Plasma exosomes as markers of therapeutic response in patients with acute myeloic leukemia

Purpose: Exosomes isolated from the plasma of newly diagnosed acute myeloid leukemia (AML) patients have elevated protein and transforming growth factor-beta 1 (TGF-beta 1) contents and inhibit natural killer (NK) cell cytotoxicity (Haematologica 96, p. 1302, 2011). A potential role of exosomes in predicting responses to chemotherapy (CT) was evaluated in AML patients undergoing treatment. Experimental Design: Plasma was obtained from AML patients at diagnosis (n = 16); postinduction CT (n = 9); during consolidation CT (n = 10); in long-term remission (Lt-CR, n = 5); and from healthy volunteers (n =7). Exosomes were isolated by size-exclusion chromatography and ultracentrifugation. The exosomal protein, soluble TGF beta-1 levels (ELISA), and the TGF-beta 1 profiles (western blots) were compared among patients' cohorts. The results were correlated with the patients' cytogenetic profile, percentage of leukemic blast, and outcome. Results: At diagnosis, protein and TGF-beta 1 levels were higher (p < 0.009 and p < 0.004) in AML than control exosomes. These values decreased after induction CT (p < 0.05 and p < 0.004), increased during consolidation CT (p < 0.02 and p < 0.005), and normalized in Lt-CR. While TGF-beta 1 and protein levels tracked one another, TGF-beta 1 pro-peptide, latency-associated peptide (LAP), or mature TGF-beta 1 differentially decorated exosomes isolated before, during, and after CT. Only TGF-beta 1 pro-peptide was seen in exosomes of controls or Lt-CR patients. During consolidation CT, exosomes carried TGF-beta 1 pro-peptide, LAP and low levels of mature TGF-beta 1. NK cell co-incubation with AML exosomes carrying all three TGF-beta 1 forms induced down-regulation of NKG2D expression. Conclusion: Changes in exosomal protein and/or TGF-beta 1 content may reflect responses to CT. The exosomal profile may suggest the presence of residual disease in patients considered to have achieved complete remission.