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

Challenges to Implementing a Vaccine for Coccidioidomycosis

A vaccine for coccidioidomycosis is likely to undergo trials in the near future. In this paper, we raise 4 questions that should be answered before its use and offer our solutions to these questions. These include defining the goals of vaccination, determining who should be vaccinated, how to measure vaccine immunity and protection, and how to address vaccine hesitancy and denial.

Harnessing the Immune Response to Fungal Pathogens for Vaccine Development

Invasive fungal infections are emerging diseases that kill over 1.5 million people per year worldwide. With the increase of immunocompromised populations, the incidence of invasive fungal infections is expected to continue to rise. Vaccines for viral and bacterial infectious diseases have had a transformative impact on human health worldwide. However, no fungal vaccines are currently in clinical use. Recently, interest in fungal vaccines has grown significantly. One Candida vaccine has completed phase 2 clinical trials, and research on vaccines against coccidioidomycosis continues to advance. Additionally, multiple groups have discovered various Cryptococcus mutant strains that promote protective responses to subsequent challenge in mouse models. There has also been progress in antibody-mediated fungal vaccines. In this review, we highlight recent fungal vaccine research progress, outline the wealth of data generated, and summarize current research for both fungal biology and immunology studies relevant to fungal vaccine development. We also review technological advancements in vaccine development and highlight the future prospects of a human vaccine against invasive fungal infections.

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.

Coccidioidomycosis: A Contemporary Review

Coccidioidomycosis, colloquially known as Valley Fever, is an invasive dimorphic fungal infection caused by Coccidioides immitis and C. posadasii. The fungi are found in the arid desert soils of the southwestern US, as well as in parts of Mexico and Central and South America. Acquisition is typically via inhalation of arthroconidia which become airborne after both natural (e.g., earthquakes, dust storms, and fires) and human-related events (e.g., military maneuvers, recreational activities, agriculture, and construction). The incidence of infection in increasing likely a result of both climatic and populational changes. Further, the recognized geographic distribution of Coccidioides spp. is expanding, as cases are being diagnosed in new areas (e.g., eastern Washington, Oregon, and Utah). Most coccidioidal infections are asymptomatic (60%); however, approximately one-third develop a pulmonary illness which is a leading cause of community-acquired pneumonia in highly endemic areas. Uncommonly (0.5–2% of cases), the infection disseminates to extrapulmonary locations (e.g., skin, bones/joints, and the central nervous system), and is most commonly seen among persons with cellular immunodeficiencies (e.g., transplant recipients, HIV, and pregnancy) and non-Caucasian races (especially African Americans and Filipinos). The diagnosis of coccidioidomycosis requires astute clinical suspicion and laboratory findings, including positive serology, cultures, and/or histopathology results. Treatment is warranted among persons with pneumonia who have risk factors for complicated disease and among those with extrapulmonary disease. Novel antifungals with improved fungicidal activity and rapidity of action with fewer side effects and drug interactions are needed. Preventive strategies (e.g., education regarding the disease, dust avoidance, mask wearing, including among select groups, antifungal prophylaxis, and surveillance laboratory testing) are advised for residents and travelers to endemic areas. Currently, no preventive vaccine is available. Coccidioidomycosis has been recognized for over a century, and an expanding wealth of knowledge has been gained regarding this emerging infectious disease which will be reviewed here.

Δcps1 vaccine protects dogs against experimentally induced coccidioidomycosis

Coccidioidomycosis is a significant health problem of dogs and humans in endemic regions, especially California and Arizona in the U.S. Both species would greatly benefit from a vaccine to prevent this disease. A live avirulent vaccine candidate, Δcps1, was tested for tolerability and efficacy to prevent pulmonary coccidioidomycosis in a canine challenge model. Vaccine injection-site reactions were transient and there were no systemic effects observed. Six of seven vaccine sites tested and all draining lymph nodes were sterile post-vaccination. Following infection with Coccidioides posadasii, strain Silveira, arthroconidia into the lungs, dogs given primary and booster vaccinations had significantly reduced lung fungal burdens (P = 0.0003) and composite disease scores (P = 0.0002) compared to unvaccinated dogs. Dogs vaccinated once had fungal burdens intermediate between those given two doses or none, but disease scores were not significantly different from unvaccinated (P = 0.675). Δcps1 was well-tolerated in the dogs and it afforded a high level of protection when given as prime and boost. These results drive the Δcps1 vaccine toward a licensed veterinary vaccine and support continued development of this vaccine to prevent coccidioidomycosis in humans.

