Immune checkpoint molecules are essential regulators of immune homeostasis, maintaining the balance between activation and tolerance. In cancer, tumours exploit checkpoint pathways to suppress antitumour immunity and promote progression. The advent of immune checkpoint inhibitors, particularly those that target the clinically validated PDL1–PD1 and CTLA4 axes, has transformed cancer therapy, and the LAG3 axis has recently entered clinical practice, yet most patients experience limited or transient benefit, often because the checkpoint molecules become dysregulated. Here, we examine how multilayered regulatory mechanisms operating at the genetic, epigenetic, transcriptional, post-transcriptional, translational and post-translational levels collectively shape checkpoint abundance and function in tumour and immune cells. We further connect these regulatory processes to immune evasion and therapeutic resistance and highlight how this knowledge informs biomarker development and mechanism-guided strategies to improve immunotherapy outcomes.
