Characterization of extracellular vesicles from human bone marrow and peripheral autologous blood samples. EVs were harvested from (1) BM-derived MKs cultured in EV-depleted media for 24 hours, (2) BM aspirates, and (3) PB patient samples, and characterized by flow cytometry. (A) MKs cultured from human bone marrow produced CD41⁺ (1452 ± 88 MV/µL) and CD62P⁺ (1276 ± 176 MV/µL) EVs. (C) To analyze EVs from patient BM and PB samples (n = 10), Megamix beads of known size were used to gauge approximate size of particles. Strict fluorescence minus 1 controls were used to determine negative population spread and set gates. (B) An example of flow cytometry gates showing CD41⁺ and Annexin 5⁺ populations from both BM and PB from the same patient. (D) Flow cytometry analyses of EV absolute counts showed significantly more EVs of all types in BM in comparison with autologous PB. (E-H) P < .05 by Mann-Whitney U test. Data were further analyzed to assess platelet activation markers within the CD41⁺ population. (I-L) *P < .05, **P < .01, ***P < .001, or nonsignificant (ns) by Mann-Whitney U test. Correlation plots of absolute counts matched from BM and PB from the same patients (see Table 1 for patient characteristics).