IV infused DiR labeled MSC<sup>exos</sup> co-localize with OX42<sup>+</sup> macrophages/microglia in the contused spinal cord.

<p>A-B: Low magnification confocal images of a representative region of a contused spinal cord 3 hours after DiR MSC<sup>exos</sup> infusion stained for GFAP (green) and OX42 (red) and counterstained with DAPI (blue) (A) or DiR fluorescence only (cyan) (B). Large numbers of DiR hotspots can be seen near the margins of the contusion site correlating with high levels of GFAP<sup>+</sup> reactive astrocytes (green) and OX42<sup>+</sup> macrophages (red). C-E: Higher magnification image of the lesion shown in A showing the relationship between DiR hotspots and OX42 staining. C<sup>1</sup>-E<sup>1</sup>: Enlarged and rotated boxed regions of the lesion shown in C-E showing that the location of DiR hotspots within OX42<sup>+</sup> cells. F-H: Representative confocal images of contused spinal cord 24 hours after DiR MSC<sup>exos</sup> (cyan) infusion shown stained for GFAP (green) and OX42 (red) and counterstained with DAPI (blue), (F), OX42 and DiR (G) or DiR fluorescence only (cyan) (H). F<sup>1</sup>-H<sup>1</sup>: Enlarged and rotated boxed regions of the lesion shown in F-H. All scale bars indicate 20 μm. Dashed line in A and B indicates the approximate border of the lesion, as defined by the reactive astrocyte boundary, with the lesion to the left and largely intact neural tissue to the right. DiR hot spots appear to be clustered more densely near the borders of the lesioned area, in regions containing both OX42<sup>+</sup> macrophages (red) and strongly GFAP<sup>+</sup> reactive astrocytes (green).</p>