Bifunctional ferritin nanoparticle blocks PD-1/PD-L1 pathway and alleviates oxidative stress for multi-target therapy of multiple sclerosis.

To address the limited immunotargeting specificity of PD-L1 antibodies and the exacerbated oxidative stress microenvironment in multiple sclerosis (MS), a bifunctional nanoplatform, Ru@Fn-PD-L1(IgV), was developed using an engineered ferritin nanocage. This system was constructed via site-specific conjugation of the PD-L1 extracellular domain(IgV) to ferritin using SpyTag-SpyCatcher bioconjugation, combined with the in-situ encapsulation of ruthenium-based nanozymes exhibiting superoxide dismutase/catalase (SOD/CAT) cascade activity within the nanocage. Ru@Fn-PD-L1 (IgV) efficiently traverses the blood-brain barrier (BBB) through transferrin receptor (TfR1)-mediated transcytosis, enabling targeted delivery to the central nervous system (CNS). Mechanistic studies demonstrated that Ru@Fn-PD-L1(IgV) selectively inhibits the programmed cell death protein 1/programmed death-ligand 1 (PD-1/PD-L1) signaling axis in activated T cells, thereby promoting apoptosis and suppressing pro-inflammatory cytokine secretion. Concurrently, the nanozymes effectively scavenge reactive oxygen species (ROS), including superoxide anions (O2·-), and hydrogen peroxide (H2O2), and induce polarization of microglia toward the M2 anti-inflammatory phenotype, substantially alleviating oxidative stress and neuroinflammatory injury. In vivo studies using a mouse model of MS demonstrated significant neuroprotection and enhanced cognitive performance, supporting the potential of Ru@Fn-PD-L1(IgV) as a novel immunotherapeutic strategy for treating MS.