In head and neck squamous cell carcinoma (HNSCC), the CHK1/2 inhibitor Prexasertib enhances the cytotoxicity of cisplatin and radiotherapy by inhibiting the Notch signaling pathway, including Hes1 (195) Immunohistochemistry of HNSCC tissues reveals that elevated Hes1 is associated with myeloid-derived suppressor cells (MDSCs), tumor-associated macrophages (TAMs), regulatory T cells (Tregs), and immune checkpoint molecules (PD1, CTLA4, TIM3, LAG3); inhibition of the Notch signaling pathway using GSIs (such as GSI-IX, DAPT) may reduce these immunosuppressive cells and molecules (137). Here, CTLA4 is linked to head and neck squamous cell carcinoma.