Vaccine immunity to coccidioidomycosis occurs by early activation of three signal pathways of T helper cell response (Th1, Th2, and Th17)

A cell wall protein-based vaccine candidate induce protective immune response against Sporothrix schenckii infection

Sporotrichosis is a subcutaneous mycosis caused by several closely related thermo-dimorphic fungi of the Sporothrix schenckii species complex, affecting humans and other mammals. In the last few years, new strategies have been proposed for controlling sporotrichosis owning to concerns about its growing incidence in humans, cats, and dogs in Brazil, as well as the toxicity and limited efficacy of conventional antifungal drugs. In this study, we assessed the immunogenicity and protective properties of two aluminum hydroxide (AH)-adsorbed S. schenckii cell wall protein (ssCWP)-based vaccine formulations in a mouse model of systemic S. schenckii infection. Fractioning by SDS-PAGE revealed nine protein bands, two of which were functionally characterized: a 44kDa peptide hydrolase and a 47kDa enolase, which was predicted to be an adhesin. Sera from immunized mice recognized the 47kDa enolase and another unidentified 71kDa protein, whereas serum from S. schenckii-infected mice recognized both these proteins plus another unidentified 9.4kDa protein. Furthermore, opsonization with the anti-ssCWP sera led to markedly increased phagocytosis and was able to strongly inhibit the fungus' adhesion to fibroblasts. Immunization with the higher-dose AH-adjuvanted formulation led to increased ex vivo release of IL-12, IFN-γ, IL-4, and IL-17, whereas only IL-12 and IFN-γ were induced by the higher-dose non-adjuvanted formulation. Lastly, passive transference of the higher-dose AH-adjuvanted formulation's anti-ssCWP serum was able to afford in vivo protection in a subsequent challenge with S. schenckii, becoming a viable vaccine candidate for further testing.

Telocinobufagin enhances the Th1 immune response and protects against Salmonella typhimurium infection

Ideal potential vaccine adjuvants to stimulate a Th1 immune response are urgently needed to control intracellular infections in clinical applications. Telocinobufagin (TBG), an active component of Venenum bufonis, exhibits immunomodulatory activity. Therefore, we investigated whether TBG enhances the Th1 immune response to ovalbumin (OVA) and formalin-inactivated Salmonella typhimurium (FIST) in mice. TBG augmented serum OVA- and FIST-specific IgG and IgG2a and the production of IFNγ by antigen-restimulated splenocytes. TBG also dramatically enhanced splenocyte proliferative responses to concanavalin A, lipopolysaccharide, and OVA and substantially increased T-bet mRNA levels and the CD3(+)/CD3(+)CD4(+)/CD3(+)CD8(+) phenotype in splenocytes from OVA-immunized mice. In in vivo protection studies, TBG significantly decreased the bacterial burdens in the spleen and prolonged the survival time of FIST-immunized mice challenged with live S. typhimurium. In vivo neutralization of IFNγ with anti-IFNγ mAbs led to a significant reduction in FIST-specific IgG2a and IFNγ levels and in anti-Salmonella effect in TBG/FIST-immunized mice. In conclusion, these results suggest that TBG enhances a Th1 immune response to control intracellular infections.

Valley fever: danger lurking in a dust cloud

Coccidioides immitis and Coccidioides posadasii contribute to the development of Valley Fever. The ability of these fungal pathogens to evade the host immune system creates difficulty in recognition and treatment of this debilitating infection. In this review, we describe the current knowledge of Valley Fever and approaches to improve prevention, detection, and treatment.

