DNA vaccine encoding peptide P10 against experimental paracoccidioidomycosis induces long-term protection in presence of regulatory T cells

The story of Paracoccidiodes gp43

This review is about Dr. Luiz Rodolpho Raja Gabaglia Travassos' scientific contributions to paracoccidioidomycosis as told by myself, Rosana Puccia, but co-written with Dr. Carlos P. Taborda, my younger scientific brother, collaborator, and dear friend. Dr. Travassos' pioneer papers and scientific insights covering biochemistry, immunology, cell biology, and molecular biology in the paracoccidiodomycosis area are key contributions that we acknowledge here, with focus on the Paracoccidioides antigen gp43. Importantly, we tell some personal stories behind the scene. Dr. Travassos' contribution to science is available in a number of quality publications, while his influence to hundreds of people who gravitated around him will be kept alive inside each one of us forever.

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.

Targeting the P10 Peptide in Maturing Dendritic Cells via the DEC205 Receptor In Vivo: A New Therapeutic Strategy against Paracoccidioidomycosis

Paracoccidioidomycosis (PCM) is a systemic mycosis caused by Paracoccidioides brasiliensis, a thermally dimorphic fungus, which is the most frequent endemic systemic mycosis in many Latin American countries, where ~10 million people are believed to be infected. In Brazil, it is ranked as the tenth most common cause of death among chronic infectious diseases. Hence, vaccines are in development to combat this insidious pathogen. It is likely that effective vaccines will need to elicit strong T cell-mediated immune responses composed of IFNγ secreting CD4⁺ helper and CD8⁺ cytolytic T lymphocytes. To induce such responses, it would be valuable to harness the dendritic cell (DC) system of antigen-presenting cells. To assess the potential of targeting P10, which is a peptide derived from gp43 secreted by the fungus, directly to DCs, we cloned the P10 sequence in fusion with a monoclonal antibody to the DEC205 receptor, an endocytic receptor that is abundant on DCs in lymphoid tissues. We verified that a single injection of the αDEC/P10 antibody caused DCs to produce a large amount of IFNγ. Administration of the chimeric antibody to mice resulted in a significant increase in the levels of IFN-γ and IL-4 in lung tissue relative to control animals. In therapeutic assays, mice pretreated with αDEC/P10 had significantly lower fungal burdens compared to control infected mice, and the architecture of the pulmonary tissues of αDEC/P10 chimera-treated mice was largely normal. Altogether, the results obtained so far indicate that targeting P10 through a αDEC/P10 chimeric antibody in the presence of polyriboinosinic: polyribocytidylic acid is a promising strategy in vaccination and therapeutic protocols to combat PCM.

Vaccine development for pathogenic fungi: current status and future directions

INTRODUCTION

Fungal infections are caused by a broad range of pathogenic fungi that are found worldwide with different geographic distributions, incidences, and mortality rates. Considering that there are relatively few approved medications available for combating fungal diseases and no vaccine formulation commercially available, multiple groups are searching for new antifungal drugs, examining drugs for repurposing and developing antifungal vaccines, in order to control deaths, sequels, and the spread of these complex infections.

AREAS COVERED

This review provides a summary of advances in fungal vaccine studies and the different approaches under development, such as subunit vaccines, whole organism vaccines, and DNA vaccines, as well as studies that optimize the use of adjuvants. We conducted a literature search of the PubMed with terms: fungal vaccines and genus of fungal pathogens (Cryptococcus spp. Candida spp. Coccidioides spp. Aspergillus spp. Sporothrix spp. Histoplasma spp. Paracoccidioides spp. Pneumocystis spp. and the Mucorales order), a total of 177 articles were collected from database.

EXPERT OPINION

Problems regarding the immune response development in an immunocompromised organism, the similarity between fungal and mammalian cells, and the lack of attention by health organizations to fungal infections are closely related to the fact that, at present, there are no fungal vaccines available for clinical use.

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.

Peptides derived from gp43, the most antigenic protein from Paracoccidioides brasiliensis, form amyloid fibrils in vitro: implications for vaccine development

Fungal infection is an important health problem in Latin America, and in Brazil in particular. Paracoccidioides (mainly P. brasiliensis and P. lutzii) is responsible for paracoccidioidomycosis, a disease that affects mainly the lungs. The glycoprotein gp43 is involved in fungi adhesion to epithelial cells, which makes this protein an interesting target of study. A specific stretch of 15 amino acids that spans the region 181–195 (named P10) of gp43 is an important epitope of gp43 that is being envisioned as a vaccine candidate. Here we show that synthetic P10 forms typical amyloid aggregates in solution in very short times, a property that could hamper vaccine development. Seeds obtained by fragmentation of P10 fibrils were able to induce the aggregation of P4, but not P23, two other peptides derived from gp43. In silico analysis revealed several regions within the P10 sequence that can form amyloid with steric zipper architecture. Besides, in-silico proteolysis studies with gp43 revealed that aggregation-prone, P10-like peptides could be generated by several proteases, which suggests that P10 could be formed under physiological conditions. Considering our data in the context of a potential vaccine development, we redesigned the sequence of P10, maintaining the antigenic region (HTLAIR), but drastically reducing its aggregation propensity.

