Construction and evaluation of a novel recombinant T cell epitope-based vaccine against Coccidioidomycosis

HLA-transgenic mouse models to study autoimmune central nervous system diseases

It is known that certain human leukocyte antigen (HLA) genes are associated with autoimmune central nervous system (CNS) diseases, such as multiple sclerosis (MS), but their exact role in disease susceptibility and etiopathogenesis remains unclear. The best studied HLA-associated autoimmune CNS disease is MS, and thus will be the primary focus of this review. Other HLA-associated autoimmune CNS diseases, such as autoimmune encephalitis and neuromyelitis optica will be discussed. The lack of animal models to accurately capture the complex human autoimmune response remains a major challenge. HLA transgenic (tg) mice provide researchers with powerful tools to investigate the underlying mechanisms promoting susceptibility and progression of HLA-associated autoimmune CNS diseases, as well as for elucidating the myelin epitopes potentially targeted by T cells in autoimmune disease patients. We will discuss the potential role(s) of autoimmune disease-associated HLA alleles in autoimmune CNS diseases and highlight information provided by studies using HLA tg mice to investigate the underlying pathological mechanisms and opportunities to use these models for development of novel therapies.

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.

A glucan-particle based tularemia subunit vaccine induces T-cell immunity and affords partial protection in an inhalation rat infection model

Tularemia is a zoonotic disease caused by the facultative intracellular gram-negative bacterium Francisella tularensis. F. tularensis has a very low infection dose by the aerosol route which can result in an acute, and potentially lethal, infection in humans. Consequently, it is classified as a Category A bioterrorism agent by the US Centers for Disease Control (CDC) and is a pathogen of concern for the International Biodefence community. There are currently no licenced tularemia vaccines. In this study we report on the continued assessment of a tularemia subunit vaccine utilising β-glucan particles (GPs) as a vaccine delivery platform for immunogenic F. tularensis antigens. Using a Fischer 344 rat infection model, we demonstrate that a GP based vaccine comprising the F. tularensis lipopolysaccharide antigen together with the protein antigen FTT0814 provided partial protection of F344 rats against an aerosol challenge with a high virulence strain of F. tularensis, SCHU S4. Inclusion of imiquimod as an adjuvant failed to enhance protective efficacy. Moreover, the level of protection afforded was dependant on the challenge dose. Immunological characterisation of this vaccine demonstrated that it induced strong antibody immunoglobulin responses to both polysaccharide and protein antigens. Furthermore, we demonstrate that the FTT0814 component of the GP vaccine primed CD4+ and CD8+ T-cells from immunised F344 rats to express interferon-γ, and CD4+ cells to express interleukin-17, in an antigen specific manner. These data demonstrate the development potential of this tularemia subunit vaccine and builds on a body of work highlighting GPs as a promising vaccine platform for difficult to treat pathogens including those of concern to the bio-defence community.

A Recombinant Multivalent Vaccine (rCpa1) Induces Protection for C57BL/6 and HLA Transgenic Mice against Pulmonary Infection with Both Species of Coccidioides

Coccidioidomycosis is caused by Coccidioides posadasii (Cp) and Coccidioides immitis (Ci), which have a 4-5% difference in their genomic sequences. There is an urgent need to develop a human vaccine against both species. A previously created recombinant antigen (rCpa1) that contains multiple peptides derived from Cp isolate C735 is protective against the autologous isolate. The focus of this study is to evaluate cross-protective efficacy and immune correlates by the rCpa1-based vaccine against both species of Coccidioides. DNA sequence analyses of the homologous genes for the rCpa1 antigen were conducted for 39 and 17 clinical isolates of Cp and Ci, respectively. Protective efficacy and vaccine-induced immunity were evaluated for both C57BL/6 and human HLA-DR4 transgenic mice against five highly virulent isolates of Cp and Ci. There are total of seven amino acid substitutions in the rCpa1 antigen between Cp and Ci. Both C57BL/6 and HLA-DR4 mice that were vaccinated with an rCpa1 vaccine had a significant reduction of fungal burden and increased numbers of IFN-γ- and IL-17-producing CD4+ T cells in the first 2 weeks post challenge. These data suggest that rCpa1 has cross-protection activity against Cp and Ci pulmonary infection through activation of early Th1 and Th17 responses.

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.

Advocating for Coccidioidomycosis to Be a Reportable Disease Nationwide in the United States and Encouraging Disease Surveillance across North and South America

Coccidioidomycosis (Valley fever) has been a known health threat in the United States (US) since the 1930s, though not all states are currently required to report disease cases. Texas, one of the non-reporting states, is an example of where both historical and contemporary scientific evidence define the region as endemic, but we don't know disease incidence in the state. Mandating coccidioidomycosis as a reportable disease across more US states would increase disease awareness, improve clinical outcomes, and help antifungal drug and vaccine development. It would also increase our understanding of where the disease is endemic and the relationships between environmental conditions and disease cases. This is true for other nations in North and South America that are also likely endemic for coccidioidomycosis, especially Mexico. This commentary advocates for US state and territory epidemiologists to define coccidioidomycosis as a reportable disease and encourages disease surveillance in other endemic regions across North and South America in order to protect human health and reduce disease burden.

They shall not grow mold: Soldiers of innate and adaptive immunity to fungi

Fungi are ubiquitous commensals, seasoned predators, and important agents of emerging infectious diseases [1 ]. The immune system assumes the essential responsibility for responding intelligently to the presence of known and novel fungi to maintain host health. In this Review, we describe the immune responses to pathogenic fungi and the varied array of fungal agents confronting the vertebrate host within the broader context of fungal and animal evolution. We provide an overview of the mechanistic details of innate and adaptive antifungal immune responses, as well as ways in which these basic mechanisms support the development of vaccines and immunotherapies.

