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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.

Vulvovaginal candidiasis is a common mucosal infection affecting a large proportion of women with some of them affected by recurrent often intractable forms of the disease. Thus, there is an increasing interest in understanding the pathogenesis of this disease. The aim of our work was to characterize, in animal models of vaginal candidiasis, the components of the host-fungus interaction at the mucosal level.The evidence of an immune response in the vaginal compartment was very encouraging to identify the proper targets for new strategies for vaccination or immunotherapy of vaginal candidiasis. Aspartyl-proteinase (Sap2), which is an important immunodominant antigens and virulence factors of C.albicans acting in mucosal infections, was assembled with virosomes and a vaccine PEV7 was obtained. The results obtained in the mouse model and in the clinical trial conducted by Pevion on women have evidenced that the vaccine PEV7, intravaginally administered, has an encouraging therapeutic potential for the treatment of recurrent vulvovaginal candidiasis. This opens the way to a modality for anti-Candida protection at mucosal level.

Mycoses are gaining increasing attention in modern medicine because of the increase in diseases associated with opportunistic fungal infections. Despite the recognized role of the immune system in the control of fungal infections, no antifungal vaccines are currently licensed for use in humans. However, numerous vaccine candidates are being developed in many laboratories, as proof of the renewed interest in integrating or replacing chemotherapy with vaccines to reduce antibiotic use and consequently limit drug resistance and toxicity. In the effort to use safer and simpler fungal antigens for vaccinations, adjuvants have become relevant as immunostimulators to elicit successful protective immune responses. To address the relevant role of adjuvants as determinants in the balance of vaccine efficacy and safety, an updated and critical review of the adjuvants used in preclinical antifungal vaccines is presented, and prospective trends are addressed. Selected recent papers and other historically relevant and innovative strategies using adjuvants in experimental fungal vaccines are highlighted.

Invasive aspergillosis is a major cause of mortality in immunocompromised patients and therapeutic options are often limited, thus a vaccine would be desirable. We presently studied acid-stable cell-wall mannan (α-1, 6-linked backbone highly branched with α-1, 2; α-1, 3; and β-1, 2-linked manno-oligomers) derived from C. albicans, with or without conjugation to bovine serum albumin (BSA), as a vaccine against systemic aspergillosis. Mice were vaccinated subcutaneously with mannan or mannan-BSA conjugate weekly 3 times, ending 2 weeks prior to infection with A. fumigatus conidia. Results showed that the protection induced by mannan is dose-dependent; 12 mg unconjugated mannan alone or0.3 mg mannan-BSA consistently enhanced survival (P0.05). Fungal burdens in brains and kidneys were reduced after0.3 mg of mannan-BSA (all P0.05). Mannan-induced protection was improved about 40-fold by conjugation of BSA to mannan. Mannan-BSA (500 kDa) was more protective than 40 kDa mannan-BSA. Mannan is a candidate for a cross-protective conjugate fungal vaccine.

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

In this study, we analyzed the impact of immunization with the peptidorhamnomannan (PRM) from the cell wall of the fungus Scedosporium (Lomentospora) prolificans in a murine model of invasive scedosporiosis. Immunization with PRM decreased the survival of mice infected with S. prolificans. Immunization of mice with PRM led to decreased secretion of pro-inflammatory cytokines and chemokines but did not affect the secretion of IL-10. Mice immunized with PRM showed an increase in IgG1 secretion, which is an immunoglobulin linked to a nonprotective response. Splenocytes isolated from mice infected with S. prolificans and immunized with PRM showed no differences in the percentages of Th17 cells and no increase in the frequency of the CD4(+)CD62L(Low) T cell population. PRM-immunized mice showed a significant increase in the percentage of Treg cells. In summary, our results indicated that immunization with PRM did not assist or improve the immunological response against S. prolificans infection. PRM exacerbated the infection process by reducing the inflammatory response, thereby facilitating colonization, virulence and dissemination by the fungus.

