Conditional Reprogramming (CR) Medium is optimized to use with 3T3-J2 Irradiated Feeder Cells (Catalog #100-0353) to expand epithelial cells without genetic modification. Mature epithelial cells have been shown to restore tissue-specific progenitor phenotype that enables proliferation in the presence of CR Medium (Liu X et al. 2012; Liu X et al. 2017). This conditional proliferative capability is deactivated once the medium is removed from the cells (Liu X et al. 2012; Liu X et al. 2017). CR Medium is suitable to propagate primary epithelial cells from healthy or tumor tissues (airway, retina, prostate, breast, intestine, pancreas, liver biliary duct, etc.; Liu X et al. 2012; Liu X et al. 2017; Suprynowicz FA et al.). This product is free of antibiotics and intended for Research Use Only. CR Medium must be supplemented with cholera toxin prior to use.