Development of vaccines for coccidioidomycosis

The Mating Type (MAT) and Virulence of Sporothrix schenckii sensu stricto Isolates Maintained in Culture Collection

In an attempt to determine the mating type of different Sporothrix schenckii sensu stricto isolates that remained viable after a long period of preservation in a culture collection and to correlate them with the degree of virulence/pathogenicity, a PCR technique using primers designed for the sequences of MAT1-1-1 and MAT1-2-1 genes and a murine experimental model were used. The results showed that there was no correlation between the mating type and virulence among the isolates. Furthermore, different degrees of virulence/pathogenicity, ranging from high to low, were found among them based on different virulence parameters. It was assumed that the long period of preservation favored the changes, yielding the isolation of variants. Thus, we believe that new technologies for studies on factors can improve our knowledge of the pathogenesis of sporotrichosis.

Vaccines to Prevent Coccidioidomycosis: A Gene-Deletion Mutant of Coccidioides Posadasii as a Viable Candidate for Human Trials

Coccidioidomycosis is an endemic fungal infection that is reported in up to 20,000 persons per year and has an economic impact close to $1.5 billion. Natural infection virtually always confers protection from future exposure, and this suggests that a preventative vaccine strategy is likely to succeed. We here review progress toward that objective. There has been ongoing research to discover a coccidioidal vaccine over the past seven decades, including one phase III clinical trial, but for reasons of either efficacy or feasibility, a safe and effective vaccine has not yet been developed. This review first summarizes the past research to develop a coccidioidal vaccine. It then details the evidence that supports a live, gene-deletion vaccine candidate as suitable for further development as both a veterinary and a human clinical product. Finally, a plausible vaccine development plan is described which would be applicable to this vaccine candidate and also useful to other future candidates. The public health and economic impact of coccidioidomycosis fully justifies a public private partnership for vaccine development, and the development of a vaccine for this orphan disease will likely require some degree of public funding.

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.

Flow Cytometric Analysis of Protective T-Cell Response Against Pulmonary Coccidioides Infection

The incidence of systemic fungal infections has increased throughout the world, spurring much interest in developing effective vaccines. Coccidioidomycosis, also known as San Joaquin Valley fever, is a potentially life-threatening respiratory mycosis. A vaccine against Coccidioides infection would contribute significantly to the well-being of the approx. 30 million residents in the Southwestern USA as well as the multitude of travelers who annually visit the endemic regions. We have applied a live, attenuated vaccine (∆T) to explore the nature of vaccine immunity in mice after intranasal challenge with a potentially lethal dose of Coccidioides spores. Coccidioides spores are airborne and highly infectious for mammalian hosts and classified as a biosafety level 3 agent. T cells are critical in the development of protective immunity against a variety of microorganisms as well as the development of autoimmune disease and allergic responses. Profiles of cytokines detected in lung homogenates of ∆T-vaccinated mice were indicative of a mixed Th1, Th2, and Th17 immune response. We have developed an intracellular cytokine staining and flow cytometric (ICS) technique to measure activated CD4(+) and CD8(+) T cells and IFN-γ-, IL-4-, IL-5-, and IL-17A-producing T cells in the lungs of mice that are challenged with a potentially lethal dose of Coccidioides spores. The numbers of pulmonary Th1 and Th17 cells during the first 2 weeks post-challenge showed a progressive increase in vaccinated mice and corresponded with reduction of fungal burden. In this protocol, we describe the methodology for culture and isolation of the live, attenuated ΔT spores of Coccidioides used to vaccinate mice, preparation of pulmonary cells, and staining protocol for cell surface markers and intracellular cytokines. This is the most reliable and robust procedure to measure frequencies and numbers of each selected T-cell subsets in lungs of vaccinated versus control mice and can be readily applied to evaluate T-cell response against other microbial infections.

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.

Saccharomyces cerevisiae as a vaccine against coccidioidomycosis

Disseminated coccidioidomycosis is a life-threatening infection. In these studies, we examined protection against systemic murine coccidioidomycosis by vaccination with heat-killed Saccharomyces cerevisiae (HKY). CD-1 mice received HKY subcutaneously or by oral gavage with or without adjuvants once weekly beginning 3 or 4 weeks prior to infection; oral live Saccharomyces was also studied. All HKY sc regimens were equivalent, prolonging survival (P<or=0.005) and reducing fungal burden versus controls. Oral live Saccharomyces, but not HKY, prolonged survival (P=0.03), but did not reduce fungal burden. Survival of mice given HKY was equivalent to vaccination with formalin-killed spherules, but inferior in reduction of fungal burden. HKY was superior to a successful recombinant vaccine, PRA plus adjuvant. This novel heterologous protection afforded by HKY vaccination offers a new approach to a vaccine against coccidioidomycosis.