Although there is considerable experimental data to support the idea, bringing a fungal vaccine to fruition has been elusive. Moreover, vaccinating the immunocompromised, susceptible to an opportunistic disease such as invasive aspergillosis, seems formidable. However, pioneering studies using Aspergillus particulate forms or homogenates, and recently, recombinant proteins, have demonstrated feasibility. Moreover, T cell receptors also recognize glycotopes if presented in the appropriate MHC-binding context. The potential role of induced antibody has been appreciated only recently. Recent studies in our laboratory with heat-killed Saccharomyces (HKY) have raised the possibility of development of a panfungal vaccine. This yeast may be nature's experimental reagent, to show the way to a protective protein-carbohydrate conjugate vaccine. Subcutaneous HKY is an effective vaccine against Aspergillus, Coccidioides or Candida challenge. We have learned the protective moiety is in the cell wall, and proteins, glucan and lipid all seem important. We have also found the cell wall glycans alone, mannan or glucan, as a vaccine each provide significant protection. This leads to consideration of the importance of glycosylated proteins and glycan polymer-protein conjugates in vaccine development. We think the most productive route to a fungal-specific vaccine may be a conjugate vaccine that combines the optimally configured glycan with a specific immunogenic protein. Our work so far suggests that some proteins may be sufficiently cross-immunogenic, such that combined with the appropriate glycan, it may be possible to develop a pan-fungal vaccine.

Despite the recent development of new anti-mould agents, there remains a significant incidence of invasive aspergillosis in the most immunocompromised hosts and the response to these agents is still dismal. There is a need for a different approach: prevention by vaccination. We have demonstrated that a hyphal sonicate of Aspergillus fumigatus was capable of conferring protection against subsequent invasive pulmonary aspergillosis in corticosteroid immunosuppressed mice. Subcutaneous vaccination was superior to nasal vaccination. Mice exposed intranasally to viable conidia were noted to respond serologically to a 19 kDa protein. This protein was identified as the allergen Asp f 3 by mass spectrometry. Vaccination with recombinant Asp f 3 was protective. Truncated forms of Asp f 3 that lacked either one of the two known IgE binding sites were cloned and also demonstrated protection against aspergillosis. Although all of these recombinant proteins required an adjuvant (TiterMax) for efficacy, a particulate preparation of rAsp f 3 was also found to be protective without requiring adjuvant. At least two T-cell epitopes (11-mer and 13-mer) have been identified in Asp f 3. There are homologues of Asp f 3 in other Aspergillus species as well as in other moulds (Coccidioides posadasii, Penicillium citrinum) and yeasts (Candida albicans, C. boidinii, Saccharomyces cerevisiae). Asp f 3, truncated non-allergenic versions of Asp f 3, and T-cells epitopes of Asp f 3 are potential candidates for vaccines potentially capable of protecting immunocompromised hosts against invasive aspergillosis.

Mucormycosis is a life-threatening infection which causes unacceptably high morbidity and mortality despite treatment. Therefore, a vaccine to prevent mucormycosis is desirable. A major barrier to developing an anti-mucormycosis vaccine is the perception that such a vaccine would not be cost-effective to deploy because the disease is rare. We used data from a recent retrospective study to calculate the annual cost to the US healthcare system caused by mucormycosis infections. We created a model to estimate the cost-efficacy of a niche, anti-mucormycosis vaccine deployed in a targeted manner to high-risk patients. We found that each case of mucormycosis results in an average direct cost to the US healthcare system of $97,743, for an overall cost of mucormycosis of $50 million per year. In the base case scenario, targeted deployment of an anti-mucormycosis vaccine would result in a net cost per quality adjusted life year saved (QUALY) of $17,249. Variations in the price of the vaccine, its market penetration, or the cost of infection could dramatically decrease the net cost, and could even result in net savings per QUALY. In conclusion, mucormycosis causes considerable cost to the US health care system. Targeted deployment of a niche vaccine could decrease infection rates and mortality from mucormycosis in a cost-effective manner.

The Candida albicans heat shock protein 90 kDa (hsp90-CA) is an important target for protective antibodies in disseminated candidiasis of experimental mice and humans. Hsp90-CA is present in the cell wall of Candida pseudohyphae or hyphae--typical pathogenic morphotypes in both mucosal and systemic Candida infections. However, the potential protective effects of hsp90-CA-specific antibodies in vaginal candidiasis has not yet been reported. In the present study we used various vaccine formulations (recombinant hsp90-CA protein and hsp90-CA-encoding DNA vaccine) and routes of administration (intradermal, intranasal, and intravenous) to induce both hsp90-CA-specific systemic and vaginal mucosa immune responses in experimental BALB/c mice. The results showed that intradermal recombinant hsp90-CA protein priming, followed by intranasal or intradermal recombinant hsp90-CA protein boosting induced significant increases in both serum and vaginal hsp90-CA-specific IgG and IgA antibodies compared to the control group, as well as enhanced hsp90-CA-specific splenocyte responses in vitro. In the intradermally boosted group, subsequent experimental vaginal Candida infection induced additional increases in the hsp90-CA specific IgG isotype, suggesting that Candida has the ability to induce a local hsp90-specific antibody (IgG) response during vulvovaginal candidiasis. Further work is required to elucidate the importance of immunity to highly conserved antigens during infection of the human female reproductive tract where a balance between immunity to and tolerance for commonly antigens such as hsp90 is necessary for the maintenance of fertility.

