**2. Exosomes contents**

The contents of the exosomes not only reflect the composition of the donor cell but also consider the controlled sorting mechanism. Composites of different proteins involving receptors, transcription factors, enzymes, extracellular matrix proteins, lipids, nucleic acids (DNA, mRNA, and miRNA) interior and present on the surface of the exosomes [18]. As compared to the other cell membranes, Exosomes manifested a superior expression of sphingomyelin, cholesterol, phosphatidylserine, and saturated fatty acids as compared to whole cell membranes, according to earlier reports [19]. The proteins present in the exosomes consist of the endosome, plasma, and nuclear proteins. An exosome of various cell types consisting of TSG101, Alix, Rab GTPases, heat shock proteins (HSP70, HSP90), integrins, tetraspanins (CD9, CD63, CD81), and MHC class II proteins. Furthermore, exosomes also carry genetic material like mRNA, long non-coding RNA, micro-RNA, and double-stranded DNA [20]. Furthermore, the contents of exosomes may differ from the cells of their parent cells due to the precise distribution of cargo into exosomes. As a result, there is not enough information on their back-and-forth mechanisms.
