Research progress on programmed death receptor 1/ ligand 1 inhibitor in immunotherapy of head and neck squamous cell carcinoma

Head and neck squamous cell carcinoma (HNSCC) is a common malignant tumor that seriously threatens human health and life. With increasing studies on the mechanism of tumor immune escape, programmed death receptor 1 (PD-1) and programmed death ligand receptor 1 (PD-L1) have been proven to be involved in tumor immune escape. The primary mechanism is that PD-1 recruits protein tyrosine phosphatase (SHP-2) to dephosphorylate downstream tyrosine kinase (SyK) and phosphatidylinositol 3-kinase (PI3K), thereby inhibiting downstream protein kinase B (AKT), extracellular regulated protein kinases (ERK) and other important signaling pathways, ultimately inhibiting T cell activation. In recent years, PD-1/PD-L1 inhibitors have become popular immunotherapies. Pembrolizumab and nivolumab have been approved for HNSCC patients by the U.S. Food and Drug Administration. Both durvalumab and atezolizumab are still in clinical trials, and published data show that both have certain safety and efficacy but still need much clinical data to support them. Meanwhile, the combination of PD-1/PD-L1 inhibitors with radiotherapy, chemotherapy and immunotherapy is still controversial in terms of clinical efficacy and adverse events, and further research is needed. However, serious immune-related adverse reactions limit the clinical application of PD-1/PD-L1 inhibitors, despite promising curative effects. Therefore, developing novel inhibitors and investigating stable and effective biomarkers and upstream and downstream signaling mechanisms are urgent issues.