Generation and characterization of recombinant pandemic influenza A(H1N1) viruses resistant to neuraminidase inhibitors.

BACKGROUND Neuraminidase inhibitors (NAIs) play a key role in the management of influenza epidemics and pandemics. Given the novel pandemic influenza A(H1N1) (pH1N1) virus and the restricted number of approved anti-influenza drugs, evaluation of potential drug-resistant variants is of high priority. METHODS Recombinant pH1N1 viruses were generated by reverse genetics, expressing either the wild-type or any of 9 mutant neuraminidase (NA) proteins (N2 numbering: E119G, E119V, D198G, I222V, H274Y, N294S, S334N, I222V-H274Y, and H274Y-S334N). We evaluated these recombinant viruses for their resistance phenotype to 4 NAIs (oseltamivir, zanamivir, peramivir, and A-315675), NA enzymatic activity, and replicative capacity. RESULTS The E119G and E119V mutations conferred a multidrug resistance phenotype to many NAIs but severely compromised viral fitness. The oseltamivir- and peramivir-resistance phenotype was confirmed for the H274Y and N294S mutants, although both viruses remained susceptible to zanamivir. Remarkably, the I222V mutation had a synergistic effect on the oseltamivir- and peramivir-resistance phenotype of H274Y and compensated for reduced viral fitness, raising concerns about the potential emergence and dissemination of this double-mutant virus. CONCLUSIONS This study highlights the importance of continuous monitoring of antiviral drug resistance in clinical samples as well as the need to develop new agents and combination strategies.