Inhibitory molecules that regulate expansion and restoration of HCV-specific CD4+ T cells in patients with chronic infection. 
Inhibitory receptors such as programmed death 1 (PD-1) and cytotoxic T lymphocyte-associated antigen (CTLA)-4 mediate CD8+ T-cell exhaustion during chronic viral infection, but little is known about roles in dysfunction of CD4+ T cells.  We investigated the functions of inhibitory molecules on hepatitis C virus (HCV)-, influenza-, and Epstein-Barr virus (EBV)-specific CD4+ T cells in patients with chronic infections compared with patients with resolved HCV infection and healthy donors.  Expression of PD-1, CTLA-4, CD305, and CD200R were analyzed on HCV-specific CD4+ T cells, isolated from peripheral blood using major histocompatibility complex class II tetramers.  We investigated the effects of in vitro inhibition of various inhibitory pathways on proliferation and cytokine production by CD4+ T cells, and we compared these effects with those from inhibition of interleukin (IL)-10 and transforming growth factor (TGF)-β1.  PD-1 and CTLA-4 were up-regulated on virus-specific CD4+ T cells from patients with chronic HCV infections.  PD-1 expression was lower on influenza- than on HCV-specific CD4+ T cells from subjects with chronic HCV infection, whereas CTLA-4 was expressed at similar levels, independent of their specificity.  CD305 and CD200R were up-regulated in HCV resolvers.  Blockade of PD-L1/2, IL-10, and TGF-β1 increased expansion of CD4+ T cells in patients with chronic HCV, whereas inhibition of IL-10 and TGF-β1 was most effective in restoring HCV-specific production of interferon gamma, IL-2, and tumor necrosis factor α.  We characterized expression of inhibitory molecules on HCV-, influenza-, and EBV-specific CD4+ T cells and the effects of in vitro blockade on CD4+ T-cell expansion and cytokine production.  Inhibition of PD-1, IL-10, and TGF-β1 is most efficient in restoration of HCV-specific CD4+ T cells.