Clinical and Economic Burden of Valley Fever in Arizona: An Incidence-Based Cost-of-Illness Analysis

BACKGROUND

Coccidioidomycosis, ie, Valley fever, is an important fungal infection in the Southwest, with half to two thirds of all cases occurring in Arizona. This endemic respiratory disease can range from primary uncomplicated pneumonia to disseminated infection such as meningitis with chronic pulmonary complications. Valley fever diagnoses have risen over recent years and cause substantial morbidity and economic burden in Arizona.

METHODS

We estimated the lifetime cost-of-illness associated with all cases of Valley fever diagnosed in 2019 in Arizona. Natural history of the disease was determined from literature and expert opinion and assigned costs from national data sources to determine lifetime direct and indirect costs (work loss).

RESULTS

Total lifetime costs of $736 million were estimated for the 10 359 cases of Valley fever diagnosed in Arizona in 2019. Direct costs of $671 million accounted for over 90% of expenditures, with $65 million in indirect costs. Disseminated infection produces the highest economic burden at $1.26 million direct and $137 400 indirect costs per person. The lowest Valley fever lifetime costs were for cases of primary uncomplicated pneumonia with $23 200 in direct costs and $1300 in lost wages. The average lifetime direct costs across all Valley fever manifestations are $64 800 per person diagnosed in Arizona in 2019 and $6300 for indirect costs.

CONCLUSIONS

Valley fever is responsible for substantial economic burden in Arizona. Our estimates underscore the value of supporting research into developing more rapid diagnostic tests, better therapies, and ultimately a preventative vaccine to address this important public health problem in Arizona.

Coccidioidomycosis in Brazil: Historical Challenges of a Neglected Disease

Coccidioidomycosis is a deep-seated fungal infection that occurs exclusively in semiarid areas in the Americas. In Brazil, coccidioidomycosis occurs exclusively in rural areas in the northeast region and affects counties that are hit by recurrent droughts, poverty and economic stagnation. Since 1978, approximately 136 cases of the disease have been reported in Brazil, according to scientific publications. However, a lack of governmental epidemiological data as well as a similarity to tuberculosis have led scientists and experts to assume that a greater number of cases occur in the country, which are not diagnosed and/or reported. In this review, general characteristics of coccidioidomycosis are presented, followed by a description of the main clinical and epidemiological data of cases in Brazil. The purpose of this article is to discuss the inclusion of coccidioidomycosis in the list of neglected tropical diseases. We believe that the adoption of coccidioidomycosis as a neglected tropical disease will enable the creation of an effective epidemiological surveillance system and the development of feasible public health solutions for its control in vulnerable populations.

Coccidioidomycosis: Changing Concepts and Knowledge Gaps

Although first described more than 120 years ago, much remains unknown about coccidioidomycosis. In this review, new information that has led to changing concepts will be reviewed and remaining gaps in our knowledge will be discussed. In particular, new ideas regarding ecology and epidemiology, problems and promises of diagnosis, controversies over management, and the possibility of a vaccine will be covered.

Update on Coccidioidomycosis in the United States and Beyond

Coccidioidomycosis is a fungal infection that is prevalent in western United States, Central America, and South America. The infection is acquired by inhalation. It can affect persons of all ages including infants and children. The majority of cases are asymptomatic and the incidence of infection is greater during a dry summer season after heavy rainfall in prior winter. For those with symptoms, they may experience a self-limiting influenza-like illness. However, some may progress toward pneumonia or disseminated diseases involving skeletal system and central nervous system. The diagnosis is based mainly on various serology testing. Antifungal treatment is generally not required for those with mild symptoms. For those with moderate to severe infections, the mainstay of treatment is azole, with fluconazole being often considered as the first line therapy. Currently there is no effective solution to prevent coccidioidomycosis. Those who work in high-risk conditions should be given appropriate protective equipment as well as education on proper precaution.