Development and evaluation of a multi-epitope subunit vaccine against group B Streptococcus infection

Streptococcus agalactiae (Group B Streptococcus, GBS) is a multi-host pathogen, even causing life-threatening infections in newborns. Vaccination with GBS crossed serotypes vaccine is one of the best options for long-term infection control. Here we built a comprehensive in silico epitope-prediction workflow pipeline to design a multivalent multiepitope-based subunit vaccine containing 11 epitopes against Streptococcus agalactiae (MVSA). All epitopes in MVSA came from the proteins which were antigenic-confirmed, virulent-associated, surface-exposed and conserved in ten GBS serotypes. The in-silico analysis showed MVSA had potential to evoke strong immune responses and enable worldwide population coverage. To validate MVSA protection efficacy against GBS infection, immune protection experiments were performed in a mouse model. Importantly, MVSA induced a high titre of antibodies, significant proliferation of mice splenocytes and elicited strong protection against lethal-dose challenge with a survival rate of 100% in mice after three vaccinations. Meanwhile, the polyclonal antibody against MVSA did not only inhibit for growth of GBS from six crucial serotypes in vitro, but also protect 100% naive mice from GBS lethal challenge. These active and passive immunity assay results suggested that MVSA could therefore be an efficacious multi-epitope vaccine against GBS infection.

Current Landscape of Coccidioidomycosis

Coccidioidomycosis, also known as Valley fever, is an endemic fungal infection commonly found in the southwestern parts of the United States. However, the disease has seen an increase in both in its area of residency and its prevalence. This review compiles some of the latest information on the epidemiology, current and in-development pharmaceutical approaches to treat the disease, trends and projections, diagnostic concerns, and the overlapping dynamics of coccidioidomycosis and COVID-19, including in special populations. This review provides an overview of the current diagnostic and therapeutic strategies and identifies areas of future development.

A Review of Coccidioides Research, Outstanding Questions in the Field, and Contributions by Women Scientists

Purpose of Review

Coccidioidomycosis is an infectious disease that gained clinical significance in the early 20th century. Many of the foundational contributions to coccidioidomycosis research, including the discovery of the fungal disease agent, Coccidioides spp., were made by women. We review recent progress in Coccidioides research and big questions remaining in the field, while highlighting some of the contributions from women.

Recent Findings

New molecular-based techniques provide a promising method for detecting Coccidioides, which can help determine the dominate reservoir host and ideal environmental conditions for growth. Genetic and genomic analyses have allowed an understanding of population structure, species level diversity, and evolutionary histories. We present a current, comprehensive genome list, where women contributed many of these entries. Several efforts to develop a coccidioidomycosis vaccine are underway.

Summary

Women continue to pioneer research on Coccidioides, including the relationships between the fungi and the environment, genetics, and clinical observations. Significant questions remain in the field of Coccidioides, including the main host reservoir, the relationships between genotypic and phenotypic variation, and the underlying cause for chronic clinical coccidioidomycosis cases.

Randomized peptide assemblies for enhancing immune responses to nanomaterials

Biomaterials capable of inducing immune responses with minimal associated inflammation are of interest in applications ranging from tissue repair to vaccines. Here we report the design of self-assembling randomized polypeptide nanomaterials inspired by glatiramoids, an immunomodulatory class of linear random copolymers. We hypothesized that peptide self-assemblies bearing similar randomized polypeptides would similarly raise responses skewed toward Type 2 immunity and T_H2 T-cell responses, additionally strengthening responses to co-assembled peptide epitopes in the absence of adjuvant. We developed a method for synthesizing self-assembling peptides terminated with libraries of randomized polypeptides (termed KEYA) with good batch-to-batch reproducibility. These peptides formed regular nanofibers and raised strong antibody responses without adjuvants. KEYA modifications dramatically improved uptake of peptide nanofibers in vitro by antigen presenting cells, and served as strong B-cell and T-cell epitopes in vivo, enhancing immune responses against epitopes relevant to influenza and chronic inflammation while inducing a KEYA-specific Type 2/T_H2/IL-4 phenotype. KEYA modifications also increased IL-4 production by T cells, extended the residence time of nanofibers, induced no measurable swelling in footpad injections, and decreased overall T cell expansion compared to unmodified nanofibers, further suggesting a T_H2 T-cell response with minimal inflammation. Collectively, this work introduces a biomaterial capable of raising strong Type 2/T_H2/IL-4 immune responses, with potential applications ranging from vaccination to tissue repair.

Vaccines for human fungal diseases: close but still a long way to go

Despite the substantial global burden of human fungal infections, there are no approved fungal vaccines to protect at risk individuals. Here, we review the progress that has been made and the challenges that lie ahead in the quest towards efficacious fungal vaccines. In mouse studies, protection has been achieved with vaccines directed against fungal pathogens, including species of Candida, Cryptococcus, and Aspergillus, that most commonly cause life-threatening human disease. Encouraging results have been obtained with vaccines composed of live-attenuated and killed fungi, crude extracts, recombinant subunit formulations, and nucleic acid vaccines. Novel adjuvants that instruct the immune system to mount the types of protective responses needed to fight mycotic infections are under development. Candidate vaccines include those that target common antigens expressed on multiple genera of fungi thereby protecting against a broad range of mycoses. Encouragingly, three vaccines have reached human clinical trials. Still, formidable obstacles must be overcome before we will have fungal vaccines licensed for human use.

Protection of Mice against Experimental Cryptococcosis by Synthesized Peptides Delivered in Glucan Particles

The high global burden of cryptococcosis has made development of a protective vaccine a public health priority. We previously demonstrated that a vaccine composed of recombinant Cryptococcus neoformans chitin deacetylase 2 (Cda2) delivered in glucan particles (GPs) protects BALB/c and C57BL/6 mice from an otherwise lethal challenge with a highly virulent C. neoformans strain. An immunoinformatic analysis of Cda2 revealed a peptide sequence predicted to have strong binding to the major histocompatibility complex class II (MHC II) H2-IAd allele found in BALB/c mice. BALB/c mice vaccinated with GPs containing a 32-amino-acid peptide (Cda2-Pep1) that included this strong binding region were protected from cryptococcosis. Protection was lost with GP-based vaccines containing versions of recombinant Cda2 protein and Cda2-Pep1 with mutations predicted to greatly diminish MHC II binding. Cda2 has homology to the three other C. neoformans chitin deacetylases, Cda1, Cda3, and Fpd1, in the high-MHC II-binding region. GPs loaded with homologous peptides of Cda1, Cda3, and Fpd1 protected BALB/c mice from experimental cryptococcosis, albeit not as robustly as the Cda2-Pep1 vaccine. Finally, seven other peptides were synthesized based on regions in Cda2 predicted to contain promising CD4+ T cell epitopes in BALB/c or C57BL/6 mice. While five peptide vaccines significantly protected BALB/c mice, only one protected C57BL/6 mice. Thus, GP-based vaccines containing a single peptide can protect mice against cryptococcosis. However, given the diversity of human MHC II alleles, a peptide-based Cryptococcus vaccine for use in humans would be challenging and likely need to contain multiple peptide sequences. IMPORTANCE Cryptococcosis, due to infection by fungi of the Cryptococcus neoformans species complex, is responsible for substantial morbidity and mortality in immunocompromised persons, particularly those with AIDS. Cryptococcal vaccines are a public health priority yet are not available for human use. We previously demonstrated mice could be protected from experimental cryptococcosis with vaccines composed of recombinant cryptococcal proteins encased in hollow highly purified yeast cell walls (glucan particles). In this study, we examined one such protective protein, Cda2, and using bioinformatics, we identified a region predicted to stimulate strong T cell responses. A peptide containing this region formulated in glucan particle-based vaccines protected mice as well as the recombinant protein. Other peptide vaccines also protected, including peptides containing sequences from proteins homologous to Cda2. These preclinical mouse studies provide a proof of principle that peptides can be effective as vaccines to protect against cryptococcosis and that bioinformatic approaches can guide peptide selection.

