Programmed Cell Death Protein 1 Engagement Impairs Cytoskeletal Forces and Nuclear Mechanotransduction in T Cells.

Programmed cell death protein 1 (PD-1) is a critical immune checkpoint that suppresses T cell activation and cytotoxicity, yet its mechanistic role in regulating T cell mechanotransduction remains unclear. Here, we reveal that PD-1 engagement attenuates T cell activation by impairing cytoskeletal force generation and nuclear mechanotransduction in a mechanically defined microenvironment. Using tunable poly(ethylene glycol) (PEG)-based hydrogels that mimic the stiffness of target cells, we show that PD-1 suppresses T cell receptor (TCR)-mediated activation in a stiffness-dependent manner, requiring immobilized ligand presentation. Mechanistically, PD-1 ligation disrupts actin polymerization, reduces traction forces, and prevents nuclear deformation, thereby impairing the nuclear translocation of mechanosensitive transcription factors yes-associated protein (YAP) and nuclear factor 1 of activated T cells (NFAT1). This inhibition is mediated by the dephosphorylation of cofilin, an actin-severing protein that restricts actin assembly and downstream mechanotransduction. Consequently, PD-1 engagement diminishes the cytokine production and effector cytotoxicity of T cells. Pharmacological or genetic restoration of actin polymerization or nuclear transport rescues nuclear YAP/NFAT1 localization and partially restores T cell activation and function. Our findings suggest PD-1 as a mechanical checkpoint that suppresses T cell immunity by dampening cytoskeletal dynamics and nuclear mechanotransduction, offering insights into the biophysical regulation of immune suppression.