Sustained exposure to trypsin causes cells to transition into a state of reversible stemness that is amenable to transdifferentiation

During cell culture, trypsin, a serine protease, is applied to cells for 5-10 minutes to separate them from each other and from the underlying substratum so that they can be transferred to a different vessel, for re-plating, after growth medium containing 10 % serum has been added to the cells, in a well-known technique known as passaging. The serum in the growth medium contains alpha-1 antitrypsin, which is a potent inhibitor of trypsin, elastase and other serine proteases. Although what is used is bovine serum in which levels of proteins could be different from levels seen in humans, normal human serum contains A1AT (> 1 mg/ml; > ~18 micromolar) as well as trypsin itself (