The Role of the Interleukin-17 Axis and Neutrophils in the Pathogenesis of Endemic and Systemic Mycoses

Systemic and endemic mycoses are considered life-threatening respiratory diseases which are caused by a group of dimorphic fungal pathogens belonging to the genera Histoplasma, Coccidioides, Blastomyces, Paracoccidioides, Talaromyces, and the newly described pathogen Emergomyces. T-cell mediated immunity, mainly T helper (Th)1 and Th17 responses, are essential for protection against these dimorphic fungi; thus, IL-17 production is associated with neutrophil and macrophage recruitment at the site of infection accompanied by chemokines and proinflammatory cytokines production, a mechanism that is mediated by some pattern recognition receptors (PRRs), including Dectin-1, Dectine-2, TLRs, Mannose receptor (MR), Galectin-3 and NLPR3, and the adaptor molecules caspase adaptor recruitment domain family member 9 (Card9), and myeloid differentiation factor 88 (MyD88). However, these PRRs play distinctly different roles for each pathogen. Furthermore, neutrophils have been confirmed as a source of IL-17, and different neutrophil subsets and neutrophil extracellular traps (NETs) have also been described as participating in the inflammatory process in these fungal infections. However, both the Th17/IL-17 axis and neutrophils appear to play different roles, being beneficial mediating fungal controls or detrimental promoting disease pathologies depending on the fungal agent. This review will focus on highlighting the role of the IL-17 axis and neutrophils in the main endemic and systemic mycoses: histoplasmosis, coccidioidomycosis, blastomycosis, and paracoccidioidomycosis.

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.

Reverse and structural vaccinology approach to design a highly immunogenic multi-epitope subunit vaccine against Streptococcus pneumoniae infection

Streptococcus pneumoniae is a pathogen that resides in the upper respiratory tract of healthy individuals, maintaining a commensal relationship with its host. However, the virulent form may be the etiology of pneumonia, meningitis, bacteremia, and other respiratory tract infections. Streptococcal diseases are preventable by vaccination; but currently available vaccines have some drawbacks, especially due to the high capsule variability of streptococci strains. Thus, an effective prevention strategy continues to be the focus of extensive research. In our work, several bioinformatics tools were used to identify immunogenic peptides from a selected pool of 46 conserved proteins from Streptococcus pneumoniae. In silico analysis showed that 10 proteins had epitopes with affinity for B and T lymphocytes, which were present in at least 26 different pathogens serotypes and were considered promiscuous. The multi-epitope protein, designated HC44, was designed based on these epitopes and specific linkers to improve stability and exposure to T lymphocytes. The recombinant HC44 protein was expressed in E.coli and Swiss-Webster mice were immunised by intraperitoneal injection. Immunisation with the multi-epitope HC44 protein resulted in the production of very high levels of IgG with title superior to 1/1.200.000. However, subtype IgG was highly unbalanced toward IgG1 and no protection was afforded after challenge with S.pneumoniae in a sepsis model. Thus, our strategy has been effective in constructing a highly antigenic protein but novel immunisation strategies should be investigated to reorient the immune system toward a protective response.

CARD9-Associated Dectin-1 and Dectin-2 Are Required for Protective Immunity of a Multivalent Vaccine against Coccidioides posadasii Infection

Coccidioides species are fungal pathogens that can cause a widely varied clinical manifestation from mild pulmonary symptom to disseminated, life-threatening disease. We have previously created a subunit vaccine by encapsulating a recombinant coccidioidal Ag (rCpa1) in glucan-chitin particles (GCPs) as an adjuvant-delivery system. The GCP-rCpa1 vaccine has shown to elicit a mixed Th1 and Th17 response and confers protection against pulmonary coccidioidomycosis in mice. In this study, we further delineated the vaccine-induced protective mechanisms. Depletion of IL-17A in vaccinated C57BL/6 mice prior to challenge abrogated the protective efficacy of GCP-rCpa1 vaccine. Global transcriptome and Ingenuity Pathway Analysis of murine bone marrow-derived macrophages after exposure to this vaccine revealed the upregulation of proinflammatory cytokines (TNF-α, IL-6, and IL-1β) that are associated with activation of C-type lectin receptors (CLR) Dectin-1- and Dectin-2-mediated CARD9 signaling pathway. The GCP formulation of rCpa1 bound soluble Dectin-1 and Dectin-2 and triggered ITAM signaling of corresponding CLR reporter cells. Furthermore, macrophages that were isolated from Dectin-1 -/-, Dectin-2 -/-, and CARD9 -/- mice significantly reduced production of inflammatory cytokines in response to the GCP-rCpa1 vaccine compared with those of wild-type mice. The GCP-rCpa1 vaccine had significantly reduced protective efficacy in Dectin-1 -/-, Dectin-2 -/-, and CARD9 -/- mice that showed decreased acquisition of Th cells in Coccidioides-infected lungs compared with vaccinated wild-type mice, especially Th17 cells. Collectively, we conclude that the GCP-rCpa1 vaccine stimulates a robust Th17 immunity against Coccidioides infection through activation of the CARD9-associated Dectin-1 and Dectin-2 signal pathways.

