Vaccine-Induced Immunological Memory in Invasive Fungal Infections - A Dream so Close yet so Far

Vaccine Strategies for Cryptococcus neoformans

Cryptococcus neoformans infections are a major worldwide concern as current treatment strategies are becoming less effective in alleviating the infection. The most extreme and fatal cases are those of immunocompromised individuals. Clinical treatments for cryptococcosis are limited to a few classes of approved drugs, and due to a rise in drug resistance, these drugs are becoming less effective. Therefore, it is essential to develop innovative ways to control this infection. Vaccinations have emerged as a safe, viable, and cost-effective solution to treat a number of diseases over the years. Currently, there are no clinically available vaccines to treat cryptococcal infections, but a number of studies have shown promising results in animal models. Here, we present step-by-step experimental protocols using live-attenuated or heat-killed C. neoformans cells as a vaccination strategy in a preventive or in a therapeutic murine model of cryptococcosis.

Modulatory immune responses in fungal infection associated with organ transplant - advancements, management, and challenges

Organ transplantation stands as a pivotal achievement in modern medicine, offering hope to individuals with end-stage organ diseases. Advancements in immunology led to improved organ transplant survival through the development of immunosuppressants, but this heightened susceptibility to fungal infections with nonspecific symptoms in recipients. This review aims to establish an intricate balance between immune responses and fungal infections in organ transplant recipients. It explores the fundamental immune mechanisms, recent advances in immune response dynamics, and strategies for immune modulation, encompassing responses to fungal infections, immunomodulatory approaches, diagnostics, treatment challenges, and management. Early diagnosis of fungal infections in transplant patients is emphasized with the understanding that innate immune responses could potentially reduce immunosuppression and promise efficient and safe immuno-modulating treatments. Advances in fungal research and genetic influences on immune-fungal interactions are underscored, as well as the potential of single-cell technologies integrated with machine learning for biomarker discovery. This review provides a snapshot of the complex interplay between immune responses and fungal infections in organ transplantation and underscores key research directions.

Palatal perforation caused by Alternaria alternata infection in an immunocompetent adolescent

Opportunistic oral mucosal fungal infection caused by Alternaria alternata is extremely rare. Herein, we present a rare palatal perforation as a result of oral infection caused by A. alternata in an immunocompetent adolescent. An 18-year-old boy, who had previously been healthy, was admitted to our institution with persistent pain in the palate for the past 12 months. Upon impression of palatal bone resorption based on computed tomography imaging and chronic granulomatous inflammation based on biopsy (hematoxylin-eosin staining), the patient was examined for commonly relevant causes such as potential tumor and Mycobacterium tuberculosis infection. All test results were inconclusive. After a thorough diagnostic investigation, an unusual fungal infection, A. alternata infection, was confirmed by next-generation sequencing and biopsy (periodic acid-Schiff staining and immunofluorescence staining). The patient underwent surgical debridement and was subjected to voriconazole treatment postoperatively for over a period of 5 months. Thus, these findings highlight the importance of considering A. alternata as a potential pathogenic factor in an etiological palatal perforation.

Candidiasis: From cutaneous to systemic, new perspectives of potential targets and therapeutic strategies

Candidiasis is an infection caused by fungi from a Candida species, most commonly Candida albicans. C. albicans is an opportunistic fungal pathogen typically residing on human skin and mucous membranes of the mouth, intestines or vagina. It can cause a wide variety of mucocutaneous barrier and systemic infections; and becomes a severe health problem in HIV/AIDS patients and in individuals who are immunocompromised following chemotherapy, treatment with immunosuppressive agents or after antibiotic-induced dysbiosis. However, the immune mechanism of host resistance to C. albicans infection is not fully understood, there are a limited number of therapeutic antifungal drugs for candidiasis, and these have disadvantages that limit their clinical application. Therefore, it is urgent to uncover the immune mechanisms of the host protecting against candidiasis and to develop new antifungal strategies. This review synthesizes current knowledge of host immune defense mechanisms from cutaneous candidiasis to invasive C. albicans infection and documents promising insights for treating candidiasis through inhibitors of potential antifungal target proteins.

