CXCL12 and chronic obstructive pulmonary disease: After 24 h, the treatment with both HS-EVs and COPD-EVs did not affect the migration of HBEC-1, HBEC-3, and HBEC-5 neither towards EGF, chemoattractant for epithelial cells (Fig. 3A and Supplementary Fig. S1A), nor towards SDF-1, the specific chemoattractant for CXCR4+ cells (Fig. 3B and Supplementary Fig. S1B).