Maize-Produced Ag2 as a Subunit Vaccine for Valley Fever

Coccidioides is the causative agent of San Joaquin Valley fever, a fungal disease prevalent in the semiarid regions of the Americas. Efforts to develop a fungal vaccine over the last 2 decades were unsuccessful. A candidate antigen, Antigen 2 (Ag2), is notoriously difficult to express in Escherichia coli, and this study sought to accumulate the antigen at high levels in maize. Transformed maize lines accumulated recombinant Ag2 at levels >1 g/kg. Mice immunized with this antigen and challenged with live Coccidioides arthroconidia showed a reduction in the fungal load when Ag2 derived from either E. coli or maize was loaded into glucan chitin particles. A fusion of Ag2 to dendritic cell carrier peptide (DCpep) induced a T-helper type 17 response in the spleen when orally delivered, indicative of a protective immune response. The maize production platform and the glucan chitin particle adjuvant system show promise for development of a Coccidioides vaccine, but further testing is needed to fully assess the optimal method of administration.

Designs of Antigen Structure and Composition for Improved Protein-Based Vaccine Efficacy

Today, vaccinologists have come to understand that the hallmark of any protective immune response is the antigen. However, it is not the whole antigen that dictates the immune response, but rather the various parts comprising the whole that are capable of influencing immunogenicity. Protein-based antigens hold particular importance within this structural approach to understanding immunity because, though different molecules can serve as antigens, only proteins are capable of inducing both cellular and humoral immunity. This fact, coupled with the versatility and customizability of proteins when considering vaccine design applications, makes protein-based vaccines (PBVs) one of today's most promising technologies for artificially inducing immunity. In this review, we follow the development of PBV technologies through time and discuss the antigen-specific receptors that are most critical to any immune response: pattern recognition receptors, B cell receptors, and T cell receptors. Knowledge of these receptors and their ligands has become exceptionally valuable in the field of vaccinology, where today it is possible to make drastic modifications to PBV structure, from primary to quaternary, in order to promote recognition of target epitopes, potentiate vaccine immunogenicity, and prevent antigen-associated complications. Additionally, these modifications have made it possible to control immune responses by modulating stability and targeting PBV to key immune cells. Consequently, careful consideration should be given to protein structure when designing PBVs in the future in order to potentiate PBV efficacy.

Co-Administration of Injected and Oral Vaccine Candidates Elicits Improved Immune Responses over Either Route Alone

Infectious diseases continue to be a significant cause of morbidity and mortality, and although efficacious vaccines are available for many diseases, some parenteral vaccines elicit little or no mucosal antibodies which can be a significant problem since mucosal tissue is the point of entry for 90% of pathogens. In order to provide protection for both serum and mucosal areas, we have tested a combinatorial approach of both parenteral and oral administration of antigens for diseases caused by a viral pathogen, Hepatitis B, and a fungal pathogen, Coccidioides. We demonstrate that co-administration by the parenteral and oral routes is a useful tool to increase the overall immune response. This can include achieving an immune response in tissues that are not elicited when using only one route of administration, providing a higher level of response that can lead to fewer required doses or possibly providing a better response for individuals that are considered poor or non-responders.

A novel vaccine platform using glucan particles for induction of protective responses against Francisella tularensis and other pathogens

Vaccines are considered the bedrock of preventive medicine. However, for many pathogens, it has been challenging to develop vaccines that stimulate protective, long-lasting immunity. We have developed a novel approach using β-1,3-D-glucans (BGs), natural polysaccharides abundantly present in fungal cell walls, as a biomaterial platform for vaccine delivery. BGs simultaneously provide for receptor-targeted antigen delivery to specialized antigen-presenting cells together with adjuvant properties to stimulate antigen-specific and trained non-specific immune responses. This review focuses on various approaches of using BG particles (GPs) to develop bacterial and fungal vaccine candidates. A special case history for the development of an effective GP tularaemia vaccine candidate is highlighted.

The Rise of Coccidioides: Forces Against the Dust Devil Unleashed

Coccidioidomycosis (Valley fever) is a fungal disease caused by the inhalation of Coccidioides posadasii or C. immitis. This neglected disease occurs in the desert areas of the western United States, most notably in California and Arizona, where infections continue to rise. Clinically, coccidioidomycosis ranges from asymptomatic to severe pulmonary disease and can disseminate to the brain, skin, bones, and elsewhere. New estimates suggest as many as 350,000 new cases of coccidioidomycosis occur in the United States each year. Thus, there is an urgent need for the development of a vaccine and new therapeutic drugs against Coccidioides infection. In this review, we discuss the battle against Coccidioides including the development of potential vaccines, the quest for new therapeutic drugs, and our current understanding of the protective host immune response to Coccidioides infection.

A review of innate and adaptive immunity to coccidioidomycosis

Coccidioidomycosis is a human fungal disease cause by inhalation of aerosol spores produced by Coccidioides posadasii or Coccidioides immitis. This disease is a common cause of community-acquired pneumonia in the endemic areas of the Southwestern United States. It also can present as a life-threatening disease as the fungal cells disseminate to skin, bone, and central nervous system. The outcome of coccidioidomycosis is largely determined by the nature of host immune response to the infection. Escalation of symptomatic infections and increased cost of long-term antifungal treatment warrant a concerted effort to better understand the innate and adaptive immune responses and the genetics associated with coccidioidomycosis susceptibility. This knowledge can be harnessed for development of a human vaccine against Coccidioides and advance clinic management of this disease. This review discusses recently reported studies on innate and adaptive immunity to Coccidioides infection, Mendelian susceptibility to disseminated disease and progress toward a human vaccine against this formidable disease.

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.

Glucan-Chitin Particles Enhance Th17 Response and Improve Protective Efficacy of a Multivalent Antigen (rCpa1) against Pulmonary Coccidioides posadasii Infection

