Exosomes: Definition and Clinical Significance

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The page below is a sample from the LabCE course Liquid Biopsy Assays. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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Exosomes: Definition and Clinical Significance

Exosomes are cell-derived vesicles present in many body fluids including blood, urine, saliva, and cerebrospinal fluid. These cell-derived vesicles are much smaller than a typical red blood cell and appear to be released from various cells and play a key role in processes such as coagulation, intercellular signaling, and waste management. Exosomes are known to be released from tumors into the blood and appear to be significantly stable when circulating in body fluids.
Exosomes contain lipids, proteins, functional messenger RNA and microRNA, and double-stranded DNA originating from their cells of origin. These circulating, cell-derived vesicles contain nucleic acids shed by both living, healthy cells as well as from tumors. Since exosomes can be released from tumors into the blood and are stable carriers of DNA, RNA, and proteins from the cell of origin, significant research is ongoing into the development of diagnostic procedures to identify exosomes as disease biomarkers.
Clinically, tumor exosomes have been linked to the stimulation of tumor cell growth, immune response suppression, and induction of angiogenesis, and have been shown to play a role in metastasis. Consequently, there is a growing interest in the clinical applications of exosomes. Exosomes can potentially be used for prognosis, therapy, and as biomarkers for health and disease. Exosomes derived from tumors are presently being used as targets in liquid biopsy assays serving as biomarkers of cancer.
Several commercial diagnostic companies have developed or are in the process of developing liquid biopsy tests using tumor exosomes. Clinical diagnostic applications using exosomes to date have been somewhat lacking because of the difficulty in the enrichment and quantitative analysis of circulating exosomes. Recently, Exosome Diagnostics Inc. of Cambridge, Massachusetts has launched the ExoDx™ Lung(ALK) test, which is the first liquid biopsy test designed to isolate and analyze exosome RNA (exoRNA) from a blood sample. This test is a plasma-based liquid biopsy test that detects mutations in patients with non-small cell lung cancer (NSCLC). More details on the ExoDx Lung (ALK) test will be presented later in this course.