Plasma exosomes as markers of therapeutic response in patients with acute myeloid leukemia.
OBJECTIVE
Exosomes isolated from the plasma of newly diagnosed acute myeloid leukemia (AML) patients have elevated protein and transforming growth factor-beta 1 (TGF-β1) 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.


METHODS
Plasma was obtained from AML patients at diagnosis (n = 16); post-induction 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 TGFβ-1 levels (ELISA), and the TGF-β1 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-β1 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-β1 and protein levels tracked one another, TGF-β1 pro-peptide, latency-associated peptide (LAP), or mature TGF-β1 differentially decorated exosomes isolated before, during, and after CT. Only TGF-β1 pro-peptide was seen in exosomes of controls or Lt-CR patients. During consolidation CT, exosomes carried TGF-β1 pro-peptide, LAP, and low levels of mature TGF-β1. NK cell co-incubation with AML exosomes carrying all three TGF-β1 forms induced down-regulation of NKG2D expression.


CONCLUSIONS
Changes in exosomal protein and/or TGF-β1 content may reflect responses to CT. The exosomal profile may suggest the presence of residual disease in patients considered to have achieved complete remission.
Department of Pathology, University of Pittsburgh Cancer Institute, University of Pittsburgh School of Medicine , Pittsburgh, PA , USA.
Chang-Sook
CS
Hong
Department of Pathology, University of Pittsburgh Cancer Institute, University of Pittsburgh School of Medicine , Pittsburgh, PA , USA.
Laurent
L
Muller
Department of Pathology, University of Pittsburgh Cancer Institute, University of Pittsburgh School of Medicine , Pittsburgh, PA , USA ; Department of Immunology, University of Pittsburgh Cancer Institute, University of Pittsburgh School of Medicine , Pittsburgh, PA , USA.
Theresa L
TL
Whiteside
Department of Medicine, University of Pittsburgh Cancer Institute, University of Pittsburgh School of Medicine , Pittsburgh, PA , USA.
Michael
M
Boyiadzis
TGF-β1; acute myelogenous leukemia; chemotherapy; exosomes; protein levels