Presence of naive-like HBV-specific CD8+ T cells in chronically infected patients despite ongoing viral replication

Abstract

In chronically HBV-infected patients, virus-specific CD8+ T cell responses are rarely detectable ex vivo by conventional tetramer staining. This lack of HBV-specific CD8+ T cell responses may be explained by insufficient priming, T cell exhustion and/or deletion. Here, we set out to address this issue by using new techniques for enumerating virus-specific T cells from human peripheral blood based on the combination of tetramer staining, magnetic-bead enrichment, and multiparametric flow cytometry. Indeed, we were able to detect and characterize CD8+ T cell populations specific for 4 well-described HLA-A0201-restricted HBV epitopes (core18 – 27, env183 – 191, env335 – 343 and pol455 – 463) in 24 chronically HBV-infected patients suggesting that these cells are not completely deleted. CD8+ T cells specific for core18 – 27, env335 – 343 and pol455 – 463 were detectable in the majority of analyzed patients (79%, 75% and 100% respectively) while env183 – 191-specific CD8+ T cells were found less frequently (54%). Interestingly, about 20% of analyzed CD8+ T cells had a naive-like phenotype with high expression of CD45RA, CCR7 and CD27 and low expression of CD11a. By contrast 39% of HBV-specific CD8+ T cells showed an effector-memory phenotype characterized by the absence of CD45RA, CCR7 and high expression of CD27 and CD11a indicating viral recognition. Of note, HBV-specific CD8+ T cell populations with naive-like and effector-memory phenotype were detected in parallel for different epitopes within the same patients (9 of 24). Importantly, the observed phenotype did not correlate with any clinical parameter such as HBeAg status, viral load or transaminases and was independent of antiviral treatment. Furthermore, viral sequence analysis revealed the presence of wild-type sequences in patients with naive-like HBV-specific CD8+ T cells indicating that the observed lack of priming is not due to infection with a variant HBV containing mismatched epitopes. Our results indicate that HBV-specific CD8+ T cells are not completely deleted in chronically infected patients, but rather maintained at a very low frequency. Furthermore, a substantial fraction of these cells display a naive-like phenotype despite ongoing viral replication. This suggests, that in addition to T cell exhaustion insufficient priming may also contribute to HBV-specific CD8+ T cell failure in chronically infected patients.