Animal models of fungal infections are, and will remain, a key tool in the advancement of the medical mycology. Many different types of animal models of fungal infection have been developed, with murine models the most frequently used, for studies of pathogenesis, virulence, immunology, diagnosis, and therapy. The ability to control numerous variables in performing the model allows us to mimic human disease states and quantitatively monitor the course of the disease. However, no single model can answer all questions and different animal species or different routes of infection can show somewhat different results. Thus, the choice of which animal model to use must be made carefully, addressing issues of the type of human disease to mimic, the parameters to follow and collection of the appropriate data to answer those questions being asked. This review addresses a variety of uses for animal models in medical mycology. It focuses on the most clinically important diseases affecting humans and cites various examples of the different types of studies that have been performed. Overall, animal models of fungal infection will continue to be valuable tools in addressing questions concerning fungal infections and contribute to our deeper understanding of how these infections occur, progress and can be controlled and eliminated.

Human infection with Histoplasma capsulatum or Blastomyces dermatitidis is sufficiently frequent to warrant exploring the development of vaccines. This review examines the advancements that have been accomplished over the last few years. The availability of molecular tools to create recombinant antigens or mutant strains has produced a small number of useful vaccine candidates. More importantly, the studies summarized herein demonstrate that understanding the host response to a protein or mutant fungus is critical to creating a vaccine that may be useful for the immunocompromised patient.

Previously we showed heat-killed yeast (HKY) of Saccharomyces cerevisiae administered as a vaccine are protective against systemic murine aspergillosis (and other mycoses) and that HKY induces antibody and cellular responses. To determine the role of antibodies in this protection, male antibody knockout mice (KO; strain B6.129S2-Igh-6 (tm1Cgn)/J) and C57BL/6 wild-type (WT) mice were vaccinated subcutaneously with 6 × 10(7) HKY or phosphate buffered saline (PBS) given three or four times. Mice were infected intravenously with 6 × 10(6) viable conidia of Aspergillus fumigatus 10AF and mortality tallied through 12 days post infection. HKY vaccination given four times proved protective in the prolongation of survival of WT and KO mice vs. the respective PBS-treated controls. In one study, survival was prolonged in vaccinated WT or KO mice (P < 0.0001). A second study confirmed these results (P < 0.0001). Additionally, a three-dose regimen of HKY was also effective, prolonging survival of WT or KO mice vs. controls (P = 0.0002); no difference was found when the effectiveness of three- or four-dose regimens was compared. No significant differences in survival were found between HKY-vaccinated WT and KO mice, nor were PBS-treated KO mice more susceptible to infection than PBS-treated WT mice. Similar results were noted in another study in which a higher infectious inoculum and a three-dose regimen were used. Overall, antibodies do not appear to play a significant role in HKY-induced prolongation of survival in systemic aspergillosis, nor do antibodies appear to play a role in the innate resistance of the mice to aspergillosis.

Resolution of lesions and subsequent protection against ringworm is primarily associated with the development of a cell-mediated immune (CMI) response, in which stimulation of Type-1 lymphocytes and cytokines such as interleukin-2 (IL-2), IL-12 and interferon gamma are significant. Type-2 lymphocyte activation and antibody formation seem a feature of chronic disease states, rather than protection, and are antagonistic to a Type-1 cell response. Initial studies on ringworm vaccines should be directed at identifying and characterizing dermatophyte antigens elaborated during spore germination and early hyphal growth, and the method of their presentation which best potentiates Type-1 cell-associated events, and primes the recipient for a subsequent CMI response.

Cryptococcosis is a relatively common fungal disease caused by Cryptococcus neoformans that has high morbidity and mortality. Numerous studies have established the feasibility of enhancing host immunity to C neoformans in naive immunocompetent animal models by vaccination. Several antigens have been identified that appear to be suitable vaccine candidates. Induced immune responses can mediate protection through both humoral and cellular immunity. Hence, a vaccine against cryptococcosis in humans is probably feasible but there are significant obstacles to vaccine development that range from uncertainties about the pathogenesis of infection to economic considerations.

