, there are no licensed monoclonal antibodies for use in the treatment of systemic mycoses, although the potential of such a vaccine is very high as indicated by the substantial promising results from several experimental models.

Therapeutic drug monitoring of systemic antifungal agents: a pragmatic approach for adult and pediatric patients

Introduction: Therapeutic drug monitoring (TDM) has been shown to optimize the management of invasive fungal infections (IFIs), particularly for select antifungal agents with a well-defined exposure-response relationship and an unpredictable pharmacokinetic profile or a narrow therapeutic index. Select triazoles (itraconazole, voriconazole, and posaconazole) and flucytosine fulfill these criteria, while the echinocandins, fluconazole, isavuconazole, and amphotericin B generally do not do so. Given the morbidity and mortality associated with IFIs and the challenges surrounding the use of currently available antifungal agents, TDM plays an important role in therapy.Areas covered: This review seeks to describe the rationale for TDM of antifungal agents, summarize their pharmacokinetic and pharmacodynamic properties, identify treatment goals for efficacy and safety, and provide recommendations for optimal dosing and therapeutic monitoring strategies.Expert opinion: Several new antifungal agents are currently in development, including compounds from existing antifungal classes with enhanced pharmacokinetic or safety profiles as well as agents with novel targets for the treatment of IFIs. Given the predictable pharmacokinetics of these newly developed agents, use of routine TDM is not anticipated. However, expanded knowledge of exposure-response relationships of these compounds may yield a role for TDM to improve outcomes for adult and pediatric patients.

Glycoconjugate vaccines: current approaches towards faster vaccine design

Introduction: Over the last decades, glycoconjugate vaccines have been proven to be a successful strategy to prevent infectious diseases. Many diseases remain to be controlled, especially in developing countries, and emerging antibiotic-resistant bacteria present an alarming public-health threat. The increasing complexity of future vaccines, and the need to accelerate development processes have triggered the development of faster approaches to glycoconjugate vaccines design. Areas covered: This review provides an overview of recent progress in glycoconjugation technologies toward faster vaccine design. Expert opinion: Among the different emerging approaches, glycoengineering has the potential to combine glycan assembly and conjugation to carrier systems (such as proteins or outer membrane vesicles) in one step, resulting in a simplified manufacturing process and fewer analytical controls. Chemical and enzymatic strategies, and their automation can facilitate glycoepitope identification for vaccine design. Other approaches, such as the liposomal encapsulation of polysaccharides, potentially enable fast and easy combination of numerous antigens in the same formulation. Additional progress is envisaged in the near future, and some of these systems still need to be further validated in humans. In parallel, new strategies are needed to accelerate the vaccine development process, including the associated clinical trials, up to vaccine release onto the market.

A Recombinant Enolase-Montanide™ PetGel A Vaccine Promotes a Protective Th1 Immune Response against a Highly Virulent Sporothrix schenckii by Toluene Exposure

The effect of vaccination in fungal strains that suffered changes in their virulence by exposure to environmental contaminants is largely known. Growing reports of resistance to antifungal drugs and the emergence of new highly virulent strains, possibly acquired in the environment, prompt the design of new vaccines able to prevent and combat emerging mycotic diseases. In this study, we evaluated the protective capacity of an enolase-based vaccine and Montanide PetGel A (PGA) as an adjuvant against S. schenckii with increased virulence by exposure to toluene. The adjuvanted vaccine induced a strong specific Th1 response and protective immunity against a challenge with either wildtype or toluene-adapted S. schenckii in Balb/c mice. This study highlights the role of the adjuvant PGA driving the quality of the anti-sporothrix immunity and the key component in the vaccine efficacy.

