Efficacy of Voriconazole against Aspergillus fumigatus Infection Depends on Host Immune Function

Abstract

Antifungal therapy can fail in a remarkable number of patients with invasive fungal disease, resulting in significant morbidity worldwide. A major contributor to this failure is that while these drugs have high potency in vitro, we do not fully understand how they work inside infected hosts. Here, we used a transparent larval zebrafish model of Aspergillus fumigatus infection amenable to real-time imaging of invasive disease as an in vivo intermediate vertebrate model to investigate the efficacy and mechanism of the antifungal drug voriconazole. We found that the ability of voriconazole to protect against A. fumigatus infection depends on host innate immune cells and, specifically, on the presence of macrophages. While voriconazole inhibits fungal spore germination and growth in vitro, it does not do so in larval zebrafish. Instead, live imaging of whole, intact larvae over a multiday course of infection revealed that macrophages slow down initial fungal growth, allowing voriconazole time to target and kill A. fumigatus hyphae postgermination. These findings shed light on how antifungal drugs such as voriconazole may synergize with the immune response in living hosts.

Evolving moldy murderers: Aspergillus section Fumigati as a model for studying the repeated evolution of fungal pathogenicity

“…The most severe form of aspergillosis is invasive aspergillosis, which primarily affects individuals with compromised immune systems or preexisting lung conditions [3]. Since drugs targeting invasive aspergillosis are not always effective due to our lack of understanding of how they function inside the human host [4] and the evolution of drug resistance [5,6], infected individuals suffer high morbidity and mortality [7]. Collectively, Aspergillus fungi affect millions of patients and cause hundreds of thousands of life-threatening infections every year [8,9].…”

The Diverse Roles of Phagocytes During Bacterial and Fungal Infections and Sterile Inflammation: Lessons From Zebrafish

“…This delay promotes the persistence of the fungus by preventing neutrophil recruitment and subsequent neutrophil-mediated killing (9). Moreover, the retardation of fungal germination allows certain fungicidal drugs, such as voriconazole, to target and kill predominantly A. fumigatus hyphae (97). In light of growing antifungal resistances and inexplicable treatment failures, the larval zebrafish A. fumigatus infection model provides an ideal platform for studying drug efficacy and their mechanistic impact on aspergillosis (97).…”

“…Moreover, the retardation of fungal germination allows certain fungicidal drugs, such as voriconazole, to target and kill predominantly A. fumigatus hyphae (97). In light of growing antifungal resistances and inexplicable treatment failures, the larval zebrafish A. fumigatus infection model provides an ideal platform for studying drug efficacy and their mechanistic impact on aspergillosis (97). Once the infection progressed further, fungal germination occasionally occured in the late phagosome causing subsequent macrophage necroptosis (98).…”

Illuminating Macrophage Contributions to Host-Pathogen Interactions In Vivo : the Power of Zebrafish

“…Because macrophages are a key first responder to many pathogens, other studies have implicated macrophages as a cell type that could be targeted with host-directed therapies to increase pathogen control. For example, the antifungal drug voriconazole requires the presence of macrophages for efficacy against A. fumigatus infection in larval zebrafish (42). Matty et al took this one step further, performing a chemical screen for drugs that specifically inhibit M. marinum growth inside live hosts (16).…”

“…Fungal pathogens can also utilize macrophages as a protective niche against other, more microbicidal, immune cells, such as neutrophils. In A. fumigatus infections, macrophages are the major cell type responsible for inhibiting spore germination into hyphae in vivo (42,49). By inhibiting this germination, macrophages actually inhibit neutrophil recruitment and neutrophil-mediated killing, both of which are primarily driven by hyphal forms of A. fumigatus (49).…”