IL-15 Overcomes Hepatocellular Carcinoma-Induced NK Cell Dysfunction

Abstract

NK cells have potent antitumor capacity. They are enriched in the human liver, with a large subset specialized for tissue-residence. The potential for liver-resident versus liver-infiltrating NK cells to populate, and exert antitumor functions in, human liver tumors has not been studied. We examined liver-resident and liver-infiltrating NK cells directly ex vivo from human hepatocellular carcinomas (HCCs) and liver colorectal (CRC) metastases, compared with matched uninvolved liver tissue. We found that NK cells were highly prevalent in both HCC and liver CRC metastases, although at lower frequencies than unaffected liver. Up to 79% of intratumoral NK cells had the CXCR6+CD69+ liver-resident phenotype. Direct ex vivo staining showed that liver-resident NK cells had increased NKG2D expression compared to their non-resident counterparts, but both subsets had NKG2D downregulation within liver tumors compared to uninvolved liver. Proliferation of intratumoral NK cells (identified by Ki67) was selectively impaired in those with the most marked NKG2D downregulation. Human liver tumor NK cells were functionally impaired, with reduced capacity for cytotoxicity and production of cytokines, even when compared to the hypo-functional tissue-resident NK cells in unaffected liver. Coculture of human liver NK cells with the human hepatoma cell line PLC/PRF/5, or with autologous HCC, recapitulated the defects observed in NK cells extracted from tumors, with downmodulation of NKG2D, cytokine production, and target cell cytotoxicity. Transwells and conditioned media confirmed a requirement for cell contact with PLC/PRF/5 to impose NK cell inhibition. IL-15 was able to recover antitumor functionality in NK cells inhibited by in vitro exposure to HCC cell lines or extracted directly from HCC. In summary, our data suggest that the impaired antitumor function of local NK cells reflects a combination of the tolerogenic features inherent to liver-resident NK cells together with additional contact-dependent inhibition imposed by HCC itself. The demonstration that IL-15 can recover hepatic NK cell function following tumor exposure supports its inclusion in immunotherapy strategies.

Natural Killer Cell Responses in Hepatocellular Carcinoma: Implications for Novel Immunotherapeutic Approaches

“…In line with our preliminary unpublished data, Easom et al [31] recently showed a decreased expression of NKG2D on NK cells derived from HCC tissue compared to matched uninvolved liver tissue. They showed that NKG2D down-modulation depended on contact between NK and HCC cells with consequent internalization of the receptor.…”

“…In the HCC setting, data from mouse models are encouraging, as shown by the inhibitory effect exerted on HCC by an NK cell line transfected with IL-15 [68]. In line with these and other findings recently obtained by Easom and colleagues [31] who showed that IL-15 could restore NK cell activity in HCC, it is possible to envision an immunotherapeutic approach by harnessing NK cell activity with IL-15 for HCC ( Figure 2). Table 1.…”

Natural Killer Cell Dysfunction in Hepatocellular Carcinoma: Pathogenesis and Clinical Implications

“…Previous report studied the immune profile of 110 patients with HCC and found that NK cells were abundant in the liver tissues of HCC individuals, with higher number of NK cells being detected in non-tumor liver tissues, than in the intratumoral regions (57). Consistent with this finding, a recent report demonstrated that NK cells were infiltrated in the intratumoral regions of HCC at a lower frequency than in the non-tumor liver tissues (34). Most intratumoral NK cells exhibited CXCR6 + CD69 + liver-resident phenotype (34).…”

“…In humans, NK cells normally exist in the liver sinusoids (31). Previous reports have demonstrated that up to 80 percent of intrahepatic NK cells are liver-resident (30,(32)(33)(34)(35)(36). Human liver-resident NK cells are characterized by expression of CXCR6 and CD69, have a distinct transcriptional and functional signature, and display memory-like features (37).…”

“…This subset expresses CD49a, and has a narrow killer-cell immunoglobulin-related receptor (KIR) profile that indicates a clonal-like expansion (37). These human liver-resident NK cells survive for a relatively long duration in the liver and are incapable of recirculation, whereas the liver-infiltrating NK cells have the transcriptional characteristics of the peripheral NK cells (34). Furthermore, the liver-resident NK cells have been found to have some attributes related to the tolerogenic characteristics of the liver (36,38).…”