In-vitro IL-2 or IFN-α-induced NKG2D and CD161 NK cell receptor expression indicates novel aspects of NK cell activation in metastatic melanoma patients.

In metastatic melanoma (MM) immunomodulating agents, such as interleukin-2 (IL-2) and interferon-α (IFN-α), have shown therapeutic benefit as they enhance antitumor immune response. Considering tumor-induced suppression of natural killer (NK) cell activity, it is of interest to study the affect of these cytokines on the functional and receptor characteristics of CD16-defined NK cells and their dim and bright subsets. Peripheral blood lymphocytes of MM patients in clinical stage IV were treated in vitro for 18 h with IFN-α (250 U/ml) and rhIL-2 (200 U/ml) at 37°C. Both the cytokines induced significant in-vitro enhancement of NK cell activity. NKG2D receptor was induced by IL-2, whereas both the NKG2D and CD161 receptor expression was induced by IFN-α on NK cells and CD16(bright) NK cell subset. However, only IL-2 mediated induction of NKG2D on CD3⁻CD16(+) NK cells correlates with enhanced NK cytotoxicity by this cytokine, whereas, on the cytotoxic CD16(bright) subset NKG2D induction by both cytokines correlates with their induction of NK cell activity. In contrast, the observed induction of these receptors on the regulatory CD16(dim) subset shows no correlation with the obtained augmentation of cytotoxicity. We found substantial specific inducibility of pSTAT1 and pSTAT5, as well as induction of interferon-regulatory transcription factor-1 transcription by investigated cytokines in peripheral blood lymphocytes of MM patients. As NK cell-mediated killing of tumor cells depends on the balance between stimulatory and inhibitory signaling, induction of activating NKG2D receptor by IL-2 and IFN-α, especially in CD16(bright) NK cell subset, gives insight to novel aspects of NK cell activation by these cytokines that are applied in immunotherapy.