Fig. 1. Schematic description of the architecture of the genetic circuits.

a The CMV-siR^TNF-α circuit contains a CMV promoter part and a TNF-α siRNA-expressing part. When the CMV-siR^TNF-α circuit is taken up and processed by the liver after intravenous injection, the CMV promoter drives the transcription of TNF-α siRNA in cytoplasm, which leads to the loading of saturated TNF-α siRNA into small extracellular vesicles (sEVs) as cargo. Subsequently, TNF-α siRNA-encapsulating sEVs facilitate the systematic distribution of siRNAs to multiple tissues and cells, including colonic macrophages. Once arriving colonic macrophages, TNF-α siRNA has the potential to regulate immune balance and relieve intestinal inflammation by inhibiting the uncontrolled release of TNF-α from macrophages. b The CMV-siR^T+B+I circuit contains a CMV promoter part and a multiple siRNA-expressing part carrying three siRNA expression cassettes organised as a head-to-tail tandem array to simultaneously drive the transcription of TNF-α siRNA, B7-1 siRNA and integrin α4 siRNA. B7-1 siRNA is expected to target antigen-presenting cells (APCs) and inhibit the costimulatory signal to T cells. Integrin α4 siRNA is expected to target α4β7⁺ CD4⁺ T cells and block T cell homing to sites of inflammation. Created with BioRender.com.