Cemiplimab Mechanism of Action: How PD-1 Inhibition Restores Antitumor Immunity

　　1.Overview and Core Mechanism

　　Cemiplimab is a recombinant human IgG4 monoclonal antibody and a PD-1 immune checkpoint inhibitor.Instead of directly killing tumor cells,it binds to programmed death receptor 1(PD-1)on T cells,blocking the interaction of PD-1 with its ligands PD-L1 and PD-L2.This reduces PD-1-mediated suppression of T-cell function,helping the immune system recognize and attack tumors.

　　2.PD-1 Pathway and Tumor Immune Evasion

　　Under normal conditions,PD-1 binding to PD-L1/PD-L2 prevents excessive T-cell activation and maintains immune balance.In the tumor microenvironment,however,this pathway is often exploited by tumor cells and related cells,leading to suppression of antitumor T cells.Reduced T-cell immune surveillance allows tumor cells to grow and evade immune attack.

　　3.How the Drug Releases Immune Suppression

　　By binding to PD-1,cemiplimab prevents PD-L1 and PD-L2 from interacting with PD-1,thereby releasing PD-1-mediated immune suppression.With this"immune brake"lifted,T-cell proliferation,cytokine secretion,and cytotoxic functions are restored or enhanced,improving antitumor immune responses.

　　4.Clinical Use and Patient Selection

　　Cemiplimab is currently used for cutaneous squamous cell carcinoma,basal cell carcinoma,and certain non-small cell lung cancers(NSCLC).Patient selection criteria vary by indication;for example,NSCLC treatment requires assessment of PD-L1 expression levels and genetic alterations such as EGFR,ALK,and ROS1.

　　5.Conclusion

　　The core of cemiplimab's mechanism lies in blocking the PD-1/PD-L1/PD-L2 pathway to release immune suppression and restore T-cell antitumor immunity.This defines its role as a key PD-1 immune checkpoint inhibitor.