Invasive aspergillosis is a disease of immunocompromised hosts and the pathogenesis of this disorder is heavily dependent upon the defect within a given host. Consequently, vaccine development is limited by our understanding of effective host responses and by limitations in our knowledge of fungal molecules that elicit protective immunity. Nonetheless, the past few years have witnessed advances in our understanding both of the immune response to this organism and in the relationship between antigenicity and the ability to confer protection. Manipulations that promote the development of T(H)1-associated responses correlate with increased resistance to disease, at least partly because of consequent enhancement of innate cellular effector function. Two areas of investigation most actively being pursued include the search for adjuvants that will allow products of Aspergillus fumigatus to become effective vaccine candidates, regardless of the form of immunity they ordinarily induce, and the identification of the specific antigens that will most effectively elicit beneficial responses. Strategies using antigen-exposed dendritic cells as adjuvants appear to be particularly promising. Though we currently are far away from a candidate that is applicable for human trials, recent progress is encouraging.

The development of a useful Candida vaccine is a distinct possibility despite the fact that individuals with a lifetime of commensal sensitization do not develop sterile immunity to the organism. An effective Candida vaccine would be invaluable in preventing hematogenously disseminated candidiasis, as well as mucocutaneous disease. This review is a discussion of our current understanding of the interplay between commensal and pathogenic forms of Candida albicans and approaches toward active and passive immunoprevention against candidiasis.

Enolase, a 46-kDa glycolytic enzyme, is an immunodominant antigen of the opportunistic pathogen Candida albicans. A recombinant 6 x His-tagged enolase was studied, in conjunction with interleukin-12 (IL-12), as an adjuvant for cytokine induction favouring protection in a murine model of haematogenous candidiasis. Mice immunized with enolase plus IL-12 showed increased antibody titres against enolase, as well as increased median survival time and decreased fungal burden in kidneys, in comparison to non-immunized or IL-12-treated mice. This increased survival was attributable to enolase-induced cell-mediated immunity as it also occurred in B-cell-deficient mice. Enolase immunization stimulated a predominant T-helper-1 (Th1) cytokine pattern in splenic cells and induced production of interferon-gamma (IFN-gamma) and interleukin-2 (IL-2) by purified CD4+ T cells. However, despite the elevation of immunogenicity, recombinant enolase induced only a modest protection against disseminated candidiasis, suggesting a form of protection likely attributable to the induction of a Th1 cell-mediated immune response.

Coccidioides is a fungal pathogen of humans which can cause a life-threatening respiratory disease in immunocompetent individuals. Recurrent epidemics of coccidioidal infections in Southwestern United States has raised the specter of awareness of this soil-borne microbe, particularly among residents of Arizona and Southern California, and has galvanized research efforts to develop a human vaccine against coccidioidomycosis. In this review, we discuss the rationale for such a vaccine, examine the features of host innate and acquired immune response to Coccidioides infection, describe strategies used to identify and evaluate vaccine candidates, and provide an update on progress toward development of a vaccine against this endemic pathogen.

The effectiveness of a mucosal vaccine composed of heat-killed Candida albicans (HK-CA) or C. albicans culture filtrate (CaCF) in conjunction with the mucosal adjuvant LT(R192G) against vulvovaginal candidiasis was examined in an estrogen-dependent murine model. Mice vaccinated intranasally with HK-CA + LT(R192G) exhibited a significant but short-lived protection accompanied by a vigorous delayed-type hypersensitivity response as well as high titers of circulating C. albicans-specific antibodies. Surprisingly, the levels of antigen-specific antibodies in the vaginal secretions of protected mice were negligible and no correlates of vaginal-associated Type 1 or Type 2 cytokines were observed. Vaginal priming with C. albicans before vaccination did not alter the protective outcome. Immunization with CaCF + LT(R192G) induced a discrete level of protection when administered intrarectally but not intranasally. These results suggest that mucosal vaccination can afford partial protection against vulvovaginal candidiasis, but the precise immune mechanisms responsible for protection are complex and as yet, not well understood.

