Combined IFN-γ and TNF-α treatment enhances the susceptibility of breast cancer cells and spheroids to Natural Killer cell-mediated killing.

NK cell-based immunotherapy of solid tumors has been shown to be increasingly successful, but much effort is still needed to optimize its efficacy. This study explores the effects of treatment with low, non-toxic doses of IFN-γ and TNF-α on the susceptibility of breast cancer (BC) cell lines (MCF-7, MDA-MB-231, and MDA-MB-468) cultured in 2D and 3D as spheroids, to NK cell-mediated antitumor function. We evaluated the expression of (i) ligands for NK cell-activating receptors on BC cells, (ii) death and adhesion molecules on BC cells, and (iii) the expression of NK cell-receptors on NK cells infiltrating BC spheroids. Cytokine treatment significantly increased the expression of FAS, TRAIL-R2, and ICAM-1 in all BC cell lines, enhancing NK cell-mediated apoptosis and promoting NK cell-tumor cell conjugate formation. Differently, the expression of ligands for activating receptors remained essentially unchanged. In BC spheroids, the treatment with IFN-γ and TNF-α enhanced NK-cell infiltration, with increased expression of activating receptors (NKG2D, DNAM-1, NKp30, and NKp46) on infiltrating NK cells. However, regardless of treatment, markers of NK cell exhaustion, such as PD-1 and CTLA-4, were also upregulated, the latter especially in triple-negative BC (TNBC) MDA-MB-231 spheroids, thus suggesting an exhausted phenotype of NK cells infiltrating spheroids despite activation. Cytokine treatment resulted in a significant NK cell-mediated reduction in spheroid size, accompanied by an increased apoptotic state, with effects more pronounced in MCF-7 than in MDA-MB-231 spheroids. These results indicate that, although the treatment with IFN-γ and TNF-α improves NK cell-mediated tumor interaction and apoptosis, its therapeutic efficacy may be dependent on the BC subtype, with TNBC spheroids showing greater resistance. These findings highlight the importance of the tumor microenvironment (TME) in shaping NK cell responses and suggest that combining IFN-γ and TNF-α treatments with NK-cell-based immunotherapeutic strategies may improve treatment outcomes, particularly for more aggressive BC subtypes.