Addressing Microbial Resistance Worldwide: Challenges over Controlling Life-Threatening Fungal Infections

Fungal infections are a serious global concern because of their ability to spread and colonize host tissues in immunocompromised individuals. Such infections have been frequently reported worldwide and are currently gaining clinical research relevance owing to their resistant character, representing a bottleneck in treating affected people. Resistant fungi are an emergent public health threat. The upsurge of such pathogens has led to new research toward unraveling the destructive potential evoked by these species. Some fungi-grouped into Candida, Aspergillus, and Cryptococcus-are causative agents of severe and systemic infections. They are associated with high mortality rates and have recently been described as sources of coinfection in COVID-hospitalized patients. Despite the efforts to elucidate the challenges of colonization, dissemination, and infection severity, the immunopathogenesis of fungal diseases remains a pivotal characteristic in fungal burden elimination. The struggle between the host immune system and the physiological strategies of the fungi to maintain cellular viability is complex. In this brief review, we highlight the relevance of drug resistance phenotypes in fungi of clinical significance, taking into consideration their physiopathology and how the scientific community could orchestrate their efforts to avoid fungal infection dissemination and deaths.

C-type lectin receptors in antifungal immunity: Current knowledge and future developments

C-type lectin receptors (CLRs) constitute a category of innate immune receptors that play an essential role in the antifungal immune response. For over two decades, scientists have uncovered what are the fungal ligands recognized by CLRs and how these receptors initiate the immune response. Such studies have allowed the identification of genetic polymorphisms in genes encoding for CLRs or for proteins involved in the signalisation cascade they trigger. Nevertheless, our understanding of how these receptors functions and the full extent of their function during the antifungal immune response is still at its infancy. In this review, we summarize some of the main findings about CLRs in antifungal immunity and discuss what the future might hold for the field.

Synergistic antifungal interaction of N-(butylcarbamothioyl) benzamide and amphotericin B against Cryptococcus neoformans

Introduction

Cryptococcus neoformans is one of the leading causes of invasive fungal infections worldwide. Cryptococcal meningoencephalitis is the main challenge of antifungal therapy due to high morbidity and mortality rates, especially in low- and middle-income countries. This can be partly attributed to the lack of specific diagnosis difficulty accessing treatment, antifungal resistance and antifungal toxicity.

Methods

In the present study, the effect of the synthetic thiourea derivative N-(butylcarbamothioyl) benzamide (BTU-01), alone and combined with amphotericin B (AmB), was evaluated in planktonic and sessile (biofilm) cells of C. neoformans.

Results

BTU-01 alone exhibited a fungistatic activity with minimal inhibitory concentrations (MICs) ranging from 31.25 to 62.5 μg/mL for planktonic cells; and sessile MICs ranging from 125.0 to 1000.0 μg/mL. BTU-01 caused a concentration-dependent inhibitory activity on cryptococcal urease and did not interfere with plasma membrane fluidity. Molecular docking was performed on Canavalia ensiformis urease, and BTU-01 showed relevant interactions with the enzyme. The combination of BTU-01 and AmB exhibited synergistic fungicidal activity against planktonic and sessile cells of C. neoformans. Microscopic analysis of C. neoformans treated with BTU-01, alone or combined with AmB, revealed a reduction in cell and capsule sizes, changes in the morphology of planktonic cells; a significant decrease in the number of cells within the biofilm; and absence of exopolymeric matrix surrounding the sessile cells. Neither hemolytic activity nor cytotoxicity to mammalian cells was detected for BTU-01, alone or combined with AmB, at concentrations that exhibited antifungal activity. BTU-01 also displayed drug-likeness properties.

Conclusion

These results indicate the potential of BTU-01, for the development of new strategies for controlling C. neoformans infections.

