Blockade of the PD-1/PD-L1 interaction was shown to improve the expansion ability and IFN-γ secretion from HCV-specific CD8+ T cells (Moreno-Cubero and Larrubia, 2016) and control HCV replication in a chimpanzee model of CHC, although the efficacy was noted only in those animals with a critical threshold of pre-existing HCV-specific CD8+ T cells (Fuller et al., 2013). The gene discussed is IFNG; the disease is cryohydrocytosis.