PO-368 Differential effects of immune activity on melanoma cell subtypes

Introduction The cytokines IFNγ and TNFα are abundantly expressed by cytotoxic T cells. These cytokines have distinct and overlapping downstream effects. In this study, we assessed the effects of IFNγ and TNFα on the expression of immune regulatory factors. Material and methods We analysed a large panel of melanoma cell lines, including BRAF mutant (n=11), NRAS mutant (n=10), BRAF and NRAS wild type (n=10) cutaneous melanomas, and GNAQ/11-mutant uveal melanomas (n=8). These cells were treated with TNFα or IFNγ for 48 hour and the expression of PD-L1, PD-L2, HLA-ABC and HLA-DR was analysed by flow cytometry. Results and discussions IFNγ showed consistently stronger induction of PD-L1, PD-L2, HLA-ABC and HLA-DR compared to TNFα. For instance, 35/39 cells (90%) showed IFNγ-mediated up regulation of PD-L1, PD-L2, HLA-ABC and HLA-DR, whereas TNFα induced expression of all immune markers in only 23/39 cells (59%). We also noted variation in the activity of IFNγ and TNFα that reflected melanoma subtypes. For instance, in the 31 cutaneous melanoma cell lines, the relative expression of HLA-ABC and HLA-DR was similar after IFNγ stimulation. In contrast, TNFα preferentially induced HLA-ABC, rather than HLA-DR, in the cutaneous cell lines and HLA-ABC was also preferentially stimulated by both cytokines in the 8 uveal melanoma cell lines. Response of the four immune markers to IFNγ and TNFα was often correlated. This was most evident in the case of PD-L2. We noted strong correlation between baseline, IFNγ- and TNFα-induced PD-L2 levels (Spearman’s rank correlation coefficient: p Conclusion These findings have important implications for immunotherapy, confirming that most melanomas are responsive to IFNγ and/or TNFα.