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Standard growth medium for most cells in culture require fetal
bovine serum (FBS) as a growth supplement to DMEM/
RPMI. FBS is derived from bovine (cow) serum and contains
a high abundance of cow-derived exosome vesicles. These exosomes
can interfere or cause significant protein background
issues when studying exosomes secreted from cells of interest
in standard culture conditions. For exosome production, we
typically modify the growth medium either serum-free media
(SFM) or a combination of SFM and Insulin Transferrin-Selenium
(ITS, 0.2–0.6 % (w/v)) (i.e., culture medium B) to
ensure cells remain viable during exosome production. Any
changes to cell growth medium supplements should be evaluated
over the time-course of exosome-production (typically
24–48 h). Further methods to modify the cell growth medium
(although still the possibility of bovine secreted proteins)
include, 1 % (w/v) bovine serum albumin (BSA) added instead
of FBS, and depletion of FCS-containing exosomes based on
ultracentrifugation (100,000 × g, 18 h), or filtration/immunodepletion
(CD63 positive, exosome-sized vesicles removed, no
measureable bovine microRNAs). This exosome-depleted FBS
growth supplement (Exo-FBS) is commercially available
(EXO-FBS-250A-1, System Biosciences).
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