Mechanical force regulates the inhibitory function of PD-1

The immune checkpoint molecule, programmed cell death 1 (PD-1), plays a pivotal role in regulating T-cell function. Upon binding to its ligands, PD-L1 or PD-L2, PD-1 suppresses T-cell receptor signaling, thereby preventing T-cell activation, making it a critical target in cancer immunotherapy. Although extensively studied, the molecular mechanism of PD-1s inhibitory function is still not fully understood, especially at the atomic level. Using the biomembrane force probe (BFP), we discovered that interactions between PD-1 and PD-L1/PD-L2 exhibit catch-slip bond behavior under force. At lower forces, catch bonds are observed, transitioning to slip bond as the force increases. Steered molecular dynamics (SMD) simulations revealed a force-induced bond state between PD-1 and its ligands, distinct from the force-free state observed in solved complex structures. Disrupting interactions that stabilize either state weakens the catch bond and diminishes PD-1s inhibitory function. Interestingly, soluble forms of PD-L1 and PD-L2 compete with their surface-bond counterparts, attenuating PD-1s suppression of T-cell activation. This suggests that soluble PD-1 ligands could potentially serve as anti-PD-1 drugs. Tumor growth studies in mice confirmed the anti-cancer activity of soluble PD-L1. Our findings highlight the critical role of mechanical force in PD-1s inhibitory function, suggesting that PD-1 may act as a mechanical sensor in suppressing T-cell activation. These insights indicate that mechanical regulation should be considered when designing PD-1 blocking inhibitors and other PD-1 related cancer immunotherapies. TeaserThis study shows that the interaction between PD-1 and its ligands is force-dependent, and soluble forms of PD-1 ligands can potentially serve as PD-1 blockers in cancer immunotherapy.