In vitro system for modeling influenza A virus resistance under drug pressure.

One of the biggest challenges in the effort to treat and contain influenza A virus infections is the emergence of resistance during treatment. It is well documented that resistance to amantadine arises rapidly during the course of treatment due to mutations in the gene coding for the M2 protein. To address this problem, it is critical to develop experimental systems that can accurately model the selection of resistance under drug pressure as seen in humans. We used the hollow-fiber infection model (HFIM) system to examine the effect of amantadine on the replication of influenza virus, A/Albany/1/98 (H3N2), grown in MDCK cells. At 24 and 48 h postinfection, virus replication was inhibited in a dose-dependent fashion. At 72 and 96 h postinfection, virus replication was no longer inhibited, suggesting the emergence of amantadine-resistant virus. Sequencing of the M2 gene revealed that mutations appeared at between 48 and 72 h of drug treatment and that the mutations were identical to those identified in the clinic for amantadine-resistant viruses (e.g., V27A, A30T, and S31N). Interestingly, we found that the type of mutation was strongly affected by the dose of the drug. The data suggest that the HFIM is a good model for influenza virus infection and resistance generation in humans. The HFIM has the advantage of being a highly controlled system where multiplicity parameters can be directly and accurately controlled and measured.