Directing traffic: IL-17 and IL-22 coordinate pulmonary immune defense

Respiratory infections and diseases are among the leading causes of death worldwide, and effective treatments probably require manipulating the inflammatory response to pathogenic microbes or allergens. Here, we review mechanisms controlling the production and functions of interleukin-17 (IL-17) and IL-22, cytokines that direct several aspects of lung immunity. Innate lymphocytes (γδ T cells, natural killer cells, innate lymphoid cells) are the major source of IL-17 and IL-22 during acute infections, while CD4(+) T-helper 17 (Th17) cells contribute to vaccine-induced immunity. The characterization of dendritic cell (DC) subsets has revealed their central roles in T-cell activation. CD11b(+) DCs stimulated with bacteria or fungi secrete IL-1β and IL-23, potent inducers of IL-17 and IL-22. On the other hand, recognition of viruses by plasmacytoid DCs inhibits IL-1β and IL-23 release, increasing susceptibility to bacterial superinfections. IL-17 and IL-22 primarily act on the lung epithelium, inducing antimicrobial proteins and neutrophil chemoattractants. Recent studies found that stimulation of macrophages and DCs with IL-17 also contributes to antibacterial immunity, while IL-22 promotes epithelial proliferation and repair following injury. Chronic diseases such as asthma and chronic obstructive pulmonary disease have been associated with IL-17 and IL-22 responses directed against innocuous antigens. Future studies will evaluate the therapeutic efficacy of targeting the IL-17/IL-22 pathway in pulmonary inflammation.

Interleukin-1 receptor but not Toll-like receptor 2 is essential for MyD88-dependent Th17 immunity to Coccidioides infection

Interleukin-17A (IL-17A)-producing CD4(+) T helper (Th17) cells have been shown to be essential for defense against pulmonary infection with Coccidioides species. However, we have just begun to identify the required pattern recognition receptors and understand the signal pathways that lead to Th17 cell activation after fungal infection. We previously reported that Card9(-/-) mice vaccinated with formalin-killed spherules failed to acquire resistance to Coccidioides infection. Here, we report that both MyD88(-/-) and Card9(-/-) mice immunized with a live, attenuated vaccine also fail to acquire protective immunity to this respiratory disease. Like Card9(-/-) mice, vaccinated MyD88(-/-) mice revealed a significant reduction in numbers of both Th17 and Th1 cells in their lungs after Coccidioides infection. Both Toll-like receptor 2 (TLR2) and IL-1 receptor type 1 (IL-1r1) upstream of MyD88 have been implicated in Th17 cell differentiation. Surprisingly, vaccinated TLR2(-/-) and wild-type (WT) mice showed similar outcomes after pulmonary infection with Coccidioides, while vaccinated IL-1r1(-/-) mice revealed a significant reduction in the number of Th17 cells in their infected lungs compared to WT mice. Thus, activation of both IL-1r1/MyD88- and Card9-mediated Th17 immunity is essential for protection against Coccidioides infection. Our data also reveal that the numbers of Th17 cells were reduced in IL-1r1(-/-) mice to a lesser extent than in MyD88(-/-) mice, raising the possibility that other TLRs are involved in MyD88-dependent Th17 immunity to coccidioidomycosis. An antimicrobial action of Th17 cells is to promote early recruitment of neutrophils to infection sites. Our data revealed that neutrophils are required for vaccine immunity to this respiratory disease.

Recent advances in our understanding of the environmental, epidemiological, immunological, and clinical dimensions of coccidioidomycosis

Coccidioidomycosis is the endemic mycosis caused by the fungal pathogens Coccidioides immitis and C. posadasii. This review is a summary of the recent advances that have been made in the understanding of this pathogen, including its mycology, genetics, and niche in the environment. Updates on the epidemiology of the organism emphasize that it is a continuing, significant problem in areas of endemicity. For a variety of reasons, the number of reported coccidioidal infections has increased dramatically over the past decade. While continual improvements in the fields of organ transplantation and management of autoimmune disorders and patients with HIV have led to dilemmas with concurrent infection with coccidioidomycosis, they have also led to advances in the understanding of the human immune response to infection. There have been some advances in therapeutics with the increased use of newer azoles. Lastly, there is an overview of the ongoing search for a preventative vaccine.

