Isolation and characterization of tumor-derived exosomes from a patient-derived xenograft mouse model of acute leukemia

Exosomal cargo has been found dysregulated in various neoplasias, including acute leukemias. Yet, in primary patients' material, it is uncertain whether the found biomarkers are derived from tumor exosomes (TEX) or from surrounding tissue. To circumvent this problem, we use a patient-derived xenograft (PDX) mouse model of acute leukemia. We capture serum exosomes with a human specific antibody against the exosomal marker CD63. Exosomes and their RNA are analyzed with human specific cytometry and PCR assays to confirm the human origin. Our assay reveals high sensitivity, detecting human exosomes in human:mouse serum titrations down to a ratio of 1:100 and in the serum of PDX mice. Bioanalyzer analysis confirms a distinctive enrichment of small RNAs. Exosome levels and their RNA amounts are increased in full-blown leukemia mice compared to control mice. Our human-specific exosome capture assay indicates that leukemic cells are utilizing exosomes to communicate with their microenvironment, and potentially distant tissues. Applying this method, we will sequence TEX-derived RNA from different ALL risk groups to detect high risk patients upfront with a serum sample at time of diagnosis.