Potential targets for next generation antimicrobial glycoconjugate vaccines

Cell surface carbohydrates have been proven optimal targets for vaccine development. Conjugation of polysaccharides to a carrier protein triggers a T-cell-dependent immune response to the glycan moiety. Licensed glycoconjugate vaccines are produced by chemical conjugation of capsular polysaccharides to prevent meningitis caused by meningococcus, pneumococcus and Haemophilus influenzae type b. However, other classes of carbohydrates (O-antigens, exopolysaccharides, wall/teichoic acids) represent attractive targets for developing vaccines. Recent analysis from WHO/CHO underpins alarming concern toward antibiotic-resistant bacteria, such as the so called ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa and Enterobacter spp.) and additional pathogens such as Clostridium difficile and Group A Streptococcus. Fungal infections are also becoming increasingly invasive for immunocompromised patients or hospitalized individuals. Other emergencies could derive from bacteria which spread during environmental calamities (Vibrio cholerae) or with potential as bioterrorism weapons (Burkholderia pseudomallei and mallei, Francisella tularensis). Vaccination could aid reducing the use of broad-spectrum antibiotics and provide protection by herd immunity also to individuals who are not vaccinated.

This review analyzes structural and functional differences of the polysaccharides exposed on the surface of emerging pathogenic bacteria, combined with medical need and technological feasibility of corresponding glycoconjugate vaccines.

Transcriptomic and Genomic Approaches for Unravelling Candida albicans Biofilm Formation and Drug Resistance-An Update

Candida albicans is an opportunistic fungal pathogen, which causes a plethora of superficial, as well as invasive, infections in humans. The ability of this fungus in switching from commensalism to active infection is attributed to its many virulence traits. Biofilm formation is a key process, which allows the fungus to adhere to and proliferate on medically implanted devices as well as host tissue and cause serious life-threatening infections. Biofilms are complex communities of filamentous and yeast cells surrounded by an extracellular matrix that confers an enhanced degree of resistance to antifungal drugs. Moreover, the extensive plasticity of the C. albicans genome has given this versatile fungus the added advantage of microevolution and adaptation to thrive within the unique environmental niches within the host. To combat these challenges in dealing with C. albicans infections, it is imperative that we target specifically the molecular pathways involved in biofilm formation as well as drug resistance. With the advent of the -omics era and whole genome sequencing platforms, novel pathways and genes involved in the pathogenesis of the fungus have been unraveled. Researchers have used a myriad of strategies including transcriptome analysis for C. albicans cells grown in different environments, whole genome sequencing of different strains, functional genomics approaches to identify critical regulatory genes, as well as comparative genomics analysis between C. albicans and its closely related, much less virulent relative, C. dubliniensis, in the quest to increase our understanding of the mechanisms underlying the success of C. albicans as a major fungal pathogen. This review attempts to summarize the most recent advancements in the field of biofilm and antifungal resistance research and offers suggestions for future directions in therapeutics development.

Phage vaccines displaying YGKDVKDLFDYAQE epitope induce protection against systemic candidiasis in mouse model

Candida albicans is a common commensal and opportunistic fungal pathogen in human, which poses threat to human health, especially in immunocompromised patients. Unfortunately, few effective prophylactic and therapeutic strategies were applied to clinic practice. Recently, the peptide YGKDVKDLFDYAQE from Fructose-bisphosphate aldolase 1 (Fba1), as a vaccine, was reported to induce protection effects against systemic candidiasis. Here, we displayed this epitope peptide on the coat proteins (pIII or pVIII) of filamentous phage, and investigated their protective effects against C. albicans infections. Mice were immunized with recombinant phages (designated as phage-3F and phage-8F) or protein (rFba1), then challenged with C. albicans yeast cells via lateral tail vein. Results demonstrated that the recombinant phages as well as rFba1 apparently induced humoral and cellular immune responses, reduced fungal burden and relieved kidney damage in infected mice and significantly improved their survival rates. Briefly, all these findings indicated that the recombinant phages displaying the epitope YGKDVKDLFDYAQE have the potential to be developed into a new vaccine against C. albicans infections.