Primary Cutaneous Coccidioidomycosis: An Update

Coccidioidomycosis is an endemic mycosis of the southern United States, Northern Mexico, and South America. Primary cutaneous coccidioidomycosis, despite being a very rare clinical presentation, has shown an increasing incidence. An extensive literature search for cutaneous coccidioidomycosis cases was performed using the OLDMEDLINE, PubMed, Cochrane, LILACS and Google Scholar databases for studies published from January 1927 through December 21, 2019. Forty-two observational studies were included totaling 82 cases of primary cutaneous coccidioidomycosis. Narrative reviews, systematic reviews, and meta-analyses were also included. Additionally, an original case was included. Patients with primary cutaneous coccidioidomycosis share the same geographical and epidemiological characteristics as those with pulmonary or disseminated coccidioidomycosis. Most of the imported cases came from endemic areas. A large portion of cases had prior local skin trauma. Tissue culture is still the leading diagnostic method; nevertheless, molecular techniques such as polymerase chain reaction (PCR) are currently relevant to differentiate between species. First-line treatment consists of azoles; however, it has an excellent prognosis even without treatment. Primary cutaneous coccidioidomycosis should be considered a differential diagnosis of unusual infections or neoformations in any part of the body in resident populations of endemic areas or in patients with a previous history of travel to these areas.

Innate Inspiration: Antifungal Peptides and Other Immunotherapeutics From the Host Immune Response

The purpose of this review is to describe antifungal therapeutic candidates in preclinical and clinical development derived from, or directly influenced by, the immune system, with a specific focus on antimicrobial peptides (AMP). Although the focus of this review is AMP with direct antimicrobial effects on fungi, we will also discuss compounds with direct antifungal activity, including monoclonal antibodies (mAb), as well as immunomodulatory molecules that can enhance the immune response to fungal infection, including immunomodulatory AMP, vaccines, checkpoint inhibitors, interferon and colony stimulating factors as well as immune cell therapies. The focus of this manuscript will be a non-exhaustive review of antifungal compounds in preclinical and clinical development that are based on the principles of immunology and the authors acknowledge the incredible amount of in vitro and in vivo work that has been conducted to develop such therapeutic candidates.

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.

New Developments in Bacterial, Viral, and Fungal Cutaneous Infections

PURPOSE OF REVIEW

This review highlights clinically relevant updates to common and significant bacterial, viral, and fungal cutaneous infection within the past 5 years. Recent developments are presented so that the clinician may provide evidence-based, high-quality patient care.

RECENT FINDINGS

New resistance patterns in cutaneous pathogens have recently emerged as a result of inappropriate antimicrobial use. Several new FDA-approved antimicrobials have been approved to treat such infections, including multi-drug resistant pathogens. Several organizational guidelines for cutaneous infection management have been updated with new recommendations for screening, diagnostic, and treatment strategies.

SUMMARY

Clinicians should be aware of the most recent evidence and guidelines for the management of cutaneous infections in order to reduce the emergence of antimicrobial resistance and most effectively treat their patients.

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.

Coccidioidomycosis: Epidemiology, Fungal Pathogenesis, and Therapeutic Development

Purpose of Review

Coccidioidomycosis can result from the inhalation of infectious spores of Coccidioides species (spp.) immitis or posadasii. Clinical manifestations range from mild flu-like disease to severe disseminated infection that can require life-long therapy. Burden of this mycosis is high in the southwest region of the USA where it is well characterized, and in many areas of Mexico and Latin America where it is inadequately characterized. Here, we provide historical data and current knowledge on Coccidioides spp. pathogenesis as well as recent progress in therapeutic and vaccine development against coccidioidomycosis.

Recent Findings

The virulence mechanisms of Coccidioides spp. are largely unknown; however, production and regulation of a spherule glycoprotein, ammonium production, and melanization have all been proposed as integral factors in Coccidioides spp.' pathogenesis. Therapeutic options are limited and not 100% effective, but individualized treatment with triazoles or amphotericin B over the course of pulmonary or disseminated infection can be effective in resolution of coccidioidomycosis. Human immunization has not been achieved but efforts are ongoing.

Summary

Advances in therapeutic and vaccine development are imperative for the prevention and treatment of coccidioidomycosis, especially for those individuals at risk either living or traveling to or from endemic areas.

Coccidioidomycosis: What a long strange trip it's been

The recorded history of coccidioidomycosis began in 1892 with the report of the illness of Domingo Escurra by Alejandro Posadas followed by a description of the first North American cases by Rixford and Gilchrist. Originally considered a protozoan, William Ophüls determined that Coccidioides was a fungus and that the lungs were the apparent initial site of infection. During the 1930s, both Gifford and Dickson determined that a self-limited illness, Valley Fever, was caused by the same fungus that caused the often fatal coccidioidal granuloma. Charles Smith, over a period of approximately 2 decades, comprehensively described the clinical and geographic epidemiology of coccidioidomycosis in California. Demosthenes Pappagianis continued this work after Smith's death. In 1957, one year before Marshall Fiese published his masterful monograph on coccidioidomycosis, the use of the first effective agent for the therapy of coccidioidomycosis, amphotericin B, was reported. This was followed by descriptions of its appropriate clinical use by William Winn and by Hans Einstein, among others. The development of the much less toxic azole antifungal agents greatly simplified therapy in many cases, but much of the management of patients with coccidioidomycosis still relies more on art than science. The search for the “Holy Grail” - a vaccine capable of preventing this disease-continues.