Developing an effective and safe recombinant vaccine requires microbe-specific antigens combined with an adjuvant/delivery system to strengthen protective immunity. In this study, we designed and expressed a multivalent recombinant Coccidioides polypeptide antigen (rCpa1) that consists of three previously identified antigens (i.e., Ag2/Pra, Cs-Ag, and Pmp1) and five pathogen-derived peptides with high affinity for human major histocompatibility complex class II (MHC-II) molecules. The purified rCpa1 was encapsulated into four types of yeast cell wall particles containing β-glucan, mannan, and chitin in various proportions or was mixed with an oligonucleotide (ODN) containing two methylated dinucleotide CpG motifs. This multivalent antigen encapsulated into glucan-chitin particles (GCP-rCpa1) showed significantly greater reduction of fungal burden for human HLA-DR4 transgenic mice than the other adjuvant-rCpa1 formulations tested. Among the adjuvants tested, both GCPs and β-glucan particles (GPs) were capable of stimulating a mixed Th1 and Th17 response. Mice vaccinated with GCP-rCpa1 showed higher levels of interleukin 17 (IL-17) production in T-cell recall assays and earlier lung infiltration by activated Th1 and Th17 cells than GP-rCpa1-vaccinated mice. Both C57BL/6 and HLA-DR4 transgenic mice that were vaccinated with the GCP-rCpa1 vaccine showed higher survival rates than mice that received GCPs alone. Concurrently, the GCP-rCpa1 vaccine stimulated greater infiltration of the injection sites by macrophages, which engulf and process the vaccine for antigen presentation, than the GP-rCpa1 vaccine. This is the first attempt to systematically characterize the presentation of a multivalent coccidioidomycosis vaccine encapsulated with selected adjuvants that enhance the protective cellular immune response to infection.

Combined Active Humoral and Cellular Immunization Approaches for the Treatment of Synucleinopathies

Dementia with Lewy bodies, Parkinson's disease, and Multiple System Atrophy are age-related neurodegenerative disorders characterized by progressive accumulation of α-synuclein (α-syn) and jointly termed synucleinopathies. Currently, no disease-modifying treatments are available for these disorders. Previous preclinical studies demonstrate that active and passive immunizations targeting α-syn partially ameliorate behavioral deficits and α-syn accumulation; however, it is unknown whether combining humoral and cellular immunization might act synergistically to reduce inflammation and improve microglial-mediated α-syn clearance. Since combined delivery of antigen plus rapamycin (RAP) in nanoparticles is known to induce antigen-specific regulatory T cells (Tregs), we adapted this approach to α-syn using the antigen-presenting cell-targeting glucan microparticle (GP) vaccine delivery system. PDGF-α-syn transgenic (tg) male and female mice were immunized with GP-alone, GP-α-syn (active humoral immunization), GP+RAP, or GP+RAP/α-syn (combined active humoral and Treg) and analyzed using neuropathological and biochemical markers. Active immunization resulted in higher serological total IgG, IgG1, and IgG2a anti-α-syn levels. Compared with mice immunized with GP-alone or GP-α-syn, mice vaccinated with GP+RAP or GP+RAP/α-syn displayed increased numbers of CD25-, FoxP3-, and CD4-positive cells in the CNS. GP-α-syn or GP+RAP/α-syn immunizations resulted in a 30-45% reduction in α-syn accumulation, neuroinflammation, and neurodegeneration. Mice immunized with GP+RAP/α-syn further rescued neurons and reduced neuroinflammation. Levels of TGF-β1 were increased with GP+RAP/α-syn immunization, while levels of TNF-α and IL-6 were reduced. We conclude that the observed effects of GP+RAP/α-syn immunization support the hypothesis that cellular immunization may enhance the effects of active immunotherapy for the treatment of synucleinopathies.SIGNIFICANCE STATEMENT We show that a novel vaccination modality combining an antigen-presenting cell-targeting glucan particle (GP) vaccine delivery system with encapsulated antigen (α-synuclein) + rapamycin (RAP) induced both strong anti-α-synuclein antibody titers and regulatory T cells (Tregs). This vaccine, collectively termed GP+RAP/α-syn, is capable of triggering neuroprotective Treg responses in synucleinopathy models, and the combined vaccine is more effective than the humoral or cellular immunization alone. Together, these results support the further development of this multifunctional vaccine approach for the treatment of synucleinopathies, such as Parkinson's disease, dementia with Lewy bodies, and multiple systems atrophy.

Coccidioides immitis and posadasii; A review of their biology, genomics, pathogenesis, and host immunity

Coccidioides immitis and C. posadasii are two highly pathogenic dimorphic fungal species that are endemic in the arid areas of the new world, including the region from west Texas to southern and central California in the USA that cause coccidioidomycosis (also known as Valley Fever). In highly endemic regions such as southern Arizona, up to 50% of long term residents have been infected. New information about fungal population genetics, ecology, epidemiology, and host-pathogen interactions is becoming available. However, our understanding of some aspects of coccidioidomycosis is still incomplete, including the extent of genetic variability of the fungus, the genes involved in virulence, and how the changes in gene expression during the organism's dimorphic life cycle are related to the transformation from a free-living mold to a parasitic spherule. Unfortunately, efforts to develop an effective subunit vaccine have not yet been productive, although two potential live fungus vaccines have been developed.

Rational selection of immunodominant and preserved epitope Sm043300e from Schistosoma mansoni and design of a chimeric molecule for biotechnological purposes

Human schistosomiasis is a neglected tropical disease of great importance in public health. A large number of people are infected with schistosomiasis, making vaccine development and effective diagnosis important control strategies. A rational epitope prediction workflow using Schistosoma mansoni hypothetical proteins was previously presented by our group, and an improvement to that approach is presented here. Briefly, immunodominant epitopes from parasite membrane proteins were predicted by reverse vaccinology strategy with additional in silico analysis. Furthermore, epitope recognition was evaluated using sera of individuals infected with S. mansoni. The epitope that stood out in both in silico and in vitro assays was used to compose a rational chimeric molecule to improve immune response activation. Out of 2185 transmembrane proteins, four epitopes with high binding affinities for human and mouse MHCII molecules were selected through computational screening. These epitopes were synthesized to evaluate their ability to induce TCD4+ lymphocyte proliferation in mice. Sm204830e and Sm043300e induced significant TCD4+ proliferation. Both epitopes were submitted to enzyme-linked immunosorbent assay to evaluate their recognition by IgG antibodies from the sera of infected individuals, and epitope Sm043300 was significantly recognized in most sera samples. Epitope Sm043300 also showed good affinity for human MHCII molecules in molecular docking, and its sequence is curiously highly conserved in four S. mansoni proteins, all of which are described as G-protein-coupled receptors. In addition, we have demonstrated the feasibility of incorporating this epitope, which showed low similarity to human sequences, into a chimeric molecule. The stability of the molecule was evaluated by molecular modeling aimed at future molecule production for use in diagnosis and vaccination trials.

