Although NK cells are considered innate, recent studies in mice revealed the existence of a unique lineage of hepatic CD49a+DX5− NK cells with adaptive-like features. Development of this NK cell lineage is, in contrast to conventional NK cells, dependent on T-bet but not Eomes. In this study, we describe the identification of a T-bet+Eomes−CD49a+ NK cell subset readily detectable in the human liver, but not in afferent or efferent hepatic venous or peripheral blood. Human intrahepatic CD49a+ NK cells express killer cell Ig-like receptor and NKG2C, indicative of having undergone clonal-like expansion, are CD56bright, and express low levels of CD16, CD57, and perforin. After stimulation, CD49a+ NK cells express high levels of inflammatory cytokines but degranulate poorly. CD49a+ NK cells retain their phenotype after expansion in long-term in vitro cultures. These results demonstrate the presence of a likely human counterpart of mouse intrahepatic NK cells with adaptive-like features.

Additional supporting information may be found in the online version of this article at the publisher's web-site Introduction Mucosal-associated invariant T (MAIT) cells are T cells with innate-like characteristics enriched in human liver and at mucosalCorrespondence: Dr. Niklas K. Björkström e-mail: niklas.bjorkstrom@ki.se sites [1,2]. They express a semi-invariant TCR carrying the Vα7.2 segment together with a restricted Vβ repertoire [1,2]. Upon activation, MAIT cells respond rapidly with cellular cytotoxicity as well as secretion of proinflammatory and anti-viral cytokines such * These authors contributed equally to this work. HCV is an extremely successful pathogen in that it establishes chronic infection in up to 90% of infected humans [9]. The reasons behind the failure of the human immune system to clear HCV are not fully understood but involve viral escape, CD4 and CD8 T-cell exhaustion, as well as NK-cell dysfunction [10][11][12] Until recently, pegylated IFN-α together with ribavirin was used to treat chronic HCV-infection. However, pegylated IFN-α in doses administered to patients has direct inhibitory effects on immune cells [15][16][17][18]. In the last years, treatment of HCV has undergone a revolution with the introduction of highly effective direct-acting antivirals (DAA) that rapidly eliminate the virus [19]. Thus, today the vast majority of patients clear HCV after such IFN-free treatment regimens. This remarkable outcome allows for studies on consequences on immune cell recovery following rapid pathogen removal. In such studies, it was recently shown that both HCVspecific CD8 T cell and NK-cell populations become reinvigorated following viral clearance [20][21][22][23]. However, whether MAIT cells recover upon HCV clearance remains unclear.Here, we performed a comprehensive analysis of MAIT cells in chronic HCV-infection. Specifically, we addressed whether MAIT cell recovery occurs upon HCV-clearance in patients receiving an IFN-free treatment regimen consisting of sofosbuvir and ribavirin. Strikingly, and in contrast to other immune cells, MAIT cells were not reinvigorated following successful HCV-clearance using IFNfree therapy. The results are discussed in relation to the current knowledge on human MAIT cell responses to other viral infections and in the context of immune exhaustion during chronic infections. Results and discussion MAIT cells are among the most severely affected immune cells in chronic HCV-infectionTo determine the impact of chronic HCV-infection on the peripheral blood immune cell compartment, we assessed the major myeloid and lymphoid immune cell subsets in a cohort of HCVpatients and healthy donors by using a 23-parameter flow cytometry staining approach as previously described [24] (Supporting Information Fig. 1). The major phenotype observed in chronic HCV was a severe loss of MAIT cells (Fig. 1A, B). Other immune cell alterations noted were in line with previous studies, including an increase in Tregs [25], a reduced frequency of pDCs [26], and a shift within the CD4...

Chronic HCV infection appears to disrupt the milieu of soluble inflammatory mediators even after viral clearance. Thus, HCV cure does not lead to complete immunological restitution.