As the field of exosome therapeutics expands, several companies are providing products sourced from different cells or tissues, often claiming equivalent or superior safety and efficacy profiles with little data to support these claims. A cursory review of scientific literature quickly reveals that not all exosomes are created equal. Exosomes are secreted by most, if not all cells. The composition of exosome content, however, is variable and dependent upon the originating cell type and its

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... onment. Therefore, understanding the primary critical attributes of the cell source will provide the end-user important information to evaluate the quality, safety, and potential efficacy of the exosome product. Currently, bone marrow-derived mesenchymal stem cells (BM-MSCs) and placenta tissuederived cells are primary cell sources for commercial products. The purpose of this paper is to elucidate important considerations of exosome origin before use.