Antifungal Resistance, Metabolic Routes as Drug Targets, and New Antifungal Agents: An Overview about Endemic Dimorphic Fungi

Diseases caused by fungi can occur in healthy people, but immunocompromised patients are the major risk group for invasive fungal infections. Cases of fungal resistance and the difficulty of treatment make fungal infections a public health problem. This review explores mechanisms used by fungi to promote fungal resistance, such as the mutation or overexpression of drug targets, efflux and degradation systems, and pleiotropic drug responses. Alternative novel drug targets have been investigated; these include metabolic routes used by fungi during infection, such as trehalose and amino acid metabolism and mitochondrial proteins. An overview of new antifungal agents, including nanostructured antifungals, as well as of repositioning approaches is discussed. Studies focusing on the development of vaccines against antifungal diseases have increased in recent years, as these strategies can be applied in combination with antifungal therapy to prevent posttreatment sequelae. Studies focused on the development of a pan-fungal vaccine and antifungal drugs can improve the treatment of immunocompromised patients and reduce treatment costs.

Immune Response to Coccidioidomycosis and the Development of a Vaccine

Coccidioidomycosis is a fungal infection caused by Coccidioides posadasii and Coccidioides immitis. It is estimated that 150,000 new infections occur in the United States each year. The incidence of this infection continues to rise in endemic regions. There is an urgent need for the development of better therapeutic drugs and a vaccine against coccidioidomycosis. This review discusses the features of host innate and adaptive immune responses to Coccidioides infection. The focus is on the recent advances in the immune response and host-pathogen interactions, including the recognition of spherules by the host and defining the signal pathways that guide the development of the adaptive T-cell response to Coccidioides infection. Also discussed is an update on progress in developing a vaccine against these fungal pathogens.

Linear Epitopes of Paracoccidioides brasiliensis and Other Fungal Agents of Human Systemic Mycoses As Vaccine Candidates

Dimorphic fungi are agents of systemic mycoses associated with significant morbidity and frequent lethality in the Americas. Among the pathogenic species are Paracoccidioides brasiliensis and Paracoccidioides lutzii, which predominate in South America; Histoplasma capsulatum, Coccidioides posadasii, and Coccidioides immitis, and the Sporothrix spp. complex are other important pathogens. Associated with dimorphic fungi other important infections are caused by yeast such as Candida spp. and Cryptococcus spp. or mold such as Aspergillus spp., which are also fungal agents of deadly infections. Nowadays, the actual tendency of therapy is the development of a pan-fungal vaccine. This is, however, not easy because of the complexity of eukaryotic cells and the particularities of different species and isolates. Albeit there are several experimental vaccines being studied, we will focus mainly on peptide vaccines or epitopes of T-cell receptors inducing protective fungal responses. These peptides can be carried by antibody inducing β-(1,3)-glucan oligo or polysaccharides, or be mixed with them for administration. The present review discusses the efficacy of linear peptide epitopes in the context of antifungal immunization and vaccine proposition.

Rational Design of T Lymphocyte Epitope-Based Vaccines Against Coccidioides Infection

Coccidioidomycosis is a potentially life-threatening mycosis endemic to the Southwestern USA and some arid regions of Central and South America. A vaccine against Coccidioides infection would benefit over 30-million people who reside in or visit the endemic regions. Vaccine candidates against systemic fungal infections come in many forms. Live attenuated vaccines are derived from disease-causing pathogens and generally stimulate excellent protective immunity. Since attenuated vaccines contain living microbes, there is a degree of unpredictability raising concerns regarding safety and stability. Generation of a subunit vaccine has initiated efforts to design a safe reagent suitable for administration to humans at risk of coccidioidomycosis. Epitope-based vaccines allow for eliciting specific protective immune responses and removal of potentially detrimental sequences to improve safety. This chapter describes methods for the identification of T cell epitopes derived from Coccidioides antigens, design, and production of a recombinant vaccine containing multiple T cell epitopes, and evaluation of its protective efficacy and vaccine immunity against pulmonary Coccidioides infection using a strain of transgenic mice that express a human MHC II molecule.

The Quest for a Vaccine Against Coccidioidomycosis: A Neglected Disease of the Americas

Coccidioidomycosis (Valley Fever) is a disease caused by inhalation of Coccidioides spp. This neglected disease has substantial public health impact despite its geographic restriction to desert areas of the southwestern U.S., Mexico, Central and South America. The incidence of this infection in California and Arizona has been increasing over the past fifteen years. Several large cities are within the endemic region in the U.S. Coccidioidomycosis accounts for 25,000 hospital admissions per year in California. While most cases of coccidioidomycosis resolve spontaneously, up to 40% are severe enough to require anti-fungal treatment, and a significant number disseminate beyond the lungs. Disseminated infection involving the meninges is fatal without appropriate treatment. Infection with Coccidioides spp. is protective against a second infection, so vaccination seems biologically plausible. This review of efforts to develop a vaccine against coccidioidomycosis focuses on vaccine approaches and the difficulties in identifying protein antigen/adjuvant combinations that protect in experimental mouse models. Although the quest for a vaccine is still in the early stage, scientific efforts for vaccine development may pave the way for future success.

Immune response characterization and vaccine potential of a recombinant chimera comprising B-cell epitope of Aeromonas hydrophila outer membrane protein C and LTB

Aeromonas hydrophila is one of the most virulent fish pathogens, causing colossal economic losses to the aquaculture industry annually. The absence of a safe and effective vaccine makes it very difficult to control this infection. Outer membrane proteins have been widely illustrated to confer protective immunity against a broad spectrum of gram negative bacteria. In the current study, we have analyzed the ability of B-cell epitopes of A. hydrophila's outer membrane protein C (OmpC) to confer protection against bacterial virulence. Bioinformatic algorithms were used to predict linear B-cell epitopes of OmpC and the corresponding nucleotide sequences were cloned in translational fusion with heat labile enterotoxin B subunit (LTB) of E. coli. Of the three recombinant LTB.epitope fusion proteins evaluated, antisera against the fusion protein comprising the epitope stretch of 143-175 amino acids gave maximum cross reactivity with the parent protein OmpC. The anti-fusion protein antisera contained both OmpC- and LTB-specific antibodies. The fusion proteins' LTB moiety retained its ability to bind to the GM₁ ganglioside receptor, an essential requirement for its adjuvanicity. Antibody isotyping, cytokine ELISA, and cytokine array analysis revealed a Th2 skewed type immune response along with the presence of some relevant Th17 and Th1 cytokines involved in conferring protective immunity. Surface exposure of the epitope_143-175 on live A. hydrophila membrane was investigated and validated using bacterial agglutination and flow cytometry analysis using anti-fusion protein antisera. Our results strongly support the potential of B-cell epitope_143-175 of OmpC of A. hydrophila, in fusion with the LTB, as an effective and promising vaccine candidate against this bacterium.

