Pyroptosis modulates multiple immune cell populations in targeted therapy–treated melanoma

Abstract Treatment of melanoma with BRAF inhibitors plus MEK inhibitors (BRAFi + MEKi) stimulates an intratumoral immune response, in part through pyroptosis mediated by the pore-forming protein gasdermin E (GSDME/Gsdme). How GSDME mediates effects on tumoral immunity is not well characterized. Using single-cell RNA-sequencing (scRNA-seq) and flow cytometry in BRAFi + MEKi treated melanoma, we show herein that isogenic Gsdme knockout (KO) tumors show decreased infiltration with T cells, natural killer (NK) cells and regulatory T cells (Tregs) compared to control tumors. Infiltrated Tregs in Gsdme KO tumors displayed decreased expression of the interleukin 2 receptor and phenotypic markers associated with suppressive function. Furthermore, intratumoral, the frequency of phenotypically suppressive Tregs were decreased after BRAFi + MEKi treatment in Gsdme KO tumors engineered to express a pyroptosis-defective mutant form of Gsdme (T6E) compared to Gsdme KO tumors engineered to re-express wild-type Gsdme. Combining BRAFi + MEKi with a TLR9 agonist limited regrowth of Gsdme-deficient tumors, and this was associated with a further reduction in intratumoral Tregs. Overall, we show a critical role of GSDME in the modulation of intratumoral immune cells in BRAFi + MEKi-treated melanoma.