Silencing SOCS1 in dendritic cells promote survival of mice with systemic Candida albicans infection via inducing Th1-cell differentiation

Enhancing the immunity conferred by dendritic cells (DCs) to fungal infection represents a promising strategy in the number of immunocompromised individuals. In a previous study, we demonstrated that suppressor of cytokine signaling 1 (SOCS1) silencing can promote the maturation of DCs and induce an immune response against Candida albicans (C. albicans) in vitro. Herein, the effectiveness of SOCS1 suppression administered by SOCS1-siRNA-treated DCs is further evaluated in systemic candidiasis mouse model. The SOCS1-silenced DCs increase mouse survival and significantly decrease fungal colonization in the kidneys. We confirm that the serum IFN-γ levels in SOCS1-siRNA-treated mice are higher than in all other infected groups at the early stages of infection, which correlates with a higher differentiation of IFN-γ⁺CD4⁺ T cells (Th1) in the spleen. Meanwhile, the differentiation of IL-4-producing CD4⁺ T (Th2) or IL-17-producing CD4⁺ T cells (Th17 cells) remain unaffected under the same treatment, suggesting that SOCS1-silenced DCs significantly affect the IFN-γ-producing CD4⁺ T cells (Th1). However, at the late stages of infection when the differentiation of Th1, Th2 and Th17 cells decreases in SOCS1-silenced-DCs-treated mice, all the serum cytokines (IFN-γ, IL-4 and IL-17) are also reduced. In summary, treatment of mice with SOCS1-silenced DCs can protect mice from systemic infection during the early stages and thereby increase overall survival. We conclude that the increase in Th1 response in early stages avoids the cascade inflammatory response in later stages that is known to place such a large fungal load on the kidneys and cause subsequent death.

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.

Mitigating amphibian chytridiomycoses in nature

Amphibians across the planet face the threat of population decline and extirpation caused by the disease chytridiomycosis. Despite consensus that the fungal pathogens responsible for the disease are conservation issues, strategies to mitigate their impacts in the natural world are, at best, nascent. Reducing risk associated with the movement of amphibians, non-amphibian vectors and other sources of infection remains the first line of defence and a primary objective when mitigating the threat of disease in wildlife. Amphibian-associated chytridiomycete fungi and chytridiomycosis are already widespread, though, and we therefore focus on discussing options for mitigating the threats once disease emergence has occurred in wild amphibian populations. All strategies have shortcomings that need to be overcome before implementation, including stronger efforts towards understanding and addressing ethical and legal considerations. Even if these issues can be dealt with, all currently available approaches, or those under discussion, are unlikely to yield the desired conservation outcome of disease mitigation. The decision process for establishing mitigation strategies requires integrated thinking that assesses disease mitigation options critically and embeds them within more comprehensive strategies for the conservation of amphibian populations, communities and ecosystems.This article is part of the themed issue 'Tackling emerging fungal threats to animal health, food security and ecosystem resilience'.

Antifungal Therapy: New Advances in the Understanding and Treatment of Mycosis

The high rates of morbidity and mortality caused by fungal infections are associated with the current limited antifungal arsenal and the high toxicity of the compounds. Additionally, identifying novel drug targets is challenging because there are many similarities between fungal and human cells. The most common antifungal targets include fungal RNA synthesis and cell wall and membrane components, though new antifungal targets are being investigated. Nonetheless, fungi have developed resistance mechanisms, such as overexpression of efflux pump proteins and biofilm formation, emphasizing the importance of understanding these mechanisms. To address these problems, different approaches to preventing and treating fungal diseases are described in this review, with a focus on the resistance mechanisms of fungi, with the goal of developing efficient strategies to overcoming and preventing resistance as well as new advances in antifungal therapy. Due to the limited antifungal arsenal, researchers have sought to improve treatment via different approaches, and the synergistic effect obtained by the combination of antifungals contributes to reducing toxicity and could be an alternative for treatment. Another important issue is the development of new formulations for antifungal agents, and interest in nanoparticles as new types of carriers of antifungal drugs has increased. In addition, modifications to the chemical structures of traditional antifungals have improved their activity and pharmacokinetic parameters. Moreover, a different approach to preventing and treating fungal diseases is immunotherapy, which involves different mechanisms, such as vaccines, activation of the immune response and inducing the production of host antimicrobial molecules. Finally, the use of a mini-host has been encouraging for in vivo testing because these animal models demonstrate a good correlation with the mammalian model; they also increase the speediness of as well as facilitate the preliminary testing of new antifungal agents. In general, many years are required from discovery of a new antifungal to clinical use. However, the development of new antifungal strategies will reduce the therapeutic time and/or increase the quality of life of patients.

