Tumor-exosome uptake by leukocytes. (A) BMC, TC, SC, LNC, PBL and PEC were incubated at 37°C with RhDHPE-labeled ASML-exosomes for the indicated periods. Exosome binding and uptake (fluorescence after 2 acid washes) was evaluated by flow-cytometry: Mean percent ± SD (3 experiments) of exosome+ leukocytes. Significant differences between exosome binding/uptake versus uptake: *. (B,C) SP-Dio18(3)-labeled exosomes (200 μg) were injected i.v. and hematopoietic organs were excised after 24 h: (C) Mean percent ± SD (3 rats) of exosome+ leukocytes evaluated by flow-cytometry. (D) Confocal microscopy showing representative examples of exosome+ cells in shock frozen lymph node, spleen and thymus (arrow: boundary cortex/medulla) sections (scale bar left: 20 μm, right: 10 μm). Tumor-exosomes bind and are taken up in vitro and in vivo by cells from all hematopoietic organs. Uptake is most rapid and abundant in PEC.