CTLA4 and hepatitis C virus infection: The PD-1+CTLA-4+ phenotype with a functional response to PD-1/CTLA-4 blockade also occurred in circulating HCV-specific CD8 T cells during acute hepatitis C. By contrast, circulating HCV-specific CD8 T cells from chronic HCV patients (e.g. with intermediate PD-1 expression without CTLA-4 co-expression) were functionally augmented by PD-1 blockade alone.