New strategies for the treatment of hepatitis C virus infection and implications of resistance to new direct-acting antiviral agents Josep Quer1–3, Maria Buti1–3, Maria Cubero1–3, Jaume Guardia1–3, Rafael Esteban1–3, Juan Ignacio Esteban1–31Liver Unit, Internal Medicine Hospital Universitari Vall d’Hebron, Institut de Recerca (VHIR), Barcelona, Spain; 2Universitat Autònoma de Barcelona, Barcelona, Spain; 3Centro de Investigación Biomédica en Red de Enfermedades Hepáticas y Digestivas (CIBERehd), Instituto de Salud Carlos III, Madrid, SpainAbstract: Persistent hepatitis C virus (HCV) infection is a leading cause of chronic hepatitis, cirrhosis, and hepatocellular carcinoma and the major indication for liver transplantation in adults. Current standard of care treatment (SOC) with pegylated-interferon-a 2 and ribavirin (RBV) has a limited efficacy and is associated with significant side effects frequently associated with poor compliance or treatment discontinuation, requiring specialized and frequent monitoring. To overcome the limited efficacy of SOC, more than 50 direct-acting antiviral agents (DAA) designed to target viral-encoded proteins essential in the HCV life cycle are currently under development. The rapid selection of resistant mutants associated with the quasispecies nature of HCV with high mutation and replication rates is one of the main challenges for the new HCV therapies. Predictive host and viral factors together with combination of DAAs with or without IFN and/or RBV need to be accurately evaluated to design the most effective individualized treatment strategy within the shortest time interval and with minimum side effects.Keywords: HCV, treatment, quasispecies, resistance