Follicular T helper cells shape the HCV-specific CD4 T cell repertoire after viral elimination.

BACKGROUND. Chronic hepatitis C virus (HCV) infection is characterized by a severe impairment of HCV-specific CD4(+) T cell help that is driven by chronic antigen stimulation. We aimed to study the fate of HCV-specific CD4(+) T cells after virus elimination. METHODS. HCV-specific CD4(+) T cell responses were longitudinally analyzed using MHC class II tetramer technology, multicolor flow cytometry, and RNA sequencing in a cohort of patients chronically infected with HCV undergoing therapy with directacting antivirals. In addition, HCV-specific neutralizing antibodies and CXCL13 levels were analyzed. RESULTS. We observed that the frequency of HCV-specific CD4(+) T cells increased within 2 weeks after initiating directacting antiviral therapy. Multicolor flow cytometry revealed a downregulation of exhaustion and activation markers and an upregulation of memory-associated markers. Although cells with a Th1 phenotype were the predominant subset at baseline, cells with phenotypic and transcriptional characteristics of follicular T helper cells increasingly shaped the circulating HCVspecific CD4(+) T cell repertoire, suggesting antigen-independent survival of this subset. These changes were accompanied by a decline of HCV-specific neutralizing antibodies and the germinal center activity. CONCLUSION. We identified a population of HCV-specific CD4(+) T cells with a follicular T helper cell signature that is maintained after therapy-induced elimination of persistent infection and may constitute an important target population for vaccination efforts to prevent reinfection and immunotherapeutic approaches for persistent viral infections.