Hepatitis C virus-specific CD4+ T cell phenotype and function in different infection outcomes.

CD4(+) T cell failure is a hallmark of chronic hepatitis C virus (HCV) infection. However, the mechanisms underlying the impairment and loss of virus-specific CD4(+) T cells in persisting HCV infection remain unclear. Here we examined HCV-specific CD4(+) T cells longitudinally during acute infection with different infection outcomes. We found that HCV-specific CD4(+) T cells are characterized by expression of a narrower range of T cell inhibitory receptors compared with CD8(+) T cells, with initially high expression levels of PD-1 and CTLA-4 that were associated with negative regulation of proliferation in all patients, irrespective of outcome. In addition, HCV-specific CD4(+) T cells were phenotypically similar during early resolving and persistent infection and secreted similar levels of cytokines. However, upon viral control, CD4(+) T cells quickly downregulated inhibitory receptors and differentiated into long-lived memory cells. In contrast, persisting viremia continued to drive T cell activation and PD-1 and CTLA-4 expression, and blocked T cell differentiation, until the cells quickly disappeared from the circulation. Our data support an important and physiological role for inhibitory receptor-mediated regulation of CD4(+) T cells in early HCV infection, irrespective of outcome, with persistent HCV viremia leading to sustained upregulation of PD-1 and CTLA-4.