Cells were isolated 72 h after injection with LNPs unless otherwise noted. Mice were perfused with 20 mL of 1× PBS through the right atrium. Tissues were finely cut and then placed in a digestive enzyme solution with collagenase type I (Sigma-Aldrich), collagenase XI (Sigma-Aldrich), and hyaluronidase (Sigma-Aldrich) at 37 °C at 550 rpm for 45 min. The digestive enzyme for heart and spleen included collagenase IV (32 (link), 37 , 45 (link)). Cell suspension was filtered through 70-μm mesh and red blood cells were lysed. Cells were stained to identify specific cell populations and sorted using the BD FacsFusion and BD Facs Aria IIIu cell sorters in the Georgia Institute of Technology Cellular Analysis Core. For in vitro experiments, BD Accuri C6 and BD FacsFusion were used. The antibody clones used were anti-CD31 (390; BioLegend), anti-CD45.2 (104; BioLegend), and anti-CD102 (3C4; BioLegend). PE anti-mCD47 (miap301; BioLegend) was used for tdTomato compensation. Representative flow gates are located in SI Appendix, Fig. S8. PBS-injected Ai14 mice were used to gate tdTomato populations for i.v. administration, while contralateral limbs were used to gate for intramuscular experiments.