Nanoparticle-Based Mycosis Vaccine

Many diseases that were considered major affliction of mankind in the past have been successfully eradicated with introduction of appropriate vaccine strategies. In order to expedite new challenges coming up to deal with various infectious diseases, nano-particulate-based subunit vaccines seem to be the demand of ordeal. The nano-vaccines can find better scope for the diseases that were not rampant in the semi-advanced world few years back. For example in present-day circumstances that corroborate with advancement in the field of medical sciences in terms of cancer chemotherapy, organ transplantation, therapy of autoimmune diseases, etc.; along with prevalence of altogether unheard diseases such as HIV infection, people are at risk of infliction with many more pathogens. In this regard, development of an effective prophylactic strategy against many opportunistic infections primarily caused by fungal pathogens needs better understanding of host pathogen relation and role of active immunity against pathogenic fungi. In the present study, we have tried to decipher effectiveness of a nano-sized vaccine delivery system in imparting protection against fungal pathogens.

Th1-Inducing Agents in Prophylaxis and Therapy for Paracoccidioidomycosis

Adjuvants and immunomodulatory molecules could be included in the treatment of P. brasiliensis infection. In this context, we reported that the therapeutic and/or prophylactic administration of Th1-inducing agents, such as immunomodulatory lectins and adjuvants, was able to provide protection against experimental paracoccidioidomycosis. Then, we described the protocols to investigate the effect of immunomodulatory agents on the course of P. brasiliensis infection. In this sense, we detailed the measurement of fungal burden and cytokine production, and the histopathological analysis used to evaluate the most effective administration regime.

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.

Newer patents in antimycotic therapy

There has been a global upsurge in fungal infections due to rise in immunodeficiencies, debilitation and situations of violated anatomical barriers. The available antifungal repertoire has limited activity and is fraught with toxicity concerns. Drug resistance has also shown a rapid upward trend. This has resulted in increased treatment failures, mortality and health care costs. Novel effective and safe antimycotics are needed. Analogues of existing antifungal compounds and new molecules are being developed. New targets are being explored for their putative role in curtailing fungal infections. Newer antigens as vaccine candidates are being researched into. Focused efforts in this direction have yielded encouraging results. This review illuminates the various antifungal strategies which hold promise for the future.

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.

Active immunizations with peptide-DC vaccines and passive transfer with antibodies protect neutropenic mice against disseminated candidiasis

We previously report that peptide-pulsed dendritic cell (DC) vaccination, which targeting two peptides (Fba and Met6) expressed on the cell surface of Candida albicans, can induce high degree of protection against disseminated candidiasis in immunocompetent mice. Passive transfer of immune sera from the peptide immunized mice or peptide-related monoclonal antibodies demonstrated that protection was medicated by peptide-specific antibodies. In this study the efficacy of active and passive immunization against disseminated candidiasis was tested in mice with cyclophosphamide-induced neutropenia. Peptide-DC vaccines were given to mice prior to induction of neutropenia. We show active immunization with either Fba or Met6 peptide-DC vaccine significantly improved the survival and reduced the fungal burden of disseminated candidiasis in those immunocompromised mice. Importantly, we show that administration of two protective monoclonal antibodies also protect neutropenic mice against the disease, implying possibility of developing a successful passive immunotherapy strategy to treat the disease and protect against disseminated candidiasis. The results of this study are crucial as they address the fundamental questions as to whether the synthetic peptide vaccine induced immunity protects the host during a neutropenic episode. We anticipate that this peptide-vaccine study will serve as the foundation of future investigations into new peptide vaccines comprised of cell surface peptides from other medically important Candida species, as well as other fungi.

