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Natural killer (NK) cells play a role in the innate and adaptive antitumor immune responses. The activity of NK cells is regulated by functionally opposing, activating and inhibitory receptors whose balance ultimately determines whether target cells will be susceptible to NK cell mediated lysis. As melanoma is an immunogenic tumor, the effect of immunomodulating agents is consistently investigated. In this study in 79 metastatic melanoma (MM) patients and 52 controls NK activity, expression of activating NKG2D and CD161 receptors and KIR receptors, CD158a and CD158b, on freshly isolated PBL and NK cells were evaluated. Native NK cell activity of melanoma patients in clinical stage I-III and MM patients was determined against NK sensitive K562, NK resistant Daudi, human melanoma FemX, HeLa and HL 60 target tumor cell lines. In addition, predictive pretherapy immunomodulating effect after 18 h in vitro treatments of PBL of MM patients with rh IL-2, IFN-alpha (IFN), 13-cis retinoic acid (RA) and combination IFN-alpha and RA was evaluated with respect to NK cell lyses against K562 and FemX cell lines. In this study we show for the first time that low expression of CD161 and activating NKG2D receptors, without increased expression of KIR receptors CD158a and CD158b, as well as a decrease in the cytotoxic, CD16(bright) NK cell subset, is associated with a significant impairment in NK cell activity in MM patients. Furthermore, the predictive pretherapy finding that IL-2, IFN, IFN and RA, unlike RA alone, can enhance NK cell activity of MM patients against FemX melanoma tumor cell line can be of help in the design and development of therapeutic regimens, considering that it has recently been shown that low-dose combination of different immunomodulators represents the most promising approach in the therapy of MM.

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In metastatic melanoma (MM) patients we evaluated natural killer (NK)-cell activity, distribution of several NK receptors and their correlation with NK function. Peripheral blood lymphocytes (PBL) of MM patients and controls were analysed for NK activity and expression of activating NKG2D, CD161 and KIR, CD158a and CD158b receptors on CD3-CD16+ NK cells. MM patients not only had significantly decreased NK activity and NK-cell interferon (IFN)-gamma production, a redistribution of NK-cell subsets with an increase in CD16(dim) and a reduction in CD16(bright) NK subsets. There was a decreased CD161 and NKG2D and an increased CD158a NK-cell expression in MM patients, with a positive correlation between NKG2D expression and NK cytotoxicity and an inverse correlation between CD158b expression and NK-cell cytotoxicity in patients. Furthermore, patients' CD3-CD16(bright) NK subset showed lower expression of CD161 and CD158a. Therefore, NKG2D, CD158a and CD158b expression in MM patients may represent several clinically useful 'biomarkers' of suppressed NK function.

Although natural killer (NK) cells play an important antitumor role, melanoma cells may affect their effector functions. In this study, we analyzed the expression of various receptors and effector molecules in NK cells and their subsets in metastatic melanoma (MM) patients compared with healthy controls (HCs). In HC and MM patients, we analyzed NK cell activity using a chromium release assay and the expression of CD107a degranulation marker, activating NKG2D, NKp46, DNAM-1, and inhibitory CD158a and CD158b receptors, IL-12R beta 1, IL-12R beta 2, intracellular interferon (IFN)-γ, perforin, and STAT-1 in CD3-CD56+ NK cells, and cytotoxic CD3-CD56 and immunoregulatory CD3-CD56 subsets by flow cytometry. MM patients compared with HC not only had significantly decreased NK cell activity, lower expression of CD107a, and impaired IFN-γ production but also had decreased expression of activating NKG2D, NKp46, and DNAM-1 receptors, which was followed by lower expression of perforin, STAT-1, and both IL-12R subunits in NK cells. In MM patients only, there was a positive correlation between NKG2D expression and degranulation capacity, as well as IFN-γ production in NK cells. Analysis of the expression of various parameters of NK cell effector functions between MM patients with different localization of distant metastases showed that patients in the unfavorable M1c subclass had decreased expression of NKG2D and NKp46 on NK cells compared with patients in the M1a+b group. Downregulated NKG2D, NKp46, and DNAM-1 receptors associated with impaired NK cell effector function are important biomarkers of advanced disease with a poor prognosis in melanoma patients.