The progression of HCV infection by gene expression analysis of liver biopsies in acutely infected chimpanzees that develop persistent infection, transient viral clearance, or sustained clearance has been examined. Transient and sustained viral clearance were uniquely associated with induction of IFN-gamma-induced genes and other genes involved in antigen processing and presentation and the adaptive immune response. The study revealed genome-wide transcriptional changes that reflect the establishment, spread, and control of infection, and they reveal potentially unique antiviral programs associated with clearance of HCV infection (5).