New insights on the development of fungal vaccines: from immunity to recent challenges

Fungal infections are emerging as a major problem in part due to high mortality associated with systemic infections, especially in the case of immunocompromised patients. With the development of new treatments for diseases such as cancer and the acquired immune deficiency syndrome pandemic, the number of immunosuppressed patients has increased and, as a consequence, also the number of invasive fungal infections has increased. Several studies have proposed new strategies for the development of effective fungal vaccines. In addition, better understanding of how the immune system works against fungal pathogens has improved the further development of these new vaccination strategies. As a result, some fungal vaccines have advanced through clinical trials. However, there are still many challenges that prevent the clinical development of fungal vaccines that can efficiently immunise subjects at risk of developing invasive fungal infections. In this review, we will discuss these new vaccination strategies and the challenges that they present. In the future with proper investments, fungal vaccines may soon become a reality.

Opportunistic yeast pathogens: reservoirs, virulence mechanisms, and therapeutic strategies

Life-threatening invasive fungal infections are becoming increasingly common, at least in part due to the prevalence of medical interventions resulting in immunosuppression. Opportunistic fungal pathogens of humans exploit hosts that are immunocompromised, whether by immunosuppression or genetic predisposition, with infections originating from either commensal or environmental sources. Fungal pathogens are armed with an arsenal of traits that promote pathogenesis, including the ability to survive host physiological conditions and to switch between different morphological states. Despite the profound impact of fungal pathogens on human health worldwide, diagnostic strategies remain crude and treatment options are limited, with resistance to antifungal drugs on the rise. This review will focus on the global burden of fungal infections, the reservoirs of these pathogens, the traits of opportunistic yeast that lead to pathogenesis, host genetic susceptibilities, and the challenges that must be overcome to combat antifungal drug resistance and improve clinical outcome.

Vaccines in the treatment of invasive candidiasis

Candida albicans is the most common cause of hematogenously disseminated candidiasis, and this disease is particularly prevalent in immunocompromised patients. The mortality of invasive candidiasis remains 40% to 50% even with the proper treatment with current antifungal drugs. Recently, with the better understanding of host-fungus interactions, notable progress has been made in antifungal vaccine research. Most antifungal vaccines exert protection by inducing either (or both) B-cell and T-cell responses. Here we summarize the current available information on C. albicans vaccines, highlight the obstacles that researchers identified, and offer several suggestions.

Protection from systemic Candida albicans infection by inactivation of the Sts phosphatases

The human fungal pathogen Candida albicans causes invasive candidiasis, characterized by fatal organ failure due to disseminated fungal growth and inflammatory damage. The suppressor of TCR signaling 1 (Sts-1) and Sts-2 are two homologous phosphatases that negatively regulate signaling pathways in a number of hematopoietic cell lineages, including T lymphocytes, mast cells, and platelets. Functional inactivation of both Sts enzymes leads to profound resistance to systemic infection by C. albicans, such that greater than 80% of mice lacking Sts-1 and -2 survive a dose of C. albicans (2.5 × 10(5) CFU/mouse) that is uniformly lethal to wild-type mice within 10 days. Restriction of fungal growth within the kidney occurs by 24 h postinfection in the mutant mice. This occurs without induction of a hyperinflammatory response, as evidenced by the decreased presence of leukocytes and inflammatory cytokines that normally accompany the antifungal immune response. Instead, the absence of the Sts phosphatases leads to the rapid induction of a unique immunological environment within the kidney, as indicated by the early induction of a proinflammatory cytokine (CXL10). Mice lacking either Sts enzyme individually display an intermediate lethality phenotype. These observations identify an opportunity to optimize host immune responses toward a deadly fungal pathogen.

Breaking the mould - novel diagnostic and therapeutic strategies for invasive pulmonary aspergillosis in the immune deficient patient

Invasive pulmonary aspergillosis (IPA) caused by the ubiquitous environmental fungus Aspergillus is a frequently fatal lung disease of immunocompromised humans accounting for more than 200,000 infections each year, with an associated mortality rate of 30-90%. This review addresses the current status of IPA diagnosis and treatment and the urgent need to develop accurate, non-invasive strategies for identifying pulmonary infections in the ever-expanding population of immune deficient patients at risk of acquiring opportunistic fungal infections including hematological malignancy and hematopoetic stem cell transplant patients. Recent advances in the use of an Aspergillus-specific monoclonal antibody, JF5, for point-of-care diagnosis of IPA using lateral-flow technology is examined, as is its use in PET/MRI bioimaging and radio-immunotherapy using radionuclide-labeled single chain antibody fragments, Fab fragments, and a fully humanized JF5 derivative.

