In vitro increased natural killer cell activity of metastatic melanoma patients with interferon-α alone as opposed to its combination with 13-cis retinoic acid is associated with modulation of NKG2D and CD161 activating receptor expression.

PURPOSE

Considering tumor-induced suppression of natural killer (NK) cell activity the aim of this study was to investigate the in vitro effect of a standard immunotherapeutic cytokine, interferon (IFN)α, and a less investigated agent, 13-cis retinoic acid (RA) on the functional and receptor characteristics of CD16-defined NK cells and their functionally diverse dim and bright subsets in patients with metastatic melanoma (MM).

METHODS

Peripheral blood lymphocytes (PBL) of patients with clinical stage IV MM were stimulated in vitro for 18 h in RPMI 1640 culture medium (CM) alone, CM supplemented with IFN-α (250 U7sol;ml), RA (10-6M) and their combination. NK cell activity was determined using standard 4 h radioactive cytotoxicity assay, while the expression of activating (NKG2D, CD1617rpar; and inhibitory (CD158a, CD158b) NK cell receptors on CD3-CD16+ NK cells and their functional bright and dim subsets were analyzed by flow cytometry.

RESULTS

NK cell cytotoxic activity was increased after in vitro treatment with IFN-α alone and in combination with RA, while only IFN-α induced increase in NKG2D and CD161 activating NK cell receptor expression. Contrary to this, RA treatment increased the expression of inhibitory KIR CD158b. IFN-α-obtained increase in CD161 expression was due to its induction on both NK cell subsets, while for NKG2D only on CD16bright subset.

CONCLUSION

The favorable enhancement of NK cell activity of MM patients obtained with IFN-α is associated with upregulation of activating NKG2D and CD161 receptors, while the lack of RA-associated upregulation is probably due to the shown increased expression of inhibitory KIR receptor CD158b after in vitro treatment with this agent.