Preclinical identification of vaccine induced protective correlates in human leukocyte antigen expressing transgenic mice infected with Coccidioides posadasii

There is an emerging interest to develop human vaccines against medically-important fungal pathogens and a need for a preclinical animal model to assess vaccine efficacies and protective correlates. HLA-DR4 (DRB1∗0401 allele) transgenic mice express a human major histocompatibility complex class II (MHC II) receptor in such a way that CD4⁺ T-cell response is solely restricted by this human molecule. In this study HLA-DR4 transgenic mice were immunized with a live-attenuated vaccine (ΔT) and challenged by the intranasal route with 50-70 Coccidioides posadasii spores, a potentially lethal dose. The same vaccination regimen offers 100% survival for C57BL/6 mice. Conversely, ΔT-vaccinated HLA-DR4 mice displayed 3 distinct manifestations of Coccidioides infection including 40% fatal acute (FAD), 30% disseminated (DD) and 30% pulmonary disease (PD). The latter 2 groups of mice had reduced loss of body weight and survived to at least 50days postchallenge (dpc). These results suggest that ΔT vaccinated HLA-DR4 mice activated heterogeneous immunity against pulmonary Coccidioides infection. Vaccinated HLA-DR4 mice displayed early expansion of Th1 and Th17 cells and recruitment of inflammatory innate cells into Coccidioides-infected lungs during the first 9dpc. While contraction rates of Th cells and the inflammatory response during 14-35dpc significantly differed among the 3 groups of vaccinated HLA-DR4 mice. The FAD group displayed a sharply reduced Th1 and Th17 response, while overwhelmingly recruiting neutrophils into lungs during 9-14days. The FAD group approached moribund by 14dpc. In contrast, vaccinated HLA-DR4 survivors gradually contracted Th cells and inflammatory response with the greatest rate in the PD group. While vaccinated HLA-DR4 mice are susceptible to Coccidioides infection, they are useful for evaluation of vaccine efficacy and identification of immunological correlates against this mycosis.

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.

Duality of β-glucan microparticles: antigen carrier and immunostimulants

Designing efficient recombinant mucosal vaccines against enteric diseases is still a major challenge. Mucosal delivery of recombinant vaccines requires encapsulation in potent immunostimulatory particles to induce an efficient immune response. This paper evaluates the capacity of β-glucan microparticles (GPs) as antigen vehicles and characterizes their immune-stimulatory effects. The relevant infectious antigen FedF was chosen to be loaded inside the microparticles. The incorporation of FedF inside the particles was highly efficient (roughly 85%) and occurred without antigen degradation. In addition, these GPs have immunostimulatory effects as well, demonstrated by the strong reactive oxygen species (ROS) production by porcine neutrophils upon their recognition. Although antigen-loaded GPs still induce ROS production, antigen loading decreases this production by neutrophils for reasons yet unknown. However, these antigen-loaded GPs are still able to bind their specific β-glucan receptor, demonstrated by blocking complement receptor 3, which is the major β-glucan receptor on porcine neutrophils. The dual character of these particles is confirmed by a T-cell proliferation assay. FedF-loaded particles induce a significantly higher FedF-specific T-cell proliferation than soluble FedF. Taken together, these results show that GPs are efficient antigen carriers with immune-stimulatory properties.

Cryptococcus and Phagocytes: Complex Interactions that Influence Disease Outcome

Cryptococcus neoformans and C. gattii are fungal pathogens that cause life-threatening disease. These fungi commonly enter their host via inhalation into the lungs where they encounter resident phagocytes, including macrophages and dendritic cells, whose response has a pronounced impact on the outcome of disease. Cryptococcus has complex interactions with the resident and infiltrating innate immune cells that, ideally, result in destruction of the yeast. These phagocytic cells have pattern recognition receptors that allow recognition of specific cryptococcal cell wall and capsule components. However, Cryptococcus possesses several virulence factors including a polysaccharide capsule, melanin production and secretion of various enzymes that aid in evasion of the immune system or enhance its ability to thrive within the phagocyte. This review focuses on the intricate interactions between the cryptococci and innate phagocytic cells including discussion of manipulation and evasion strategies used by Cryptococcus, anti-cryptococcal responses by the phagocytes and approaches for targeting phagocytes for the development of novel immunotherapeutics.

Protection against Experimental Cryptococcosis following Vaccination with Glucan Particles Containing Cryptococcus Alkaline Extracts

A vaccine capable of protecting at-risk persons against infections due to Cryptococcus neoformans and Cryptococcus gattii could reduce the substantial global burden of human cryptococcosis. Vaccine development has been hampered though, by lack of knowledge as to which antigens are immunoprotective and the need for an effective vaccine delivery system. We made alkaline extracts from mutant cryptococcal strains that lacked capsule or chitosan. The extracts were then packaged into glucan particles (GPs), which are purified Saccharomyces cerevisiae cell walls composed primarily of β-1,3-glucans. Subcutaneous vaccination with the GP-based vaccines provided significant protection against subsequent pulmonary infection with highly virulent strains of C. neoformans and C. gattii. The alkaline extract derived from the acapsular strain was analyzed by liquid chromatography tandem mass spectrometry (LC-MS/MS), and the most abundant proteins were identified. Separation of the alkaline extract by size exclusion chromatography revealed fractions that conferred protection when loaded in GP-based vaccines. Robust Th1- and Th17-biased CD4⁺ T cell recall responses were observed in the lungs of vaccinated and infected mice. Thus, our preclinical studies have indicated promising cryptococcal vaccine candidates in alkaline extracts delivered in GPs. Ongoing studies are directed at identifying the individual components of the extracts that confer protection and thus would be promising candidates for a human vaccine.

The encapsulated yeast Cryptococcus neoformans and its closely related sister species, Cryptococcus gattii, are major causes of morbidity and mortality, particularly in immunocompromised persons. This study reports on the preclinical development of vaccines to protect at-risk populations from cryptococcosis. Antigens were extracted from Cryptococcus by treatment with an alkaline solution. The extracted antigens were then packaged into glucan particles, which are hollow yeast cell walls composed mainly of β-glucans. The glucan particle-based vaccines elicited robust T cell immune responses and protected mice from otherwise-lethal challenge with virulent strains of C. neoformans and C. gattii. The technology used for antigen extraction and subsequent loading into the glucan particle delivery system is relatively simple and can be applied to vaccine development against other pathogens.

