Evaluation of the Functional Capacity of NK Cells of Melanoma Patients in an In Vitro Model of NK Cell Contact with K562 and FemX Tumor Cell Lines

NK cells of metastatic melanoma (MM) patients display impaired function, making them incapable to mount an effective antitumor response. In this study, we evaluated immunophenotypic characteristics and functional capacity of CD3(-)CD16(+) NK cells of MM patients in an in vitro model based on NK cell contact with an NK sensitive, K562, and a tumor-specific, melanoma FemX tumor cell line. Although our results indicate similar NK cell antitumor cytotoxic potential of MM patients in contact with both cell lines based on the expression of CD107a degranulation marker, there is a discrepancy in NK cell IFN gamma production, as it is not significantly induced by FemX tumor cells, found to be, contrary to K562, HLA class I positive. Furthermore, we show NKG2D receptor downregulation by K562 tumor cell line, only. This may result from the obtained higher gene expression of TGF beta and VEGFA growth factors in K562 tumor cells that can negatively regulate NKG2D expression. Additionally, aside from postcontact downmodulation of activating CD16 receptor, there are no significant changes in the expression of CD161, CD158a, and CD158b NK cell receptors. Therefore, the applied in vitro model shows that, compared to the full NK cell functional capacity of MM patients displayed in a tumor-sensitive setting represented by contact with K562 cells, tumor-specific melanoma setting provided by FemX tumor cells leads to reduced NK functional potential. The obtained insight into NK cell capacity may be of use for evaluation of the state of disease and can help in selecting effective immunotherapeutic agents for MM patients.