Polyomavirus microRNAs circulating in biological fluids during viral persistence

Increasing evidence suggests that microRNA-mediated gene silencing, detected during exosome intercellular communication between cells, may be exploited by persistent human viruses. Recently, it has been reported that human polyomaviruses encode microRNAs that downregulate large T expression and target host factors, helping the virus to escape immune elimination. Consequently, viral microRNAs and their genetic variability may have roles in the induction of polyomavirus reactivation, the success of persistence or replication and the development of diseases. In vitro experiments have detected polyomavirus JC (JCPyV) microRNAs in exosomes obtained from cell supernatants after viral infection and showed that they can be carried into uninfected cells. JCPyV and BKPyV microRNAs have been sought in clinical samples obtained from patients with or at risk of severe polyomavirus-associated diseases and from healthy subjects. Variable expressions of JCPyV and BKPyV microRNAs circulating in blood, urine, and cerebrospinal fluid samples were found in patients who were polyomavirus DNA positive and were also observed in negative subjects. Differences in the relationship between the JCPyV and BKPyV microRNA expressions and viral DNA load have been observed. All the data point towards a potential role of polyomavirus exosome microRNAs in viral persistence and suggest that further work is warranted to define their role in viral reactivation and to identify potential new antiviral strategies targeting these viruses.