Protective Response in Experimental Paracoccidioidomycosis Elicited by Extracellular Vesicles Containing Antigens of Paracoccidioides brasiliensis

Paracoccidioidomycosis (PCM) is a systemic disease caused by Paracoccidioides spp. PCM is endemic in Latin America and most cases are registered in Brazil. This mycosis affects mainly the lungs, but can also spread to other tissues and organs, including the liver. Several approaches have been investigated to improve treatment effectiveness and protection against the disease. Extracellular vesicles (EVs) are good antigen delivery vehicles. The present work aims to investigate the use of EVs derived from Paracoccidioides brasiliensis as an immunization tool in a murine model of PCM. For this, male C57BL/6 were immunized with two doses of EVs plus adjuvant and then infected with P. brasiliensis. EV immunization induced IgM and IgG in vivo and cytokine production by splenocytes ex vivo. Further, immunization with EVs had a positive effect on mice infected with P. brasiliensis, as it induced activated T lymphocytes and NKT cell mobilization to the infected lungs, improved production of proinflammatory cytokines and the histopathological profile, and reduced fungal burden. Therefore, the present study shows a new role for P. brasiliensis EVs in the presence of adjuvant as modulators of the host immune system, suggesting their utility as immunizing agents.

Neutrophil Cells Are Essential for The Efficacy of a Therapeutic Vaccine against Paracoccidioidomycosis

Paracoccidioidomycosis (PCM), caused by the Paracoccidioides species, is a systemic disease endemic in several Latin American countries, mainly in Brazil, Colombia, Argentina, and Venezuela. Current treatment approaches are challenging as they require prolonged durations of antifungal drugs that have potential toxicities, and despite antifungals, relapses are common. Hence, new therapeutic approaches, such as vaccines, are being investigated. The therapeutic vaccine consisting of peptide P10 associated with lipid cationic DODAB (P10+DODAB) is effective in murine models of PCM. However, the specific immune mechanisms required for the protective response has not been fully elucidated. The present work aims at evaluating the participation of neutrophils in the immune response induced by P10+DODAB. We found that the vaccine reduced both the influx of pulmonary neutrophils and the fungal load in comparison to infected animals that did not receive this treatment. The parenchymal architecture of the lungs of P10+DODAB-treated animals was largely preserved with only a few granulomas present, and tissue cytokine analysis showed a Th1 cytokine profile with augmented levels of IL-12, IFN-γ and TNF-α, and low levels of IL-4. When neutrophils were depleted 24 h prior to each treatment, the effectiveness of the P10+DODAB vaccine was completely lost as the fungal burdens remained high and histological examination showed a marked inflammation and fungal dissemination with a dysregulated cytokine response. In conclusion, these findings indicate that neutrophils are vital to ensure the triggering of an effective immune response to P10+DODAB.

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.

Regulatory T cells in paracoccidioidomycosis

This review addresses the role of regulatory T cells (Tregs), which are essential for maintaining peripheral tolerance and controlling pathogen immunity, in the host response against Paracoccidioides brasiliensis, a primary fungal pathogen. A brief introduction on the general features of Treg cells summarizes their main functions, subpopulations, mechanisms of suppression and plasticity. The main aspects of immunity in the diverse forms of the P. brasiliensis infection are presented, as are the few extant studies on the relevance of Treg cells in the control of severity of the human disease. Finally, the influence of Toll-like receptors, Dectin-1, NOD-like receptor P3 (NLRP3), Myeloid differentiation factor-88 (MyD88), as well as the enzyme indoleamine 2,3 dioxygenase (IDO) on the expansion and function of Treg cells in a murine model of pulmonary paracoccidioidomycosis (PCM) is also discussed. It is demonstrated that some of these components are involved in the negative control of Treg cell expansion, whereas others positively trigger the proliferation and activity of these cells. Finally, the studies here summarized highlight the dual role of Treg cells in PCM, which can be protective by controlling excessive immunity and tissue pathology but also deleterious by inhibiting the anti-fungal immunity necessary to control fungal growth and dissemination.

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.