Altered dynamics of Candida albicans phagocytosis by macrophages and PMNs when both phagocyte subsets are present

An important first line of defense against Candida albicans infections is the killing of fungal cells by professional phagocytes of the innate immune system, such as polymorphonuclear cells (PMNs) and macrophages. In this study, we employed live-cell video microscopy coupled with dynamic image analysis tools to provide insights into the complexity of C. albicans phagocytosis when macrophages and PMNs were incubated with C. albicans alone and when both phagocyte subsets were present. When C. albicans cells were incubated with only one phagocyte subtype, PMNs had a lower overall phagocytic capacity than macrophages, despite engulfing fungal cells at a higher rate once fungal cells were bound to the phagocyte surface. PMNs were more susceptible to C. albicans-mediated killing than macrophages, irrespective of the number of C. albicans cells ingested. In contrast, when both phagocyte subsets were studied in coculture, the two cell types phagocytosed and cleared C. albicans at equal rates and were equally susceptible to killing by the fungus. The increase in macrophage susceptibility to C. albicans-mediated killing was a consequence of macrophages taking up a higher proportion of hyphal cells under these conditions. In the presence of both PMNs and macrophages, C. albicans yeast cells were predominantly cleared by PMNs, which migrated at a greater speed toward fungal cells and engulfed bound cells more rapidly. These observations demonstrate that the phagocytosis of fungal pathogens depends on, and is modified by, the specific phagocyte subsets present at the site of infection.

Extensive work investigating fungal cell phagocytosis by macrophages and PMNs of the innate immune system has been carried out. These studies have been informative but have examined this phenomenon only when one phagocyte subset is present. The current study employed live-cell video microscopy to break down C. albicans phagocytosis into its component parts and examine the effect of a single phagocyte subset, versus a mixed phagocyte population, on these individual stages. Through this approach, we identified that the rate of fungal cell engulfment and rate of phagocyte killing altered significantly when both macrophages and PMNs were incubated in coculture with C. albicans compared to the rate of either phagocyte subset incubated alone with the fungus. This research highlights the significance of studying pathogen-host cell interactions with a combination of phagocytes in order to gain a greater understanding of the interactions that occur between cells of the host immune system in response to fungal invasion.

Synthetically prepared glycooligosaccharides mimicking Candida albicans cell wall glycan antigens--novel tools to study host-pathogen interactions

The immunobiological efficacy of synthetically prepared mannooligosaccharides and a glucooligosaccharide mimicking the structure of Candida albicans cell wall glycans was assessed in vivo and in vitro to exploit immune responses. The exposure of mice splenocytes to BSA-based conjugates of synthetic oligomannosides and oligoglucoside revealed intense influence on T-cell subset polarization. The conjugates biased the immune responses towards Th1 and Th17 with respect to the prevalence of interferon-gamma (IFN-γ) and interleukin (IL)-17 (IL-17) over IL-4 and IL-10 levels. The inflammatory activity of the conjugates has been evaluated based on the induction of pro-inflammatory cytokines. Postvaccination, antimannooligosaccharide and antiglucooligosaccharide antisera were subjected to an evaluation of the structure-immunomodulation activity relationship. Clinical isolates of C. albicans CCY 29-3-32 and C. albicans CCY 29-3-164 were applied to study interactions between Candida cells and anti-oligosaccharide antibodies. In situ recognition of parietal oligomannosyl and oligoglucosyl sequences in C. albicans cell wall by the antisera raised against BSA-based conjugates of synthetic oligomannosides and oligoglucoside revealed the effective recognition of specific distribution of natural oligosaccharide sequences in the cell wall of C. albicans serotype A. With respect to these results, it can be concluded that new, synthetically prepared oligosaccharides mimicking Candida cell wall structures represent prospective immunobiologically effective components for further immunopharmacologically relevant Candida vaccine design.