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.

Dendritic cell-based immunization induces Coccidioides Ag2/PRA-specific immune response

Valley Fever, or coccidioidomycosis, is caused by a soil-borne, highly virulent fungal pathogen, Coccidioides spp. Infection with Coccidioides can be life-threatening. Since an effective treatment is not available and the T cell-mediated immune response is protective, vaccine development is of interest. In this study, a primary dendritic cell (DC)-vaccine was evaluated for its ability to stimulate Coccidioides antigen-specific immune response in an extremely susceptible BALB/c mouse model. The DC-vaccine (Ag2-DC) was prepared by non-virally transfecting the primary bone marrow-derived DCs with a plasmid DNA encoding Ag2/PRA (protective epitope of Coccidioides). Mice were intranasally immunized with Ag2-DC on days 2 and 10. Immunized mice were necropsied on days 8, 32, and 44. Major organs and blood samples were harvested. The most common indicators of injury (protein, lactate, and albumin), Ag/PRA-specific cytokine-secreting cells, and IgG and its isotypes were determined by biochemical and immunologic assays, respectively. No signs of sickness were noted. Similarly, no significant changes were observed in the levels of total lung protein, lactate, and albumin, in immunized mice compared with healthy control mice. Interferon (IFN-γ), and interleukin (IL)-4 and IL-17 cytokine-secreting cells were observed in lung and lymph nodes upon Ag2-DC immunization. Our results showed that the levels of serum IgG and its isotypes were increased in Ag2-DC-immunized mice. This report provides evidence of DC immunization-stimulated Ag2/PRA-specific immune responses.

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.

Molecular characterization and identification of facilitative glucose transporter 2 (GLUT2) and its expression and of the related glycometabolism enzymes in response to different starch levels in blunt snout bream (Megalobrama amblycephala)

Facilitative glucose transporters (GLUT) are transmembrane transporters involved in glucose transport across the plasma membrane. In this study, blunt snout bream GLUT2 gene was cloned, and its expression in various tissues and in liver in response to diets with different carbohydrate levels (17.1; 21.8; 26.4; 32.0; 36.3; and 41.9% of dry matter). Blunt snout bream GLUT2 was also characterized. A full-length cDNA fragment of 2577 bp was cloned, which contains a 5'-untranslated region (UTR) of 73 bp, a 3'-UTR of 992 bp, and an open reading frame of 1512 bp that encodes a polypeptide of 503 amino acids with predicted molecular mass of 55.046 kDa and theoretical isoelectric point was 7.52. The predicted GLUT2 protein has 12 transmembrane domains between amino acid residues at 7-29; 71-93; 106-123; 133-155; 168-190; 195-217; 282-301; 316-338; 345-367; 377-399; 412-434; and 438-460. Besides, the conservative structure domains located at 12-477 amino acids belong to the sugar porter family which is the major facilitator superfamily (MFS) of transporters. Blunt snout bream GLUT2 had the high degree of sequence identity to four GLUT2s from zebrafish, chicken, human, and mouse, with 91, 63, 57, and 54% identity, respectively. Quantitative real-time (qRT) PCR assays revealed that GLUT2 expression was high in the liver, intestine, and kidney; highest in the liver and was regulated by carbohydrate intake. Compared with the control group (17.1%), fed by 3 h with higher starch levels (32.0; 36.3; and 41.9%), increased plasma glucose levels and glycemic level went back to basal by 24 h after treatment. Furthermore, higher dietary starch levels significantly increase GLUT2, glucokinase (GK), and pyruvate kinase (PK) expression and concurrently decrease phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6P) mRNA levels (P < 0.05), and these changes were also back to basal levels after 24 h of any dietary treatment. These results indicate that the blunt snout bream is able to regulate their ability to metabolize glucose by improving GLUT2, GK, and PK expression levels and decreasing PEPCK and G6P expression levels.

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.