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.

Peptide Vaccine Against Paracoccidioidomycosis

The chapter reviews methods utilized for the isolation and characterization of a promising immunogen candidate, aiming at a human vaccine against paracoccidioidomycosis. Peptide P10 carries a T-CD4+ epitope and was identified as an internal sequence of the major diagnostic antigen known as gp43 glycoprotein. It successfully treated massive intratracheal infections by virulent Paracoccidioides brasiliensis in combination with chemotherapy.An introduction about the systemic mycosis was found essential to understand the various options that were considered to design prophylactic and therapeutic vaccine protocols using peptide P10.

Peptides Derived from a Phage Display Library Inhibit Adhesion and Protect the Host against Infection by Paracoccidioides brasiliensis and Paracoccidioides lutzii

Paracoccidioides brasiliensis and Paracoccidioides lutzii are dimorphic fungi and are the etiological agents of paracoccidioidomycosis (PCM). Adhesion is one of the most important steps in infections with Paracoccidioides and is responsible for the differences in the virulence of isolates of these fungi. Because of the importance of adhesion to the establishment of an infection, this study focused on the preliminary development of a new therapeutic strategy to inhibit adhesion by Paracoccidioides, thus inhibiting infection and preventing the disease. We used two phage display libraries to select peptides that strongly bind to the Paracoccidioides cell wall to inhibit adhesion to host cells and extracellular matrix (ECM) components (laminin, fibronectin, and type I and type IV collagen). This approach allowed us to identify four peptides that inhibited up to 64% of the adhesion of Paracoccidioides to pneumocytes in vitro and inhibited the adhesion to the ECM components by up to 57%. Encouraged by these results, we evaluated the ability of these peptides to protect Galleria mellonella from Paracoccidioides infection by treating G. mellonella larvae with the different peptides prior to infection with Paracoccidioides and observing larval survival. The results show that all of the peptides tested increased the survival of the larvae infected with P. brasiliensis by up to 64% and by up to 60% in those infected with P. lutzii. These data may open new horizons for therapeutic strategies to prevent PCM, and anti-adhesion therapy could be an important strategy.

PARACOCCIDIOIDOMYCOSIS: CHALLENGES IN THE DEVELOPMENT OF A VACCINE AGAINST AN ENDEMIC MYCOSIS IN THE AMERICAS

Paracoccidioidomycosis (PCM), caused by Paracoccidioides spp, is an important endemic mycosis in Latin America. There are two recognized Paracoccidioides species, P. brasiliensis and P. lutzii, based on phylogenetic differences; however, the pathogenesis and disease manifestations of both are indistinguishable at present. Approximately 1,853 (~51,2%) of 3,583 confirmed deaths in Brazil due to systemic mycoses from 1996-2006 were caused by PCM. Antifungal treatment is required for patients with PCM. The initial treatment lasts from two to six months and sulfa derivatives, amphotericin B, azoles and terbinafine are used in clinical practice; however, despite prolonged therapy, relapses are still a problem. An effective Th1-biased cellular immune response is essential to control the disease, which can be induced by exogenous antigens or modulated by prophylactic or therapeutic vaccines. Stimulation of B cells or passive transference of monoclonal antibodies are also important means that may be used to improve the efficacy of paracoccidioidomycosis treatment in the future. This review critically details major challenges facing the development of a vaccine to combat PCM.

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.

Paracoccidioidomycosis: eco-epidemiology, taxonomy and clinical and therapeutic issues

Acquired by inhalation of the thermal dimorphic fungi Paracoccidioides spp. conidia, paracoccidioidomycosis ranges from symptomatic to severe and potentially fatal disseminated disease. The main focus of this review is to highlight clinical aspects of paracoccidioidomycosis and, its pathogens’ diversity ecology and particularities. In addition, we present strategies for therapy, including DNA vaccines and nanostructured drugs. Molecular and morphological data supported the split of the Paracoccidioides genus into two species, Paracoccidioides brasiliensis and Paracoccidioides lutzii. An acute form of the disease affects approximately 5% of cases and involves the phagocytic mononuclear system, resulting in progressive lymphadenopathy. The chronic form affects adult men and frequently involves lungs, skin and mucous membranes, lymph nodes, and adrenal glands. The clinical manifestations depend on the ability of the host to control the fungal multiplication and dissemination. The long survival time of the fungus in the host tissues allows it to evade immune responses; therefore, successful treatment often requires long-time therapy. The consensus for treatment must consider the severity of the disease and includes sulfone derivatives, amphotericin B and azoles. Novel strategies for therapy, based on DNA vaccines and nanostructured drugs are also presented and discussed in this review.