In vivo metabolic tagging and targeting of circulating red blood cells

Engineering red blood cells (RBCs) has been widely explored for drug delivery, imaging, vaccination, and other applications. However, effective strategies to directly engineer RBCs in vivo are still lacking. Here, we report successful metabolic glycan labeling of RBCs in vivo. We demonstrate that systemically administered azido-sugars can metabolically label circulating RBCs with azido groups, through labeling of both mature RBCs and RBC precursor cells. The surface azido tags on RBCs can persist for over 42 days in female mice (nearly the lifespan of RBCs), while tags on leukocytes decay to negligible levels within 3 days. Azido-labeled RBCs can covalently capture dibenzocyclooctyne-bearing cargos in vivo via click chemistry, extending cargo circulation from hours to over 35 days. This RBC tagging and targeting technology can improve fluorescence imaging of blood vessels, enable long-term MRI of brain vasculatures with a single gadolinium dose, and improve the pharmacokinetics of drugs.