Experimental animal models of coccidioidomycosis

Experimental models of coccidioidomycosis performed using various laboratory animals have been, and remain, a critical component of elucidation and understanding of the pathogenesis and host resistance to infection with Coccidioides spp., as well as to development of more efficacious antifungal therapies. The general availability of genetically defined strains, immunological reagents, ease of handling, and costs all contribute to the use of mice as the primary laboratory animal species for models of this disease. Five types of murine models are studied and include primary pulmonary disease, intraperitoneal with dissemination, intravenous infection emulating systemic disease, and intracranial or intrathecal infection emulating meningeal disease. Each of these models has been used to examine various aspects of host resistance, pathogenesis, or antifungal therapy. Other rodent species, such as rat, have been used much less frequently. A rabbit model of meningeal disease, established by intracisternal infection, has proven to model human meningitis well. This model is useful in studies of host response, as well as in therapy studies. A variety of other animal species including dogs, primates, and guinea pigs have been used to study host response and vaccine efficacy. However, cost and increased needs of animal care and husbandry are limitations that influence the use of the larger animal species.

Coccidioidomycosis: changing perceptions and creating opportunities for its control

The perceptions of coccidioidomycosis as a medical problem has undergone sequential and dramatic metamorphoses since its first description more than a century ago. First thought to be rare and lethal, coccidioidomycosis was subsequently found to be common and often mild. During World War II, its overall impact upon large populations came sharply into focus and the consequences for public health became clearer. Early treatments had significant limitations and toxicities, and therefore treatment of coccidioidomycosis was reserved for only the sickest patients. Since then, safer oral therapies have become commonplace. Despite their availability, there has been no investigation of their use in the less severe and much more common early infections. Even newer drugs such as nikkomycin Z, which might actually cure infections, until very recently have had trouble finding a sponsor to move it through clinical trials. Perceptions once formed by the understanding of coccidioidomycosis as a medical problem now appear to hinder the future study of newer therapeutic opportunities. It is suggested in this review that it is time to revisit and possibly change these perceptions if we are to improve our care of patients.

Murine models of blastomycosis, coccidioidomycosis, and histoplasmosis

Animal models have contributed much to the knowledge of fungal infections and their corresponding therapeutic treatments. This is true for animal models of the primary fungal pathogens, Blastomyces dermatitidis, Coccidioides immitis, and Histoplasma capsulatum. This review gives a brief background of human diseases associated with these organisms and describes the development, details, and utility of murine models of blastomycosis, as well as coccidioidomycosis and histoplasmosis.

Experimental evolution of parasites

Serial passage experiments are a form of experimental evolution that is frequently used in applied sciences; for example, in vaccine development. During these experiments, molecular and phenotypic evolution can be monitored in real time, providing insights into the causes and consequences of parasite evolution. Within-host competition generally drives an increase in a parasite's virulence in a new host, whereas the parasite becomes avirulent to its former host, indicating a trade-off between parasite fitnesses on different hosts. Understanding why parasite virulence seldom escalates similarly in natural populations could help us to manage virulence and deal with emerging diseases.

Serology of coccidioidomycosis

Serologic tests have assisted in the diagnosis and prognosis of coccidioidomycosis for a half-century. The causative agent, Coccidioides immitis, is a dimorphic fungus existing in a hyphal form with arthroconidia in nature and in the usual culture. The arthroconidia represent the inhaled infective forms which in vivo and under special laboratory conditions form spherules which endosporulate. The culture filtrate/autolysate (coccidioidin) from the hyphal phase has provided antigens of suitable reliability for currently used serologic tests. These tests are primarily to determine the two major antibody responses: the early immunoglobulin M (IgM) response is useful in the diagnosis of acute primary coccidioidomycosis. Later, IgG is produced and usually outlasts the IgM, persisting in chronic coccidioidomycosis. The IgM is detectable by tube precipitin, a corresponding immunodiffusion, or latex particle agglutination tests. The pertinent antigen(s) is heat stable and pronase resistant and appears to be largely carbohydrate, mainly mannose with some 3-O-methyl mannose. The IgG detectable in the serum and other body fluids by complement fixation and a corresponding immuno-diffusion is useful in diagnosis, and its quantitation provides an indicator of progression of disease (increasing titer) or regression (decreasing titer). The pertinent antigen appears to be a heat-labile, pronase-sensitive protein which in an unreduced form has a molecular weight of 110,000. A third very useful serologic procedure is the exoantigen test for identification of putative cultures of C. immitis.

