Characterization of Circulating and Bone Marrow Derived Exosomes in Multiple Myeloma Patients
Authors: Ferreira Bruna Velosa , Lucio Paulo , Neves Manuel , Parreira Antonio , Costa-Silva Bruno , Joao Cristina 
Published: October 2019

Abstract
Background: Multiple myeloma (MM) is characterized by clinical and biological heterogeneity, translating to variable outcome. High International Staging System (ISS), high risk cytogenetics, elevated LDH, poor response to novel drugs or extramedullary-disease (EMD) are associated to poor prognosis. Exosomes (EXO) are extra vesicular particles implicated in intercellular communication. Exosomal cargo has recently been studied as prognostic factors in cancer. MM-EXO may act as biomarkers of disease aggressiveness and potentially be used for better stratification of high risk disease in the clinical setting as liquid biopsies.
Aims: To characterize peripheral blood (PB) and bone marrow aspirates (BM) EXO in MM and MGUS patients versus healthy donors (HD) and to analyze its potential use as a prognostic biomarker.
Methods: EXO were isolated from PB and BM samples by ultracentrifugation. EXO protein quantity (EXOcargo) was determined by the ratio between total quantity of proteins and the total number of exosomes. Comparisons among groups of patients (MM, MGUS) and HD were made regarding EXO total protein cargo (PB and BM).
Results: MM patients revealed 5x times higher EXOcargo in PB (ug/EXO) when compared to MGUS patients (p=0.007, n=15 MM and n=8 MGUS); MM median 2.34 (1.08-6.5) ug/EXO versus MGUS median 0.51 (0.29-1.04) ug/EXO. There was no differences regarding the EXOcargo between the MGUS and HD (n=6, HD median 0.88 (0.57-1.83)ug/EXO). In BM, MM EXOcargo was also higher than in MGUS: MM 2.09 (0.49-3.85)ug/EXO versus MGUS 0.53 (0.21-0.831)ug/EXO. Analyzing the patients with higher EXOcargo, we found that patients with EMD (n=4) are among the ones with higher circulating exosomal protein cargo (median 5.76 (4.36-7.95). A positive correlation in EXOcargo between PB and BM in MM and MGUS (Spearman r=0.85; p< 0.0001) was found. We also studied circulating EXOcargo at response evaluation (T2) compared to EXOcargo before MM treatment (T1): patients with deeper response had significant lower EXOcargo (CR T2 median 0.85 (0.65-1.35) p<0,05); patients in VGPR (T2 median 1.52 (0.86-2.34) p=0.36) PR (T2 median 2.68 (2.03-3.33) p=0.94) and progression (T2 median 2.22 (1.0-2.46) p=0.58).
Conclusion: 1-The positive correlation of the exosomal protein cargo in PB and BM samples may be a reflection of the BM compartment and potentially supports the use of EXO as liquid biopsies for biomarkers of BM disease, in a less invasive method. 2-MM patients have higher circulating exosomal protein cargo in PB when compared to MGUS patients and HD. 3- Patients with extramedullary disease and more aggressive forms of multiple myeloma have a higher exosomal cargo in the PB and this might be related to different biological features of the disease. The longitudinal evaluation in 2 different time-points suggests a correlation between EXO protein cargo and response to treatment, to be confirmed in a larger cohort.
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Disclosures
No relevant conflicts of interest to declare.