Proteomic contributions to our understanding of vaccine and immune responses

Vaccines are one of the greatest public health successes; yet, due to the empirical nature of vaccine design, we have an incomplete understanding of how the genes and proteins induced by vaccines contribute to the development of both protective innate and adaptive immune responses. While the advent of genomics has enabled new vaccine development and facilitated understanding of the immune response, proteomics identifies potentially new vaccine antigens with increasing speed and sensitivity. In addition, as proteomics is complementary to transcriptomic approaches, a combination of both approaches provides a more comprehensive view of the immune response after vaccination via systems vaccinology. This review details the advances that proteomic strategies have made in vaccine development and reviews how proteomics contributes to the development of a more complete understanding of human vaccines and immune responses.

Evaluating Common Humoral Responses against Fungal Infections with Yeast Protein Microarrays

We profiled the global immunoglobulin response against fungal infection by using yeast protein microarrays. Groups of CD-1 mice were infected systemically with human fungal pathogens (Coccidioides posadasii, Candida albicans, or Paracoccidioides brasiliensis) or inoculated with PBS as a control. Another group was inoculated with heat-killed yeast (HKY) of Saccharomyces cerevisiae. After 30 days, serum from mice in the groups were collected and used to probe S. cerevisiae protein microarrays containing 4800 full-length glutathione S-transferase (GST)-fusion proteins. Antimouse IgG conjugated with Alexafluor 555 and anti-GST antibody conjugated with Alexafluor 647 were used to detect antibody-antigen interactions and the presence of GST-fusion proteins, respectively. Serum after infection with C. albicans reacted with 121 proteins: C. posadasii, 81; P. brasiliensis, 67; and after HKY, 63 proteins on the yeast protein microarray, respectively. We identified a set of 16 antigenic proteins that were shared across the three fungal pathogens. These include retrotransposon capsid proteins, heat shock proteins, and mitochondrial proteins. Five of these proteins were identified in our previous study of fungal cell wall by mass spectrometry (Ann. N. Y. Acad. Sci. 2012, 1273, 44-51). The results obtained give a comprehensive view of the immunological responses to fungal infections at the proteomic level. They also offer insight into immunoreactive protein commonality among several fungal pathogens and provide a basis for a panfungal vaccine.

Whole glucan particles as a vaccine against systemic coccidioidomycosis

We reported previously that yeast-derived whole glucan particles (WGPs), with or without conjugation to BSA, used as a vaccine protected against systemic aspergillosis in mice. Here, we examined their utility as a potential vaccine against coccidioidomycosis. WGPs were prepared from Saccharomyces cerevisiae; conjugation with BSA (WGP-BSA) was done using 1-cyano-4-dimethylaminopyridinium tetrafluoroborate-mediated conjugation. Heat-killed S. cerevisiae (HKY) was used as a positive-control vaccine. CD-1 mice were vaccinated with WGPs or WGP-BSA, HKY or PBS once weekly, beginning 21 days prior to infection. Mice were infected intravenously with arthroconidia of Coccidioides posadasii. In the low-mortality study, 50 % of PBS-treated controls died. Only WGP-BSA at 0.6 mg per dose induced significant protection compared with PBS treatment. All surviving mice were infected in all three organs examined. Those given WGP-BSA at 0.6 mg per dose had fewer c.f.u. in liver and lungs (P = 0.04), and those given WGPs at 6 mg per dose had fewer in lungs (P < 0.02), compared with PBS. In the high-mortality study, 90 % of PBS mice died. Vaccination with HKY, and WGPs or WGP-BSA at 6 or 12 mg per dose significantly prolonged survival (P ≤ 0.05). No surviving mice were free of infection. HKY and WGP-BSA at 12 mg per dose reduced c.f.u. in the liver and lungs (P < 0.05) and WGP-BSA at 6 mg per dose reduced c.f.u. in the lungs (P < 0.05); unconjugated WGPs did not reduce infection. WGPs or WGP-BSA acted as a vaccine that protected against mortality caused by coccidioidomycosis. Thus, WGP protection against coccidioidomycosis and aspergillosis provides the basis for development of a pan-fungal vaccine.

Exploiting fungal cell wall components in vaccines

Innate recognition of fungi leads to strong adaptive immunity. Investigators are trying to exploit this observation in vaccine development by combining antigens with evolutionarily conserved fungal cell wall carbohydrates to induce protective responses. Best studied is β-1,3-glucan, a glycan that activates complement and is recognized by dectin-1. Administration of antigens in association with β-1,3-glucan, either by direct conjugation or complexed in glucan particles, results in robust humoral and cellular immune responses. While the host has a host of mannose receptors, responses to fungal mannoproteins generally are amplified if cells are cooperatively stimulated with an additional danger signal such as a toll-like receptor agonist. Chitosan, a polycationic homopolymer of glucosamine manufactured by the deacetylation of chitin, is being studied as an adjuvant in DNA and protein-based vaccines. It appears particularly promising in mucosal vaccines. Finally, universal and organism-specific fungal vaccines have been formulated by conjugating fungal cell wall glycans to carrier proteins. A major challenge will be to advance these experimental findings so that at risk patients can be protected.

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.

Cryptococcus antigens and immune responses: implications for a vaccine

Cryptococcosis is a fungal disease primarily occurring in immunocompromised individuals, such as AIDS patients, and is associated with high morbidity and mortality. However, cryptococcosis can occur within immunocompetent populations as observed during an outbreak in Vancouver Island, British Columbia, Canada, the Pacific Northwest and other regions of the USA and in Mediterranean Europe. Mortality rates due to cryptococcosis have significantly declined in economically developed countries since the widespread implementation of highly active antiretroviral therapy. However, the incidence and mortality of this disease remains high in economically undeveloped areas in Africa and Asia where HIV infections are high and availability of HAART is limited. The continuing AIDS epidemic coupled with the increased usage of immunosuppressive drugs to prevent organ transplant rejection or to treat autoimmune diseases has resulted in an increase in individuals at risk for developing cryptococcosis. The purpose of this review is to discuss the need, challenges and potential for developing vaccines against cryptococcosis.