TNF and arthritic joint disease: developed PEI‐based IL‐15 receptor β chain (IL‐15Rβ) siRNA composite NPs, effectively silencing IL‐15Rβ.[180] Weekly intravenous injections of IL‐15Rβ siRNA/PEI NPs led to a significant TNF‐α and IL‐1β reduction in the ankle joints of adjuvant‐induced arthritis (AIA) rats, providing substantial relief from clinical arthritis symptoms after 3 weeks, along with a notable reduction in synovial tissue inflammation and cartilage/bone damage.