PDCD1 and melanoma: Studies further confirmed that STING agonist-loaded lipid nanoparticles (STING-LNPs) activate hepatic macrophages to produce type I interferons (IFN-I), which mobilize systemic NK cells—particularly PD-1+ NK cells—to overcome PD-1 inhibitor resistance in B16F10 melanoma lung metastasis models (80).