Chemically-defined media contain only components that are entirely known (i.e. no hydrolysates, no native human serum-derived proteins, etc.).  Due to developments in the drug industry, there has been an increased focus on contaminants that may cause unfavorable reactions with patient material. Thus, our TheraPeak™ MSCGM™ is considered serum-free, but not chemically-defined because it contains proteins of human origin.