Prognostic significance and response to immune checkpoint inhibitors of RIPK3, MLKL and necroptosis in non-small cell lung cancer

Lung cancer remains the leading cause of cancer death. Treatment with immune checkpoint inhibitor (ICI) alone or combination with chemotherapy served as first-line therapy in non-small cell lung cancer (NSCLC). However, only 20-50% of NSCLC patients respond to ICI. Necroptosis, an inflammatory form of cell death plays an important role in the regulation of tumor immune microenvironment which may affect prognosis and ICI response but its clinical significance in NSCLC patients has remained largely unknown. Therefore, we aimed to analyze the correlation between key necroptotic proteins and necroptosis and clinical outcomes, the status of tumor-infiltrating immune cells, and response to ICI in NSCLC patients. The expression of receptor-interacting protein kinase 3 (RIPK3), mixed lineage kinase domain-like protein (MLKL) and phosphorylated MLKL (pMLKL) were immunolocalized in 125 surgically resected NSCLC patients and 23 NSCLC patients administered with ICI therapy. CD8 + and FOXp3 + T cells and CD163 + M2 macrophages were also immunolocalized. High RIPK3 status was positively correlated with survival of the patients and RIPK3 turned out an independent favorable prognostic factor of the patients. RIPK3 was negatively correlated with CD8 + T cells, while MLKL positively correlated with CD163 + M2 macrophages, suggesting the possible involvement of RIPK3 and MLKL in formulating immunosuppressive microenvironment. In addition, high RIPK3 status tended to be associated with clinical resistance to ICI therapy (P-value = 0.057). Furthermore, NSCLC cells-expressing RIPK3 suppressed T cells response to ICI therapy in vitro. Therefore, RIPK3 and MLKL could induce an immunosuppressive microenvironment, resulting in low response to ICI therapy in NSCLC.