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.

Hidden killers: human fungal infections

Although fungal infections contribute substantially to human morbidity and mortality, the impact of these diseases on human health is not widely appreciated. Moreover, despite the urgent need for efficient diagnostic tests and safe and effective new drugs and vaccines, research into the pathophysiology of human fungal infections lags behind that of diseases caused by other pathogens. In this Review, we highlight the importance of fungi as human pathogens and discuss the challenges we face in combating the devastating invasive infections caused by these microorganisms, in particular in immunocompromised individuals.

Universal fungal vaccines: could there be light at the end of the tunnel?

The complex nature of fungal pathogens, the intricate host-pathogen relationship and the health status of subjects in need of antifungal vaccination continue to hamper efforts to develop fungal vaccines for clinical use. That said, the rise of the universal vaccine concept is hoped to revive fungal vaccine research by expanding the pool of vaccine candidates worthy of clinical evaluation. It can do so through antigenic commonality-based screening for vaccine candidates from a wide range of pathogens and by reassessing the sizable collection of already available experimental and approved vaccines. Development of experimental vaccines protective against multiple fungal pathogens is evidence of the utility of this concept in fungal vaccine research. However, universal fungal vaccines are not without difficulties; for instance, development of vaccines with differential effectiveness is an issue that should be addressed. Additionally, rationalizing the development of universal fungal vaccines on health or economic basis could be contentious. Herein, universal fungal vaccines are discussed in terms of their potential usefulness and possible drawbacks.

C-type lectin receptors orchestrate antifungal immunity

Immunity to pathogens critically requires pattern-recognition receptors (PRRs) to trigger intracellular signaling cascades that initiate and direct innate and adaptive immune responses. For fungal infections, these responses are primarily mediated by members of the C-type lectin receptor family. In this Review, we highlight recent advances in the understanding of the roles and mechanisms of these multifunctional receptors, explore how these PRRs orchestrate antifungal immunity and briefly discuss progress in the use of these receptors as targets for antifungal and other vaccines.

Host defense pathways against fungi: the basis for vaccines and immunotherapy

Fungal vaccines have long been a goal in the fields of immunology and microbiology to counter the high mortality and morbidity rates owing to fungal diseases, particularly in immunocompromised patients. However, the design of effective vaccination formulations for durable protection to the different fungi has lagged behind due to the important differences among fungi and their biology and our limited understanding of the complex host–pathogen interactions and immune responses. Overcoming these challenges is expected to contribute to improved vaccination strategies aimed at personalized efficacy across distinct target patient populations. This likely requires the integration of multifaceted approaches encompassing advanced immunology, systems biology, immunogenetics, and bioinformatics in the fields of fungal and host biology and their reciprocal interactions.

Recent progress in vaccines against fungal diseases

Diseases caused by fungi are increasingly impacting the health of the human population and now account for a large fraction of infectious disease complications in individuals with impaired immunity or breached tissue defenses. Antifungal therapy is often of limited effectiveness in these patients, resulting into treatment failures, chronic infections and unacceptable rates of mortality, morbidity and their associated costs. Consequently there is a real medical need for new treatments and preventive measures to combat fungal diseases and, toward this goal, safe and efficacious vaccines would constitute major progress. After decades of complacency and neglect of this critically important field of research, remarkable progress has been made in recent years. A number of highly immunogenic and protective vaccine formulations in preclinical setting have been developed, and at least two have undergone Phase 1 clinical trials as preventive and/or therapeutic tools against candidiasis.

Fungal cell wall vaccines: an update

This discussion is intended to be an overview of current advances in the development of fungal cell wall vaccines with an emphasis on Candida; it is not a comprehensive historical review of all fungal cell wall vaccines. Selected, more recent, innovative strategies for developing fungal vaccines will be highlighted. Both scientific and logistical obstacles related to the development of, and clinical use of, fungal vaccines will be discussed.