Vaccinated C57BL/6 mice develop protective and memory T cell responses to Coccidioides posadasii infection in the absence of interleukin-10

High concentrations of lung tissue-associated interleukin-10 (IL-10), an anti-inflammatory and immunosuppressive cytokine, correlate with susceptibility of mice to Coccidioides spp. infection. In this study, we found that macrophages, dendritic cells, neutrophils, and both CD8(+) and CD4(+) T cells recruited to Coccidioides posadasii-infected lungs of nonvaccinated and vaccinated mice contributed to the production of IL-10. The major IL-10-producing leukocytes were CD8(+) T cells, neutrophils, and macrophages in lungs of nonvaccinated mice, while both Foxp3(+) and Foxp3(-) subsets of IL-10(+) CD4(+) T cells were significantly elevated in vaccinated mice. Profiles of the recruited leukocytes in lungs revealed that only CD4(+) T cells were significantly increased in IL-10(-/-) knockout mice compared to their wild-type counterparts. Furthermore, ex vivo recall assays showed that CD4(+) T cells isolated from vaccinated IL-10(-/-) mice compared to vaccinated wild-type mice produced significantly higher amounts of IL-2, gamma interferon (IFN-γ), IL-4, IL-6, and IL-17A in the presence of a coccidioidal antigen, indicating that IL-10 suppresses Th1, Th2, and Th17 immunity to Coccidioides infection. Analysis of absolute numbers of CD44(+) CD62L(-) CD4(+) T effector memory T cells (TEM) and IFN-γ- and IL-17A-producing CD4(+) T cells in the lungs of Coccidioides-infected mice correlated with better fungal clearance in nonvaccinated IL-10(-/-) mice than in nonvaccinated wild-type mice. Our results suggest that IL-10 suppresses CD4(+) T-cell immunity in nonvaccinated mice during Coccidioides infection but does not impede the development of a memory response nor exacerbate immunopathology of vaccinated mice over at least a 4-month period after the last immunization.

The hierarchical process of differentiation of long-lived antibody-secreting cells is dependent on integrated signals derived from antigen and IL-17A

Switched CD19-positive memory B cells purified from mice with chronic immune response against Thalassophrynenattereri venom proteins were cultured with venom or cytokines. Our results confirm the existence of a hierarchic process of differentiation: activated memory B cells progressively acquire increasing levels of CD138 and decreasing levels of CD45R/B220 to finally arrive at ASC with B220^neg phenotype, which are IgG1-secreting cells. Only Bmem from peritoneal cavity or bone marrow of VTn immunized mice presented the capacity to generate ASC functionally active. IL-17A or IL-21/IL-23/IL-33 improves the ability of venom to induce intracellular IgG of peritoneal derived-ASC. Cognate stimulation with venom and IL-17A is sufficient to down-regulate the expression of CD45R/B220. BAFF-R is up-regulated in splenic or medullar derived-ASC stimulated by venom, CpG or cytokines. Only splenic derived-ASC up-regulate Bcl-2 expression after CpG or the combination of IL-21/IL-23/IL-33 stimulation. Finally, the activation of ASC for IgG1 secretion is triggered by venom proteins in peritoneal cavity and by IL-17A in medullar niche. These results show the importance of the integration of signals downstream of BCR and IL17-A receptors in modulating ASC differentiation, focusing in the microenvironment niche of their generation.

Interleukin 1 enhances vaccine-induced antifungal T-helper 17 cells and resistance against Blastomyces dermatitidis infection

Vaccine-induced T-helper 17 (Th17) cells are necessary and sufficient to protect against fungal infection. Although live fungal vaccines are efficient in driving protective Th17 responses and immunity, attenuated fungi may not be safe for human use. Heat-inactivated formulations and subunit vaccines are safer but less potent and require adjuvant to increase their efficacy. Here, we show that interleukin 1 (IL-1) enhances the capacity of weak vaccines to induce protection against lethal Blastomyces dermatitidis infection in mice and is far more effective than lipopolysaccharide. While IL-1 enhanced expansion and differentiation of fungus-specific T cells by direct action on those cells, cooperation with non-T cells expressing IL-1R1 was necessary to maximize protection. Mechanistically, IL-17 receptor signaling was required for the enhanced protection induced by IL-1. Thus, IL-1 enhances the efficacy of safe but inefficient vaccines against systemic fungal infection in part by increasing the expansion of CD4(+) T cells, allowing their entry into the lungs, and inducing their differentiation to protective Th17 cells.

