Expansion of HCV-specific T cells with a follicular T helper cell phenotype after DAA mediated antigen removal

In the natural course of Hepatitis C Virus (HCV) infection, CD4 T cells play a key role as important regulators of the immune response. Nevertheless, the fate of HCV-specific CD4 T cells is largely unknown. Mouse models of chronic viral infection have demonstrated that CD4 T cells predominantly differentiate into T follicular helper (Tfh) cells as the infection progresses. In HCV-infection in humans, however, Tfh cells are mostly present in the acute phase of the infection. In this study, we aimed to define whether removal of the antigen following direct acting antiviral (DAA) therapy results in the formation of Tfh cell memory.

Virus specific CD4 T cells of HCV-infected patients were analyzed using MHC class II tetramer-based bead enrichment. The expression of various Tfh-related surface receptors and cytokines was analyzed by flow cytometry. Moreover, HCV specific neutralizing antibody titers in treated patients were analyzed.

Our analyses suggest that the frequency of virus-specific CD4 T cells increases two weeks after initiation of DAA therapy. Surprisingly, cells with a Tfh-phenotype appear to expand within the HCV-specific CD4 T cell compartment, but not the bulk CD4 population, suggesting an antigen-specific effect. Moreover, the activation status of HCV-specific CD4 T cells declines, while the expression of memory markers increases during the course of DAA therapy. In addition, neutralizing antibody titers gradually decline after DAA treatment.

Collectively, our study suggests the formation of Tfh cell memory within HCV-specific CD4 T cells following DAA therapy. Further studies will focus on the transcriptional profile of these cells and their helper capacity towards B cells via cloning of HCV-specific T cells to define the functionality of DAA-induced Tfh cell memory.