Nanobody-mediated neutralization of candidalysin prevents epithelial damage and inflammatory responses that drive vulvovaginal candidiasis pathogenesis.

Candida albicans can cause mucosal infections in humans. This includes oropharyngeal candidiasis, which is commonly observed in human immunodeficiency virus infected patients, and vulvovaginal candidiasis (VVC), which is the most frequent manifestation of candidiasis. Epithelial cell invasion by C. albicans hyphae is accompanied by the secretion of candidalysin, a peptide toxin that causes epithelial cell cytotoxicity. During vaginal infections, candidalysin-driven tissue damage triggers epithelial signaling pathways, leading to hyperinflammatory responses and immunopathology, a hallmark of VVC. Therefore, we proposed blocking candidalysin activity using nanobodies to reduce epithelial damage and inflammation as a therapeutic strategy for VVC. Anti-candidalysin nanobodies were confirmed to localize around epithelial-invading C. albicans hyphae, even within the invasion pocket where candidalysin is secreted. The nanobodies reduced candidalysin-induced damage to epithelial cells and downstream proinflammatory responses. Accordingly, the nanobodies also decreased neutrophil activation and recruitment. In silico mathematical modeling enabled the quantification of epithelial damage caused by candidalysin under various nanobody dosing strategies. Thus, nanobody-mediated neutralization of candidalysin offers a novel therapeutic approach to block immunopathogenic events during VVC and alleviate symptoms.IMPORTANCEWorldwide, vaginal infections caused by Candida albicans (VVC) annually affect millions of women, with symptoms significantly impacting quality of life. Current treatments are based on anti-fungals and probiotics that target the fungus. However, in some cases, infections are recurrent, called recurrent VVC, which often fails to respond to treatment. Vaginal mucosal tissue damage caused by the C. albicans peptide toxin candidalysin is a key driver in the induction of hyperinflammatory responses that fail to clear the infection and contribute to immunopathology and disease severity. In this pre-clinical evaluation, we show that nanobody-mediated candidalysin neutralization reduces tissue damage and thereby limits inflammation. Implementation of candidalysin-neutralizing nanobodies may prove an attractive strategy to alleviate symptoms in complicated VVC cases.

The impact of the Fungus-Host-Microbiota interplay upon Candida albicans infections: current knowledge and new perspectives.

Candida albicans is a major fungal pathogen of humans. It exists as a commensal in the oral cavity, gut or genital tract of most individuals, constrained by the local microbiota, epithelial barriers and immune defences. Their perturbation can lead to fungal outgrowth and the development of mucosal infections such as oropharyngeal or vulvovaginal candidiasis, and patients with compromised immunity are susceptible to life-threatening systemic infections. The importance of the interplay between fungus, host and microbiota in driving the transition from C. albicans commensalism to pathogenicity is widely appreciated. However, the complexity of these interactions, and the significant impact of fungal, host and microbiota variability upon disease severity and outcome, are less well understood. Therefore, we summarise the features of the fungus that promote infection, and how genetic variation between clinical isolates influences pathogenicity. We discuss antifungal immunity, how this differs between mucosae, and how individual variation influences a person's susceptibility to infection. Also, we describe factors that influence the composition of gut, oral and vaginal microbiotas, and how these affect fungal colonisation and antifungal immunity. We argue that a detailed understanding of these variables, which underlie fungal-host-microbiota interactions, will present opportunities for directed antifungal therapies that benefit vulnerable patients.

Binary interactions between the yeast Candida albicans and two gut-associated Bacteroides species.

The yeast Candida albicans forms part of the natural gut microbiota of healthy human individuals and its interactions with other microbial symbionts can impact host well-being. We therefore studied binary interactions between potentially pathogenic representatives of the gut-associated bacterial genus Bacteroides and C. albicans using anaerobic bacteria/yeast co-cultures prepared with a quarter-strength brain heart infusion (» BHI; 9.25 g/l) broth. We found that, except for minor changes observed in the cell numbers of one out of four C. albicans strains tested, yeast growth was largely unaffected by the presence of the bacteria. In contrast, growth of Bacteroides fragilis NCTC 9343 and Bacteroides vulgatus ATCC 8482 was significantly enhanced in the presence of C. albicans. Supplementation of Bacteroides monocultures with dead Candida albicans CAB 392 cells, containing intact outer cell wall mannan layers, resulted in increased bacterial concentrations. Subsequent culturing of the Bacteroides strains in a liquid minimal medium supplemented with candidal mannan demonstrated that B. vulgatus ATCC 8482, unlike B. fragilis NCTC 9343, utilized the mannan. Furthermore, by reducing the initial oxygen levels in monocultures prepared with » BHI broth, bacterial numbers were significantly enhanced compared to in monocultures prepared with » BHI broth not supplemented with the reducing agent l-cysteine hydrochloride. This suggests that C. albicans can stimulate Bacteroides growth via aerobic respiration and/or antioxidant production. The cell-free supernatant of 24-h-old C. albicans CAB 392 monocultures was also found to increase Bacteroides growth and chloramphenicol sensitivity.