Spotlight on Three Rs Progress.

Abstract

The mechanisms by which viruses evolve new characteristics (e.g. resistance to therapy) when passing between human hosts have been challenging to study, partly due to the scarcity of appropriate preclinical models, and the complexity and costs of the studies required. To determine whether this gap could be addressed with microfluidics technology, Si et al. created a system of interconnected human lung organ-on-a-chip devices that permitted the sequential passage of virus strains via the air channel and the administration of antivirals via the blood channel. Drug pressure was applied by infecting the chips with an influenza virus (H1N1) and treating them with known antiviral medication (amantadine or oseltamivir). Both drugs became less effective with increasing passages. The same approach was used to test the human serine protease inhibitor, nafamostat, which did not induce viral resistance. The data obtained with the chip system are in agreement with that from the clinic, in that the drugs targeting viral proteins led to the emergence of resistant strains, while the drug targeting the host protein did not, even after 30 chip-to-chip passages. Furthermore, the systemwas inoculatedwith three virus strains at the same time (one drug-sensitive, and two amantadineand oseltamivir-resistant, respectively) in the presence of oseltamivir and amantadine. Sequencing revealed the presence of double mutant strains that were resistant to both drugs. To test whether the system could support influenza virus antigenic shift through gene reassortment, as is the case when different virus strains coinfect the same host, two influenza strains (H3N2 and H1N1) were introduced into the system. After two days, viruses were isolated and their genome sequenced to identify the presence of novel strains. While parental viral strains were the most common, distinct genotypes were detected. Of note, one of the reassortants predicted by the on-chip system was detected in patients during an influenza season in which H1N1 and H3N2 cocirculated. A deeper understanding of the mutation and gene reassortment mechanisms involved in viral infections, and a better ability to predict the evolution of viral resistance will improve society’s preparedness to fight global threats due to viral infections. This in vitro system might represent a potential tool in such cases by permitting the study of within-host viral evolution, including of viral drug resistance and likely future mutations.