Extracellular ammonia at sites of pulmonary infection with Coccidioides posadasii contributes to severity of the respiratory disease

Coccidioides is the causative agent of a potentially life-threatening respiratory disease of humans. A feature of this mycosis is that pH measurements of the microenvironment of pulmonary abscesses are consistently alkaline due to ammonia production during the parasitic cycle. We previously showed that enzymatically active urease is partly responsible for elevated concentrations of extracellular ammonia at sites of lung infection and contributes to both localized host tissue damage and exacerbation of the respiratory disease in BALB/c mice. Disruption of the urease gene (URE) of Coccidioides posadasii only partially reduced the amount of ammonia detected during in vitro growth of the parasitic phase, suggesting that other ammonia-producing pathways exist that may also contribute to the virulence of this pathogen. Ureidoglycolate hydrolase (Ugh) expressed by bacteria, fungi and higher plants catalyzes the hydrolysis of ureidoglycolate to yield glyoxylate and the release CO2 and ammonia. This enzymatic pathway is absent in mice and humans. Ureidoglycolate hydrolase gene deletions were conducted in a wild type (WT) isolate of C. posadasii as well as the previously generated Δure knock-out strain. Restorations of UGH in the mutant stains were performed to generate and evaluate the respective revertants. The double mutant revealed a marked decrease in the amount of extracellular ammonia without loss of reproductive competence in vitro compared to both the WT and Δure parental strains. BALB/c mice challenged intranasally with the Δugh/Δure mutant showed 90% survival after 30 days, decreased fungal burden, and well-organized pulmonary granulomas. We conclude that loss of both Ugh and Ure activity significantly reduced the virulence of this fungal pathogen.

Factors regulated by interferon gamma and hypoxia-inducible factor 1A contribute to responses that protect mice from Coccidioides immitis infection

Background

Coccidioidomycosis results from airborne infections caused by either Coccidioides immitis or C. posadasii. Both are pathogenic fungi that live in desert soil in the New World and can infect normal hosts, but most infections are self-limited. Disseminated infections occur in approximately 5% of cases and may prove fatal. Mouse models of the disease have identified strains that are resistant (e.g. DBA/2) or susceptible (e.g. C57BL/6) to these pathogens. However, the genetic and immunological basis for this difference has not been fully characterized.

Results

Microarray technology was used to identify genes that were differentially expressed in lung tissue between resistant DBA/2 and sensitive C57BL/6 mice after infection with C. immitis. Differentially expressed genes were mapped onto biological pathways, gene ontologies, and protein interaction networks, which revealed that innate immune responses mediated by Type II interferon (i.e., IFNG) and the signal transducer and activator of transcription 1 (STAT1) contribute to the resistant phenotype. In addition, upregulation of hypoxia inducible factor 1A (HIF1A), possibly as part of a larger inflammatory response mediated by tumor necrosis factor alpha (TNFA), may also contribute to resistance. Microarray gene expression was confirmed by real-time quantitative PCR for a subset of 12 genes, which revealed that IFNG HIF1A and TNFA, among others, were significantly differentially expressed between the two strains at day 14 post-infection.

Conclusion

These results confirm the finding that DBA/2 mice express more Type II interferon and interferon stimulated genes than genetically susceptible strains and suggest that differential expression of HIF1A may also play a role in protection.

Progress Toward a Human Vaccine Against Coccidioidomycosis

Coccidioidomycosis (San Joaquin Valley fever) is a human respiratory disease caused by a soil-borne mold, and is recognized as an intransigent microbial infection by physicians who treat patients with the potentially life-threatening, disseminated form of this mycosis. Epidemiological studies based on surveys of skin-test reactivity of people who reside in the endemic regions of the Southwestern US have shown that at least 150,000 new infections occur annually. The clinical spectrum of coccidioidomycosis ranges from an asymptomatic insult to a severe pulmonary disease in which the pathogen may spread from the lungs to the skin, bones, brain and other body organs. Escalation of symptomatic infections and increased cost of long-term antifungal treatment warrant a concerted effort to develop a vaccine against coccidioidomycosis. This review examines recently reported strategies used to generate such a vaccine and summarizes current understanding of the nature of protective immunity to this formidable disease.

