Utilizing a chemoselective ligation detection method, we found RDEB cells that were treated simultaneously with BM-MSC EVs and an l-methionine analog, l-homopropargylglycine (HPG), synthesized collagen VII alpha chain protein that contained the alkyne group of HPG to react (i.e. undergo the Click-iT<sup>®</sup> reaction) with azide-modified Alexa 594, suggesting de novo synthesis of type VII collagen by RDEB fibroblasts.