Vaccination with Live or Heat-Killed Aspergillus fumigatus ΔsglA Conidia Fully Protects Immunocompromised Mice from Invasive Aspergillosis

Aspergillus fumigatus causes invasive aspergillosis (IA) in immunocompromised patients, resulting in high mortality rates. Currently, no vaccine formulations to promote immune protection in at-risk individuals have been developed. In this work, we deleted the sterylglucosidase-encoding gene, sglA, in Aspergillus fumigatus and investigated its role in fungal virulence and host vaccine protection. The ΔsglA mutant accumulated sterylglucosides (SGs), newly studied immunomodulatory glycolipids, and exhibited reduced hyphal growth and altered compositions of cell wall polysaccharides. Interestingly, the ΔsglA mutant was avirulent in two murine models of IA and was fully eliminated from the lungs. Both corticosteroid-induced immunosuppressed and cyclophosphamide-induced leukopenic mice vaccinated with live or heat-killed ΔsglA conidia were fully protected against a lethal wild-type A. fumigatus challenge. These results highlight the potential of SG-accumulating strains as safe and promising vaccine formulations against invasive fungal infections. IMPORTANCE Infections by Aspergillus fumigatus occur by the inhalation of environmental fungal spores called conidia. We found that live mutant conidia accumulating glycolipids named sterylglucosides are not able to cause disease when injected into the lung. Interestingly, these animals are now protected against a secondary challenge with live wild-type conidia. Remarkably, protection against a secondary challenge persists even with vaccination with heat-killed mutant conidia. These results will significantly advance the field of the research and development of a safe fungal vaccine for protection against the environmental fungus A. fumigatus.

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.

The prophylactic effects of monoclonal antibodies targeting the cell wall Pmt4 protein epitopes of Candida albicans in a murine model of invasive candidiasis

Candida albicans (C. albicans) is the most prevalent opportunistic human pathogen, accounting for approximately half of all clinical cases of candidemia. Resistance to the existing antifungal drugs is a major challenge in clinical therapy, necessitating the development and identification of novel therapeutic agents and potential treatment strategies. Monoclonal antibody-based immunotherapy represents a promising therapeutic strategy against disseminated candidiasis. Protein mannosyltransferase (Pmt4) encodes mannosyltransferases initiating O-mannosylation of secretory proteins and is essential for cell wall composition and virulence of C. albicans. Therefore, the Pmt4 protein of C. albicans is an attractive target for the discovery of alternative antibody agents against invasive C. albicans infections. In the present study, we found that monoclonal antibodies (mAbs) C12 and C346 specifically targeted the recombinant protein mannosyltransferase 4 (rPmt4p) of C. albicans. These mAbs were produced and secreted by hybridoma cells isolated from the spleen of mice that were initially immunized with the purified rPmt4p to generate IgG antibodies. The mAbs C12 and C346 exhibited high affinity to C. albicans whole cells. Remarkably, these mAbs reduced the fungal burden, alleviated inflammation in the kidneys, and prolonged the survival rate significantly in the murine model of systemic candidiasis. Moreover, they could activate macrophage opsonophagocytic killing and neutrophil killing of C. albicans strain in vitro. These results suggested that anti-rPmt4p mAbs may provide immunotherapeutic interventions against disseminated candidiasis via opsonophagocytosis and opsonic killing activity. Our findings provide evidence for mAbs as a therapeutic option for the treatment of invasive candidiasis.

Antibodies targeting Candida albicans Als3 and Hyr1 antigens protect neonatal mice from candidiasis

