CTSG and Immunodeficiency: Non-obese diabetic (NOD)-scid, NOD.Cg-PrkdcscidIl2rgtm1Wjl/SzJl (NSG), or NOD.Cg-PrkdcscidIl2rgtm1Sug/ShiJic (NOG) mice, which are characterized by a relatively high immunodeficiency due to a decrease or complete lack of natural killer (NK) cell functions, are the major tools for PDX establishment [8,9].