IDO1 and dry eye syndrome: We believe that the possible mechanism of the Ad-MSCs in KCS is based on their immunomodulatory and anti-inflammatory capacity, stimulated by proinflammatory cytokines released in the process (TNF, IFN, and IL-6) [5, 21] and through secretion of immunomodulatory soluble factors as TGF-β, HGF, PGE2, and IDO [11].