Subset diversification of virus-specific CD8+ T-cells in chronic HCV monoinfection and HCV/HIV coinfection

Chronic viral infections like Hepatitis C virus (HCV) and Human immunodeficiency virus (HIV) lead to considerable morbidity and mortality worldwide. HIV/HCV coinfection is very common among certain risk groups and has significant clinical and therapeutical impacts, e.g. faster progression of HCV-related liver disease compared to HCV monoinfection. Immunologically, the persistent antigen exposure in both chronic HCV and HIV infection induces CD8+ T-cell exhaustion that is characterized by impaired functional capacity e.g. reduced proliferation, cytotoxicity and cytokine production, increased co-expression of inhibitory receptors and a distinct transcriptional profile. An increasing body of data from the mouse model of chronic Lymphocytic choriomeningitis virus (LCMV) infection has unraveled progenitor-progeny heterogeneity among exhausted virus-specific CD8+ T-cells. However, in human viral infection little is known about exhausted virus-specific CD8+ T-cell subsets. In this study, we therefore focused on subset diversification of exhausted virus-specific CD8+ T-cells in HCV monoinfection compared to HIV/HCV coinfection.

For this, we analyzed HCV- specific CD8+ T-cells of chronically HCV-infected patients (n = 20) as well as HCV- and HIV-specific CD8+ T-cells of HIV/HCV coinfected patients (n = 7) and of HIV-infected patients with resolved HCV (n = 4). Following a peptide/HLA-A*02 -tetramer-based enrichment via magnetic cell separation, virus-specific CD8+ T-cells were analyzed on a single-cell level by multicolor flow cytometry for their expression of surface receptors and transcription factors.

In HCV monoinfection, we found that HCV-specific CD8+ T-cells expressing the inhibitory receptor PD1 could be subdivided into cells either expressing or lacking CD127, the IL-7R α-chain that is required for T-cell homeostasis. The CD127-PD1+ subset expressed high levels of the ectonucleotidase CD39 and the transcription factor Eomes characteristic for terminal CD8+ T-cell exhaustion. In contrast, the CD127+PD1+ HCV-specific CD8+ T-cells appear to represent a less differentiated subset characterized by expression of TCF1, a transcription factor that is associated with the proliferative capacity of CD8+ T-cells. This subset diversification in less differentiated and terminal subsets could also be found among HCV- and HIV-specific T-cells targeting single epitopes in HIV/HCV coinfection.

In summary, we could identify heterogeneous subsets of HCV-specific CD8+ T-cells in chronic HCV monoinfection as well as in HCV/HIV coinfection defined by CD127/PD1 co-expression. Due to distinct characteristics of these subsets, the exact composition of virus-specific CD8+ T-cell populations has implications for CD8+ T-cell immunity during chronic viral infection, specifically for immunotherapeutic approaches that should target less exhausted T cell subsets.