Hepatitis C virus (HCV) is a rapidly mutating virus and establishes persistent infection in 75% of patients. Immune escape against CD8+ T cells has been associated to establishment of persistent infection. However, some CD8+ T cell epitopes remain conserved during chronic infection, often resulting in loss of functional activity overtime, thus implying the existence of additional mechanisms of immune failure. CD8+ T cells exhibiting an exhausted phenotype have been extensively reported during the chronic HCV, where several inhibitory receptors such as PD-1, Tim-3 and CD160 are upregulated on HCV-specific CD8+ T cells. To date the kinetics of emergence and co-expression patterns of these inhibitory receptors and their relationship with immune escape during primary HCV infection remains unknown. We analysed longitudinally HCV-specific CD8+ T cells from early stages of infection and assessed the kinetics of T cell exhaustion and its relationship with immune escape.
Subjects (n=29) infected with HCV from Hepatitis C Incidence and Transmission Study in prison (HITS-p) were recruited with sample available from few weeks postinfection until the outcome of infection was apparent. For each subject, analysis of transmitted/founder viruses was performed followed by MHC class I specific epitopes prediction. Autologous peptides were synthesized, and IFN-g ELISpot assays were performed, and based on these HLA restricted epitopes dextramers were generated (Immudex). Expression of several inhibitory markers (PD-1, CD160, TIM-3, KLRG1 and 2B4) and two functional markers (CD127 and CD38) were assessed on HCV-specific CD8+ T cells using a thirteen-color flow panel. HCV-specific CD8+ T cell responses against transmitted/viruses were identified in three of the seven subjects analysed. Immune escape was observed in ~33% of all identified epitopes. Interestingly, preliminary analysis on two subjects with chronic outcome, revealed an exhaustion phenotype within the first 100 days post-infection from CD8+ T cell responses targeting conserved as well as escape variants. These data suggest that complex patterns of CD8+ T cell exhaustion and escape contribute to HCV outcome.