PDA TR 83 is designed to cover manufacturing processes using in vitro mammalian and other eukaryotic cell cultures to produce biopharmaceutical products. While many of the principles and practices discussed here may be applicable to the production of Advanced Therapy Medicinal Products (ATMPs), such as engineered human T-cells, such ATMPs present additional challenges outside the scope of this document due to the lack of downstream virus clearance operations as part of the overall virus risk control strategy. Likewise, although many of the principles and suggested guidance may be applicable to production by other organisms, bacteria and yeast, for example, those additional host systems are not within the scope of this document either because they are not subject to mammalian virus infection.