Mechanical stiffness of membrane-anchored backpacks modulates innate immune function in dendritic cells and...

Phagocytosis-resistant cellular backpacks hold transformative potential for engineering innate immune cells via mechanotransduction. However, the design principles linking the stiffness of the backpacks to innate immune cell function remain inadequately explored in the context of mechano-immunology. Here, we fabricate membrane-anchored backpacks with tunable stiffness using biocompatible silk fibroin and poly (lactic-co-glycolic acid), covering stiffness values across three distinct orders of magnitude (5 kPa, 500 kPa, 50 MPa). Through a chemically optimized membrane-intercalation strategy with hydrophobic alkyl segments, we achieved >70% binding efficiency to bone marrow-derived dendritic cells and macrophages, enabling efficient mechanical force transduction. Stiffness-dependent phenotypic reprogramming was observed, with high-stiffness (50 MPa) backpacks significantly enhancing dendritic cell maturation and macrophage polarization, secretion of pro-inflammatory cytokines (TNF-α, IL-6), and CD8⁺ T cell activation in vitro. Mechanistically, high-stiffness backpacks inhibited the Hippo pathway via actin polymerization-mediated mechanosensing, reducing LATS1 and YAP phosphorylation and promoting YAP nuclear translocation to amplify inflammatory responses. In a B16F10 melanoma model, dendritic cells and macrophages carrying backpacks significantly suppressed tumor growth and improved survival, correlating with enhanced cytotoxic T cell responses and immune memory. This work establishes stiffness-tunable cellular backpacks as a powerful platform for innate immune cell engineering, elucidating critical chemical structure and function relationships and mechanotransduction pathways to advance immunotherapeutic design.