Mycovirus therapy for invasive pulmonary aspergillosis?

Medical Mycology, 2019, 57, S179–S188 doi: 10.1093/mmy/myy073 Review Article Review Article Mycovirus therapy for invasive pulmonary aspergillosis? Wendy W. J. van de Sande∗ and Alieke G. Vonk ∗ To whom correspondence should be addressed. Wendy W. J. van de Sande, PhD, ErasmusMC, Department of Medical Microbiology and Infectious Diseases, Wytemaweg 80, 3015 CE Rotterdam, The Netherlands. E-mail: Received 25 April 2018; Revised 21 June 2018; Editorial Decision 24 July 2018 Abstract With the current revived interest in the use of bacteriophages for the treatment of bacterial infections, the study of mycoviruses as novel therapeutic solutions for invasive aspergillosis is the logical next step. Although ssRNA, dsRNA, and ssDNA mycoviruses have been identified, the majority of characterised mycoviruses have dsRNA genomes. Prevalence of dsRNA mycoviruses in Aspergillus spp. varies, and mycoviruses can have different effects on their fungal hosts: hypovirulence, hypervirulence, or a killer phenotype. Therapeutically, extracellular transmission of the mycovirus is essential. DsRNA mycoviruses lack an extracellular phase; however, a single ssDNA mycovirus with homologues in Aspergillus genomes has been described with an extracellular mode of transmission. Mycoviruses can induce hypovirulence or a killer phenotype, and both can be exploited therapeutically. Mycoviruses inducing hypovirulence have been used to control chestnut blight, however for aspergillosis no such mycovirus has been identified yet. Mycovirus encoded killer toxins or anti-idiotypic antibodies and killer peptides derived from these have been demonstrated to control fungal infections including aspergillosis in animals. This indicates that mycoviruses inducing both phenotypes could be exploited therapeutically as long as the right mycovirus has been identified. Introduction The large and unmet clinical need for new antifungal agents is continuously growing. This growth is due to the increased number of immunocompromised patients with severe fungal infections such as invasive (pulmonary) aspergillosis (IA).1 The morbidity and mortality rates of IA are high despite antifungal treatment.2 Only a few antifungal agents are used to treat IA and azole resistance is emerging in Aspergillus fumigatus.3 To be able to combat invasive fungal infection in the future, new therapeutic solutions are needed. In homology to the difficult to treat respiratory fungal infections, bacterial respiratory tract infections are increasingly difficult to treat due to evolving antibiotic resistance.4 This gave rise to a renewed interest in the use of bacteriophages to treat bacterial infections. Bacteriophages selectively infect bacteria and can either enter into a lytic cycle where the virus replicates and lyses the cell or into a lysogenic cycle in which the prophage is integrated into the bacterial genome.4 Preclinical studies in which bacteriophages were used to treat experimentally induced respiratory infections caused by Pseudomonas aeruginosa, Escherichia coli, Klebsiella pneumoniae, Burkholderia cepacia, or Staphylococcus aureus are supportive in the use of bacteriophages as therapeutic strategy.4,5 For instance, in a murine model of a chronic P. aeruginosa lung infection intranasal administered phage PELP20 24 to 60 hours post infection resulted in complete clearance of P. aeruginosa from the lungs.5 Also, intranasal administration of a single dose of phage 1513 in a lethal multidrug resistant K. pneumoniae mouse model 2 hours post-infection was able to save mice from a lethal pneumonia.6 Next to being effective in mice, it also appeared to be effective in human. For instance, a cystic fibrosis patient with a multidrug resistant Achromobacter xylosoxidans chronic lung infection was treated successfully with an Achromobacter bacteriophage cocktail.7 A patient with a multidrug resistant P. aeruginosa septicaemia was treated with purified phage cocktail BFC1 for 10 days and blood cultures turned negative, C-reactive protein levels dropped and fever disappeared.8 Next to individual patients, the efficacy of a  C The Author(s) 2019. Published by Oxford University Press on behalf of The International Society for Human and Animal Mycology. All rights reserved. For permissions, please e-mail: S179 ErasmusMC, Department of Medical Microbiology and Infectious Diseases, Wytemaweg 80, 3015 CE Rotterdam, The Netherlands S180 Characteristics of a mycovirus for therapeutic use Not every mycovirus can be used as a therapeutic antifungal agent. For successful mycoviral therapy; several conditions need to be met (Fig. 1). First of all, the mycovirus should be deliverable by inhalation or injection to reach the fungus in the lung and subsequently infect the fungus. When the fungus is infected, it should either induce hypovirulence, which halts the infection, lyse the fungal cell, or induce a killer phenotype in which the fungi in the surroundings are killed. On top of that, the mycovirus itself should not be antigenic or in any other way cause harm to the patient. Mycoviruses and their prevalence Mycoviruses were described for the first time in 1962,11 and since then several different families of fungal viruses have been identified. The viruses identified so far are divided into viruses with a linear dsRNA genome, a linear positive-sense ssRNA (+RNA) genome, a linear negative-sense ssRNA (−RNA) genome or with a circular ssDNA genome.12 Currently, mycoviruses with dsDNA genome are not described13 (Table 1). Based on total RNA sequencing, it is estimated that 73– 75.4% of identified mycoviruses have a ssRNA genome, and only 8.8–15% of identified mycoviruses have a dsRNA genome.14,15 However, since research so far has concentrated on the identification of dsRNA mycoviruses, the majority of the characterised mycoviruses have dsRNA genomes and are grouped in eight different families: Alternaviridae, Chrysoviridae, Endornaviridae, Megabirnaviridae, Quadriviridae, Partititviridae, Reoviridae, and Totiviridae. The families mainly differ in the number of genome segments and the way they are packaged. An almost universal trait of the dsRNA mycovirus is the presence of capsids, which are selectively porous protein compartments in which the genome and replicas are contained. DsRNA mycoviruses are not surrounded by an envelope.16 Regarding Aspergillus spp., although in the genomes of A. fumigatus, A. nidulans, and A. niger ssDNA mycovirussequences resembling the sequences of Sclerotinia sclerotiorum hypovirulence-associated DNA virus 1 (SsHADV-1)17 have been found,18 no ssDNA mycoviruses were identified, and the only described mycoviruses in Aspergillus have a dsRNA genome.12 The prevalence of dsRNA mycoviruses in Aspergillus spp. ranged from 0 to 25.4% and was dependent on the species evaluated and the group size (Table 2). One of the first groups to determine the prevalence of mycoviruses in Aspergillus spp. was that of Varga et al., who det (...truncated)