Pre-term infants in neonatal intensive care units are vulnerable to fungal sepsis. In this patient population, Candida albicans remains the predominant fungal pathogen causing high morbidity and mortality, despite antifungal therapy. Thus, new preventative/therapeutic strategies against neonatal candidiasis are needed. Previously, we have reported that vaccination with recombinant forms of the C. albicans N-termini of the cell wall proteins Als3 (rAls3p-N) and Hyr1 (rHyr1p-N) protected adult mice from disseminated candidiasis. Further, in a Phase 1b/2a NDV-3A (an rAls3p-N formulated with alum) protected women from recurrent vulvovaginal candidiasis, with anti-Als3p IgG2 isotype being a biomarker for efficacy. Here, we performed a proof of concept study to evaluate if anti-Als3p or anti-Hyr1p antibodies are important for prevention of disseminated candidiasis in neonates. Als3 and Hyr1 antigens when adjuvanted with complete Freund’s adjuvant (CFA)/incomplete Freund’s adjuvant (IFA) induced a robust antibody response with a ten-fold higher titer of IgG2, than attained by either antigen formulated with alum. Transplacental transfer of these antibodies significantly reduced fungal burden in the kidneys of mice pups, and adoptive transfer of vaccinated mothers’ sera into pups displayed similar levels of protection. Neutrophils were found important for this efficacy. Finally, anti-Hyr1 antisera potentiated the activity of fluconazole in protecting from C. albicans infection. Our current studies are the first in the field to emphasize the importance of anti-Als3 and anti-Hyr1 antibodies in preventing neonatal candidiasis. Considering that Candida infections in low birthweight infants is a lethal infection, active and passive vaccination strategies using these antigens could have profound clinical relevance.

Immunity to Invasive Fungal Diseases

Invasive fungal diseases are rare in individuals with intact immunity. This, together with the fact that there are only a few species that account for most mycotic diseases, implies a remarkable natural resistance to pathogenic fungi. Mammalian immunity to fungi rests on two pillars, powerful immune mechanisms and elevated temperatures that create a thermal restriction zone for most fungal species. Conditions associated with increased susceptibility generally reflect major disturbances of immune function involving both the cellular and humoral innate and adaptive arms, which implies considerable redundancy in host defense mechanisms against fungi. In general, tissue fungal invasion is controlled through either neutrophil or granulomatous inflammation, depending on the fungal species. Neutrophils are critical against Candida spp. and Aspergillus spp. while macrophages are essential for controlling mycoses due to Cryptococcus spp., Histoplasma spp., and other fungi. The increasing number of immunocompromised patients together with climate change could significantly increase the prevalence of fungal diseases.

Expected final online publication date for the Annual Review of Immunology, Volume 40 is April 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Antibody- Based Immunotherapy Combined With Antimycotic Drug TMP- SMX to Treat Infection With Paracoccidioides brasiliensis

Monoclonal antibodies (mAbs) are promising alternatives to treat infectious diseases, especially given their potential for applications in combination therapies with antimicrobial drugs to enhance the antifungal efficacy. Protection mediated by mAbs used to treat experimental paracoccidioidomycosis (PCM) has been demonstrated previously. Our aim in the present work was to characterize a monoclonal antibody (mAbF1.4) raised against a cell wall glycoconjugate fraction of Paracoccidioides spp. and to analyze its efficacy combined with trimethoprim-sulfamethoxazole (TMP/SMX) as treatment for experimental PCM. We demonstrated that the epitope recognized by mAbF1.4 is consistent with branched glucose residues present on a cell wall β-glucan polymer. In vitro, mAbF1.4 increased the phagocytic capacity and nitric oxide concentration induced by the macrophage cell line J774.1A, and this resulted in a significant reduction in the viability of the opsonophagocytized yeasts. In vivo, we detected a significant reduction in pulmonary fungal burdens of mice treated with mAbF1.4 in association with TMP/SMX, which correlated with increased pulmonary concentrations (determined by ELISA) of IFN- γ, TNF-α, IL-10 and IL-17. In parallel, we observed a decrease in IL-4, suggesting that the treatment was associated with a mixed Th1-Th17 type immune response. Histopathology of lung segments from mice receiving the combination therapy showed a significant reduction in granulomas, which were well-defined, and improved maintenance of lung architecture. These findings demonstrate that mAbF1.4 + TMP/SMX therapy is a promising approach to combat PCM as well as decrease disease sequelae and highlights the potential benefits of immune mediators in PCM combined immunotherapy.