Adaptive NK cells with decreased antitumor activity are expanded in HBV-associated HCC

Hepatocellular carcinoma (HCC) is one of the most frequent cancers in both incidence and mortality worldwide. Since treatment options are limited new treatment strategies for HCC are urgently needed. As NK cells have antitumor activity and account for up to 40% of all liver immune cells they offer a potential target for HCC treatment. Importantly, the human NK-cell repertoire is highly diverse and subsets differ in their phenotype and effector function. Therefore, a better understanding of NK-cell subsets is needed for the design of effective NK-cell involving immunotherapeutic approaches in HCC. The deepest knowledge of NK-cell diversification has been gained in the context of cytomegalovirus (CMV) infection. CMV-associated heterogeneous NK-cell subsets have been described including adaptive NK cells that are characterized by upregulation of CD57 and downregulation of PLZF, Helios and FcεRIγ. Compared to conventional NK cells, adaptive NK cells exhibit enhanced antibody-dependent cellular cytotoxicity but decreased cytokine responsiveness. Yet, only very little is known about frequency and antitumor activity of adaptive NK cells in solid tumors like HCC.

To address phenotypic and functional NK-cell diversification in HCC, we compared circulating NK cells derived from 45 HCC patients and 24 healthy donors (HD) considering HCC etiology and CMV serostatus. Our data revealed that the presence of adaptive FcεRIγ- NK cells in HCC patients is dependent on CMV seropositivity. Interestingly, compared to HD, a significant expansion of adaptive NK cells could only be observed in HCC patients with underlying cHBV infection. Of note, adaptive NK cells in HCC patients and HD displayed a comparable phenotype characterized by decreased expression of PLZF and Helios and increased expression of CD57. To test antitumor activity we performed co-culture experiments with different hepatoma cell lines assessing degranulation and cytokine production by NK cells. Importantly, we observed that adaptive NK cells had an impaired antitumor activity compared to conventional NK cells. This suggests that the expansion of adaptive NK cells in HBV-associated HCC may impact NK cell antitumor activity.

In sum, our data demonstrate a highly heterogeneous NK-cell repertoire in HCC including the presence of adaptive NK-cell subsets depending on CMV seropositivity. Importantly, the occurrence of CMV-associated NK-cell diversification is linked to HCC etiology, specifically chronic HBV infection. Adaptive NK cells show reduced antitumor activity compared to conventional NK cells and the NK cell repertoire should therefore be considered in the design of NK-cell involving immunotherapies.