In the past two decades, numerous studies have documented the importance of acquired immunity for host defense against invasive fungal infections. There is widespread consensus in the field of medical mycology that cellular immunity is critical for successful host defense against fungi. However, in recent years several studies have established the potential efficacy of humoral immunity in host protection against two major fungal pathogens: Candida albicans and Cryptococcus neoformans. For C. albicans, antibodies to mannan, proteases and a heat shock proteins have been associated with protection against infection. Furthermore, anti-idiotypic antibodies to antibodies recognizing killer toxin from Pichia anomala and mimicking natural anti-killer toxin receptor antibodies can protect against C. albicans and other microorganisms. For C. neoformans, antibodies to the capsular glucuronoxylomannan have been shown to mediate protection in animal models of infection. Vaccines that induce protective antibodies have been shown to protect against experimental C. albicans and C. neoformans infection. In contrast, humoral immunity has not yet been demonstrated to mediate protection against Coccidioides immitis. For C. immitis, protection against infection is thought to rely on T cell mediated immunity, and the emphasis is on identifying the antigens that stimulate protective cellular immune responses and several candidate vaccines have been identified. These results provide encouragement for the view that acquired immune responses can be mobilized for the prevention and treatment of fungal infections.

Vaccine approaches to infectious diseases are widely applied and appreciated. Disciplines such as bacteriology and virology have a rich history of successful vaccine development. The complexity of eukaryotic systems presents additional challenges to the development of vaccines against them. These challenges are being met in the fields of parasitology, and are being revisited for application in oncology. Vaccine opportunities exist in medical mycology. The National Institute of Allergy and Infectious Diseases has held a series of workshops in medical mycology where the need to develop vaccines for fungal diseases was noted and where important opportunities were discussed. Major advances in vaccinology and the technology of antigen preparation and delivery have increased feasibility and heightened interest. The recent epidemic of coccidioidomycosis in the American Southwest has demonstrated the need for developing a vaccine as an effective preventive measure for those living in and for those who subsequently move into regions with the endemic mycoses. The XIIth Congress of the International Society for Human and Animal Mycology included a symposium that summarized new vaccination strategies for selected fungi: Candida albicans, Coccidioides immitis, and Trichophyton verrucosum. The goal of the present summary is to provide representative examples of continuing efforts relating to vaccine development within the medical mycological community highlighting Blastomyces dermatidis, Cryptococcus neoformans, Histoplasma capsulatum, Paracoccidioides brasiliensis, and Pythiumn insidiosum.

Three cases of respiratory crytococcosis are described, one diagnosed only after thoracotomy and two after cytology. All were confirmed by cultures, biological and biochemical tests. The patients are alive and well 14 years, 5 years, and 5 years after treatment with crytococcal vaccines and mycostatin. Vaccines proved very effective when given intradermally in small doses and no dangerous reactions were encountered. Cytology of the sputum appears to be a very useful tool in diagnosis of fungal infections of the respiratory tract, especially when supravital staining is used. Difficulties in diagnosis, treatment, and significance of positive sputum findings are discussed.

A new coccidioidin, derived from the spherule phase of Coccidioides immitis cultured in vitro, was examined for its capacity to elicit delayed dermal hypersensitivity reactions in mice and guinea pigs. Mycelial coccidioidin, widely used in diagnostic procedures, was studied in parallel. The animals were sensitized either by infection with arthrospores or by vaccination with formalin-killed spherules or mycelium; sensitivity reactions were determined 3–5 weeks later or, in 1 experiment, afte 18 months. The capacities of the preparations to detect reactions augmented anamnestically by a booster dose of vaccine given 18 months after original sensitization were compared, as well as reactions induced with a strain of C. immitis not used in the preparation of either reagent.In each comparison above, the spherule coccidioidin was judged to be more sensitive than the mycelial in that a lower dose (1) elicited stronger reactions, (2) showed higher ratios of sensitized animals to be reactive, and (3) induced reacti...

The role of cells in immunity to pulmonary infection with Coccidioides immitis was studied in mice vaccinated with formalin-killed spherules and endospores and infected intranasally with arthrospores. Postinfection changes in lung and body wt., lung histology, and numbers of inflammatory cells obtained by tracheobronchial washing commenced more rapidly in vaccinated mice than in nonvaccinated controls. However, once begun, the changes were greater in the latter animals. In tracheobronchial washings made 12 hr. after infection, the percentage of alveolar macrophages with intracellular arthrospores was the same in both groups of animals. But after 24 hr. a much smaller percentage of macrophages had intracellular spherules in the washings from vaccinated mice than in those from controls. It is postulated that macrophages of vaccinated mice ingest arthrospores in vivo at the same rate as macrophages of control animals, but are better able to prevent the intracellular spores from developing into spherules.