Virulence of Paracoccidiodes brasiliensis: the influence of in vitro passage and storage

Stability of virulence in P. brasiliensis isolates was studied with respect to the in vitro culture history and methods used for storage. Virulence in yeast-form P. brasiliensis isolates was tested in a chronic pulmonary murine model of paracoccidiodomycosis where progression of disease was quantitated in terms of colony forming units recoverable from lungs. Four isolates of P. brasiliensis, including recently isolated form patients or experimental animals, caused chronic progressive disease. Two isolates with a history of subculturing showed attenuation by causing resolving but chronic disease. An attenuated isolate became avirulent subsequent to 15 more years of subculturing. These findings suggest that virulence of P. brasiliensis can be attenuated or lost subsequent to cycles of subculturing over long periods. Our data suggest that the use of fresh P. brasiliensis isolates may be needed to provide reproducible virulence for experimental systems.

A skin test survey of valley fever in Tijuana, Mexico

Results of a study of the prevalence of valley fever among 1128 residents of Tijuana, Baja California are presented. Children from primary and middle schools (n = 497) and adults from technical institutes and maquiladoras (assembly plants) were tested for reaction to both spherulin and coccidioidin during 1985-1986, and they completed a questionnaire containing 23 variables on their socio-environment. Place of residence was mapped. The population sampled is largely middle class. Discriminant analysis indicates the distribution of positive cases is not clustered, nor can it be correlated with geomorphic factors such as mesa tops, canyons, or valley bottoms.

Characterization of a soluble protein of Coccidiodes immitis with activity as an immunodiffusion-complement fixation antigen

A 48-kilodalton (kDa) electrophoretically distinct antigen from Coccidioides immitis mycelial- and spherule-endospore-phase filtrates was previously associated by immunoblotting with the immunodiffusion band that corresponds to complement-fixing activity (ID-CF). To characterize this antigen and its precursor, both mycelial- and spherule-endospore-phase filtrates were fractionated by size exclusion chromatography, lectin affinity chromatography, and nondenaturing electrophoresis. By size exclusion chromatography, most of the protein and carbohydrate of the crude filtrates eluted in a peak of average molecular size less than 30 kDa, although other components were detected. ID-CF activity was associated with the component at a relative mobility of 110 kDa. Fractions containing the ID band that corresponded to tube precipitin activity occurred from 200 to 40 kDa. The appearance of the 48-kDa band in denaturing sodium dodecyl sulfate-polyacrylamide gel electrophoresis (PAGE) specifically coincided with the fractions containing ID-CF activity. Nondenaturing PAGE of filtrates showed silver-stainable and immunoblot-reactive bands in the region of 110 kDa. Prior treatment with pronase destroyed this electrophoretically separable antigen, whereas periodate had no effect. Trypsin did not affect the 110-kDa band in unheated or unreduced antigen. Mycelial filtrates were chromatographed on lentil lectin or concanavalin A-Sepharose 4B to deplete them of glucose- or mannose-containing carbohydrate. The effluent fraction contained ID-CF activity and, upon denaturing electrophoresis, the 48-kDa antigen. The 110-kDa protein represents the ID-CF antigen which is heat labile and denatured to a 48-kDa band by sodium dodecyl sulfate-PAGE.

Vaccines against fungal infections

The state-of-the-art reached in developing protective immunity against fungal infections through vaccination makes a survey of methodologies and results timely. This review describes experimental vaccinations against dermatophytes, pathogenic yeasts, and dimorphic fungi with special attention to the anti-Coccidioides immitis vaccine, which has reached clinical trials, and to the anti-Candida albicans and anti-Histoplasma capsulatum ribosomal vaccines. Also covered are vaccination experiments in compromised hosts aimed at eliciting acquired resistance to opportunistic fungal infections which constitute risk factors for these hosts. Immunization procedures include live, killed, and attenuated organisms, as well as different subcellular fractions such as cytoplasmic extracts, fungal culture filtrates, cell walls, or ribosomal fractions. A variety of experimental animal models and isolated human trials constitute the subjects in these studies. Acquired immunity has been evaluated through assessment of resistance to infection and determination of specific immune responses. It has been demonstrated that fungal vaccines do elicit both humoral and cell-mediated immunity in the immunized host. For some vaccines (e.g., H. capsulatum), a correlation between the induced immunity and protection was observed and the immunity could be adoptively transferred. In view of the potential of vaccines against fungal infections, a perspective on their applicability, significance, and value for human use is discussed.