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

Clinical and animal studies of coccidioidomycosis have demonstrated that activated CD4(+) T lymphocytes are essential for protection against this fungal respiratory disease. We previously reported a vaccine against Coccidioides infection which contained three recombinant CD4(+) T cell-reactive proteins and induced a robust, protective immune response in mice. Due to the anticipated high cost of production and clinical assessment of this multivalent vaccine, we generated a single protein which contained immunodominant T cell epitopes of the three polypeptides. Epitopes were initially identified by computational prediction of their ability to bind promiscuously to human major histocompatibility complex class II (MHC II) molecules. Cellular immunoassays confirmed the immunogenicity of the synthesized epitope peptides, while in vitro binding assays revealed a range of peptide affinity for MHC II. A DNA construct was synthesized for bacterial expression of a recombinant protein vaccine which contained five epitopes with the highest affinity for human MHC II, each fused with leader and spacer peptides proposed to optimize epitope processing and presentation to T cell receptors. Recall assays of immune T lymphocytes obtained from human MHC II-expressing HLA-DR4 transgenic mice confirmed that 4 of the 5 epitope peptides were processed. Mice immunized with the epitope-based vaccine admixed with a synthetic oligodeoxynucleotide adjuvant or loaded into yeast glucan particles and then challenged intranasally with Coccidioides showed early lung infiltration of activated T helper-1 (Th1), Th2, and Th17 cells, elevated gamma interferon (IFN-γ) and interleukin (IL)-17 production, significant reduction of fungal burden, and prolongation of survival compared to nonvaccinated mice. This is the first report of an epitope-based vaccine against coccidioidomycosis.

Immunity to fungi

The global increase in fungal disease burden, the emergence of novel pathogenic fungi, and the lack of fungal vaccines have focused intense interest in elucidating immune defense mechanisms against fungi. Recent studies in animal models and in humans identify an integrated role for C-type lectin and Toll-like receptor signaling in activating innate and adaptive responses that control medically relevant fungi. Beyond the critical role of phagocytes in host defense, the generation and balance of specific T helper subsets contributes to sterilizing immunity. These advances form a basis for the development of fungal vaccines and immune-based therapeutic adjuncts.

An agonist of human complement fragment C5a enhances vaccine immunity against Coccidioides infection

Coccidioides is a fungal pathogen and causative agent of a human respiratory disease against which no clinical vaccine exists. In this study we evaluated a novel vaccine adjuvant referred to as EP67, which is a peptide agonist of the biologically active C-terminal region of human complement component C5a. The EP67 peptide was conjugated to live spores of an attenuated vaccine strain (ΔT) of Coccidioides posadasii. The non-conjugated ΔT vaccine provided partial protection to BALB/c mice against coccidioidomycosis. In this report we compared the protective efficacy of the ΔT-EP67 conjugate to the ΔT vaccine in BALB/c mice. Animals immunized subcutaneously with the ΔT-EP67 vaccine showed significant increase in survival and decrease in fungal burden over 75 days postchallenge. Increased pulmonary infiltration of dendritic cells and macrophages was observed on day 7 postchallenge but marked decrease in neutrophil numbers had occurred by 11 days. The reduced influx of neutrophils may have contributed to the observed reduction of inflammatory pathology. Mice immunized with the ΔT-EP67 vaccine also revealed enhanced expression of MHC II molecules on the surface of antigen presenting cells, and in vitro recall assays of immune splenocytes showed elevated Th1- and Th17-type cytokine production. The latter correlated with a marked increase in lung infiltration of IFN-γ- and IL-17-producing CD4(+) T cells. Elevated expression of T-bet and RORc transcription factors in ΔT-EP67-vaccinated mice indicated the promotion of Th1 and Th17 cell differentiation. Higher titers of Coccidioides antigen-specific IgG1 and IgG2a were detected in mice immunized with the EP67-conjugated versus the non-conjugated vaccine. These combined results suggest that the EP67 adjuvant enhances protective efficacy of the live vaccine by augmentation of T-cell immunity, especially through Th1- and Th17-mediated responses to Coccidioides infection.

Recent progress in vaccines against fungal diseases

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

Fungal cell wall vaccines: an update

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