PDCD1 and chronic hepatitis C virus infection: In a randomized, double-blind, placebo-controlled study assessing the efficacy of a single dose of anti-PD-1 monoclonal antibody for the treatment of chronic hepatitis C in human patients, a protocol-defined clinical response (HCV RNA reductions of more than 0.5 log10 IU/mL were observed on 2 or more consecutive visits) was observed in five out of 45 patients.