Comparison of immunoblot analyses of spherule-endospore-phase extracellular protein and mycelial-phase antigen of Coccidioides immitis

The extracellular proteins produced by Coccidioides immitis during growth of the spherule-endospore-phase and mycelial-phase antigen (coccidioidin) were studied by polyacrylamide gel electrophoresis followed by immunoblot analysis to detect specific serologic function. Filtrates obtained from 28- and 120-h growth of the spherule-endospore phase were compared with each other and with coccidioidin by using negative, immunoglobulin M (IgM) precipitin-positive, or complement fixation-positive pooled and single human sera followed by peroxidase-labeled anti-human IgA, IgE, IgG, or IgM (heavy chain specific) or peroxidase-labeled concanavalin A to detect the reaction. A total of 35 bands was seen in the stained gels. Different patterns were noted among the two spherule-endospore preparations and unheated and heated coccidioidin. At least 15 electrophoretically separate antigens were detected with positive serum ranging in approximate molecular weight (Mr) from 100,000 to 18,000. Most were clustered between 45 and 60 kilodaltons (kDa). Common bands were noted at 48 and 18 kDa. At least one band at 48 kDa was strongly reactive with complement fixation-positive serum demonstrated by reaction with anti-IgG and anti-IgE. In contrast, doublet bands in the 50- to 65-kDa area were highly reactive with IgM precipitin-positive serum detected by anti-IgM. IgM antibodies present in both positive sera reacted with a band at 46 kDa which was not reactive with IgG. Heating the antigens altered the reactivity of many of the antigens, including the 48-kDa band, but not the 46-kDa band.

Models of cell differentiation in conidial fungi

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Morphogenesis throughout saprobic and parasitic cycles of Coccidioides immitis

The fungus, Coccidioides immitis, differs from other dimorphic pathogens in that its parasitic stage is a complex morphogenic cycle, raising the question that changes and composition during morphogenesis might influence host responses. As a prelude to examining the interaction of fungal morphogenesis and host responses, the life cycle of this fungus has been examined in greater detail than previously accomplished. During saprobic development, alternating enterothallic arthroconidia are formed as infectious propagules. The outer wall is broken and loosely adherent. Under in vitro conditions supporting the parasitic cycle, multinucleate arthroconidia transform into uninucleate round cells. Rapid, synchronous, nuclear replication is initiated, accompanied by increase in cell mass and deposition of new cell wall substance. As karyokinesis ceases, morphologic differentiation begins with invagination of the inner layers of the spherule wall and then is progressive, eventually segmenting the protoplasm into uninucleate endospores grouped in clusters within a hyaline membrane. Endospores, escaping through a break in the spherule wall, are held in aggregates by fibrils which are stretched and broken as endospores separate. It would seem that rapid production of hundreds of progeny from an original single cell, protected during development by an enclosing spherule wall and then released in clusters, should favor establishment of the fungus in a host, and dynamic changes in the cell wall during morphogenesis should influence the host response.

Antigenic analysis of coccidioidin and spherulin determined by two-dimensional immunoelectrophoresis

Immunological tests are valuable aids for diagnosis of mycotic infections and, in some cases, as objective guides for clinical management and prognosis. The usefulness of these procedures is limited to the extents that crude antigen preparations are employed, that these are difficult to standardize uniformly, and that they contain antigens common to several species of pathogenic fungi. Analysis by two-dimensional immunoelectrophoresis methods of the two crude preparations used for coccidioidomycosis demonstrated that coccidioidin contained at least 26 antigens, with 10 of these found also in spherulin. In addition, spherulin contained two antigens not demonstrated in coccidioidin. No single test detected all antigens present, and multiple procedures were required to display the complete array of antigens. A reference system was established for coccidioidin and precipitated immunoglobulins from a burro hyperimmunized with coccidioidin. Evaluation of the reference system demonstrated that it was highly reproducible with respect to the reagents used, to repeated tests by the same person, and to comparative tests by two individuals using the same reagents. Applications of this reference system for standardization of reagents, for detecting common antigens, for monitoring successive steps during fractionation of crude preparations, and for fingerprinting strains for ecological and epidemiological studies are presented.