Differentiated Oral Tumors Are Resistant to NK Cell Lysis

Objective: NK cells lyse a great number of cancer stem cells but not their differentiated counter-parts. This study demonstrates that de-differentiation of oral tumors increases their sensitivity to NK cell mediated lysis Methods: HEp2 oral tumors were de-differentiated by blocking NFkB (HEp2-IkB(S32AS36A)). HEp2-IkB(S32AS36A) cells and their vector alone transfected HEp2 cells (HEp2-vec) were characterized for their surface expression and their sensitivity to NK-cell mediated lysis. Patient derived oral squamous cancer stem cells (OSCSC) and their differentiated oral squamous carcinoma cells (OSCC) were used as controls. Highly purified human NK cells were left untreated or treated with either IL-2 or anti-CD16 mAb or and used in cytotoxicity assays against oral tumors. The function of NK cells was assessed by using 51Cr release assay, secretion of IFN-g, IL-6 and VEGF by multiplex cytokine array or specific ELISAs. Flow cytometry was used to determine surface characteristics of tumors. Results: De-differentiated HEp2 cells similar to patient derived cancer stem cells expressed significantly higher levels of CD44 and CD54 and secreted no or very low levels of IL-6 and higher levels of VEGF when compared to their differentiated counter parts. In contrast differentiated tumors were higher in the expression of B7H1 and EGFR when compared to cancer stem cells. Untreated and IL-2 treated NK cells significantly lysed de-differentiated HEp2 cells and OSCSCs. Triggering of the CD16 receptor, inhibited NK cell cytotoxicity against oral tumors but augmented IFN-g secretion by the NK cells and increased differentiation of oral tumors. No IFN-g secreted when NKs cultured with differentiated oral tumors. Conclusion: To support differentiation of oral cancer stem cells, NK cells lyse a great number of stem cells and/or those which are either defective or incapable of full differentiation in order to lose their cytotoxic function and gain in cytokine secretion capacity (split anergy).